Co-reporter:Chia-Chun Lin, Matteo Cargnello, Christopher B. Murray, Nigel Clarke, Karen I. Winey, Robert A. Riggleman, and Russell J. Composto
ACS Macro Letters August 15, 2017 Volume 6(Issue 8) pp:869-869
Publication Date(Web):August 1, 2017
DOI:10.1021/acsmacrolett.7b00533
Polymer diffusion is enhanced when nanorods (NRs) in a polymer nanocomposite are mobile relative to nanocomposites containing immobile NRs. NR mobility is tuned by varying the molecular weight of the matrix polymer and the NR concentration, and diffusion of deuterated polystyrene (dPS) tracers with varying molecular weight is studied using elastic recoil detection. When dPS diffuses faster than the NRs such that the NRs are “immobile” on the time scale of dPS, the tracer diffusion coefficient (D) monotonically decreases as the nanorod concentration increases; we interpret these results as though the nanorods provide additional topological constraints that slow diffusion of dPS. When the tracer diffusion is slow relative to NR diffusion (i.e., “mobile” NRs), diffusion is enhanced relative to the immobile NR case. This enhanced diffusion is captured by a slip-link model with two populations of topological constraints: one fixed population attributed to the PS matrix, and a second population of constraints with a finite constraint release time determined by the diffusion time of the NRs relative to dPS. These experimental and computational results provide fundamental insights into the nature of entanglements and constraint release in NR-containing polymer nanocomposites.
Co-reporter:Prathima C. Nalam, Hyun-Su Lee, Nupur Bhatt, Robert W. Carpick, David M. Eckmann, and Russell J. Composto
ACS Applied Materials & Interfaces April 19, 2017 Volume 9(Issue 15) pp:12936-12936
Publication Date(Web):February 21, 2017
DOI:10.1021/acsami.6b14116
Stimuli-responsive polymer films play an important role in the development of smart antibacterial coatings. In this study, we consider complementary architectures of polyelectrolyte films, including a thin chitosan layer (CH), poly(acrylic acid) (PAA) brushes, and a bilayer structure of CH grafted to PAA brushes (CH/PAA) as possible candidates for targeted drug delivery platforms. Atomic force microscopy (AFM) was employed to study the structure–mechanical property relationship for these mono- and bi-layered polymer grafts at pH 7.4 and 4.0, corresponding to physiological and biofilm formation conditions, respectively. Herein, the surface interactions between polymer grafts and the negatively charged silica colloid attached to an AFM lever are considered as representative interactions between the antibacterial coating and a bacteria/biofilm. The bilayered structure of CH/PAA showed significantly reduced adhesive interactions in comparison to pure CH but slightly higher interactions in comparison to PAA films. Among PAA and CH/PAA films, upon grafting CH over the PAA brushes, the normal stiffness increased by 10-fold at pH 7.4 and 20-fold at pH 4.0. Notably, the study also showed that the addition of an antibiotic drug such as multicationic Tobramycin (TOB) impacts the mechanical properties of the antibacterial coatings. Competition between TOB and water molecules for the PAA chains is shown to determine the structural properties of PAA and CH/PAA films loaded with TOB. At high pH (7.4), the TOB molecules, which remain multicationic, strongly interact with polyanionic PAA, thereby reducing the film’s compressibility. On the contrary, at low pH (4.0), the water molecules preferentially interact with TOB in comparison to uncharged PAA chains and, upon TOB release, results in a stronger film collapse together with an increase in adhesive interactions between the probe, the surface, and the elastic modulus of the film. The bacterial proliferation on these platforms when compared to the measured mechanical properties shows a direct correlation; hence, understanding nanomechanical properties can provide insights into designing new antibacterial polymer coatings.Keywords: antibacterial coatings; atomic force microscopy; drug delivery; nanomechanics; pH responsive polymers; polyelectrolyte grafts;
Co-reporter:Jihoon Choi, Nigel Clarke, Karen I. Winey, and Russell J. Composto
Macromolecules April 11, 2017 Volume 50(Issue 7) pp:3038-3038
Publication Date(Web):March 22, 2017
DOI:10.1021/acs.macromol.7b00086
Given the exceedingly high interfacial area-to-volume ratios in polymer nanocomposites and the ability to manipulate the polymer/nanoparticle interfacial interactions, manipulating the chain dynamics at these interfaces has immense potential for impacting macroscopic properties. There, the polymer center-of-mass tracer diffusion coefficient (D) from attractive (hydroxyl-terminated) and athermal (phenyl-terminated or polymer-grafted) substrates was measured over a range of temperatures and tracer molecular weights using elastic recoil detection. The tracer polymer diffusion slows significantly relative to the bulk when polymers are in direct contact with an attractive substrate and exhibits a weaker molecular weight dependence, D ∼ M–1.4. For polymers without direct contacts on the attractive substrates and for athermal substrates, the diffusion coefficients are similar to the bulk case. The temperature dependence of these diffusion coefficients indicates that the slower diffusion at the interfaces is coupled to differences in polymer conformation and smaller fractional free volumes. These deviations from bulk are more pronounced for higher molecular weights and more attractive interfaces.
Co-reporter:Ethan C. Glor;Robert C. Ferrier, Jr.;Chen Li;Zahra Fakhraai
Soft Matter (2005-Present) 2017 vol. 13(Issue 11) pp:2207-2215
Publication Date(Web):2017/03/15
DOI:10.1039/C6SM02403C
In this work, we develop a novel, in situ characterization method to measure the orientation order parameter and investigate the reorientation and reshaping dynamics of polymer grafted gold nanorods (AuNRs) in polymer nanocomposite (PNC) thin films. The long aspect-ratio of AuNRs results in two well-defined plasmon resonance modes, allowing the optical properties of the PNC to be tuned over a wide spectral range. The alignment of the AuNRs in a particular direction can also be used to further tune these optical properties. We utilize variable angle spectroscopic ellipsometry as a unique technique to measure the optical properties of PNC films containing AuNRs at various angles of incidence, and use effective index of refraction analysis of the PNC to relate the birefringence in the film due to changes of the plasmon coupling to the orientation order parameter of AuNRs. Polymer thin films (ca. 70 nm) of either polystyrene (PS) or poly(methyl methacrylate) (PMMA) containing PS grafted AuNRs are probed with ellipsometry, and the resulting extinction coefficient spectra compare favorably with more traditional analytical techniques, electron microscopy (EM) and optical absorbance (vis-NIR) spectroscopy. Furthermore, variable angle spectroscopic ellipsometry measures optical birefringence, which allows us to determine the in- and out-of plane order of the AuNRs, a property that is not easily accessible using other measurement techniques. Additionally, this technique is applied in situ to demonstrate that AuNRs undergo a rapid (ca. 1–5 hours) reorientation before undergoing a slower (ca. 24 hours) rod to sphere shape transition. The reorientation behavior is different depending on the polymer matrix used. In the athermal case (i.e. PS matrix), the AuNRs reorient isotropically, while in PMMA the AuNRs do not become isotropic, which we hypothesize is due to PMMA preferentially wetting the silica substrate, leaving less vertical space for the AuNRs to reorient.
Co-reporter:Robert C. Ferrier, Yun Huang, Kohji Ohno and Russell J. Composto
Soft Matter 2016 vol. 12(Issue 9) pp:2550-2556
Publication Date(Web):25 Jan 2016
DOI:10.1039/C5SM02460A
This study investigates the parameters that affect the dispersion of polymer grafted mesoscopic iron-oxide rods (FeMRs) in polymer matrices. FeMRs (212 nm long by 36 nm in diameter) are grafted with poly(methyl methacrylate) (PMMA) at three different brush molecular weights: 3.7 kg mol−1, 32 kg mol−1, and 160 kg mol−1. Each FeMR sample was cast in a polymer thin film consisting of either PMMA or poly(ethylene oxide) (PEO) each at a molecular weight much higher or much lower than the brush molecular weight. We find that the FeMRs with 160 kg mol−1 brush disperse in all matrices while the FeMRs with 32 kg mol−1 and 3.7 kg mol−1 brushes aggregate in all matrices. We perform simple free energy calculations, taking into account steric repulsion from the brush and van der Waals attraction between FeMRs. We find that there is a barrier for aggregation for the FeMRs with the largest brush, while there is no barrier for the other FeMRs. Therefore, for these mesoscopic particles, the brush size is the main factor that determines the dispersion state of FeMRs in polymer matrices with athermal or weakly attractive brush-matrix interactions. These studies provide new insight into the mechanisms that affect dispersion in polymer matrices of mesoscopic particles and therefore guide the design of composite films with well-dispersed mesoscopic particles.
Co-reporter:Boris Rasin, Huikuan Chao, Guoqian Jiang, Dongliang Wang, Robert A. Riggleman and Russell J. Composto
Soft Matter 2016 vol. 12(Issue 7) pp:2177-2185
Publication Date(Web):06 Jan 2016
DOI:10.1039/C5SM02442K
Although significant progress has been made in controlling the dispersion of spherical nanoparticles in block copolymer thin films, our ability to disperse and control the assembly of anisotropic nanoparticles into well-defined structures is lacking in comparison. Here we use a combination of experiments and field theoretic simulations to examine the assembly of gold nanorods (AuNRs) in a block copolymer. Experimentally, poly(2-vinylpyridine)-grafted AuNRs (P2VP–AuNRs) are incorporated into poly(styrene)-b-poly(2-vinylpyridine) (PS-b-P2VP) thin films with a vertical cylinder morphology. At sufficiently low concentrations, the AuNRs disperse in the block copolymer thin film. For these dispersed AuNR systems, atomic force microscopy combined with sequential ultraviolet ozone etching indicates that the P2VP–AuNRs segregate to the base of the P2VP cylinders. Furthermore, top-down transmission electron microscopy imaging shows that the P2VP–AuNRs mainly lie parallel to the substrate. Our field theoretic simulations indicate that the NRs are strongly attracted to the cylinder base where they can relieve the local stretching of the minority block of the copolymer. These simulations also indicate conditions that will drive AuNRs to adopt a vertical orientation, namely by increasing nanorod length and/or reducing the wetting of the short block towards the substrate.
Co-reporter:Robert C. Ferrier Jr., Jason Koski, Robert A. Riggleman, and Russell J. Composto
Macromolecules 2016 Volume 49(Issue 3) pp:1002-1015
Publication Date(Web):January 20, 2016
DOI:10.1021/acs.macromol.5b02317
We investigate, both experimentally and through hybrid particle/self-consistent field theoretic (hSCFT) calculations, the dispersion state of gold nanorods (AuNRs) grafted with homopolymer, bidispersed, or mixed polymer brushes. AuNRs are grafted with 11.5 kg/mol PS (HNRs), 11.5 kg/mol PS, and 5.3 kg/mol PS (BNRs) or 11.5 kg/mol PS and 5K poly(methyl methacrylate) (PMMA) (MBNRs) and cast in PS or PMMA films consisting of short to very long chains compared to the grafted brush. We further investigated the MBNR systems by varying the length of the PS brush. Overall, we find that the MBNRs dispersed markedly better than the other brush types (HNRs or BNRs) in PS matrices. We utilize hSCFT calculations, in particular potential of mean force (PMF) and brush profile calculations, to elucidate the thermodynamics of these systems. The PMFs and brush profiles exhibit similar trends for the BNRs and MBNRs where the short grafted chain forces the longer grafted chain away from the AuNR surface and promotes wetting by the matrix chains. The hSCFT calculations demonstrated qualitative trends consistent with the aggregation observed for AuNRs in PMMA matrices. Therefore, we have demonstrated that MBNR dispersion in polymer matrices is enhanced compared to the HNR and BNR cases, which extends the dispersion window for new combinations of nanorods and polymers.
Co-reporter:Chia-Chun Lin, Emmabeth Parrish, and Russell J. Composto
Macromolecules 2016 Volume 49(Issue 16) pp:5755-5772
Publication Date(Web):August 3, 2016
DOI:10.1021/acs.macromol.6b00471
Dynamic properties play an important role in designing functional polymer nanocomposites, impacting molecular transport and phase separation kinetics. When nanoparticle (NP) size is comparable to polymer chain size, segmental relaxations may be influenced by changes in chain conformations and packing at the polymer/NP interface. Following the reptation model, these changes can perturb the longest relaxation time, in particular, the center-of-mass (COM) dynamics of polymer chains in entangled melts. This Perspective focuses on unsolved issues in polymer COM diffusion and local dynamics and segmental motions in the presence of NPs. The article introduces the effect of NP size, shape, surface modification, and enthalpic interactions on polymer diffusion and further relates dynamic studies in PNCs to macromolecular transport in bio-related systems and nanopores. Studies of local dynamics also provide insights into how entanglement density, monomeric friction, and chain conformation are influenced by NPs and how the interplay between these key parameters relates to COM dynamics to provide a unified picture across length scales. Moving forward, new studies investigating dynamics in PNCs are needed to address these unresolved problems and motivate potential applications from membranes for separations to NP carriers for drug delivery.
Co-reporter:Scott P. O. Danielsen;Jihoon Choi
Journal of Polymer Science Part B: Polymer Physics 2016 Volume 54( Issue 2) pp:301-307
Publication Date(Web):
DOI:10.1002/polb.23929
ABSTRACT
The thermal reshaping of gold nanorods has been slowed by grafting a diblock copolymer [P(S-b-S-N3)] containing an outer polystyrene (PS) brush and a short, inner photo-cross-linkable PS-azide block. The P(S-b-S-N3)-Au NRs were dispersed in a PS thin film and reshaping was investigated using scanning electron microscopy and UV–Vis spectroscopy. For P(S-b-S-N3)-Au NRs in PS, the longitudinal surface plasmon resonance decreased from about 880 toward 750 nm upon annealing at 100 °C, 150 °C, and 200 °C. This blue shift increased in strength as temperature increased. However, this reshaping of P(S-b-S-N3)-Au NRs was slower than that of Au NRs grafted with a poly(ethylene glycol) brush that was dispersed in poly(methyl methacrylate). By slowing down reshaping at elevated temperature, polymer thin film devices that heat during use (e.g., polarization dependent filters) can exhibit a longer lifetime. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 301–307
Co-reporter:Jihoon Choi, Matteo Cargnello, Christopher B. Murray, Nigel Clarke, Karen I. Winey, and Russell J. Composto
ACS Macro Letters 2015 Volume 4(Issue 9) pp:952
Publication Date(Web):August 20, 2015
DOI:10.1021/acsmacrolett.5b00348
Nanorod diffusion in polymer melts is faster than predicted by the continuum model (CM). Rutherford backscattering spectrometry is used to measure the concentration profile of titanium dioxide (TiO2) nanorods (L = 43 nm, d = 5 nm) in a polystyrene (PS) matrix having molecular weights (M) from 9 to 2000 kDa. In the entangled regime, the tracer diffusion coefficients (D) of TiO2 decrease as the M–1.4, whereas the CM predicts DCM ∼ M–3.0 using the measured zero-shear viscosity of TiO2(1 vol %): PS(M) blends. By plotting D/DCM versus M/Me, where Me is the entanglement molecular weight, diffusion is enhanced by a factor of 10–103 as M/Me increases. The faster diffusion is attributed to decoupling of nanorod diffusion from polymer relaxations in the surrounding matrix, which is facilitated by the nanorod dimensions (i.e., L greater than and d less than the entanglement mesh size, 8 nm).
Co-reporter:Robert C. Ferrier Jr.
The Journal of Physical Chemistry C 2015 Volume 119(Issue 31) pp:17899-17909
Publication Date(Web):June 30, 2015
DOI:10.1021/acs.jpcc.5b04785
A novel nanohybrid assembly consisting of gold nanorods (AuNRs) and organic semiconductors (OSCs) to tune optical properties is presented. OSCs are bound to specific areas of the AuNRs (e.g., end or side) by controlling the surface chemistry of the AuNRs. AuNRs anisotropically functionalized with cetrimonium bromide (CTAB) cysteine, poly(ethylene oxide) (PEO), and/or DNA. Rhodamine B (RhB) 5(6)-carboxyfluorescein (CF), or cyanine3 (Cy3) are incubated with the anisotropically functionalized AuNRs. The resulting optical properties of the dispersed AuNRs are characterized via steady-state UV–vis absorption and photoluminescence (PL) spectroscopies as a function of OSC concentration. We found that CF and RhB adsorb to the AuNR differently depending on the AuNR surface chemistry, which results in unique optical properties of the assembly. The distinctive spectra were used to determine the interaction between the OSC and the AuNR. Finally, we found that attaching Cy3 specifically to the ends of the AuNR via a DNA tether results in a larger emission quenching process than when Cy3 is not attached. This method of nanohybrid assembly can be extended to other metal nanostructures and OSCs. Its generic nature qualifies it as new methodology to precisely assemble nano- and molecular objects with controlled (opto)electronic properties.
Co-reporter:Hyun-Su Lee, Sana S. Dastgheyb, Noreen J. Hickok, David M. Eckmann, and Russell J. Composto
Biomacromolecules 2015 Volume 16(Issue 2) pp:
Publication Date(Web):January 13, 2015
DOI:10.1021/bm501751v
A stimuli-responsive, controlled release bilayer for the prevention of bacterial infection on biomaterials is presented. Drug release is locally controlled by the pH-responsiveness of the bilayer, comprised of an inner poly(acrylic acid) (PAA) monolayer grafted to a biomaterial and cross-linked with an outer chitosan (CH) brush. Tobramycin (TOB) is loaded in the inner PAA in part to minimize bacteria resistance. Because biofilm formation causes a decrease in local pH, TOB is released from PAA and permeates through the CH, which is in contact with the biofilm. Antibiotic capacity is controlled by the PAA thickness, which depends on PAA brush length and the extent of cross-linking between CH and PAA at the bilayer interface. This TOB-loaded, pH-responsive bilayer exhibits significantly enhanced antibacterial activity relative to controls.
Co-reporter:Jihoon Choi, Nigel Clarke, Karen I. Winey, and Russell J. Composto
ACS Macro Letters 2014 Volume 3(Issue 9) pp:886
Publication Date(Web):August 22, 2014
DOI:10.1021/mz500344h
Polymer nanocomposites (PNCs) have characteristic length scales associated with both the nanoparticles (i.e., size and interparticle distance) and the polymer molecules (i.e., tube diameter of entanglement and radius of gyration; Rg). When the nanoparticle (NP) and polymer length scales are comparable, the polymer dynamics exhibit contrasting behavior for NPs differing only in size and shape. For spherical NPs and short anisotropic NPs, the polymer diffusion coefficient decreases monotonically with NP concentration. However, for long anisotropic NPs, polymer diffusion slows down at low NP concentration and recovers for NP concentrations above the critical concentration for network formation. By spanning intermediate ranges of nanoparticle size and shape, the role of the NP geometric parameters on the polymer dynamics is substantially advanced, thereby providing new routes toward controlling polymer dynamics and viscoelasticity of PNCs.
Co-reporter:M. Carme Coll Ferrer, Sana Dastgheyb, Noreen J. Hickok, David M. Eckmann, Russell J. Composto
Acta Biomaterialia 2014 Volume 10(Issue 5) pp:2105-2111
Publication Date(Web):May 2014
DOI:10.1016/j.actbio.2014.01.009
Abstract
We have developed a novel and simple synthesis route to create nanosized (∼5 nm) silver nanoparticles (Ag NPs) embedded in a biocompatible nanogel (NG) comprising degradable, natural polymers, namely dextran and lysozyme. In this study, we prepared hybrid nanogels with varying lysozyme content, evaluated their potential to reduce Ag NPs in situ (using ultraviolet–visible spectroscopy, cryo-transmission electronic microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy) and determined their antibacterial properties against Escherichia coli and Staphylococcus aureus. Lysozyme was found to enhance nucleation and stabilization of Ag NPs while limiting their growth. As lysozyme concentration increased, larger nanogels with greater loading of smaller Ag NPs were obtained. The antibacterial properties of hybrid NGs were found to depend upon nanogel type and bacterial conditions. Hybrid nanogels with the largest Ag NPs showed the lowest minimum inhibition concentration. However, the greatest bacterial killing efficiency (up to 100%) occurred within 1 h if the bacteria were exposed to hybrid nanogels with smaller Ag NPs while agitating the medium. These results suggest that nanogel properties as well as antibacterial activity can be tuned by varying the lysozyme content. By targeting drug delivery (e.g. ligand grafted surface), these nanogels can be used to prevent biofilm formation and control infection without the complications (i.e. overexposure) associated with classical antibiotic delivery platforms.
Co-reporter:Dongliang Wang, Michael J. A. Hore, Xingchen Ye, Chen Zheng, Christopher B. Murray and Russell J. Composto
Soft Matter 2014 vol. 10(Issue 19) pp:3404-3413
Publication Date(Web):07 Mar 2014
DOI:10.1039/C3SM52514G
The dispersion, local orientation and optical absorption of polystyrene (PS, degree of polymerization P) nanocomposites containing PS-grafted gold nanorods (Au NRs, PS degree of polymerization N), with aspect ratios (ν = length/diameter) ranging from 2.5 to 6.3, are studied using quantitative scanning electron microscopy (SEM) and optical spectroscopy. The experimentally observed nanorod assemblies and optical absorptions are compared with predictions from self-consistent field theory (SCFT) and finite difference time domain (FDTD) calculations, respectively. A pair correlation function for Au NRs is calculated from SEM images, and contains no correlation peaks for P/N = 0.9, indicating nanorods are dispersed within the nanocomposite. Large correlation peaks are observed for P/N = 7.6, representative of interparticle separation distances within nanorod aggregates, which do not vary with ν. On the basis of SCFT calculations, aggregation is attributed to significant depletion–attraction forces in the composite for P/N > 1. When Au NRs disperse, the longitudinal surface plasmon resonance (LSPR) peak red shifts from the visible into the near-IR as ν increases. No shift in the dispersed LSPR position is observed for v = 2.5 and 3.3 upon aggregation because the ratio of the interparticle distance to the nanorod length is too large for surface plasmon coupling. However, for v = 6.3, significant coupling between surface plasmons leads to a blue shift of the LSPR by approximately 140 nm, in agreement with FDTD calculations.
Co-reporter:Michael J. A. Hore and Russell J. Composto
Macromolecules 2014 Volume 47(Issue 3) pp:875-887
Publication Date(Web):December 9, 2013
DOI:10.1021/ma402179w
Because of their shape anisotropy, nanorods are attractive components for creating functional polymer nanocomposites. In many cases, this anisotropy is the basis of physical properties that are distinct from those obtained from isotropic particles, such as nanospheres. For instance, the shape of gold nanorods makes them ideal candidates for applications involving the manipulation of incident light and sensitive molecular spectroscopy due to enhanced polarizability of the particle. On the other hand, semiconducting nanorods, such as those composed of CdSe, have shown promise in polymer-based photovoltaic devices as sites for electron transport and charge transfer. In this Perspective, we motivate the fabrication of functional polymer nanocomposites based specifically upon the inclusion of nanorods over other nanoparticle shapes and discuss ways in which the anisotropy of the individual nanoparticles enhances assembly in and the properties of polymer nanocomposites in comparison to spherical nanoparticles. We briefly summarize methods to successfully disperse and organize nanorods within polymers and discuss applications of polymer nanocomposites involving sensing, energy harnessing, and mechanical enhancement. Finally, we comment on unresolved issues for fabricating nanorod-based polymer composites and suggest topics warranting future investigation.
Co-reporter:Robert C. Ferrier Jr., Hyun-Su Lee, Michael J. A. Hore, Matthew Caporizzo, David M. Eckmann, and Russell J. Composto
Langmuir 2014 Volume 30(Issue 7) pp:1906-1914
Publication Date(Web):2017-2-22
DOI:10.1021/la404588w
A novel, solution-based method is presented to prepare bifunctional gold nanorods (B-NRs), assemble B-NRs end-to-end in various solvents, and disperse linked B-NRs in a polymer matrix. The B-NRs have poly(ethylene glycol) grafted along its long axis and cysteine adsorbed to its ends. By controlling cysteine coverage, bifunctional ligands or polymer can be end-grafted to the AuNRs. Here, two dithiol ligands (C6DT and C9DT) are used to link the B-NRs in organic solvents. With increasing incubation time, the nanorod chain length increases linearly as the longitudinal surface plasmon resonance shifts toward lower adsorption wavelengths (i.e., red shift). Analogous to step-growth polymerization, the polydispersity in chain length also increases. Upon adding poly(ethylene glycol) or poly(methyl methacrylate) to chloroform solution with linked B-NR, the nanorod chains are shown to retain end-to-end linking upon spin-casting into PEO or PMMA films. Using quartz crystal microbalance with dissipation (QCM-D), the mechanism of nanorod linking is investigated on planar gold surfaces. At submonolayer coverage of cysteine, C6DT molecules can insert between cysteines and reach an areal density of 3.4 molecules per nm2. To mimic the linking of Au NRs, this planar surface is exposed to cysteine-coated Au nanoparticles, which graft at 7 NPs per μm2. This solution-based method to prepare, assemble, and disperse Au nanorods is applicable to other nanorod systems (e.g., CdSe) and presents a new strategy to assemble anisotropic particles in organic solvents and polymer coatings.
Co-reporter:Jihoon Choi, Michael J. A. Hore, Nigel Clarke, Karen I. Winey, and Russell J. Composto
Macromolecules 2014 Volume 47(Issue 7) pp:2404-2410
Publication Date(Web):March 19, 2014
DOI:10.1021/ma500235v
We show that polymer diffusion in polymer nanocomposites (PNCs) is controlled by the architecture of polymer brushes grafted to hard spherical nanoparticles (NPs). At high grafting density, diffusing chains are excluded from the polymer brush leading to greater confinement. However, at lower grafting density, these chains penetrate the brush and diffusion is similar to the hard NP case, compared at the same NP loading. We calculate the effective interparticle spacing (IDeff) by modeling polymer penetration into the grafted brush using self-consistent field theory. When plotted against a confinement parameter (IDeff/2Rg, where Rg is the radius of gyration of the diffusing polymer), reduced diffusion coefficients (D/Do) fall on a master curve independent of brush architecture. These findings show that brush architecture provides a new route toward controlling polymer dynamics and viscoelasticity of PNCs.
Co-reporter:Chia-Chun Lin, Kohji Ohno, Nigel Clarke, Karen I. Winey, and Russell J. Composto
Macromolecules 2014 Volume 47(Issue 15) pp:5357-5364
Publication Date(Web):July 16, 2014
DOI:10.1021/ma501113c
Diffusion of deuterated polystyrene (dPS) is probed in PS matrices containing stringlike chained nanoparticles (cNP) grafted with PS. This investigation connects prior diffusion studies in model spherical and cylindrical NP systems and provides insight for technological applications, which typically involve irregularly shaped NPs such as carbon black. We report that the presence of chained NPs in PS matrices induces a minimum in the diffusion coefficient (D) with increasing cNP concentration when the key length scale, 2Rg/L ≤ 1.5, where Rg is the gyration radius of dPS and L is the mean length of the impenetrable core of the chained NPs. When 2Rg/L > 1.5, D decreases monotonically as the NP concentration increases. Note that in all cases 2Rg is larger than the diameter of these short-stringy NPs. The diffusion minimum is attributed to anisotropic diffusion in the vicinity of the chained NPs and requires that the long dimension of the cNP be comparable to or longer than the tracer molecule. Two normalizations are explored to provide insight about the diffusion mechanism: D/D0 where D0 is the diffusion coefficient in a pure homopolymer matrix and D/De where De is an effective diffusion coefficient that accounts for the distinct dynamics in the PS matrix and PS brush regions. For D/D0, a sharp transition from a diffusion minimum to a monotonic decrease is observed as dPS molecular weight increases, while for D/De the transition is more gradual. These studies show not only that the NPs act as impenetrable obstacles for polymer diffusion but that the polymer brush grafted to the cNP provides an alternative pathway to control polymer dynamics.
Co-reporter:Jihoon Choi, Michael J. A. Hore, Jeffrey S. Meth, Nigel Clarke, Karen I. Winey, and Russell J. Composto
ACS Macro Letters 2013 Volume 2(Issue 6) pp:485
Publication Date(Web):May 20, 2013
DOI:10.1021/mz400064w
Nanoparticles are new and valuable additives that can favorably tune thermomechanical, electric, optical, and magnetic properties of polymeric materials. The addition of nanoparticles can also enhance or slow down polymer dynamics depending on the mixture thermodynamics and key length scales, namely, nanoparticle size, interparticle spacing (ID), and the polymer radius of gyration (Rg). Presently, a framework for understanding how nanoparticles affect polymer dynamics is not available, in part, because of a lack of wide-ranging experimental studies. Here, tracer diffusion is studied in model nanocomposites containing silica nanoparticles grafted with either polymer brushes (soft nanoparticles) or short ligands (hard nanoparticles). Over a wide range of tracer molecular weights and nanoparticle loadings, the normalized diffusion coefficient collapses onto a universal curve for both soft and hard nanoparticles when plotted against a confinement parameter, defined as ID/Rg, which accounts for tracer penetration into the brush. These experimental results provide new insights into the fundamental principles required to construct predictive models of polymer dynamics in nanocomposites.
Co-reporter:Chia-Chun Lin, Sangah Gam, Jeffrey S. Meth, Nigel Clarke, Karen I. Winey, and Russell J. Composto
Macromolecules 2013 Volume 46(Issue 11) pp:4502-4509
Publication Date(Web):May 24, 2013
DOI:10.1021/ma4000557
Diffusion of deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles, from 13 to 50 nm in diameter and at loadings up to 40 vol %. At constant T – Tg = 75 K, the normalized diffusion coefficients (D/D0) collapse onto a master curve, when plotted against the confinement parameter, ID/2Rg, where ID is interparticle distance and 2Rg is probe size. This result suggests that the confinement parameter captures the effect of nanoparticle size, size polydispersity, and volume fraction on polymer dynamics for the PMMA composite. For ID < 2Rg, the master curve exhibits a strongly confined region where D/D0 decreases by up to 80%, whereas for ID > 2Rg, the curve falls in a weakly confined region where D/D0decreases only moderately by up to 15%. Surprisingly, D/D0 is reduced even when ID is 8 times larger than 2Rg. A comparison between the master curves for PMMA and polystyrene nanocomposites indicates that attractive interactions in the PMMA system do not significantly alter the center-of-mass diffusion of macromolecules in polymer nanocomposites.
Co-reporter:Sana S. Dastgheyb, David M. Eckmann, Russell J. Composto, Noreen J. Hickok
Journal of Photochemistry and Photobiology B: Biology 2013 Volume 129() pp:27-35
Publication Date(Web):5 December 2013
DOI:10.1016/j.jphotobiol.2013.09.006
•Meso-Tetra (4-aminophenyl) porphine (TAPP) is a light, dose, and time-dependent antimicrobial.•Antibiotics + illuminated TAPP are at least additive for S. aureus, S. epidermidis, MRSA, and E. coli.•TAPP can be used for several cycles before losing phototoxicity through photodegradation.Staphylococcal infections have become difficult to treat due to antibiotic insensitivity and resistance. Antimicrobial combination therapies may minimize acquisition of resistance and photodynamic therapy is an attractive candidate for these combinations. In this manuscript, we explore combined use of antibiotics and meso-tetra (4-aminophenyl) porphine (TAPP), a cationic porphyrin, for treatment of Staphylococcus aureus contamination. We characterize the antimicrobial activity of photoactivated TAPP and show that activity is largely lost in the presence of a radical scavenger. Importantly, TAPP can be reactivated with continued, albeit attenuated, antibacterial activity. We then show that the antimicrobial activity of illuminated TAPP is additive with chloramphenicol and tobramycin for S. aureus and Escherichia coli, and synergistic for MRSA and Staphylococcus epidermidis. Chloramphenicol + methylene blue, another photosensitizer, also show additivity against S. aureus. In contrast, ceftriaxone and vancomycin do not strongly augment the low level effects of TAPP against S. aureus. Eukaryotic cells exhibit a dose-dependent toxicity with illuminated TAPP. Our results suggest that even sub-minimum inhibitory concentrations of photo-activated TAPP could be used to boost the activity of waning antibiotics. This may play an important role in treatments reliant on antibiotic controlled release systems where augmentation with photo-active agents could extend their efficacy.
Co-reporter:Hyun-Su Lee, Michael Q. Yee, Yonaton Y. Eckmann, Noreen J. Hickok, David M. Eckmann and Russell J. Composto
Journal of Materials Chemistry A 2012 vol. 22(Issue 37) pp:19605-19616
Publication Date(Web):26 Jul 2012
DOI:10.1039/C2JM34316A
This study investigates the swelling of grafted polycationic brushes as a function of pH and anion type. The brushes are chitosan (CH) and chitosans with 27% and 51% degrees of substitution (DS) of quaternary ammonium salts, denoted as CH-Q25 and CH-Q50, respectively. The water content and swelling behaviors are monitored using in situ quartz-crystal microbalance with dissipation (QCM-D). The pH varies from ∼3.5 to 8.5, and the counter anion types include chloride, acetate, and citrate. At fixed pH, the water content and brush swelling increase as the DS increases. While the CH-Q50 brush layer shows symmetric swelling with a minimum near pH = 4.5, the swelling of CH and CH-Q25 is relatively constant as pH decreases from 8.2 to 5.5, and then begins to increase near pH 4. These studies indicate that the symmetric swelling of CH-Q50 is likely attributed to increasing protonation of primary amines at pH values below 6.5 and the quaternary ammonium salts above pH 6.5. At pH 4, the swelling of the CH brush increases upon exchanging the smaller chloride with bulkier acetate anions, which is less effective in screening intra/inter-molecular repulsion. In contrast, upon exchanging the acetate with trifunctional citrate anions, CH and CH-Q25 brushes collapse by 53 and 42%, respectively, because the citrate anions form ionic cross-links. To test antibacterial properties, silicon oxide, CH and CH-Q50 brush layers are exposed to 107–108 cfu ml−1 of S. aureus for two days at 37 °C and to stepped shear stresses at 2 min intervals. While an S. aureus biofilm adheres strongly to silicon oxide and CH for stresses up to 12 dyne per cm2, biofilms on CH-Q50 detach at a relatively low shear stress, 1.5 dyne per cm2. Due to their high degree of swelling that can be tuned via pH, counterion size and type, chitosan and quaternary modified chitosans have potential as responsive coatings for applications including MEMS/NEMS devices and drug eluting implants.
Co-reporter:Hyun-Joong Chung, Jinyong Kim, Kohji Ohno, and Russell J. Composto
ACS Macro Letters 2012 Volume 1(Issue 1) pp:252
Publication Date(Web):December 30, 2011
DOI:10.1021/mz200068p
This paper investigates controlling the location of nanoparticles (NPs) in a phase-separated polymer blend of deuterated poly(methyl methyl methacrylate) (dPMMA) and poly(styrene-ran-acrylonitrile) (SAN). Silica NPs are grafted with PMMA brushes having molecular weights of 1800, 21000, and 160000 at fixed grafting density. Using ion beam milling combined with SEM imaging, NP location and morphology are investigated for blends containing 10 wt % NP. With increasing brush length, the NPs are found to segregate to the dPMMA/SAN interface, partition between the interface and dPMMA phase, or locate in the dPMMA phase, respectively.
Co-reporter:Michael J. A. Hore, Amalie L. Frischknecht, and Russell J. Composto
ACS Macro Letters 2012 Volume 1(Issue 1) pp:115
Publication Date(Web):November 23, 2011
DOI:10.1021/mz200031g
Optical absorption due to surface plasmon resonances in ensembles of gold nanorods (Au NRs) depends strongly on the nanorod separation and orientation. Here, we study the dispersion of polystyrene-functionalized Au NRs in polystyrene (PS) thin films using UV–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM) and find that Au NRs are dispersed for brush chain lengths that exceed the PS matrix chain length and are aggregated otherwise. Monte Carlo simulations using parameters from classical density functional theory (DFT) calculations indicate that this behavior is due to substantial depletion–attraction forces for brush chain lengths that are much smaller than the PS matrix chain length. Both UV–vis measurements and discrete dipole approximation (DDA) calculations confirm that optical absorption is a facile method to determine nanorod morphology in nanocomposite films (i.e., aggregation or dispersion). Futhermore, a dispersion map is constructed showing the conditions required for nanorod dispersion and, correspondingly, the optical absorption properties of Au NR:PS nanocomposites. Using this information, optically active materials with tunable morphologies can be fabricated and routinely characterized using optical spectroscopic methods.
Co-reporter:Hyun-Su Lee, Shannon Tsai, Chin-Chen Kuo, Alice W. Bassani, Brian Pepe-Mooney, Davide Miksa, James Masters, Richard Sullivan, Russell J. Composto
Journal of Colloid and Interface Science 2012 Volume 385(Issue 1) pp:235-243
Publication Date(Web):1 November 2012
DOI:10.1016/j.jcis.2012.06.074
Polymer adsorption onto an artificial saliva (AS) layer is investigated using quartz-crystal microbalance with dissipation (QCM-D) and chitosan as the model polymer. QCM-D is utilized in an innovative manner to monitor in situ adsorption of chitosan (CH) onto a hydroxyapatite (HA) coated crystal and to examine the ability of the adsorbed layer to “protect” the HA upon sequential exposure to acidic solutions. After deposition of a thin AS layer (16 nm), the total thickness on the HA substrate increases to 37 nm upon exposure to CH at pH 5.5 for 10 min. Correspondingly, the surface charge changes from negative (i.e., AS) to positive, consistent with the adsorption the polycationic CH onto or into the AS layer. Upon exposure to an oxidizing agent, the chitosan cross-links and collapses as noted by a decrease in thickness to 10 nm and an increase in the shear modulus by an order of magnitude. Atomic force microscopy (AFM) is used to determine the surface morphology and RMS roughness of the coated and HA surfaces after citric acid challenges. Both physisorbed and cross-linked chitosan are demonstrated to limit and prevent the erosion of HA, respectively.Graphical abstractHighlights► Monitoring in situ chitosan adsorption onto an artificial saliva layer using QCM-D. ► Evaluating chitosan layers’ ability to protect HA upon sequential acid exposure. ► Cross-linked chitosan is found to prevent acid-erosion of HA efficiently.
Co-reporter:Sangah Gam, Jeffrey S. Meth, Steve G. Zane, Changzai Chi, Barbara A. Wood, Karen I. Winey, Nigel Clarke and Russell J. Composto
Soft Matter 2012 vol. 8(Issue 24) pp:6512-6520
Publication Date(Web):14 May 2012
DOI:10.1039/C2SM25269D
The tracer diffusion of deuterated polystyrene (dPS) is measured in a polystyrene nanocomposite containing silica nanoparticles (NPs), with number average diameters dn of 28.8 nm and 12.8 nm, using elastic recoil detection. The volume fractions of the large and small NPs (ϕNP) range from 0 to 0.5, and 0 to 0.1, respectively. At the same volume fraction of NPs, the tracer diffusion of dPS is reduced as NP size decreases because the interparticle distance between NPs (ID) decreases. The reduced diffusion coefficient, defined as the tracer diffusion coefficient in the nanocomposite relative to pure PS (D/D0), plotted against the confinement parameter, namely ID(dn) relative to tracer size, ID(dn)/2Rg, nearly collapses onto a master curve, although D/D0 is slightly greater for the more polydisperse, smaller NPs. Using a log normal distribution of NP size from SAXS, the average ID of the smaller NPs is shown to increase by 25% at ϕNP = 0.1 as polydispersity (σ) increases from 1 to 1.39. By accounting for polydispersity, the confinement parameter better represents the effect of NP spacing on polymer diffusion. These experiments demonstrate that polymer tracer diffusion in polymer nanocomposites is empirically captured by the confinement parameter and that an increase in the average ID due to NP polydispersity has a secondary effect on model NP systems with a narrow distribution of sizes. However, for commercial systems, where polydispersity can be quite large, the effect of size distribution can significantly increase ID which in turn will influence polymer dynamics.
Co-reporter:M. Carme Coll Ferrer, Noreen J. Hickok, David M. Eckmann and Russell J. Composto
Soft Matter 2012 vol. 8(Issue 8) pp:2423-2431
Publication Date(Web):11 Jan 2012
DOI:10.1039/C2SM06969E
In this work, we present a novel method to prepare a hybrid coating based on dextran grafted to a substrate and embedded with silver nanoparticles (Ag NPs). First, the Ag NPs are synthesized in situ in the presence of oxidized dextran in solution. Second, the oxidized dextran is exposed to an amine functionalized surface resulting in the simultaneous grafting of dextran and the trapping of Ag NPs within the layer. The NP loading is controlled by the concentration of silver nitrate, which is 2 mM (DEX-Ag2) and 5 mM (DEX-Ag5). The dried film thickness increases with silver nitrate concentration from 2 nm for dextran to 7 nm and 12 nm for DEX-Ag2 and DEX-Ag5, respectively. The grafted dextran film displays features with a diameter and height of ∼50 nm and 2 nm, respectively. For the DEX-Ag2 and DEX-Ag5, the dextran features as well as individual Ag NPs (∼5 nm) and aggregates of Ag NPs are observed. Larger and more irregular aggregates are observed for DEX-Ag5. Overall, the Ag NPs are embedded in the dextran film as suggested by AFM and UVO studies. In terms of its antimicrobial activity, DEX-Ag2 resists bacterial adhesion to a greater extent than DEX-Ag5, which in turn is better than dextran and silicon. Because these antibacterial hybrid coatings can be grafted to a variety of surfaces, many biomedical applications can be envisioned, ranging from coating implants to catheters.
Co-reporter:Guoqian Jiang, Michael J. A. Hore, Sangah Gam, and Russell J. Composto
ACS Nano 2012 Volume 6(Issue 2) pp:1578
Publication Date(Web):January 27, 2012
DOI:10.1021/nn2045449
In this paper, polymer nanocomposite films containing gold nanorods (AuNRs) and poly(2-vinyl pyridine) (P2VP) have been investigated for their structure–optical property relationship. Using transmission electron microscopy (TEM), the assembly of AuNRs (7.9 nm × 28.4 nm) grafted with a P2VP brush in P2VP films is examined as a function of the AuNR volume fraction ØAuNRs and film thickness h. For h ∼ 40 nm, AuNRs are confined to align parallel to the film and uniformly dispersed at low ØAuNRs. Upon increasing ØAuNRs, nanorods form discrete aggregates containing mainly side-by-side arrays due to depletion–attraction forces. For ØAuNRs = 2.7%, AuNRs assemble into a 2D network where the discrete aggregates are connected by end-to-end linked nanorods. As ØAuNRs further increases, the polymer-rich regions of the network fill in with nanorods and rod overlap is observed. Monte Carlo simulations capture the experimentally observed morphologies. The effect of film thickness is investigated at ØAuNRs = 2.7%, where thicker films (40 and 70 nm) show a dense array of percolated nanorods and thinner films (20 nm) exhibit mainly isolated nanorods. Using Rutherford backscattering spectrometry (RBS), the AuNRs are observed to segregate near the substrate during spin-casting. Optically, the longitudinal surface plasmon resonance (LSPR) peaks are correlated with the local orientation of the AuNRs, where side-by-side and end-to-end alignments induce blue and red shifts, respectively. The LSPR undergoes a red shift up to 51 nm as ØAuNRs increases from 1.6 to 2.7%. These studies indicate that the optical properties of polymer nanocomposite films containing gold nanorods can be fine-tuned by changing ØAuNRs and h. These results are broadly applicable and provide guidelines for dispersing other functional nanoparticles, such as quantum dots and carbon nanotubes.Keywords: gold nanorods; Monte Carlo simulation; nanocomposite films; optical properties; percolation network; poly(2-vinyl pyridine); transmission electron microscopy
Co-reporter:Matthew A. Caporizzo, Yujie Sun, Yale E. Goldman, and Russell J. Composto
Langmuir 2012 Volume 28(Issue 33) pp:12216-12224
Publication Date(Web):July 28, 2012
DOI:10.1021/la302250x
Using a controllable nanoengineered surface that alters the dynamics of filamentous actin (F-actin) adhesion, we studied the tunability of biomolecular surface attachment. By grafting aminated nanoparticles, NPs, with diameters ranging from 12 to 85 nm to a random copolymer film, precise control over surface roughness parameters is realized. The ability to selectively generate monodisperse or polydisperse features of varying size and areal density leads to immobilized, side-on wobbly, or end-on F-actin binding as characterized by total internal reflection fluorescence (TIRF) microscopy. The interaction between the surface and actin is explained by a worm-like chain model that balances the bending energy penalty required for actin to conform to topographical features with the electrostatic attraction engineered into the surface. A Myosin V motility assay demonstrates that electrostatically immobilized actin retains its ability to direct myosin motion, indicating that nanoengineered surfaces are attractive candidates for biomolecular device fabrication.
Co-reporter:Michael J. A. Hore and Russell J. Composto
Macromolecules 2012 Volume 45(Issue 15) pp:6078-6086
Publication Date(Web):July 20, 2012
DOI:10.1021/ma300992e
To fully utilize their optical absorption and polarizing abilities, the dispersion of Au nanorods (NRs) in a matrix, such as a polymer film, must be controlled. By functionalizing NRs with a polymer brush chemically similar to the matrix, NR dispersion and aggregation can be controlled by varying the ratio of brush (N) to matrix (P) chain length. For P/N > 2, aggregates containing mainly side-by-side arrangements of NRs are observed. Here, polystyrene (PS) functionalized Au NRs are incorporated into miscible thin film blends of PS and poly(2,6-dimethyl-p-phenylene oxide) (PPO) (P/N ≈ 30) and characterized using a combination of transmission electron microscopy (TEM) and UV–visible spectroscopy (UV–vis). As the volume fraction of PPO (ϕPPO) increases from 0.00 to 0.50, the NRs remain mainly aggregated; however, at ϕPPO = 0.75 they begin to disperse and finally completely disperse in a pure PPO matrix. Correspondingly, the longitudinal surface plasmon resonance peak undergoes a red shift, consistent with improved dispersion (i.e., individual NRs). A novel outcome of this work is to utilize UV–vis to detect nanometer-scale changes in Au nanorod dispersion. To understand the role of the PPO matrix chains, which favorably interact with the PS brush, self-consistent field theory (SCFT) calculations were performed to determine the brush and matrix density profiles. The brush profile is initially parabolic for ϕPPO < 0.25 and has a thickness that is nearly the radius of gyration of the brush. However, for ϕPPO = 0.50, the brush begins to stretch because of PPO matrix chain penetration. Finally, for ϕPPO = 0.75 and 1.00, the brush thickness increases by about 50%. These SCFT results help interpret the dispersion of nanorods determined from TEM and UV–vis.
Co-reporter:Sangah Gam, Aysenur Corlu, Hyun-Joong Chung, Kohji Ohno, Michael J. A. Hore and Russell J. Composto
Soft Matter 2011 vol. 7(Issue 16) pp:7262-7268
Publication Date(Web):01 Jul 2011
DOI:10.1039/C1SM05619K
The addition of nanoparticles (NPs) to polymer blends is an attractive route for controlling their morphology. Here, we investigate the phase separation of poly(methyl methacrylate) (PMMA):poly(styrene-ran-acrylonitrile) (SAN) films with thicknesses from 140 nm to 2500 nm and silica NP concentrations from 1 to 10 wt%. Atomic force microscopy (AFM) and focused ion beam (FIB) etching combined with scanning electron microscopy (SEM) are used to identify the morphology as discrete or bicontinuous. FIB/SEM is introduced as a facile method to locate NPs at the PMMA/SAN interface and construct 3D images of the morphology of thick films. With increasing film thickness, the concentration of NPs required to stabilize a bicontinuous morphology decreases from 10 wt% to 2 wt%. A jamming map of the discrete and bicontinuous morphologies is constructed to examine the interplay between NP concentration and film thickness. The delineation between these jammed morphologies agrees with a simple geometric model based on arranging spherical NPs at the PMMA/SAN interface. The bicontinuous morphology is an especially attractive structure for applications requiring high interfacial area such as organic solar cells, membranes, catalysis, and fuel cells.
Co-reporter:Hyun-Su Lee, David M. Eckmann, Daeyeon Lee, Noreen J. Hickok, and Russell J. Composto
Langmuir 2011 Volume 27(Issue 20) pp:12458-12465
Publication Date(Web):September 6, 2011
DOI:10.1021/la202616u
Charged polymer brushes grafted to surfaces are of great interest for antibacterial, biosensor, nanofluidic, and drug delivery applications. In this paper, chitosans with quaternary ammonium salts, CH-Q, were immobilized on silicon oxide and characterized by in situ quartz-crystal microbalance with dissipation, QCM-D, and in situ spectroscopic ellipsometry, SE. Both methods showed that the hydrated film exhibited a minimum thickness of ∼40 nm near pH 5 that increased strongly (up to ∼80 nm) at lower and higher pH. This symmetric swelling is surprising because CH-Q is a cationic polymer. The CH-Q grafted layer was stable for pH values from 3 to 8 and exhibited rapid, reversible swelling and contraction upon varying pH. The CH-Q layer also reduced S. aureus colonization by a factor of ∼30× compared to bare silicon oxide and an amine terminated silane grafted to silicon oxide. This antibacterial characteristic of CH-Q is attributed to the quaternary ammonium salts and the flexible polymer brush.
Co-reporter:Sangah Gam, Jeffrey S. Meth, Steve G. Zane, Changzai Chi, Barbara A. Wood, Michelle E. Seitz, Karen I. Winey, Nigel Clarke, and Russell J. Composto
Macromolecules 2011 Volume 44(Issue 9) pp:3494-3501
Publication Date(Web):April 6, 2011
DOI:10.1021/ma102463q
Macromolecular motion is reduced in crowded polymer nanocomposites. Tracer diffusion is measured for deuterated polystyrene (dPS) into a polystyrene (PS):silica nanoparticle (NP) matrix using elastic recoil detection. This nanocomposite is ideal for studying diffusion in a crowded system because the interparticle distance (ID) that defines confinement can be varied from much greater than to much less than the size of the dPS chain, which is described by 2Rg, the radius of gyration, and varies from 10 to 40 nm in this study. Diffusion is observed to be significantly slower than that predicted by the Maxwell model. The tracer diffusion coefficient of dPS in the nanocomposite relative to the pure PS matrix (D/D0) plotted against the NP separation relative to probe size (i.e., ID/2Rg) falls on a master curve, indicating that crowding is a property of both the dPS size and confinement in the nanocomposite. Moreover, the normalized diffusion coefficient decreases more rapidly when ID/2Rg is less than ∼1, suggesting strong confinement conditions. The scaling of the diffusion coefficient with chain length is in excellent agreement with the entropic barrier model that accounts for the slowing down associated with the loss of chain entropy due to constrictive bottlenecks.
Co-reporter:Marla D. McConnell, Matthew J. Kraeutler, Shu Yang and Russell J. Composto
Nano Letters 2010 Volume 10(Issue 2) pp:603-609
Publication Date(Web):January 11, 2010
DOI:10.1021/nl903636r
Multiregion and patchy optically active Janus particles were synthesized via a hierarchical self-assembly process. Gold nanoparticles were assembled on the top surfaces of nano- and submicrometer silica particles, which were selectively protected on their bottom surfaces by covalent attachment to a copolymer film. The morphologies of the gold particle layer, and the resulting optical properties of the Janus particles, were tuned by changing the surface energy between the silica and gold particles, followed by annealing.
Co-reporter:Jung Hyun Park, Yujie Sun, Yale E. Goldman and Russell J. Composto
Soft Matter 2010 vol. 6(Issue 5) pp:915-921
Publication Date(Web):21 Dec 2009
DOI:10.1039/B918304C
We demonstrate a novel route to control attachment of filamentous actin (F-actin) on hydrogel films. By incorporating an amine-terminated silane, the hydrogel surface charge and surface topography are varied. With increasing silane content, F-actin reorients from perpendicular to parallel to the hydrogel surface, ceases to wobble, and forms mainly elongated or cyclic structures. F-Actin coverage reaches a maximum at 2.5 vol% silane and declines at higher silane content. This biphasic behavior is explained by the simultaneous increase in surface charge and the self-assembly of a micron scale pattern of positively charged islands. Our approach provides guidelines for constructing nanoscale tracks to guide motor proteins underlying nano-engineered devices such as molecular shuttles.
Co-reporter:Marla D. McConnell;Yu Liu;Andrew P. Nowak;Shira Pilch;James G. Masters
Journal of Biomedical Materials Research Part A 2010 Volume 92A( Issue 4) pp:1518-1527
Publication Date(Web):
DOI:10.1002/jbm.a.32493
Abstract
Bacterial adhesion to oral hard materials is dependent on various factors, for example, surface roughness and surface composition. In this study, bacteria retention on three oral hard substrates, hydroxyapatite (HAP), enamel, and polished enamel (p-enamel) were investigated. The surface morphology and roughness of the three substrates were measured by scanning probe microscopy. HAP had the roughest surface, followed by enamel and polished enamel. For each individual substrate type, the roughness was shown to increase with scan size up to 50 μm × 50 μm. For HAP and enamel, roughness decreased considerably after formation of a pellicle, while addition of polymer coating to the pellicle layer reduced roughness much less in comparison. Bacterial surface coverage was measured at 30 min, 3 h, and 24 h on both native and surface-modified substrates, which were coated with two different polycarboxylate-based polymers, Gantrez S97 and Carbopol 940. As a result, the polymer coated surfaces had reduced bacteria coverage compared with the native surfaces over all time points and substrates measured. The reduction is the combined effect of electrostatic repulsion and sequestering of Ca2+ ions at the surface, which plays a key role in the initial adhesion of bacteria to enamel surfaces in models of plaque formation. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res 2010
Co-reporter:Jung Hyun Park, Yujie Sun, Yale E. Goldman and Russell J. Composto
Langmuir 2010 Volume 26(Issue 13) pp:10961-10967
Publication Date(Web):May 11, 2010
DOI:10.1021/la100985a
We describe an approach to create nanoscale, functionalized channels in block copolymer films and demonstrate their use as templates for attaching filamentous actin (F-actin). Topographic and chemical patterns on the surface are created and controlled by exposure to UV-ozone (UVO) and reacting with an amine-terminated silane, respectively. Continuous UVO exposure degrades polymer domains by an autocatalytic reaction, and thus, film thickness decreases in a sigmoidal manner. Utilizing the differential etching rates of each domain, nanoscale channels with tunable depth and width are created by varying UVO exposure time and block copolymer molecular weight, respectively. For a perpendicular lamellar morphology poly(styrene-b-methyl methacrylate), P(S-b-MMA), films (65 nm), initially exhibiting higher MMA domains, undergo a height inversion after 3 min of UVO because MMA domains etch twice as fast as S domains. The maximum height difference between domains is ∼16 nm after ∼10 min of UVO. Similar behavior is observed for UVO etching of a parallel cylinder morphology. UVO exposure also produces reactive polar groups on the surfaces of poly(styrene) and poly(methyl methacrylate) as well as their corresponding domains in P(S-b-MMA). By exposing UVO-treated films to 3-aminopropyltriethoxysilane (APTES), P(S-b-MMA) surface becomes enriched with amine groups which act as binding sites for biomolecules. Under physiological conditions (pH ∼ 7.4), these positively charged nanostructures attract negatively charged F-actin by an electrostatic interaction.
Co-reporter:Michael J. A. Hore and Russell J. Composto
ACS Nano 2010 Volume 4(Issue 11) pp:6941
Publication Date(Web):November 3, 2010
DOI:10.1021/nn101725j
Metallic nanoparticles that absorb and concentrate light are leading to greater efficiencies in nanophotonic devices. By confining gold nanorods (Au NRs) in a polymer film, we can control their spacing and orientation and, in turn, the absorption and polarization characteristics of the nanocomposite. In this study, we systematically increase the volume fraction of Au NRs (ϕrod) (aspect ratio ν = 3.3) while maintaining a uniform dispersion. As ϕrod increases from 1 to 16 vol %, the spacing between rods decreases from 120 to 20 nm and scales as ϕrod−0.4. Simultaneously, the local 2D orientational order parameter increases linearly with ϕrod, although the rods are globally isotropic. The Au NR dispersion is found to depend on the enthalpic interactions between poly(ethylene glycol) brush grafted to the Au NRs and the poly(methyl methacrylate) matrix chains. Furthermore, the plasmon resonance exhibits a red shift with increasing ϕrod, and coupling is observed for separations up to 70 nm. Because NR spacing and orientation can be finely controlled using polymer matrix, these films are ideally suited for understanding fundamental behavior (e.g., plasmon coupling) as well as practical devices (e.g., solar cells).Keywords: alignment; gold nanorods; polymer nanocomposites; surface plasmon coupling
Co-reporter:M. Carme Coll Ferrer, Shu Yang, David M. Eckmann and Russell J. Composto
Langmuir 2010 Volume 26(Issue 17) pp:14126-14134
Publication Date(Web):August 16, 2010
DOI:10.1021/la102315j
In this work, we report the preparation of photoactive dextran and demonstrate its utility by photochemically attaching it onto various polymeric substrates. The attachment of homogeneous and patterned dextran films was performed on polyurethane and polystyrene, with detailed analysis of surface morphology, swelling behavior, and the protein resistance of these substrates. The described photoactive dextran and attachment procedure is applicable to a wide variety of substrates while accommodating surfaces with complex surface geometries. Dextran with azide content between 22 and 0.3 wt % was produced by esterification with p-azidobenzoic acid. Dextran (1.2 wt % azide) was photografted onto plasma oxidized polyurethane and polystyrene and displayed thicknesses of 5 ± 3 and 7 ± 3 nm, respectively. The patterned dextran on oxidized polyurethane was patchy with a nominal height difference between dextranized and nondextranized regions. The azidated dextran on oxidized polystyrene exhibited a distinct step in height. In the presence of phosphate buffered saline (PBS), the dextranized regions became smoother and more uniform without affecting the height difference at the oxidized polyurethane boundary. However, the dextranized regions on oxidized polyurethane were observed to swell by a factor of 3 relative to the dried thickness. These dissimilarities were attributed to hydrogen bonding between the dextran and oxidized polyurethane and were confirmed by the photoimmobiliization in the presence of LiCl. The resulting surface was the smoothest of all the azidated dextran samples (Rrms = 1 ± 0.3 nm) and swelled up to 2 times its dried thickness in PBS. The antifouling properties of dextran functionalized surfaces were verified by the selective adsorption of FITC-labeled human albumin only on the nondextranized regions of the patterned polyurethane and polystyrene substrates.
Co-reporter:Yu Liu, Eric N. Mills and Russell J. Composto
Journal of Materials Chemistry A 2009 vol. 19(Issue 18) pp:2704-2709
Publication Date(Web):05 Mar 2009
DOI:10.1039/B901782H
The thermal reshaping of gold nanorods (NRs) in a poly(methyl methacrylate) (PMMA) nanocomposite film is investigated by UV-vis and TEM. To ensure dispersion, the NRs are modified with PEG brushes, and then dispersed in PMMA. Thermal annealing of the PMMA–NR film results in a blue shift of the longitudinal plasmon resonance, caused by a decrease in the length of the NR. The rate of the blue shift increases as temperature increases from 100 °C to 200 °C, and the longitudinal absorption peak approaches a constant value that scales linearly with temperature. We demonstrate a potential application by fabricating a device with a gradient in optical properties.
Co-reporter:Marla D. McConnell, Alice W. Bassani, Shu Yang and Russell J. Composto
Langmuir 2009 Volume 25(Issue 18) pp:11014-11020
Publication Date(Web):June 12, 2009
DOI:10.1021/la901331q
In this paper, amine-modified silica nanoparticles (NPs) with diameters (d) from 15 to 230 nm are covalently linked to poly(styrene-random-acrylic acid) (P(S-ran-AA)) films, and wettability is studied as a function of diameter and NP surface coverage. During attachment, films swell and exhibit long and short scale roughness, consisting of a ridged, honeycomb structure, ∼1 μm wide and 45−50 nm deep, which encircles nanoscale features 10−15 nm high and ∼50 nm apart. A maximum NP coverage of ∼70% was achieved for d less than or nearly equal to the nanoscale roughness induced by surface swelling. For d several times greater than this nanoscale roughness, the maximum coverage was limited by interparticle repulsion and reached only ∼30%. For NPs with diameters of 15−106 nm, the water contact angle increased from 75° to 120° as NP coverage increased from 0 to 70%. At low and high NP coverage, the Wenzel and Cassie models, respectively, accurately describe the data. However, at intermediate NP coverage, neither model is satisfactory. An increase in surface roughness alone cannot account for this discrepancy. Atomic force microscopy (AFM) studies show that the NPs partially embed into the swollen P(S-ran-AA) surface, suggesting that the amine-coated NPs are wet by the copolymer, exposing low surface energy styrene. These studies demonstrate that control over surface properties of coatings, such as wetting, can be achieved by selecting NP sizes that complement film roughness.
Co-reporter:Marla D. McConnell, Shu Yang and Russell J. Composto
Macromolecules 2009 Volume 42(Issue 2) pp:517-523
Publication Date(Web):December 19, 2008
DOI:10.1021/ma8023156
We present a novel class of nanoparticle-decorated surfaces: amine-functionalized silica nanoparticles covalently attached to poly(styrene-random-acrylic acid) films and carboxylic acid-terminated self-assembled monolayers (SAMs). The dependence of the particle attachment kinetics on the concentration of particles in solution and acrylic acid moieties in the polymer backbone was investigated and was compared to the observed kinetics with SAM substrates. The kinetics on the polymer films included three distinct stages, which were governed by the acrylic acid concentration-dependent morphological changes of the films under the reaction conditions. The first stage was an induction period with little change in the particle coverage with time, followed by a rapid rise in the coverage, and finally a plateau. The maximum coverage achieved for the polymer films, 70%, was nearly twice that of the SAM substrates, which followed diffusion-limited coverage kinetics prior to reaching saturation. This enhanced coverage is attributed to the swelling of the acrylic acid groups at the film surface in the reaction solvent, which increases the surface area and roughness of the substrate. This approach is a reproducible way of preparing nanoparticle-decorated, chemically robust surfaces with controlled coverages and have potential applications for controlling surface wettability, optical properties, and cellular adhesion.
Co-reporter:Chen Xu, Kohji Ohno, Vincent Ladmiral, Daniel E. Milkie, James M. Kikkawa and Russell J. Composto
Macromolecules 2009 Volume 42(Issue 4) pp:1219-1228
Publication Date(Web):February 3, 2009
DOI:10.1021/ma8022266
We investigate self-assembly of nanocomposite films composed of lamellar-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and PMMA-grafted magnetite (Fe3O4) nanoparticles (NPs). The Fe3O4 NPs are grafted with PMMA brushes with molecular weights ranging from 2700 to 35 700 g/mol. For the NP with the lowest molecular weight brush, the morphology of the nanocomposite film depends on the NP concentration (ϕNP). At low ϕNP, the block copolymer self-assembles into mixed morphology of perpendicular lamellae (⊥Lam) and parallel lamellae (∥Lam), and the ⊥Lam are stabilized by individual NPs or small NP aggregates. The NPs can also retard the dynamics of self-assembly of block copolymer films. At high ϕNP, NPs form small aggregates which inhibit the formation of a lamellar structure. As the molecular weight of the PMMA brush increases to 13 300 or 35 700 g/mol, the Fe3O4 NPs form aggregates in the as-cast nanocomposite films, and this behavior is attributed to aggregation of NPs in the solution state. Since the size of NP aggregates is larger than the copolymer domain size, the block copolymer has to self-assemble around these aggregates. The magnetic properties of these nanocomposite films are characterized, and typical superparamagnetic behavior is observed.
Co-reporter:Jung Hyun Park, Yujie Sun, Yale E. Goldman and Russell J. Composto
Macromolecules 2009 Volume 42(Issue 4) pp:1017-1023
Publication Date(Web):January 16, 2009
DOI:10.1021/ma8023393
A morphological transition of asymmetric poly(styrene-b-acrylic acid) (PS-b-PAA) films is observed by in situ scanning probe microscopy (SPM) in aqueous media. Upon initial exposure to buffer solution at pH 7.4, spherical PAA domains swell through a glassy PS surface layer to form negatively charged mushroom caps. With further exposure, the PAA caps coalesce to produce a smooth, highly wettable surface. However, if films are exposed to a buffer solution containing 3-aminopropyltriethoxysilane (APTES) for 1 h, the PAA domain swelling is greatly reduced and the mushroom caps stabilize at a diameter of 33 nm. This stabilization results from a cross-linking reaction between PAA and APTES, which also converts the PAA domains from a net negative to net positive charge. By varying molecular weights of PAA block in PS-b-PAA, the feature size and spacing can be tuned. To demonstrate an application for this template with positively charged domains, a cytoskeletal filament, F-Actin with a net negative charge, is organized on the PS-b-PAA template via electrostatic interactions under physiological conditions. F-Actin shows a tendency to align along the modified PAA mushroom caps.
Co-reporter:Russel M. Walters, Andreas Taubert, Joon-Seop Kim, Karen I. Winey and Russell J. Composto
Macromolecules 2008 Volume 41(Issue 23) pp:9299-9305
Publication Date(Web):November 7, 2008
DOI:10.1021/ma801756g
The surface segregation of cations in a poly(styrene-ran-methacrylic acid) ionomer fully neutralized with Cs was demonstrated using Rutherford backscattering spectrometry (RBS), scanning force microscopy (SFM), and scanning transmission electron microscopy (STEM). Whereas spin-cast films and those annealed below ∼120 °C exhibit a uniform distribution of Cs, a surface excess of Cs was observed for films annealed at higher temperatures. At long times (>30 h) and high temperatures (>145 °C), the surface concentration of Cs approached a constant value of two-thirds of the total Cs in the film. Although Cs-rich vesicular aggregates (∼8−85 nm diameter) were observed in all films, the surface excess of Cs coincided with nanometer-sized features on the surface. Based on these results, a mechanism was proposed that accounts for cation mobility and a driving force for surface segregation. At elevated temperatures, Cs ions initially in cation-acid lone pairs are solubilized by favorable cation-π interactions facilitated by styrene monomers. Above ∼120 °C, these solubilized cations are sufficiently mobile to diffuse. The driving force to the surface arises from the concentration gradient established when Cs at the surface scavenges Cl from the environment to form CsCl. In the polystyrene-based ionomers, surface segregation is not observed if either the cation mobility is reduced by using a divalent cation or the driving force for surface segregation is removed by eliminating atmospheric Cl.
Co-reporter:Pimpon Uttayarat;George K. Toworfe;Franziska Dietrich;Peter I. Lelkes;Pimpon Uttayarat;George K. Toworfe;Franziska Dietrich;Peter I. Lelkes
Journal of Biomedical Materials Research Part A 2005 Volume 75A(Issue 3) pp:668-680
Publication Date(Web):18 AUG 2005
DOI:10.1002/jbm.a.30478
To mimic the uniformly elongated endothelium in natural linear vessels, bovine aortic endothelial cells (BAECs) are cultured on micro- to nanogrooved, model poly(dimethylsiloxane) (PDMS) substrates preadsorbed with about 300 ng/cm2 of fibronectin. BAEC alignment, elongation, and projected area were investigated for channel depths of 200 nm, 500 nm, 1 μm, and 5 μm, as well as smooth surfaces. Except for the 5 μm case, the ridge and channel widths were held nearly constant about 3.5 μm. With increasing channel depth, the percentage of aligned BAECs increased by factors of 2, 2, 1.8, and 1.7 for 1, 4, 24, and 48 h. Maximum alignment, about 90%, was observed for 1 μm deep channels at 1 h. The alignment of BAECs on grooved PDMS was maintained at least until cells reached near confluence. F-actin and vinculin at focal adhesions also aligned with channel direction. Analysis of confocal microscopy images showed that focal adhesions localized at corners and along the sidewalls of 1-μm deep channels. In contrast, focal adhesions could not form on the bottom of the 5-μm deep channels. Cell proliferation was similar on grooved and smooth substrates. In summary, PDMS substrates engraved with micro- and nanochannels provide a powerful method for investigating the interplay between topography and cell/cytoskeletal alignment. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Co-reporter:Michael JA Hore, Russell J Composto
Current Opinion in Chemical Engineering (February 2013) Volume 2(Issue 1) pp:95-102
Publication Date(Web):1 February 2013
DOI:10.1016/j.coche.2012.10.001
Nanorods composed of either noble metals or semiconducting materials have shape anisotropy that imparts nanocomposites with unique optical and electrical properties. This review describes methods for dispersing nanorods within a polymer host, which itself can self-assemble, and controlling nanorod self-assembly, spacing and orientation. In addition, applications of aggregated morphologies are discussed with an emphasis on their use in sensing applications.Highlights► Both aggregated and dispersed nanorod morphologies are desirable for applications. ► The target morphology is dependent upon the physical properties needed for the application. ► Nanorods can be spatially organized within polymers with block copolymer templates. ► External fields can be applied to obtain long range ordering of nanorods. ► Processing conditions can influence long range ordering and need to be considered.
Co-reporter:Hyun-Su Lee, Michael Q. Yee, Yonaton Y. Eckmann, Noreen J. Hickok, David M. Eckmann and Russell J. Composto
Journal of Materials Chemistry A 2012 - vol. 22(Issue 37) pp:NaN19616-19616
Publication Date(Web):2012/07/26
DOI:10.1039/C2JM34316A
This study investigates the swelling of grafted polycationic brushes as a function of pH and anion type. The brushes are chitosan (CH) and chitosans with 27% and 51% degrees of substitution (DS) of quaternary ammonium salts, denoted as CH-Q25 and CH-Q50, respectively. The water content and swelling behaviors are monitored using in situ quartz-crystal microbalance with dissipation (QCM-D). The pH varies from ∼3.5 to 8.5, and the counter anion types include chloride, acetate, and citrate. At fixed pH, the water content and brush swelling increase as the DS increases. While the CH-Q50 brush layer shows symmetric swelling with a minimum near pH = 4.5, the swelling of CH and CH-Q25 is relatively constant as pH decreases from 8.2 to 5.5, and then begins to increase near pH 4. These studies indicate that the symmetric swelling of CH-Q50 is likely attributed to increasing protonation of primary amines at pH values below 6.5 and the quaternary ammonium salts above pH 6.5. At pH 4, the swelling of the CH brush increases upon exchanging the smaller chloride with bulkier acetate anions, which is less effective in screening intra/inter-molecular repulsion. In contrast, upon exchanging the acetate with trifunctional citrate anions, CH and CH-Q25 brushes collapse by 53 and 42%, respectively, because the citrate anions form ionic cross-links. To test antibacterial properties, silicon oxide, CH and CH-Q50 brush layers are exposed to 107–108 cfu ml−1 of S. aureus for two days at 37 °C and to stepped shear stresses at 2 min intervals. While an S. aureus biofilm adheres strongly to silicon oxide and CH for stresses up to 12 dyne per cm2, biofilms on CH-Q50 detach at a relatively low shear stress, 1.5 dyne per cm2. Due to their high degree of swelling that can be tuned via pH, counterion size and type, chitosan and quaternary modified chitosans have potential as responsive coatings for applications including MEMS/NEMS devices and drug eluting implants.
Co-reporter:Yu Liu, Eric N. Mills and Russell J. Composto
Journal of Materials Chemistry A 2009 - vol. 19(Issue 18) pp:NaN2709-2709
Publication Date(Web):2009/03/05
DOI:10.1039/B901782H
The thermal reshaping of gold nanorods (NRs) in a poly(methyl methacrylate) (PMMA) nanocomposite film is investigated by UV-vis and TEM. To ensure dispersion, the NRs are modified with PEG brushes, and then dispersed in PMMA. Thermal annealing of the PMMA–NR film results in a blue shift of the longitudinal plasmon resonance, caused by a decrease in the length of the NR. The rate of the blue shift increases as temperature increases from 100 °C to 200 °C, and the longitudinal absorption peak approaches a constant value that scales linearly with temperature. We demonstrate a potential application by fabricating a device with a gradient in optical properties.
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![Poly[oxy(2,6-dimethyl-1,4-phenylene)]](http://img.cochemist.com/ccimg/25000/24938-67-8_b.png)
