Co-reporter:Namrata Salunke, Asritha Nallapaneni, Guangcui Yuan, Christopher M. Stafford, Hui Niu, Matthew D. Shawkey, R. A. Weiss, and Alamgir Karim
ACS Applied Materials & Interfaces October 11, 2017 Volume 9(Issue 40) pp:35349-35349
Publication Date(Web):September 19, 2017
DOI:10.1021/acsami.7b07245
We report a first-order like sharp surface wettability transition with varying film thickness dependent morphology in cast films of an amphiphilic triblock copolymer. Films composed of poly(2-(N-ethylperfluorooctanesulfonamido) ethyl methyl acrylate), poly(FOSM), and poly(N,N′-dimethyl acrylamide), poly(DMA), with thickness (h) in the transition-range, 200 < h < 300 nm, exhibited an abrupt hydrophobic to hydrophilic dynamic water contact angle transition. After an induction time, ti ≈ 40 to 180 s, water contact angle varied as θc ≈ 116° to 40° with an ultrafast contact angle decay time constant, ≈ −18°/s. This behavior is a result of competing heterogeneous and antagonistic effects of bumpy poly(DMA) wetting domains against a nonwetting planar poly(FOSM) background, with a “jump percolation” wetting transition when the poly(DMA) domain density reaches unity. Outside of this film thickness range, relatively shallow decreasing water contact angle gradients were observed with a monotonically increasing poly(DMA) domain area coverage with increasing film thickness in the overall range of 40 nm (hydrophobic, θc ≈ 118°) < h < 500 nm (hydrophilic, θc ≈ 8°). The optical diffuse reflectance properties of these rough surfaces exhibit an onset of diffuse reflectance maxima correlated to the transition morphology film thickness.Keywords: confinement effects; hydrophilicity; hydrophobicity; jump percolation;
Co-reporter:Danielle Grolman, Diya Bandyopadhyay, Abdullah Al-Enizi, Ahmed Elzatahry, and Alamgir Karim
ACS Applied Materials & Interfaces June 21, 2017 Volume 9(Issue 24) pp:20928-20928
Publication Date(Web):May 31, 2017
DOI:10.1021/acsami.7b00779
Synthetic topographically patterned films and coatings are typically contoured on one side, yet many of nature’s surfaces have distinct textures on different surfaces of the same object. Common examples are the top and bottom sides of the butterfly wing or lotus leaf, onion shells, and the inside versus outside of the stem of a flower. Inspired by nature, we create dual (top and bottom) channel patterned polymer films. To this end, we first develop a novel fabrication method to create ceramic line channel relief structures by converting the oligomeric residue of stamped poly(dimethylsiloxane) (PDMS) nanopatterns on silicon substrates to glass (SiOx, silica) by ultraviolet-ozone (UVO) exposure. These silica patterned substrates are flow coated with polystyrene (PS) films and confined within an identically patterned top confining soft PDMS elastomer film. Annealing of the sandwich structures drives the PS to rapidly mold fill the top PDMS pattern in conjunction with a dewetting tendency of the PS on the silica pattern. Varying the film thickness h, from less than to greater than the pattern height, and varying the relative angle between the top-down and bottom-up patterned confinement surfaces create interesting uniform and nonuniform digitized defects in PS channel patterns, as also a defect-free channel regime. Our dual patterned polymer channels provide a novel fabrication route to topographically imprinted Moiré patterns (whose applications range from security encrypting holograms to sensitive strain gauges), and their basic laser light diffractions properties are illustrated and compared to graphical simulations and 2D-FFT of real-space AFM channel patterns. While traditional “geometrical” and “fringe” Moiré patterns function by superposition of two misaligned optical patterned transmittance gratings, our topographic pattern gratings are quite distinct and may allow for more unique holographic optical characteristics with further development.Keywords: confinement; dewetting; Moiré patterns; self-organization; thin films;
Co-reporter:Monali N. Basutkar, Saumil Samant, Joseph Strzalka, Kevin G. Yager, Gurpreet Singh, and Alamgir Karim
Nano Letters December 13, 2017 Volume 17(Issue 12) pp:7814-7814
Publication Date(Web):November 14, 2017
DOI:10.1021/acs.nanolett.7b04028
Template-free directed self-assembly of ultrathin (approximately tens of nanometers) lamellar block copolymer (l-BCP) films into vertically oriented nanodomains holds much technological relevance for the fabrication of next-generation devices from nanoelectronics to nanomembranes due to domain interconnectivity and high interfacial area. We report for the first time the formation of full through-thickness vertically oriented lamellar domains in 100 nm thin polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films on quartz substrate, achieved without any PMMA-block wetting layer formation, quartz surface modification (templating chemical, topographical) or system modifications (added surfactant, top-layer coat). Vertical ordering of l-BCPs results from the coupling between a molecular and a macroscopic phenomenon. A molecular relaxation induced vertical l-BCP ordering occurs under a transient macroscopic vertical strain field, imposed by a high film thermal expansion rate under sharp thermal gradient cold zone annealing (CZA-S). The parametric window for vertical ordering is quantified via a coupling constant, C (= v∇T), whose range is established in terms of a thermal gradient (∇T) above a threshold value, and an optimal dynamic sample sweep rate (v ∼ d/τ), where τ is the l-BCP’s longest molecular relaxation time and d is the Tg,heat – Tg,cool distance. Real-time CZA-S morphology evolution of vertically oriented l-BCP tracked along ∇T using in situ grazing incidence small angle X-ray scattering (GISAXS) exhibited an initial formation phase of vertical lamellae, a polygrain structure formation stage, and a grain coarsening phase to fully vertically ordered l-BCP morphology development. CZA-S is a roll-to-roll manufacturing method, rendering this template-free through-thickness vertical ordering of l-BCP films highly attractive and industrially relevant.Keywords: block copolymer; Cold zone annealing; in situ; vertical lamellae;
Co-reporter:Saumil P. Samant, Christopher A. Grabowski, Kim Kisslinger, Kevin G. Yager, Guangcui Yuan, Sushil K. Satija, Michael F. Durstock, Dharmaraj Raghavan, and Alamgir Karim
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 12) pp:7966
Publication Date(Web):March 4, 2016
DOI:10.1021/acsami.5b11851
Emerging needs for fast charge/discharge yet high-power, lightweight, and flexible electronics requires the use of polymer-film-based solid-state capacitors with high energy densities. Fast charge/discharge rates of film capacitors on the order of microseconds are not achievable with slower charging conventional batteries, supercapacitors and related hybrid technologies. However, the current energy densities of polymer film capacitors fall short of rising demand, and could be significantly enhanced by increasing the breakdown strength (EBD) and dielectric permittivity (εr) of the polymer films. Co-extruded two-homopolymer component multilayered films have demonstrated much promise in this regard showing higher EBD over that of component polymers. Multilayered films can also help incorporate functional features besides energy storage, such as enhanced optical, mechanical, thermal and barrier properties. In this work, we report accomplishing multilayer, multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP) as a novel application of this important class of self-assembling materials. Results of a model PS-b-PMMA system show ∼50% enhancement in EBD of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. The enhancement in EBD is attributed to the “barrier effect”, where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. The increase in EBD corresponds to more than doubling the energy storage capacity using a straightforward directed self-assembly strategy. This approach opens a new nanomaterial paradigm for designing high energy density dielectric materials.Keywords: barrier effect; block copolymer; breakdown strength; capacitor; cold zone annealing−soft shear; dielectric; directed self-assembly; lamellae
Co-reporter:Ali Ammar, Abdullah M. Al-Enizi, Mariam AlAli AlMaadeed, Alamgir Karim
Arabian Journal of Chemistry 2016 Volume 9(Issue 2) pp:274-286
Publication Date(Web):March 2016
DOI:10.1016/j.arabjc.2015.07.006
Abstract
This paper expresses a short review of research on the effects of graphene oxide (GO) as a nanocomposite element on polymer morphology and resulting property modifications including mechanical, barrier, and electrical conductivity. The effects on mechanical enhancement related to stress measurements in particular are a focus of this review. To first order, varying levels of aggregation of GO in different polymer matrices as a result of their weak inter-particle attractive interactions mainly affect the nanocomposite mechanical properties. The near surface dispersion of GO in polymer/GO nanocomposites can be investigated by studying the surface morphology of these nanocomposites using scanning probe microscopy such as atomic force microscope (AFM) and scanning electron microscope (SEM). In the bulk, GO dispersion can be studied by wide-angle X-ray scattering (WAXD) by analyzing the diffraction peaks corresponding to the undispersed GO fraction in the polymer matrix. In terms of an application, we review how the hydrophilicity of graphene oxide and its hydrogen bonding potential can enhance water flux of these nanocomposite materials in membrane applications. Likewise, the electrical conductivity of polymer films and bulk polymers can be advantageously enhanced via the percolative dispersion of GO nanoparticles, but this typically requires some additional chemical treatment of the GO nanoparticles to transform it to reduced GO.
Co-reporter:Berhanu Zewde;Praveen Pitliya;Dharmaraj Raghavan
Macromolecular Materials and Engineering 2016 Volume 301( Issue 5) pp:542-548
Publication Date(Web):
DOI:10.1002/mame.201500279
Co-reporter:Abul F. Huq, Manish Kulkarni, Arvind Modi, Detlef-M. Smilgies, Abdullah M. Al-Enizi, Ahmed Elzatahry, Dharmaraj Raghavan, Alamgir Karim
Polymer 2016 Volume 82() pp:22-31
Publication Date(Web):15 January 2016
DOI:10.1016/j.polymer.2015.10.049
•PCBM nanoparticles in amphiphilic PS-PEO block copolymer films.•Vertical ordering of block copolymer with high loading ∼30 wt%.•Effects of casting solvents, single and mixed solvents.•Potentially impact on block copolymer solar cells.We demonstrate selective dispersion of photosensitive electron acceptor phenyl-C61-butyric acid methyl ester (PCBM) in cylinder forming polystyrene-b-poly (ethylene oxide) (PS-b-PEO) block copolymer (BCP). Neat PS-b-PEO is structurally robust to forming vertically oriented nanoscale morphology of PEO cylinders in the PS matrix directly after solvent casting. Varying amounts of PCBM nanoparticles were mixed with PS-b-PEO BCP in solvent mixtures and films were spin cast on UV/ozone treated clean silicon wafers. We studied in detail the BCP morphology orientation effect of different solvents and solvent mixtures for varying PCBM loading (ϕPCBM) in the films, range from 0 to 50 weight percent relative to the BCP. The key accomplishments of this work include vertical orientation control even at large concentration of PCBM ∼30% (w/w) particles relative to polymer mass and preferential segregation of PCBM in PS block via mixed solvent strategy which otherwise is difficult to realize due to segregation of PCBM on polar substrate. We explain the preferential dispersion of particles in films by demarcating limits in terms of critical Hansen solubility parameter. This value is close to the percolation threshold of PCBM, so a conducting polymer matrix can be expected, especially when it is partitioned preferentially in the matrix PS domain. We report changes in PEO cylinder diameter, cylinder center-to-center distance with PCBM incorporation into PS matrix, change of film thickness with overall PCBM incorporation and root mean square roughness of the film surface, for a range of casting solvents, solvent mixture compositions and ϕPCBM. Notably, the film thickness increased as the PCBM content in film was increased for same processing condition, so that domain swelling by nanoparticles was self-adjusting with film thickness increment.
Co-reporter:Melanie Longanecker, Arvind Modi, Andrey Dobrynin, Seyong Kim, Guangcui Yuan, Ronald Jones, Sushil Satija, Joona Bang, and Alamgir Karim
Macromolecules 2016 Volume 49(Issue 22) pp:8563-8571
Publication Date(Web):November 11, 2016
DOI:10.1021/acs.macromol.6b01690
Block copolymers (BCPs) can function as nanoscale templates to organize nanoparticles within selective domains. Most functional applications of nanofilled BCPs generally require a high loading of nanoparticles, which is difficult to achieve due to particle aggregation, slow kinetics of ordering, and disruption of block copolymer order. A key parameter is the periodic domain spacing, L0, which is important for tuning functional properties. We demonstrate direct immersion annealing (DIA) as a promising directed self-assembly (DSA) method to overcome these problems. DIA is shown to fully order highly filled (10.5 vol % Au-PSrPMMA nanoparticles) lamellar poly(styrene-b-methyl methacrylate) (PS–PMMA) BCP films, whose lamellar ordering is practically unimpeded by filler loading. Neutron reflection (NR) further confirms that DIA sharpens the interfacial width between PS–PMMA domains by ∼20%. In situ NR studies further reveal that DIA predominantly induced film ordering in a 5 wt % anisotropic organoclay (C93A) filled PS–PMMA film in less than 30 s! In contrast, identical C93A nanofilled PS–PMMA films that were thermally annealed (19 h at 160 °C) only exhibit partial ordering near the free surface. DIA films also exhibit ∼50% reduced L0, resulting in twice the number of BCP domains, potentially useful to film functional properties such as gas barrier when filled with clay or plasmonics for gold nanoparticles. We further model this reduced L0 in DIA processed films with a scaling approach to correlate the final structure to degree of polymerization, N. Our results reveal that DIA, a roll-to-roll (R2R) compatible DSA method, can enable real-time manufacture of nanofilled block copolymers for functional applications.
Co-reporter:Ren Zhang, Bongjoon Lee, Michael R. Bockstaller, Sanat K. Kumar, Christopher M. Stafford, Jack F. Douglas, Dharmaraj Raghavan, and Alamgir Karim
Macromolecules 2016 Volume 49(Issue 10) pp:3965-3974
Publication Date(Web):May 12, 2016
DOI:10.1021/acs.macromol.6b00228
The controlled organization of nanoparticle (NP) constituents into superstructures of well-defined shape, composition, and connectivity represents a continuing challenge in the development of novel hybrid materials for many technological applications. We show that the phase separation of polymer-tethered nanoparticles immersed in a matrix of a chemically different polymer provides an effective and scalable method for fabricating well-defined submicron-sized amorphous NP domains in melt polymer thin films. We investigate this phenomenon with a view toward a better understanding and control of the phase separation process in these novel “blends”. In particular, we consider isothermally annealed thin films of polystyrene-grafted gold nanoparticles (AuPS) dispersed in a poly(methyl methacrylate) (PMMA) matrix. A morphology transition from discrete AuPS domains to bicontinuous to inverse domain structure is observed with increasing nanoparticle loading, consistent with composition dependence of classic binary polymer blends phase separation. However, the phase separation kinetics of the NP–polymer blends exhibit unique features compared to the parent PS/PMMA homopolymer blends. We further illustrate how to manipulate the AuPS nanoparticle domain shape, size, and location through the imposition of an external symmetry-breaking perturbation. Specifically, topographically patterned elastomer confinement is introduced to direct the nanoparticles into long-range ordered submicron-sized domains having a dense and well-dispersed distribution of noncrystallizing nanoparticles. The simplicity, versatility, and roll-to-roll adaptability of this novel method for controlled nanoparticle assembly should make it useful in creating desirable patterned nanoparticle domains for a variety of functional materials and applications.
Co-reporter:Saumil Samant, Joseph Strzalka, Kevin G. Yager, Kim Kisslinger, Danielle Grolman, Monali Basutkar, Namrata Salunke, Gurpreet Singh, Brian Berry, and Alamgir Karim
Macromolecules 2016 Volume 49(Issue 22) pp:8633-8642
Publication Date(Web):October 31, 2016
DOI:10.1021/acs.macromol.6b01555
Dynamic thermal gradient-based processes for directed self-assembly of block copolymer (BCP) thin films such as cold zone annealing (CZA) have demonstrated much potential for rapidly fabricating highly ordered patterns of BCP domains with facile orientation control. As a demonstration, hexagonally packed predominantly vertical cylindrical morphology, technologically relevant for applications such as membranes and lithography, was achieved in 1 μm thick cylinder-forming PS-b-PMMA (cBCP) films by applying sharp thermal gradients (CZA-Sharp) at optimum sample sweep rates. A thorough understanding of the molecular level mechanisms and pathways of the BCP ordering that occur during this CZA-S process is presented, useful to fully exploit the potential of CZA-S for large-scale BCP-based device fabrication. To that end, we developed a customized CZA-S assembly to probe the dynamic structure evolution and ordering of the PS-b-PMMA cBCP film in situ as it undergoes the CZA-S process using the grazing incidence small-angle X-ray scattering (GISAXS) technique. Four distinct regimes of BCP ordering were observed within the gradient that include microphase separation from an “as cast” unordered state (Regime I), evolution of vertical cylinders under a thermally imposed strain gradient (Regime II), reorientation of a fraction of cylinders due to preferential substrate interactions (Regime III), and finally grain-coarsening on the cooling edge (Regime IV). The ordering pathway in the different regimes is further described within the framework of an energy landscape. A novel aspect of this study is the identification of a grain-coarsening regime on the cooling edge of the gradient, previously obscure in zone annealing studies of BCPs. Such insights into the development of highly ordered BCP nanostructures under template-free thermal gradient fields can potentially have important ramifications in the field of BCP-directed self-assembly and self-assembling polymer systems more broadly.
Co-reporter:Arvind Modi, Sarang M. Bhaway, Bryan D. Vogt, Jack F. Douglas, Abdullah Al-Enizi, Ahmed Elzatahry, Ashutosh Sharma, and Alamgir Karim
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 39) pp:21639
Publication Date(Web):September 9, 2015
DOI:10.1021/acsami.5b06259
We demonstrate ordering of thin block copolymer (BCP) films via direct immersion annealing (DIA) at enhanced rate leading to stable morphologies. The BCP films are immersed in carefully selected mixtures of good and marginal solvents that can impart enhanced polymer mobility, while inhibiting film dissolution. DIA is compatible with roll-to-roll assembly manufacturing and has distinct advantages over conventional thermal annealing and batch processing solvent-vapor annealing methods. We identify three solvent composition-dependent BCP film ordering regimes in DIA for the weakly interacting polystyrene–poly(methyl methacrylate) (PS–PMMA) system: rapid short-range order, optimal long-range order, and a film instability regime. Kinetic studies in the “optimal long-range order” processing regime as a function of temperature indicate a significant reduction of activation energy for BCP grain growth compared to oven annealing at conventional temperatures. An attractive feature of DIA is its robustness to ordering other BCP (e.g. PS-P2VP) and PS-PMMA systems exhibiting spherical, lamellar and cylindrical ordering.Keywords: block copolymer ordering; direct immersion annealing; kinetics; mixed solvents
Co-reporter:Kevin G. Yager, Christopher Forrey, Gurpreet Singh, Sushil K. Satija, Kirt A. Page, Derek L. Patton, Jack F. Douglas, Ronald L. Jones and Alamgir Karim
Soft Matter 2015 vol. 11(Issue 25) pp:5154-5167
Publication Date(Web):01 Jun 2015
DOI:10.1039/C5SM00896D
Block-copolymer orientation in thin films is controlled by the complex balance between interfacial free energies, including the inter-block segregation strength, the surface tensions of the blocks, and the relative substrate interactions. While block-copolymer lamellae orient horizontally when there is any preferential affinity of one block for the substrate, we recently described how nanoparticle-roughened substrates can be used to modify substrate interactions. We demonstrate how such ‘neutral’ substrates can be combined with control of annealing temperature to generate vertical lamellae orientations throughout a sample, at all thicknesses. We observe an orientational transition from vertical to horizontal lamellae upon heating, as confirmed using a combination of atomic force microscopy (AFM), neutron reflectometry (NR) and rotational small-angle neutron scattering (RSANS). Using molecular dynamics (MD) simulations, we identify substrate-localized distortions to the lamellar morphology as the physical basis of the novel behavior. In particular, under strong segregation conditions, bending of horizontal lamellae induce a large energetic cost. At higher temperatures, the energetic cost of conformal deformations of lamellae over the rough substrate is reduced, returning lamellae to the typical horizontal orientation. Thus, we find that both surface interactions and temperature play a crucial role in dictating block-copolymer lamellae orientation. Our combined experimental and simulation findings suggest that controlling substrate roughness should provide a useful and robust platform for controlling block-copolymer orientation in applications of these materials.
Co-reporter:Kai Wang, Chang Liu, Pengcheng Du, Long Chen, Jiahua Zhu, Alamgir Karim, Xiong Gong
Organic Electronics 2015 Volume 21() pp:19-26
Publication Date(Web):June 2015
DOI:10.1016/j.orgel.2015.02.023
•Efficiency of 11.88% was obtained using ~600 nm thick perovskite film.•Device performance was correlated with the perovskite film thickness and morphology.•Perovskite film morphologies are dependent on the perovskite film thicknesses.•Both perovskite film thickness and morphologies affect the device performance.Perovskite hybrid solar cells (pero-HSCs) have been intensively investigated due to their promising photovoltaic performance. However, the correlations between the efficiencies of pero-HSCs and thin film thicknesses and morphologies of CH3NH3PbI3−xClx perovskite layers are rarely addressed. In this study, we report the correlation between the efficiencies of “planar heterojunction” (PHJ) pero-HSCs and the thin film thicknesses and morphologies of solution-processed CH3NH3PbI3−xClx perovskite layers. Investigation of absorption spectra, X-ray diffraction patterns, atomic force microscopy and scanning electron microscopy images of CH3NH3PbI3−xClx layers indicate that the efficiencies of PHJ pero-HSCs are dependent on the film thickness, as the thickness of CH3NH3PbI3−xClx is less than 400 nm; whereas the efficiencies are significantly dependent on the film morphologies of CH3NH3PbI3−xClx layers as the thickness is larger than 400 nm. Our studies provide a promising pathway for fabricating high efficiency PHJ pero-HSCs.
Co-reporter:Sudeshna Roy, Diya Bandyopadhyay, Alamgir Karim, and Rabibrata Mukherjee
Macromolecules 2015 Volume 48(Issue 2) pp:373-382
Publication Date(Web):January 15, 2015
DOI:10.1021/ma501262x
It is known that dewetting of a polystyrene (PS) thin film on a silicon substrate gets completely suppressed upon addition of small amount of C60 nanoparticles (NP).1 The NPs migrate to the film–substrate interface and forms an enriched surface layer of the particles that eventually stabilizes the film by apparent pinning. In this article we quantitatively highlight the unexplored effect of substrate surface energy (γS) on the migration of the NPs to the film–substrate interface and their contribution on dewetting suppression. Depending on the relative magnitudes of NP concentration (CNP) and γS, we identify three distinct stability regimes. In regime 1 (CNP < 0.2%) there is no suppression of dewetting and the final polygonal arrangement of droplets closely resemble dewetted structures in particle free films. However, the size of the polygons becomes smaller in NP containing films when γS < γC60 (NP surface energy) and larger as γS exceeds γC60. In regime 2 (0.3% < CNP < 0.75%) the films dewet partially, and the extent of dewetting is seen to strongly dependent on the relative magnitudes of γC60 and γS. While dewetting proceeds up to the stage of partial hole growth and coalescence when γS < γC60, some random isolated holes are seen to form when γS > γC60. On the basis of direct AFM imaging, we show that in both regimes 1 and 2 the NPs migrate to the substrate–film interface only when γS > γC60. We show complete suppression of dewetting in regime 3 (CNP > 1.0%), where the particles are seen to migrate to the substrate for all values of γS. The work highlights that entropy driven migration of particles takes place on substrates with any γS only above a critical NP concentration (CNPC) and only on substrates with γS > γC60 when CNP < CNPC. The findings, apart from dewetting suppressing, can guide potential design criteria for applications such as electron extracting layer in organic photovoltaic.
Co-reporter:Saumil Samant;Shimelis T. Hailu;Abdullah M. Al-Enizi;Dharmaraj Raghavan
Journal of Polymer Science Part B: Polymer Physics 2015 Volume 53( Issue 8) pp:604-614
Publication Date(Web):
DOI:10.1002/polb.23684
ABSTRACT
Nanoparticles provide an attractive route to modifying polymer thin film properties, yet controlling the dispersion and morphology of functionalized nanoparticle filled films is often difficult. Block copolymers can provide an ideal template for directed assembly of nanoparticles under controlled nanoparticle-polymer interactions. Previously we observed that neat films of cylinder forming poly(styrene-b-methyl methacrylate) PS-b-PMMA block copolymer (c-BCP) orient vertically with dynamic sharp thermal cold zone annealing (CZA-S) over wide range of CZA-S speed (0.1–10) μm/s. Here, we introduce a low concentration (1–5 wt %) of nanoparticles of phenolic group functionalized CdS (fCdS-NP), to PMMA cylinder forming polystyrene-b-poly (methyl methacrylate) block copolymer (c-BCP) films. Addition of the fCdS-NP induces a vertical to horizontal orientation transition at low CZA-S speed, V = 5 μm/s. The orientation flip studies were analyzed using AFM and GISAXS. These results confirm generality of our previously observed orientation transition in c-BCP under low speed CZA-S with other nanoparticles (gold [Au-NP], fulleropyrrolidine [NCPF-NP]) in the same concentration range, but reveal new aspects not previously examined: (1) A novel observation of significant vertical order recovery from 5–10% vertical cylindrical fraction at V = 5 μm/s to 46–63% vertical cylindrical fraction occurring at high CZA-S speed, V = 10 μm/s for the fCdS nanoparticle filled films. (2) We rule out the possibility that a nanoparticle wetting layer on the substrate is responsible for the vertical to horizontal flipping transition. (3) We demonstrate that the orientation flipping results can be achieved in a nanoparticle block copolymer system where the nanoparticles are apparently better-dispersed within only one (matrix PS) domain unlike our previous nanoparticle system studied. We consider facile processing conditions to fabricate functionalized nanoparticles filled PS-PMMA block copolymer films with controlled anisotropy, a useful strategy in the design of next generation electronic and photonic materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 604–614
Co-reporter:Hongyi Yuan, Gurpreet Singh, Dharmaraj Raghavan, Abdullah M. Al-Enizi, Ahmed Elzatahry, and Alamgir Karim
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 16) pp:13378
Publication Date(Web):July 25, 2014
DOI:10.1021/am5026819
Structure–interaction–mechanical property correlation in bionanocomposite thin films is an area of growing interest for research and application areas from barrier to molecular transport to UV blocking layers for polymer solar cells to dielectric properties modification. Here we study flow coated ultrathin to thin films (70–150 nm) of clay bionanocomposites to understand the nanoparticle dispersion and its effect on nanomechanical properties. Binary and ternary thin film systems of polylactide (PLA), polycaprolactone (PCL), and Cloisite 30B (C30B) clay platelets were investigated. While C30B was only partially intercalated by PLA, it was almost completely intercalated by PCL due to strong hydrogen bonding. In addition, the dispersion of C30B improved continuously and linearly with increasing PCL content in homogeneously cast blended PLA:PCL. GIWAXS confirmed that the intercalated clay platelets in PLA and PCL were dominantly oriented parallel to the substrate. The method of strain induced elastic buckling instability for mechanical measurements (SIEBIMM) showed that pure PLA and PCL had in-plane modulus unchanged from bulk values for this range of ultrathin–thin films. In PLA/C30B nanocomposite thin films, the in-plane elastic modulus rapidly increased by up to 26% with 2 wt % C30B, but saturated thereafter up to 10 wt % C30B forming C30B aggregates. On the other hand, the in-plane elastic modulus of PCL/C30B thin films increased linearly by up to 43% with 10 wt % C30B due to the higher interaction driven dispersion, results that were shown to fit well with the Halpin–Tsai model. We conclude that the different strengthening behavior came from different interaction driven dispersion states of C30B in polymer matrices, governed by their molecular structures.Keywords: biopolymer; clay; elastic modulus; nanocomposite thin films; state of dispersion
Co-reporter:Xiaohua Zhang, Kevin G. Yager, Jack F. Douglas and Alamgir Karim
Soft Matter 2014 vol. 10(Issue 20) pp:3656-3666
Publication Date(Web):19 Mar 2014
DOI:10.1039/C4SM00238E
We examine the effect of a moving in-plane temperature gradient on the ordering of cylinder-forming block-copolymers (BCP) in films containing immobilized nanoparticles that span the film thickness. In a previous paper, we reported the effect of static step oven-annealing of these films above the glass transition temperature Tg for a long period before ordering the BCP film at a much higher temperature. In the dynamic film annealing method of the present work, termed cold zone annealing (CZA), the material is continuously raised to a temperature somewhat above the glass transition temperature and then well above it, with a control of the heating time and thermal gradient. Oven annealing before ordering has been found to relieve residual stresses in the film associated with large thermal expansion of the film upon heating, eliminating the large scale target patterns induced by stresses effects associated with residual solvent and thermal expansion. By comparison, CZA naturally suppresses undesirable target patterning with enhanced ordering kinetics created through this thermal history.
Co-reporter:Diya Bandyopadhyay, Gurpreet Singh, Matthew L. Becker, and Alamgir Karim
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 10) pp:4006
Publication Date(Web):April 12, 2013
DOI:10.1021/am4002502
We show that temporary confinement of polystyrene thin films by an elastomeric capping layer possessing nanoimprinted subcapillary wavelength (λ ≪ λcap (20 μm)) line channels (amplitude A ≈ 120 nm) can suppress film dewetting on thermodynamically unfavorable substrates by arresting the amplitude growth and in-plane propagation of the destabilizing surface capillary waves. Confinement by either a smooth elastomer capping layer (A ≈ 1 nm) or with pattern features above the threshold dimension only retards dewetting but does not prevent it. The nanoimprint pattern is therefore essential to preventing dewetting, illustrating that only the penalty of elastomer deformation and interfacial tension reduction is insufficient.Keywords: capillary wave; dewetting; flexible confinement; nanopattern; polymer films;
Co-reporter:Brian C. Berry, Gurpreet Singh, Ho-Cheol Kim, and Alamgir Karim
ACS Macro Letters 2013 Volume 2(Issue 4) pp:346
Publication Date(Web):April 8, 2013
DOI:10.1021/mz400054y
Directed self-assembly of cylinder forming block copolymer (c-BCP) thin films via a dynamic thermal field on multidimensional symmetric graphoepitaxy channels is reported. A synergy of dynamic thermal and static boundary fields induces highly aligned c-BCP cylinders inside the channels with a power law dependence of orientational order parameter f, on trench width, f ∼ d–0.3, analogous to dual-field alignment of semiconducting metals and liquid crystals on graphoepitaxy surfaces, f′ ∼ d–1. Static thermal annealing of identical films in a vacuum oven for several days fails to produce comparable results. Furthermore, we demonstrate global c-BCP cylinder alignment over mesas and trenches by tuning the synergy between the dynamic thermal field and asymmetry of the graphoepitaxy static field.
Co-reporter:Ren Zhang;Gurpreet Singh;Alei Dang;Lu Dai;Michael R. Bockstaller;Bulent Akgun;Sushil Satija
Macromolecular Rapid Communications 2013 Volume 34( Issue 20) pp:1642-1647
Publication Date(Web):
DOI:10.1002/marc.201300485
Co-reporter:Jolanta E. Marszalek;Carl G. Simon Jr.;Charles Thodeti;Ravi Kumar Adapala;Ananth Murthy
Journal of Biomedical Materials Research Part A 2013 Volume 101A( Issue 5) pp:1502-1510
Publication Date(Web):
DOI:10.1002/jbm.a.34439
Abstract
Previously, we used 2D films to identify an annealed PCL-PDLLA phase-separated blend morphology which provided nanoscale surface texture and patterning that stimulated osteoblast differentiation. In order to translate these 2D surface nanopatterning effects to the walls of 3D salt-leached scaffolds, the blend phase morphology of scaffold walls must be characterized. For salt-leached scaffolds, NaCl is used as a porogen, which may affect phase separation in PCL-PDLLA blends. However, it is not possible to characterize the surface blend morphology of 3D scaffold walls using standard approaches such as AFM or optical microscopy, since scaffolds are too rough for AFM and do not transmit light for optical microscopy. We introduce a 2.5D approach that mimics the processing conditions of 3D salt-leached scaffolds, but has a geometry amenable to surface characterization by AFM and optical microscopy. For the 2.5D approach, PCL-PDLLA blend films were covered with NaCl crystals prior to annealing. The presence of NaCl significantly influenced blend morphology in PCL-PDLLA 2.5D constructs causing increased surface roughness, higher percent PCL area on the surface and a smaller PCL domain size. During cell culture on 2.5D constructs, osteoblast (MC3T3-E1) and dermal endothelial cell (MDEC) adhesion were enhanced on PCL-PDLLA blends that were annealed with NaCl while chondrogenic cell (ATDC5) adhesion was diminished. This work introduces a 2.5D approach that mimicked 3D salt-leached scaffold processing, but enabled characterization of scaffold surface properties by AFM and light microscopy, to demonstrate that the presence of NaCl during annealing strongly influenced polymer blend surface morphology and cell adhesion. Published 2012 Wiley Periodicals, Inc.† J Biomed Mater Res Part A, 2013.
Co-reporter:Diya Bandyopadhyay, Danielle Grolman, Gurpreet Singh, Jack F. Douglas, Alamgir Karim
Polymer 2013 Volume 54(Issue 22) pp:6206-6209
Publication Date(Web):18 October 2013
DOI:10.1016/j.polymer.2013.08.063
We examine the effects of high fullerene nanoparticle (f-NP) concentrations, ϕf-NP ∼ (10–20) mass% on polystyrene (PS)/polybutadiene (PB) blend thin film stability. Dewetting of the polymer blend around spinodally clustered f-NPs in this high concentration limit leads to a spinodal like dewetting morphology. This is in contrast to our previously observed results on the stabilization effects of f-NPs on PS/PB blend thin films in the intermediate f-NP concentration range of 7–10 mass%, wherein, after saturating the polymer–blend interface, the NPs stabilize the film by segregating to the blend–substrate interface. We determine three regimes of polymer blend film stability as a function of filler concentration: a) ϕf-NP < 7 mass% where preferential segregation of the f-NPs to the polymer–polymer interface leads to macroscopic dewetting, b) ϕf-NP ∼ (7–10) mass% where PS/PB blend films exhibit complete film stability, and c) ϕf-NP ∼ (11–20) mass%, where spinodal clustering of the f-NPs gives rise to polymer–NP phase exclusion and subsequent dewetting.
Co-reporter:Gurpreet Singh, Saurabh Batra, Ren Zhang, Hongyi Yuan, Kevin G. Yager, Miko Cakmak, Brian Berry, and Alamgir Karim
ACS Nano 2013 Volume 7(Issue 6) pp:5291
Publication Date(Web):May 6, 2013
DOI:10.1021/nn401094s
Large-scale roll-to-roll (R2R) fabrication of vertically oriented nanostructures via directed self-assembly of cylindrical block copolymer (c-BCP) thin films is reported. Nearly 100% vertical orientation of cylinders in sub-100 nm c-BCP films under optimized processing via a dynamic sharp temperature gradient field termed Cold Zone Annealing-Sharp or ‘CZA-S’ is achieved, with successful scale-up on a prototype custom-built 70 ft × 1 ft R2R platform moving at 25 μm/s, with 9 consecutive CZA units. Static thermal annealing of identical films in a conventional vacuum oven fails to produce comparable results. As a potential for applications, we fabricate high-density silicon oxide nanodot arrays from the CZA-S annealed BCP thin film template.Keywords: block copolymer; directed self assembly; roll to roll; zone annealing
Co-reporter:Amit Sehgal, Dipankar Bandyopadhyay, Kajari Kargupta, Ashutosh Sharma and Alamgir Karim
Soft Matter 2012 vol. 8(Issue 40) pp:10394-10402
Publication Date(Web):28 Aug 2012
DOI:10.1039/C2SM26369F
We study templating and patterning strategies of an ultrathin (<100 nm) polystyrene (PS) film on substrates with varying lateral confinement produced by linear chemical patterns. The patterned surfaces are fabricated by coating self-assembled monolayers (SAMs) of alternating less (–CH3) and more wettable (–COOH) micro-stripes on gold-coated silicon surfaces. The width of the less wettable stripe was changed from 1 to 15 μm to uncover the influence of the lateral confinement on the dewetted patterns while keeping constant the film thickness (65 nm) and the width of the more wettable stripes (3 μm). When the less wettable stripes are highly confined (<6 μm), both experiments and simulations show a finite amplitude periodic deformation of the PS free surface that replicates the substrate pattern without film rupture. For moderately confined less wettable stripes, ideal templating of the substrate patterns on the polymer surface was observed by film rupture. Combined ridge and drop morphologies were observed when the less wettable stripes have higher widths (low confinement). Shallow ridges are found to form over the more wettable stripes at the initial stages of dewetting whereas larger droplets are found to form over the less wettable stripes at the later stages of dewetting. Interestingly, the arrangement of the droplets does not randomize even when the lateral confinement of the less wettable patterns is rather low, reflecting a long-term memory of boundary effects. A parametric kinetic study uncovered the following morphologies: (i) small aspect ratio pattern replication when the less wettable stripes are highly confined; (ii) larger aspect ratio for the ridges on a substrate with moderately confined less wettable stripes; (iii) near equilibrium morphology when the ridges and droplets coexist on a less wettable stripe with very low confinement. In the latter case, although the droplets are much larger than the ridges, they have similar aspect ratios.
Co-reporter:Manish M. Kulkarni, Kevin G. Yager, Ashutosh Sharma, and Alamgir Karim
Macromolecules 2012 Volume 45(Issue 10) pp:4303-4314
Publication Date(Web):May 1, 2012
DOI:10.1021/ma300169a
Morphology control of block copolymer (BCP) thin films through substrate interaction via controlled roughness parameters is of significant interest for numerous high-tech applications ranging from solar cells to high-density storage media. While effects of substrate surface energy (SE) and roughness (R) on BCP morphology have been individually investigated, their synergistic effects have not been explored in any systematic manner. Interestingly, orientation response of BCP to changes in SE can be similar to what can be accomplished with variations in R. Here we present a novel approach for orienting lamellar BCP films of poly(styrene)-block-poly(methyl methacrylate) (PS–PMMA) on spin-coated xerogel (a dried gel of silica nanoparticle network) substrate with simultaneously tunable surface energy, γs ∼ 29–53 mJ/m2, by UVO exposure and roughness, Rrms ∼ 0.5–30 nm, by sol–gel processing steps of regulating the catalyst concentration and sol aging time. As in previous BCP orientation studies on 20 nm diameter monodisperse silica nanoparticle coated surface, we find a similar but broadened oscillatory BCP orientation behavior with film thickness due to the random rather than periodic rough surfaces. We also find that higher random roughness amplitude is not the necessary criteria for obtaining a vertical orientation of BCP lamellae. Rather, a high surface fractal dimension (Df > 2.4) of the rough substrate in conjunction with an optimal substrate surface energy γs ∼29 mJ/m2 results in 100% vertically oriented lamellar microdomains. The AFM measured film surface microstructure correlates well with the internal 3D BCP film structure probed by grazing incidence small-angle X-ray scattering (GISAXS) and rotational small-angle neutron scattering (SANS). In contrast to tunable self-assembled monolayer (SAM)-coated substrates, the xerogel films are very durable and retain their chemical properties over period of several months. These results also highlight importantly that BCP orientation control for nanotechnology is possible not only on specially prepared patterned substrates but also on industrially viable sol–gel substrates.
Co-reporter:Diya Bandyopadhyay, Jack F. Douglas, and Alamgir Karim
Macromolecules 2012 Volume 45(Issue 11) pp:4716-4722
Publication Date(Web):June 1, 2012
DOI:10.1021/ma300008e
We investigate the effects of fullerene nanoparticles (f-NP) on the dewetting morphology in the immiscible temperature regime of blend films of polystyrene (PS) and polybutadiene (PB) on silicon substrate. As in our former work in the miscible temperature regime of this blend film, competitive partitioning of the f-NPs to the polymer–polymer and the substrate interfaces in blend films requires a larger concentration of f-NPs (∼10 mass %) to suppress film dewetting than in homopolymer components (∼2 mass %). In contrast, however, phase-separated blend films rapidly dewet into hemispherical droplets due to finite interfacial tension of internal blend components unlike irregular shape droplets obtained in miscible blend films. The effect of the f-NPs (1 mass % to 5 mass % f-NP) is to simultaneously reduce the size and contact angle of the dewet droplets, but the hemispherical shape of droplets is maintained, suggesting the f-NPs act to (a) only reduce the phase-separated blend interfacial tension but not fully compatibilize it into single phase and (b) reduce the blend substrate interfacial tension progressively. Selective solvent etching of the PS blend component reveals a spherical PS core enclosed within a circular PB shell at all f-NP concentrations. Confocal fluorescence microscopy reveals that the f-NPs are distributed in both phases consistent with the hemispherical shape and calculations that predict only a weak reduction of interfacial tension. The dewet blend droplet contact angle (likewise polymer–substrate interfacial tension) measured by atomic force microscopy shows a bimodal behavior, reducing rapidly (by 40%) at low (0.1 mass %) f-NP levels and significantly slowing down at higher f-NP concentrations. Molecular surfactant like behavior of the f-NPs in the blend films then provides an effective means of tuning dewetting blend film morphology dimensions without compromising phase behavior for potential applications in nanotechnology and nanomedicine.
Co-reporter:Gurpreet Singh, Kevin G. Yager, Brian Berry, Ho-Cheol Kim, and Alamgir Karim
ACS Nano 2012 Volume 6(Issue 11) pp:10335
Publication Date(Web):October 24, 2012
DOI:10.1021/nn304266f
As demand for smaller, more powerful, and energy-efficient devices continues, conventional patterning technologies are pushing up against fundamental limits. Block copolymers (BCPs) are considered prime candidates for a potential solution via directed self-assembly of nanostructures. We introduce here a facile directed self-assembly method to rapidly fabricate unidirectionally aligned BCP nanopatterns at large scale, on rigid or flexible template-free substrates via a thermally induced dynamic gradient soft-shear field. A localized differential thermal expansion at the interface between a BCP film and a confining polydimethylsiloxane (PDMS) layer due to a dynamic thermal field imposes the gradient soft-shear field. PDMS undergoes directional expansion (along the annealing direction) in the heating zone and contracts back in the cooling zone, thus setting up a single cycle of oscillatory shear (maximum lateral shear stress ∼12 × 104 Pa) in the system. We successfully apply this process to create unidirectional alignment of BCP thin films over a wide range of thicknesses (nm to μm) and processing speeds (μm/s to mm/s) using both a flat and patterned PDMS layer. Grazing incidence small-angle X-ray scattering measurements show absolutely no sign of isotropic population and reveal ≥99% aligned orientational order with an angular spread Δθfwhm ≤ 5° (full width at half-maximum). This method may pave the way to practical industrial use of hierarchically patterned BCP nanostructures.Keywords: block copolymer; flexible substrate; hierarchical patterning; PDMS template; thermal expansion induced shear; unidirectional nanostructures; zone annealing
Co-reporter:Gurpreet Singh, Kevin G. Yager, Detlef-M. Smilgies, Manish M. Kulkarni, David G. Bucknall, and Alamgir Karim
Macromolecules 2012 Volume 45(Issue 17) pp:7107-7117
Publication Date(Web):August 22, 2012
DOI:10.1021/ma301004j
Fabricating vertically ordered and etchable high aspect ratio nanodomains of block copolymer (BCP) thin films on diverse substrates via continuous processing dynamic cold zone annealing (CZA) is particularly attractive for nanomanufacturing of next-generation electronics. Previously, we reported dynamic CZA studies with a shallow thermal gradient (maximum ∇T ∼ 14 °C/mm) that produced only BCP cylinders oriented parallel to substrate. Here, we report a CZA utilizing a dynamic sharp thermal gradient (∇T ∼ 45 °C/mm) (i.e., CZA-S). This method allows for production of etchable and vertically oriented cylindrical domains of poly(styrene-b-methyl methacrylate) in 100–1000 nm thick films on low thermal conductivity rigid (quartz) and flexible (PDMS, Kapton) substrates. Competing substrate wetting interactions dominate BCP orientation in films below 100 nm while broadening of the thermal gradient profile in films thicker than 1000 nm leads to loss of vertical orientation. An optimal dynamic sweep rate (∼5 μm/s) produces the best vertical order. At too fast a sweep rate (>10 μm/s) the BCP film ordering is kinetically hindered, while at too slow a sweep rate (<1 μm/s), polymer relaxation and preferential surface wetting dynamics favor parallel BCP orientation. Equivalent static gradient conditions produce vertically aligned BCP cylinders only at the maximum ∇T. CZA-S mechanism involves propagating this vertically oriented BCP zone across the sample.
Co-reporter:Ryan Schmidt, Jason Benkoski, Kevin Cavicchi and Alamgir Karim
Soft Matter 2011 vol. 7(Issue 12) pp:5756-5763
Publication Date(Web):12 May 2011
DOI:10.1039/C1SM05057E
Directed self-assembly of nanomaterials via external fields is an attractive processing tool for industry as it is inherently inexpensive and flexible. Direct observations of this process are however challenging due to the nano and meso length scales involved. The self-assembly of magnetic nanoparticles in particular has gained much recent interest for applications ranging from biomedical imaging and targeted cancer therapy to ferrofluid mechanical damping devices, that rely on the state of aggregation and alignment of the nanoparticles. We utilize an oil–water platform to directly observe directed self-assembly of magnetic nanoparticles that are field ordered into two-dimensional mesostructures through the fossilized liquid assembly (FLA) method. Our system consisted of polymer-coated iron-oxide nanoparticles (25 nm) which were assembled in the vicinity of the interface between a crosslinkable hydrophobic monomer (UV-polymerizable) oil, and water through the use of external magnetic fields, and then cured with UV light. This flash curing system effectively provides a snapshot of the assembly process and allows for direct visualization of assemblies through the use of both atomic force and optical microscopy. In this study, entire magnetic flux field lines in various geometrical configurations were successfully modelled and mapped out by the magnetic nanoparticles, both in-plane and in perpendicular orientations utilizing FLA. The assemblies showed strong directional selectivity and alignment with the flux field lines and provided evidence of strong dipole interactions which partially caused aggregate sedimentation.
Co-reporter:Diya Bandyopadhyay, Jack F. Douglas, and Alamgir Karim
Macromolecules 2011 Volume 44(Issue 20) pp:8136-8142
Publication Date(Web):September 28, 2011
DOI:10.1021/ma201201v
We investigate the influence of fullerene (C60) nanoparticle (NP) additives on a thermodynamically miscible polymer blend thin film of polystyrene (PS) and polybutadiene (PB). In this system both homopolymer components individually dewet from the commonly used silicon substrate. Three NP concentration regimes having distinct blend nanocomposite film morphologies are observed: (a) In the neat blend and low NP mass (0–1%) range, the blend films rapidly dewet, apparently due to fluctuations in the polymer surface tension arising from the composition fluctuations of a surface enrichment layer at the film air boundary. This behavior is in sharp contrast to the corresponding NP-filled homopolymer films where dewetting is progressively slowed by the segregation of NPs to the solid substrate in this same concentration range. (b) In the intermediate NP concentration range of 1–5 mass %, the C60 additive acts as a “compatibilizing agent”, progressively reducing the size of the dewetted droplets with increasing NP concentration. Dewetting is fully suppressed in the homopolymer films in this NP concentration range. We conclude that C60 segregation to polymeric interfaces within blend film competes with the NP film stabilizing effect. (c) At higher NP concentrations between 5 and 10 mass %, the NPs enrich the substrate sufficiently to fully inhibit the blend film dewetting through a percolating blend–NP structure. At very high NP concentrations (10–15 mass %), the NPs form clusters within the blend film giving rise to a “spinodal clustering” NP morphology.
Co-reporter:Guangcui Yuan, Clive Li, Sushil K. Satija, Alamgir Karim, Jack F. Douglas and Charles C. Han
Soft Matter 2010 vol. 6(Issue 10) pp:2153-2159
Publication Date(Web):08 Apr 2010
DOI:10.1039/C002046J
We examine the evolution (‘healing’) of the interface between two polymer films at various temperatures below the glass transition temperature, Tg. Specifically, neutron reflectometry is used to study the relaxation of the interface between both unentangled and entangled deuterated polystyrene (d-PS) and hydrogenated polystyrene (h-PS) films in the glass state where these bilayer films are supported on silicon substrates. We find that the initially sharp interface between the glassy polymer layers broadens with time (t), but the average interfacial thickness Δσ(t) between these layers then saturates after long time to a thickness (ξp) in a range between 1 nm and 3 nm after a long annealing time (≥1 h) for the range of temperatures investigated. This characteristic scale, and the temperature dependence of the interfacial relaxation time τ, were unanticipated, and we thus investigated the dependence of ξp and τ on molecular mass (M), annealing temperature (T) and the thickness (hf) of the PS films. We find that ξp increases with hf at a fixed T and increases with T at fixed hf. Our observation of a ‘healing length’ ξp, regardless of whether the polymers are entangled or not, and the dependence of ξp on T rule out an interpretation of this parameter in terms of the reptation model. On the other hand, ξp has a scale comparable to the mobile interfacial layer thickness reported in both small molecule and polymeric materials in the glass state, suggesting that ξp is a well-defined dynamical length scale characterizing the interfacial properties of glassy materials. The existence of such an interfacial layer has numerous implications for the processing and scientific understanding of thin polymer films.
Co-reporter:Jung Jin Park, Michael C. Weiger, Silvia H. De Paoli Lacerda, Denis Pristinski, Matthew L. Becker, Jack F. Douglas, Dharmaraj Raghavan and Alamgir Karim
Langmuir 2010 Volume 26(Issue 7) pp:4822-4830
Publication Date(Web):January 25, 2010
DOI:10.1021/la903581w
The kinetics of nanoparticle (NP) adsorption on a model biological interface (collagen) is measured in microfluidic channels using surface plasmon resonance (SPR) imaging over a range of CdSe/ZnS quantum dot concentrations to investigate the underlying binding process. Spherical CdSe/ZnS core−shell NP, derivatized with 3-mercaptopropionic acid (3-MPA), were considered to be model NPs because of their widespread use in biological applications and their relatively monodisperse size. The kinetic adsorption data suggests that the binding between the NP and the collagen substrate is irreversible at room temperature (pH ∼7.4), and this type of adsorption process was further characterized in the context of a surface absorption model. Specifically, diffusion-limited adsorption was found to predominate the adsorption process at lower concentrations (<0.4 μmol/L), and NP adsorption was reaction-limited at higher concentration (>0.4 μmol/L). A limited pH study of our system indicates that NPs desorb from collagen under acidic conditions (pH 5.5); no significant desorption was observed under neutral and basic pH conditions. These observations are consistent with electrostatic interactions being the dominant force governing NP desorption from collagen substrates. Our present methodology for characterizing the seemingly irreversible NP adsorption complements our earlier study where NP adsorption onto weakly adsorbing surfaces (self-assembled monolayers) was characterized by Langmuir NP adsorption measurements.
Co-reporter:Abul F. Huq, Ali Ammar, Abdullah M. Al-Enizi, Alamgir Karim
Polymer (24 March 2017) Volume 113() pp:
Publication Date(Web):24 March 2017
DOI:10.1016/j.polymer.2017.01.067
Effect of casting solvents on drop cast thin films of conductive conjugated polymers is largely studied by characterizing post processed films. However, the results have often been inconclusive due to the complexity of the in-situ evolution of structures. In this research we implement in-situ grazing incidence wide angle x-ray scattering (GIWAXS) approach to extracting morphological evolution information during film formation in model Poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend films that have otherwise been widely studied. Casting solvents include chloroform, benzene and tetrahydrothiophene (THT), carefully selected for their relative solubilities of P3HT and PCBM. Individual casting solvent studies show that the casting solvents' solubility for P3HT and pure solvent boiling point, along with residual solvent content in the films have significant implications on final thin film morphology and crystallization of its constituent components. For example, the orientations of P3HT in P3HT:PCBM films, cast from different solvents, are largely affected by the individual solubilities of P3HT and PCBM, and substrate surface energy. On the other hand PCBM crystal growth from different PCBM solutions predominantly depends on the solubilities of PCBM in the solvents and boiling points of solvents. In this study we correlate and distinguish the drying behavior of the blend films with respect to the drying behavior of its constituent components. These results have important ramifications for controlling desired morphology for polymer electronics, such as organic photovoltaics (OPV), organic field effect transistor (OFET) and photo-detectors.
Co-reporter:Ali Ammar, Ahmed Elzatahry, Mariam Al-Maadeed, Abdullah M. Alenizi, Abul F. Huq, Alamgir Karim
Applied Clay Science (1 March 2017) Volume 137() pp:123-134
Publication Date(Web):1 March 2017
DOI:10.1016/j.clay.2016.12.012
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![Thieno[3,4-b]thiophene-2-carboxylic acid, 4,6-dibromo-, 2-ethylhexyl ester](/data/chemimg/189600/1160823-81-3.png)
![Thieno[3,4-b]thiophene-2-carboxylic acid, 4,6-dibromo-, 2-ethylhexyl ester](/data/chemimg/189600/1160823-81-3_b.png)
![Poly[(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c']dipyrrole-2,6(1H,3H)-diyl)-1,4-phenyleneoxy-1,4-phenylene]](http://img.cochemist.com/ccimg/25100/25036-53-7.png)
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![Poly[oxy(1-oxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25300/25248-42-4.png)
![Poly[oxy(1-oxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25300/25248-42-4_b.png)
