Co-reporter:Lauren R. Finkenauer, Qingyun Lu, Ilhem F. Hakem, Carmel Majidi, and Michael R. Bockstaller
Langmuir September 26, 2017 Volume 33(Issue 38) pp:9703-9703
Publication Date(Web):August 28, 2017
DOI:10.1021/acs.langmuir.7b01322
A methodology based on light scattering and spectrophotometry was developed to evaluate the effect of organic surfactants on the size and yield of eutectic gallium/indium (EGaIn) nanodroplets formed in organic solvents by ultrasonication. The process was subsequently applied to systematically evaluate the role of headgroup chemistry as well as polar/apolar interactions of aliphatic surfactant systems on the efficiency of nanodroplet formation. Ethanol was found to be the most effective solvent medium in promoting the formation and stabilization of EGaIn nanodroplets. For the case of thiol-based surfactants in ethanol, the yield of nanodroplet formation increased with the number of carbon atoms in the aliphatic part. In the case of the most effective surfactant system–octadecanethiol–the nanodroplet yield increased by about 370% as compared to pristine ethanol. The rather low overall efficiency of the reaction process along with the incompatibility of surfactant-stabilized EGaIn nanodroplets in nonpolar organic solvents suggests that the stabilization mechanism differs from the established self-assembled monolayer formation process that has been widely observed in nanoparticle formation.
Co-reporter:Jianan Zhang, Yang Song, Maciej Kopeć, Jaejun Lee, Zongyu Wang, Siyuan Liu, Jiajun Yan, Rui Yuan, Tomasz Kowalewski, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Journal of the American Chemical Society September 20, 2017 Volume 139(Issue 37) pp:12931-12931
Publication Date(Web):September 8, 2017
DOI:10.1021/jacs.7b08133
An aqueous-based approach for the scalable synthesis of nitrogen-doped porous carbons with high specific surface area (SSA) and high nitrogen content is presented. Low molecular weight polyacrylonitrile (PAN) is solubilized in water in the presence of ZnCl2 that also acts as a volatile porogen during PAN pyrolysis to form mesoporous structures with significantly increased SSA. By templating with commercial SiO2 nanoparticles, nanocellulose fillers or filter paper, nanocarbons with SSA = 1776, 1366, and 1501 m2/g, respectively and 10 wt % N content were prepared. The materials formed by this benign process showed excellent catalytic activity in oxygen reduction reaction via the four-electron mechanism.
Co-reporter:Jianan Zhang, Yang Song, Maciej Kopeć, Jaejun Lee, Zongyu Wang, Siyuan Liu, Jiajun Yan, Rui Yuan, Tomasz Kowalewski, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Journal of the American Chemical Society September 20, 2017 Volume 139(Issue 37) pp:12931-12931
Publication Date(Web):September 8, 2017
DOI:10.1021/jacs.7b08133
An aqueous-based approach for the scalable synthesis of nitrogen-doped porous carbons with high specific surface area (SSA) and high nitrogen content is presented. Low molecular weight polyacrylonitrile (PAN) is solubilized in water in the presence of ZnCl2 that also acts as a volatile porogen during PAN pyrolysis to form mesoporous structures with significantly increased SSA. By templating with commercial SiO2 nanoparticles, nanocellulose fillers or filter paper, nanocarbons with SSA = 1776, 1366, and 1501 m2/g, respectively and 10 wt % N content were prepared. The materials formed by this benign process showed excellent catalytic activity in oxygen reduction reaction via the four-electron mechanism.
Co-reporter:Zongyu Wang, Siyuan Liu, Jianan Zhang, Jiajun Yan, Yepin Zhao, Clare Mahoney, Rachel Ferebee, Danli Luo, Joanna Pietrasik, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Langmuir October 31, 2017 Volume 33(Issue 43) pp:12276-12276
Publication Date(Web):October 10, 2017
DOI:10.1021/acs.langmuir.7b02492
Severe water pollution issues present an important contemporary challenge that drives the development and advancement of efficient and environmentally benign photocatalysts that enable the degradation of pollutants upon visible light irradiation. One example is zinc oxide/carbon (ZnO/C) hybrid materials that have been shown to be effective photocatalysts. To maximize the effectiveness of ZnO/C hybrids, materials with high accessible surface area of ZnO are required. Here, a novel strategy is presented to enable the synthesis of fine dispersions of ZnO nanoparticles within a porous carbon matrix. The synthesis entails the grafting of ZnO nanparticles with polystyrene-b-poly(styrene-co-acrylonitrile) (PS-b-PSAN) block copolymer and subsequent pyrolysis of the material under inert gas (N2) atmosphere. During the pyrolysis process, the PS block effectively prevents agglomeration of ZnO particles, thus resulting in a fine dispersion of ZnO nanocrystals within a prorous C matrix. Materials are found to exhibit a dye adsorption capacity of 125 mg g–1 (from a methylene blue aqueous solution with a concentration of 305 mg L–1) and dye degradation rate constant of 0.021 min–1. The significant increase of effective surface area and degradation efficacy (as compared to ZnO/C synthesized by the pyrolysis of binary PSAN/ZnO blends) is rationalized as a consequence of the increased porosity that promotes dye adsorption and transport within the hybrid material.
Co-reporter:Zongyu Wang, Siyuan Liu, Jianan Zhang, Jiajun Yan, Yepin Zhao, Clare Mahoney, Rachel Ferebee, Danli Luo, Joanna Pietrasik, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Langmuir October 31, 2017 Volume 33(Issue 43) pp:12276-12276
Publication Date(Web):October 10, 2017
DOI:10.1021/acs.langmuir.7b02492
Severe water pollution issues present an important contemporary challenge that drives the development and advancement of efficient and environmentally benign photocatalysts that enable the degradation of pollutants upon visible light irradiation. One example is zinc oxide/carbon (ZnO/C) hybrid materials that have been shown to be effective photocatalysts. To maximize the effectiveness of ZnO/C hybrids, materials with high accessible surface area of ZnO are required. Here, a novel strategy is presented to enable the synthesis of fine dispersions of ZnO nanoparticles within a porous carbon matrix. The synthesis entails the grafting of ZnO nanparticles with polystyrene-b-poly(styrene-co-acrylonitrile) (PS-b-PSAN) block copolymer and subsequent pyrolysis of the material under inert gas (N2) atmosphere. During the pyrolysis process, the PS block effectively prevents agglomeration of ZnO particles, thus resulting in a fine dispersion of ZnO nanocrystals within a prorous C matrix. Materials are found to exhibit a dye adsorption capacity of 125 mg g–1 (from a methylene blue aqueous solution with a concentration of 305 mg L–1) and dye degradation rate constant of 0.021 min–1. The significant increase of effective surface area and degradation efficacy (as compared to ZnO/C synthesized by the pyrolysis of binary PSAN/ZnO blends) is rationalized as a consequence of the increased porosity that promotes dye adsorption and transport within the hybrid material.
Co-reporter:Yu Cang, Anna N. Reuss, Jaejun Lee, Jiajun Yan, Jianan Zhang, Elena Alonso-Redondo, Rebecca Sainidou, Pascal Rembert, Krzysztof Matyjaszewski, Michael R. Bockstaller, and George Fytas
Macromolecules November 14, 2017 Volume 50(Issue 21) pp:8658-8658
Publication Date(Web):October 30, 2017
DOI:10.1021/acs.macromol.7b01752
Polymer-tethered colloidal particles (aka “particle brush materials”) have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush–brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems.
Co-reporter:Jianan Zhang, Rui Yuan, Sittichai Natesakhawat, Zongyu Wang, Yepin Zhao, Jiajun Yan, Siyuan Liu, Jaejun Lee, Danli Luo, Eric Gottlieb, Tomasz Kowalewski, Michael R. Bockstaller, and Krzysztof Matyjaszewski
ACS Applied Materials & Interfaces November 1, 2017 Volume 9(Issue 43) pp:37804-37804
Publication Date(Web):October 17, 2017
DOI:10.1021/acsami.7b11910
Functional nanoporous carbon spheres (NPC-S) are important for applications ranging from adsorption, catalysis, separation to energy storage, and biomedicine. The development of effective NPC-S materials has been hindered by the fusion of particles during the pyrolytic process that results in agglomerated materials with reduced activity. Herein, we present a process that enables the scalable synthesis of dispersed NPC-S materials by coating sacrificial protective layers around polyacrylonitrile nanoparticles (PAN NPs) to prevent interparticle cross-linking during carbonization. In a first step, PAN NPs are synthesized using miniemulsion polymerization, followed by grafting of 3-(triethoxysilyl)propyl methacrylate (TESPMA) to form well-defined core–shell structured PAN@PTESPMA nanospheres. The cross-linked PTESPMA brush layer suppresses cross-linking reactions during carbonization. Uniform NPC-S exhibiting diameters of ∼100 nm, with relatively high accessible surface area (∼424 m2/g), and high nitrogen content (14.8 wt %) was obtained. When compared to a regular nanoporous carbon monolith (NPC-M), the nitrogen-doped NPC-S demonstrated better performance for CO2 capture with a higher CO2/N2 selectivity, an increased efficiency in catalytic oxygen reduction reactions, as well as improved electrochemical capacitive behavior. This miniemulsion polymerization-based strategy for the preparation of functional PAN NPs provides a new, facile approach to prepare high-performance porous carbon spheres for diverse applications.Keywords: carbon; core−shell nanoparticle; miniemulsion polymerization; nanoporous carbon; polyacrylonitrile; SI-ATRP;
Co-reporter:Jianan Zhang, Rui Yuan, Sittichai Natesakhawat, Zongyu Wang, Yepin Zhao, Jiajun Yan, Siyuan Liu, Jaejun Lee, Danli Luo, Eric Gottlieb, Tomasz Kowalewski, Michael R. Bockstaller, and Krzysztof Matyjaszewski
ACS Applied Materials & Interfaces November 1, 2017 Volume 9(Issue 43) pp:37804-37804
Publication Date(Web):October 17, 2017
DOI:10.1021/acsami.7b11910
Functional nanoporous carbon spheres (NPC-S) are important for applications ranging from adsorption, catalysis, separation to energy storage, and biomedicine. The development of effective NPC-S materials has been hindered by the fusion of particles during the pyrolytic process that results in agglomerated materials with reduced activity. Herein, we present a process that enables the scalable synthesis of dispersed NPC-S materials by coating sacrificial protective layers around polyacrylonitrile nanoparticles (PAN NPs) to prevent interparticle cross-linking during carbonization. In a first step, PAN NPs are synthesized using miniemulsion polymerization, followed by grafting of 3-(triethoxysilyl)propyl methacrylate (TESPMA) to form well-defined core–shell structured PAN@PTESPMA nanospheres. The cross-linked PTESPMA brush layer suppresses cross-linking reactions during carbonization. Uniform NPC-S exhibiting diameters of ∼100 nm, with relatively high accessible surface area (∼424 m2/g), and high nitrogen content (14.8 wt %) was obtained. When compared to a regular nanoporous carbon monolith (NPC-M), the nitrogen-doped NPC-S demonstrated better performance for CO2 capture with a higher CO2/N2 selectivity, an increased efficiency in catalytic oxygen reduction reactions, as well as improved electrochemical capacitive behavior. This miniemulsion polymerization-based strategy for the preparation of functional PAN NPs provides a new, facile approach to prepare high-performance porous carbon spheres for diverse applications.Keywords: carbon; core−shell nanoparticle; miniemulsion polymerization; nanoporous carbon; polyacrylonitrile; SI-ATRP;
Co-reporter:Hangjun Ding, Jiajun Yan, Zongyu Wang, Guojun Xie, Clare Mahoney, Rachel Ferebee, Mingjiang Zhong, William F.M. Daniel, Joanna Pietrasik, Sergei S. Sheiko, Christopher J. Bettinger, Michael R. Bockstaller, Krzysztof Matyjaszewski
Polymer 2017 Volume 123(Volume 123) pp:
Publication Date(Web):11 August 2017
DOI:10.1016/j.polymer.2017.06.078
Co-reporter:Zongyu Wang, Zhao Lu, Clare Mahoney, Jiajun YanRachel Ferebee, Danli Luo, Krzysztof Matyjaszewski, Michael R. Bockstaller
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 8) pp:
Publication Date(Web):February 7, 2017
DOI:10.1021/acsami.6b12666
Development of high refractive index glasses on the basis of commodity polymer thermoplastics presents an important requisite to further advancement of technologies ranging from energy efficient lighting to cost efficient photonics. This contribution presents a novel particle dispersion strategy that enables uniform dispersion of zinc oxide (ZnO) particles in a poly(methyl methacrylate) (PMMA) matrix to facilitate hybrid glasses with inorganic content exceeding 25% by weight, optical transparency in excess of 0.8/mm, and a refractive index greater than 1.64 in the visible wavelength range. The method is based on the application of evaporative ligand exchange to synthesize poly(styrene-r-acrylonitrile) (PSAN)-tethered zinc oxide (ZnO) particle fillers. Favorable filler–matrix interactions are shown to enable the synthesis of isomorphous blends with high molecular PMMA that exhibit improved thermomechanical stability compared to that of the pristine PMMA matrix. The concurrent realization of high refractive index and optical transparency in polymer glasses by modification of a thermoplastic commodity polymer could present a viable alternative to expensive specialty polymers in applications where high costs or demands for thermomechanical stability and/or UV resistance prohibit the application of specialty polymer solutions.Keywords: hybrid material; ligand exchange; nanocomposite; refractive index; transparency; zinc oxide (ZnO);
Co-reporter:Guowei Wang, Zongyu Wang, Bongjoon Lee, Rui Yuan, Zhao Lu, Jiajun Yan, Xiangcheng Pan, Yang Song, Michael R. Bockstaller, Krzysztof Matyjaszewski
Polymer 2017 Volume 129(Volume 129) pp:
Publication Date(Web):27 October 2017
DOI:10.1016/j.polymer.2017.09.029
•Polymerization-induced self-assembly (PISA) of acrylonitrile (AN) successfully accomplished by atom transfer radical polymerization (ATRP).•Initiators for continuous activator regeneration (ICAR) ATRP with low ppm Cu used for synthesis of PAN-based nano-objects demonstrated.•A highly active ATRP macroinitiator, mPEO-BPA was used as both macroinitiator and stabilizer.•The molecular weight of the macroinitiator determined the structure of self-assembled objects.Polymerization-induced self-assembly (PISA) has attracted growing interest as facile fabrication process of polymer-based nanomaterials. However, PISA of acrylonitrile (AN) by atom transfer radical polymerization (ATRP) has remained an outstanding challenge due to the high activity of AN and poor solubility of polyacrylonitrile (PAN) in AN monomer. Here the application of PISA by using an initiators for continuous activator regeneration (ICAR) ATRP for the synthesis of PAN-based nano-objects is demonstrated. A highly active ATRP macroinitiator, methoxy-poly(ethylene oxide) 2-bromo-2-phenylacetate (mPEO-BPA) was synthesized by esterification and used also as a stabilizer. The molecular weight of the macroinitiator was found to determine the structure of self-assembled nano-objects. The high molecular macroinitiator (mPEO113-BPA) formed nano-objects with spherical or worm-like morphology, while the lower molecular weight analogue (mPEO45-BPA) resulted in precipitation in most cases due to insufficient stabilization of the nano-objects.Download high-res image (359KB)Download full-size image
Co-reporter:Jianan Zhang, Jaejun Lee, Zongyu Wang, Jiajun Yan, Zhao Lu, Siyuan Liu, Danli Luo, Krzysztof Matyjaszewski, Michael R. Bockstaller
Polymer 2017 Volume 126(Volume 126) pp:
Publication Date(Web):22 September 2017
DOI:10.1016/j.polymer.2017.08.028
•Densely PMMA-tethered gibbsite nanoplatelets was developed by SI-ATRP.•Gibbsite nanocomposite film of high transparency was obtained by a simple drop casting method.•The film of gibbsite nanoplatelet brushes demonstrated nacre-like lamellae morphology.An efficient method for the polymer modification of gibbsite (γ-Al(OH)3) nanoplatelet particles with poly(methyl methacrylate) (PMMA) by surface-initiated atom transfer radical polymerization (SI-ATRP) was developed. A newly developed initiator system based on 12-(2-bromoisobutyramido) dodecanoic acid (BiBADA) enable grafting densities in excess of 0.4 nm−2 with minimal amount of free homopolymer impurities and narrow molecular weight distribution. The gibbsite brush nanoplatelets were shown to organize into transparent films with nacre-like lamellae morphology. A significant increase of the glass transition temperature (as compared to pristine PMMA) was observed and attributed to the increase of steric confinement in planar brush architectures. The applicability of the presented methodology to a wide range of ATRP-compatible chemistries could be a basis for the development of novel functional materials in which properties depend on the directionality of brush nanoplatelet orientation and interaction.Download high-res image (286KB)Download full-size image
Co-reporter:Michael Schmitt, Jihoon Choi, Chin Min Hui, Beibei Chen, Emrullah Korkmaz, Jiajun Yan, Shlomo Margel, O. Burak Ozdoganlar, Krzysztof Matyjaszewski and Michael R. Bockstaller
Soft Matter 2016 vol. 12(Issue 15) pp:3527-3537
Publication Date(Web):11 Mar 2016
DOI:10.1039/C6SM00095A
The effect of polymer modification on the deformation characteristics and processibility of particle assembly structures is analyzed as a function of particle size and degree of polymerization of surface-tethered chains. A pronounced increase of the fracture toughness (by approximately one order of magnitude) is observed as the degree of polymerization exceeds a threshold value that increases with particle size. The threshold value is interpreted as being related to the transition of tethered chains from stretched-to-relaxed conformation (and the associated entanglement of tethered chains) and agrees with predictions from scaling theory. The increase in toughness is reduced with increasing particle size – this effect is rationalized as a consequence of the decrease of entanglement density with increasing dimension of interstitial (void) space in particle array structures. The increased fracture toughness of particle brush materials (with sufficient degree of polymerization of tethered chains) enables the fabrication of ordered colloidal films and even complex 3D shapes by scalable polymer processing techniques, such as spin coating and micromolding. The results, therefore, suggest new opportunities for the processing of colloidal material systems that could find application in the economical fabrication of functional components or systems compromised of colloidal materials.
Co-reporter:Rachel Ferebee, Ilhem F. Hakem, Amelie Koch, Maggie Chen, Yi Wu, Derek Loh, David C. Wilson, Jennifer L. Poole, Jeremy P. Walker, George Fytas, and Michael R. Bockstaller
The Journal of Physical Chemistry B 2016 Volume 120(Issue 20) pp:4591-4599
Publication Date(Web):May 5, 2016
DOI:10.1021/acs.jpcb.6b03097
The effect of polymer conjugation on the interactions between proteins in solution is evaluated by systematic analysis of the second virial coefficient (A2) for the particular example of single- and double-PEGylated bovine serum albumin (PEG-BSA) in dilute PBS solution. The effect of PEGylation on A2 is found to sensitively depend on both the composition and the distribution of PEG segments within the conjugate. Most importantly, at a given PEG volume fraction, A2 significantly increases with the degree of polymerization of tethered chains. Hence, a lesser number of long chains is more effective in solubilizing BSA than a correspondingly larger number of short chains. Analysis of the hydrodynamic radii of protein–PEG conjugates suggests that the increased solubility is concurrent with a structural transition in the case of high molecular PEG grafts that results in compact core–shell-type structures. The results reveal a link between the composition, structure, and solubility of polymer conjugates that might benefit the understanding of their biochemical characteristics and their design for functional material applications.
Co-reporter:Zongyu Wang, Clare Mahoney, Jiajun Yan, Zhao Lu, Rachel Ferebee, Danli Luo, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Langmuir 2016 Volume 32(Issue 49) pp:13207-13213
Publication Date(Web):November 30, 2016
DOI:10.1021/acs.langmuir.6b03827
Poly(styrene-co-acrylonitrile) (PSAN)-capped ZnO nanoparticles (NPs) were synthesized by a “ligand exchange” method. First, octylamine (OA)-capped ZnO NPs were prepared by reaction of OA and zinc 2-ethylhexanoate (Zn(EH)2). Then PSAN polymer ligands were synthesized by activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) and were efficiently exchanged with OA ligands on the ZnO particle surface benefiting from the relatively low boiling point of OA (175 °C). The morphology, content of ZnO, and grafting density of the nanocomposite were well controlled by altering the ratio between OA and polymer ligands as well as the molecular weight of PSAN-NH2 used in the exchange reaction. The resulting ZnO/polymer nanocomposites were stable in THF with narrow size distributions and varying grafting densities from 0.9 to 2.5 nm–2. With excess amount of polymer ligands, individual dispersed ZnO NPs were observed. However, with a limited amount of ligands, NPs clusters were formed, as confirmed by TEM and DLS.
Co-reporter:Hangjun Ding, Jiajun Yan, Zongyu Wang, Guojun Xie, Clare Mahoney, Rachel Ferebee, Mingjiang Zhong, William F.M. Daniel, Joanna Pietrasik, Sergei S. Sheiko, Christopher J. Bettinger, Michael R. Bockstaller, Krzysztof Matyjaszewski
Polymer 2016 Volume 107() pp:492-502
Publication Date(Web):19 December 2016
DOI:10.1016/j.polymer.2016.09.022
•ZnO hybrids were prepared via “grafting-from”, “grafting-onto”, & “templating”.•ZnO hybrids with relatively high size uniformity and dispersibility were obtained.•ZnO hybrid nanoparticles were prepared using molecular bottlebrush templates.Zinc oxide (ZnO) is a wide bandgap semiconductor material that has attracted widespread interest as particle filler in polymer nanocomposite materials. However, its applications have been hindered by the limited dispersibility and surface-modification techniques. Herein, three distinct approaches for the synthesis of polymer-tethered ZnO hybrid materials are compared in terms of uniformity and yield of the particle-brush product: “grafting-from”, “grafting-onto”, and “grafted-copolymer template” methods. In the “grafting-from” method, pristine ZnO nanoparticles (NP) were first functionalized with atom transfer radical polymerization (ATRP) initiators followed by grafting-from process to form poly(methyl methacrylate) (PMMA) or poly(styrene-co-acrylonitrile) (PSAN) tethered polymer chains. In the “grafting-onto” method, PMMA-b-PAA (poly[acrylic acid]) and PSAN-b-PAA diblock copolymers were prepared and attached onto the surface of ZnO NPs using sonication bath. For the “grafted-copolymer template” method, PSAN-b-PtBA-Br (poly[tert-butyl acrylate]-Br) macroinitiators were crosslinked with divinylbenzene (DVB) to form PSAN-b-PtBA-PDVB core-shell star polymers. After hydrolysis to form PSAN-b-PAA-PDVB star polymers, the functional stars were used as polymer templates for the synthesis of ZnO NPs within the PAA-core of the stars. Core-shell molecular bottlebrushes with PAA-b-PS block-copolymer side chains were also used as anisotropic analogues of star template to prepared worm-like ZnO particles. Several ZnO precursors, zinc nitrite, zinc 2-ethylhexanoate, and zinc acetate were evaluated as precursors of ZnO. Conditions were identified that enable the synthesis of polymer-tethered ZnO with excellent size uniformity and dispersion characteristics using the star-template method.
Co-reporter:Clare Mahoney, Ching Ming Hui, Shubhaditya Majumdar, Zongyu Wang, Jonathan A. Malen, Maxim N. Tchoul, Krzysztof Matyjaszewski, Michael R. Bockstaller
Polymer 2016 Volume 93() pp:72-77
Publication Date(Web):14 June 2016
DOI:10.1016/j.polymer.2016.04.014
•Thermal conductivity of nanocomposites is sensitive to ligand/matrix interactions.•Attractive ligand/matrix interactions raise thermal boundary conductance.•Polymer graft modification increases thermal conductivity in nanocomposites.The role of polymeric tethers on the effective thermal conductivity of polymer nanocomposites is evaluated for the particular case of silica particle fillers dispersed within poly(methyl methacrylate) (PMMA). The effective thermal conductivity of both thin film and bulk composites is found to sensitively depend on the interaction between tethered and matrix chains. In particular, tethering of polymeric chains exhibiting favorable interactions with the matrix (such as poly(styrene-r-acrylonitrile), PSAN with molar composition S:AN = 3:1) is shown to raise the effective thermal conductivity. The results point to the relevance of the ‘ligand phase’ (constituted of the tethered chains) as well as the tether/matrix interface in determining the thermal transport in polymer nanocomposites and suggest opportunities to raise the thermal conductivity of nanocomposite materials by the deliberate design of polymeric tethers to facilitate attractive ligand/matrix interactions.
Co-reporter:Guowei Wang, Michael Schmitt, Zongyu Wang, Bongjoon Lee, Xiangcheng Pan, Liye Fu, Jiajun Yan, Sipei Li, Guojun Xie, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Macromolecules 2016 Volume 49(Issue 22) pp:8605-8615
Publication Date(Web):November 7, 2016
DOI:10.1021/acs.macromol.6b01966
Polymerization-induced self-assembly (PISA) was achieved by conducting an initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) at low ppm of copper catalyst concentration. A poly(oligo(ethylene oxide) methyl ether methacrylate)50 (POEOMA50) macroinitiator and stabilizer was synthesized by an aqueous ICAR ATRP using CuIICl2/tris(pyridin-2-ylmethyl)amine (TPMA) complex. Subsequently, the dispersion polymerization of benzyl methacrylate (BnMA) in ethanol was realized with a CuIIBr2/TPMA complex either at room temperature or at 65 °C using V-70 or AIBN as radical initiators, respectively. The effect of catalyst concentration, radical initiators, targeted degree of polymerization (DP) of PBnMA, solids content, and temperature on the molecular characteristics and self-assembly behavior of block copolymers POEOMA–PBnMA was evaluated by gel permeation chromatography (GPC), transmission electron microscopy (TEM), and dynamic light scattering (DLS). Block copolymers assembled into spheres, wormlike aggregates, and vesicles with diameters ranging from 100 to 600 nm, depending on the temperature, solids content, and the DP of PBnMA. The effect of the temperature on the polymerization behavior and morphological evolution was attributed to the temperature-dependent plasticization of the core-forming PBnMA block above and below its glass transition temperature (Tg = 54 °C).
Co-reporter:Tejank Shah, Chetali Gupta, Rachel L. Ferebee, Michael R. Bockstaller, Newell R. Washburn
Polymer 2015 Volume 72() pp:406-412
Publication Date(Web):18 August 2015
DOI:10.1016/j.polymer.2015.04.073
Understanding of the governing parameters that control the interaction of bio-sourced fillers with synthetic polymer materials is a long-standing challenge for their exploitation as a platform for material engineering. For the case of graft-lignin embedded in poly (methyl methacrylate) (PMMA) it is demonstrated that tethering of polymeric chains with appropriate chain length to the surface of lignin-fillers dramatically increases the mechanical properties of PMMA/lignin composites, suggesting the PMMA grafts significantly enhanced filler–matrix interactions. Most metrics were maximized at 1% loading, with a 3-fold increase in yield stress, a 4-fold increase in tensile strength, and a 7-fold increase in toughness, with a combination of properties that compare favorably to high-performance engineering polymers and polymer nanocomposites based on inorganic nanoparticles. The versatility of the surface-initiated controlled radical polymerization used for polymer graft modification suggests that the approach should be broadly applicable to a wide range of commodity and engineering polymers.
Co-reporter:Jiajun Yan, Tyler Kristufek, Michael Schmitt, Zongyu Wang, Guojun Xie, Alei Dang, Chin Ming Hui, Joanna Pietrasik, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Macromolecules 2015 Volume 48(Issue 22) pp:8208-8218
Publication Date(Web):November 9, 2015
DOI:10.1021/acs.macromol.5b01905
The modification of the surface of nanoparticles with polymeric chains is ubiquitously used to engineer the physicochemical properties of nanoparticle fillers and to enable new material technologies based on polymer hybrid materials with controlled microstructure. The tethering of particles with polymeric chains of distinct (high and low) degree of polymerization (so-called “bimodal polymer grafts”) has emerged as a particularly interesting strategy to combine the synergistic benefits of dense and sparse polymer grafts (i.e., good control of particle interactions facilitated by densely grafted polymer chains with the high inorganic content characteristic for sparsely grafted systems). In this contribution, surface-initiated atom transfer radical polymerization (SI-ATRP) is demonstrated to be a versatile tool that enables the synthesis of bimodal graft modifications with precise control of the degree of polymerization of the respective graft species. For the particular case of polystyrene-tethered silica particles, it was demonstrated that the presence of even small fractions of “long” chains provided an order-of magnitude increase of the mechanical toughness of particle films that is comparable to values found in densely tethered particle systems only in the limit of high degree of polymerization of tethered chains (and corresponding low inorganic content).
Co-reporter:Michael R. Bockstaller
Progress in Polymer Science 2015 40() pp: 1-2
Publication Date(Web):January 2015
DOI:10.1016/j.progpolymsci.2014.11.001
Co-reporter:Chin Ming Hui, Joanna Pietrasik, Michael Schmitt, Clare Mahoney, Jihoon Choi, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Chemistry of Materials 2014 Volume 26(Issue 1) pp:745
Publication Date(Web):August 14, 2013
DOI:10.1021/cm4023634
Surface-initiated atom transfer radical polymerization (SI-ATRP) has become an indispensable tool for engineering the structure and properties of polymer/inorganic and polymer/organic interfaces. This article describes the progress and challenges that are associated with the application of SI-ATRP to precisely control the molecular characteristics of polymer chains tethered to nanoparticle surfaces and explores the properties and potential applications of the resulting particle brush materials. Even for the conceptually most “simple” particle brush systems—that is, spherical particles uniformly grafted with amorphous nonpolar polymers—the complex superposition of interactions as well as time- and length-scales related to particle core and tethered chains provides a rich and largely unexplored parameter space for the design of novel functional materials. The application of the particle brush approach to the development of materials for applications ranging from photonic inks and paints to advanced high “k” dielectrics for energy storage and advanced nanocomposite materials with improved optical, mechanical, or transport characteristics is discussed.Keywords: ATRP; controlled radical polymerization; nanocomposite; nanostructure; particle brush;
Co-reporter:Dirk Schneider, Michael Schmitt, Chin Ming Hui, Rebecca Sainidou, Pascal Rembert, Krzysztof Matyjaszewski, Michael R. Bockstaller, and George Fytas
ACS Macro Letters 2014 Volume 3(Issue 10) pp:1059
Publication Date(Web):October 6, 2014
DOI:10.1021/mz500433h
The concurrent evaluation of the vibration eigenfrequencies in densely polymer-tethered particle systems (“particle brushes”) by Brillouin light scattering and elastodynamic theory reveals a distinctive change of acoustic eigenmode formation associated with polymer graft modification of colloidal particles. The eigenfrequencies of particle brushes reveal a characteristic red-shift compared to uniform core-shell particles that can only be rationalized by assuming imperfect boundary conditions and anisotropic elastic properties of the graft layer. The distinct characteristics of vibration modes in particle brush materials provide direct evidence for the implications of chain confinement on the nanomechanical properties of tethered chains. The results highlight a rich and hitherto unexplored parameter-space for controlling properties and interactions in particle–brush based systems that could spur the development of hybrid materials with novel functionalities.
Co-reporter:Yali Qiao, Rachel Ferebee, Bongjoon Lee, Indranil Mitra, Nathaniel A. Lynd, Jeffery Hayat, Gila E. Stein, Michael R. Bockstaller, and Chuanbing Tang
Macromolecules 2014 Volume 47(Issue 18) pp:6373-6381
Publication Date(Web):September 2, 2014
DOI:10.1021/ma501057m
The synthesis, characterization, and self-assembly of a series of linear poly(ethylene-b-styrene-b-isoprene) (PEO−PS−PI) triblock copolymers containing nearly equal volume fractions of PEO and PI (fPEO ≈ fPI) and various fractions of the middle PS block (70.8 vol % ≤ fPS ≤ 75.6 vol %) is reported. A range of azide-functionalized poly(ethylene oxide-b-styrene) diblock copolymers were prepared by atom transfer radical polymerization (ATRP) of styrene using the same batch of PEO-macroinitiator, followed by azide-functionalization. Monohydroxyl-terminated poly(cis-1,4-isoprene) was first alkyne-functionalized and then sequentially attached to azide-functionalized PEO−PS via copper(I)-catalyzed azide−alkyne cycloaddition reaction, producing PEO−PS−PI triblock copolymers with low dispersity. Bulk samples of each linear triblock copolymer reveal the formation of a binary microdomain structure in which a PS and PI domains mix to form a uniform matrix for spherical PEO microdomains, and the PEO microdomains are arranged in a BCC lattice. Additionally, the thin film ordering of these triblock copolymers was investigated using a high-humidity solvent annealing process, both with and without low concentrations of a lithium salt. The morphology was analyzed by atomic force microscopy and GISAXS, revealing layers of spherical PEO domains arranged with in-plane hexagonal symmetry. The inclusion of salt increased both the size and periodicity of PEO domains.
Co-reporter:Chin Ming Hui, Alei Dang, Beibei Chen, Jiajun Yan, Dominik Konkolewicz, Hongkun He, Rachel Ferebee, Michael R. Bockstaller, and Krzysztof Matyjaszewski
Macromolecules 2014 Volume 47(Issue 16) pp:5501-5508
Publication Date(Web):August 11, 2014
DOI:10.1021/ma501319m
Surface-initiated atom transfer radical polymerization (SI-ATRP) has emerged as a powerful tool to synthesize polymer-tethered particles (here called particle brushes) that can self-assemble into hybrid materials with well-defined microstructure, morphology, and enhanced mechanical properties or optical transparency, as compared to binary particle/polymer nanocomposite materials. However, side reactions—such as the thermal self-initiation (TSI) of some monomers, such as styrene, during the polymerization—can result in the formation of varying amounts of homopolystyrene, in addition to particle brushes. The presence of homopolystyrene impurity reduces the predictability of properties and impedes the interpretation of structure–property relations in particle brush materials. This contribution presents a systematic evaluation of the formation of TSI homopolystyrene and its implications on the properties of polystyrene-tethered silica based particle brush materials. Kinetic and molecular weight studies reveal that the fraction of untethered chains generated by TSI depends on reaction conditions and increases with the degree of polymerization of surface-tethered chains. The presence of homopolystyrene results not only in a decrease of the softening temperature but also in an increase of ductility and toughness of particle brush solids. Structural analysis of particle brush assemblies admixed with small particle tracer inclusions suggests that the increase in ductility is related to the preferential segregation of the polystyrene impurity within the corner regions of the Wigner–Seitz cell of the particle brush array.
Co-reporter:Hyung Ju Ryu, Jane Sun, Apostolos Avgeropoulos, and Michael R. Bockstaller
Macromolecules 2014 Volume 47(Issue 4) pp:1419-1427
Publication Date(Web):February 4, 2014
DOI:10.1021/ma4021714
The effect of filler addition on the grain coarsening characteristics of block copolymer materials is analyzed for the particular case of a lamellar poly(styrene-b-isoprene)-type block copolymer and polystyrene as well as polystyrene-grafted nanoparticle fillers. Filler addition is shown to reduce the rate of grain growth and to induce grain size distributions that deviate from the log-normal type that is characteristic for pristine block copolymer systems. The retardation of grain growth is shown to be associated with the segregation of filler additives into high energy grain boundary defects—a process that bears similarities to the segregation of impurity atoms within grain boundary structures in ceramics or metals. The analysis of grain boundary energy, grain size distribution, and grain coarsening kinetics suggests two major mechanisms for the interference of filler additives with grain coarsening: First, the segregation of fillers into boundary regions lowers the relative grain boundary energy and hence the driving pressure for grain growth. Second, the formation of particle aggregates along grain boundaries gives rise to a “pinning pressure” that counteracts grain growth and that limits the ultimate grain size during thermal annealing. This is in contrast to pristine block copolymer systems in which continuous grain growth is observed during thermal annealing. The results highlight the fundamental differences between structure evolution in pristine and mixed block copolymer systems and suggest that thermal annealing (in the absence of structure-guiding fields) is an inefficient path to facilitate the controlled growth of large grains in athermal block copolymer blend materials.
Co-reporter:Alei Dang, Satyajeet Ojha, Chin Ming Hui, Clare Mahoney, Krzysztof Matyjaszewski, and Michael R. Bockstaller
Langmuir 2014 Volume 30(Issue 48) pp:14434-14442
Publication Date(Web):2017-2-22
DOI:10.1021/la5037037
The role of polymeric ligands on the optical transparency of polymer–matrix composites is analyzed by evaluating the effect of surface modification on the scattering cross-section of particle fillers in uniform particle dispersions. For the particular case of poly(styrene-r-acrylonitrile)-grafted silica particles embedded in poly(methyl methacrylate), it is shown that the tethering of polymeric chains with appropriate optical properties (such as to match the effective refractive index of the brush particle to the embedding matrix) facilitates the reduction of the particle scattering cross-section by several orders of magnitude as compared to pristine particle analogues. The conditions for minimizing the scattering cross-section of particle fillers by polymer-graft modification are established on the basis of effective medium as well as core–shell Mie theory and validated against experimental data on uniform liquid and solid particle dispersions. Effective medium theory is demonstrated to provide robust estimates of the “optimum polymer-graft composition” to minimize the scattering cross-section of particle fillers even in the limit of large particle dimensions (comparable to the wavelength of light). The application of polymer-graft modification to the design of large (500 nm diameter) silica particle composites with reduced scattering cross-section is demonstrated.
Co-reporter:Sudarshan Narayanan, Jihoon Choi, Lisa Porter, and Michael R. Bockstaller
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 10) pp:4093
Publication Date(Web):April 23, 2013
DOI:10.1021/am303211g
Suitable design of periodic metal/polymer composite materials is shown to facilitate resonant tunneling of light at absorbing wavelengths and to provide a means to significantly reduce optical absorption losses in polymer-based metallodielectric composite structures. The conditions for resonant tunneling are established based on the concept of “photonic band edge alignment” in 1D-periodic systems. For the particular case of a four-layer gold/polystyrene laminate structure, it is shown that the matching of the lower band edge of the 1D-periodic structure with the plasma frequency of the metal component facilitates the increase of optical transmission by about 500% as compared to monolithic film structures of equal total thickness. The effect of sheet thickness on the optical properties of thin metal films is determined and shown to be an important prerequisite for the reliable prediction of resonant metallodielectric structures. The resonant 1D-periodic metal/polymer heterostructures are shown to retain the flexural stability of the polymer matrix and thus could find application as flexible transparent conductors in areas such as “plastic electronics”.Keywords: composite; photonic crystal; plastic electronics; thin metal film; transparent conductor;
Co-reporter:Satyajeet Ojha, Alei Dang, Chin Ming Hui, Clare Mahoney, Krzysztof Matyjaszewski, and Michael R. Bockstaller
Langmuir 2013 Volume 29(Issue 28) pp:8989-8996
Publication Date(Web):2017-2-22
DOI:10.1021/la401522v
The governing parameters controlling the miscibility of particle additives within polymeric host media are analyzed for the particular case of silica particle fillers embedded within a poly(methyl methacrylate) (PMMA) matrix. For athermal polymer-graft modification of particles (corresponding to equal chemical composition of graft and matrix polymer), compatibility is found to be a sensitive function of the degree of polymerization of graft and host polymer chains as well as the particle radius. In agreement with theoretical predictions, uniform particle dispersion is observed if the degree of polymerization of grafted chains is comparable to (or exceeds) the corresponding value of the polymer matrix. The resulting restriction to high degree of polymerization limits the accessible inorganic fraction that is attainable in athermal particle/polymer blends. In contrast, favorable interaction between grafted polymer chains and the polymeric host (as realized in the case of poly(styrene-r-acrylonitrile)-grafted particles embedded within PMMA matrix) is shown to facilitate thermodynamically stable and uniform particle dispersion across the entire compositional range even in the limit of large particle size, short grafted chains, and high molecular matrix chains. The synthesis of thermoplastic composite materials with inorganic fraction exceeding 50 vol % combining quantitative optical limiting within the UV frequency range and polymer-like mechanical properties is demonstrated.
Co-reporter:Jihoon Choi, Chin Ming Hui, Michael Schmitt, Joanna Pietrasik, Shlomo Margel, Krzysztof Matyjazsewski, and Michael R. Bockstaller
Langmuir 2013 Volume 29(Issue 21) pp:6452-6459
Publication Date(Web):May 1, 2013
DOI:10.1021/la4004406
The propensity of particle brush materials to form long-ranged ordered assembly structures is shown to sensitively depend on the brush architecture (i.e., the particle radius as well as molecular weight and grafting density of surface-bound chains). In the limit of stretched chain conformations of surface-grafted chains the formation of regular particle array structures is observed and interpreted as a consequence of hard-sphere-type interactions between polymer-grafted particles. As the degree of polymerization of surface-grafted chains increases beyond a threshold value, a reduction of the structural regularity is observed that is rationalized with the increased volume occupied by relaxed polymer segments. The capacity of polymer grafts to increase or decrease order in particle brush assembly structures is interpreted on the basis of a mean-field scaling model, and “design criteria” are developed to help guide the future synthesis of colloidal systems that are capable of forming mechanically robust yet ordered assembly structures.
Co-reporter:Alei Dang;Chin Ming Hui;Rachel Ferebee;Joshua Kubiak;Tiehu Li;Krzysztof Matyjaszewski
Macromolecular Symposia 2013 Volume 331-332( Issue 1) pp:9-16
Publication Date(Web):
DOI:10.1002/masy.201300062
Summary
The governing parameters controlling the glass transition temperature of polymer-grafted particle systems are analyzed for the particular case of polystyrene (PS)-grafted silica colloids in the dense grafting limit. At a given degree of polymerization of surface-grafted chains the glass transition temperature is found to increase as compared to linear chain polymers of equivalent degree of polymerization. The difference in the glass transition temperature between polymer-grafted particle systems and their respective linear polymer analogs increases with decreasing degree of polymerization of surface-grafted chains and levels off at similar plateau values for particle brushes of distinct particle core size. The trend toward increased glass transition temperature is interpreted as a consequence of the increased steric hindrance in polymer-grafted particles that counteracts the relaxation of surface-grafted polymer chains. The increase in glass transition temperature is shown to be approximately consistent with the chain conformational regimes that are predicted on the basis of a Daoud-Cotton type scaling model.
Co-reporter:Ilhem F. Hakem;Anna M. Leech;Justin Bohn;Jeremy P. Walker
Biopolymers 2013 Volume 99( Issue 7) pp:427-435
Publication Date(Web):
DOI:10.1002/bip.22193
The compositional heterogeneity associated with polymer conjugation reactions of biomolecules is analyzed for the particular case of nonspecific PEGylation reactions. It is shown that the distribution of the number of PEG moieties grafted to biomolecules such as proteins is a binomial-type function of two parameters—the reaction efficiency as well as the number of binding sites per biomolecule. The nature of this distribution implies that uniform compositions are favored for increasing number of coupling sites per biomolecule as well as for increasing efficiency of the modification process. Therefore, the binomial distribution provides a rationale for the pronounced heterogeneity that is observed for PEGylated small enzyme systems even at high coupling efficiencies. For the particular case of PEGylated trypsin it is shown that the heterogeneity results in a broad distribution of deactivation times that is captured by a stretched exponential decay model. The presented analysis is expected to apply to general modification processes of compounds in which partial functionalization of a fixed number of reactive sites is achieved by means of a nonspecific coupling reaction. © 2012 Wiley Periodicals, Inc. Biopolymers 99: 427–435, 2013.
Co-reporter:Jihoon Choi, Chin Ming Hui, Joanna Pietrasik, Hongchen Dong, Krzysztof Matyjaszewski and Michael R. Bockstaller
Soft Matter 2012 vol. 8(Issue 15) pp:4072-4082
Publication Date(Web):01 Feb 2012
DOI:10.1039/C2SM06915F
The effect of polymer-graft modification on the structure formation and mechanical characteristics of inorganic (silica) nanoparticle solids is evaluated as a function of the degree of polymerization of surface-grafted chains. A transition from ‘hard-sphere-like’ to ‘polymer-like’ mechanical characteristics of particle solids is observed for increasing degree of polymerization of grafted chains. The elastic modulus of particle solids increases by about 200% and levels off at intermediate molecular weights of surface-grafted chains, a trend that is rationalized as a consequence of the elastic modulus being determined by dispersion interactions between the polymeric grafts. A pronounced increase (of about one order of magnitude) of the fracture toughness of particle solids is observed as the degree of polymerization of grafted chains exceeds a threshold value that is similar for both polystyrene and poly(methyl methacrylate) grafts. The increased resistance to fracture is interpreted as a consequence of the existence of entanglements between surface-grafted chains that give rise to energy dissipation during fracture through microscopic plastic deformation and craze formation. Within the experimental uncertainty the transition to polymer-like deformation characteristics is captured by a mean field scaling model that interprets the structure of the polymer shell of polymer-grafted particles as effective ‘two-phase’ systems consisting of a stretched inner region and a relaxed outer region. The model is applied to predict the minimum degree of polymerization needed to induce polymer-like mechanical characteristics and thus to establish ‘design criteria’ for the synthesis of polymer-modified particles that are capable of forming mechanically robust and formable particle solid structures.
Co-reporter:Jessica Listak;Xiaolong Jia;Andrzej Plichta;Mingjiang Zhong;Krzysztof Matyjaszewski
Journal of Polymer Science Part B: Polymer Physics 2012 Volume 50( Issue 2) pp:106-116
Publication Date(Web):
DOI:10.1002/polb.22339
Abstract
The effect of homopolymer (hP) addition on the structure formation in lamellar amorphous block copolymers (BCP) with narrow- and broad-molecular weight distribution (MWD) was studied using small-angle X-ray scattering and transmission electron microscopy. The systems in our study consist of blends of a poly(styrene-b-methyl acrylate) copolymer with block-selective broad MWD of the poly(methyl acrylate) domain as well as polystyrene and poly(methyl acrylate) hPs with molecular weight less than the corresponding block of the copolymer. Homopolymer addition to the broad MWD domain of the BCP is found to induce structural changes similar to narrow MWD BCP/hP blend systems. Conversely, addition of hP to the narrow MWD domain is found to induce a more pronounced expansion of lamellar domains due to the segregation of the hP to the center region within the host copolymer domain. With increasing hP concentration, the formation of a stable two-phase regime with coexisting lamellar/gyroid microphases is observed that is bounded by uniform lamellar phase regimes that differ in the distribution of hP within the corresponding narrow MWD block domain. The segregation of low-molecular weight hP to the center region of the narrowdisperse domains of a broad MWD BCP is rationalized as a consequence of the more stretched chain conformations within the narrowdisperse block that are implied by the presence of a disperse adjacent copolymer domain. The increase of chain stretching reduces the capacity of the narrowdisperse block to solubilize hP additives and thus provides a driving force for the segregation of hP chains to the center of the host copolymer domain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 106–116, 2012
Co-reporter:Heidrun A. Keul, Hyung Ju Ryu, Martin Möller and Michael R. Bockstaller
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 30) pp:13572-13578
Publication Date(Web):12 Jul 2011
DOI:10.1039/C1CP20518H
The relevance of anion structure on the shape regulating effect of 3-ethyl-1-methylimidazolium-based ionic liquids during the seed-induced growth of gold nanocrystals is evaluated for the particular case of lactate, acetate, methylsulfate, ethylsulfate and tosylsulfonate anion systems. Carboxylate-based anions (lactate and acetate) are found to inhibit the reduction of the gold precursor salt presumably due to the deprotonation of the reducing agent ascorbic acid. The formation of non-uniform, ‘head-tail’-type anisotropic particle structures is observed in both methyl- and ethylsulfate anion systems whereas rapid precipitation is observed in the case of tosylsulfonate anions. The particular efficiency of the ethylsulfate solvent system in promoting shape anisotropic growth is interpreted to be a consequence of both reduced anion/cation interactions that act to support the coordination of imidazolium to the metal surface and the enhanced capacity of anions to participate in the particle stabilization process.
Co-reporter:Heidrun A. Keul, Martin Möller and Michael R. Bockstaller
CrystEngComm 2011 vol. 13(Issue 3) pp:850-856
Publication Date(Web):11 Oct 2010
DOI:10.1039/C0CE00267D
Control of the crystallographic orientation of nanocrystal facets is widely recognized to be a key prerequisite for the synthesis of highly efficient nanocrystal-based catalysts. Here, we demonstrate that the facet evolution during the synthesis of gold nanocrystals can effectively be controlled by the addition of auxiliary metal ions during the kinetically controlled reduction of precursor salts. In particular, in the presence of Cu2+ the formation of predominantly {111} faceted particles is observed, whereas the addition of Ag+ and Pb2+ is found to result in the selective exposition of {110} and {100} crystal facets. The effect of auxiliary metal ions to induce the exposition of facets with particular crystallographic orientation is interpreted as a consequence of kinetic selection due to underpotential deposition (upd) during the kinetically controlled growth of nanocrystals. In this regard, the observed trends in facet exposition are in agreement with the respective trends of underpotential deposition of the various auxiliary metal additives on single-crystalline planar gold substrates.
Co-reporter:Panayiotis Voudouris, Jihoon Choi, Nikos Gomopoulos, Rebecca Sainidou, Hongchen Dong, Krzysztof Matyjaszewski, Michael R. Bockstaller, and George Fytas
ACS Nano 2011 Volume 5(Issue 7) pp:5746
Publication Date(Web):June 20, 2011
DOI:10.1021/nn201431w
The in-plane and out-of-plane elastic properties of thin films of “quasi-one-component” particle-brush-based nanocomposites are compared to those of “classical” binary particle–polymer nanocomposite systems with near identical overall composition using Brillouin light scattering. Whereas phonon propagation is found to be independent of the propagation direction for the binary particle/polymer blend systems, a pronounced splitting of the phonon propagation velocity along the in-plane and out-of-plane film direction is observed for particle-brush systems. The anisotropic elastic properties of quasi-one-component particle-brush systems are interpreted as a consequence of substrate-induced order formation into layer-type structures and the associated breaking of the symmetry of the film. The results highlight new opportunities to engineer quasi-one-component nanocomposites with advanced control of structural and physical property characteristics based on the assembly of particle-brush materials.Keywords: Brillouin light scattering; elasticity; nanocomposite; particle brush; self-assembly
Co-reporter:Ilhem F. Hakem ; Anna M. Leech ; Jermaine D. Johnson ; Scott J. Donahue ; Jeremy P. Walker
Journal of the American Chemical Society 2010 Volume 132(Issue 46) pp:16593-16598
Publication Date(Web):October 26, 2010
DOI:10.1021/ja107139c
Chemical modification of nanoparticles or particlelike systems is ubiquitously being used to facilitate specific pharmaceutical functionalities or physicochemical attributes of nanocrystals, proteins, enzymes, or other particlelike systems. Often the modification process is incomplete and the functional activity of the product depends upon the distribution of functional ligands among the different particles in the system. Here, the distribution function describing the spread of ligands in particlelike systems undergoing partial modification reactions is derived and validated against a conjugated enzyme model system by use of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The distribution function is shown to be applicable to describe the distribution of ligands in a wide range of particlelike systems (such as enzymes, dendrimers, or inorganic nanocrystals) and is used to establish guidelines for the synthesis of uniformly modified particle systems even at low reaction efficiencies.
Co-reporter:Jihoon Choi ; Hongchen Dong ; Krzysztof Matyjaszewski
Journal of the American Chemical Society 2010 Volume 132(Issue 36) pp:12537-12539
Publication Date(Web):August 20, 2010
DOI:10.1021/ja105189s
Surface-initiated atom-transfer radical polymerization is used to synthesize particle brushes with controlled fraction of extended and relaxed conformations of surface-grafted chains. In the semidilute brush limit, the grafting of polymeric ligands is shown to facilitate the formation of ordered yet plastic-compliant particle array structures in which chain entanglements give rise to fracture through a polymer-like crazing process that dramatically increases the toughness and flexibility of the particle assembly.
Co-reporter:Michael R. Bockstaller, Hyung Ju Ryu, Satyajeet Ojha and Jihoon Choi
Journal of Materials Chemistry A 2010 vol. 20(Issue 42) pp:9339-9341
Publication Date(Web):27 Jul 2010
DOI:10.1039/C0JM01810D
The formation of hierarchical 1D periodic bimetallic superstructures by co-assembly of ternary block copolymer/particle blend systems is reported. The results point to the relevance of entropy-driven morphology selection processes in enthalpic neutral block copolymer/particle blends that should render the presented approach applicable to a wide range of polymer/particle compositions.
Co-reporter:Satyajeet Ojha, Benjamin Beppler, Hongchen Dong, Krzysztof Matyjaszewski, Stephen Garoff and Michael R. Bockstaller
Langmuir 2010 Volume 26(Issue 16) pp:13210-13215
Publication Date(Web):July 16, 2010
DOI:10.1021/la1019372
The effect of polymer functionalization on the two-dimensional (2-D) assembly of uniform as well as highly asymmetric binary colloidal mixtures with both neutral and incompatible polymer grafts is presented. In ordered assemblies of uniform particle brush systems, the observed size-segregation is analogous to that of hard sphere colloidal systems, suggesting that lateral capillary interactions are responsible for the crystal nucleation in the early stages of assembly formation. Structure formation in binary blends of asymmetric particle brush systems is found to be strongly influenced by three major energetic contributions, that is, the interfacial energies associated with the particle brush/air boundaries, the interfacial energies between the distinct brush components, as well as the elastic energy associated with the stretching of the polymer-brush to fill the interstitial regions within locally ordered particle arrays. Our results demonstrate the relevance of capillary interactions in soft particle brush systems but also highlight distinctive differences in the order formation as compared to hard sphere colloidal systems. In particular, the compliant response of grafted polymer chains is shown to promote phase separation in binary blends of incompatible and asymmetric colloidal systems.
Co-reporter:Jessica Listak, Ilhem F. Hakem, Hyung Ju Ryu, Sofia Rangou, Nikolaos Politakos, Konstantinos Misichronis, Apostolos Avgeropoulos and Michael R. Bockstaller
Macromolecules 2009 Volume 42(Issue 15) pp:5766-5773
Publication Date(Web):July 15, 2009
DOI:10.1021/ma900600n
The effect of block copolymer chain connectivity on the structure formation in binary blends comprising block copolymer hosts and enthalpically neutralized particle fillers is investigated for linear diblock (AB) and triblock (ABA and BAB) as well as four-arm star copolymer architectures (AB3 and A3B). For particles with approximately constant effective size (defined here as the ratio of filler particle diameter to host polymer radius of gyration), miscibility was observed only within diblock copolymers and within the domains formed by the end blocks of triblock copolymers. The limitation of particle miscibility within the triblock mid-domain is interpreted as a consequence of the entropy loss associated with particle deposition due to the stretched configuration of bridged midblock chains. Particle aggregation was observed in both star copolymer samples irrespective of the architecture of the particle-loaded polymer domain. In the case of particle loading of the branched copolymer domain, this is rationalized as a consequence of the increased effective particle size, whereas the incompatibility of particle fillers in the linear block domain of miktoarm copolymer hosts is interpreted as a result of the coupling of dimensional changes within the microstructure along with the reduced axial compressibility of the particle-free branched domain. The sensitive dependence of the particle compatibility on the chain architecture of the polymer host illustrates a yet unexplored parameter space that will need to be taken into account if particle blends are to be designed with branched or multiblock host copolymer architectures.
Co-reporter:HyungJu Ryu;Luz Sanchez;HeidrunA. Keul;Aanchal Raj;MichaelR. Bockstaller Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 40) pp:7639-7643
Publication Date(Web):
DOI:10.1002/anie.200802185
Co-reporter:Heidrun A. Keul, Martin Moeller and Michael R. Bockstaller
The Journal of Physical Chemistry C 2008 Volume 112(Issue 35) pp:13483-13487
Publication Date(Web):2017-2-22
DOI:10.1021/jp803799k
We report the effect of solvent isotopic replacement on the structure evolution of gold nanorods synthesized in aqueous solution using the Ag(I)-mediated seeded-growth method (see Nikoobakht, B.; El-Sayed, M. A. Chem. Mater.2003, 15, 1957). With increasing replacement of water by deuterium oxide, both higher yields and aspect ratios are observed. With increasing reaction time the variance of particle anisotropy is found to decrease in deuterium oxide and increase in regular aqueous solution. The effect is interpreted as a consequence of the reduced solubility of the surfactant and metal salts that extends a complex and multifaceted effect on the reaction process, including mass transport and chemical potential, but also on surface reconstruction processes that have been related to the shape evolution in gold nanorod solutions. The increase in efficiency of the seeded-growth process in D2O solution furthermore is shown to facilitate the reduction of the surfactant concentration during particle synthesis by an order of magnitude as compared to regular aqueous solution.
Co-reporter:HyungJu Ryu;Luz Sanchez;HeidrunA. Keul;Aanchal Raj;MichaelR. Bockstaller Dr.
Angewandte Chemie 2008 Volume 120( Issue 40) pp:7751-7755
Publication Date(Web):
DOI:10.1002/ange.200802185
Co-reporter:Ilhem F. Hakem;Jyotsana Lal
Journal of Polymer Science Part B: Polymer Physics 2006 Volume 44(Issue 24) pp:3642-3650
Publication Date(Web):10 NOV 2006
DOI:10.1002/polb.21014
This article presents a comparative study of the structure formation of poly (ethylene oxide) PEO/Li complexes in aqueous and acetonitrile solutions using small-angle neutron scattering (SANS). We demonstrate that in acetonitrile solutions, Li-cations coordinate to the ether–oxygen of the monomeric unit, and this results in charging and stretching of the polymer chains. This is found to be in contrast to aqueous solutions, where the ions remain free in solution. In particular, we demonstrate that the “binding” and “screening” regimes that were observed in case of PEO/K+ solutions in acetonitrile are also found in the respective PEO/Li+ solutions. The addition of water to solutions in acetonitrile increasingly diminishes the ion-coordination to the polymer, eventually resulting in neutral polymer chains at water contents above ϕ*water = 30% (w/v). The preferential adsorption of water on PEO in mixtures of acetonitrile and water is evidenced by the pronounced stretching of polymer chains, in particular, at a water content of ϕwater = 25% and 33.33% (w/v) where complete stretching of the chains is observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3642–3650, 2006
Co-reporter:Heidrun A. Keul, Hyung Ju Ryu, Martin Möller and Michael R. Bockstaller
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 30) pp:NaN13578-13578
Publication Date(Web):2011/07/12
DOI:10.1039/C1CP20518H
The relevance of anion structure on the shape regulating effect of 3-ethyl-1-methylimidazolium-based ionic liquids during the seed-induced growth of gold nanocrystals is evaluated for the particular case of lactate, acetate, methylsulfate, ethylsulfate and tosylsulfonate anion systems. Carboxylate-based anions (lactate and acetate) are found to inhibit the reduction of the gold precursor salt presumably due to the deprotonation of the reducing agent ascorbic acid. The formation of non-uniform, ‘head-tail’-type anisotropic particle structures is observed in both methyl- and ethylsulfate anion systems whereas rapid precipitation is observed in the case of tosylsulfonate anions. The particular efficiency of the ethylsulfate solvent system in promoting shape anisotropic growth is interpreted to be a consequence of both reduced anion/cation interactions that act to support the coordination of imidazolium to the metal surface and the enhanced capacity of anions to participate in the particle stabilization process.
Co-reporter:Michael R. Bockstaller, Hyung Ju Ryu, Satyajeet Ojha and Jihoon Choi
Journal of Materials Chemistry A 2010 - vol. 20(Issue 42) pp:NaN9341-9341
Publication Date(Web):2010/07/27
DOI:10.1039/C0JM01810D
The formation of hierarchical 1D periodic bimetallic superstructures by co-assembly of ternary block copolymer/particle blend systems is reported. The results point to the relevance of entropy-driven morphology selection processes in enthalpic neutral block copolymer/particle blends that should render the presented approach applicable to a wide range of polymer/particle compositions.
Co-reporter:Jessica Listak ; Wojciech Jakubowski ; Laura Mueller ; Andrzej Plichta ; Krzysztof Matyjaszewski
Macromolecules () pp:
Publication Date(Web):July 2, 2008
DOI:10.1021/ma800816j
Polystyrene-b-poly(methyl acrylate) (PS−PMA) copolymers were synthesized using activators regenerated by electron transfer (ARGET) for atom transfer radical polymerization (ATRP). Polydispersity of the PMA block was varied by adjusting the amount of copper catalyst in ARGET ATRP, and the resulting molecular weight distributions were found to be approximately symmetric. At a composition of 35 vol % of PMA, the formation of a hexagonally perforated lamellar (HPL) morphology was observed for a polydisperse PS−PMA copolymer for short- and long-term solvent-casting conditions. No order−order transitions were observed at elevated temperatures or after prolonged thermal annealing. The observed stabilization of the HPL morphology—that is considered to be metastable in narrow-disperse diblock copolymers as well as diblock copolymers with selective block polydispersity given by a Schulz−Zimm distribution—suggests that the skewness of the distribution of block molecular weights is an important parameter for the structure selection during the microphase separation process. In particular, the results indicate that near-symmetric block molecular weight distributions (as realized by the ARGET ATRP technique) facilitate the stabilization of microdomain morphologies with increased standard deviation of mean curvature. The results point to the relevance of controlling both the width and symmetry of molecular weight distribution as a potential route toward the tailored synthesis of nonregular microstructures with particular topological properties that might be of future technological interest.
Co-reporter:Hyung Ju Ryu ; David B. Fortner ; Sukbin Lee ; Rachel Ferebee ; Marc De Graef ; Konstantinos Misichronis ; Apostolos Avgeropoulos
Macromolecules () pp:
Publication Date(Web):December 19, 2012
DOI:10.1021/ma3015382
The evolution of grain size and shape as well as type and frequency of grain boundary structures during thermal annealing of lamellar diblock copolymer microstructures is established using large area image reconstruction and analysis. Grain coarsening is found to proceed via an initial transient stage that is characterized by the rapid relaxation of unstable “frozen-in” defects such as kink boundaries and the subsequent quasi-stationary coarsening that is dominated by the continuous relaxation of low-angle symmetric tilt boundaries. The particular relevance of low-angle symmetric tilt boundaries to grain coarsening is interpreted as the consequence of both the associated decrease of boundary energy as well as the availability of favorable kinetic pathways—such as grain boundary splitting—to facilitate the coarsening process. The inverse relation between grain boundary energy and frequency suggests that the reduction of boundary energy is a relevant governing parameter for the evolution of grain boundary structures—as it is in inorganic materials. The existence of “inert” boundary types (such as asymmetric tilt and twist) that—within the experimental window—do not participate in the coarsening process is expected to have dominant influence on the final morphology that can be attained by thermal annealing of the microstructure. The reduction of the density of inert boundaries during the film preparation process should therefore provide a strategy for increasing the coarsening kinetics in block copolymer films during thermal annealing and thus a path toward a higher degree of order in block copolymer microstructures.
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