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The design of functional polymeric materials with tunable response requires a synergetic use of macromolecular architecture and interactions. Here, we combine experiments with computer simulations to demonstrate how physical properties of gels can be tailored at the molecular level, using star block copolymers with alternating block sequences as a paradigm. Telechelic star polymers containing attractive outer blocks self-assemble into soft patchy nanoparticles, whereas their mirror-image inverted architecture with inner attractive blocks yields micelles. In concentrated solutions, bridged and interpenetrated hexagonally packed nanocylinders are formed, respectively, with distinct structural and rheological properties. The phase diagrams exhibit a peculiar re-entrance where the hexagonal phase melts upon both heating and cooling because of solvent–block and block–block interactions. The bridged nanostructure is characterized by similar deformability, extended structural coherence, enhanced elasticity, and yield stress compared to micelles or typical colloidal gels, which make them promising and versatile materials for diverse applications.

It is easy to understand the self-assembly of particles with anisotropic shapes or interactions (for example, cobalt nanoparticles or proteins) into highly extended structures. However, there is no experimentally established strategy for creating a range of anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles uniformly grafted with macromolecules ('nanoparticle amphiphiles') robustly self-assemble into a variety of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. Theory and simulations suggest that this self-assembly reflects a balance between the energy gain when particle cores approach and the entropy of distorting the grafted polymers. The effectively directional nature of the particle interactions is thus a many-body emergent property. Our experiments demonstrate that this approach to nanoparticle self-assembly enables considerable control for the creation of polymer nanocomposites with enhanced mechanical properties. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications., The original document contains color images. Pub. in Nature Materials, v8, p354-359, Apr 2009. Sponsored in part by National Science Foundation grants nos. DMR-0804647 and DMR-0642573, Department of Energy grant no. DE-AC02-06CH11357.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986., MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE, Bibliography: v.2, leaves 200-208., by Athanassios Z. Panagiotopoulos., Ph.D.

We present a systematic study of the effect of the ion pairing on the gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a class of dipolar dimer models that depend on a parameter Rc , the maximum separation between the ions that compose the dimer. This parameter can vary from s6 that corresponds to the tightly tethered dipolar dimer model to Rc!` that corresponds to the Stillinger-Lovett description of the free ion system. The coexistence curve and critical point parameters are obtained as a function of Rc by grandcanonical Monte Carlo techniques. Our results show that this dependence is smooth but nonmonotonic and converges asymptotically towards the free ion case for relatively small values of Rc . This fact allows us to describe the gas-liquid transition in the free ion model as a transition between two dimerized fluid phases. The role of the unpaired ions can be considered as a perturbation of this picture

We present a systematic study of the effect of the ion pairing on the gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a class of dipolar dimer models that depend on a parameter Rc , the maximum separation between the ions that compose the dimer. This parameter can vary from s6 that corresponds to the tightly tethered dipolar dimer model to Rc!` that corresponds to the Stillinger-Lovett description of the free ion system. The coexistence curve and critical point parameters are obtained as a function of Rc by grandcanonical Monte Carlo techniques. Our results show that this dependence is smooth but nonmonotonic and converges asymptotically towards the free ion case for relatively small values of Rc . This fact allows us to describe the gas-liquid transition in the free ion model as a transition between two dimerized fluid phases. The role of the unpaired ions can be considered as a perturbation of this picture

We present a systematic study of the effect of the ion pairing on the gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a class of dipolar dimer models that depend on a parameter Rc , the maximum separation between the ions that compose the dimer. This parameter can vary from s6 that corresponds to the tightly tethered dipolar dimer model to Rc!` that corresponds to the Stillinger-Lovett description of the free ion system. The coexistence curve and critical point parameters are obtained as a function of Rc by grandcanonical Monte Carlo techniques. Our results show that this dependence is smooth but nonmonotonic and converges asymptotically towards the free ion case for relatively small values of Rc . This fact allows us to describe the gas-liquid transition in the free ion model as a transition between two dimerized fluid phases. The role of the unpaired ions can be considered as a perturbation of this picture

We present a systematic study of the effect of the ion pairing on the gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a class of dipolar dimer models that depend on a parameter Rc , the maximum separation between the ions that compose the dimer. This parameter can vary from s6 that corresponds to the tightly tethered dipolar dimer model to Rc!` that corresponds to the Stillinger-Lovett description of the free ion system. The coexistence curve and critical point parameters are obtained as a function of Rc by grandcanonical Monte Carlo techniques. Our results show that this dependence is smooth but nonmonotonic and converges asymptotically towards the free ion case for relatively small values of Rc . This fact allows us to describe the gas-liquid transition in the free ion model as a transition between two dimerized fluid phases. The role of the unpaired ions can be considered as a perturbation of this picture

We present a systematic study of the effect of the ion pairing on the gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a class of dipolar dimer models that depend on a parameter Rc , the maximum separation between the ions that compose the dimer. This parameter can vary from s6 that corresponds to the tightly tethered dipolar dimer model to Rc!` that corresponds to the Stillinger-Lovett description of the free ion system. The coexistence curve and critical point parameters are obtained as a function of Rc by grandcanonical Monte Carlo techniques. Our results show that this dependence is smooth but nonmonotonic and converges asymptotically towards the free ion case for relatively small values of Rc . This fact allows us to describe the gas-liquid transition in the free ion model as a transition between two dimerized fluid phases. The role of the unpaired ions can be considered as a perturbation of this picture

Liquid-vapor coexistence curves and critical parameters for hard-core 1:1 electrolyte models with diameter ratios l s 2 s 1 1 to 5.7 have been studied by fine-discretization Monte Carlo methods. Normalizing via the length scale s 6 1 2 s 1 1s 2 , relevant for the low densities in question, both T c ( k B T c s 6 q 2 ) and r c ( r c s 3 6 ) decrease rapidly (from 0.05 to 0.03 and 0.08 to 0.04, respectively) as l increases. These trends, which unequivocally contradict current theories, are closely mirrored by results for tightly tethered dipolar dimers (with T c lower by 0% 11% and r c greater by 37% 12% )

Liquid-vapor coexistence curves and critical parameters for hard-core 1:1 electrolyte models with diameter ratios l s 2 s 1 1 to 5.7 have been studied by fine-discretization Monte Carlo methods. Normalizing via the length scale s 6 1 2 s 1 1s 2 , relevant for the low densities in question, both T c ( k B T c s 6 q 2 ) and r c ( r c s 3 6 ) decrease rapidly (from 0.05 to 0.03 and 0.08 to 0.04, respectively) as l increases. These trends, which unequivocally contradict current theories, are closely mirrored by results for tightly tethered dipolar dimers (with T c lower by 0% 11% and r c greater by 37% 12% )

Liquid-vapor coexistence curves and critical parameters for hard-core 1:1 electrolyte models with diameter ratios l s 2 s 1 1 to 5.7 have been studied by fine-discretization Monte Carlo methods. Normalizing via the length scale s 6 1 2 s 1 1s 2 , relevant for the low densities in question, both T c ( k B T c s 6 q 2 ) and r c ( r c s 3 6 ) decrease rapidly (from 0.05 to 0.03 and 0.08 to 0.04, respectively) as l increases. These trends, which unequivocally contradict current theories, are closely mirrored by results for tightly tethered dipolar dimers (with T c lower by 0% 11% and r c greater by 37% 12% )

Liquid-vapor coexistence curves and critical parameters for hard-core 1:1 electrolyte models with diameter ratios l s 2 s 1 1 to 5.7 have been studied by fine-discretization Monte Carlo methods. Normalizing via the length scale s 6 1 2 s 1 1s 2 , relevant for the low densities in question, both T c ( k B T c s 6 q 2 ) and r c ( r c s 3 6 ) decrease rapidly (from 0.05 to 0.03 and 0.08 to 0.04, respectively) as l increases. These trends, which unequivocally contradict current theories, are closely mirrored by results for tightly tethered dipolar dimers (with T c lower by 0% 11% and r c greater by 37% 12% )

Liquid-vapor coexistence curves and critical parameters for hard-core 1:1 electrolyte models with diameter ratios l s 2 s 1 1 to 5.7 have been studied by fine-discretization Monte Carlo methods. Normalizing via the length scale s 6 1 2 s 1 1s 2 , relevant for the low densities in question, both T c ( k B T c s 6 q 2 ) and r c ( r c s 3 6 ) decrease rapidly (from 0.05 to 0.03 and 0.08 to 0.04, respectively) as l increases. These trends, which unequivocally contradict current theories, are closely mirrored by results for tightly tethered dipolar dimers (with T c lower by 0% 11% and r c greater by 37% 12% )