We develop a computer simulation for the dynamic behavior of a phase-separating binary mixture that contains mobile, solid particles. The system models “filled polymers”, which contain not only a blend of different macromolecules, but also solid fillers. We focus on the case where one of the components preferentially wets the surface of the particles. By combining a mesoscopic, coarse-grained description of the fluids with a discrete model for the particles, we show that the addition of hard particles significantly changes both the speed and the morphology of the phase separation. To probe the late-stage properties of the system, we also develop a mean-field rate-equation model for the mixture. The results indicate that the phase separation is arrested in the late stage; the “steady-state” domain size depends strongly on both the particle diffusion constant and the particle concentration. To obtain insight into the effects of processing on the properties of such composites, we also investigated the behavior of the binary fluid/particle mixture under shear. For sufficiently large particle densities, we find that the anisotropic growth caused by the imposed shear is destroyed by the randomly moving particles, and the domains are isotropic in shape even for large shear strains. Finally, we apply our models to mixtures of diblock copolymers and fillers. Overall, our findings reveal how the solid additives can be used to tailor the morphology of the complex mixture, and thereby control the macroscopic properties (such as mechanical integrity) of the composite.

SignificanceThe range of allowed deformation modes currently described for the actuation of microstructures is limited. In this work we introduce magnetic-field–guided encoding of highly controlled molecular anisotropy into 3D liquid-crystalline elastomer microstructures capable of displaying unique multiresponsive, shape-changing behaviors. The richness of the predetermined and self-regulated deformations and region-specific motions in these microstructural arrays gives rise to physicochemical insights, as well as potential applications in controlled adhesion, information encryption, soft robotics, and self-regulated light–material interactions.

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Structurally tailored and engineered macromolecular (STEM) gels constitute part of an emerging field of smart materials. STEM gels are polymer networks containing latent initiator sites available for postsynthesis modification. STEM gels synthesized by controlled radical polymerization (CRP) are presented. First, reversible addition–fragmentation chain transfer (RAFT) polymerization was used to copolymerize (meth)­acrylate monomer, di­(meth)­acrylate cross-linker, and inimer for the subsequent atom transfer radical polymerization (ATRP) grafting-from process. The resulting STEM gels were infiltrated with a second monomer, which formed side chains grafted from the inimer sites by photoactivated ATRP. This approach permits significant spatial and temporal control over the structure of the resulting material. Here, the technique was used to transform primary STEM gels into single-piece amphiphilic and hard/soft materials.

Using an atomic force microscope (AFM) with an attachment specifically designed for indentation, we measured the mechanical properties of demineralized human dentin under three conditions: in water, in air after desiccation, and in water after rehydration. The static elastic modulus (E(h)r = 134 kPa) and viscoelastic responses (tau(epsilon) = 5.1 s and tau(sigma) = 6.6 s) of the hydrated, demineralized collagen scaffolding were determined from the standard linear solid model of viscoelasticity. No significant variation of these properties was observed with location. On desiccation, the samples showed considerably larger elastic moduli (2 GPa), and a hardness value of 0.2 GPa was measured. Upon rehydration the elastic modulus decreased but did not fully recover to the value prior to dehydration (381 kPa).