Using a hybrid computational approach, we introduce A-like nanorods into a phaseseparating AB blend, which has 45/55 composition. In the absence of the rods, the minority A phase forms droplets in the matrix of B. With the addition of N = 670 rods that interact solely through a short range repulsive interaction (mimicking the steric stabilization provided by a coating of A ligands), the mixture retains this droplet morphology. When, however, we add an effective attraction between the sterically stabilized rods, the nanoparticles form extensive networks in the A phase, which can form a continuous phase. In addition to altering the morphology of the mixture, the attractive interaction influences the rate of domain growth. In particular, at early times, the mutually attractive rods increase the growth rate of the domains in the early stage. At late times, the domain growth crosses over to a slow growth regime. Our findings demonstrate that the morphology and coarsening of a rod-filled blend can be controlled by varying the rod-rod interaction and hence, provides guidelines for tailoring the electrical and mechanical properties of the nanocomposites.

Via the Dissipative Particle Dynamics (DPD) approach, we study the self-assembly of hybrid structures comprising lipids and end-functionalized nanotubes. Individual lipids are composed of a hydrophilic head group and two hydrophobic tails. Each bare nanotube encompasses an ABA architecture, with a hydrophobic shaft (B) and two hydrophilic ends (A). To allow for regulated transport through the nanotube, we also introduce hydrophilic hairs at one end of the tube. The amphiphilic lipids are composed of a hydrophilic head group (A) and two hydrophobic tails (B). We select the dimensions of the nanotube architecture to minimize its hydrophobic mismatch with the lipid bilayer. We find the amphiphilic lipids and functionalized nanotubes to self-assemble into a stable hybrid vesicle or a bicelle in the presence of a hydrophilic solvent. We demonstrate that the morphology of the self-assembled functionalized nanotube-lipid hybrid structures is controlled by the rigidity of the lipid molecules and concentration of the nanotubes.

We consider a theoretical model of a reactive polymer gel in which the reaction can proceed in an oscillatory regime and generate traveling chemical waves accompanied by waves of local swelling-deswelling. This type of gel could be used for fabricating chemo-mechanical devices with self-sustained rhythmic action, and gel-based pumps. We assume that the Belousov-Zhabotinsky (BZ) reaction takes place in the reactive gel. The BZ reaction generates periodic reduction-oxidation (redox) changes of a metal catalyst covalently bonded to a hydrogel that is immersed in a solution containing the rest of the BZ reagents. The redox changes in the metal affect the polymer-solvent interactions, resulting in variations in the gel volume. The self-oscillation of the gel volume, and the traveling waves of local swelling in a hydrogel with the BZ reaction have been experimentally observed by Yoshida and co-workers. To describe the system theoretically, we employ the Oregonator model of the BZ reaction, and the two-fluid model of gel dynamics. Propagation of one-dimensional wave trains through the reactive gel is simulated. The structure of the traveling swelling-deswelling waves is studied.

Phase separating binary fluids with the addition of immobile particles, which act as osmotic force centres, were simulated using a Lattice Boltzmann model in two dimensions. In the hydrodynamic over-damped limit, where the flow is entirely driven by capillary effects, the presence of particles that are preferentially wetted by one of the fluid components significantly affects the kinetics of the growth of the fluid domains. The late time dynamics is governed by the wetting interactions and the final size of the domains can be tailored by varying the strength of the particles-fluid interaction as well as the particles concentration. These features are predicted within a simple theoretical model and are amenable of experimental checks.

Using scaling theory, we determine the equilibrium behavior of a melt of functionalized and non-functionalized polymers confined between two infinite, planar surfaces, which model clay sheets. The functionalized chains contain two end-groups (one at each chain-end) that are highly attracted to the surfaces. Through these calculations, we delineate the conditions for the formation of thermodynamically stable polymer/clay mixtures in terms of the end-group adsorption energy, volume fraction of the end-functionalized chains, and polymer chain lengths.

We analyze the thermodynamics of polymer-clay mixtures within the framework of density functional theory (DFT). The interaction potential between clay particles is calculated using the self-consistent field (SCF) method and is strongly dependent on the length and density of grafted short-chain organic modifiers. By combining the DFT and SCF techniques, we determine the role of the grafted chains on the equilibrium phase behavior of the mixtures.

The articles in this issue illustrate how various theoretical and computer models have been used to probe behavior of polymers at penetrable and impenetrable interfaces. Interest in polymer interfaces stems from the control interfaces commonly have over macroscopic properties—such as the strength or biocompatibility of the material. Consider the “alloying” or blending of existing polymers. This technique provides an inexpensive means of fabricating new materials that can display the desirable properties of the individual components. Most polymer pairs however are immiscible, and the mixture segregates into macroscopic domains separated by relatively weak interfaces. To enhance the structural integrity of the blend, copolymer “compatibilizers” are added to the mixture. These chains localize at the interface between the immiscible polymers, enhance the adhesion between the phase-separated regions, and thereby improve the mechanical properties of the blend.

On an impenetrable interface, polymer films or coatings are commonly used to modify the properties of the underlying substrate. For example the polymer layer can be utilized to tailor biocompatibility, wettability, or roughness of the surface. Polymers anchored to solid surfaces can also be used to control the interaction between these surfaces. Thus the tethered layer can promote the adhesion between dissimilar solids or prevent the aggregation of colloidal particles.

Polymer films that contain well-defined patterns can be used in a variety of novel applications. For example such films can serve as the scaffolding in fabricating organic/inorganic composites with controlled architectures. One means of forming patterned films is to anchor the ends of homopolymers onto a substrate (so that the ends are fixed and cannot move) and immerse the system in a poor solvent. The incompatibility between the polymer and solvent drives the system to phase-separate. Since the ends are immobilized however, the polymers can only escape the unfavorable solvent by clustering with neighboring chain s into distinct aggregates or “pinned micelles.” These micelles have a uniform size and spacing, and form a regular array on the surface. In this article, we use theoretical models to extend this concept and show that, by tethering copolymers—chains that contain more than one type of monomer—we can drive the system to form more complicated surface patterns. These copolymer patterns provide a handle for engineering the interaction between surfaces and thus facilitate the fabrication of novel optical devices. If the copolymer films are composed of both hydrophilic and hydrophobic domains, the surface can also be used as a template for growing biological cells with tailored shapes and sizes.

Polymers tethered by one end onto a solid surface are referred to as polymer “brushes”. We consider brushes composed of copolymers that contain both A and B monomers. The A monomers are compatible with the surrounding solvent, while the B sites are solventincompatible. The solvent incompatibility causes the B sites to associate into domains or clusters within the layer. We use Monte Carlo computer simulations and self-consistent field calculations to determine the effect of copolymer architecture on the structure of the polymer brush. In particular, we alter the copolymer sequence distribution (the arrangement of the A and B monomers along the length of the chain) and determine how both the vertical and lateral morphology of the brush are effected by these variations. The results provide guidelines for controlling the size and shape of the B domains, and consequently, the morphology of the tethered layer.

The presence of copolymers at an interface between two immiscible fluids is crucial to such processes as emulsion stabilization and microemulsion formation [1]. Recently Marques and Joanny [2] and Garel et al. [3] have studied the behavior of a random copolymer at a liquid-liquid interface. However, the arrangement or sequence distribution of the monomers in a copolymer can vary widely from random to blocky or purely alternating. In this paper, we use both analytic arguments and molecular dynamics simulations to determine how the sequence distribution affects the adsorption and conformation of a single macromolecule at the boundary between two immiscible fluids [4]. In particular, we derive an expression for the free energy of a copolymer at the interface and compare the resulting predictions with the outcome of the simulations. Our findings yield design criteria for fabricating polymers that display the desired interfacial properties.

A reversible diffusion-limited aggregation model for self-assembling polymers has been developed with the aid of computer simulations. The calculations have been performed in three dimensions and apply to linear chains bearing an associating site at each terminus. The results reveal that the associating sites form finite-sized clusters that, in turn, lead to the assemblage of a supermolecular network. The average cluster size is found to vary with the degree of reversibility of site binding.