Within the broad theme of "Engineering Entropy and Order in Nanomaterials via Molecular Simulation", the types of materials that have been studied can be classified into colloids and polymers. (a) Colloidal suspensions (see group "A" in publication list). We have shown, for example, that nanoparticles of various geometrical shapes (like having polyhedral shape or rigid and flexible parts) self-assemble into liquid crystalline and plastic solids that either are new or confirm recent experimental observations. Such phases have potential uses in materials involving light matter interactions (such as photonic band-gap materials and superlattices for solar cells). (b) Polymers (publication groups B-E). We have studied the thermodynamic and conformational behavior of many polymeric systems have been studied, from single chains to melts to networks, from fully flexible to rod-like molecules, from bulk to nanopore confinement, and from homopolymers to block copolymers to proteins. In the case of diblock copolymers (publication group "C"), one key contribution has been to understand the conditions under which bicontinuous structures (which are ideal templates to create structures of large surface area and uniform nanosized pores, for use in certain types of solar cells and membranes). In fact, our group was the first to simulate (using particle-based simulations) the gyroid phase in a pure diblock copolymer melt and the so-called "plumber's nightmare phase" in blends of diblock copolymer and homopolymer. Regarding polymer networks or elastomers (publication group "E"), we have elucidated the effect on the tensile behavior, swelling, and toughness (total energy absorbed before break-up) of such structural features as permanently trapped entanglements, temporary chain interspersion, inhomogeneities in crosslinking (e.g., brought about by chains of different molecular weights), order (e.g., due to alignment tendencies of semiflexible chains), and topological regularity and defects. We have proposed a new design of elastomer having super-toughness and extensibility by virtue of a modular mechanism (involving the strain-driven formation of successive smectic domains) resulting in a stress-strain behavior similar to that of abalone shells' glue. Regarding proteins (publication group "B") our group has pioneered the simulation of "nanobodies", a type of mini-antibody that can only be found in Camelids and that offers a new platform for biotechnological applications, with the advantage of being more stable and versatile than conventional antibodies.
While most of our studies have dealt with bulk properties, some have focused on interfacial properties (publication group "F") as these are relevant to many applications and processing conditions. For example, we have determined how confinement within a slit pore can alter the structure and mobility of polymers and particles, how nanoscale roughness can make solid surfaces super oleophobic (i.e., not easily wetted by oils), and how incipient phases nucleate on homogeneous or heterogeneous environments.
Regarding simulation methods (publication groups "G", "H" and "I"), the contributions have concentrated on developing new techniques to quantify the thermodynamics (e.g., via expanded ensembles) and kinetics (e.g., via forward flux sampling) of the polymeric and colloidal systems of interest in situations where components are complex, have large asymmetries or where size polydispersity exists. In particular, these methods have allowed us to detail how transitions occur between two states of a system or between two phases with different degrees or order (e.g., between conformers of a protein or between a liquid and a solid).
The poster below provides pictorial summaries of our current areas of research.