From nematic shells to nematic droplets: energetics and defect transitions.

In this work, we investigate the possibility of inducing valence transitions, transitions between different defect configurations, by transforming a nematic shell into a nematic droplet. Our shells are liquid crystal droplets containing a smaller aqueous droplet inside, which are suspended in an aqueous phase. When osmotically de-swelling the inner droplet, the shell progressively increases its thickness until it eventually becomes a single droplet.

Amphiphile-Induced Phase Transition of Liquid Crystals at Aqueous Interfaces.

Monolayer assemblies of amphiphiles at planar interfaces between thermotropic liquid crystals (LCs) and an aqueous phase can give rise to configurational transitions of the underlying LCs. A common assumption has been that a reconfiguration of the LC phase is caused by an interdigitation of the hydrophobic tails of amphiphiles with the molecules of the LC at the interface. A different mechanism is discovered here, whereby reorientation of the LC systems is shown to occur through lowering of the orientation-dependent surface energy of the LC due to formation of a thin isotropic layer at the aqueous interface.

Insight into induced charges at metal surfaces and biointerfaces using a polarizable Lennard-Jones potential.

Metallic nanostructures have become popular for applications in therapeutics, catalysts, imaging, and gene delivery. Molecular dynamics simulations are gaining influence to predict nanostructure assembly and performance; however, instantaneous polarization effects due to induced charges in the free electron gas are not routinely included. Here we present a simple, compatible, and accurate polarizable potential for gold that consists of a Lennard-Jones potential and a harmonically coupled core-shell charge pair for every metal atom.

SSAGES: Software Suite for Advanced General Ensemble Simulations.

Molecular simulation has emerged as an essential tool for modern-day research, but obtaining proper results and making reliable conclusions from simulations requires adequate sampling of the system under consideration. To this end, a variety of methods exist in the literature that can enhance sampling considerably, and increasingly sophisticated, effective algorithms continue to be developed at a rapid pace. Implementation of these techniques, however, can be challenging for experts and non-experts alike.

Water Flux Induced Reorientation of Liquid Crystals.

It is well understood that the adsorption of solutes at the interface between a bulk liquid crystal phase and an aqueous phase can lead to orientational or anchoring transitions. A different principle is introduced here, whereby a transient reorientation of a thermotropic liquid crystal is triggered by a spontaneous flux of water across the interface. A critical water flux can be generated by the addition of an electrolyte to the bulk aqueous phase, leading to a change in the solvent activity; water is then transported through the liquid crystal phase and across the interface.

Nature of peptide wrapping onto metal nanoparticle catalysts and driving forces for size control.

Colloidal metal nanocrystals find many applications in catalysis, energy conversion devices, and therapeutics. However, the nature of ligand interactions and implications on shape control have remained uncertain at the atomic scale. Large differences in peptide adsorption strength and facet specificity were found on flat palladium surfaces versus surfaces of nanoparticles of 2 to 3 nm size using accurate atomistic simulations with the Interface force field.

Segregation of liquid crystal mixtures in topological defects.

The structure and physical properties of liquid crystal (LC) mixtures are a function of composition, and small changes can have pronounced effects on observables, such as phase-transition temperatures. Traditionally, LC mixtures have been assumed to be compositionally homogenous. The results of chemically detailed simulations presented here show that this is not the case; pronounced deviations of the local order from that observed in the bulk at defects and interfaces lead to significant compositional segregation effects.

Molecular Structure of Canonical Liquid Crystal Interfaces.

Numerous applications of liquid crystals rely on control of molecular orientation at an interface. However, little is known about the precise molecular structure of such interfaces. In this work, synchrotron X-ray reflectivity measurements, accompanied by large-scale atomistic molecular dynamics simulations, are used for the first time to reconstruct the air-liquid crystal interface of a nematic material, namely, 4-pentyl-4'-cyanobiphenyl (5CB).

Understanding Atomic-Scale Behavior of Liquid Crystals at Aqueous Interfaces.

The ordered environment presented by liquid crystals at interfaces enables a range of novel functionalities that is only now beginning to be exploited in applications ranging from light focusing devices to biosensors. One key feature of liquid crystals is that molecular events occurring at an interface propagate over large distances through the bulk. In spite of their importance, our fundamental understanding of liquid crystal-water and liquid crystal-air interfaces remains limited.

Simulations of inorganic-bioorganic interfaces to discover new materials: insights, comparisons to experiment, challenges, and opportunities.

Natural and man-made materials often rely on functional interfaces between inorganic and organic compounds. Examples include skeletal tissues and biominerals, drug delivery systems, catalysts, sensors, separation media, energy conversion devices, and polymer nanocomposites. Current laboratory techniques are limited to monitor and manipulate assembly on the 1 to 100 nm scale, time-consuming, and costly.

Atomic-scale identification of Pd leaching in nanoparticle catalyzed C-C coupling: effects of particle surface disorder.

C-C coupling reactions are of great importance in the synthesis of numerous organic compounds, where Pd nanoparticle catalyzed systems represent new materials to efficiently drive these reactions. Despite their pervasive utility, the catalytic mechanism of these particle-based reactions remains highly contested. Herein we present evidence of an atom leaching mechanism for Stille coupling under aqueous conditions using peptide-capped Pd nanoparticles.

Elucidation of peptide-directed palladium surface structure for biologically tunable nanocatalysts.

Peptide-enabled synthesis of inorganic nanostructures represents an avenue to access catalytic materials with tunable and optimized properties. This is achieved via peptide complexity and programmability that is missing in traditional ligands for catalytic nanomaterials. Unfortunately, there is limited information available to correlate peptide sequence to particle structure and catalytic activity to date.

A rational biomimetic approach to structure defect generation in colloidal nanocrystals.

Controlling the morphology of nanocrystals (NCs) is of paramount importance for both fundamental studies and practical applications. The morphology of NCs is determined by the seed structure and the following facet growth. While means for directing facet formation in NC growth have been extensively studied, rational strategies for the production of NCs bearing structure defects in seeds have been much less explored.

Exploiting localized surface binding effects to enhance the catalytic reactivity of peptide-capped nanoparticles.

Peptide-based methods represent new approaches to selectively produce nanostructures with potentially important functionality. Unfortunately, biocombinatorial methods can only select peptides with target affinity and not for the properties of the final material. In this work, we present evidence to demonstrate that materials-directing peptides can be controllably modified to substantially enhance particle functionality without significantly altering nanostructural morphology.

Stability, surface features, and atom leaching of palladium nanoparticles: toward prediction of catalytic functionality.

Surfactant-stabilized metal nanoparticles have shown promise as catalysts although specific surface features and their influence on catalytic performance have not been well understood. We quantify the thermodynamic stability, the facet composition of the surface, and distinct atom types that affect rates of atom leaching for a series of twenty near-spherical Pd nanoparticles of 1.8 to 3.

Tailoring molecular specificity toward a crystal facet: a lesson from biorecognition toward Pt{111}.

Surfactants with preferential adsorption to certain crystal facets have been widely employed to manipulate morphologies of colloidal nanocrystals, while mechanisms regarding the origin of facet selectivity remain an enigma. Similar questions exist in biomimetic syntheses concerning biomolecular recognition to materials and crystal surfaces. Here we present mechanistic studies on the molecular origin of the recognition toward platinum {111} facet.