Ligand Tail Controls the Conformation of Indium Sulfide Ultrathin Nanoribbons.

We report the conformational control of 2D ultrathin indium sulfide nanoribbons by tuning their amine ligands' alkyl chain. The initial orthorhombic InS nanoribbons bare -octylamine ligands and display a highly curved geometry with a characteristic figure of eight shapes. Exchanging the native ligand by oleylamine induces their complete unfolding to yield flat board-shaped nanoribbons.

Ligand-induced incompatible curvatures control ultrathin nanoplatelet polymorphism and chirality.

The ability of thin materials to shape-shift is a common occurrence that leads to dynamic pattern formation and function in natural and man-made structures. However, harnessing this concept to rationally design inorganic structures at the nanoscale has remained far from reach due to a lack of fundamental understanding of the essential physical components. Here, we show that the interaction between organic ligands and the nanocrystal surface is responsible for the full range of chiral shapes seen in colloidal nanoplatelets.

Brownian dynamics simulations of bottlebrush polymers in dilute solution under simple shear and uniaxial extensional flows.

We study the dynamics of bottlebrush polymer molecules in dilute solutions subjected to shear and uniaxial extensional flows using Brownian dynamics simulations with hydrodynamic interaction (HI). Bottlebrush polymers are modeled using a coarse-grained representation, consisting of a set of beads interacting pairwise via a purely repulsive potential and connected by finitely extensible nonlinear springs. We present the results for molecular stretching, stress, and solution viscosity during the startup of flow as well as under steady state as a function of side chain length while keeping the backbone length fixed.

Interaction potential for coarse-grained models of bottlebrush polymers.

Bottlebrush polymers are a class of highly branched macromolecules that show promise for applications such as self-assembled photonic materials and tunable elastomers. However, computational studies of bottlebrush polymer solutions and melts remain challenging due to the high computational cost involved in explicitly accounting for the presence of side chains. Here, we consider a coarse-grained molecular model of bottlebrush polymers where the side chains are modeled implicitly, with the aim of expediting simulations by accessing longer length and time scales.

Dilute solution structure of bottlebrush polymers.

Bottlebrush polymers are a class of macromolecules that have recently found use in a wide variety of materials, ranging from lubricating brushes and nanostructured coatings to elastomeric gels that exhibit structural colors. These polymers are characterized by dense branches extending from a central backbone and thus have properties distinct from linear polymers. It remains a challenge to specifically understand conformational properties of these molecules, due to the wide range of architectural parameters that can be present in a system, and thus there is a need to accurately characterize and model these molecules.

Dynamics of Miura-patterned foldable sheets in shear flow.

We study the dynamics of piecewise rigid sheets containing predefined crease lines in shear flow. The crease lines act like hinge joints along which the sheet may fold rigidly, i.e.

Shear-Induced Desorption of Isolated Polymer Molecules from a Planar Wall.

We use Brownian dynamics simulations with hydrodynamic interactions to reconcile the apparent contradictions in experiments on the effect of shear flow on desorption of polymers. Our simulations show that desorption is governed by an interplay between chain-wall attraction and wall-induced hydrodynamic repulsion. When adsorption is weak, the chains form large loops and tails that generate stronger hydrodynamic interactions in the presence of the imposed shear flow, causing longer chains to desorb faster than shorter ones.

Dynamics of polymer adsorption from dilute solution in shear flow near a planar wall.

Adsorption of polymers from dilute solution subject to shear flow near a planar wall is studied using kinetic theory. A dumbbell model consisting of two beads connected by a nonlinear spring is used to describe the polymer molecules, and the beads interact with the wall via a short-range exponential potential. Bead-bead and bead-wall hydrodynamic interactions are also included in the theory.

Adsorption of single polymer molecules in shear flow near a planar wall.

Adsorption of homopolymers from a dilute solution to a planar wall in the presence of shear flow is studied using a bead-spring dumbbell model. The bead-bead and bead-wall interactions are described by generalized Lennard-Jones potentials. A kinetic theory incorporating bead-wall hydrodynamic interaction is developed in order to obtain an analytical expression for the steady-state dumbbell concentration profile.

Continuous-time random walk models of DNA electrophoresis in a post array: part II. Mobility and sources of band broadening.

Using the two-state, continuous-time random walk model, we develop expressions for the mobility and the plate height during DNA electrophoresis in an ordered post array that delineate the contributions due to (i) the random distance between collisions and (ii) the random duration of a collision. These contributions are expressed in terms of the means and variances of the underlying stochastic processes, which we evaluate from a large ensemble of Brownian dynamics simulations performed using different electric fields and molecular weights in a hexagonal array of 1 μm posts with a 3 μm center-to-center distance. If we fix the molecular weight, we find that the collision frequency governs the mobility.