Mechanical properties of silicone based composites as a temperature insensitive ballistic backing material for quantifying back face deformation.

This paper describes a new witness material for quantifying the back face deformation (BFD) resulting from high rate impact of ballistic protective equipment. Accurate BFD quantification is critical for the assessment and certification of personal protective equipment, such as body armor and helmets, and ballistic evaluation. A common witness material is ballistic clay, specifically, Roma Plastilina No.

Optimal Feedback Controlled Assembly of Perfect Crystals.

Perfectly ordered states are targets in diverse molecular to microscale systems involving, for example, atomic clusters, protein folding, protein crystallization, nanoparticle superlattices, and colloidal crystals. However, there is no obvious approach to control the assembly of perfectly ordered global free energy minimum structures; near-equilibrium assembly is impractically slow, and faster out-of-equilibrium processes generally terminate in defective states. Here, we demonstrate the rapid and robust assembly of perfect crystals by navigating kinetic bottlenecks using closed-loop control of electric field mediated crystallization of colloidal particles.

Reconfigurable multi-scale colloidal assembly on excluded volume patterns.

The ability to create multi-scale, periodic colloidal assemblies with unique properties is important to emerging applications. Dynamically manipulating colloidal structures via tunable kT-scale attraction can provide the opportunity to create particle-based nano- and microstructured materials that are reconfigurable. Here, we report a novel tactic to obtain reconfigurable, multi-scale, periodic colloidal assemblies by combining thermoresponsive depletant particles and patterned topographical features that, together, reversibly mediate local kT-scale depletion interactions.

Direct Measurement of Macromolecule-Coated Colloid-Mucus Interactions.

We report measurements of macromolecule-coated colloids interacting with mucus to understand colloidal particle diffusion near mucus-coated surfaces. Total internal reflection microscopy is used to measure colloids with adsorbed poly(ethylene glycol) (PEG), bovine serum albumin (BSA), and polyelectrolyte bilayers (PEB) interacting with mucus to obtain kT-scale energy landscapes and nanometer-scale diffusivity landscapes. Energy landscapes are quantified as a superposition of van der Waals, steric, and tethering potentials, and diffusivity landscapes are modeled by considering lubrication in the presence of permeable layers.

Modeling depletion mediated colloidal assembly on topographical patterns.

This work reports a model and Monte Carlo simulations of excluded volume mediated interactions between colloids and topographically patterned substrates in the presence of thermosensitive depletants. The model is matched to experiments to yield density, free energy, and potential energy landscapes that quantitatively capture particle microstructures varying from immobilized non-close packed configurations to random fluid states. A numerical model of local excluded volume affects is developed to enable computation of local depletion attraction in the presence of arbitrary geometries.

Colloidal crystal grain boundary formation and motion.

The ability to assemble nano- and micro- sized colloidal components into highly ordered configurations is often cited as the basis for developing advanced materials. However, the dynamics of stochastic grain boundary formation and motion have not been quantified, which limits the ability to control and anneal polycrystallinity in colloidal based materials. Here we use optical microscopy, Brownian Dynamic simulations, and a new dynamic analysis to study grain boundary motion in quasi-2D colloidal bicrystals formed within inhomogeneous AC electric fields.

Controlling colloidal particles with electric fields.

In this instructional review, we discuss how to control individual colloids and ensembles of colloids using electric fields. We provide background on the electrokinetic transport mechanisms and kT-scale equilibrium colloidal interactions that enable such control. We also describe the experimental configurations, microscopy methods, image analyses, and material systems for which these mechanisms have been successfully employed.

Self-consistent colloidal energy and diffusivity landscapes in macromolecular solutions.

We report a dynamic analysis to simultaneously measure colloidal forces and hydrodynamic interactions in the presence of both adsorbed and unadsorbed macromolecules. A Bayesian inference method is used to self-consistently obtain the position-dependent potential energy (i.e.

Depletion-mediated potentials and phase behavior for micelles, macromolecules, nanoparticles, and hydrogel particles.

We report a simple depletion potential that captures measured potentials and phase behavior for micrometer-sized colloids in the presence of unadsorbing charged micelles, charged nanoparticles, nonionic macromolecules, and nonionic hydrogel particles. Total internal reflection microscopy (TIRM) is used to measure net potentials between colloids and surfaces, and video microscopy (VM) is used to measure quasi-2D phase behavior in the same material systems. A modified Asakura-Oosawa (AO) depletion potential is developed to accurately quantify particle-wall potentials and interfacial crystallization via particle-particle potentials in Monte Carlo (MC) simulations.