Modeling the structure and relaxation in glycerol-silica nanocomposites.

The relationship between the dynamics and structure of amorphous thin films and nanocomposites near their glass transition is an important problem in soft-matter physics. Here, we develop a simple theoretical approach to describe the density profile and the α-relaxation time of a glycerol-silica nanocomposite (S. Cheng , , 2015, , 194704).

Polyurea-Graphene Nanocomposites-The Influence of Hard-Segment Content and Nanoparticle Loading on Mechanical Properties.

Polyurethane and polyurea-based adhesives are widely used in various applications, from automotive to electronics and medical applications. The adhesive performance depends strongly on its composition, and developing the formulation-structure-property relationship is crucial to making better products. Here, we investigate the dependence of the linear viscoelastic properties of polyurea nanocomposites, with an IPDI-based polyurea (PUa) matrix and exfoliated graphene nanoplatelet (xGnP) fillers, on the hard-segment weight fraction (HSWF) and the xGnP loading.

Combined Description of the Equation of State and Diffusion Coefficient of Liquid Water Using a Two-State Sanchez-Lacombe Approach.

Water is one of the most important compounds on Earth, yet its material properties are still poorly understood. Here, we use a recently developed two-state, two-(time)scale (TS2) dynamic mean-field model combined with the two-state Sanchez-Lacombe (SL) thermodynamic theory in order to describe the equation of state (density as a function of temperature and pressure) and diffusivity of liquid water. In particular, it is shown that in a relatively wide temperature and pressure range (160 K < < 360 K; 0 < < 100 MPa), density and self-diffusion obey a special type of dynamic scaling, similar to the "τTV" scaling of Casalini and Roland, but with the negative exponent .

Surfactant in a Polyol-CO Mixture: Insights from a Classical Density Functional Theory Study.

Silicone-polyether (SPE) surfactants, made of a polydimethyl-siloxane (PDMS) backbone and polyether branches, are commonly used as additives in the production of polymeric foams with improved properties. A key step in the production of polymeric foams is the nucleation of gas bubbles in the polymer matrix upon supersaturation of dissolved gas. However, the role of SPE surfactants in the nucleation of gas bubbles is not well understood.

Combined description of pressure-volume-temperature and dielectric relaxation of several polymeric and low-molecular-weight organic glass-formers using SL-TS2 approach.

We apply our recently-developed mean-field "SL-TS2" (two-state Sanchez-Lacombe) model to simultaneously describe dielectric α-relaxation time, , and pressure-volume-temperature () data in four polymers (polystyrene, poly(methylmethacrylate), poly(vinyl acetate) and poly(cyclohexane methyl acrylate)) and four organic molecular glass formers (-terphenyl, glycerol, PCB-62, and PDE). Previously, it has been shown that for all eight materials, the Casalini-Roland thermodynamical scaling, = (γsp) (where is temperature and is specific volume) is satisfied (R. Casalini and C.

Combined description of polymer and relaxation data using a dynamic "SL-TS2" mean-field lattice model.

We develop a combined model to describe the pressure-volume-temperature () thermodynamics and the - and -relaxation time dynamics in glass-forming amorphous materials. The results are described using a two-state modification of the Sanchez-Lacombe equation of state (SL-EoS). The minimization of the Sanchez-Lacombe free energy expression allows one to calculate the density (or specific volume) and the "solid fraction" as a function of temperature and pressure.

Nonelectrostatic Adsorption of Polyelectrolytes and Mediated Interactions between Solid Surfaces.

Polymer-mediated interaction between two solid surfaces is directly connected to the properties of the adsorbed polymer layers. Nonelectrostatic interactions with a surface can significantly impact the adsorption of polyelectrolytes to charged surfaces. We use a classical density functional theory to study the effect of various polyelectrolyte solution properties on the adsorption and interaction between two like-charged surfaces.

A simple mean-field model of glassy dynamics and glass transition.

We propose a phenomenological model to describe the equilibrium dynamic behavior of amorphous glassy materials. It is assumed that a material can be represented by a lattice of cooperatively re-arranging regions (CRRs), with each CRR having two states, the low-temperature "solid" and the high-temperature "liquid". At low temperatures, the material exhibits two characteristic relaxation times, corresponding to the slow large-scale motion between the "solid" CRRs (α-relaxation) and the faster local motion within individual CRRs (β-relaxation).

On the origin of oscillatory interactions between surfaces mediated by polyelectrolyte solution.

We use a numerical implementation of polymer classical density functional theory with an incompressibility condition to study the system consisting of nonadsorbing polyelectrolytes confined by two planar surfaces and quantify the effective interaction between the two planar surfaces as a function of the polyelectrolyte and salt concentrations. Our results indicate that for the uncharged surfaces (and weakly charged surfaces), the effective interaction primarily consists of a short-range attraction due to the depletion followed by repulsion due to the electric double layer overlapping and electrostatic correlations. For salt-free and low salt concentration systems, the magnitude of the repulsion barrier is determined by the overlap between the electric double layers, while at relatively high salt concentrations, the magnitude of the repulsion barrier is determined by the electrostatic correlations.

Rheology of Cellulose Ether Excipients Designed for Hot Melt Extrusion.

A new family of cellulosic ether polymeric excipients has been recently engineered for fabrication of amorphous solid dispersions of active pharmaceutical ingredients via hot-melt extrusion (HME). These hydroxypropyl methyl cellulose excipients enable plasticizer-free melt processing at much lower temperatures (135-160 °C) due to their substantially reduced glass transition temperatures ( T = 98-110 °C). The novel amorphous cellulose ethers were found to be rheologically solidlike well above their glass transition ( T + 70 °C).

Oscillatory and Steady Shear Rheology of Model Hydrophobically Modified Ethoxylated Urethane-Thickened Waterborne Paints.

Hydrophobically modified ethoxylated urethane (HEUR) thickeners are widely used as rheology modifiers for waterborne paints. Although the rheology of HEUR solutions in water is fairly well-understood, their impact on the rheology of waterborne latex/pigment suspensions (formulated paints) is more complicated. We study the shear rheology of model HEUR/latex/TiO suspensions in water and investigate the dependence of both oscillatory and steady shear behaviors on the strength of the HEUR hydrophobes.

Density functional theory for charged fluids.

An improved density functional theory (DFT) for an inhomogeneous charged system (including electrolyte and/or polyelectrolyte) is proposed based on fundamental measure theory, thermodynamic perturbation theory and mean-spherical approximation. Our DFT combines the existing treatment of hard-sphere contributions using fundamental measure theory (FMT) with a new treatment of the electrostatic correlations for the non-bonded ions and chain connectivity that are approximated by employing a first-order Taylor expansion, with the reference fluid density determined using the technique from Gillespie et al. [D.

Formulation-Controlled Positive and Negative First Normal Stress Differences in Waterborne Hydrophobically Modified Ethylene Oxide Urethane (HEUR)-Latex Suspensions.

Hydrophobically modified ethylene oxide urethane (HEUR) associative thickeners are widely used to modify the rheology of waterborne paints. Understanding the normal stress behavior of the HEUR-based paints under high shear is critical for many applications such as brush drag and spreading. We observed that the first normal stress difference, , at high shear (large Weissenberg number) can be positive or negative depending on the HEUR hydrophobe strength and concentration.

Modeling the interfacial tension in oil-water-nonionic surfactant mixtures using dissipative particle dynamics and self-consistent field theory.

We use two mesoscale simulation methods, dissipative particle dynamics (DPD) and self-consistent field theory (SCFT), to model interfacial tension in ternary oil/water/surfactant mixtures. For model systems where the oil is dodecane and the surfactant is a linear alkyl ethoxylate, the two methods show a good semiquantitative agreement among themselves and with experimental data. We further discuss the advantages and limitations of the two methods and their possible use for surfactant screening in specific industrial applications.

Modeling polymer-induced interactions between two grafted surfaces: comparison between interfacial statistical associating fluid theory and self-consistent field theory.

The interaction between two polymer grafted surfaces is important in many applications, such as nanocomposites, colloid stabilization, and polymer alloys. In our previous work [Jain et al., J.

Modeling the thermodynamics of the interaction of nanoparticles with cell membranes.

Interactions between nanoparticles and cell membranes may play a crucial role in determining the cytotoxicity of nanoparticles as well as their potential application as drug delivery vehicles or therapeutic agents. It has been shown that such interactions are often determined not by biochemical but by physicochemical factors (e.g.

Effect of hydrodynamic interactions on the evolution of chemically reactive ternary mixtures.

We investigate the structural evolution of an A/B/C ternary mixture in which the A and B components can undergo a reversible chemical reaction to form C. We developed a lattice Boltzmann model for this ternary mixture that allows us to capture both the reaction kinetics and the hydrodynamic interactions within the system. We use this model to study a specific reactive mixture in which C acts as a surfactant, i.