Valeriy V. Ginzburg

Simulation of Hard Particles in a Phase-Separating Binary Mixture

We simulate the motion of spherical particles in a phase-separating binary mixture. By combining cell dynamical equations with Langevin dynamics for particles, we show that the addition of hard particles significantly changes both the speed and the morphology of the phase separation. At the late stage of the spinodal decomposition process, particles significantly slow down the domain growth, in qualitative agreement with earlier experimental data. {copyright} {ital 1999} {ital The American Physical Society}

Three-dimensional simulations of diblock copolymer/particle composites☆

Abstract We develop a coarse-grained model to investigate the influence of nanoscale particles on the phase separation and the morphology of symmetric AB diblock copolymer melts. The microphase separation is modeled by the cell dynamical systems (CDS) equations, while the particle dynamics is described by a Langevin equation. We assume that the particles have a selective affinity to the A block and thus, can self-assemble and form clusters within A-domains. By varying the particle volume fraction, φp, we study the coupling between the microphase separation of the diblocks and the cluster formation for the particles. We also estimate the percolation threshold, φ∗, for the particles and find that the presence of diblocks decreases φ∗ by a factor slightly greater than two relative to the case of particles in a homopolymer ( φ ∗ ≈9% in a diblock vs. 22% in a homopolymer). This result can be useful in designing new composites with increased electrical conductivity and/or mechanical strength.

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. Chem. Phys. 128, 154910 (2008)], we showed that interfacial statistical associating fluid density theory (iSAFT) successfully calculates the structure of grafted polymer chains in the absence/presence of a free polymer. In the current work, we have applied this density functional theory to calculate the force of interaction between two such grafted monolayers in implicit good solvent conditions. In particular, we have considered the case where the segment sizes of the free (sigma(f)) and grafted (sigma(g)) polymers are different. The interactions between the two monolayers in the absence of the free polymer are always repulsive. However, in the presence of the free polymer, the force either can be purely repulsive or can have an attractive minimum depending upon the relative chain lengths of the free (N(f)) and grafted polymers (N(g)). The attractive minimum is observed only when the ratio alpha = N(f)/N(g) is greater than a critical value. We find that these critical values of alpha satisfy the following scaling relation: rho(g) square root(N(g)) beta(3) proportional to alpha(-lambda), where beta = sigma(f)/sigma(g) and lambda is the scaling exponent. For beta = 1 or the same segment sizes of the free and grafted polymers, this scaling relation is in agreement with those from previous theoretical studies using self-consistent field theory (SCFT). Detailed comparisons between iSAFT and SCFT are made for the structures of the monolayers and their forces of interaction. These comparisons lead to interesting implications for the modeling of nanocomposite thermodynamics.

Spinodal decomposition of a binary fluid with fixed impurities

The phase separation dynamics of a binary fluid containing randomly distributed fixed impurities is studied in two dimensions (d=2). The impurities act as osmotic force centers and favor one component of the fluid. We found, as expected, that hydrodynamic flow promotes the coalescence of the domains in the early stage of phase separation; at later stages for sufficiently high particle density and strong preferential interaction strength, the domain growth slows down and finally is pinned at a finite domain size independent of the hydrodynamics. The density of impurities in the unfavorable phase is shown to satisfy a scaling form involving the total impurity density n0 and the ratio R/R0 with R the domain size and R0=n0−1/d the average distance between the impurities.

LIQUID CRYSTAL PHASE DIAGRAM OF THE GAY-BERNE FLUID BY DENSITY FUNCTIONAL THEORY

We calculate the liquid crystal phase diagram for a model fluid with Gay-Berne interparticle potential using the Tarazona smoothed-density approximation of density functional theory. Vapour, liquid, nematic and smectic A phases are considered. For length to breadth ratio kappa 3 and energy anisotropy kappa 5, comparison with the simulation data of de Miguel et al. shows reasonable agreement.

Parametrization of atomic force microscopy tip shape models for quantitative nanomechanical measurements

The uncertainty of the shape of the tip is a significant source of error in atomic force microscopy (AFM) based quantitative nanomechanical measurements. Using transmission electron microscopy, scanning electron microscopy, or tip reconstruction images, it is possible to parametrize the models of real AFM tips, which can be used in quantitative nanomechanical measurements. These measurements use algorithms described in this article that extend classical elastic, plastic, and adhesive models of contact mechanics. Algorithms are applicable to the tips of arbitrary axisymmetric shapes. Several models of AFM tip have been utilized. The goal of tip model parameterization is to develop AFM tip-independent quantitative mechanical measurements at the nanometer scale. Experimental results demonstrate independence of the AFM measurements from tips and their closeness to bulk measurements where available. In this article the authors show the correspondence between microtensile, nanoindentation, and AFM based indenta...

Theoretical modelling and implementation of elastic modulus measurement at the nanoscale using atomic force microscope

Quantitative studies of mechanical behaviour and primarily elastic modulus are essential for material science at the nanometer scale. AFM nanoindentation is the most promising approach to address the problem. In our study we perform AFM-based nanoindentation (deflection-versus-distance curves) on a set of polymer materials with microscopic moduli ranging from 1 MPa to 10 GPa. The measurements were done with probes of different tip shapes and force levels from 100 nN to 3 μN. The tip geometry was evaluated from TEM and SEM micrographs and piecewise linearly interpolated for the use of analysis software; probe spring constant was determined from thermal tune data. The comparative analysis of nanoindentation data was carried out using models of Sneddon and Oliver-Pharr. We derived Sneddons integrals in closed form for any practical tip shape using a piecewise linear interpolation. Oliver-Pharrs method to account for plasticity for the unloading curve was adapted for Sneddons integrals. An interactive software implementation with both models was developed and applied.

STUDIES OF NEMATIC-ISOTROPIC TRANSITION FOR A GAY-BERNE FLUID USING THE SECOND VIRIAL APPROXIMATION

Abstract In this paper we use the second virial approximation to study the nematic-isotropic (N-I) transition for a Gay-Berne liquid for a broad range of parameters. For Gay-Berne hard Gaussian overlap (HGO) fluid particles we found that a N-I transition exists as a function of density for all length to breadth ratios k > 4, in reasonable agreement with other theoretical studies and results of Monte Carlo simulations. For the full Gay-Berne potential (GB) the location of the N-I transition as a function of density for different temperatures was studied for several values of shape and energy anisotropy parameters k and k′. It was shown that the transition temperature increases or the transition density decreases with increasing k and/or decreasing k′. Wherever the molecular dynamics (MD) or Monte Carlo (MC) data were available, comparison was made. For each system, coexistence density and pressure were calculated, and, wherever possible, also compared with MC or MD data to show qualitative agreement. The r...

Designing new materials and processes for directed self-assembly applications

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. The most widely studied material for DSA is poly(styrene-block-methyl methacrylate) (PS-PMMA), but this material has a relatively weak segregation strength that has limited its utility to patterns above 24 nm pitch. This paper reports on some of Dows efforts to develop new materials capable of extending DSA to smaller pitch by development of new BCP copolymer materials with stronger segregation strength. Some preliminary efforts are reported on new substrate treatments that stabilize perpendicular orientations in a high-χ block copolymer that also incorporate an etch-resistant block to facilitate patterning at small dimensions. In addition, development of new block copolymer materials that have a χ-parameter that is large enough to drive defect reduction and but not so high that it precludes thermal annealing are also presented. DSA of these new materials is demonstrated using thermal annealing processes at pitch ranging from 40 to 16 nm, and etch capability is also demonstrated on a material with 18 nm pitch. These technologies hold promise for the extension of DSA to sub 24 nm pitch.