101 research outputs found
Recommended from our members
Equilibrium characteristics of semiflexible polymer solutions near probe particles
We present a numerical analysis of the mean-field theory for the structure of semiflexible polymer solutions near spherical surfaces, and use the framework to study the depletion characteristics of semiflexible polymers near colloids and nanoparticles. Our results suggest that the depletion characteristics depend sensitively on the polymer concentrations, the persistence lengths, and the radius of the particles. Broadly, two categories of features are identified based on the relative ratios of the persistence lengths to the correlation length of the polymer solution. For the limit where the correlation length is larger than the persistence length, the correlation length proves to be the critical length scale governing both the depletion thickness and the curvature effects. In contrast, for the opposite limit, the depletion thickness and the curvature effects are dependent on a length scale determined by an interplay between the persistence length and the correlation length. This leads to nontrivial (numerical) scaling laws governing the concentration and radii dependence of the depletion thicknesses. Our study also highlights the manner by which the preceding features rationalize the parametric dependencies of insertion free energies of small probes in semiflexible polymer solutions.Robert A.Welch FoundationUS Army Research Office W911NF-07-1-0268American Chemical Society Petroleum ResearchIndian Institute of Science, BangaloreChemical Engineerin
Comment on “No-Slip Condition for a Mixture of Two Liquids”
A Comment on the Letter by Joel Koplik and Jayanth R. Banavar, Phys. Rev. Lett. 80, 6125 (1998). The authors of the Letter offer a Reply
Fluctuation effects in ternary AB+A+B polymeric emulsions
We present a Monte Carlo approach to incorporating the effect of thermal
fluctuations in field theories of polymeric fluids. This method is applied to a
field-theoretic model of a ternary blend of AB diblock copolymers with A and B
homopolymers. We find a shift in the line of order-disorder transitions from
their mean-field values, as well as strong signatures of the existence of a
bicontinuous microemulsion phase in the vicinity of the mean-field Lifshitz
critical point. This is in qualitative agreement with a recent series of
experiments conducted with various three-dimensional realizations of this model
system. Further, we also compare our results and the performance of the
presently proposed simulation method to that of an alternative method involving
the integration of complex Langevin dynamical equations.Comment: minor changes, references adde
Structural anomalies of fluids: Origins in second and higher coordination shells
Compressing or cooling a fluid typically enhances its static interparticle correlations. However, there are notable exceptions. Isothermal compression can reduce the translational order of fluids that exhibit anomalous waterlike trends in their thermodynamic and transport properties, while isochoric cooling (or strengthening of attractive interactions) can have a similar effect on fluids of particles with short-range attractions. Recent simulation studies by Yan [Phys. Rev. E 76, 051201 (2007)] on the former type of system and Krekelberg [J. Chem. Phys. 127, 044502 (2007)] on the latter provide examples where such structural anomalies can be related to specific changes in second and more distant coordination shells of the radial distribution function. Here, we confirm the generality of this microscopic picture through analysis, via molecular simulation and integral equation theory, of coordination shell contributions to the two-body excess entropy for several related model fluids which incorporate different levels of molecular resolution. The results suggest that integral equation theory can be an effective and computationally inexpensive tool for assessing, based on the pair potential alone, whether new model systems are good candidates for exhibiting structural (and hence thermodynamic and transport) anomalies.Chemical Engineerin
Model for the free-volume distributions of equilibrium fluids
We introduce and test via molecular simulation a simple model for predicting
the manner in which interparticle interactions and thermodynamic conditions
impact the single-particle free-volume distributions of equilibrium fluids. The
model suggests a scaling relationship for the density-dependent behavior of the
hard-sphere system. It also predicts how the second virial coefficients of
fluids with short-range attractions affect their free-volume distributions.Comment: 7 pages, 5 figure
Achieving Bicontinuous Microemulsion Like Morphologies in Organic Photovoltaics
It is believed that the optimal morphology of an organic solar cell may be characterized by cocontinuous, interpenetrating donor and acceptor domains with nanoscale dimensions and high interfacial areas. One well-known equilibrium morphology that fits these characteristics is the bicontinuous microemulsion achieved by the addition of block copolymer compatibilizers to flexible polymer–polymer blends. However, there does not exist design rules for using block copolymer compatibilizers to produce bicontinuous microemulsion morphologies from the conjugated polymer/fullerene mixtures typically used to form the active layer of organic solar cells. Motivated by these considerations, we use single chain in mean field simulations to study the equilibrium phase behavior of semiflexible polymer + flexible–semiflexible block copolymer + solvent mixtures. Based on our results, we identify design rules for producing large channels of morphologies with characteristics like that of the bicontinuous microemulsion
Machine learning-assisted design of material properties
Designing functional materials requires a deep search through multidimensional spaces for system parameters that yield desirable material properties. For cases where conventional parameter sweeps or trial-and-error sampling are impractical, inverse methods that frame design as a constrained optimization problem present an attractive alternative. However, even efficient algorithms require time- and resource-intensive characterization of material properties many times during optimization, imposing a design bottleneck. Approaches that incorporate machine learning can help address this limitation and accelerate the discovery of materials with targeted properties. In this article, we review how to leverage machine learning to reduce dimensionality in order to effectively explore design space, accelerate property evaluation, and generate unconventional material structures with optimal properties. We also discuss promising future directions, including integration of machine learning into multiple stages of a design algorithm and interpretation of machine learning models to understand how design parameters relate to material properties.This work was primarily supported by the National Science Foundation through the Center
for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No.
DMR-1720595. The authors acknowledge an Arnold O. Beckman Postdoctoral Fellowship
(ZMS) and the Welch Foundation (Grant Nos. F-1599 and F-1696) for support.Center for Dynamics and Control of Material
Multiscale modeling of solute diffusion in triblock copolymer membranes
We develop a multiscale simulation model for diffusion of solutes through
porous triblock copolymer membranes. The approach combines two techniques:
self-consistent field theory (SCFT) to predict the structure of the
self-assembled, solvated membrane and on-lattice kinetic Monte Carlo (kMC)
simulations to model diffusion of solutes. Solvation is simulated in SCFT by
constraining the glassy membrane matrix while relaxing the brush-like membrane
pore coating against the solvent. The kMC simulations capture the resulting
solute spatial distribution and concentration-dependent local diffusivity in
the polymer-coated pores; we parameterize the latter using particle-based
simulations. We apply our approach to simulate solute diffusion through
nonequilibrium morphologies of a model triblock copolymer, and we correlate
diffusivity with structural descriptors of the morphologies. We also compare
the model's predictions to alternative approaches based on simple lattice
random walks and find our multiscale model to be more robust and systematic to
parameterize. Our multiscale modeling approach is general and can be readily
extended in the future to other chemistries, morphologies, and models for the
local solute diffusivity and interactions with the membrane
- …