@article {2256,
title = {Bridging the gap between phenomenology and microscopic theory: Asymptotes in nematic colloids},
journal = {Physical Review E},
volume = {77},
number = {4},
year = {2008},
note = {ISI Document Delivery No.: 295EDTimes Cited: 3Cited Reference Count: 28Sokolovska, T. G. Sokolovskii, R. O. Patey, G. N.Part 1},
month = {Apr},
pages = {10},
type = {Article},
abstract = {The Ornstein-Zernike equation is applied to nematic colloids with up-down symmetry to determine how the electrostatic analogy and other phenomenological results appear in molecular theory. In contrast to phenomenological approaches, the molecular theory does not assume particular boundary conditions (anchoring) at colloidal surfaces. For our molecular parameters the resulting anchoring appears to be realistic, neither rigid nor infinitely weak. For this case, the effective force between a colloidal pair at large separation remains essentially constant over the entire region of nematic stability. We show that a simple van der Waals approximation gives a potential of mean force that in some important aspects is similar to the phenomenological results obtained in the limit of weak anchoring; at large separations the potential varies as Sigma(8), where Sigma is the colloidal diameter. In contrast, the more sophisticated mean spherical approximation yields a Sigma(6) dependence consistent with phenomenological calculations employing rigid boundary conditions. We show that taking proper account of the correlation (or magnetic coherence) length xi inherent in the nematic sample is essential in an analysis of the Sigma dependence. At infinite xi the leading Sigma dependence is Sigma(6), but this shifts to Sigma(8) when xi is finite. The correlation length also influences the orientational behavior of the effective interaction. The so-called quadrupole interaction that determines the long-range behavior at infinite xi transforms into a superposition of screened "multipoles" when xi is finite. The basic approach employed in this paper can be readily applied to a broad range of physically interesting systems. These include patterned and nonspherical colloids, colloids trapped at interfaces, and nematic fluids in confined geometries such as droplets.},
keywords = {ELASTIC-CONSTANTS, FIELD, FORCES, LIQUID-CRYSTALS, PARTICLES, PHASE, STATISTICAL-THEORY, TOPOLOGICAL DEFECTS},
isbn = {1539-3755},
url = {://000255456900069},
author = {Sokolovska, T. G. and Sokolovskii, R. O. and Patey, G. N.}
}
@article {1225,
title = {Entropic interaction chromatography: Separating proteins on the basis of size using end-grafted polymer brushes},
journal = {Biotechnology and Bioengineering},
volume = {90},
number = {1},
year = {2005},
note = {ISI Document Delivery No.: 909ETTimes Cited: 9Cited Reference Count: 48},
month = {Apr},
pages = {1-13},
type = {Article},
abstract = {Partitioning of a macromolecule into the interfacial volume occupied by a grafted polymer brush decreases the configurational entropy (Delta S(c)brush) of the terminally attached linear polymer chains due to a loss of free volume. Self-consistent field theory (SCF) calculations are used to show that Delta S(c)brush is a strong function of both the size (MW,) of the partitioning macromolecule and the depth of penetration into the brush volume. We further demonstrate that the strong dependence of Delta S(c)brush on MW, provides a novel and powerful platform, which we call entropic interaction chromatography (EIC), for efficiently separating mixtures of proteins on the basis of size. Two EIC columns, differing primarily in polymer grafting density, were prepared by growing a brush of poly(methoxyethyl acrylamide) chains on the surface of a widepore (1,000-angstrom pores, 64-mu m diameter rigid beads) resin (Toyopearl AF-650M) bearing surface aldehyde groups. Semipreparative 0.1-L columns packed with either EIC resin provide reduced-plate heights of 2 or less for efficient separation of globular protein mixtures over at least three molecular-weight decades. Protein partitioning within these wide-pore EIC columns is shown to be effectively modeled as a thermodynamically controlled process, allowing partition coefficients (K-p) and elution chromatograms to be accurately predicted using a column model that combines SCF calculation of Kp values with an equilibrium-dispersion type model of solute transport through the column. This model is used to explore the dependence of column separation efficiency on brush properties, predicting that optimal separation of proteins over a broad MW, range is achieved at low to moderate grafting densities and intermediate chain lengths. (c) 2005 Wiley Periodicals, Inc.},
keywords = {ADSORPTION, CHAIN MOLECULES, CONSISTENT-FIELD THEORY, entropic interaction chromatography, equilibrium dispersion, EXCLUSION CHROMATOGRAPHY, GEL FILTRATION, grafted polymer brush, HUMAN SERUM-ALBUMIN, LIQUID-CHROMATOGRAPHY, MODEL, MOLECULAR-WEIGHT, MONTE-CARLO, protein purification, size exclusion chromatography, STATISTICAL-THEORY},
isbn = {0006-3592},
url = {://000227843800001},
author = {Pang, P. and Koska, J. and Coad, B. R. and Brooks, D. E. and Haynes, C. A.}
}