@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 {1259, title = {Colloid-induced structure in liquid crystal media}, journal = {Journal of Chemical Physics}, volume = {122}, number = {12}, year = {2005}, note = {ISI Document Delivery No.: 915HDTimes Cited: 7Cited Reference Count: 26}, month = {Mar}, pages = {8}, type = {Article}, abstract = {The structural perturbations induced by colloidal particles immersed in a model nematic subjected to an external field are calculated employing integral equation methods. Maps of the density-orientational distribution about a colloidal particle are obtained, and these provide a microscopic picture of the colloid{\textquoteright}s nematic coat. We focus on colloidal particles that favor homeotropic anchoring, but planar anchoring cases are also considered. The range and structure of the nematic coat is shown to be significantly influenced by the nature of the anchoring, the size of the colloidal particle, the range and strength of the colloid-nematogen interaction, and the external field strength. All of these factors are discussed.}, keywords = {FIELD, FLUIDS, INTEGRAL-EQUATION THEORY, PHASE, SIMULATION, SPHERICAL-PARTICLE, TOPOLOGICAL DEFECTS}, isbn = {0021-9606}, url = {://000228287900062}, author = {Sokolovska, T. G. and Sokolovskii, R. O. and Patey, G. N.} } @article {1044, title = {NMR measurement of smectic ordering and nematic-smectic-A coupling in a liquid crystal}, journal = {Chemical Physics Letters}, volume = {398}, number = {4-6}, year = {2004}, note = {ISI Document Delivery No.: 867OVTimes Cited: 11Cited Reference Count: 31}, month = {Nov}, pages = {517-521}, type = {Article}, abstract = {The nuclear magnetic resonance (NMR) spectra of three substituted benzenes as solutes in the liquid crystal 8CB were investigated. The orientational order of all solutes was obtained in the nematic and smectic-A phases. A change in temperature dependence of orientational ordering was observed at the nematic to smectic-A phase transition. We analyzed these results via Kobayashi-McMillan theory applied to solutes, i.e. by incorporating smectic-A layering and nematic smectic-A coupling into a mean-field orientational Hamiltonian. By fitting to experiment, we fully determined Hamiltonian prefactors. The nematic smectic coupling, determined for the first time by NMR, appears solute independent. Solute smectic-A order parameters were self-consistently determined. (C) 2004 Published by Elsevier B.V.}, keywords = {BINARY-MIXTURES, FIELD, NUCLEAR-MAGNETIC-RESONANCE, orientational order, PHASE-TRANSITION, SHAPE, SOLUTES, TEMPERATURE-DEPENDENCE, TRICRITICAL POINT}, isbn = {0009-2614}, url = {://000224852800044}, author = {Yethiraj, A. and Sun, Z. M. and Dong, R. Y. and Burnell, E. E.} } @article {764, title = {Hot model of muonium formation in liquids}, journal = {Canadian Journal of Chemistry-Revue Canadienne De Chimie}, volume = {81}, number = {3}, year = {2003}, note = {ISI Document Delivery No.: 663NGTimes Cited: 4Cited Reference Count: 22}, month = {Mar}, pages = {199-203}, type = {Article}, abstract = {The mechanism of formation of muonium atoms from positive muons was studied here through measurements of the yield of diamagnetic muon states in dipolar aprotic solvents and for scavenger solutions in hexane and methanol. The results are compared with published data on common solvents covering a full range of the physicochemical properties of liquids that affect an ionic formation mechanism, namely their static dielectric constants, electron mobilities, and radiolysis yields of electrons. It is concluded that muonium is not formed by a thermal charge-neutralization reaction in these chemically-active media, though that mechanism does contribute to muonium formation in inert media like liquefied noble gases. It is clear that muonium materializes on a much shorter timescale than the recently proposed "delayed" mechanism (microseconds) and the earlier "spur" model (nanoseconds). In contrast, the data referring to all these liquids are consistent with the intra-track "hot" model. This is the only Mu-formation model proposed so far in which the immediate precursors of Mu (Mu((hot))) are neither scavengable nor ionic.}, keywords = {delayed-muonium-formation model, diamagnetic yields, FIELD, formation mechanism, GASES, hot model, muonium atoms, RESONANCE, spur model}, isbn = {0008-4042}, url = {://000182011200002}, author = {Walker, D. C. and Karolczak, S. and Gillis, H. A. and Porter, G. B.} } @article {5063, title = {Pure rotational spectra, structures, and hyperfine constants of OC-AuX (X = F, Cl, Br)}, journal = {Inorganic Chemistry}, volume = {40}, number = {24}, year = {2001}, note = {ISI Document Delivery No.: 492RMTimes Cited: 20Cited Reference Count: 54}, month = {Nov}, pages = {6123-6131}, type = {Article}, abstract = {Rotational spectra of OC-AuX (X = F, Cl, Br) have been measured in the frequency range 5-21 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating. Au metal with a Nd:YAG laser and allowing the vapor to react with CO plus a halide precursor contained in the Ar backing gas of the jets. For OC-AuCl and OC-AuBr these are I the first high-resolution spectroscopic measurements; for OC-AuF these are the first observations of any kind. Ail three molecules are linear. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants have been precisely evaluated. The geometries determined for all three molecules show CO bond lengths close to that of free CO, plus relatively long Au-C bonds. These results are corroborated by ab initio calculations, which have also produced Mulliken populations showing significant sigma -donation from CO to Au, plus some pi -back-donation from An to CO. There are major changes in the Au, Cl, and Br nuclear quadrupole coupling constants when CO bonds to AuX, consistent with the formation of strong Au-C bonds. The structural properties of OC-AuF are somewhat different from those of OC-AuCl and OC-AuBr.}, keywords = {AUCL, CARBONYL, COMPLEXES, CU(CO)CL, FIELD, GAUSSIAN-BASIS SETS, GOLD, MICROWAVE-SPECTRA, MOLECULAR CALCULATIONS, SPECTROSCOPY}, isbn = {0020-1669}, url = {://000172181400007}, author = {Evans, C. J. and Reynard, L. M. and Gerry, M. C. L.} } @article {4479, title = {A Monte Carlo study of model electrorheological fluids}, journal = {Journal of Chemical Physics}, volume = {111}, number = {7}, year = {1999}, note = {ISI Document Delivery No.: 222GBTimes Cited: 4Cited Reference Count: 26}, month = {Aug}, pages = {3278-3287}, type = {Article}, abstract = {Monte Carlo results for both spherical and nonspherical electrorheological (ER) particles are described. The ER particles are modeled as hard spheres or hard ellipsoids of revolution with much smaller charged hard spheres (ions) constrained to their inner surface. NVT Monte Carlo calculations show that these models display the strong polarization and chain formation characteristic of ER fluids. Both prolate and oblate ER particles align with their longest axis directed along the applied field allowing for larger induced dipole moments than those obtained for spherical ER particles of equal volume. In all cases it is found that chaining occurs at relatively high fields where the induced dipole moments are approaching their maximum value. An interesting feature of nonspherical ER particles is the field-induced orientational order. It is found that even slightly nonspherical ER particles are highly ordered by fields which are weaker than those required to induce chain formation. Very weak fields are sufficient to generate strong orientational order in prolate ER particles with moderate aspect ratios. Further, field-ordered oblate ER particles tend to align their symmetry (short) axes to form a biaxial phase at high densities. The field-induced, liquid-crystal-like behavior of nonspherical ER particles is discussed in detail. (C) 1999 American Institute of Physics. [S0021-9606(99)51131-8].}, keywords = {COMPUTER-SIMULATION, FIELD, FORCES, POINT-DIPOLE LIMIT, SHEAR RATE RESPONSE, SUSPENSIONS}, isbn = {0021-9606}, url = {://000081774700051}, author = {Blair, M. J. and Patey, G. N.} } @article {4220, title = {A simple model of spin transitions in polymeric materials}, journal = {Journal of Physics-Condensed Matter}, volume = {10}, number = {48}, year = {1998}, note = {ISI Document Delivery No.: 150QPTimes Cited: 1Cited Reference Count: 18}, month = {Dec}, pages = {10909-10917}, type = {Article}, abstract = {Recent experiments have-shown that first-order spin transitions can occur in polymeric Fen compounds. In such materials the metal ions are linked by ligand groups to form polymeric chains. Existing theories of the spin transition in crystalline materials are discussed, but we argue that the physical justification of these theories may be inappropriate for polymeric compounds. We describe a possible mechanism in which local strain in the ligand network can drive the transition. A model Hamiltonian is presented and solved and the effects of pressure and dopant concentration on the spin transition are investigated. We also point but that the model describes many of the effects observed in experiments on crystalline materials.}, keywords = {COMPLEXES, FIELD, IRON II, pressure, T-5(2) TRANSITION, THERMAL HYSTERESIS}, isbn = {0953-8984}, url = {://000077677000012}, author = {Camp, P. J. and Patey, G. N.} } @article {4114, title = {Analysis of single and multiple quantum NMR spectra of 1,3-dichloro-2-ethenylbenzene in liquid crystal solvents}, journal = {Molecular Physics}, volume = {90}, number = {4}, year = {1997}, note = {ISI Document Delivery No.: WN909Times Cited: 10Cited Reference Count: 37}, month = {Mar}, pages = {541-551}, type = {Article}, abstract = {The single and multiple quantum NMR spectra of 1,3-dichloro-2-ethenylbenzene as solute in two different nematic liquid crystals have been measured and analysed in terms of dipolar couplings and chemical shift differences. Because the single quantum spectra did not yield to straightforward analysis, normal and frequency selective multiple quantum experiments were used to aid the analysis. The results from four spectra were combined to yield structural information and the order matrix in each solution. The structure of the ring is very close to that of 1,3-dichlorobenzene, and that of the ethenyl group very close to that of ethenyl-benzene. The dihedral angle between the ethenyl group and the aromatic ring is found to be 454 +/- 1.0 degrees, and the C-CC=C angle is found to be 127.3 +/- 0.3 degrees.}, keywords = {EQUILIBRIUM, FIELD, MAGNETIC-RESONANCE, MIXTURES, MOLECULAR-STRUCTURE, orientational order, ROTATION, SHAPE, SOLUTES, SPECTROSCOPY}, isbn = {0026-8976}, url = {://A1997WN90900005}, author = {Rendell, J. C. T. and Burnell, E. E.} } @article {4115, title = {Orientational order of 1,3-dichloro-2-ethenylbenzene in liquid crystal solvents}, journal = {Canadian Journal of Chemistry-Revue Canadienne De Chimie}, volume = {75}, number = {8}, year = {1997}, note = {ISI Document Delivery No.: XX043Times Cited: 2Cited Reference Count: 38}, month = {Aug}, pages = {1156-1161}, type = {Article}, abstract = {The order parameter matrices of a molecule that has no symmetry, 1,3-dichloro-2-ethenylbenzene, dissolved in two different nematic liquid-crystal solvents are analyzed in terms of various models for the intermolecular mean-field potential. In a mixture of liquid crystals for which the interaction between the molecular quadrupole moment tensor and the average electric field gradient of the nematic solvent has been minimized, the orientational order is best described by models for the short-range anisotropic potential. The most successful potentials are written in terms of anisotropic interactions between the solute surface and the liquid-crystal mean field. This represents a strong test of such models because they simultaneously fit the five independent orientational parameters obtained from the same solute, thus removing the problems associated with comparing results among different solutes in either the same or a different sample tube.}, keywords = {ALKYL CHAINS, ANISOTROPIC, FIELD, INTERMOLECULAR FORCES, liquid crystals, MAGNETIC-RESONANCE, MIXTURES, MOLECULES, NEMATIC SOLVENT, NMR, order parameters, PHASES, SHAPE, SOLUTES}, isbn = {0008-4042}, url = {://A1997XX04300014}, author = {Rendell, J. C. T. and Zimmerman, D. S. and vanderEst, A. J. and Burnell, E. E.} } @article {2836, title = {THE MICROWAVE ROTATIONAL SPECTRUM OF THE VAN-DER-WAALS COMPLEX KR-N2}, journal = {Journal of Chemical Physics}, volume = {99}, number = {10}, year = {1993}, note = {ISI Document Delivery No.: MH744Times Cited: 23Cited Reference Count: 50}, month = {Nov}, pages = {7510-7520}, type = {Article}, abstract = {Pure rotational transitions in the vibrational ground state of the van der Waals complex Kr-N2 have been measured using a cavity microwave Fourier transform spectrometer. For the isotopomers Kr-84-N-14(2), Kr-86-N-14(2), Kr-84-N-15(2), Kr-86-N-15(2) Kr-82-N-15(2) and Kr-83-N-15(2) a-type transitions with K(a) = 0 and 1 have been measured, confirming a C2v symmetry of the complex. A value for the N-14 nuclear quadrupole coupling constant in free nitrogen N-14(2) has been estimated from an analysis of the nuclear hyperfine structure in complexes of N-14(2). N-15 spin-rotation hyperfine structure could be observed and analyzed in the 2(1,2)-1(1,1) and 2(1,1)-1(1,0) rotational transitions of Kr-84-N-15(2). Rotational transitions of Kr-83-N-15(2) showed a nuclear hyperfine splitting due to Kr-83 with nuclear spin 9/2 which has been attributed to the weak bonding with N-15(2). For Kr-84-N-14-N-15 and Kr-86-N-14-N-15, only transitions involving energy levels with K(a) = 0 have been found.}, keywords = {AR-HCN, ATOMS, DIPOLE-MOMENT, FIELD, HCN DIMER, J-DEPENDENCE, KR-83, MOLECULES, QUADRUPOLE COUPLING-CONSTANT, SPECTROSCOPY}, isbn = {0021-9606}, url = {://A1993MH74400024}, author = {Jager, W. and Xu, Y. J. and Heineking, N. and Gerry, M. C. L.} }