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  • 1
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    Online Resource
    The influence of structure on diffusion in screened Coulombic suspensions
    AIP Publishing ; 1994
    In:  The Journal of Chemical Physics Vol. 101, No. 6 ( 1994-09-15), p. 4975-4985
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 101, No. 6 ( 1994-09-15), p. 4975-4985
    Abstract: The static structure factor and hydrodynamics, characterized by the functions S(q) and H(q), respectively, will modify the short-time q-dependent diffusion coefficient from its free particle value, D0, as D(q)=D0[H(q)/S(q)]. We probe these dynamics with diffusing wave spectroscopy on low volume fraction suspensions of highly charged, monodisperse colloidal particles, where we can neglect the hydrodynamic contributions and probe the effect of structure alone. We vary the range of the screened Coulombic interactions via suspension ionic strength to obtain a range of interparticle structures from liquid-like to ordered crystalline arrays. From the initial decay of the autocorrelation function of the multiply scattered laser light, we obtain a q-weighted average of D(q). Modeling the interactions with the hard-core Yukawa pair potential and the structure with the rescaled mean spherical approximation, we attribute slowed dynamics in the suspension to peaks in S(q). We vary the particle size, laser wavelength, and suspension volume fraction to probe the effect of various features in S(q) on the dynamics.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.467420
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1994
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    Online Resource
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    Predictions of birefringence and dichroism of hard sphere suspensions in combined electric and shear fields
    AIP Publishing ; 1989
    In:  The Journal of Chemical Physics Vol. 91, No. 10 ( 1989-11-15), p. 6282-6289
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 91, No. 10 ( 1989-11-15), p. 6282-6289
    Abstract: We present the optical anisotropy of a hard sphere suspension subjected to combined electric and shear fields. We model the particle structure factor as a shear induced perturbation of the anisotropic structure induced by electric field. We renormalize the nonconvergent birefringence integral to allow calculation of birefrigence from the particle structure factor. The principle axes of the birefringence and dichroism tensors vary with the Mason number, a measure of the relative strength of shear forces to electric dipole interaction forces. The principle axes only coincide in the shear dominated and the electric field dominated limits. The magnitudes of birefringence and dichroism are sensitive to the particle size relative to the wave-length of light employed. We compare theoretical predictions in the limit of pure shear to the experiments of Wagner et al., J. Chem. Phys. 89, 1580 (1988), employing a simple affine deformation theory for the structure factor, which yields fair agreement with experiment for the dichroism but poor agreement for the birefringence. The prediction of optical properties provides both a test for theories of microstructure and insight into the effects of shear and electric fields on microstructure.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.457394
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1989
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
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    Online Resource
    Crystallization of power-law fluids: A modified weighted density approximation model with a solid reference state
    AIP Publishing ; 1999
    In:  The Journal of Chemical Physics Vol. 110, No. 5 ( 1999-02-01), p. 2522-2528
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 110, No. 5 ( 1999-02-01), p. 2522-2528
    Abstract: We investigate the freezing behavior of particles interacting with an inverse nth power potential under the modified weighted density approximation (MWDA) formalism of Denton and Ashcroft [A. R. Denton and N. W. Ashcroft, Phys. Rev. A 39, 470 (1989)]. We model the liquid state with the perturbative hypernetted chain (PHNC) integral equation [H. S. Kang and F. H. Ree, J. Chem. Phys. 103, 3629 (1995)] , chosen for its small computational time and high degree of accuracy. The deterioration of MWDA predictions of equilibrium properties with decreasing n is traced to its inability to accurately estimate the free energy in the static solid limit. An improvement in the MWDA theory is suggested by incorporating information on the static lattice into the model. This is done by moderating the direct correlation function via the Ornstein–Zernicke equation. It is found that this new model can drastically improve results for the coexisting densities for inverse nth power fluids. Other properties, such as the Lindemann parameter, are also improved in this new scheme.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.477957
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1999
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
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    Starlike dendrimers in solutions: Structural properties and internal dynamics
    AIP Publishing ; 2006
    In:  The Journal of Chemical Physics Vol. 125, No. 20 ( 2006-11-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 125, No. 20 ( 2006-11-28)
    Abstract: We measured the shape and the internal dynamics of starlike dendrimers under good solvent conditions with small-angle neutron scattering and neutron spin-echo (NSE) spectroscopy, respectively. Architectural parameters such as the spacer length and generation were varied in a systematic manner. Structural changes occurring in the dendrimers as a function of these parameters are discussed, i.e., in terms of the fractal dimension and deviations of the radius of gyration from the Gaussian value. A first cumulant evaluation of the NSE spectra for each scattering vector q separately yields the length scale dependent relaxation rates. We observe a local minimum in the normalized relaxation rates Ω(q)∕q3 on length scales corresponding to the overall dendrimer dimension. The dynamics is discussed within a Rouse-Zimm approach generalized to the case of starlike dendrimers of arbitrary geometry. The model allows an identification of the modes contributing to the relaxation of the dendrimer in the q and time range of the NSE experiment. The local minimum is due to collective breathing motions of (parts of) the dendrons relative to each other. Shape fluctuations are not observed.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.2364895
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
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    Online Resource
    Optical anisotropy in colloidal crystals
    AIP Publishing ; 1990
    In:  The Journal of Chemical Physics Vol. 93, No. 11 ( 1990-12-01), p. 8294-8299
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 93, No. 11 ( 1990-12-01), p. 8294-8299
    Abstract: We use the theory of dynamical diffraction to interpret polarization-dependent light attenuation phenomena in thin colloidal crystals. We measure light attenuation anisotropies, resulting from coherent and incoherent scattering from a suspension of monodisperse aqueous polystyrene microspheres, with rotary polarization modulating polarimetry. Measured anisotropies are in excellent agreement with dynamical diffraction predictions. These measurements provide a new means to quantify crystal orientation in thin cells. We relate anisotropy to crystal color observed between crossed polarizers and to crystal structure, volume fraction and orientation.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.459311
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1990
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 6
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    Simple Ordering in Complex Fluids
    AIP Publishing ; 1998
    In:  Physics Today Vol. 51, No. 12 ( 1998-12-01), p. 24-30
    Details
    In: Physics Today, AIP Publishing, Vol. 51, No. 12 ( 1998-12-01), p. 24-30
    Abstract: Ordering and the formation of crystals have long fascinated mankind. The reverence bestowed on gem-stones and the fantastic properties attributed to crystalline matter arise from the unique optical, geometric and physical properties of the ordered state. Although scientific inquiry has focused mostly on molecular and atomic crystals, much also can be learned from the study of super-molecular and colloidal arrays.
    Type of Medium: Online Resource
    ISSN: 0031-9228 , 1945-0699
    URL: Article
    DOI: 10.1063/1.882495
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1998
    detail.hit.zdb_id: 2031187-4
    detail.hit.zdb_id: 208863-0
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  • 7
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    Commentary: Physicists without borders
    AIP Publishing ; 2017
    In:  Physics Today Vol. 70, No. 1 ( 2017-01-01), p. 10-11
    Details
    In: Physics Today, AIP Publishing, Vol. 70, No. 1 ( 2017-01-01), p. 10-11
    Type of Medium: Online Resource
    ISSN: 0031-9228 , 1945-0699
    URL: Article
    DOI: 10.1063/PT.3.3411
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 2031187-4
    detail.hit.zdb_id: 208863-0
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  • 8
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    A microscopic model of electrorheology
    AIP Publishing ; 1988
    In:  The Physics of Fluids Vol. 31, No. 10 ( 1988-10-01), p. 2757-2768
    Details
    In: The Physics of Fluids, AIP Publishing, Vol. 31, No. 10 ( 1988-10-01), p. 2757-2768
    Abstract: An electrorheological fluid is modeled as a concentrated suspension of hard spheres with aligned field-induced electric dipole moments. The presence of dipole moments causes clustering of the particles into an anisotropic suspension characterized by a particle probability distribution function. The elastic shear modulus and the dynamic viscosity are calculated from a perturbation to the particle distribution as a result of a small amplitude, high frequency, oscillatory flow. The high frequency elastic shear modulus and the dynamic viscosity are shown as a function of particle concentration and electric dipole strength. Both the modulus and the viscosity increase strongly with particle concentration. Dynamic viscosity is insensitive to dipole strength, but elastic shear modulus increases strongly with dipole strength indicating the relative importance of the particle distribution to elastic properties. The results of these calculations provide insight into the relationship between the macroscopic properties of an electrorheological fluid and microscopic structural changes.
    Type of Medium: Online Resource
    ISSN: 0031-9171
    URL: Article
    DOI: 10.1063/1.866983
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1988
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 9
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    Online Resource
    Aggregation kinetics of paramagnetic colloidal particles
    AIP Publishing ; 1995
    In:  The Journal of Chemical Physics Vol. 102, No. 13 ( 1995-04-01), p. 5492-5498
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 102, No. 13 ( 1995-04-01), p. 5492-5498
    Abstract: Magnetic-field-induced chain formation of superparamagnetic latex particles is investigated via optical microscopy and digital image analysis. Our experiment is unique in that the aggregation process takes place in the bulk, where particles are free to diffuse in three dimensions, rather than on a surface. We find that the mean chain size 〈s(t)〉 has a power-law dependence on time, 〈s(t)〉∼tz, as predicted by the Smoluchowski equation and three-dimensional simulations of diffusion-limited aggregation of oriented particles. The value of the exponent z is found to have a weak inverse dependence on particle volume fraction φ and dimensionless dipole strength λ. We propose a new model for a characteristic time scale proportional to 1/λ and 1/φ. Comparison with experimental observations shows this scaling to be very effective but to break down suddenly above a critical volume fraction.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.469278
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 10
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    Online Resource
    Crystallization of a Yukawa fluid via a modified weighted density approximation with a solid reference state
    AIP Publishing ; 2000
    In:  The Journal of Chemical Physics Vol. 112, No. 6 ( 2000-02-08), p. 2826-2833
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 112, No. 6 ( 2000-02-08), p. 2826-2833
    Abstract: We investigate the freezing behavior of particles interacting with a Yukawa potential using extensions of the Denton and Ashcroft modified weighted density approximation (MWDA) model of density functional theory [A. R. Denton and N. W. Ashcroft, Phys. Rev. A 39, 470 (1989)]. An attempt is made to incorporate properties of the static solid into the fluid-based MWDA model via our previous model for the crystallization of inverse nth-power fluids [D. C. Wang and A. P. Gast, J. Chem. Phys. 110, 2522 (1999)] , as well as a model that includes the Einstein vibrations of the localized particles. Both extensions yield improvements over the MWDA model in terms of coexisting densities and the ability to stabilize a body-centered cubic solid compared with computer simulation data. The fractional change in density upon freezing also compares favorably with results from available simulation studies and those for the inverse nth-power system. Reasons for the differences in results obtained for freezing properties of the Yukawa system among computer simulation data, theoretical approaches, and experimental studies are discussed.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.480857
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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