Showing papers by "David S. Cannell published in 1984"

Fractal geometry of colloidal aggregates

Abstract: Measurement of the fractal dimension, $D$, of colloidal aggregates of small silica particles is reported. We observe power-law decay of the structure factor $[S(k)\ensuremath{\sim}{k}^{\ensuremath{-}D}]$ by both light and x-ray scattering showing that the aggregates are fractal. $D$ is found to be 2.12\ifmmode\pm\else\textpm\fi{}0.05, which is intermediate between recent numerical results for the kinetic models of diffusion-limited aggregation ($D=2.5$) and cluster aggregation ($D=1.75$), but is rather close to the value for lattice animals ($D=2.0$), which are equilibrium structures.

Dynamics of Long-Wavelength Concentration Fluctuations in Solutions of Linear Polymers

Abstract: We report experimental results for a dynamic length scale ${\ensuremath{\xi}}_{H}$ as a function of polymer concentration $c$ for various molecular weight polystyrenes in the two solvents toluene and methyl ethyl ketone. We find that the quantity $\frac{{\ensuremath{\xi}}_{H}}{{R}_{H}}$ is a function only of the reduced concentration $\mathrm{kc}$, where ${R}_{H}$ is the hydrodynamic radius and $k$ is determined from a virial expansion of the diffusion coefficient. However, the dynamic and static length scales are not proportional.

Osmotic susceptibility and diffusion coefficient of charged bovine serum albumin

Abstract: We report measurements of the osmotic susceptibility and mutual diffusion coefficient of solutions of charged bovine serum albumin molecules made using laser light scattering. The measurements were made as a function of solution ionic strength for various macromolecular charge states ranging from −4e to −13e. We find that the osmotic susceptibility data may be interpreted quantitatively in terms of the simple Verwey–Overbeek interaction potential, provided that adequate care is taken in computing the radial distribution function. Current theoretical treatments of the dynamics, with hydrodynamic interactions included to first order in the concentration, are found to deviate significantly (≲50%) from the diffusion coefficient data. The deviations occur under all conditions of charge and ionic strength for which the susceptibility has been reduced to less than half the ideal gas value.

Marginal stability curve and linear growth rate for rotating Couette-Taylor flow and Rayleigh-Bénard convection

Abstract: Results of high numerical accuracy are reported for the growth rate σ of axisymmetric disturbances to circular Couette flow between concentric cylinders with the inner one rotating and of two‐dimensional disturbances of the pure conduction state of a Boussinesq fluid between horizontal parallel plates heated from below. When σ is positive, the former case leads to Couette–Taylor (CT) flow and the latter to Rayleigh–Benard (RB) convection. The curve of vanishing growth rate (marginal stability curve) Tc(q) or Rc(q), where q is the wave vector of the disturbance and T and R are the Taylor and Rayleigh number, respectively, is obtained for both cases. The correlation length amplitude ξ0 is calculated by obtaining the curvature of the marginal stability curve. The amplitude σ0 of σ was determined from data with T>Tc(q) or R>Rc(q). In that range, the wave vector qm of maximum σ is also found. For the CT system, the calculations were performed systematically as a function of radius ratio η for 0.975≥η≥0.1. For ...

Nonlinear effects in supercritical quenches of a binary fluid

Abstract: Etude de l'evolution du facteur de structure S (la, t) d'un melange fluide binaire pres du point critique apres trempe rapide qui conserve le systeme dans la region stable a une phase