George D. J. Phillies

An introduction to dynamic light scattering by macromolecules

Dynamic light scattering (DLS) techniques provide information about size, shape, and flexibility of particles as well as offering insight concerning the nature of the interactions between particles and their environments. This book offers a study of DLS by macromolecular and polyelectrolyte solution

Diffusion in protein solutions at high concentrations: A study by quasielastic light scattering spectroscopy

Quasielastic light scattering spectroscopy was used to study the mutual diffusion coefficient Dm of bovine serum albumin over the pH range 4.3–7.6 for concentrations ranging as high as 334 g/l. Using literature measurements of the tracer diffusion coefficient DT and the osmotic compressibility (∂π/∂c)P,T, we find that Dm depends on concentration and pH as predicted by the generalized Stokes–Einstein relation Dm=DT(∂π/∂c)P,T (1−φ)/KBT, φ being the volume fraction of solute and KB being Boltzmann’s constant. Our data show that Dm and DT depend quite differently on solute concentration; DT can be a factor of 3 smaller than Dm at protein concentrations exceeding 200 g/l.

Study of the crystallization of zeolite NaA by quasi-elastic light-scattering spectroscopy and electron microscopy

A study of the crystallization of the molecular sieve zeolite NaA from clear aluminosilicate solutions is reported. It was determined by powder X-ray diffraction that zeolite NaA was the only phase in the solid precipitate. The syntheses were monitored in situ by quasi-elastic light scattering spectroscopy. Characteristics of the products were examined by scanning and transmission electron microscopy. Our data show that nuclei formed from the clear aluminosilicate solution, that crystal growth occurred from the solution, that crystal growth was accelerated at elevated temperatures, and that aging the solution at room temperature before raising the synthesis temperature increased both the number of nuclei that formed and also the crystal growth rate for aging times up to a limit. Adding crushed seed crystal fragments to an unaged synthesis solution produced similar results to aging the solution, including reduced induction times, increased crystal growth rates, and polycrystalline product formation.

Phenomenological scaling laws for semidilute macromolecule solutions from light scattering by optical probe particles

Polymer solution dynamics may be inferred from light scattering spectra of dissolved optical probe particles. We compare a variety of probes in solutions of several polymers. In the ‘‘overlapping’’ concentration/molecular weight regime, the Stokes–Einstein equation fails by up to a factor of 2, while the probe diffusion coefficient D follows a scaling law D/D0=exp(−aMγcνRδ) (c, M, and R are the polymer concentration, molecular weight, and the probe radius, respectively). Experimentally, γ=0.8±0.1, ν=0.6–1.0, and δ=−0.1 to 0, contrary to the theoretical predictions γ=0 and δ=1. With very high molecular‐weight polymers, we observe a further ‘‘entangled’’ regime, characterized by huge (104) failures of the Stokes–Einstein equation and the appearance of ‘‘fast’’ modes in the scattering spectrum.

Suppression of multiple scattering effects in quasielastic light scattering by homodyne cross‐correlation techniques

By studying cross correlations in the intensity of light scattered by a fluid sample in different directions at different times, it is possible to measure the dynamic scattering function S(k,t) for the fluid. The multiple scattering contribution to the time‐dependent cross correlations is very substantially less than the multiple scattering contribution to S(k,t) as obtained by a conventional single‐detector quasielastic light scattering system.

Excess chemical potential of dilute solutions of spherical polyelectrolytes

The excess chemical potential of a dilute solution of spherical polyelectrolytes is calculated in the limit of the linear Debye‐Huckel theory. The charge distribution within each polyelectrolyte is expanded in terms of its spherical harmonics. The calculation includes the effect of the finite radius of both of a pair of polyelectrolytes on the screening of their electostatic interactions. It is found that the term in the excess chemical potential of a minimum‐salt protein solution that depends on the square root of the protein concentration arises from fluctuations in the net charge of each protein molecule. Fluctuations in the dipole moment of each protein molecule give rise to a term linearly proportional to the protein concentration. Interactions among the net charges Ze of protein molecules in a minimum‐salt solution give rise to a concentration‐independent term in the chemical potential of the form KT|Z|.

Coupling model analysis of polymer dynamics in solution: Probe diffusion and viscosity

The coupling model of Ngai et al. [K. L. Ngai, Disorder Effects in Relaxation Processes, edited by R. Richert and A. Blumen (Springer‐Verlag, Berlin, 1994)] is applied to treat polymer dynamics in solution. Important dynamic quantities considered here include the zero‐shear viscosity η and the light‐scattering spectrum (field correlation function) g(1)(t) of optical probes suspended in solution. The coupling model describes systems in terms of two times, a basic relaxation time τ0 and a crossover time tc, and a coupling exponent n. Use of scaling arguments allows us to extract values for n from the concentration dependence of η and, by three separate paths, from the concentration, time, and scattering vector dependencies of g(1)(t). Values of n from these four distinct physical approaches are shown to be mutually consistent, especially in the higher‐concentration, large‐probe‐particle regime in which the scaling arguments are most likely to be valid. The behavior of n above the solutionlike–meltlike visco...

On the contribution of nonhydrodynamic interactions to the concentration dependence of the drag coefficient of rigid macromolecules

The Stokes’ law drag coefficient for a rigid macromolecule in solution has long been known to depend on the macromolecule concentration. This concentration dependence has generally been interpreted entirely in terms of hydrodynamic interactions between the macromolecules. It is argued here from a fluctuation–dissipation relation that direct (e.g., hard sphere, electrostatic) interactions between macromolecules also contribute to the drag coefficient. An approximate calculation indicates that the contribution of direct intermacromolecular interactions to the drag coefficient can be as important as the contribution of hydrodynamic intermacromolecular interactions.

PROBE DIFFUSION IN POLYACRYLIC-ACID WATER - EFFECT OF POLYMER MOLECULAR-WEIGHT

Abstract Quasi-elastic light scattering spectroscopy was used to measure the mutual diffusion coefficient D of car☐ylate-modified polystyrene latex spheres (of radii 204A˚, 800A˚, 0.62 μm, and 1.5 μm) dissolved in water: polyacrylic acid. Polymer molecular weights were 5 × 10 4 and 1 × 10 6 . In solutions of the 5 × 10 4 amu polymer, D followed the Stokes-Einstein equation. The Stokes-Einstein equation fails badly (by up to 10 4 ) for spheres in high-molecular-weight polymer solutions. Comparison with previous data by T.-H. Lin and G. D. J. Phillies shows that D is not independent of the polymer molecular weight, even at very high polymer concentrations.

Continuum hydrodynamic interactions and diffusion

The Oseen tensor is not an adequate characterization for the contribution of hydrodynamic interactions to the homodyne (’’self‐beat’’) spectrum of light scattered from a dilute macromolecule solution. Physical constraints on the possible form of the true cross diffusion tensor DT(R), which describes hydrodynamic interactions in macromolecule solutions, indicate that hydrodynamic interactions do not by themselves contribute to the homodyne spectrum. However, if the macromolecules in a solution interact directly as well as hydrodynamically, the direct and hydrodynamic interactions couple to contribute jointly to the mutual diffusion coefficient of the solute molecules, and thence to the spectrum of the quasielastically scattered light. Tracer diffusion techniques may be used to study the cross‐diffusion tensor. Comparison with the available experimental data indicates that the joint contribution of direct and coherent hydrodynamic interactions to diffusion need not be large, even in extremely concentrated s...