Dynamic sound scattering: Field fluctuation spectroscopy with singly scattered ultrasound in the near and far fields.

Dynamic sound scattering (DSS) is a powerful acoustic technique for investigating the motion of particles or other inclusions inside an evolving medium. In DSS, this dynamic information is obtained by measuring the field autocorrelation function of the temporal fluctuations of singly scattered acoustic waves. The technique was initially introduced 15 years ago, but its technical aspects were not adequately discussed then. This paper addresses the need for a more complete account of the method by describing in detail two different implementations of this sound scattering technique, one of which is specifically adapted to a common experimental situation in ultrasonics. The technique is illustrated by the application of DSS to measure the mean square velocity fluctuations of particles in fluidized suspensions, as well as the dynamic velocity correlation length. By explaining the experimental and analytical methods involved in realizing the DSS technique in practice, the use of DSS will be facilitated for future studies of particulate suspension dynamics and particle properties over a wide range of particle sizes and concentrations, from millimeters down to nanometers, where the use of optical techniques is often limited by the opacity of the medium.

Effects of the positive feedback loop in polymerization on the reaction-induced phase separation of polymer mixtures.

Phase separation of mixtures composed of a guest polymer dissolved in monomer of a host polymer was induced by photopolymerization. From the polymerization kinetics, it was found that for the host polymer with the glass transition temperature (Tg) higher than the experimental temperature, the Trommsdorff-Norrish effect emerges, providing a method to terminate the phase separation at various intermediate stages of the process and thereby a variety of morphologies can be constructed. For the host polymers with (Tg) lower than the experimental temperature, the freezing process of morphology is not complete, leading to the secondary phase separation inside the domains already generated by the primary process. The kinetics of this secondary phase separation indicates that the peculiar morphology like "sunny-side-up egg"-like structures was generated via spinodal decomposition. The experimental results obtained in this study show that the competition between photopolymerization and phase separation can provide a useful method of materials design in the micro- and sub-micrometer scales.

Ordered conformation of succinoglycan in aqueous sodium chloride.

Succinoglycan samples ranging in weight-average molecular weight from 1.0 x 10(5) to 8.7 x 10(6) (in 0.1 M aqueous NaCl at 25 degrees C), prepared by ultrasonication of a native sample (Rheozan), followed by fractionation, were investigated by static light scattering, sedimentation equilibrium, and viscometry in 0.1 M aqueous NaCl at 25 degrees C where the polysaccharide assumes a certain ordered (helical) conformation. The measured radii of gyration and intrinsic viscosities showed the polysaccharide to behave like a semirigid chain in the aqueous salt. Their analysis based on the unperturbed wormlike chain yielded about 1500 nm-1 and 50 nm for the linear mass density and the persistence length, respectively. The former value was almost twice that expected for the single succinoglycan molecule, and thus it was concluded that the predominant molecular species of succinoglycan present in the aqueous salt is a double helix or an aggregate composed of paired single helices.

Viscosity behaviour and persistence length of sodium xanthan in aqueous sodium chloride.

Zero-shear-rate intrinsic viscosities [eta] of sodium xanthan in aqueous NACl at 25 degrees C were determined for five samples ranging in weight- average molecular weight from 2 x 10(5) to 4 x 10(6) at salt concentrations Cs between 0.005 and 1 M, at which the polysaccharide maintains its double-helical structure. The measured [eta] for every sample was almost independent of Cs, in contrast to usual observations on flexible polyelectrolytes. The persistence length q of sodium xanthan was determined as a function of Cs by use of the theory of Yamakawa et al. for [eta] of an unperturbed worm-like cylinder, and from its Cs dependence the intrinsic persistence length q(o) ( = q at infinite ionic strength) was estimated to be 106 nm. This q(o) value was roughly twice as large as that of double-stranded DNA, indicating a high intrinsic rigidity of the xanthan double helix. The electrostatic contribution ( = q - q(o)) to q was only about 10% even at the lowest Cs of 0.005 M. Thus, it was concluded that above Cs = 0.005 M, the double- helical structure of sodium xanthan is hardly stiffened by electrostatic interactions between charged groups.

Correlation between the antitumor activity of a polysaccharide schizophyllan and its triple-helical conformation in dilute aqueous solution.

Eight samples of a polysaccharide schizophyllan ranging in weight-average molecular weight Mw (in water) from 5 x 10(3) to 1.3 x 10(5) were prepared and their antitumor activity (expressed in terms of the tumor inhibition ratio) against Sarcoma 180 ascites, intrinsic viscosities [eta], and gel-filtration chromatograms in aqueous solution were determined. The tumor inhibition ratio was essentially unity for samples with Mw higher than 9 x 10(4), but reduced to zero or even to a negative value when Mw was lower than 10(4). The [eta] data combined with the chromatographic data showed that above Mw approximately 9 x 10(4) the predominant species of schizophyllan in aqueous solution is the previously found rigid triple helix, whereas below Mw approximately 9 x 10(4) both triple helices and single chains coexist in the solution and the fraction of triple helices decreases monotonically to zero as Mw is decreased to 5 x 10(3). From these findings it was concluded that the antitumor potency of schizophyllan in water is related to the amount of triple helices relative to that of single chains.

Photoinduced size change of membrane vesicles from bovine retinal rod outer segment.

Quasielastic light-scattering measurements were made on isolated, osmotically swollen, bovine rod outer segment (ROS) disk membranes in aqueous Ficoll. The translational diffusion coefficients determined were (1.66 +/- 0.21) X 10(-9) and (2.31 +/- 0.14) X 10(-9) cm2/s at 25 degrees C for the unbleached and bleached membranes in 5% Ficoll, respectively, yielding the Stokes radii of 0.53 +/- 0.07 micronm for the former and 0.38 +/- 0.02 micronm for the latter. This photoinduced size decrease, which corresponds to a 60% decrease in the intravesicular volume, is far more pronounced than thos reported by others for ROS fragments.

Intact photoreceptor membrane from bovine rod outer segment: size and shape in bleached state.

Photoreceptor disk membranes isolated from bovine rod outer segments are suspended in dilute aqueous sucrose (4.36 X 10(-3%)) and bleached, and their size and shape are determined with quasielastic and elastic light scattering. They are found to be extremely homogeneous spherical vesicles with a radius of 0.49 +/- 0.07 mum which appear to have derived from the native disk shape by osmotic swelling.