Generalized hydrodynamics suggests that at high frequencies, there should be significant departire from classical hydrodynamics behavior in simple fluids. In particular, the frequency dependence of transport coefficients is not negligible and should introduced observable effects into the propagation of hyper-sound. This work which analyzes rayleigh-Brillouin spectra measured in liquid Argon and Neon reports one of the first experimental investigations of generalized hydrodynamic behavior in simple liquids

/pdf/laser-light-scattering-in-fluid-systems-3vg3t0ldfs.pdf

Laser light scattering in fluid systems

New polarized time resolved fluorescence techniques are implemented to determine the full angular motion of a probe molecule in an anisotropic environment. Studies of rhodamine 6G and resorufin molecules aligned in a free ethylene glycol jet show that the presence of net molecular order is accompanied by a distinct anisotropy in alignment relaxation following photoselection. Diffusion coefficients for φ and θ motion (D∥ and D⊥) in a jet fixed axis system are determined from the cylindrically symmetric and asymmetric alignment relaxation rates for the isotropic and anisotropic regions of the jet. The presence of net negative molecular alignment as the free jet is formed is seen to correspond to restricted φ motion (D∥<D⊥), with a net positive steady state alignment the anisotropy in the diffusion dynamics is reversed. The differences in D∥ and D⊥ are attributed to anisotropy in the solvent viscosity as a consequence of flow. The combination of linear and circular polarization techniques is seen to provide ...

/pdf/picosecond-polarized-fluorescence-studies-of-anisotropic-1pembecc6f.pdf

Picosecond polarized fluorescence studies of anisotropic fluid media. II. Experimental studies of molecular order and motion in jet aligned rhodamine 6G and resorufin solutions

Rheooptical detection of shear-induced orientation of high molar mass polystyrene in dilute solution

A combined rheometer and light scattering photometer has been constructed to examine the light scattering behavior of polymer melts and solutions under the influence of a simple shear field. The device utilizes a special lens system and a two‐dimensional charge‐coupled device array detector which has not been used previously in an apparatus of this type to quantitatively measure the scattering intensity as a function of shear rate. The accessible q range of the instrument is from 3.75×10−4 to 3.0×10−3 nm−1 (2.2°–17.4° scattering angle, with λ=632.8 nm). The rheometer utilizes a cone and plate geometry to generate the shear gradient and is capable of measuring torque (1.8 N m maximum) and normal forces (50 N maximum). An 8% solution of a 50:50 polystyrene/polybutadiene blend in dioctyl phthalate was used to test the apparatus. This sample shows a shear‐induced mixing behavior which is consistent with previous measurements by other investigators.

A rheometer with two‐dimensional area detection for light scattering studies of polymer melts and solutions

The time dependent orientation distribution function for ellipsoids of revolution (a,b,b) in shear flow is obtained as an expansion in terms of the parameter r=[1−(b/a)2]/[1+(b/a)2]. Our results reduce to Peterlin’s steady state results at infinite time (t=∞). Using this distribution, the orientation correlation function and its contribution to the light spectrum of polarized light are calculated. The results for the correlation function as an expansion in r lead also simultaneously to an expansion in the ratio σ of the shear rate to the Brownian rotation diffusion coefficient, σ=γ/D. The expansion procedure is thus valid for reasonably high shear rates in the case of nearly spherical spheroids (r≪1) or for small shear rates but large values of r (‖r‖?1, rods and disks).

Light scattering from spheroids in shear flows. I. The orientation correlation

A brief introduction is given into the theory of radiation scattering by rigid spheroids and deformable random coils dispersed or dissolved in a liquid medium subjected to flow at a well‐defined velocity gradient. The theory is limited, in the former instance, to spheroids whose largest dimension does not exceed 13 of the wavelength of the incident radiation. It is shown that the radiation scattering increment produced by flow makes it possible to determine not only the axial ratio, as obtainable by streaming birefringence, but also the numerical values of semimajor and semiminor axis of a spheroid provided two orthogonal components of incident linearly polarized light are used. Essentials of the construction and operation of an apparatus designed for the study of hydrodynamic radiation scattering are described.

M. Nakagaki

Papers

Flow Light Scattering. I. Theoretical Principles of the Effect and Apparatus for Its Measurement