Rayleigh Linewidth Measurements Research Articles

Rayleigh Linewidth Measurements on Binary Liquid Films near the Critical Point

The first measurements are reported of the Rayleigh linewidth of binary liquid films near the critical point for which the correlation length is comparable to the film thickness. The present data are in good agreement with the predictions of renormalization-group theory for binary liquids in three spatial dimensions with no adjustable fitting parameters. No influence of finite size or bounding surfaces on the linewidth are observed.

Rayleigh linewidth measurements on polar liquids in the critical region

Rayleigh linewidth measurements have been performed on methanol and acetonitrile in the critical region using a light-beating spectrometer. The result of this study was that neither the dipole moments nor the strong associations seem to have any influence on the critical behavior of the liquids since the critical exponent $\ensuremath{\nu}$ for the correlation length $\ensuremath{\xi}$ measured for methanol and acetonitrile agrees fairly well with the values published for simple liquids. The experimental setup is described and fundamental problems in locating the critical point are treated extensively.

Rayleigh-Linewidth Measurements near the Critical Point of a Binary Fluid

We report careful measurements of the Rayleigh linewidth of light scattered from a critical binary fluid. Laser heating and multiple-scattering effects are accounted for. With use of independent data for $\ensuremath{\xi}$ and the shear viscosity, a parameter-free fit is obtained with theory in the region $55>k\ensuremath{\xi}>0.32$. The renormalization-group-modified mode theory is shown to be necessary; however, we find a value of the dynamical exponent $z=2.992\ifmmode\pm\else\textpm\fi{}0.014$ instead of 3.065.

Spectral broadening of light scattered from polysaccharide gels

Light scattering Rayleigh linewidth measurements have been made on 0.5% calcium alginate gels using the autocorrelation method. The degree of spectral broadening has been found to be small (∼2%) although two relaxation times (∼7 and ∼50 msec) within the broadened component have been measured. The variations in the degree of spectral broadening and the relaxation times with angle of scatter were found to be much less than predicted by any existing theory, and no systematic variation in any of the parameters with temperature was detected within the range 3° to 88°C. By scanning through the gel with the focused laser beam, however, it has been shown that long range (tenths of millimetres), long term (tens of minutes), fluctuations in alginate density occur. It is possible that the observed relaxation times represent the continual rearrangements of polymer chains which, assuming a junction zone type of structure, would be necessary for these fluctuations to take place. Oscillations were generally found to be superimposed upon the autocorrelation functions and these have been positively identified with bulk oscillations of the specimen. A theory is advanced explaining why bulk oscillations manifest themselves in the autocorrelation function and predicting the marked increase in amplitude with angle of scatter observed experimentally. Experiments are also described in which the diffusion coefficients of dextran fractions and globular proteins within 0.5% gels were measured by investigating the heterodyne beat spectrum. It was found that the movement of macromolecules with 1 D 20W less than 3 × 10 4 sec/mm 2 was virtually unimpeded by the gel. Diffusion constants fell to about one third of those in aqueous solution for values of 1 D 20W ∼ 9 × 10 4 sec/ mm 2 . Thus there are large interstitial spaces within the gel and if a junction zone type of structure is correct, each junction zone must consist of an association of some hundreds of chains. Some preliminary results are presented of experiments with agarose and bovine vitreous humour.

Spectral broadening of light scattered from alginate gels

AbstractLight scattering Rayleigh linewidth measurements have been made on calcium alginate gels using the autocorrelation method. The degree of broadening has been found to be small (∼2%) although two relaxation times (∼7 and 50 msec) within the broadened component have been measured. Oscillations were generally found to be superimposed upon the autocorrelation function and these have been positively identified with bulk oscillations of the specimen. By scanning through the gel with the focused laser beam it has been shown that there are long range (tenths of millimeters), long term (tens of minutes), fluctuations in alginate density.Experiments were also carried out in which the diffusion constants of dextran fractions and globular proteins within the gel were measured by investigating the heterodyne beat spectrum. It was found that the movement of macromolecules with hydrodynamic diameters less than 10 nm was virtually unimpeded by the gel. Diffusion constants fell to about one third of those in aqueous solution for hydrodynamic diameters of ∼30 nm.

The effect of double scattering on critical fluid Rayleigh linewidth measurements

We apply recent work on the intensity correlation function of light double scattered from a system of brownian diffusing balls to the case of a fluid near the critical point. We evaluate the relative intensities and intensity correlation times of the polarized and depolarized components of the double scattered light as a function of k 0ξ. We compare these correlation times to those found for single scattering and find that the more intense polarized component of the double scattered light has a correlation time nearly equal to the singly scattered light in the critical region where k 0 ξ ⪆ 8 .

Rayleigh linewidth and turbidity measurements near a multicomponent fluid tricritical point

Rayleigh linewidth measurements have been performed near the tricritical point of an ethanol–water–benzene–ammonium sulfate mixture. We approached the tricritical temperature Tt along various paths of constant composition using several different samples. The linewidth always varies linearly with temperature in both two phase and three phase regions near Tt (but in the hydrodynamic regime). Since the linewidth is inversely proportional to the correlation length ξ in this regime, we find an exponent ν=1.0 in both two and three phase regions, as expected from mean field theory for thermodynamic paths of constant composition. Because of the strong temperature dependence of ξ, the hydrodynamic regime extends only to T−Tt?1 K. Measurements of the turbidity τ indicate that the product Γτ1/2 is constant within our experimental uncertainties, from which we infer that the susceptibility exponent γ?2 along paths of constant composition near the tricritical point.

Light scattering Rayleigh linewidth measurements upon solutions of globular proteins containing high molecular weight impurities

A theory is presented showing that the effect of a very small amount of high molecular weight impurity on a globular protein solution is to decrease the measured diffusion constant and increase the weight average molecular weight in equal proportions. This applies when the diffusion constant is determined by a light scattering Rayleigh linewidth measurement using the autocorrelation method. Experimental verification of this is provided by the results of measurements upon a solution of bovine plasma albumin containing a high molecular weight impurity. The effects of different amounts of impurity were simulated by making measurements at different angles of scatter. The limitations of the theory are discussed.

Light scattering Rayleigh linewidth measurements on some dextran solutions

Light scattering Rayleigh linewidth measurements have been made upon eight fractions of dextran from Leuconostoc mesenteroides B512 with molecular weights ranging from 10 to 500 kg/mol and the relationship D 20 = 2.25 × 10 −4 M −0.45 ( D in mm 2/s, M in kg/mol) was established. No concentration dependence of diffusion constant was detected within experimental error (±3%). The measurements were corrected for the polydispersity of the fractions. The results are compared with diffusion constants obtained by conventional techniques and with viscosity data.

Light scattering Rayleigh linewidth measurements on some solutions of cellulose trinitrate

Light scattering Rayleigh linewidth measurements have been made upon three cellulose trinitrate samples in ethyl acetate by obtaining the autocorrelation function of fluctuations in scattered intensity. The weight average degrees of polymerization (DPw) were in the range 2400 to 3300 and DPwDPn ∼ 1.3. Measurements were made at concentrations below 2 × 10−3 g/ml and no concentration dependence was detected within experimental error (±7%). No effects due to internal motion of the polymer chains were observed even though current theories predict that these effects should be quite large. Reasons for this are discussed and it is suggested that the effects of internal motion are diminished when the second virial coefficient is large and positive. Absolute values of translational diffusion constant calculated from the results lie well within the range of those obtained by other authors using conventional techniques. Over the limited range of degrees of polymerization investigated the equivalent hydrodynamic diameter per monomer unit was found to be 0.45 ± 0.03 Å. The effects of polydispersity on the results are discussed.

Effects of a finite-diameter laser beam on Rayleigh linewidth measurements in a fluid near the critical point

Effects of a finite-diameter laser beam on Rayleigh linewidth measurements in a fluid near the critical point

Determination of the molecular weight and hydrodynamic dimensions of micelles formed from a block copolymer

An investigation has been made of micelle formation by a polystyrene-polyisoprene two-block copolymer in n-decane. For the sample studied the number-average molecular weights of the polystyrene block and overall copolymer chain were 13 000 and 51 000 respectively. Light-scattering studies in n-decane were made within the temperature range 25–65°C. Conventional light scattering was used to obtain weight-average molecular weights; at 25°C, M w of the micelles was 1·73±0·14×10 6. Translational diffusion coefficients were determined from Rayleigh linewidth measurements; the micelles were found to have a hydrodynamic radius of 19·6nm at 25°C. Intrinsic viscosities were determined for the copolymer in n-decane and methyl cyclohexane within the temperature range −20° to 75°C. Finally, data obtained earlier in an electron microscopy study of freezeetched specimens were compared with the results obtained in the present study.

Light scattering Rayleigh linewidth measurements on some globular protein solutions

An apparatus previously described for investigating the Rayleigh linewidth of light scattered from macromolecular solutions by means of the optical homodyne technique has been modified so as to obtain the autocorrelation function of the fluctuations in scattered intensity. Its operation is described and some results presented for three commercially obtainable globular proteins: chymotrypsinogen, bovine plasma albumin and urease. Measurements were made in unbuffered 0.2M NaCl aqueous solutions and the diffusion constants, D 20w, found to be 7.4±0.3×10 −7cm 2s −1, 5.8±0.1×10 −7cm 2s −1 and 3.4±0.1×10 −7cm 2s −1 respectively. There was no detectable concentration dependence. In each case the results agreed well with theoretical predictions both as regards angular variation and shape of the autocorrelation function. The effects of polydispersity are discussed.

Light scattering rayleigh linewidth measurements on some macromolecular solutions

AbstractSome light scattering Rayleigh linewidth measurements upon three globular proteins: chymotrypsinogen, bovine plasma albumin, and urease, are described. Measurements were made in 0.2 M NaCl and the diffusion constants calculated showed no concentration dependence. The measurements agreed well with theoretical predictions both as regards angular variation and frequency distribution.