A least-squares method for correlation function profile analysis using a histogram approximation is described. The method is completely general, especially for bimodal distributions, and compares favorably with the method of cumulants. The measured photoelectron time-correlation function yields a histogram of the linewidth distribution which can be related uniquely to the particle size. The analysis is tested using simulated data with unimodal and bimodal size distributions. In our verification of the method using aqueous suspensions of Dow latex spheres, we have shown that our method is not only consistent with the results from electron microscopy, but that it is more precise and truly measures the hydrodynamic size of particles suspended in fluids.
Intensity and linewidth measurements of light scattered by the isobutyric acid in water system are reported for various equilibrium states in the critical neighborhood of the temperatureconcentration diagram. By extrapolation of these data to zero scattering angle and then to (unrealized) states below the phase separation temperature one may determine a common 'Qseudospinodal curve" T (X) described by T -Ts QQ -lX-X I /P where X is the concentration, and we find P~=0.37+0.04. As expected on the grounds of the homogeneity hypotheses, the value of P4 is essentially the same as the previously observed value of the exponent p for the coexistence curve. Empirical equations of the form I& 0 tx: fT -T {X) js p and Doc [T-T (X) p' are used to effect the extrapolations to determine Ts (X). Here IC 0 sp Sp and D are the extrapolated zero-angle scattering intensity and the diffusion coefficient, while y and y are corresponding critical exponents. We show theoretically, however, that a value P~& 2 is inconsistent with the general validity of these empirical formulas, which should thus be discarded as over-all representations of the variations of D and I~0. A tentative test is made of a more general scaling equation for Ig 0 by a convenient plot. Moderate success is obtained. The measurements confirm the exponent values y=1.24+0.03 and y =0.67+0.03.The distinction between pseudospinodal curves, determined by extrapolation from stable thermodynamics states, and a true spinodal curve which (if it exists) can only be observed by measurements on metastable states, is emphasized.
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