Dispersions of colloidal particles exhibit thermodynamic properties similar to those of molecular systems, including a hard sphere disorder-to-order transition. In experiments with organophilic silica in cyclohexane, gravity settling was used to concentrate the particles. With small particles the slow sedimentation permits rearrangement into the iridescent ordered phase, but larger particles form amorphous sediments instead. Scanning electron microscopy of the crystalline sediment indicates hexagonally closepacked layers. X-ray attenuation measurements reveal a discontinuity coincident with the observed boundary between iridescent and opaque regions. Sediments accumulating faster than the maximum rate of crystallization produce a glass, in accord with the classical theory for crystal growth.

The geometrical optics approach is used to derive i(1)(theta) = |S(1)(theta)|(2) and i(2)(theta) = |S(2)(theta)|(2), the angular intensity functions for light scattered by a spherical water droplet of a radius comparable with or larger than the wavelength of light. In contrast to previously published results, these functions are obtained in closed form and as functions of the scattering angle theta, which greatly enhance their usefulness in numerical work and in the reduction of large sphere scattering data. The range of validity of these expressions is investigated by graphical comparison of calculated angular intensity patterns with those obtained from rigorous Mie theory. Our main objective is to study the feasibility of using the geometrical optics expressions as a basis for practical laser water droplet sizing work. A criterion is established for the range of applicability of the relationship I(theta,R) = K(theta)R(2), which relates the scattering intensity at a particular angle theta to the radius R of the droplet. Accuracy of the laser water droplet sizing technique is thus quantitatively established.

Suspensions of colloidal particles execute Brownian motion and thus exhibit thermodynamic properties analogous to those of molecular systems. Hard-sphere colloidal silica suspensions undergo a disorder-rder transition, i.e. freezing or crystallization, at high volume fractions. In suspensions of small particles the slow sedimentation permits the transition to occur at the bottom where the bulk of the crystalline sediment is formed by one-dimensional crystallization, as illustrated with photographs and scanning electron microscopy. X-Ray tomography measurements reveal a volume fraction discontinuity coincident with the observed crystal boundary occurring between the sediment and hindered settling region of the Kynch theory. Larger particles, however, form amorphous sediments because their rate of accumulation at the bottom exceeds the maximum crystal growth rate, in accord with classical kinetic theory. This theory is paired with Kynch's kinematic theory using an experimental sedimentation coefficient to interpret observations of settling suspensions.

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