2004 ANNUAL SCIENTIFIC SEMINAR 407 remain in good solvent conditions under all conditions of storage. (iv) Reasonably thick adsorbed layers of the order of 5 - 10 run .. 0/W emulsions based on HMI were prepared and their stability in water and in electrolyte solutions was investigated using optical microscopy. Very stable emulsions were produced both at room temperature and 50°C. The reason for this high stability was attributed to the multipoint anchoring of the polymeric surfactant by several alkyl groups and the strong hydration of the polyfructose loops in water and high electrolyte concentrations and at high temperature. The hydration of the polyfructose chains was confrrmed by cloud point measurements in water and high electrolyte concentrations. W/0 emulsions prepared using PHS-PEO-PHS block copolymer could be prepared at high water volume :fraction( 0.6). These emulsions were fluid as confirmed by viscosity measurements. They also remained stable both at room temperature and 50°C. The last two sections in this overview are concerned with the problems of creaming or sedimentation and phase inversion. Creaming or sedimentation could be prevented by the use of"thickeners" in the continuous phase, e.g. hydroxethylcellulose or xanthan gum. These molecules produce non-Newtonian systems that will have a very high residual or zero shear viscosity. The latter which may exceed 1000 Pas could prevent any creaming or sedimentation of the emulsion. Syneresis of the emulsion could be prevented by control of the bulk (or elastic) modulus of the system. Phase inversion of 0/W emulsions could be prevented using HMI, since the polymeric surfactant is insoluble in the oil phase. As long as coalescence and Ostwald ripening are prevented the emulsion could remain stable for very long periods of time at room temperature and 50°C.

408 JOURNAL OF COSMETIC SCIENCE DISPERSION OF PARTICULATES David Schlossman and Yun Shao, Ph.D. Kobo Products, Inc., South Plainfield, NJ Introduction The popularity of personal care formulations containing particulates with consumers depends on sensory characteristics such as their color, gloss, wear, wrinkle hiding power, transparency, softness, spreadability, blendability, and smoothness, in addition to stability in the finished product. Thus, dispersions of particulates are important to cosmetic chemists, because the desirable properties of the particulates are likely to be influenced by the degree of their dispersion in the formulation. Terms such as dispersions, slum.es, grinds, pastes, suspensions and gels are all used by cosmetic chemists to describe mixing particles in a liquid medium. The elements of particulate dispersion technology, wetting, stabilizing, and grinding are frequently cited in patents. Home, et al. claimed a novel silicone elastomer gel processed from the flow induced shearing through an orifice of a cross linked particulate to create a unique multiple particle size distribution with improved spreadability and substance (I). Gardlik, et al. patented a low residue antiperspirant gel-solid stick comprised of a particulate dispersion of antiperspirant actives held within a non-polymeric crystalline gel-solid matrix (2). Skin care compositions to improve skin appearance containing a charged particulate material dispersed in a thickened hydrophilic carrier were disclosed by Ha, et al. (3) Numerous references can be found describing methods to disperse and emulsify inorganic ultraviolet filters to enhance their SPF and efficacy in formulations (4,5,6,7). Dispersions of particulates have been extensively studied and numerous mathematical models have been proposed to describe their behavior. In practice, however, the formulation and testing of a particulate dispersion is still considered to be much of an art. In this presentation, both science and art will be acknowledged. Princiules of Disnersions Volumes of articles, chapters and textbooks have been published on the science of dispersions. Dispersion is a stepwise process. The objective is to produce in an application medium a stable and uniform milling of finely-divided particles, i.e. aggregates and primary particles. Mechanical Breakdown In order to achieve mechanical breakdown it is necessary to use energy to break down the cohesive forces, the intermolecular forces of attraction that hold the solid particles together. The primary particles always aggregate to form secondary particles due to their high surface energy such as Van der Waal's forces, electrostatic force, hydrogen bonding of surface hydroxyl groups and water bridging between the primary particles (8) The hardness and morphology of the particulate, its percent solids in the carrier and the viscosity of the pre-mix are all likely to influence the mechanical process. High pressure homogenizers, sonolators, and bead mills are all well suited to disperse particulates. Wetting The oil absorption value of a particulate will give an indication about its wetting. Theoretically, the wetting of a solid by a liquid is often described in tenns of the equilibrium contact angle formed at the solid-liquid-vapor (air) triple interface or the spreading coefficient. Both are functions of the three paired interfaces as shown in Figure l. The maximum wetting occurs when the contact angle is zero or when the spreading coefficient has a large positive value (9). Besides surface treatment, dispersing aids are frequently added to increase wetting and stabilization. They also reduce the amount of mixing and milling time, which may prevent the over milling and fracturing of the particles. The finesses of the pigment grind will be detennined by the wetting of the particles in the carrier. (9). Stabilization Unless the particulates are immobilized by the high viscosity of the slurry, after the mechanical forces that accompany the dispersion process are removed, the forces between the particles will start to come into effect that will lead to sedimentation and flocculation or stabilization. The close approach of particles can be repelled by Coulombic interactions between similarly charged particles in polar media or through steric interactions between long-chain molecules adsorbed on the particulate surfaces. These interactions are shown as Figures 2 and 3, respectively. Steric stabilization can operate in both aqueous and non-aqueous media (9). The ideal stabilizing molecule must be capable of being absorbed on the particles surface (and swollen around each particle) and being solvated and extended into the carrier. Particles possess potential attractive and repulsive energies whose actions are strongly determined by their distance of separation. As the distance between particles is increased the interaction energy is