528 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Approximately linear relations were obtained in some powders be- tween the amount of adsorption and SP, as is obvious from Figs. 1-3. But in the case of Lake Red C, which is regarded as a hydrophobic pow- der, the amount of adsorption changed little with SP. With liquids hav- ing a low SP, the difference in the number of molecules adsorbed was not obvious among the powders. SP is defined as se = where E is the energy of vaporization and V is the molar volume (4). It can be considered that the higher the SP, the stronger the intermolecular n hexane acetone methanol wat,•r cyclo •xane n prap. ano! b•nzene • •ltanlum dioxide Solubd•ty Parameter Figure ]. Re]aLionship beLweeu nmnber or molecules adsorbed and solubility parameLer [or titanium dioxide (A) and titanium dioxide n hexane acetone methanol wa•er cyc•ot]exane An propanol • 10 •%zene • & Carbon black • B ) ///Carbon black •,A } $01uhhty Parameler Figure 2. Relationship between number of molecules adsorbed and solubility parameter for carbon black (A) and carbon black (B)

POWDER SURFACE PROPERTIES 529 ....... -•-•-Lake red C -•/ ,O 15 20 25 Solubd•ty Parameter Figure 3. Relationship between number of molecules adsorbed and solubility parameter for iron oxide hydrate, talc, and Lake Red C force of the liquid. A similar relation is considered to hold in the ad- sorption of a liquid molecule on powder surface in this case, the higher the SP, the stronger the adsorption force, and consequently the amount of adsorption increases. When the liquids were rearranged in other order, like dipole moment or dielectric constant, less clear relations were obtained. Liquid A bso?ption Figure 4 shows the results of liquid absorption. It increased as the SP decreased in the case of powders like titanium dioxide or iron oxide hydrate which were considered to be hydrophilic. On the other hand, there was no relation between liquid absorption and SP in case of carbon black or Lake Red C and liquid absorption was almost constant in any SP. Talc showed intermediate behavior. 4O • 2c • /• [::3 Talc • •T[tanmm dmxlde{A• ,=• • _ •, •. Titamum dmx•detB) = •- • • Carbon black(B) 1'0 1'5 20 5 8olubd•ty Parameler Figure 4. Relationship between liquid absorption volume and solubility parameter