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

53O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I • (• Inethanoi • ß • ß n propanol i / VI acetone I • ß benzene I • • c¾clo.hexane /• ß n hexane Nu•er of Molecules •s•bed •x10'a/cm • ) Figure 5. Relationship between wettabilit¾ and number of molecules adsorbed Wettability Figure 5 shows the relation between wettability and number of mole- cules adsorbed. With a liquid having a large SP, powders which ad- sorbed higher amounts of the molecule were wet more easily by the liquid. As the SP of the liquid became lower, this relation became less recognizable. It has been reported that there was high positive correla- tion between the number of water molecules adsorbed and wettability to water using 20 kinds of powder (3). Multiple Regression Analysis Hansen and Skaarup proposed the concept that SP is a vector co•n- posed of hydrogen bonding, and polar and dispersion components (5). In order to examine how these related to adsorption phenomena, mul- tiple regression analysis was performed with an IBM computer,* except for titanium dioxide (B) and carbon black (B) for which there was insuf- ficient data. The results are shown in Tables IV and V. The factors in- dicating large values of to or Fo are important.* It will be obvious that the polar component contributes to adsorption more strongly than other two components. * IBM 360 Model 40, 2-12 Roppongi 3 Chome Miuatoku, Japan. * Both to and Fo are the statistical values defined in multiple regression analysis. When they have large values, the adsorption of liquids is found to be contributed by the com- popent of SP.