Heat of immersion of silica gel in normal alkanes and alcohols

Abstract

In order to differentiate phenomena on a smooth surface from those related to surface curvature, they must, strictly speaking, study these phenomena separately on completely nonporous and porous adsorbents of the same chemical nature. However, it is virtually impossible to obtain a completely nonporous adsorbent with a sufficiently developed surface. Thus, a permissible compromise for solving this problem lies in the selection of a porous adsorbent such that, on one hand, the effect of surface curvature is excluded due to wide pores and, on the other hand, reliable quantitative data for the properties of this surface with virtually zero curvature are obtained due to the development of the surface. For these purposes, they used a modification of their previous method and obtained silica gel (SG) with a developed surface s = 218 m/sup 2//g and broad pores D/sub max/ = 20 nm. They found that mesoporous silica gel with 20 nm pore diameter may be taken as a practical model of nonporous amorphous silica, according to the liquid immersion heats. The heats of wetting of the hydrated amorphous silica surface by normal aliphatic alcohols and hydrocarbons are independent of the number of carbon atoms in the molecules and are 220more » and 65 mJ/m/sup 2/, respectively. The interphase (liquid-solid) surface layer or normal alcohol molecules on silica gel is a Langmuir palisade with the OH alcohol groups directed toward the silica surface.« less