Abstract
Purely thermal measurements indicate that the physical reënforcement of rubber, i. e., the increase in the work expended in rupturing, brought about by the admixture of active fillers, depends upon the free surface energy between rubber and filler, besides a work of friction, and can be measured in absolute units. Experience has shown that the addition of so-called active fillers to rubber improves the physical properties of the latter, the work expended in breaking the rubber mixture being considerably greater than that expended in breaking the pure rubber. Furthermore, it has been found that the finer the active filler, e. g., carbon black or zinc oxide, the greater is the reenforcing effect. Obviously then the wetting of rubber and filler is the cause of the reenforcing action. In developing from these basic principles a theory of the action of fillers, the free surface energy between rubber and filler must be considered responsible for the increased work of breaking the loaded rubber. It is desirable, therefore, to find a way to determine this free surface energy. Now if a rubber-zinc oxide mixture is swollen in benzine, the rubber component swells and the zinc oxide is wet. This process is accompanied by a heat tone which can be measured calorimetrically, and which is not the sum of the heat of swelling of the same quantity of rubber and the heat of wetting of the zinc oxide when these are measured separately, but shows a distinctly different value. This difference represents the heat of adhesion of the filler and rubber. It also represents the total surface energy, and therefore is not a measure of the free surface energy to which is attributed the increase in the work of rupture.
The Applicability of a Drop Penetration Method to Measure Contact Angles on TiO2 and ZnO Nanoparticles
