Microscopy of Pigment-Elastomer Systems

Rubber technologists have always been fascinated by the remarkable effects produced in rubber by carbon black. Many people have contributed to an understanding of these phenomena. We have referred to some, but by no means all of such individuals' efforts in this review. In retrospect, it may not be inappropriate to recall some observations made 40 years ago by Ellwood Spear. In a remarkably perceptive paper on carbon black reinforcement, published in 1923, he said: “It is believed that the rubber is adsorbed on the surface of the carbon particles and that adsorption … is the real cause of the effect of carbon black in rubber”. And further: “The distinction between mere fillers … and those substances which reinforce rubber to an appreciable degree, lies in the hypothesis that the latter adsorb rubber strongly, whereas the former form a very weak union with it”. There are perhaps few chemists, physicists, rubber compounders, or microscopists who will disagree with these observations. But the measure of their success in unravelling the mysteries of carbon reinforcement of rubber will be the real facts they are able to find in support of such speculations. We hope that the present review will be helpful to others in their search for such facts. If we have succeeded in answering a few questions as well as in evoking some new ones, then perhaps our efforts will have been worthwhile.