Abstract
In the literature the problem of whether or not filler particles adhere to a polymer is still under discussion. This point is already of interest in the mixing process because here the question resolves itself into whether the particles clog together or each becomes separately surrounded by polymer only. The problem is also of paramount interest with regard to the properties of the final mixture because upon the interaction depends whether or not a filler has a reinforcing action. This is a key problem, especially in the rubber industry. Essentially, the problem of dispersing a filler in a polymer is of the same type as that of dissolving a polymer in a solvent, and for the thermodynamic considerations we know that dispersing occurs if (leaving the entropy factor out of discussion) ΔU(U=internal energy) is negative, that is, heat is liberated. Here the historical measurements of Hock and his coworkers show that, on mixing rubber with carbon black, 11 gcal. per gram of black (which is of the order of 1 gcal. per mole) extrapolated to zero concentration, are developed. This heat is found to decrease with increasing proportion of filler, showing that all particles are no longer in contact with the rubber because of clogging. It has long been a problem to explain the outstanding reinforcing properties of carbon black with the aid of these low values found by Hock. Smith and Schaeffer showed that the initial heat of adsorption between carbon black and C4 hydrocarbons is of the order of magnitude of 15 kcal. per mole, decreasing sharply until about 40 per cent of a monolayer is formed. This indicates that 40 per cent of the carbon black surface is covered with sites of high adsorptive capacity. Between 40 and 100 per cent of this monolayer formation the surface appears to be quite uniform with regard to adsorptive capacity; at the monolayer the values again decrease and approach the heat of liquefaction, EL, of the adsorbate. These results are shown in Figure 1. From the data obtained, it can be derived that the heat of adsorption per CH2 group to carbon black is about 4 kcal./mole.
Entropy factor for randomness quantification in neuronal data
