N. Lazaridis et al., Steric stabilization in emulsion polymerization using oligomeric nonionic surfactants, CHEM ENG SC, 54(15-16), 1999, pp. 3251-3261
Although nonionic surfactants show improved stabilization characteristics i
n emulsion polymerization as well as superior shear and freeze thaw stabili
ty of the final latex, their behaviour is generally not well understood. In
the present paper a steric stabilization model is developed for describing
particle stabilization in emulsion polymerization systems in the presence
of nonionic oligomeric surfactants. The model takes into account the effect
of unequal particle sizes on the steric interaction potential and the resu
lting enhanced heterocoagulation. An additional feature of the model is the
incorporation of a possible surfactant lateral migration mechanism, which
may be significant in the case of oligomeric nonionic surfactants. The prop
osed model can simulate reasonably well the experimentally observed convers
ion profiles and average particle sizes as a function of the surfactant mol
ecular structure (i.e., lengths of stabilizing and adsorbing moieties) and
surfactant concentration. As a result of the competing effects of the adsor
bed volume fraction and surface coverage on particle stability, an optimum
hydrophobicity/hydrophilicity ratio for the oligomeric nonionic surfactants
can be derived. (C) 1999 Elsevier Science Ltd. All rights reserved.