Coalescence in polymer blends: Solved and open problems

Problems with microrheological description of the coalescence of dispersed droplets in polymer blends are discussed. Apparently, the coalescence in qu iescent polymer blends is caused by molecular forces and Brownian motion. T he coalescence rate is controlled by drainage of the matrix film between un deformed droplets. For further development of the theory: description of th e coalescence induced by the Brownian motion should be improved, mutual inf luence of the Brownian and molecular forces should be considered and simult aneous interaction of three and more droplets should be investigated. Probability, P-c, that the collision of droplets in a shear flow is followe d by their fusion, is controlled by the competition between their approach and rotation around their common centre of inertia. The velocity of the dro plet approach is controlled by drainage of the matrix between flattened dro plets. The dependence of P-c on properties of the components is determined by the model of interface mobility, the magnitude of P-c depends on the des cription of the competition between approach and rotation of the droplets. The main shortcoming of the present theories of blends with a high content of the dispersed phase is neglecting any effect of other droplets on the co llision of a certain pair of droplets.