The effect of anisometry of dispersed droplets on their coalescence during annealing of polymer blends

• DOI: 10.1007/s00396-011-2507-8
• Publication Date: 2011-09-26T02:56:47Z
• Authors: Ivan Fortelný; Josef Jůza; Taťana Vacková; Miroslav Šlouf
• Keywords: Coalescence (physics); Volume fraction; Polypropylene

Approximate theory of van der Waals forces-induced coalescence in polymer blends containing anisometric droplets at the coalescence origin was derived. The results were compared with the phase structure evolution during annealing polypropylene/cyclic olefin copolymer (PP/COC) (70/30) blends with highly anisometric dispersed particles. The droplet anisometry caused a decrease in the distance between a droplet and its nearest neighbor, 〈h〉, for systems with randomly arranged centers of the droplets and relaxation of the droplet shape affected the approach of coalescing droplets. The results showed that the droplet anisometry remarkably influenced 〈h〉 and, consequently, maximum volume fraction of droplets for which the removal of the continuous phase trapped between the droplets was the decisive step of the coalescence. On the other hand, our calculations confirmed that the course of the coalescence was only slightly affected by the droplet anisometry in blends where 〈h〉 at the coalescence origin was substantially larger than the critical distance for rupture of the continuous phase between the droplets, hc. Also, orientation of anisometric droplets in these systems played a minor role. Experimental data from PP/COC blends with highly elongated COC particles were in agreement with the theoretical calculations: particles retracted rapidly to spherical shape during the first 5 min of the annealing, while their volume increased slowly due to the coalescence during the whole time.