Effect of block copolymer architecture on the interfacial tension between immiscible polymers
The effect of block copolymer additives on the interfacial tension (σ) is studied for the systems polydimethylsiloxane/polyethyleneoxide (A/B) and polyethylmethylsiloxane/polypropyleneoxide by means of a sessile-drop and a pendant-drop-apparatus. Diblockcopolymers (A-block-B), triblockcopolymers (A-block-B-block-A) and “tooth-brush” like copolymers (A backbone, B brushes) served as additives.
Measurements of σ were performed as a function of concentration and temperature; σ plateau, the maximum reduction of the interfacial tension, was calculated for each copolymer. To compare the efficiency of additives of different molecular architecture, equivlent diblockcopolymers are constructed by summing up the numbers of A and B units. The data demonstrate that σ plateau — keeping the number of A units constant — does not depend on the number of B units in case of the present copolymers. A plot of σ plateau versus the number of A units shows that the maximum reduction is independent of the particular architecture of the copolymer and can be estimated from the mere knowledge of the number of A units, the copolymer contains.