Immiscible Polymer Blends and Interfacial Tension

Lack of miscibility has also been observed with polybutadiene and its styrene copolymer (SBR). These have the following structural imits. 

Polybutadiene and SBR have a striking UCST and a possible LCST at much higher temperatures [39,40]. The details depends notably on the styrene content. 

Most binary polymer blends are immiscible. To a large extent the characteristics of these immiscible blends are determined by the state of the interface between the blend components. The interaction of two melts at an interface is primarily represented by a quantity, k, called the interfacial tension. Interfacial tension is the excess free energy caused by the existence of an interface, arising from unbalanced molecular forces. It has units of force divided by length (F/L) or energy divided by area (FL/L ). 

The study of interfacial tension between two immiscible low molecular weight liquids dates to the 19 century [43, 52, 53] and was discussed by Maxwell [43] among others in this period. It has been recognized by many researches that interfacial tension plays a key role in determining the shape, breakup, and coalescence of dispersed phases. 

Considerations and measurements of interfacial tension between polymer melts dates to the 1960s and 1970s [54 to 57]. Several different methods have been used to measure interfacial tension. Extensive use has been made of 1) the shape of drops emerging from a capillary into a second phase (falling drop) [56 to 60] and 2) thread breakage, the breakup of stationary hlaments in a second liquid phase by a capillary instability [59 to 61 ]. The latter analysis is based on the work of Tomotika [62]. Other methods have been used. 

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