Use of the pendant drop method to measure interfacial tension between molten polymers

Abstract

In this paper the pendant drop method to measure interfacial tension between molten polymer s is reviewed. A typical pendant drop apparatus is presented. The algorithms used to infer i nterfacial tension from the geometrical profile of the pendant drop are described in details, in parti cular a new routine to evaluate correctly the value of the radius at the apex of the drop, necessary to th e calculation of interfacial tension is presented. The method was evaluated for the possibility of measur ing the interfacial tension between polyethylene and polystyrene. It is shown that the method is un suitable for the measurement of interfacial tension between high density polyethylene and polystyr ene due possibly to a too small difference of density between the two polymers. Values of interfac ial tension between low density polyethylene (LDPE) and polystyrene (PS) as a function of the molecula r weight of PS are presented. It was shown that the interfacial tension between LDPE and PS incr eased as a function of molecular weight of PS up to values of molecular weight of roughly 40,000 g/m ol, value for which entanglements occur.