AbstractA method is proposed to determine the interfacial tension of immiscible blends containing a liquid crystalline polymer (LCP) and a flexible‐molecule polymer, under flow conditions.The method is based on Taylor's theorem for immiscible fluids, i.e., that a suspended drop of liquid A in liquid matrix B is deformed in shear or elongational flow in proportion to the ratio of interfacial to viscous stresses. Taylor's theorem, as originally derived, applies to low concentrations, Newtonian fluids and small deformations. Thus, the theorem was modified to account for “Power Law” fluids in elongational flow and large deformations, more applicable to the system under investigation.The elongational viscosities of the LCP and the flexible polymer (polycarbonate) as a function of elongational rate were determined using converging type flow. The two polymers exhibited a Power‐Law behavior in elongational flow and, hence, the experimental constitutive equations of state were used to quantify the viscous stresses.The interfacial stresses were modified for large deformations by taking into consideration the deformed shape and hence increased surface area of the elongated LCP particle. Using the modified expression, the interfacial tension of LCP and PC was determined to be in the range of 5–6.
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