Dynamic interfacial properties between a flexible‐chain polymer and a thermotropic liquid crystalline polymer investigated by an ellipsoidal drop retraction method

Abstract

ABSTRACT:In this study, the dynamic interfacial properties between an isotropic polymer and a thermotropic liquid crystalline polymer (TLCP) were investigated by measuring the time-dependent interfacial tension between them. As a TLCP drop retracts in a flexible polymer matrix, the evolution of its shape is recorded by microscopy. By fitting the ellipsoidal model of Maffettone and Minale, the model of Marrucci and Santo, and large deformation ellipsoidal models by Jackson-Tucker and Yu-Bousmina, the interfacial tension could then be determined. It was found that the retraction of a TLCP ellipsoidal drop in a flexible polymer cannot be described by these models as accurately as in Newtonian systems. The apparent interfacial tension obtained from these models evolves with time; the evolution is ascribed to the slow relaxation of domain orientation within the TLCP drop.

Interfacial forces and Marangoni flow on a nematic drop retracting in an isotropic fluid

“…Since the drop is elliptic, the initial n field deviates from the easy direction over much of the interface in both cases. The calculations are in 2D, but we expect the physical insights gained here to be relevant both to the sharp-interface theory [13] and to 3D experiments [19,20]. Fig.…”

“…Then the drop begins to retract under the action of interfacial tension. This roughly represents the drop retraction experiments that start by melting a short LCP fiber sandwiched between layers of a flexible polymer (e.g., [20]). We assume that the fluids are highly viscous and the retraction is slow so that inertia is negligible.…”

“…Experimentally, Yu et al [20] found that the retraction of a thermotropic LCP drop deviates from the exponential law in Eq. (11).…”

“…Unfortunately, this could not be determined for the thermotropic LCP drops in Ref. [20]. Visualizations on a drop of a different LCP indicate that this is indeed the case [32].…”

“…Second, this problem is relevant to using drop retraction as a means to measure interfacial tension between the two components [17,18]. Thus, there are experimental observations [19,20] with which our results can be compared. We will confine our discussion to nematic drops in a Newtonian matrix.…”