Application of large double-step shear strains to analyze deformation and shape recovery of a polymer droplet in an immiscible polymer matrix

摘要

The deformation and shape recovery of a soft polymer droplet in an immiscible polymer matrix with higher viscosity were directly observed from two directions after application of large double-step shear strains. After application of the first-step strain γ_1 (|γ_1| = 5), the deformed droplet changes its shape, starting from a flat ellipsoid to a rodlike shape then to a dumbbell, an ellipsoid of revolution, and finally back to a sphere. When a large second-step strain γ_2 is applied in the same or opposite direction to the first strain during the recovery, the shape of the droplet and the orientation angle depend on both γ_2 and the shape during the recovery. Just after application of γ_2 (0 < γ_2 ≦ 5) in the opposite direction to the first strain γ_1(=-5), the droplet having a rod-like or dumbbell shape significantly deforms at both ends and stretches more than expected from the assumption of affine deformation. The deformed droplet under strain γ_2 has two orientation angles, θ_1 and θ_2, to the shear direction. The main angle θ_1 of the inclined droplet is equal to the angle given by the total strain γ_1 + γ_2, i.e., cot2θ_1 = (γ_1 + γ_2)/2. On the other hand, another angle θ_2 observed at both ends of the deformed droplet, is close to the angle given only by γ_2, i.e., cot2θ_2 = γ_2/2. This difference in the orientation angle suggests a faster recovery at both ends and a slower recovery (remaining effects of the first strain) in the central part.