Shearing of Polymer Drops with Interface Modification

Nonequilibrium Behaviors of Entangled Diblock Copolymers at the Entangled Polymer-Polymer Interface under Steady Shear Flow

The slip phenomena and the individual configuration dynamics of interfacial copolymer chains in the entangled polymer-polymer interface under fast shear flow are analyzed using mDPD simulations on ternary blends of A125/B125/C125D125 with different incompatibilities or interface strengths. We observe two distinct power-law regions of slip velocity against interfacial shear stress: from Vs ∼ σ5 to Vs ∼ σ1 at an increasing shear rate with the interface strength. At the micro level, the two regions correspond to the integrated and incomplete interfacial entanglement network with the shear-induced disentanglement of interfacial chains, respectively. For the individual chain dynamics of interfacial copolymers, we clarify that for the weak incompatibility, the tumbling event of interfacial copolymer chains is irregular and occasional and includes six processes: align and flip, collapse, tumble, stretch, reflip, and recoil and tumble. For the system with strong incompatibility, the interfacial copolymer chain undergoes the stretched-coil conformational transition via elastic retraction. As the interfacial entanglement network disintegrates, the hairpin-like configuration is dominant during the tumbling motion or elastic retraction of the interfacial copolymer chain.

Molecular dynamics study of the effect of surfactants on droplet deformation in shear flows

We use molecular dynamics simulations to study the effect of surfactants on the mechanism of drop deformation in shear flows. Our results show deviations from fluid mechanics predictions, in both the high and the low surfactant concentration limits. We find that these deviations are a result of the local conformation of the surfactant layer which mediates the stress transfer across the interface. We show that the ability of the surfactant to affect the stress transfer across the interface is a result of the interplay between the architecture of the surfactant and the surface coverage.