Di-block Ring Polymers as Topological Adhesives at Immiscible Polymer Interfaces

Disparate polymers often do not mix well, and the resulting immiscible interfaces are mechanically weaker than the bulk. Large-scale molecular simulations are performed to study the effectiveness of di-block ring polymers in enhancing the adhesive strength at an immiscible polymer interface. A simulation protocol mimicking the lap joint shear test is used. The shear stress σ as a function of the shear strain γ is calculated for the sandwich system consisting of immiscible linear chains of types A and B and a middle layer of di-block AB rings. The peak stress σ_p and the corresponding failure strain γ_p increase with the block length and the areal density of di-block rings when the rings are not too crowded to expel the linear chains. σ_p and γ_p that are comparable with the respective values for the bulk polymers are observed. Breaking the AB rings into pairs of AB linear chains creates a reference sandwich system for comparison. The simulations show that the AB rings raise both σ_p and γ_p remarkably more than the corresponding AB linear chains. Furthermore, Gauss linking number is employed to quantify the topology at the immiscible interface. The topological analysis demonstrates that the threading of the AB rings by linear chains from the two opposite sides, which resembles the hook-and-loop process in Velcro tapes, is the key mechanism for the stronger interfacial adhesion due to the di-block rings.