Computer Simulations of Soft Responsive Gels with Embedded Regular Arrangements of Stiff Fibers

Designing polymeric composites that enhance the material's resilience and mechanical properties is vital in the production of such technologically important systems as aeronautic components, biomimetic architectures and thin film displays. Taking advantage of the rich deformation behavior exhibited by regular, geometric arrangements of stiff fibers, we used computer simulations to analyze the properties of composites formed by embedding a layer of fibers, arrayed into rectangular, hourglass and honeycomb structures, into the middle of a thicker hydrogel. We determined how the geometry of fiber layer affected the composite's resistance to finite deformations and changes in shape. Our computer simulations revealed cooperative interactions between the embedded stiff fibers and the gel matrix that led to mechanical reinforcement under both small and finite shear and tensile deformations, and to shape changes under finite tensile deformations. The latter effects depended on a mismatch between the Poisson's ratio of the gel matrix and fiber geometry of the fiber layer. When the Poisson's ratio for the fiber layer and the gel were both positive and comparable in value, the composite did not undergo significant shape change, as evidenced in the case involving the rectangular fiber arrangement. The computer simulations showed that for particular fiber arrangements (hourglass and honeycomb), the composite could exhibit the auxetic behavior (negative Poisson's ratio) in one or two directions. Our results yield design rules for enhancing the resilience and mechanical properties of the polymer matrices and thus yield superior composites for technological applications.