On the role of topology and micro-structure on the adhesion and fracture of soft materials

With recent progress in characterization, synthesis and manufacturing techniques, soft materials are playing an increasingly important role in many emerging technologies in different fields, such as biomedical, industrial, and electric engineering fields. In many of these applications, the performance of soft materials is largely limited by their strength and toughness, either in the bulk or at the interface. Thus, the adhesion and fracture properties of soft materials have been the main focus of many experimental and theoretical studies. In this research, we focus on the effects of the macro and micro scale topology on the adhesion and fracture of soft materials. We start by investigating the possibility of manipulating interfacial adhesion by patterning geometric and structural features in the bulk. Inspired by the natural example of mussel adhesion, we show that even for planar homogeneous interfaces, topological design of the bulk may lead to enhancement of the interfacial adhesion properties. We demonstrate this by showing examples of bulk patterned voids and distributed sacrificial cuts. We also show that by manipulating the topology, it is possible to realize peeling adhesion asymmetry such that the force required to peel a strip is significantly dependent on the peeling direction. We then study the role of the microstructure of soft materials on their fracture properties. Most of the existing methodologies for investigating damage and fracture in soft materials adapt continuum approaches, which may lead to the negligence of essential microscale features in the vicinity of propagating cracks or may require information on the fracture energy or material length scales which are difficult to measure. On the other hand, it is computationally prohibitive to adopt fully discrete approaches to capture the local topology effects for large samples. To address this challenge, we develop a novel numerical approach for simulating fracture in polymer networks, the building blocks for many natural and artificial soft materials, using an extended version of the Quasicontinuum (QC) method. Explicit representation of the polymer chains is retained in regions of high interest, in the vicinity of cracks for example. Away from the imperfections, the network structure is computationally homogenized and only a fraction of the network nodes is solved. Dynamic mesh adaptivity enables transition between the two representations. The method enables accurate modeling of crack initiation and propagation without apriori constraint on the fracture energy. The accuracy and computational efficiency of the method are demonstrated by applying it to study the fracture of large-scale networks with and without rate dependent effects