Lots of materials that you use every day, like the tires on your car, super-absorbent polymers in a baby-diaper, are made of polymer networks. These networks are like nets made of molecular chains that are connected points known as cross-links. Ideally, we imagine these networks are perfect like this network made of black strings. But in reality, networks contain various types of defects, like loops represented by these red rubber bands for the chains doesn’t connected to separate junctions, or like double bridges represented by these blue rubber bands where two different chains connect to the same crosslink points. These different types of defect weakened the network.
Until recently there was no way to count these defects in polymer networks. So we did not really understand how the impact the properties of our materials. However, our team recently developed a family known as network disassemly spectrometry that enables us to count the number of loops represented here by the red rubber bands. Using new data from the method, we were able to validate new computational method that count not only the loops but also the double bridges and all types of higher order of defects as well such as this one. Now that we know the number of defects in a polymer network, we can try to calculate their impact on the properties of the materials. In our science article we measure the moduli of several polymer networks and counted the number of the loops in the same network for the first time which allows us to quantify how the network defects affect mechanical properties. Despite accounting for the defects, we found the existing models did not match the properties of polymer networks. Therefore, we developed a new theory known as the real elastic network theory that can quantitatively predict the modulus of a polymer network.
This theory is based on the phantom polymer network theory which calculates the modulus of the network by assuming that each chain is connected to the network in an ideal tree-like structure like this model of rubber bands. When you stretch the rubber-like [没听清] tire, you stretch individual molecules like the rubber band in the center of the model. The challenges are that when the network has defects each of chains stretches by a different amount. For example, here is a model of the loop in the network structure. When you stretch the network, the rubber band in the loop and the connecting chains do not strtch at all, so they do not contribute to the modulus of the network. This weaken the network. The same is true when two chains connect the same two crosslinks. In this rubber band model, you see that the chains in the center deform very little because the connection is stiff. This also leads to a weakening of the network. Using [疑似 experiment] computation, we counted the number of defects in our polymer network and we applied our theory [没听清] to calculate quantitatively how these defects affect the network properties. This gives us the ability to design networks better than before, which should have a large impact on industries such as biomedical materials, consumer products, and car tires.