In today’s Academic Minute, Dr. Rafael Verduzco of Rice University explains the development of a new silicone material that becomes stronger with repeated use.
Rafael Verduzco is the Louis Owen Assistant Professor in the Department of Chemical and Biomolecular Engineering at Rice University in Houston, Texas. His laboratory carries out research involving polymers, with the specific goal of utilizing the self-assembly in polymeric materials to improve organic solar cells, engineering surface properties, and drug encapsulation and delivery. He holds a Ph.D. in chemical engineering from the California Institute of Technology.
Dr. Rafael Verduzco, Rice University – Stiffening Silicone
Biological tissues are remarkable because they become stronger when you stretch, compress, and deform them. For example, muscles increase in strength when we lift weights, and bones become tougher when supporting weight. We see the opposite behavior in man-made materials, most of which become weaker and eventually fail; think of a rubber band that snaps when you pull it too far or a concrete structure that breaks down over time. Recently, engineers found a new type of elastic material – or elastomer - that can actually become stronger when stretched. Similar to biological tissue, the elastomer only becomes stronger when it is stretched or compressed repeatedly. One sample studied doubled in stiffness after 600,000 cycles of compression over the course of 16 hours. The engineers termed this phenomena “self-stiffening” since the material becomes tougher by itself when stretched or pressed.
Rubber bands or elastomers are made up of tiny spring-like molecules known as polymers, and when we stretch a rubber band we are literally stretching and deforming these individual molecules. What’s unique about “self-stiffening” elastomers is that they contain liquid crystals – the same molecules used in flat panel displays. It may sound strange to add liquid crystals to rubber bands, but there’s good reason to do so. Liquid crystals interact with light in useful ways and they are very sensitive to electricity and temperature changes. By adding liquid crystals to elastomers, engineers found that the spring-like molecules were now like magnets that all want line up in the same direction. By repeatedly compressing the material, the molecules fall into place and end up pointing in the same direction, making the elastic material much tougher. What’s more, this stiffening effect can be erased by simply heating the material. With these “self-stiffening” materials, engineers are now closer to bio-mimetic materials that can get stronger with time, like the bones and muscles in our bodies.