Many consumer products, such as clothes and food packaging, are made of blends of polymers, long molecules consisting of repeating chemical units. The attractiveness of using blends of different polymers arises from the engineers’ desire to combine multiple unique properties of each individual polymer, such as transparency, stretchability, and breathability, into a seamless whole. However, different polymers are not necessarily miscible, a term scientists use to describe whether two materials mix at the molecular level. Miscibility isn’t a one-and-done kind of deal: scientists and engineers have known for years how to make polymer blends mix by careful temperature control. What if there were conditions other than temperature to achieve polymer blend miscibility? This may ultimately help in industrial processing of polymer blends. In this week’s paper, Professors Annika Kriisa and Connie B. Roth from Emory University in Atlanta, Georgia, explore the mixing dynamics of two polymers by using a strong electric field.
When an experiment doesn’t behave the way we expect, either our understanding of the relevant physics is flawed, or the phenomenon is more complicated than it appears. When a theoretical prediction is off by two orders of magnitude – like what was observed in this recent paper by Hua Yung Lo, Yuan Liu, and Lei Xu of the Chinese University of Hong Kong – something is seriously wrong.
Scientists often draw inspiration from biological organisms to describe phenomena, even when they are studying outside the realm of biology. Physicist Pierre-Gilles de Gennes was no exception. In 1971, after being inspired by the movement of snakes, he proposed reptation theory, or the reptation model, which has since been widely used to describe motions of polymers. As the name “reptation” suggests, de Gennes assumed polymer chains move like snakes. As shown in Figure 1, the model describes a polymer chain’s motion in an environment that is highly populated by other chains (shown in gray) by assuming that the chain is confined in a virtual tube (shown in red) formed by surrounding polymer chains. According to reptation theory, the chain wiggles through this tube, similar to a snake slithering through the woods. As one might imagine, directly imaging the snake-like slithering of polymers is a challenging affair; however, in today’s study, Maram Abadi and coworkers from King Abdullah University of Science and Technology were able to do just that with DNA chains – an example of a polymer – and compared their results to prevailing theory.