Researchers Find Simple Formula to Calculate Surface Tension of Polymer Melts

Throwing polymer chains of various lengths into a mix can produce surprising results better than playing with Legos. In a new research published in EPJ E, Physicists study how mixing chemically identical chains into a melt yields unique effects on their surface. This is due to how long and short polymer chains interact with each other.

In these types of melts, polymer chain ends, over time, have a preference for the surface. Now, Mark Matsen and Pendar Mahmoudi from the University of Waterloo, Ontario, Canada, have explored the effects of improving long-chain polymer melts with short-chain polymers. They carried out numerical simulations in order to explain the reduced tension on the surface of the melts, because of short chains segregating at the surface eventually as disorder grows in the melt. The Researchers found a simple formula to calculate the surface tension of these melts, linked to the relative weight of their components.

The Authors of this study model individual polymers as a bead-spring model connecting a series of monomers attached by freely-jointed bonds. After that, they use a theory called self-consistent field theory (SCFT), which assists in modeling what takes place on the surface of the polymer melt. The Authors also model the surplus concentration of short polymers merged with the effect on the surface tension with regard to disorder energy.

Then, the Authors compare their simulation with estimated equations. They deduct a simple mathematical formula that describes the interfacial tension between immiscible long- and short-chain polymers as a function of the polymers’ molecular weight in the mix. Additionally, they find that the molecular weight also influences the segregation level between long- and long-chain polymers.