Abstract.
Chain ends are known to have an entropic preference for the surface of a polymer melt, which in turn is expected to cause the short chains of a polydisperse melt to segregate to the surface. Here, we examine this entropic segregation for a bidisperse melt of short and long polymers, using self-consistent field theory (SCFT). The individual polymers are modeled by discrete monomers connected by freely-jointed bonds of statistical length a , and the field is adjusted so as to produce a specified surface profile of width \(\xi\). Semi-analytical expressions for the excess concentration of short polymers, \(\delta\phi_{s}(z)\), the integrated excess, \(\theta_{s}\) , and the entropic effect on the surface tension, \(\gamma_{en}\), are derived and tested against the numerical SCFT. The expressions exhibit universal dependences on the molecular-weight distribution with model-dependent coefficients. In general, the coefficients have to be evaluated numerically, but they can be approximated analytically once \(\xi \gtrsim a\). We illustrate how this can be used to derive a simple expression for the interfacial tension between immiscible A- and B-type polydisperse homopolymers.
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Mahmoudi, P., Matsen, M.W. Entropic segregation of short polymers to the surface of a polydisperse melt. Eur. Phys. J. E 40, 85 (2017). https://doi.org/10.1140/epje/i2017-11575-7
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DOI: https://doi.org/10.1140/epje/i2017-11575-7