Entropic segregation of short polymers to the surface of a polydisperse melt

• Published in: The European physical journal. E, Soft matter and biological physics Soft matter and biological physics, 2017-10, Vol.40 (10), p.85-9, Article 85
• Main Authors: Mahmoudi, P., Matsen, M. W.
• Format: Article
• Language: English
• Subjects: Biological and Medical Physics; Biophysics; Bonded joints; Chemical bonds; Complex Fluids and Microfluidics; Complex Systems; Condensed matter physics; Field theory; Mathematical models; Monomers; Nanotechnology; Physics; Physics and Astronomy; Polymer melts; Polymer Sciences; Polymers; Regular Article; Soft and Granular Matter; Surface tension; Surfaces and Interfaces; Thin Films
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2017-11575-7

. 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 ξ . Semi-analytical expressions for the excess concentration of short polymers, δ ϕ s ( z ) , the integrated excess, θ s , and the entropic effect on the surface tension, γ e n , 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 ξ ≳ 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. Graphical abstract