Nanoscopic confinement through self-assembly: Crystallization within micellar cores exhibits simple Gibbs-Thomson behavior

Abstract

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Less is known about liquids spontaneously confined through self-assembly into micellar structures. Here we demonstrate, using a very well-defined n-alkyl-poly(ethylene oxide) polymer system with a tunable structure, that n-alkane(s) forming 2–3 nm small micellar cores are affected considerably by confinement in the form of melting point depressions. Moreover, comparing the reduction in melting points, ΔTm, determined through volumetric and calorimetric methods with the micellar core radius, Rc, obtained from small-angle x-ray scattering, we find excellent agreement with the well-known Gibbs-Thomson equation, ΔTm∼R−1c. This demonstrates that the reduced size, i.e., the Laplace pressure, is the dominant parameter governing the melting point depression in micellar systems. © 2014 American Physical Society