Crystallization in Micellar Cores: confinement effects and dynamics

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Here we demonstrate that n-alkanes forming 2-3 nm small micellar cores are considerably affected by confinement in analogue with hard confined systems. We study micelles form by self-assembly of a series of well-defined n-Alkyl-PEO polymers in aqueous solutions [1]. By using small-angle X-ray scattering (SAXS), densiometry and differential scanning calorimetry (DSC), we show that n-alkane exhibit a first-order phase transition i.e. melting. Correlating the structural and thermodynamic data, we find that a melting depression can be accurately described by the Gibbs-Thomson equation [2]. $\backslash $f1 The effect of core crystallinity on the molecular exchange kinetics is investigated using time-resolved small-angle neutron scattering (TR-SANS) [3-6]. We show that there are considerable entropic and enthalpic contributions from the chain packing that affect the kinetic stability of micelles. [7]$\backslash $pard[1] T. Zinn \textit{et al}., \textit{Soft Matter}, 2014, \textbf{10}, 5212.$\backslash $pard[2] T. Zinn, L. Willner and R. Lund, \textit{Phys. Rev. Lett.} \textbf{113} (2014) 238305.3] R. Lund, L. Willner, D. Richter, \textit{Adv. Polym. Sci.} \textbf{204} (2013) 51.5] R. Lund\textit{ et al}. Phys. Rev. Lett., 2006, 96, 068302.6] S.-H. Choi \textit{et al}. \textit{Phys. Rev. Lett.} 104 (2010) 1.7] T. Zinn, L. Willner, V. Pipich, D. Richter and R. Lund, \textit{ACS Macro Lett.}, 2015, \textbf{4}, 651--655.