In this work we study the crystallization of n-alkane confined in small micellar cores formed by a series of well-defined n-Alkyl-PEO (CnH2n+1-PEO5 with n = 21,24,27,28) polymers in water. By using a range of techniques including small-angle X-ray scattering (SAXS), densiometry [1] and differential scanning calorimetry (DSC) we show that n-alkane crystallizes within the core microdomains.
By varying the temperature we find a discontinuity in the scattering behaviour at high Q with SAXS. We show that this discontinuity can be attributed to a change in contrast. The specific volume confirms the latter by exhibiting a jump at the same temperature. From both results a first-order phase transition is suggested. Hence due to crystallization the specific heat capacity (Cp) shows a clear peak and thus put forward an order-disorder phase transition that can be associated to the melting of the n-alkanes. Interestingly, the melting points are very much reduced with respect to those of the pure n-alkane.
In the presentation we will further discuss the relation between crystallization versus recently observed exchange kinetics revealed by time-resolved small-angle neutron scattering (TR-SANS) [2,3].
References:
[1] C. Sommer; et al., J. Phys. Chem. B 2004, 108, 6242-6249.
[2] T. Zinn; et al., Soft Matter 2012, 8, 623-626.
[3] R. Lund; et al., Adv. Polym. Sci. 2013.
tzinn@kjemi.uio.no
