Study of Microphase Separation in Solid, Binary Alkane Mixtures by Small Angle Neutron and X-ray Scattering

A combination of small angle neutron (SANS) and small angle X-ray scattering (SAXS) is used to study phase separation following crystallization in 1:1 mixtures of n -C 30 H 62 / n -C 36 D 74 quenched from the melt to room temperature. The SAXS data show that the quenched mixture is a solid solution with a well-defined lamellar structure which is established on a time scale of minutes after quenching from the melt. On this initial time scale the SANS data indicate that the deuterated and protonated chains remain essentially randomly mixed. At longer times the scattering curves from both techniques show features consistent with phase separation in the form of nonrandom stacking of lamellae that are alternately enriched in one of the components. The possible effect on the neutron scattering of lateral intralamellar phase separation appears to be overwhelmed by this interlamellar phase separated structure.