Electron crystallography of the polymethylene chain. 2. The lamellar interface of n-paraffin solid solutions 1

Electron diffraction measurements were made on a series of binary solid solutions formed from n -C 24 H 50 and n -C 26 H 54 . When the longer chain is most dilute, crystal structure analyses favor a mixed-chain packing arrangement, based on an average n -C 25 H 52 layer, a model that can incorporate the chain-end conformational disorder measured by vibrational spectroscopy. Published x-ray data from a 3:1 binary combination can also be interpreted to support this model. The alternative view, requiring an all- trans chain with methyl groups from the longer chain component protruding into the lamellar interface, is neither consistent with the spectroscopic measurements nor with independent measurements of lamellar surface flatness.