On perpendicular and tilted chains in lamellar crystals

DE SILVA, D. S. M., ZENG, X. B., UNGAR, G. and SPELLS, S. J. (2002). On perpendicular and tilted chains in lamellar crystals. Journal of macromolecular science-physics,, B42 (3-4), 915-927.

Full text not available from this repository.
Link to published version:: https://doi.org/10.1081/MB-120021615


Small-angle X-ray scattering (SAXS) and infrared spectroscopy (IR) are employed in a study of chain tilt and disorder in solution-crystallized long alkanes C198H398 and C12D25C192H384C12HD24 in extended and once-folded conformations. The as-grown crystals have chains perpendicular to the lamellar surface, but around 90 °C they start tilting relative to the layer normal. The tilt increases gradually to reach 35° just below melting point. The end-labeled alkane allows independent IR probing of molecular disorder at the deuterated surface layer and in the hydrogenous interior of the crystals. The initially small splitting of the CD2 bending mode doublet and the presence of a singlet component indicated a rough surface in as-grown crystals, with considerable translational disorder. The increase in splitting and decrease in absorbance of the singlet which occur on annealing at progressively higher temperatures showed a steady improvement in translational surface order, oncomitant with an increase in chain tilt angle. Thus, it is concluded that the absence of tilt in as-grown crystals is not due to high surface order, as in the case of shorter odd n-alkanes, but rather to high nonequilibrium surface disorder with chain ends or folds protruding out of or sunk beneath the surface. It is also concluded that chain tilt only becomes necessary as the crystal surface becomes translationally more ordered and the crystal-amorphous interface sharpens. IR also demonstrated the reversible increase in conformational disorder in the surface layer with increasing temperature and an almost negligible increase in the crystal interior. The gradual change in tilt angle and the existence of noncrystallographic basal planes is interpreted in terms of translational molecular disorder at the surface. The increased central SAXS scatter during the tilting process indicates the creation of voids associated with ridge formation and corrugation of the lamellae.

Item Type: Article
Additional Information: © Informa plc
Research Institute, Centre or Group - Does NOT include content added after October 2018: Materials and Engineering Research Institute > Advanced Coatings and Composites Research Centre > Polymers, Composites and Spectroscopy Group
Identification Number: https://doi.org/10.1081/MB-120021615
Page Range: 915-927
Depositing User: Ann Betterton
Date Deposited: 16 Aug 2007
Last Modified: 19 Mar 2021 01:00
URI: https://shura.shu.ac.uk/id/eprint/942

Actions (login required)

View Item View Item


Downloads per month over past year

View more statistics