J. Phys. II France
Volume 6, Numéro 1, January 1996
Page(s) 77 - 89
DOI: 10.1051/jp2:1996168
J. Phys. II France 6 (1996) 77-89

An X-Ray Study of a Smectic C and Smectic A Liquid Crystal Polyacrylate

O. Francescangeli1, D. Rinaldi1, M. Laus2, G. Galli3 and B. Gallot4

1  Dipartimento di Scienze dei Materiali e della Terra, Università di Ancona, Via Brecce Bianche, 60131 Ancona, Italy and Istituto Nazionale di Fisica della Materia
2  Dipartimento di Chimica Industriale e dei Materiali, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
3  Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy
4  Laboratoire des Matériaux Organiques, CNRS, BP 24, 69390 Vernaison, France

(Received 7 June 1995, revised 4 September 1995, accepted 25 September 1995)

An X-ray study was performed on powder specimens and on stretched oriented fibres of a smectic polyacrylate. The X-ray diffraction patterns showed the existence of monolayer smectic A and bilayer smectic C mesophases that coexisted over a well defined range of temperature. In the latter mesophase the mesogenic groups were titled with respect to the smectic layer normal by an angle $\beta\approx 30^\circ$. The electron density profile $\rho(z)$ along the direction normal to the smectic layers in the smectic C mesophase was determined by Fourier inversion and indicated the presence of a minor interdigitation of the terminal substituents. The phase problem related to the Fourier inversion was solved by using a pattern recognition approach based on the histogram of the electron density map. The positional smectic layer order parameters were also calculated for the first five harmonics of the positional distribution function of the smectic layers and their values suggested a well ordered layer structure.

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