Volume 34, Number 7, June I 1996
|Page(s)||501 - 506|
|Section||Condensed matter: structure, thermal and mechanical properties|
|Published online||01 September 2002|
Pressure-induced stabilization of the smectic A* phase in a chiral polyacrylate
Dipartimento di Scienze dei Materiali e della Terra,
Università di Ancona Via Brecce Bianche, I-60131, Ancona, Italy
Istituto Nazionale per la Fisica della Materia - Ancona, Italy
2 European Synchrotron Radiation Facility - BP 220, F-38043 Grenoble Cedex, France
Accepted: 11 April 1996
The pressure-temperature phase diagram of a chiral liquid crystal polyacrylate has been studied in situ by X-ray diffraction. Hydrostatic pressures of the order of 100–200 MPa strongly influence the polymorphic behaviour of the sample. The smectic A* mesophase, which at ambient pressure coexists with an interdigitated smectic C* structure, is stabilized over a temperature range which increases with pressure. The formation of the smectic C* phase is inhibited at 220 MPa and occurs only upon the first heating process at 133 MPa. A transition sequence from the isotropic melt through the smectic A* phase to a new crystalline structure is found by cooling isobarically down to room temperature. The proposed phase diagram suggests the occurrence of peculiar disorder-order-disorder transitions as pressure is reduced isothermally.
PACS: 61.30.Eb – Experimental determinations of smectic, nematic, cholesteric, and lyotropic structures / 61.10.Lx – Experimental diffraction and scattering techniques (including small-angle scattering, EXAFS, NEXAFS, and XANES)
© EDP Sciences, 1996
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