Copolymer-Like Structures of Nematic Nitroimine Dimers.
Abstract
A series of nitroimine, Siamese-twin dimers joined by an aliphatic chain with n = 2 to 10 were examined by DSC, microscopy, and x-ray diffraction. All dimers except the one having n = 3 undergo transitions to a nematic mesophase without exhibiting distinct relationships. The N-I transitions, in contrast, exhibit a very pronounced alternation with even numbered spacers having much higher clearing temperatures. Magnetically aligned monodomains of the nematic mesophase were examined by x-ray diffraction. In addition to the broad equatorial arcs (yielding interchain separations 1.5 to 5.7A), up to eight aperiodically spaced meridional reflections were recorded. By positing two possible 'coupling' modes in which either one or both phenyl rings in neighboring dimers overlap, a linear array of coupled nitroimine dimers having two repeating distances along its length is produced. Using such a copolymer- like model, the spacings of the aperiodic meridional reflections and their relative intensities could be reproduced for a random sequence of the two repeat distances and an equal (50:50) probability of single or double overlapped phenyl rings. Keywords: Liquid crystals; Copolymers.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 29, 1990
- Accession Number
- ADA217574
Entities
People
- Agya R. Saini
- Anselm C. Griffin
- Jack M. Gromek
- L. V. Azaroff
Organizations
- University of Connecticut