Phase transitions and orientational ordering of polymer liquid crystals

Thesis/Dissertation · Thu Dec 31 04:00:00 EST 1992

OSTI ID:111320

Yang, Shi-Jun

The Onsager virial approximation for the isotropic-nematic transition of thin rodlike particles is extended to semiflexible polymers and liquid crystal density. Theories for the orientational entropy and excluded volume interaction for persistent chain polymers at intermediate degree of chain flexibility were utilized for liquid like densities. The results is shown to satisfactorily account for experimental data on the volume fractions of polymer at the coexistence of isotropic and anisotropic phases, the concentration dependence of the order parameter within the lyotropic liquid crystal, and the osmotic pressure equation of state for several extended chain polymers. A downhill simplex algorithm was used for solving multi-dimensional nonlinear equations. Orientational ordering of polymer liquid crystal solution was also experimentally studied using FTIR and deuterium NMR in this thesis. Concentration and molecular weight dependence of nematic order parameters of poly-{gamma}-benzyl-l-glutamate (PBLG) was determined by measuring the dichroic ratio of amide A band which is the N-H stretching vibration in the peptide group. The samples with molecular weight of 51,000, 125,000, and 238,000, dissolved in 1,1,2 trichloroethane, were used for orientational studies. Solvent dependence of the order parameter was studied by measuring quadrupolar splitting from deuterium labelled PBLG (backbone labelled) using solid state deuterium nuclear magnetic resonance and the persistent chain effect on polymer liquid crystal orientation was reported. The determining effects of molecular weight, concentration, and persistent length on orientational ordering of lyotropic liquid crystal were discussed. the experimental results are compared with the extended density theory and other theories.

• Research Organization: Louisville Univ., KY (United States)
• OSTI ID: 111320
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
LIQUID CRYSTALS
NMR SPECTRA
ORIENTATION
PHASE TRANSFORMATIONS
POLYMERS