1991 Fiscal Year Final Research Report Summary
Molecular mechanisms of structural phase transitions in smectic liquid crystals
| Project/Area Number |
01550012
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied materials
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| Research Institution | Nagoya University |
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Principal Investigator |
KIMURA Hatsuo Nagoya University, School of Engineering, Professor, 工学部, 教授 (60023032)
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| Project Period (FY) |
1989 – 1991
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| Keywords | Phase transition in hard rods / Excluded volume effect / Effect of molecular attractions / Smectic A phase / Hexagonal columnar phase / Haxagonal crystal phase / 3rd virial approximation / Layer compression modulus |
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| Research Abstract |
The free energy of the smectic A phase, the hexagonal columnar phase and a crystalline phase in a system of perfectly aligned hard cylinders with length L and diameter D is calculated up to the 3rd virial terms as a function of the order parameters.
1. Assuming only hard core repulsive force between molecules, the following results are obtained. (1)The system exhibits the second order nematic to smectic A lyotropic phase transition at a packing fraction eta = eta_c = 0.355 where the smectic layer spacing is d = d_c = 1.35L. (2)Further increasing the density, at eta = 0.39 the smectic A to crystalline phase transition of the first order occurs. The crystalline phase has a hexagonal structure with the lattice parameters a <similar or equal> 1.35D and c <similar or equal>= 1.26L and exists together with the smectic A phase for 0.39 < eta < 0.53. The crystalline phase is the most stable state for eta > 0.53. (3)The hexagonal columnar phase is shown to be more stable than the snematic phase for eta > 0.47 and than the smectic A phase for eta > 0.78, but always less stable than the crystalline phase. These results show that the excluded volume effect due to the hard core repulsion plays the essentially important role to form the smectic A liquid crystalline order.
2. Incorporating ah attractive potential, the system is shown to exhibit the second order thermotropic transition between the snematic and smectic A phases at a temperature T_c even though eta < eta_c. Molecular theoretical expressions of the transition temperature T_c, the layer spacing d and the layer compression modulus B for the smectic A phase are given.
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