Fibrous and crystal structures of a helical polymer, poly-L-lactic acid (PLLA), were analyzed by using x-ray diffraction experiments. It was confirmed that the molecular residues were arranged on a nonintegral 10/3 helix as De Santis and Kovacs [Biopolymers 6, 299 (1968)] reported. The atomic positions in a monomeric unit, which were proposed by Hoogsteen, Postema, Pennings, ten Brinke, and Zugenmaier [Macromolecules 23, 634 (1990)], were validated. However, the previous reports on the positions of the two helical chains were found to be in error. The correct positions were determined. The second helical chain shifts from the base center by 0.45, 0.25, and 0.61 Å along a, b, and c axes. Besides, the second chain rotates by 2.46° with respect to the first. Distribution function of the crystallites in various drawn fibers were determined as a function of spiral angle. Optical gyrations of PLLA and poly-D-lactic acid fibers were successfully measured by using high accuracy universal polarimeter, as functions of temperature and drawing ratio. By using x-ray data of the change of the fibrous structure by drawing treatments, the gyration tensor components of PLLA could be calculated. It is of great interest that gyration tensor component g33 along the helical axis is extremely large, ∼(3.85±0.69)×10−2, which corresponds to a rotatory power of (9.2±1.7)×103°/mm, about two orders of magnitude larger than those of ordinary crystals. This is the first experimental evidence that helical polymers will produce enormous optical activity in the solid state. Helical polymers will be important for the elucidation of gyro-optical properties of solids and promising for new optical applications utilizing their large optical activity.
The domain switching of ferroelectric triglycine sulfuric acid and Rochelle salt was studied by observing optical gyration along the ferroelectric axes and measuring rotation of the indicatrices around the same axes. It was established experimentally that the antipolar domains of triglycine sulfuric acid were united by a symmetric twin mechanism and those of Rochelle salt by a hemitrope (rotation twin). It was shown that the high-accuracy universal polarimeter method can become a new general method for distinguishing the twinning mechanism of the ferroelectric domains.
Abstract X-ray dilatometric measurements were made on lattice strains of KH2PO4 and KD2PO4 as a function of temperature and biasing electric field near the Curie point. The electrostriction contained in the lattice strains x1, x2 along the a-and b-axes cannot be explained in terms of the ordinary electrostrictive effect. In order to interpret these new effects, the phenomenological theory of improper ferroelectrics has been successfully applied. The difference of the transition mechanism between KH2PO4 and KD2PO4 is discussed from the same viewpoint of improper ferroelectrics.
By applying the HAUP (high-accuracy universal polarimeter) method, [N(CH3)4]2CuCl4 was found to be optically active in its incommensurate phase, e.g., g23=3.9×10−5 at 24 °C. The temperature dependence of g23 was obtained. By making use of the fact that the commensurate phase of [N(CH3)4]2CuCl4 is ferroelastic and centrosymmetric, the temperature dependence of the soliton density in its incommensurate phase was deduced by this optical measurement. It is suggested that the HAUP method will become a new and direct method for measuring soliton densities of incommensurate states.
Abstract The optical activity of DOBAMBC was successfully measured by using the high accuracy universal polarimeter. It is revealed that the smectic A phase is optical active. Temperature dependence of the gyration and electrogyration coefficients in the smectic C phase are also measured.
Abstract Effects of the electric field on the structure of incommensurate phases of [N(CH3)4]2 ZnCl4, [N(CH3)4]2coCl4, [N(CH3)4]2FeCl4 and [N(CH3)4]2CuCl4 were studied by using x-rays. It was clearly observed that the commensurate domains never reflect x-rays in the whole temperature range of the incommensurate phases when the electric field was not applied. As to the response to the electric fields, the crystals could be classified into two types; the one type contains [N(CH3)4]2ZnCl4, [N(CH3)4]2CoCl4 and [N(CH3)4]2FeCl4 where the reflections from the domains coexisted with those from the incommensurate modulation, and the other does [N(CH3)4]2CuCl4 where the reflections do not take place from the domains. These phenomena reflect the change of the crystal texture by the application of the electric fields. The interpretations of these phenomena are given briefly.
