Fraser P. Price

Precision recording dilatometer with results for cholesteryl nonanoate

A capillary dilatometer has been automated by means of a capacitive transducer technique. The precision is 1 : 105 over a range in volume of 4% for a sample volume of 2 ml. Differential scanning dilatometry is achieved by comparing the sample dilatometer with a reference dilatometer. Some results for the density changes associated with the liquid‐crystal transformations in cholesteryl nonanoate are presented.

The Structure of Mesophases of Cholesteryl Esters

Abstract The mesophases and the isotropic melt phase of several cholesteryl esters of saturated aliphatic acids have been studied by X-ray diffraction. The data are presented and briefly analyzed in terms of the angular position of the diffraction lines, their intensity, their integral width, and their shape. Both the cholesteric and the smectic phases are characterized by layerstructures with the long molecular axes perpendicular to the layers. Within the layers of the mesophases, the molecules are arranged anti-parallel to each other; the lateral order is nearly random. The isotropic phase is also characterized by groups of parallel molecules. Just above the temperature of transition into this phase, the molecules are still in their extended form.

Volumetric Behavior of Liquid Crystal N-p-Cyanobenzylidene-p-Octyloxyaniline

Abstract Using a differential dilatometer technique, we have measured the volume changes associated with the liquid crystal phase transitions in n-p-cyanobenzylidene-p-octyloxyaniline (CBOOA). A volume discontinuity is not observed at the smectic A to nematic transition, and we conclude that it is less than 10−5 ml/g. The volume behavior in a range ± 15[ddot]C about the nematic-isotropic transition has been studied. The critical exponent derived from this data is consistent with the mean field theory of the isotropic phase.

Volumetric pretransition in cholesterics

Volumetric studies of the phase transitions in the following cholesterol derivatives are reported: cholesteryl chloride, C. laurate, C. myristate, C. nonanoate, and C. oleate. Pretransition volumetric behavior in the smectic, cholesteric, and isotropic phases is interpreted in terms of a ’’critical’’ exponent. In the isotropic phase the data are consistent with the de Gennes–Landau theory. The transformation from the cholesteric focal conic texture to the ’’blue phase’’ has a transition enthalpy and volume of approximately 5% of the transition to the isotropic phase.

An X-ray Diffraction Study of Crystalline Cholesteryl Myristate and Cholesteryl Stearate

Abstract Powdered samples of the solid crystalline phase of cholesteryl myristate and stearate, crystallized at various temperatures from the melt and from solution, were studied by X-ray diffraction. The type and parameters of the unit cell were determined. The myristate and the stearate have monoclinic unit cells that are nearly identical except that the stearate has a larger c parameter. The structure has essentially no similarity to the corresponding structure in the mesophase. Temperature dependent measurements show that in a temperature range below the melting point imperfections are introduced. These imperfections are concentrated in directions perpendicular to the long axis of the molecules. This result is discussed in terms of the structure of the mesophase.

Orienting Effects of Substrates on Cholesteryl Esters

Abstract A given substrate favors a certain orientation of mesophase molecules at the substrate-mesophase interface. This favored orientation extends from the surface into the bulk of the mesophase, thus producing a certain thickness of uniform orientation. We selected five cholesteryl esters from the homologous series of aliphatic esters of cholesterol and studied the thicknesses of the uniformly oriented mesophases produced in fine glass capillaries. The inside walls of the capillaries were either bare glass or coated with thin films of various chemicals. The results show a wide variety in the thickness of uniform orientation depending upon the mesophase textures and the treatment of substrate surface.

X-Ray Diffraction Studies of the Solid Phases of Cholesteryl Acetate

Abstract The solid phases of cholesteryl acetate were studied by x-ray diffraction techniques. The data were analyzed in terms of the angular position of the reflections, their intensity, and their integral width. The unit cell is monoclinic with the parameters a, b, c, and β respectively equal to 10.00 A, 7.36 A, 37.2 A and 95°. The space group is either c2 or cm. The dimensions of the unit cell are the same for all three solid phases. Temperature dependent measurements show that the broad melting range of the transition into the isotropic phase is not a true melting range. Increasing lack of short range order occurring along the direction of the long axis of the molecule causes an increase of the expansion coefficient in that range.

Effect of impingement of rods on the Avrami equation

Phase transformations involving growth and impingement of randomly centered and oriented rods, fixed in number and cross section, have been studied using computer modeling techniques. As expected, the Avrami equation does not adequately describe the process. Deviations of up to 15% from the Avrami predictions are frequently encountered. The biggest deviations are in the Avrami constant K, which contains the rate constants, rather than in the time exponent n, which reflects growth and nucleation modes.

Cylindrically Symmetric Textures in Mesophases of Cholesteryl Esters

We have produced cylindrically symmetric single crystal textures of the cholesteric and smectic phases of cholesteryl esters by containing them in glass capillaries of smaller than 50 μ radius and inducing shear either by air-pressure changes from one end of the capillary or by volume changes on phase transformations of the sample itself. In the cholesteric phase, when the long axes of the molecules at the capillary interface are aligned parallel to the tube axis, the optic (twist) axes of the weakly negative uniaxial indicatrix are all radially oriented. In the smectic phase, when the molecules are aligned perpendicular to the substrate, the optic axes of the somewhat stronger positive uniaxial indicatrix are again radial. With the molecules aligned parallel to the tube axis, the optic axes of the smectic phase are everywhere parallel to the tube axis. These cylindrically symmetric orientations allow determination of the birefringence of the mesophase. The axial ratios of the refractive index ellipsoids are close to unity, for example, 1.014 and 1.028 respectively for the cholesteric and smectic phases of cholesteryl nonanoate. So far as we know these birefringences have been measured for the first time from cylindrical textures.