Rod-like Liquid Research Articles

Thermal diffusivity in mesophases: A systematic study in 4-4′-di-(n-alkoxy) azoxy benzenes

We present a systematic study of thermal diffusivity in the nematic liquid crystalline phase of 4-4′-di-(n-alkoxy) azoxy benzenes and several other materials. The data allow to separate the respective contributions of the rigid central core and of the flexible aliphatic chains. For the component of the diffusivity tensor parallel to the long molecular axis, it is found that they differ by as much as a factor of 6 in favor of the core contribution. Combining the present observations with our earlier results, we are now able to draw general conclusions on the thermal diffusivity in a nematic and smetic A, B, and C phases. We have also developed two semiquantitative models based, one on a static network of distributed resistances, and the other on an extension of the Eyring kinetic model for the thermal conductivity of simple liquids. Only the dynamic model yields a satisfactory description of our data. The distance over which the thermal energy is not transferred instantaneously upon collision between two neighboring molecules is found to correspond to the aliphatic chain length (calculated for a freely rotating chain). Using this formalism, a priori calculations of the thermal diffusivities can be performed, to better than 20%, for any rodlike liquid crystalline material.

The role of liquid crystals in the formation of graphitizable carbons (cokes)

AbstractThe formation of cokes and graphites proceeds via the creation from the isotropic fluid phase of carbonization of pitch and coal, of lamellar nematic liquid crystals or mesophase. This anisotropic fluid, deformable mesophase, develops as spheres within which constituent molecules are stacked parallel to an equatiorial plane. This type of structure facilitates coalescence to a coherent mass which eventually forms a graphitisable carbon. The ‘onion‐skin’ structure of mesophase spheres cannot so coalesce. Different optical textures of cokes and graphites owe their origin to different chemical reactivities and fluidities of mesophase, the lower the fluidity the smaller the size of the optical texture. Mesophase from lameller molecules is compared with conventional rod‐like nematic liquid crystals. Structures in needle‐cokes, metallurgical coke, coke from solvent refiend coal and carbon fibre from pitch are discussed in terms of formation and properties of lamellar nematic liquid crystals.

銅-鉛合金の偏晶反応凝固

Principles of monotectic solidification of the binary copper-lead alloy are introduced from the observation of crystallizing courses of direction-free and unidirectional solidification in the monotectic and hyper-monotectic alloys. In the direction-free solidification the α-solid of a monotectic product grows in volume spherically unlike dendritic growth in the hypo-monotectic alloy. The released L2 liquid accompanied by generation of the α-solid lies in the α-solid sphere radiately, while the initial L2 does in the boundaries. Columnar growth of the α-solid of a monotectic product occurs in an opposite direction of heat flow during unidirectional solidification. The monotectic cell is produced in which the α-solid of a monotectic product grows in an opposite direction of heat flow surrounding the released rod-like L2 liquid. In the unidirectional solidification at temperature gradient 50°C/cm and freezing rate 60 mm/min abnormal condensation of the L2 in the liquid in advance of the monotectic cell results in the bell-shape aggregation in the hyper-monotectic copper-50% lead alloy. At temperature gradient 10° to 30°C/cm and freezing rate 0.5 to 4.0 mm/min widening the (L1+L2) layer causes arrangement of coarse and rod-like L2 liquid within the monotectic cell. The inter-rod spacing is in inverse proportion to the square root of freezing rate and is reduced with temperature gradient in the liquid. Both copper and lead in the monotectic cell grow preferentially in the 〈110〉 direction at high rate of freezing and in 〈111〉 at slow rate.