Uniaxial orientation

In general, you should recall that the tensile strength and modulus of fibers must be much higher than that for plastics and their elongation must be much lower. Synthetic fibers are usually stretched and oriented uniaxially to increase their degree of parallel chains and increase their strength and modulus. 

Polymer sheets are cooled without stretching by convected cold air (or an inert gas), by immersion into a fluid bath, or by passage over chilled rolls. Flat films are usually stretched and oriented uniaxially and cooled by either of the methods previously mentioned. Films are also cast and cooled on rolls for optimal clarity purposes. 

The simplest case to consider is that where the fluorescent molecules are rigidly oriented uniaxially as could be the case for a highly oriented fiber which had been dyed with a fluorescent substance. Suppose we excite the fluorescence with linearly polarized light with the electric vector... 

In order to create a strong molecular orientation, uniaxially stretched samples have been investigated. Large deformations (draw ratios up to 4) have been applied to enhance non linear relaxation phenomena that are dominant in most processing techniques. The predictions of molecular models have been compared with experimental data in order to identify various possible relaxation processes and eventually to introduce some improvements. 

The properties of a two-phase system consisting of a continuous "matrix" phase and a discontinuous "filler" phase are calculated in tenns of the component properties and volume fractions. It is assumed that the thennoelastic properties within each phase domain are homogeneous and isotropic, and that there is perfect adhesion between adjacent phase domains. The shapes of the filler particles are assumed to have biaxial symmetry. If a filler particle is anisotropic (as in fibers or platelets), it is oriented uniaxially at this stage of the calculation. Particle shape is described by the aspect ratio Af (defined as the ratio of the largest dimension of the filler divided by its smallest dimension), and if Af l then also by... 

The observation of optical properties in an applied electric field, which are similar to those of a collection of oriented uniaxial crystallites, suggests that within each domain the molecules are cooperatively oriented. It remains to be determined whether or not the observed domains present a net spontaneous polarization. Previous experiments with nematic p-azoxyani-sole indicated that dielectric peculiarities did accompany the formation of domains which appear when thin samples of this material are subjected to an electric field (4). 

Although the properties of ferroelectric superlattices can be governed by domain structure, no systematic study of this effect has been performed. In other words, the physics of the domain structure formation at the FE phase transition temperature T=Tc in the FE multilayers remains poorly understood. Here we address the question of a phase transition temperature in a periodic superlattice structure consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. To get rid of the effect of 90° ferroelastic domains we assume that FE layers have either natural or strain-induced c-oriented uniaxial symmetry. 

Mechanical properties of PMC are strongly influenced by the filler (by its size, type, concentration and dispersion) and by the properties of the matrix, as well as the extent of interfacial interactions and adhesion between them and their micro-structural configurations. The interrelation of these variables is rather complex. In FRC, the system is anisotropic where fibres are usually oriented uniaxially or randomly in a plane during the fabrication of the composite, and properties are dependent on the direction of measurement. Generally, the rule of mixture equations are used to predict the elastic modulus of a composite with uniaxially oriented (continuous) fibres under iso-strain conditions for the upper bound longitudinal modulus in the orientation direction (Equation 6.10). 

Uniformly oriented uniaxial nematic liquid crystals have non-polar cylindrical symmetry in the absence of an external electric field. If the liquid crystal molecules have a permanent dipole along the long molecular axis, the potential for the orientation of the dipole has reflection symmetry about the plane perpendicular to the director n, and the dipole has the same probability to be parallel and anti-parallel to the director, as shown in Figure 4.3(a). If the permanent dipole is perpendicular to the long molecular axis, the potential for the orientation of the dipole is... 

Uniaxial film is an anisotropic birefringent film with only one optical axis. For simplicity, let us limit our discussions to non-absorption uniaxial films. From the viewpoint of optical axis orientation, uniaxial films can be classified into a film and c film. An a film s optical axis is parallel to the film surface, while a c film s optical axis is perpendicular to the film surface. 

Mechanical Properties. Naphthalate presence improves mechanical properties such as modulus and tensile strengths. Like PET, PEN can be oriented uniaxially (fiber) or biaxially (film and bottle) and heat-treated in a variety of ways. Consequently, mechanical properties vary over a wide range depending upon the exact fabrication parameters used. Furthermore, in films, mechanical properties may differ between the machine (MD) and transverse (TD) directions balanced films have very similar properties between the MD and the TD, whereas in... 

Extensive measurements of the Prederiks transition in various smectic C liquid crystals have been carried out by the Halle group [117, 118]. In experiments, the conventional sandwich cells with optically transparent electrodes were used. The director was oriented uniaxially by rubbing the electrodes and the smectic layers were tilted with respect to the cell plane (a bookshelf geometry). An electric field applied along the cell normal ( -direction), due to positive dielectric anisotropy, induces the director rotation around the normal to the smectic layers. Fig. 6.32. Two optical effects are observed ... 

Orientation, uniaxial Also called axial orientation, mono-axial orientation, or UO.. This is the stretching only in one direction that is usually in the machine direction. 

For partially oriented uniaxial samples, two linearly independent spectra can be obtained from an experiment, irrespective of the mode of measurement and the polarization state of the absorbed light. The obvious procedure is to record two absorption spectra, one with the electric vector of light parallel to U, the unique axis of the sample Ei), the other with the electric vector perpendicular to the unique axis (Ey). The spectra must be baseline-corrected by subtracting the curves recorded on pure solvents. This yields the largest difference between the tow linearly independent spectra. Other alternatives are also possible. A combination of Ey or Ey with the spectrum of an isotropic sample, E =[E + 2Ey]/3) is easily obtained in liquid crystal. In cases where the sample geometry precludes the measurement of both Ey and the isotropic spectrum (membranes), the two spectra are Ey and the latter recorded with the incidence angle nlZ-co, and with the plane of polarization containing the U axis (the tilted plate method ). 

The piezoelectric material itself may be a composite. For example, combinations of piezoelectric polymers and piezoelectric ceramics have been made. Spom and Schoenecker discuss ceramic fibers in a polymer matrix. First, PZT fibers with diameters <30 mm oriented uniaxially in a planar fiber architecture along with interdigital electrodes. Then the fiber/electrode architectures are embedded within glass fiber-reinforced polymers and the fibers are poled and become piezoelectric. 

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