Uniform alignment

However, due to the helical structure of the SmC mesophase, no net spontaneous polarization results. Macroscopic nonvanishing polarization is only obtained when the helix is unwound. This requirement has been a severe limitation for the determination of Ps, and we had to wait until 1988 for the first observation of ferroelectric switching in a side chain SmC LCP [65]. Even now, the measurement of remains delicate and its reliability is directly connected to the quality of the uniform alignment achieved. 

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Non-uniform moleeular alignment that eannot be transformed into a uniform alignment without ereating other defeets. 

Note 1 In the equation for g, the term go is usually equal to zero because the undistorted state of nematics is the state of uniform alignment. However, for chiral nematics, a nonzero value of go allows for the intrinsic twist in the structure. In order to describe g for smectic phases, an additional term must be added, due to the partially solid-like character of the smectic state and arising from positional molecular deformations. 

Elastic deformation of the director, induced by a magnetic induction or electric field, in a uniformly aligned, thin sample of a nematic confined between two surfaces. 

A precondition for the investigation of deformation of a I.c. in an external field is a uniform alignment of the I.c. with respect to the measuring cell, in order to get quantitative informations. Normally the I.c. is aligned by surface effects in the measuring cell, which usually consists of two glass plates separated by a distance of about 10 pm. We will consider three principal modes of alignment of the I.c. (Fig. 16) ... 

Guide Guides the stem in order to have a perfect and uniform alignment to transmit the spring force on the disc. It is a very critical component for the correct operation of the SRV and also a vulnerable one because it is easily subject to galling, corrosion and so forth. 

Two approaches are commonly used for NMR investigations of biological membranes and membrane-bound peptides first, the measurement of static spectra of uniformly aligned samples second measurement of the sample spun under MAS. The former method requires precise preparation and well-oriented samples in order to provide the high-resolution data. In the latter approach, individual species of PLs are randomly oriented in the rotor. The MAS technique is used for averaging the spin interactions (see Section 2.1). A method that combines both the above approaches (MAOSS) will be discussed in Section 3.1.3.2. 

In MAOSS, the PLs are uniformly aligned on a thin glass disc which is next settled on the rotor probe (Figure 29). The sample may be used as powder or adsorbed on a polymer sheet (Figure 30). 

Figure 29 Rotor design for MAOSS A standard 7-mm Bruker MAS rotor contains a stack of thin glass plates with uniformly aligned phospholipid membranes. The membrane normal n is parallel to the rotor axis z, which is tilted with respect to B0 by the magic angle 54.7°. Taken from Ref. [111].

Here, we shall content ourselves with obtaining an analytic result for the minimum field necessary to induce the first slight reorientation away from uniform alignment. If the director field is only very slightly distorted, then the angle 6 is small, and Eq. (AlO-8) reduces to... 

Cross-linked liquid crystalline polymers with the optical axis being macroscopically and uniformly aligned are called liquid single crystalline elastomers (LSCE). Without an external field cross-linking of linear liquid crystalline polymers result in macroscopically non-ordered polydomain samples with an isotropic director orientation. The networks behave like crystal powder with respect to their optical properties. Applying a uniaxial strain to the polydomain network causes a reorientation process and the director of liquid crystalline elastomers becomes macroscopically aligned by the mechanical deformation. The samples become optically transparent (Figure 9.7). This process, however, does not lead to a permanent orientation of the director. 

Describing the width of the index card as 10.16 cm indicates that the ruler has 0.1-cm calibrations and the 0.06 cm is an estimation. Similarly, the uniform alignment of the edge of the index card with the ruler indicates that the measurement 10.16 cm is also an accurate measurement of width. ... 

In order to exclude the appearance of rotational domains in the initial stage of growth we have used a Cu(llO) substrate and have studied the growth of pentacene films on this substrate quite extensively. In fact, a highly ordered submonolayer and a saturated monolayer phase are found which exhibit a uniform alignment of the flat lying molecules with their long axes orientated parallel to the (110 )-azimuth direction of the substrate [46, 52]. 

Channel-Forming Peptides in Uniformly Aligned Multilayers of Membranes... 

Uniformly aligned multilayers of membranes (containing proteins) possess one-dimensional structural order perpendicular to the plane of the membrane and preserve the orientational order of proteins relative to the plane of the membrane. Both the one-dimensional structure and the orientation of proteins can be measured with the methods to be described. We stress that proteins in these samples are in the membrane active forms. With time-resolved measurement, our methods can be extended to study the structural dynamics of membrane proteins. 

In the next section, uniformly aligned multilayers of membranes are described. The third section illustrates the theoretical basis and applications of the method of oriented circular dichroism (OCD). The OCD study of alamethicin is discussed in the fourth section and the last section is devoted... 

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