Anchoring strength

However, for h initial conditions LRO may not always hold. For higher w, the LRO structure may be replaced by QLRO or even SRO. We give some indication of this in Fig. 3, where we plot s(p) for different anchoring strengths w for d=2 and L = 250. The plot suggests that for each there is a critical value such that for w > = 0. If this is the case, SRO or QLRO... 

In Figs. 4 we plot the stretched exponential parameter m as a function of p and w. We do not observe any systematic changes in behaviour of m below and above the percolation threshold on varying p. Indeed, values of m are strongly scattered because the structural details of G r) are relatively weakly -dependent. The parameter m appears always to be essentially independent of the impurity concentration p. For h initial conditions it is also independent of the anchoring strength w. In all cases m is close to unity. Only for r initial conditions do we see any noticeable dependence on w. This dependence only occurs at low w, at increases m up to about 1.4. 

Here, the case of an anisotropic NP immersed in a nematic LC is considered, where the anchoring strength at the NP-LC interface is relatively strong (i.e.,... 

We first consider the moderate anchoring strengths. The average distortions in the nematic director field are roughly given by V 1 /, where stands... 

Fig. 3.21. Forces (a) and refractive indices (b) for a 5CB droplet between aligned bare mica sheets (T=27°C). (a) Force runs approaching the surfaces (filled circles and triangles) a residual repulsion is observed in retraction (open circles) a jump-out from the minimum of a layering oscillations is shown. The continuous lines represent the elastic twist force F D)/R = ttK220 /D (see [50] for details), calculated assuming an infinite anchoring strength with K22 = 6.5 x N. The twist...

The common feature of all ordered structures in a hybrid nematic cell is the repulsive character of the structural force. The repulsion is due to the antagonistic boundary conditions, which always lead to at least small deformations, and to the fact that within a certain ordered structure the frustration is stronger if the confining substrates are brought closer to each other. The magnitude of the force is tuned by the anchoring strength at both substrates. 

We stress however that this deduction is based on the elastic theory for the nematics, that fails to explain the forces in planar samples. Moreover, the discussion does not take into account the specific curved geometry of the SFA, which is not compatible with the hybrid anchoring conditions. In particular, even by considering a finite anchoring strength, a line defect is expected at the center of the cell (as sketched tentatively in Fig. 3.22), that has not been observed yet. 

Fig. 4.7. Relaxation time r for the fundamental twist fluctuation mode dots) as a function of sample thickness d. The aligning layer was rubbed Nylon, the liquid crystal was 4-n-pentyl-4 -cyanobiphenyl (5CB) in the nematic phase (T = 32° C). Comparison between the best fit of the theoretically derived equation (solid line) and the best fit assuming infinite anchoring strength (dashed line) is made [32].

All the discussion so far was concerning only the fundamental fluctuation mode. This is dominant mode for small sample thickness, t3 icaUy up to a micron or two. In thicker samples, the influence of higher fluctuation modes becomes apparent the inci ease in the relaxation time is no longer purely parabolic (or linear, depending on the anchoring strength), but reaches a maximum and decreases towards the bulk value with increasing thickness (Fig. 4.10). 

As discussed in Chapter 1, photo-polymers that have been unidirectionally modified by exposure to linearly polarized light have the ability to induce alignment of liquid crystals [37-41]. This works presumably via anisotropic van der Waals forces [38], similar to the alignment on conventionally rubbed polymer layers [18,22]. In spite of this similarity, generally there are large differences found between the surface anchoring strengths of these two types of... 

Here W2 is the strength of the interaction and Qs is the preferred value of the tensor order parameter at the substrate, located at z = zs- In the case of uniaxial nematic order the anchoring strength W2 can be related to the anchoring strength W for the bare director description as W = 3iC2 S. ... 

W. Guo, C. Bahr, Influence of anchoring strength on focal conic domains in smectic films. Phys. Rev. E 79, 011707 (2009)... 

The first such possibility was pointed out by Meyer in the original paper on the subject, in which he showed, assuming that the anchoring strength = 0, As = 0 and ei = —es, a DC field can generate a periodic structure along the direction of the field-free orientation of the director n. Under the field, n develops alternate bend-rich and splay-rich distortions. 

M. Buczkowska and G. Derfel, Analysis of deformations of flexoelectric homeotropic liquid crystal layers with various anchoring strengths, Opto-Electronics Review 19(1), 56-60, (2011). doi 10.2478/sl 1772-010-0065-0... 

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