Smectic interlayer distance

On a global scale, the linear viscoelastic behavior of the polymer chains in the nanocomposites, as detected by conventional rheometry, is dramatically altered when the chains are tethered to the surface of the silicate or are in close proximity to the silicate layers as in intercalated nanocomposites. Some of these systems show close analogies to other intrinsically anisotropic materials such as block copolymers and smectic liquid crystalline polymers and provide model systems to understand the dynamics of polymer brushes. Finally, the polymer melt-brushes exhibit intriguing non-linear viscoelastic behavior, which shows strainhardening with a characteric critical strain amplitude that is only a function of the interlayer distance. These results provide complementary information to that obtained for solution brushes using the SFA, and are attributed to chain stretching associated with the space-filling requirements of a melt brush. 

Recently we studied several polymers of structure 36 in Table 1 that were identified by texture observation as being smectic X-ray diffraction patterns showed a spacing at approximately 5 A and others at 28, 31, and 29 A for the polymers with 9,10, and 12 methylene groups in the spacer, respectively. Such repeat lengths are not consistent with the presence of fully extended chains in the smectic A mesophase for these polymers. Instead, the polymer with a nonamethylene spacer appears to form a smectic C phase in which the polymer chain is tilted with respect to the layers, as suggested by the small interlayer distances. 

SmA is a one-dimensional lamellar crystal with the interlayer distance almost rigidly fixed. In order to discuss elasticity we need an additional variable that would describe the lamellar structure. Consider a small distortion of smectic layers [17]. In Fig. 8.23 dash and solid lines indicate undisturbed and distorted layers, respectively. Short rods perpendicular to the lowest solid line indicate local directors, which are always perpendicular to the layers. Now, we introduce a layer displacement along the z-axis, u = Uz.ln fact, it is a scalar field y, z), depending generally on aU the three co-ordinates. Its derivatives describe two types of elasticity ... 

In the experiment, it is possible to create a dilatation of the smectic layers with piezoelectric drivers. Evidently, an increase of the interlayer distance would cost a lot of energy. Instead, at a certain critical dilatation Xc = Tiks/d, where Xs =, a wave-like or undulation distortion is observed as illustrated by... 

SAXS-reflexes gave a peak for the lamellar phase-separation of the blocks. From this the interlayer distance was calculated to be 154 A. The second peak confirms the existence of a smectic texture. The distance of the smectic layers within the LC phase is... 

The word smectic comes form the Greek word anriyua, meaning soap and reflects the mechanical properties displayed by many of these materials. All smectics are layered structures having well-defined interlayer distances. Smectic materials are therefore more ordered than nematic ones and occur at a temperature below that for the nematic phase. A number of smectic phases have been identified. ... 

The elastic theory of SmC has beep considered by the Orsay groupand by Rapini. Both approaches use the Oseen description of smectic A, neglecting all changes in internal parameters such as density, interlayer distance, and tilt angle. The Orsay group used the Lagrai an description for the elastic strains with a vector IKF) describing the local rotation of the director. In order to be consistent with the elastic theory for NLC s, we shall use the Eulerian description developed by Rapini based on the director. 

In smectic A liquid crystals the only allowed deformation is specific undulation of the smectic layers, such that interlayer distance is kept constant and the director remains normal to the layer. According to [31] this deformation imposes the following limitation to the director field ... 

In the smectic A phase the director is always perpendicular to the plane of the smectic layers. Thus, only the splay distortion leaves the interlayer distance unchanged [7], and only the elastic modulus K i is finite while K22 and Kzz diverge when approaching the smectic A phase from the nematic phase. On the other hand, the compressibility of the layered structure and the corresponding elastic modulus B is taken into account when discussing the elastic properties of smectic phases. The free energy density for the smectic A phase, subjected to the action of an external electric field, is... 

There were two reports of the same bis(al-koxylsalicylidene) ethylenediamine complexes of Ni(II) and Cu(II), 52. The material was reported as giving a SmA phase at elevated temperature [122] and a noniden-tified mesophase [123]. Ohta later [124] found that the nickel complexes showed two smectic liquid crystalline phases, SmE and SmA. The SmE-SmA phase transition in the nickel complex is accompanied by a reversible stretching of the interlayer distances. This phenomenon can be ascribed to a dimer SmE-monomer SmA phase transition. 

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