Hybrid biaxial

The equilibrium ordering of a hybrid nematic film can exhibit either a distorted (hybridly bent) or undistorted (hybrid biaxial and uniform) director structure. Which of the two possible configurations will actually occur depends on the temperature and film thickness. The existence of either of the two undistorted structures depends on the strength of the surface coupling. 

Patel et al. [70] in a recent publication have explored the adhesive action of the mbber-siUca hybrid nanocomposites on different substrates. The rubber-silica hybrid nanocomposites are synthesized through in situ silica formation from TEOS in strong acidic pH within acryhc copolymer (EA-BA) and terpolymer (EA-BA-AA) matrices. The transparent nanocomposites have been apphed in between the aluminum (Al), wood (W), and biaxially oriented polypropylene (PP) sheets separately and have been tested for peel strength, lap shear strength, and static holding power of the adhesive joints. 

Further studies have tackled the director dynamics [8] and the geometrically caused frustration [52,53], Theoretical studies of the highly frustrated sub-micron hybrid systems where the order becomes biaxial [10,54,55] have recently been delhonstrated also by MC simulations [16] but experimental evidence is still lacking. 

In the bent-director structure the biaxiality can be neglected and the scalar order parameter corresponds to its bulk value at the temperature 0eff — 0+ (37t /4) due to elastic deformation of the director field the temperature of the hybrid system effectively increases [10]. The increase of the ef-... 

Near the bulk isotropic-nematic phase transition temperature, Tjv/ — T = 0.1 K, and in a hybrid film of a typical LC material (such as 5CB) the nematic order is distorted if the film is thicker than dt 47 nm, and it is biaxial otherwise. The metastable biaxial structm e ceases to exist if the film thickness is larger than ds 71 nm. As the temperature is decreased both values decrease and so does the difference between them. The same structural transition can be realized if the film thickness is held constant and the temperature is varied. The (dis)continuity of the structrual transition can be changed if the temperature and film thickness are low enough [10,54,55]. The two different regimes of the transition are separated with a tricritical point below which the transition is continuous. Our estimation for its upper limit is Tjvi — Trp = 0.28 K and drp = 34 nm for 5CB [10]. 

Our illustration of pretransitional behavior in frustrated NLC systems is restricted to fluctuations in the biaxial structure of the hybrid nematic cell with equal strengths of homeotropic and planar anchorings. The detailed analysis of the pretransitional dynamics of all five degrees of freedom around the bent-director configuration is somewhat more complicated because of the nonuniformity of the base tensors. 

Since the equilibrium profiles of the biaxial hybrid structure are described by two nonzero amphtudes, the corresponding fluctuation modes are coupled. 

Fig. 8.11. (a) Structural force per unit area in a heterophase paranematic (thick lines) and nematic system with molten boundary layers (thin lines). Solid lines correspond to the force in the nematic phase and dashed lines to the force in the isotropic phase. For the thicknesses above the corresponding verticals the isotropic (paranematic) or nematic phase is stable, respectively. The force is short-range and attractive, (b) Structural presure in the hybrid nematic system in a biaxial structure (solid line) and bent-director structure (dashed line). In both cases the interaction is long-range and repulsive. 

Y. Wang, H. Yoon, H.K. Bisoyi, S. Kumar, Q. Li, Hybrid rod-like and bent-core liquid crystal dimers exhibiting biaxial smectic-A and nematic phases. J. Mater. Chem. 22, 20363-20367 (2012)... 

A carbon/glass hybrid epoxy construction is used by Glasforms to make a stiff, resilient and light weight tube for the masts and battens of wind surfers. The tapered masts and the constant cross-section battens are made by filament winding with the continuous hybrid reinforcement using a multiple construction of axial and biaxial plies. 

Figure 13.1 (a) Biaxial fabric from Selcom Multiaxial Technology, Italy, (b) Triaxial fabric structure from Selcom Multiaxial Technology, Italy, (c) Quadriaxial hybrid fabric from Selcom Multiaxial Technology, Italy. 

The flavor permeation rates were measured on both uncoated and hybrid polymer coated biaxially oriented polypropylene (BOPP) films. Here, a thermally curable epoxysilane based coating sol was used. Figure 15 shows that the permeation rates of the flavor... 

In order to investigate the gap between dis-cotic and calamitic liquid crystals and in an attempt to obtain biaxial nematics, Fletcher and Luckhurst [235] synthesized hybrids of rod-like and disk-like mesogens, by linking two units to dimers. Among the several compounds of this type is one example that shows nematic behaviour (21) however, the... 

PPT fibres are used in advanced composite applications in combination with epoxy. However, to attain good properties the fibres have to be pre-dried to a very low moisture content. To overcome the weak compressive and shear strength of the PPT fibres in applications where these properties are crucial, hybrids with carbon fibre can be used. High-performance composites made from laminated PPT and biaxially oriented polyester films are used in racing sails,... 

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