Self nematics

For structures with a high curvature (e.g., small micelles) or situations where orientational interactions become important (e.g., the gel phase of a membrane) lattice-based models might be inappropriate. Off-lattice models for amphiphiles, which are quite similar to their counterparts in polymeric systems, have been used to study the self-assembly into micelles [ ], or to explore the phase behaviour of Langmuir monolayers [ ] and bilayers. In those systems, various phases with a nematic ordering of the hydrophobic tails occur. 

This can be inserted in equation (02.2.3) to give tlie orientational distribution function, and tlius into equation (02.2.6) to deteniiine the orientational order parameters. These are deteniiined self-consistently by variation of tlie interaction strength iin equation (c2.2.7). As pointed out by de Gemies and Frost [20] it is possible to obtain tlie Maier-Saupe potential from a simple variational, maximum entropy metliod based on tlie lowest-order anisotropic distribution function consistent witli a nematic phase. 

Short-time Brownian motion was simulated and compared with experiments [108]. The structural evolution and dynamics [109] and the translational and bond-orientational order [110] were simulated with Brownian dynamics (BD) for dense binary colloidal mixtures. The short-time dynamics was investigated through the velocity autocorrelation function [111] and an algebraic decay of velocity fluctuation in a confined liquid was found [112]. Dissipative particle dynamics [113] is an attempt to bridge the gap between atomistic and mesoscopic simulation. Colloidal adsorption was simulated with BD [114]. The hydrodynamic forces, usually friction forces, are found to be able to enhance the self-diffusion of colloidal particles [115]. A novel MC approach to the dynamics of fluids was proposed in Ref. 116. Spinodal decomposition [117] in binary fluids was simulated. BD simulations for hard spherocylinders in the isotropic [118] and in the nematic phase [119] were done. A two-site Yukawa system [120] was studied with... 

Pii-8, like Pii-5, is designed to self-assemble at high pH. Comparable shifts in properties were found when studying Pn-8 solutions in 130 mM NaCl (Fig. 12). The p-sheet to random coil transition is lowered by 3 pD units and the pD range over which it forms nematic gels is extended down to pD 8.5 in aqueous NaCl... 

Synthesis of the first mesoionic nematic and smectic A liquid crystals derived from sydnones has been described and their self-organization into liquid crystal phases has been studied by optical, calorimetric, and powder X-ray diffraction methods <2005CC1552>. 

The non-collective motions include the rotational and translational self-diffusion of molecules as in normal liquids. Molecular reorientations under the influence of a potential of mean torque set up by the neighbours have been described by the small step rotational diffusion model.118 124 The roto-translational diffusion of molecules in uniaxial smectic phases has also been theoretically treated.125,126 This theory has only been tested by a spin relaxation study of a solute in a smectic phase.127 Translational self-diffusion (TD)29 is an intermolecular relaxation mechanism, and is important when proton is used to probe spin relaxation in LC. TD also enters indirectly in the treatment of spin relaxation by DF. Theories for TD in isotropic liquids and cubic solids128 130 have been extended to LC in the nematic (N),131 smectic A (SmA),132 and smectic B (SmB)133 phases. In addition to the overall motion of the molecule, internal bond rotations within the flexible chain(s) of a meso-genic molecule can also cause spin relaxation. The conformational transitions in the side chain are usually much faster than the rotational diffusive motion of the molecular core. 

The aggregates created by amphiphiles are usually spherical (as in the case of micelles), but may also be disc-like (bicelles), rodlike, or biaxial (all three micelle axes are distinct) (Zana, 2008). These anisotropic self-assembled nanostructures can then order themselves in much the same way as liquid crystals do, forming large-scale versions of all the thermotropic phases (such as a nematic phase of rod-shaped micelles). 

AggeU A, BeU M, Boden N, Camck LM, Strong AE. Self-assembling peptide polyelectrol3de beta-sheet complexes form nematic hydrogels. Angew Chem Int Ed 2003 42 5603-5606. 

Prominent exceptions are studies on the liquid crystal phase formation and self-assembly of two-dimensional disc- or sheet-like nanomaterials such as the organization of nanodiscs or nanoplatelets into nematic, smectic, or columnar morphologies [263-270] (see Fig. 2 for an example of the self-assembly of nanoclay in aqueous suspensions) or the synthesis of CuCl nanoplatelets from ionic liquid crystal precursors as described by Taubert and co-workers [271-273]. 

On a side note, Ouskova and co-workers also reported that the composite of magnetic /i-FejOs nanorods in 5CB showed lower threshold voltages than pure 5CB, and that the sensitivity of the nematic liquid crystal to external magnetic fields was increased in the presence of such magnetic nanorods [451]. Finally, several groups interested in the macroscopic organization and orientation of nanorods also reported on the formation of a lyotropic liquid crystal phase induced by the self-assembly of polymer-coated semiconductor nanorods [453—457], which might be used to improve the device performance, for example, of solar cells. 

Finally, an area that will most likely see an explosive growth over the next few years is the self-assembly of nanoparticles covered with mesogenic and pro-mesogenic capping agents. A number of different approaches have been summarized in this review, and the formation of nematic, smectic-like, cubic, and columnar phases and/or superstructures have been demonstrated. Once more, the possibilities to produce such metamaterials using nanoparticles and liquid crystal motifs are endless, and future research will surely discover other, in part, more complex phase morphologies as well as uniquely tunable nanoscale properties as a result of liquid crystal phase formation. 

Abstract We use Nuclear Magnetic Resonance relaxometry (i.e. the frequency variation of the NMR relaxation rates) of quadrupolar nucleus ( Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements. 

Porion, P., Rodts, S., Al-Mukhtar, M., Faugere, A.M. and Delville, A. (2001) Anisotropy of the Solvent Self-Diffusion Tensor as a Probe of Nematic Ordering within Dispersions of Nanocomposites. Physical Review Letters 87, 208302-208700... 

The nematic mean-field U, the molecule-field interaction potential, WE, and the induced dipole moment, ju d, are evaluated at different orientations using Equation (2.263), and then the coefficients of their expansion on a basis of Wigner rotation matrices can be calculated, according to Equation (2.268). The permittivity is obtained by a self-consistency procedure, because the energy WE and the induced dipole moment / md, as well as the reaction field contribution to the nematic distribution function p( l), themselves depend on the dielectric permittivity. 

Aggeli, A., Bell, M., Boden, N., Carrick L.M., and Strong A.E. "Self-assembling peptide polyelectrolyte beta-sheet complexes form nematic hydrogels". Angew. Chem. Int. Ed. 42(45), 5603-5606 (2003a). 

Aggeli, A., Bell, M., Carrick, L.M., Fishwick, C.W.G., Harding, R., Mawer, P.J., Radford, S.E., Strong A.E., and Boden, N. "pH as a trigger of peptide beta-sheet self-assembly and reversible switching between nematic and isotropic phases". J. Am. Chem. Soc. 125(32), 9619-9628 (2003b). 

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