Shear-induced orientation

As discussed below, the quality of the alignment (and even its direction in the case of lamellar morphology), is influenced by temperature, as well as the frequency and strain amplitude of the aligning shear field. No general theory for the alignment of block-copolymer phases has yet been developed. However, studies of a number of different block-copolymer systems show that in ordered states with cylindrical domains, shear orients the cylinders parallel to the flow, while for lamallar microdomains, two different shear-induced orientations are commonly found, depending on alignment conditions in both of these orientations, the flow direction lies in the plane of the lamellae. 

Ebeling T, Paillet M, Borsali R et al (1999) Shear-induced orientation phenomena in suspensions of cellulose microcrystals, revealed by small angle X-ray scattering. Langmuir 15 6123-6126... 

Shear-Induced Orientation in Side-Chain Liquid-Crystalline Copolysiloxanes... 

Directing self-assembly (such as shear-induced orientation, templating techniques, confinement or selective annealing regimes) is not covered in this chapter, and the reader is directed elsewhere for a comprehensive review of this area. ... 

Figure 8 Scheme of the shear-induced orientation of (a) flexible and (b) rigid rode macromolecules passed through a spinneret. Arrows indicate the direction of shear. 

Roux DC, Berret JF, Porte G, Peuvrel-Disdier E, Lindner P (1995) Shear-induced orientations and textures of nematic wormlike micelles. Macromolecules 28(5) 1681-1687... 

Seki M, Thurman DW, Oberhauser JP, Komfield JA (2002) Shear-induced orientation in the crystallization of an isotactic polypropylene nanocomposite. Macromolecules 35 2583 Siddiqui MA, Ahmed Z (2005) Mineralogy of the Swat kaolin deposits, Pakistan. Arab J Sci Eng 30 195-218... 

Kenig, S., Shear-induced orientation in liquid crystalline polymers, Polym. Eng. Sci. 29 1136 (1989). 

As a drawback, only the antifcrroelectric state is stable and does not need a power supply, whereas the ferroelectric state roust be roaintained by a DC bias voltage. Moreover, to achieve full contrast, a tilt angle of 45 is required, and this can only be met by materials possessing the ScA ch-i phase sequence. It is not known whether the shear-induced orientation process of FLC polymers as demoostraied by Idemitsu [115] also... 

Relatively speaking the polymer field has not yet reached this stage, to some degree in fibers and films but even here there is much room for improvement. We have many tools to help us produce the optimtim structiire, and optimum properties pressure induced crystallization, shear induced orientation and crystallization, polymer blend composition to control melt rheology as well as the synthesis processes to produce the desired relationship between internal structure and application properties. This is the area of future research that deserves our attention. 

Rienacker and Hess (1999) studied theoretically shear induced orientational dynamics of nematic liquid crystals (Rienacker and Hess 1999). LCPs exhibit different types of orientation at different shear rate. The rods like molecules start to tumble with shear and rotate from tumble to wagging after certain critical shear rate. With the increase of shear the wagging region transforms to flow aligning... 

Bafna A, Beaucage G, Mirabella F, Mehata S (2002), Shear induced orientation and associated property enhancement in polymer/clay nanocomposites. Proc. Nanocomposites 2002 ECM Publication, Sept. 23-25, San Diego, California, USA. 

The nematic-to-isotropic transition also occurs for lyotropic smaU-mol-ecule liquid crystals. Looking at Fig. 5.1b and 5.1c, one can easily imagine that the oriented molecules would slide past one another with relative ease in the nematic. In isotropic melts the molecules at rest have no preferred orientation and would interfere with each other to a greater extent when sheared. Also, they would be expected to display shear-thinning as shear-induced orientation is created. Thus one would expect a lower zero-shear viscosity in the nematic melt, although it exists at a lower temperature than the isotropic melt. This is indeed the case, and a sudden increase in viscosity at the clearing temperature is seen in many nematics as the orientational... 

Wi therefore characterizes the relative intensity of fluid relaxation and shear-induced molecular alignment. Thus, for Wi 1, relaxation outcompetes shear-induced orientation and disentanglement, so shear has little effect on polymer structure and a Newtonian fluid behavior is observed. However, for Wi 1, polymer molecules are... 

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