Flow-aligning materials

The rheological and flow properties of ordered block copolymers are extraordinarily complex these materials are well-deserving of the apellation complex fluids. Like the liquid-crystalline polymers described in Chapter 11, block copolymers combine the complexities of small-molecule liquid crystals with those of polymeric liquids. Hence, at low frequencies or shear rates, the rheology and flow-alignment characteristics of block copolymers are in some respects similar to those of small-molecule liquid crystals, while at high shear rates or frequencies, polymeric modes of behavior are more important. 

Ductile with flow. These materials show still greater deformability than the typical ductile materials. Initially, the stress-strain dependence resembles that described for ductile resin, but before the rupture there is a zone of deformation where the stress remains about constant. Within this zone there is flow of material that usually leads to molecular alignment and/or to changes to the crystalline structure (viz. deformation of polyolefins). 

Infrared photothermal radiometry can be used to measure thermal anisotropy, by displacing excitation and detection spots on the sample, and measuring the transverse heat flow between these spots. As the direction of the spot displacement is varied, directional variations are sampled. Entire images of the thermal anisotropy may be scanned using this method. Such images may be used to detect defects in aligned materials, where a defect destroys the local alignment of bulk fibers or molecular chains. 

Now consider the case when IA2I < A5. No flow alignment can occur when this inequality holds and therefore a non-stationary flow must develop. As remarked by Gill and Leslie [113], it is expected that this effect may be similar in nature to the tumbling effect exhibited by some nematic materials as described by Carlsson [30]. 

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