Rheological Measurements and Properties

We already have reported on the replacement of the terephthalic acid with kinked diphenylether dicarboxylic acids (4). 3,4 - and 4,4 -Dicarboxydiphenylether (3,4 -0 and 4,4 -0) were synthesized and all-aromatic polyesters were prepared represented by structure 1. These polyesters were thermotropic with melt transitions decreasing to about 200°C with increasing replacement of the terephthalic acid with the kinked monomers. The polymers generally were thermally stable without measurable weight loss until well over 400°C. We wish here to supplement our previous studies with rheological measurements and fiber spinning of the polymers, including some measurements of fiber properties. 

Both bulk and interfacial rheological measurements and foaming properties show a large effect of pH on these properties of glycinin dispersions. This is undoubtedly related to the change in conformation of the glycinin molecule with pH as expressed in the presence of different amounts of the 3S, 7S and 11S form at different pH.11-13... 

Aspects of viscosity, elasticity, and morphology have been discussed in general terms by various workers [73-76]. Rheological studies specific to particular polymers include dynamic rheological measurements and capillary rheometry of rubbers [77], capillary rheometry of PP [78], degradation of PP [79], torsion rheometry of PE [80], viscosity effects in blends of PC with styrene-acrylonitrile and acrylonitrile-butadiene-styrene [81], peel adhesion of rubber-based adhesives [82], and the effect of composition of melamine-formaldehyde resins on rheological properties [83]. 

Finally, morphological information can also be obtained indirectly from methods that reflect the composite morphology into other macroscopic properties. Within the focus of this book, two examples of such methods can be mentioned rheological measurements and cone calorimetry flammability methods. Both methods can sensitively detect well-dispersed nanofillers in a polymer matrix and can distinguish them from the respective conventional composites based on the same polymer and fillers but without nanometer-scale dispersion of the latter. We shall not provide further details on this we just point the interested reader discussions of the cone calorimetry approach in subsequent chapters, and to a few representative references for the rheology. ... 

Moreover, novel redox-responsive polycationic hydrogels of AAf-diethylacrylamide (DEAAm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) were successfully synthesized by cross-linking reactions via quaternary ammonium compounds with a disulfide. The ability of the polymer netwoik to enclose and release substances by reductive cleavage or oxidative formation of disulfide bonds was shown exemplarily using different dyes. The redox-responsive character was proven by oscillatory rheological measurements and different material properties of polycationic polymer discs were also investigated. Because of its polycationic structure, this polymeric system could be a promising compound for complexation of DNA-like substances. Its ability for selective release in reductive environments, like tumor tissues, could possibly be used in medical applications or in chemotherapy [162]. 

Rheological measurements were carried out to investigate the rheological properties of emulsions stabilized by different fat-water interfaces and the influence of fat droplets on the formation of the protein networks during a process of gelation. 

The starting time for rheological measurements correspond to t = 120 min. Indeed, the rheological parameters were only recorded during the rennet-induced coagulation phase to avoid structural modifications during the acidification phase which may consequently influence the gelation process. Elastic and viscous properties of reconstituted milks... 

The theoretical basis for spatially resolved rheological measurements rests with the traditional theory of viscometric flows [2, 5, 6]. Such flows are kinematically equivalent to unidirectional steady simple shearing flow between two parallel plates. For a general complex liquid, three functions are necessary to describe the properties of the material fully two normal stress functions, Nj and N2 and one shear stress function, a. All three of these depend upon the shear rate. In general, the functional form of this dependency is not known a priori. However, there are many accepted models that can be used to approximate the behavior, one of which is the power-law model described above. 

The most useful parameters commonly measured to assess the effect of stress conditions on emulsions include phase separation, rheological property determination, electrical property measurements, and particle size analysis. 

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