Dynamic rheological measurements

Kinetics of Gelation Studied by Dynamic Rheological Measurements... 

Dynamic rheological measurements have recently been used to accurately determine the gel point (79). Winter and Chambon (20) have determined that at the gel point, where a macromolecule spans the entire sample size, the elastic modulus (G ) and the viscous modulus (G") both exhibit the same power law dependence with respect to the frequency of oscillation. These expressions for the dynamic moduli at the gel point are as follows ... 

Wu G, Asai S, Sumita M, Hattori T, Higuchi R, Washiyama J (2000) Estimation of flocculation structure in filled polymer composites by dynamic rheological measurements. Colloid Polym Sci 278 220-228... 

Rao, M. A and Cooley, H. J. 1993. Dynamic rheological measurement of stmcmre development in high-meflioxyl pectin/fruclDse gels. 7. FoodSci. 58 876-879. 

Although providing only a qualitative determination of the level of branching, comparing the linear viscoelastic data of samples from dynamic rheology measurements is a common technique. Plots of the loss angle, as a function of frequency are altered because of branching ... 

Mixes of S13TMSx and T30TMSx silylated silicas and a silicone oil (Wacker-Chemie AKIOOO) were submitted to dynamic rheological measurements using an oscillating cone/plane rheometer. In Fig. 14, the evolution of the viscosity, measured at 25°C and 0.278 Hz, with the silica surface coverage ratio is shown. 

The phase separation behaviors of PMMA/SAN blends with and without fumed silica (Si02) have been investigated using time-resolved small-angle lightscattering and dynamic rheological measurements. It is found that the effect of Si02 on the phase separation behavior of PMMA/SAN blend obviously depends on the composition of the blend matrix (Du et al. 2013). 

For characterization of polymer blends, low strain dynamic rheological measurements are preferred over steady-state shearing (e.g., in a capillary viscometer). Since... 

Chen CR, Zatz JL. Dynamic rheologic measurement of the interaction between xanthan gum and colloidal magnesium aluminum sUicate. J Soc Cosmet Chem 1992 43 1-12. 

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]. 

Rosalina I, Bhattacharaya M. Dynamic rheological measurements and analysis of starch gels. Carbohydr Polym 2002 48 191-202. 

To increase the viscosity of polymer blends, additives [such as traditional fire retardants (mainly oxides) and, more recently, nanoclays] are added to polymer blend systems. The present authors recently conducted dynamic rheological measurements for the EVA/LDPE nanocomposite, as reported in [27]. Figure 8.3 (a) and (b) compare the complex viscosity of the EVA/LDPE blend with and without nanoclay as a function of frequency and temperature, respectively. Measurements were carried out on 1 mm-thick samples using a Rheometrics RDA n Dynamic Analyzer rheometer. The frequency-sweep tests were conducted from 0.1 to 100 rad/s with constant temperature (140 °C) and strain amplitude (1%). Eor the temperature-sweep measurements, samples were heated from 300 to 530 °C (15 °C/min) under nitrogen with constant frequency (10 rad/s) and strain amplitude (10%). In both experiments, there is a significant increase of viscosity above that for the neat... 

These quantities can be determined by dynamic rheological measurements which yield the complex viscosity r, the storage modulus G and the loss modulus G" for the studied solution as a function of the oscillation frequency /. Many surfactant solutions have turned out to behave like a Maxwell element with one single shear modulus Go and one single structural relaxation time t. An example of this is shown in Figure 10.2. The typical features of such solutions can be seen in this figure which presents a double... 

Dynamic rheological measurements confirm this behaviour, as can be seen from the example presented in Figure 10.11. In these systems, G and G" are... 

Dynamic rheological measurements show that the cubic phases behave like the viscoelastic vesicle phases, as can be seen from the two examples shown in Figure 10.19. As can be seen, G is independent of the frequency and at least one order of magnitude higher than G", and rj increases to infinity when the frequency approaches zero. However, as can be expected from the stiffness of the samples, both Go and cry are several orders of magnitude higher than for the vesicle phases. As has been found for the latter, the cubic phases have energy elasticity, i.e. the moduli break down at deformations beyond about 10%. 

In order to overcome this problem, it was necessary to improve the frequency range for the dynamic rheological measurements. For this purpose a dynamic rheometer (HF rheometer) with a frequency range from 1 Hz up to 1 kHz was built. For samples with a high modulus (G 1 kPa) the measurements can even be extended to 2 kHz. 

Dynamic rheological measurements will be briefly described. In dynamic measurements an oscillatory microscopic strain is given and the corresponding stress is measured. This method gives information on viscoelastic behavior even in the region where no viscous flow takes place. The measurements can be carried out by using the rotating cylinder viscometer or the cone and plate viscometer. 

The dynamic rheological measurements, i.e. storage and loss moduli can be used to determine the MWD. Size exclusion chromatography (SEC) has been around for decades for determining MWD. It requires dissolution of the sample for SEC and... 

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