Dynamic rheometry

In a current rheological study [296], the galactoxyloglucan from Hymenia courbaril was mixed with starch containing 66% amylose and with waxy corn starch (amylopectin). The gel mixtures showed, under static rheological conditions, an increase in paste viscosity compared to those of the polysaccharides alone. Dynamic rheometry indicated that the interactions resulted in increased thermal stability of the gel formed in comparison to that of the starch alone. 

Dynamic rheometers have been widely used to study the viscoelastic characteristics of liquid, solid, and semi-solid foods. However, to our knowledge, very few studies on the rheological characteristics of potato flesh using dynamic rheometry have been carried out. The dynamic rheological behavior of potato tubers may be helpful to have a quick idea about potato texture and... 

Table 10.3 Rheological parameters of starches from different botanical sources during heating from 30 to 75°C, studied using dynamic rheometry...

In this section, some case studies will be presented on the characterization of CMP pad and slurry [17-20] using such advanced analytical techniques as dynamic mechanical analysis (DMA), modulated differential scanning calorimetry (MDSC), thermal gravimetric analysis (TGA), thermal mechanical analysis (TMA), dynamic rheometry, dual emission laser induced fluorescence (DELIF), and the dynamic nuclear magnetic resonance (DNMR). More specifically, these techniques were used to characterize (a) the effect of heat... 

Biliaderis, C. G. 1992. Characterization of starch networks by small strain dynamic rheometry, in Developments in Carbohydrate Chemistry, eds. R. J. Alexanda and H. F. Zobel, American Association of Cereal Chemists, St. Paul, MN. 

Dynamic rheometry was not (and, apparently, cannot be) employed for studying melt fracture of neat plastics and composite materials. This has been done so far only using capillary rheometry. However, dynamic oscillatory measurements can produce the most reliable rheological data on filled polymers [2,4]. It should be noted that measurements at dynamic oscillatory conditions bellow frequency of 0.1 rad/s likely produce erroneous results due to the increased time for reaching steady state at low frequencies [4]. 

Figure 5 (a) Elastic and viscous moduli as functions of shear stress obtained from oscillatory shear dynamic rheometry (see text and Ref 80 for details) performed at the oil-water interfece. The system consisted of 40 ml of water on to which 35 ml of an oil phase was layered, consisting of 0.75% (w/v) B6 asphaltenes dissolved in 50% (v/v) toluene in heptane. The asphaltenes were allowed to adsorb for 8 h at which point the rheometrical measurements were performed. The frequency of oscillation of the biconical hob was 1 rad/s. (b) Elastic and viscous moduh as functions of frequency. The same system and experiment as described for Fig. 5a were used with the exception that the shear stress was fixed at 1 mPa and the frequency was varied. Asphaltenes were allowed to adsorb for a period of 8 h. 

Figure 8 Elastic modulus as a function of frequency obtained from oscillatory shear dynamic rheometry (see text) performed at the oil-water interface. The proportions of oleic and aqueous phase are the same as described for Fig. 5. Concentrations of 0.25, 0.75, and 1.5% (w/v) B6 asphaltenes were dissolved in the oleic phase (50% yh toluene in heptane) before adsorption. Samples were aged for 8 or 24 h. Shear stress was held constant at 1 mPa.

With dynamic rheometry, the measurement of the dynamic moduli G and G" in small amplitude oscillatory shear is exploited. The gelation point is reported to be the intersection point of the curves of storage and loss moduli, i.e. the moment at which tan 8 equals one [49]. However, the crossover is observed to correspond to the gel point only for stoichiometrically balanced network polymers and networks with excess crosslinking agent at temperatures much above Tg [50]. 

As seen in Figure 2.26, the Tg — x data obtained from the residual cure (MT)DSC experiments are well described by the optimised Tg— x relationship [Eq. (27)] of the diffusion-controlled cure model (Tg is the solid line and Tga is the dashed line). The departure of the experimental data from the continuous dashed line is due to the effect of increasing crosslinking beyond the gel point. The conversion at gelation correlates well with the value of 25% measured with dynamic rheometry (using the criterion G = G ). 

Figure 2.30. TXT cure diagram for an epoxy-anhydride thermosetting system. MTDSC results (o) DF%, ( ) DF% s (A) DFl. Data obtained with dynamic rheometry ( ) ...

Table 2.1. MTDSC and dynamic rheometry results for the epoxy systems studied. The symbols are defined in the text.

Dynamic rheometry isothermal cure of epoxy systems... 

PA-6/PC/epoxy resin Mechanical properties/DSC/SEM/ dynamic rheometry/effects of 3 different mixing sequences Wang et al. 2012c... 

Patel M. Viscoelastic properties of polystyrene using dynamic rheometry. Polym Test 2004 23(1) 107-112. 

Changes in modulus of thermogelling polymer aqueous solutions can be determined by dynamic rheometry (Fig. 11). 

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