Oscillatory rheometry

Satisfactory agreement is achieved from these equations for depiction of the main features of linear viscoelastic properties that can be obtained with the experimental tools, either in transient or in oscillatory rheometry. 

Chou, T.C., Pintauro, N. and Kokini, J.L. 1991. Conformation of citrus pectin using amplitude oscillatory rheometry, J. Food Sci., 56(5) 1365-1368, 1371. 

Oscillatory rheometry, a nonsample destructive technique in which an oscillatory stress is applied to the sample over a range of frequencies and the resultant strain determined, usually at a defined (controlled) temperature. 

Oscillatory rheometry and dynamic mechanical thermal analysis, both termed dynamic oscillatory methods, allow for the convenient, accurate, and rapid quantification of the viscoelastic properties of pharmaceutical and biomedical systems. In light of this, considerations of the theory, practice, and applications of these methods will form the basis of this chapter. 

Strain the amount by which the sample is deformed. In oscillatory rheometry, the strain is horizontal (torsional) and is measured in radians, whereas in dynamic mechanical thermal analysis, the strain is termed amplitude (distance) owing to the vertical nature of the deformation. 

In continuous tests the deformation is large so the structure of the sample is destroyed. In oscillatory rheometry the deformation is small so the structure remains intact. Both viscous and elastic properties can be measured simultaneously. The elastic, solid-like component of the response (the storage modulus, G ) is in phase with the deformation and the viscous, liquid-like component (the loss modulus G") is out of phase. The ratio G /G is a measure of the relative importance of the viscous and elastic components. Thus, for example, ice cream that has a high G and a low G"/G is more solid-like than liquid-like. 

Variable Temperature Oscillatory Rheometry of Food Additives... 

DQM Craig, S Tamburic, G Buckton, JM Newton, An investigation on the structure and properties of Carbopol 934 gels using dielectric spectroscopy and oscillatory rheometry. J. Controlled Release 30 213-223, 1994. 

However, ar rheometry presents an important drawback, i.e.. the sample microsmicture may be destroyed during the test run. This is especially true for weak gels or pastes, even at low shear rates or shear stresses. Much information about the fluid microstnicture is lost in this manner, in this case, creep and oscillatory rheometry are more convenient. The creep and viscoelastic parameters may be related to the strength of flocculation or aggregation, and a better knowledge of the microstructure is obtained. Useful information about the application of these methods for the study of suspensions of clay paniclc.s. creams, and concentrated suspensions of latex particles can be found in Refs. 12.49. and 50. respectively. 

FIGURE 4.18 Frequency dependence of storage und loss modulus for star-(polyethylene glycol)-heparin hydrogel obtained by means of oscillatory rheometry. Reproduced with permission from Ref. 37. 

Phase angle n. In many cychc processes, particularly ones at high frequency, there is usually a time lag between the impulses driving the processes and the responses to those impulses. The lag time divided by the cycle period and multiplied by 2n is the phase angle (radians). This occurs in oscillatory rheometry, where the shear applied... 

Elastic Modulus. The elastic shear modulus of swollen superabsorbent polymer is commonly measured by means of oscillatory rheometry, using any of a variety of commercially available instruments (31). The sample to be analyzed is screened to the desired particle size cut such that the swollen particle size is smaller than the gap between the measuring plates. The sample is swollen in the desired liquid, usually 0.9 wt% NaCl solution or synthetic urine. Excess liquid is removed from the swollen hydrogel by blotting to minimize interparticle slippage. The hydrogel typically is placed onto the lower circular plate. An upper conical plate is positioned at the proper sample gap, which is packed with the gel. An oscillating torque is applied at a known frequency to the upper plate and the... 

Ethylene-propylene random copolymer Plateau modulus and entanglement GPC, DSC, oscillatory rheometry 120... 

Tamburic et al. [16] investigated polymeric thickener (acrylate) containing emulsions (0.2-0.4 wt. %) with high oil content (30 wt. %). The thickener is a poly(acrylic acid) with hydrophobic side chains (C10-C30) and cross linked by allylpentaerythritol. Continuous flow and oscillatory rheometry as well as texture analysis show that viscosity and elasticity of emulsions increase with higher acrylate concentrations, which is confirmed by our own measurements on emulsions with lower oil content (17 wt. %). 

Dynamic mechanical analysis in the rheology mode (oscillatory rheometry in cone and plate or parallel-plate geometries see Fig. 5.50) can be used to... 

Gomez-Carracedo, A., Alvarez-Lorenzo, C., Gomez-Amoza, J. L., Concheiro, A. (2003), Chemical structure and glass transition temperature of non-ionic cellulose ethers DSC, TMDSC (r) - oscillatory rheometry study, J. Therm. Anal. Calorim., 73, 587-96. 

Cone/Plate Viscometry Co-Axial Cylinder Viscometry Parallel Plate Viscometry Tensile or Extensional Viscometry Dynamic or Oscillatory Rheometry Morphological Analysis... 

Rides, M., AHen, C. R. G. Round robin for parallel plate oscillatory rheometry using polyethylene and polypropylene melts. Report CMMT( A) 11, Centre for Materials Measurement and Technology, Natl. Phys. Laboratory, Teddington, United Kingdom... 

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