Rheological studies

Rheological studies, as well as drug release studies, were carried out to analyze the properties of the new polymer as matrix-forming excipient. 

COMPOSITION OF WOOD-PLASTIC COMPOSITES COUPLING AGENTS 

It is rather striking that, as it is seen from Fignre 5.3, at high shear rates (above 200 s ) all three conpling agents produce shear stress lower than that of the control, uncoupled WPC. At the first thought, this is nonsense. However, it just reflects a complex interplay of various factors in the system, and the wall slip plays a significant role there. A correction for wall slip shows how important is the factor (Fig. 5.4). 

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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. 

Prud homme, RK Wu, G Schneider, DK, Structure and Rheology Studies of Poly(oxyethy-lene-oxypropylene-oxyethylene) Aqueous Solution, Langmuir 12, 4651, 1996. 

Hill, R. G. Wilson, A. D. (1988b). A rheological study of the role of additives on the setting of glass ionomer cements. Journal of Dental Research, 68, 89-94. 

Rheo-NMR [86] methods have been shown to be well-suited to emulsion rheology studies [28] and could be combined with any of the topics described above. The combination of structural and rheological measurements is a promising area for further research. 

Rheology is the study of flow and deformation of materials under the influence of external forces. It involves the viscosity characteristics of powders, liquids, and semisolids. Rheological studies are also important in the industrial manufacture and applications of plastic materials, lubricating materials, coatings, inks, adhesives, and food products. Flow properties of pharmaceutical disperse systems can be of particular importance, especially for topical products. Such systems often exhibit rather complex rheological properties, and pharmaceutical scientists have conducted fundamental investigations in this area [58-64],... 

Rheological studies explore the flow of a material as an external force acts upon it. This flow depends not only on the magnitude and directionality of the external force, but also on the molecular composition and structure of the material that experiences the force. In this chapter, we will focus on the flow behavior of molten polymers, as it relates to their molecular structure. It is important to note that the molecular characteristics that determine a molten polymer s behavior also define the polymer s solid state behavior. Therefore, many of the concepts introduced in this chapter will reappear in Chapter 8, Solid State Properties of Polymers., ... 

Reidenbach, V.G. Harris, P.C. Lee, Y.N. Lord, D.L. "Rheological Study of Foam Fracturing Fluids Using Nitrogen and Carbon Dioxide", SPE paper 12026, 1983 SPE Annual Technical Conference and Exhibition, San Francisco, October 5-8. 

Rheological Studies of Aqueous Concentrated Polystyrene Latex Dispersions with Adsorbed Poly(vinyl alcohol) Layers... 

In this paper we report some rheological studies of aqueous concentrated polystyrene latex dispersions, in the presence of physically adsorbed poly(vinyl alcohol). This system has been chosen in view of its relevance to many practical systems and since many of the parameters needed for interpretation of the rheological results are available (15-18). The viscoelastic properties of a 20% w/w latex dispersion were investigated as a function of polymer coverage, using creep measurements. 

Moreover, rheological studies were carried out on a dispersion (25% w/w) which was flocculated either by addition of sufficient electrolyte (Na2S04) or by raising the temperature at a constant electrolyte concentration. 

UV Cross-Linking of Thiol-ene Polymers A Rheological Study... 

In summary, the rheological studies of PATE are consistent with a proposed molecular association model for PATE solutions. Kinematic viscosity evaluation shows that at concentrations of 15% to 20% solids, a gelatinous solution results. The apparent viscosity measurements illustrate that network formation can be overcome by heating indicating that the association is electrostatic in nature. 

Thus, dendrimers exhibit a unique combination of (a) high molecular weights, typical for classical macromolecular substances, (b) molecular shapes, similar to idealized spherical particles and (c) nanoscopic sizes that are larger than those of low molecular weight compounds but smaller than those of typical macromolecules. As such, they provide unique rheological systems that are between typical chain-type polymers and suspensions of spherical particles. Notably, such systems have not been available for rheological study before, nor are there yet analytical theories of dense fluids of spherical particles that are successful in predicting useful numerical results. 

Finally we compare the temperature dependencies reported for the structural relaxation and the self-motion of hydrogens studied by NSE. For PI, the shift factors used for the construction of the master curve on Q,T) (Fig. 4.17) are identical to those observed for the structural relaxation time [8]. This temperature dependence also agrees with DS and rheological studies. The case of PIB is more complex [ 147]. The shift factors obtained from the study of Teif(Q>T) (Fig. 4.14b) reveal an apparent activation energy close to that reported from NMR results (-0.4 eV) [136]. This temperature dependence is substantially weaker than that observed for the structural relaxation time (=0.7 eV, coinciding with rheological measurements) in the same temperature range (see Fig. 4.20). 

The criteria by which these resins are evaluated include thermal analysis, cure kinetics and rheological studies of the uncured resin. Mechanical properties including hot/wet sample testing and thermal analysis are then obtained from cured neat resin speciswns. The results from these tests run on the neat resin will give some indication of the suitability of that resin for use as a composite matrix material and future studies to be conducted. 

An appropriate cure cycle was established based on the results obtained from the thermal analysis and cure rheology studies of the resin and cured BCB bar and dogbone shaped samples were fabricated for testing. Bar shaped specimens had the dimensions of 3.5 x 0.5 X 0.125 and were used to stake compact tension specimens for fracture toughness studies and for dynamic mechanical analysis of a torsion bar. Dogbone shaped specimens for tensile tests had a gauge area of 1 x 0.15 and were approximately 0.040 thick. 

Tsai, H.-H. Phase Equilibrium and Rheological Studies of Solutions of Rodlike, Articulated Polymers and Their Mixtures, Ph.D. Thesis, Carnegie-Mellon University, Pennsylvania, 1983... 

Many fundamental material properties are accessible in rheological and mechanical testing experiments [60]. Rheological properties are not only very relevant for the processing of polymers, they are also the basis for understanding chain motion and relaxation processes in (linear) polymers. Relatively few rheological studies have been reported on PPC, often only in combination with the processing of PPC [15,61]. 

Rheological studies involving Fe oxides appear to be sparse. Most are carried out on acicular crystals, usually maghemite. Details of the method of synthesis or properties of the particles are often lacking. 

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