Viscoelastic properties, aqueous

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. 

Figure 8.12 illustrates the effect of complex formation between protein and polysaccharide on the time-dependent surface shear viscosity at the oil-water interface for the system BSA + dextran sulfate (DS) at pH = 7 and ionic strength = 50 mM. The film adsorbed from the 10 wt % solution of pure protein has a surface viscosity of t]s > 200 mPa s after 24 h. As the polysaccharide is not itself surface-active, it exhibited no measurable surface viscosity (t]s < 1 niPa s). But, when 10 wt% DS was introduced into the aqueous phase below the 24-hour-old BSA film, the surface viscosity showed an increase (after a further 24 h) to a value around twice that for the original protein film. Hence, in this case, the new protein-polysaccharide interactions induced at the oil-water interface were sufficiently strong to influence considerably the viscoelastic properties of the adsorbed biopolymer layer. 

Gliadin. Gliadin is that portion of the gluten proteins that is soluble in 70% aqueous ethanol. It comprises approximately 35 to 40% of the flour proteins. Gliadin imparts the viscous component to the viscoelastic properties of gluten. 

Measurement of the viscoelastic properties of foams and dense emulsions is also complicated by slip at the rheometer surfaces (Yoshimura and Prud homme 1988). The liquid in an aqueous foam lubricates flat rheometer fixtures, reducing the strain imposed on the bulk foam. This lubrication is a desirable feature of some foam products such as shaving cream, but it complicates rheological studies. The use of roughened surfaces, such as sandpaper bonded to the rheometer fixtures, seems to be an effective countermeasure (Khan et al. 1988). ... 

In this work we studied the regularities of a horseradish peroxidase (HRP) layer formation from its aqueous solutions on bare gold surface and that modified with a polyethyleneimine/polystyrene sulfonate bilayer using the quartz crystal microbalance (QCM) technique in liquid phase allowing to achieve highly sensitive mass detection and obtain information on viscoelastic properties of the adsorbed layers [3,4]. 

Chronakis IS, Doublier J-L, Piculell L (2000) Viscoelastic properties for kappa- and iota-carrageenan in aqueous Nal from the liquid-like to the solid-like behaviour. Int J Biol Macromol 28 1-14... 

When the polymer concentration (or molecular mass) is sufficiently high and viscosity of solution exceeds essentially that of solvent, the rheological effects in bubble dynamics become much more pronounced. In Figure 7.2.7, data are presented for the relative damping decrement of free oscillations of air bubble with Ro = 2.8 mm in aqueous solution of POE via concentration. The dashed line represents theoretical values of the decrement, corresponding to Newtonian liquid with 13 =T)p. The actual energy losses, characterized by experimental points, remained almost unchanged, despite the sharp rise in the Newtonian decrement, Ap, with c. This result correlates well with the above theoretical predictions and it is explained by viscoelastic properties of the solution. The same explanation has the phe-... 

In the literature, viscoelastic measuinnents before the gel point of gelatin solutions are largely unreported. As far as the author knows, Djabourov et aL [469] were the first to report measuronents of viscoelastic properties of aqueous gelatin solutions before the gel point (down to G = 7 x 10 N/m ) of a 4.7 /o aqueous solution. In about 3 h the system gradually changes from a Newtonian... 

Djabourov et al. [458,469, 508-510] determined the relationship between viscoelastic properties and optical rotation. From optical rotation the weight fraction, %, of helices present in an aqueous gelatin system could be calculated, because of the big difference in optical rotations in the coiled and the helical (collagenlike) states ... 

Due to difference in sulfate content between agarose and carrageenans, the viscoelastic properties of aqueous solutions and gels of these bipolymers are quite different. 

A wheat protein derivative with molecular weight of 250-500 kDa has been studied in aqueous solution and in an 0/W emulsion for its effects on the viscoelastic properties of the skin. A slight increase in skin extensibility and elasticity was found and related to its moisturizing and film-forming effects. This derivative is proposed in skin care preparation for transient skin Arming-tightening effects (54). 

Block Ionomers. The block ionomers to be discussed are of AB or ABA type, in which one of the blocks is ionic (eg, sodium methacrylate) and the other consists of nonionic units (eg, polystyrene). While ionic block copolymers in a micelle form in both aqueous and nonaqueous solutions have been studied extensively (99-101,130,131), the viscoelastic properties of block ionomers in bulk have not received much attention (132-137). If the short ionic blocks formed micelle-like aggregates, which were surrounded by nonionic blocks, the viscoelastic properties of the diblock ionomers would be very similar to those of stars or polymers of low molecular weight (136). Thus, above the Tg of the nonionic blocks, as the temperature increased the modulus dropped rapidly with a very short rubbery plateau. For example, in a dynamic mechanical study, it was found that a homopolymer containing 490 styrene units showed a Tg at ca 115°C, and started to flow at ca 150°C. However, in the case of a diblock ionomer containing 490 styrene units and 40 sodium methacrylate ionic units showed a Tg at ca 116°C, and flow behavior was observed above ca 165°C, which was only 15°C higher than that of nonionic polystyrene (135). 

In fact, it could be shown that Eq. 2 (and more general relations) can be successfully applied to determine the viscosity or viscoelastic properties of not only aqueous or organic systems [10-13, 15, 17], or of conducting polymers [11, 42-46], but also of ionic liquids [14,18,19]. Ionic liquids are very viscous electrolytes, having a viscosity 50-100 times larger than that of aqueous systems. 

Shikata T, Hirata K, Kotaka T (1987) Micelle formation of detergent molecules in aqueous media. 1. viscoelastic properties of aqueous cetyltrimethylammonium bromide solutions. Langmuir 3 1081-1086... 

---