Interface viscoelastic properties

Braithwaite, G. J. C. and Luckham, P. F. (1999). The simultaneous determination of the forces and viscoelastic properties of adsorbed polymer layers. /. Colloid Interface Sci. 218,97-111. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

The surface characteristics of these species are determined by the particulates and stress transfer across the membrane will tend to be low, reducing internal circulation within the drop. The structure of the interface surrounding the drop plays a significant role in determining the characteristics of the droplet behaviour. We can begin our consideration of emulsion systems by looking at the role of this layer in determining linear viscoelastic properties. This was undertaken by... 

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. 

It is very well known that the nature of the monolayer partially depends on the strength of interfacial interactions with substrate molecules and that of polymer in-tersegmental interactions. And it is normal to expect that the viscoelastic properties of polymer monolayer are also dependent on these factors. The static and dynamic properties of several different polymer monolayers at the air - water interface have been examined with the surface quasi-elastic Light Scattering technique combined with the static Wilhelmy plate method [101]. 

Fatigue resistance is a major factor in industrial applications of textile materials (conveyer belts, automobile tyres, etc.). The fatigue resistance depends on the viscoelastic properties (mechanical damping) of the material, but equally on the soundness of bonds between the surfaces or interfaces. 

In summary, the QCM-D technique has successfully demonstrated the adsorption of pectin on the BSA surface as well as determined the viscoelastic properties of the pectin layer. As pectin concentrations increase, the adsorbed mass of pectin estimated from the Voigt model show higher values than those estimated from the Sau-erbrey equation because the former takes into account the hydrated layer. But the similar increase of thickness of pectin suggests that the pectin chains form a multilayer structure. In agreement with our previous rheology results, the main elastic character of the pectin layer in terms of Q-tool software tells us the network structure of the pectin layer on the BSA surface. In summary, QCM-D cannot only help to better understand the polysaccharide/protein interactions at the interface, but also to gain information of the nanoscale structure of polysaccharide multilayers on protein surface. 

Galli Marxer, C., Collaud Coen, M., and Schlapbach, L. (2003). Study of adsorption and viscoelastic properties of proteins with a quartz crystal microbalance by measuring the oscillation amplitude. J. Colloid Interface Sci., 261, 291-298. 

Polymer melts are complex fluids. Their viscoelastic properties during flow depend not only on their molecular structure but also on the interactions they are likely to develop at the walls, depending on the physical and chemical features of the interface and the flow conditions. In addition, not all their properties can be determined and the constitutive equations used are in practice often limited to considerations on the shear viscosity. From a theoretical point of view, considerable difficulties are involved and the problem to be studied here has not been solved. In particular, even though the boundary conditions considered in... 

Boersma, W. H., Laven, J., and Stein, H. N. 1992. Viscoelastic properties of concentrated shear-thickening dispersions. 7. Colloid and Interface Sci. 149 10-22. 

Stauffer, D., Introduction to Percolation Theory, Taylor Friends, London, 1985. Yanez, J.A., Laarz, E., and Bergstrom, L., Viscoelastic properties of particle gels, J. Colloid Interface ScL, 209, 162, 1999. 

Naumann CA, Brooks CF, Fuller GG, Knoll W, Frank CW (1999) Viscoelastic properties of lipopolymers at the air-water interface a combined interfacial stress rheometer and film balance study. Langmuir 15 7752-7761... 

Coffman JP, Naumann CA (2002) Molecular weight dependence of viscoelastic properties in two-dimensional physical polymer networks amphiphilic lipopolymer monolayers at the air-water interface. Macromolecules 35 1835-1839... 

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