Surface layers rheology

Surface shear rheology at the oil-water interface is a sensitive probe of protein-polysaccharide interactions. In particular, there is considerable experimental evidence for a general increase in surface shear viscosity of protein adsorbed layers as a result of interfacial complexation with polysaccharides (Dickinson et al., 1998 Dickinson and Euston, 1991 Dickinson and Galazka, 1992 Semenova et al., 1999a Jourdain et al., 2009). One such example is the case of asi-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = - 334 x 10 cm /mol) the interfacial viscosity after 24 hours was found to be five times larger in the presence of pectin (i.e., values of 820 80 and 160 20 mN m 1 with and without pectin, respectively) (Semenova et al., 1999a). 

Protein-polysaccharide complexation affects the surface viscoelastic properties of the protein interfacial layer. Surface shear rheology is especially sensitive to the strength of the interfacial protein-polysaccharide interactions. Experimental data on BSA+ dextran sulfate (Dickinson and Galazka, 1992), asi-casein + high-methoxy pectin (Dickinson et al., 1998), p-lactoglobulin + low-methoxy pectin (Ganzevles et al., 2006), and p-lactoglobulin + acacia gum (Schmitt et al., 2005) have all demon-... 

Surface layers (adsorbed, solvated, ionic) are of considerable importance in controlling the stability and rheological properties of colloidal systems. Sedimentation methods have proven effective in the measurement of adsorbed layer thickness using equations similar to Equation 1 when the density of the layer could be estimated ( 7,8). The equation can be considerably simplified if the density... 

Stable particle suspensions exhibit an extraordinarily broad range of rheological behavior. which depends on particle concentration, size, and shape, as well as on the presence and type of stabilizing surface layers or surface charges, and possible viscoelastic properties of the suspending fluid. Some of the properties of suspensions of spheres are now reasonably well understood, such as (a) the concentration-dependence of the zero-shear viscosity of hard-sphere suspensions and (b) the effects of deformability of the steric-stabilization layers on the particles. In addition, qualitative understanding and quantitative empirical equations... 

The lateral liquid und surface layer movement is influenced by surface rheology which is coupled with the exchange of matter process (surface relaxations). This coupling creates great difficulties in the quantitative description of dynamic adsorption layers (DAL). A brief introduction into surface rheology and surface relaxations is given and results are specified for use in Chapters 8,9,10 and 11. 

Some consequences which result from the proposed models of equilibrium surface layers are of special practical importance for rheological and dynamic surface phenomena. For example, the rate of surface tension decrease for the diffusion-controlled adsorption mechanism depends on whether the molecules imdergo reorientation or aggregation processes in the surface layer. This will be explained in detail in Chapter 4. It is shown that the elasticity modulus of surfactant layers is very sensitive to the reorientation of adsorbed molecules. For protein surface layers there are restructuring processes at the surface that determine adsorption/desorption rates and a number of other dynamic and mechanical properties of interfacial layers. 

Dilational rheological experiments are based on area changes by keeping the shape of the interface constant. Models for the exchange of matter, which sets in after a compression or expansion of the interface, are generally applicable to both harmonic and transient types of relaxations (178). Stress-relaxation experiments may yield results different from those obtained from measurements on small disturbances as the composition of the surface layer can vary (179). Overviews on experimental and theoretical aspects of dilational rheology were given recently in Refs 180—182. 

Rheological properties of formed surface layers can be considered as the strong demonstration of protein adsorption at a/w surface. These properties show the formation of a surface film of definite structure, that can be regarded as a thin layer of a third phase [36]. 

The modification of theological properties also may be achieved by addition of a small amount of another polymer which is not miscible with matrix P0I3 -mer. Thus, the general conclusion may be drawn that the peculiarities of the rheological properties of filled polymers are determined by the combined action of various factors, namely, by hydrod3mamic effects, the interaction between the filler particle and a matrix, leading to the formation of the surface layers and the formation of the structural frame by the filler particles. 

In rheological experiments, that is, when the surface layer is periodically compressed and expanded around the equilibrium state, we also meet the situation that molecules desorb from the interface, increasing the local concentration of monomers such that micelles have to either take up molecules or form new micelles. In this case, a diffusion flux of monomers and micelles from and to the interface exists, depending on the respective situation at the interface [16, 25]. The peculiarities of the micellar kinetics in various systems are discussed in several papers however, the general principles hold [30-34]. 

---