Elasticity interfacial

There is currently little understanding of the influence of interfacial composition and (nano)structure on the kinetics of enzymatic hydrolysis of biopolymers and lipids. However, a few preliminary studies are beginning to emerge (McClements et al., 2008 Dickinson, 2008). Thus, for example, Jourdain et al. (2009) have shown recently that, in a mixed5 sodium caseinate + dextran sulfate system, the measured interfacial viscosity increased from qs = 220 mN s m 1 without enzyme to qs = 950 mN s m 1 with trypsin present. At the same time, the interfacial elasticity was initially slightly reduced from (7S = 1.6 mN m 1 to (h = 0.7 mN m, although it later returned to close to its original value. Conversely, in the... 

Smaby JM, Momsen MM, Brockman HL, Brown RE. Phosphatidylcholine acyl unsaturation modulates the decrease in interfacial elasticity induced by cholesterol. Biophys J 1997 73 1492-1505. 

Smaby JM, Momsen MM, Brockman HL, Brown RE. Phosphatidylcholine acyl chain unsaturation modulates the decrease in interfacial elasticity induced by cholesterol. Biophys J 1997 73 1492-1505. Souvignet C, Pelosin JM, Daniel S, Chambaz EM, Ransac S, Verger R. Activation of protein kinase C in lipid... 

The droplet deformation increases with increases in the Weber number which means that, in order to produce small droplets, high stresses (i.e., high shear rates) are require. In other words, the production of nanoemulsions costs more energy than does the production of macroemulsions [4]. The role of surfactants in emulsion formation has been described in detail in Chapter 10, and the same principles apply to the formation of nanoemulsions. Thus, it is important to consider the effects of surfactants on the interfacial tension, interfacial elasticity, and interfacial tension gradients. 

These subjects will be described explicitly in the subsequent chapters. It is evident that both the mechanical properties and the exchange of matter at interfaces are of general interest for an improved understanding of the foaming and emulsification processes. Experimental access to these properties of adsorption layers is given by relaxations experiments which provide simultaneously information about the exchange of matter and the dilational interfacial elasticity defined by... 

Figure 6. Interfacial mobility, or dimensionless drainage velocity, versus dimensionless film thickness, at three values of the dimensionless interfacial elasticity number. (Reproduced with permission from reference 21. Copyright 1991 Butterworth—Heinemann.)...

The drop-shape oscillation technique as developed by Tian et al. (206, 207) is another technique suitable for closing the gap in the experimental methods for liquid/liquid interfaces. This method is based on the analysis of drop-shape oscillation modes and yields again the matter-ex-change mechanism and the dila-tional interfacial elasticity. The method is similar to the transient relaxation methods applicable only for comparatively low oscillation frequencies. 

Williams and Janssen (20) studied the behavior of droplets in a simple shear flow in the presence of a protein emulsifier. The effect of two structurally diverse protein emulsifiers, P-lactoglobulin and P-casein, upon the breakup behavior of a single aqueous droplet in a Couette flow field has been studied over a wide range of protein concentrations. It was found that P-casein and low concentrations of P-lactoglobulin cause the droplets to be at least as stable as expected from conventional theories based on the equilibrium interfacial tension. In such cases the presence of the emulsifier at the deforming interface is thought to enhance the interfacial elasticity. This effect can be characterized by... 

The initial (maximum) film tension after the expansion in the film stress-relaxation experiments can also be used to determine the film elasticity (7). A plot of the initial film tension versus the logarithm of the relative film expansion is shown in Fig. 5. For comparison, the initial single interfacial tensions obtained in the experiments with the respective single oil/water interface are also plotted. The film elasticity obtained from the top of the curve is equal, within experimental error, to twice the interfacial elasticity of the single interface. 

Rheology is the study of the deformation and flow of materials under the influence of an applied stress. The interfacial rheology of a surfactant film normally accounts for the interfacial viscosity and elasticity of the film. The interfacial viscosity can be classified with interfacial shear viscosity and interfacial dilational viscosity. Films are elastic if they resist deformation in the plane of the interface and if the surface tends to recover its natural shape when the deforming forces are removed. The interfacial elasticity can also be classified with interfacial shear elasticity and interfacial dilational elasticity (6, 7, 12). Malhotra and... 

Interfacial rheological properties are expressed as interfacial elasticity and interfacial viscosity. Based on the study of coalescence of cmde oil droplets, Malhotra and Wasan (70, 71) concluded that there is a good correlation between coalescence time and interfacial viscosity, i.e., the higher... 

The function accounts for the effect of the surface mobility. For large interfacial elasticity one has d —>0, see Eq. (53) then T —>1 and Eq. (61) acquires a simpler form, corresponding to drops of tangentially immobile interfaces. In the other limit, small interfacial elasticity, one has d 1 and in such a case T oc 1/ln J, i.e., T decreases with the increase in d, that is, with the decrease in Eq. A numerical solution to this problem is reported in Ref 24. The effect of the interfacial viscosity on the transitional distance, which is neglected in Eq. (61), is examined in Ref 141. It is established therein that the critical distance, h, can be with in about 10% smaller than hp... 

Nonionic surfactants generally have less initial foam and less stability. The large surface area/molecule leads to lower interfacial elasticity, and the big bulky head groups are slow to diffuse to new interfaces. 

Van Hemelrijck Ellen, Van Puyvelde Peter, Macosko Christopher, and Moldenaers Paula. The effect of block copolymer architecture on the coalescence and interfacial elasticity in compatibilized polymer blends. J. Rheol. 49 no. 3 (2005) 783-798. 

FIG. 15 Dimensionless drainage time for the film to drain from a dimensionless thickness, fi, to the thickness, hf, vs. Boussinesq number, at various values of the dimensionless interfacial elasticity number. (From Ref. 110.)... 

MPa the elastic modulus of the SiC whisker E = 400 GPa, and Poisson s ratio Vf = 0.16 the interfacial layer of the material is isotropic, Poisson s ratio is 0.2, and interfacial elastic modulus is E. The elastic-plastic modulus is calculated by using a different interfacial modulus E value. The exterior stress Oq is set at 0.85 MPa, and the influence of different interfacial bonding states on stress concentration coefficient, interfacial shear stress, and axial stress of whisker end face is simulated. Figure 4.12 is the stress concentration coefficient... 

With the increase of interfacial elastic modulus, the stress concentration of the whisker end face gradually increases, which indicates that a good interfacial bonding condition is an effective way to improve the reinforcing capability of whiskers. 

The role of surfactants on emulsion formation is detailed in Chapter 6 and the same principles apply to the formation of nano-emulsions. Thus, one must consider the effect of surfactants on the interfadal tension, interfacial elasticity, and interfacial tension gradients. 

The minimization of the total free energy F -f F2) with the radius gives the equilibrium droplet radius / , which depends on the natural radius Ro, the interfacial elasticity k and the energy of inter-droplet interactions F2, as follows ... 

In order to explain this experimental feature, Leodidis and co-workers developed a thermodynamic model where the chemical potential depends on the curvature of the film and on the bending moment or interfacial elastic constant C. The variation of Kx with curvature can be derived from the equality between the chemical potential of an amino acid in excess water and in the interface, as follows ... 

Figure 9 Interfacial elasticity Eq, diffusion relaxation time t and interfacial dilatation viscosity T rf versus pH of solutions of 0.0125 wt% BSA the other phase is decane. pH is maintained by a phosphate buffer the ionic strength, I, is adjusted by NaCl. The droplet expansion method is applied. (After Ref. 84.)...

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