Surface rheological measurements

THE RELATIONSHIP OF FRAP MEASUREMENTS OF SURFACE DIFFUSION AND OTHER SURFACE RHEOLOGICAL MEASUREMENTS... 

Figure 24. A comparison of the data obtained from a range of surface rheological measurements of samples of /3-lg as a function of Tween 20 concentration. ( ), The surface diffusion coefficient of FITC-jS-lg (0.2 mg/ml) at the interfaces of a/w thin films (X), the surface shear viscosity of /3-lg (0.01 mg/ml) at the o/w interface after 5 hours adsorption ( ), the surface dilational elasticity and (o) the dilational loss modulus of /3-lg (0.2 mg/ml).

There have now been attempts to determine rheological properties on the nanoscale. The nano-rheological properties (surface viscoelasticity) of emulsion droplets have been estimated through modelling based on data from atomic force microscope measurements [371]. 

Adamson [15] and Miller et al. [410] illustrate some techniques for measuring surface shear viscosity. Further details on the principles, measurement and applications to foam stability of interfacial viscosity are reviewed by Wasan et al. [301,412], It should be noted that most experimental studies deal with the bulk and surface viscosities of bulk solution rather than the rheology of films themselves. 

We could use a simplified form of rj z) = ri f z). Here is the bulk viscosity, and /(z) can be experimentally determined. Here, z is the distance normal to the solid surface. A partial justification for the above functional form can be drawn from the temperature dependence of the surface diffusion coefficient and the bulk viscosity,or the fly stiction correlation with the bulk viscosity. To develop a rigorous hydro-dynamic model, we need better rheological data and more details are given in the following section on Rheology Measurement. 

FIG. 4.22 Schematic of biconical tool for surface rheology measurements using the Paar Physica interfacial rheometer. (Courtesy of American Institute of Physics.)... 

P. G. de Gennes, Physics of Polymer Surfaces and Interfaces, edited by Isaac C. Sanchez (Butterworth-Heinemann, Burlington, MA (1992), Chap. 3, pp. 55-71 J. L. Goveas and G. H. Fredrickson (1992), Apparent slip at a polymer-polymer interface, Eur. Phys. J. B2,79-92 (1998) R. Zhao and C. W. Macosko, Slip at polymer-polymer interfaces Rheological measurements on coextruded multilayers, J. Rheol. 46, 145-67 (2002). 

FIGURE 10.33 Principles of interfacial rheological measurements, (a) In shear. A thin disc (D) is at an O-W interface and is made to rotate (or oscillate) the torque on the disc can be measured, e.g., via a torsion wire (T). (b) In expansion/compression. Barriers (B) at an O-W interface are moved, thereby increasing or decreasing the interfacial area between them the interfacial tension is measured by means of a Wilhelmy plate (P). Both kinds of measurement can also be made at A-W and A-O surfaces. 

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