Surface light scattering

Surface Light Scattering Adapted to the Advanced Undergraduate Laboratory 37... 

However, for the temperatures above 15°C the agreement is not quantitative. It is also important to remember that the kilohertz region has been explored by the surface Light Scattering (SLS) technique. The results obtained are compatible... 

The system uses a helium-neon laser to scan a wafer surface. Light scattered by defects is collected and amplified, and the resulting photomultiplier signals reveal the location and nature of the defect. Particles as small as 0.3 micron can be detected. 

BS. Buffone, C. J., Cross, R. E., Savory, J., and Soodak, C., Measurement of laser-induced near front surface light scattering with a parallel fast analyzer system. Anal. Chetn. 46, 2047-2049 (1974). 

Keywords Monolayers Surface light scattering Capillary waves Dispersion equation Dilational elastic modulus Dilational loss modulus Scaling exponent... 

We shall not pursue this approach here because it does not help us much in finding a molecular interpretation, certainly not for U°. Even in the absence of waves (solidified liquids), U° is substantial. Rather, this interpretation deals with a contribution to y than with y itself. However, we recall that the capillary wave connection had already occurred in the technique for measuring surface tensions from surface light scattering, see Mandelstam s equation [1.10.1], from which an explicit formula for y may be derived. 

Figure 4.18. As previous figure surface tensions obtained from surface light scattering. Temperature 25°C. (Redrawn from Hard and Johannson, loc. cit.)...

Finally, we recall that surface light scattering is another modem technique. Essentially. thermal capillary waves can be studied and this enables us to derive interfacial tensions and binding constants. We discussed this matter in sec. 1.10. 

Perhaps the most striking property of a microemulsion in equilibrium with an excess phase is the very low interfacial tension between the macroscopic phases. In the case where the microemulsion coexists simultaneously with a water-rich and an oil-rich excess phase, the interfacial tension between the latter two phases becomes ultra-low [70,71 ]. This striking phenomenon is related to the formation and properties of the amphiphilic film within the microemulsion. Within this internal amphiphilic film the surfactant molecules optimise the area occupied until lateral interaction and screening of the direct water-oil contact is minimised [2, 42, 72]. Needless to say that low interfacial tensions play a major role in the use of micro emulsions in technical applications [73] as, e.g. in enhanced oil recovery (see Section 10.2 in Chapter 10) and washing processes (see Section 10.3 in Chapter 10). Suitable methods to measure interfacial tensions as low as 10 3 mN m 1 are the sessile or pendent drop technique [74]. Ultra-low interfacial tensions (as low as 10 r> mN m-1) can be determined with the surface light scattering [75] and the spinning drop technique [76]. 

The present state of surface rheology and surface light-scattering research into relaxation times at liquid interface will be dealt with later. Famous scientists like Einstein (1920), Liebermann (1949), Frenkel Obraztsor (1940) and Yao (1981) developed mathematical algorithms to... 

Elastic and inelastic light scattering are nowadays widely used techniques for the characterization of fluids. In particular, these techniques have been extensively and successfully used with microemulsion systems to obtain information about droplet sizes. Surface light scattering is a less common technique but has been used with microemulsion interfaces, in particular to measure the ultralow interfacial tensions found in these systems. In this chapter we discuss these aspects, first recalling the theoretical background and illustrating the potential of the techniques with experimental results. 

Because the surface light scattering method is less well known than the bulk scattering one, we will give some details about its principle. In the surface scattering method, a laser beam impinges on the surface. Because of thermal motion, the surface is not perfectly flat and scatters light in all directions around the specularly reflected beam. The surface displacement C can be described as a superposition of sinusoidal deformations C = where r is the position in the equilibrium plane of the surface and q is... 

The surface light scattering method has been used to show that the low interfaciai tensions in the Winsor I and II systems (O/W microemulsion in equilibrium with excess oil and W/O microemulsion in equilibrium with excess water, respectively) are due to the large surface pressure of the surfactant monolayer coating the interface, which almost balances the bare oil/water interfaciai tension [36,37]. Schulman and Montagne [38] proposed early that the low interfaciai tensions in microemulsion systems should be associated with these large surface pressures tt, i.e., 7 = 70 - tc 0. In other models, the origin of the low interfaciai tensions was attributed to the vicinity of critical points [39,40]. 

In this paragraph we will briefly recall the main features of the surface light scattering technique. Further details can be found in reference (4). 

PlatzerWJ, Bergkvist M(1993) Bulk and surface light scattering from transparent silica aerogel. Solar Energy Mater Solar Cells 31 243-251... 

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