Optical reflectometry

The polymer concentration profile has been measured by small-angle neutron scattering from polymers adsorbed onto colloidal particles [70,71] or porous media [72] and from flat surfaces with neutron reflectivity [73] and optical reflectometry [74]. The fraction of segments bound to the solid surface is nicely revealed in NMR studies [75], infrared spectroscopy [76], and electron spin resonance [77]. An example of the concentration profile obtained by inverting neutron scattering measurements appears in Fig. XI-7, showing a typical surface volume fraction of 0.25 and layer thickness of 10-15 nm. The profile decays rapidly and monotonically but does not exhibit power-law scaling [70]. 

Figure 1.4 Comparison of the application ranges of techniques that are sensitive to nearsurface strains. Minimum detection limits are plotted against depth resolution of the measurement. XRD X-ray diffraction DOR differential optical reflectometry. RBS Rutherford back scattering MEIS medium energy ion scattering TEM transmission electron microscopy...

In the field of protein adsorption, Interfaclal transcon— formations have been published by several authors. We observed an expansion of an adsorbed fibrinogen layer upon increasing the pH. Also thermal denaturation of the end-nodules, detected in solution between 50 and 60 (24), was observed by hydrodynamic ( 3) as well as optical reflectometry measurements (unpublished results). 

Figure 5 Schematic sketch of an optical reflectometry system. The activated-carbon chimney is perforated to admit the optical fiber (or laser beam directly when used in interferometry mode). The detector used in reflectometry is a photodiode coupled to a high-impedance pre-amplifier, the signal from which is passed through the A/D converter to the digital recorder.

PAA brushes were prepared on flat silicon wafers coated with polystyrene using the LB technique as described earlier in this chapter. Adsorption and desorption were monitored using fixed-angle optical reflectometry [58]. The kinetics and reversibility of the formation of a zipper brush are demonstrated in Figure 7.9, representing a typical reflectometry experiment of the adsorption and desorption of P2MVP-PEO to a PAA brush. 

Adsorption of the protein bovine serum albumin in a planar p>oly(acrylic add) brush layer as measured by optical reflectometry. 24 6575-6584. 

The chapter is organized as follows. Section 8.2 provides a short reminder of what acoustic shear waves can and cannot do. Shear waves have distinct advantages (compared to other surface anal3Ttical techniques like optical reflectometry or atomic force microscopy [AFM]), but there are also some caveats to be kept in mind. Section 8.3 briefly summarizes some predictions from simple planar models of slip. An experimental result, which stands as an example for an experience in the authors laboratory, is presented in section 8.4. Section 8.5 provides the results from FEM calculations. Section 8.6 discusses nonlinear phenomena and acoustic streaming, in particular. 

Adsorption of surfactants [Q] with X = OH and various values of x at silica surfaces have been investigated by optical reflectometry [31] (Fig. 6). The adsorbed amount of each surfactant on hydrophilic silica was about twice that on hydrophobic silica. The adsorbed amount depends little on x in the case of hydrophobic silica but decreases upon increasing x for hydrophilic silica, showing the effect of steric hindrance from the relatively larger head group. It was concluded that surfactants [Q] are better packed at solid-liquid interfaces than conventional surfactants. 

Until recently, the fast rate at which a surfactant layer forms at the solid-liquid interface has prevented accurate investigation of the adsorption process. As a result, the mechanism of surfactant adsorption has been inferred from thermodynamic data. Such explanations have been further confused by misinterpretation of the equilibrium morphology of the adsorbed surfactant as either monolayers or bilayers, rather than the discrete surface aggregates that form in many surfactant-substrate systems.2 However, the recent development of techniques with high temporal resolution has made possible studies of the adsorption, desorption,25>38,4i,48-6o exchange rates of surfactants. In this section, we describe the adsorption kinetics of C ,TAB surfactants at the silica-aqueous solution interface, elucidated by optical reflectometry in a wall-jet flow cell. The adsorption of C jTAB surfactants to silica is the most widely studied system - and hence the adsorption kinetics can be related to the adsorption process with great clarity. For a more thorough review of adsorptions isotherms, the t5q)es of surfactant structures that form at the solid-liquid interface, and the influence of these factors on adsorption, the reader is directed to Reference 24. 

In optical reflectometry (OR) a linearly polarized light beam is reflected from a surface and the reflectivity of s- and p-polarized components is measured (Figure 8.9). The intensity... 

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