Polymers, adsorption 300 INDEX

In the last 10-15 years, neutron reflectometry has been developed into a powerful technique for the study of surface and interfacial structure, and has been extensively applied to the study of surfactant and polymer adsorption and to determine the structure of a variety of thin films [14, 16]. Neutron reflectivity is particularly powerful in the study of organic systems, in that hydrogen/deu-terium isotopic substitution can be used to manipulate the refractive index distribution without substantially altering the chemistry. Hence, specific components can be made visible or invisible by refractive index matching. This has, for example, been extensively exploited in studying surfactant adsorption at the air-solution interface [17]. In this chapter, we focus on the application of neutron reflectometry to probe surfactant adsorption at the solid-solution interface. 

FIGURE 20 Effect of partial reduction by CO of the more reactive sites, followed by selective poisoning of the reduced sites by CO adsorption at 25 °C, on the activity (above) and polymer melt index (below). 

Fourier transform infrared speetroseopy (FTIR) in the mode of attenuated total re-fleetion (ATR) has been sueeessfully applied for studying polymer adsorption or exehange on the surfaee of an infrared prism eonsisting of, e.g., germanium or sil-ieon [44, 45]. In an ATR eell a beam of light is totally refleeted at the boundary of the interfaee between the prism and the solution. The prism has a refraetive index higher than that of the solution. An evaneseent wave penetrates the medium of lower refraetive index (polymer solution side) with a penetration depth of the order of the... 

Synthetic, nonionic polymers generally elute with little or no adsorption on TSK-PW columns. Characterization of these polymers has been demonstrated successfully using four types of on-line detectors. These include differential refractive index (DRI), differential viscometry (DV), FALLS, and MALLS detection (4-8). Absolute molecular weight, root mean square (RMS) radius of gyration, conformational coefficients, and intrinsic viscosity distributions have... 

The variation of refractive index n(D) of the medium separating the mica surfaces is shown in figure 6b (for PE02), both before and after adsorption of polymer, as well as following replacement of the polymer solution by pure electrolyte after adsorption. The results show that adsorption of the PEO is essentially irreversible, and that little polymer appears to desorb either following compression/decompression cycles, or in pure solvent. The value of the adsorbance T estimated from the n(D) profiles is 4 1.5 mg m-2 for both polymers. 

Fig. 9.7 The effective index change induced by the adsorption of a 2 nm thick molecular layer with index n 1.5, calculated as a function of core thickness for the TM mode propagating in glass, polymer, silicon nitride, and silicon waveguides. The right vertical axis shows the equiva lent modal sensitivity...

Ellipsometry27,60 62) is based on the principle that light undergoes a change in polarizability when it is reflected at a surface. The refractive index of the surface and the reflection coefficient of a system can be calculated from the change in the phase retardation A and the change in the amplitude ratio tan ip. Adsorption of a polymer on a surface gives rise... 

Analyte adsorption swells the polymer film vertically, which incorporates more of the evanescent field as it swells. The interferometer response is the result of a positive change in the refractive index of the film, and a negative change in phase as the propagating light beam is slowed down by the expanding film. Swelling of a... 

In search of less expensive, less toxic, and lower viscosity eluants, a few authors have proposed diluting the active ingredient with a common SEC eluant such as toluene, dichloromethane, or chloroform. To lower the operating temperature and minimize polymer degradation, mixtures of m-cresol with chlorobenzene (50 50, v/v, 43°C), dichloromethane (50 50, room temperature), and chloroform have been used, with 0.25 wt% benzoic acid added to prevent adsorption. In the same vein, o-chlorophenol has been diluted with chloroform (25 75) and used at 20°C. The main disadvantage in this latter solvent was a small dnidc for the polymer, which rendered refractive index measurements difficult. In addition, careful purification of the phenol is required to obtain a detection signal. Dichloroacetic acid diluted to 20 vol% with dichloromethane has been proposed as the mobile phase. However, even at this concentration, PA tends to degrade at room temperature. 

A further illustration of IGC as a source of data for acid/base characterization of polymers and of solid constituents of complex polymer systems, is given by Osmont and Schreiber (49), who rate the inherent acid/base interaction potentials of glass fiber surfaces and of polymers by a comparative index, based on the Drago acid/base concepts (SO). The interaction index is conveniently measured by IGC and is shown to differentiate clearly among untreated and variously silane-modified glass fiber surfaces. Conventional methods are used to determine adsorption isotherms for fiber-polymer pairs, and the IGC data ate used to demonstrate the relationship between acid/base interactions and the quantity of polymer retained at fiber surfaces. 

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