Oxide surfaces, polymers adsorbed

Several experimental parameters have been used to describe the conformation of a polymer adsorbed at the solid-solution interface these include the thickness of the adsorbed layer (photon correlation spectroscopy(J ) (p.c.s.), small angle neutron scattering (2) (s.a.n.s.), ellipsometry (3) and force-distance measurements between adsorbed layers (A), and the surface bound fraction (e.s.r. (5), n.m.r. ( 6), calorimetry (7) and i.r. (8)). However, it is very difficult to describe the adsorbed layer with a single parameter and ideally the segment density profile of the adsorbed chain is required. Recently s.a.n.s. (9) has been used to obtain segment density profiles for polyethylene oxide (PEO) and partially hydrolysed polyvinyl alcohol adsorbed on polystyrene latex. For PEO, two types of system were examined one where the chains were terminally-anchored and the other where the polymer was physically adsorbed from solution. The profiles for these two... 

The adsorption of an anionic surfactant on a positively charged oxide surface is significantly reduced by the presence of a pre-adsorbed anionic polymer. 

Conformation and Mobility of Polymers Adsorbed on Oxide Surfaces by ESR Spectroscopy... 

For adsorption studies the labeled polymer was dissolved in reagent grade solvent, the oxide surface added, and the sample was stirred magnetically for at least 2k hrs. (sometimes up to 3 days). The oxide with adsorbed polymer was separated from the unadsorbed polymer by gravity settling, or where necessary by low field centrifugation. The oxide together with adsorbed polymer was washed with fresh solvent until no ESR activity was detectable in the supernatant. The ESR spectrum was then taken of the polymer on the surface either in the presence of solvent, or after solvent removal as a function of temperature. 

Chibowski, Pyrocarbons prepared by carbonisation of polymers adsorbed or synthesised on a surface of silica and mixed oxides, Appl. Surf. Sci. 227, 219-243 (2004). 

Polymers may adsorb readily on solid surfaces. Somasundaran et al. (1964) have investigated the effect of chain length on the adsorption of alkylammonium cations and of surfactant anions on oxide surfaces. These authors consider that the adsorption is influenced by the van der Waals energy of interaction or... 

Conductive polymers may be synthesized via either chemical or electrochemical polymerization methods. Electrodeposition of conductive polymers from electrolytes is, thus, feasible provided that the depositing polymer is not soluble in the electrolyte.206 Conductive polymers can be deposited from the electrolytes containing the monomers via either electrooxidation or electroreduction, based on the monomer type used. Similar to that of metals, the electrodeposition of polymers is based on nucleation and growth. The deposition mechanism involves oxidation of monomers adsorbed on the electrode surface, diffusion of the oxidized monomers and oligomerization, formation of clusters, and eventually film growth.213... 

By chemical modification of the oxide surfaces it has become possible to design new, reliable, highly-specified adsorbents, selective catalysts, polymer extenders, efficient thickeners of dispersive media. The interest in the modified oxides has increased for a few years as a result of favourable perspectives for their application for various kinds of the chromatographic separation, preparation of grafed metal complex catalysts, immobilized enzymes and other biologically active compounds. Introduction of the surface... 

This last form of acidity can build up at low pH on the surfaces of variable-charge minerals (A1 and Fe oxides, allophane, and Al-hydroxy and Fe-hydroxy polymers adsorbed on layer silicate clays). 

This technique makes use of the change in polymer solubility upon change in the ionic charge on the polymer. For example, poly(vinylferrocene) films can be deposited onto the surface of an electrode from dichloromethane by oxidizing the polymer to its less soluble ferricinium form which then adsorbs at the electrode surface [134-137]. In some ways this process is similar to metal plating. Recently this approach has been extended to make use of micellar disruption brought about electrochemically. In this approach the coating material is dissolved in a micellar solution and the micelles are disrupted by oxidation. 

Conducting polymers, for example, polyaniline, polypyrrol, have been extensively investigated taking into account its possible technological applications. From the specific point of view of modified surfaces, it has been shown that, when adsorbed on oxide surfaces such as molybdenum [1], arsenic [2,3], and iron [3] oxides, polyaniUne exerts remarkable effects on their redox properties [4] and/or thermal stabihty of the respective oxides. This chapter presents a brief outline about the achievements on this field of investigation. 

Disperse oxides unmodified or modified by organics (OC) or OSC are used as fillers, adsorbents, or additives [1-11]. OSCs are used as promoters of adhesion, inhibitors of corrosion, for the stabilization of monodisperse oxides and the formation of the nanoscaled particles. Oxide modification by alcohols or other OC is of interest for synthesis of polymer fillers, as such modification leads to plasticization and reinforcement of the filled coating, but in this case a question arises about hydrolyz-ability of the =M—O—C bonds between oxide surface and alkoxy groups, as those are less stable than =M—O— M= formed, for example, upon the silica modification by silanes or siloxanes. The high dispersity, high specific surface area, and high adsorption ability of fumed oxides have an influence on their efficiency as fillers of polymer systems. 

Chemical modification of oxide surfaces, immobilization of polymers on them, addition of different surfactants or solvents (e.g., alcohols) to the aqueous suspensions can be responsible for alterations in the hydrogen bond network and the free energy of the interfacial layers, surface charge distribution, and so on, which can affect the dispersion stability and other characteristics of both suspensions and powders prepared from these suspensions [9-15]. The last with adsorbed molecules (e.g., drugs, PVP, proteins, cellulose, etc.) can be of interest for medicine, biotechnology, etc. 

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