Surfactant contaminated surface

The direct electrochemical deposition methods for the preparation of electrocatalysts allow to localize the catalyst particles on the top surface of the carbon support, as close as possible to the solid polymer electrolyte and does not need heat (oxidative and/or reducing) treatment, as most of the chemical methods do, in order to clean the catalytic particles from surfactant contamination [27,28], This will prevent catalyst sintering due to the agglomeration of nanoparticles under thermal treatment. 

Cationic surfactants are positively charged in an aqueous solution (e.g., quaternary ammonium and pyridinium), and expensive. Because of their bactericidal action, they are widely used for other applications such as preservatives, sterilizing contaminated surfaces, and emulsions. 

The impact of a surfactant on a turbulent shear layer near the air-sea interface was studied by direct numerical simulations [311] which show that the inviscid blocking effect of a clean interface, the attenuation of vertical fluctuating velocities and the increase in horizontal turbulence intensities is significantly reduced by surfactant contamination. If the surface is covered by a surfactant, concentration gradients are formed by the impinging turbulent eddies which diminish the renewal of near-surface fluids and reduce the scalar transfer rate. 

Liithi and Luisi [44] have used a hoUow fiber membrane reactor for peptide synthesis catalyzed by a-chymotrypsin in microemulsion. Chang et al. [110] described the immobilization of lipase on liposomes, which, in turn, were solubilized in AOT/isooctane reversed micelles and used for the continuous glycerolysis of olive oil in an ultrafiltration cell. The half-Ufe of the Chromo. viscosum lipase was 7 weeks. The development of an ultrafiltration ceramic membrane bioreactor for the simultaneous lipolysis of olive oil and product separation in AOT/isooctane reversed micellar media has been also reported [106,107], Cutinase performance was also evaluated in a ceramic membrane reactor [9]. An attempt to minimize the surfactant contamination problem was based on the use of an electro-ultrafiltration method which can decrease the gel formation in the membrane surface, improving the filtration flux, achieving the separation of the AOT reverse micelles [187],... 

Low molecular cationic polymers or alum can also be used to flocculate pitch, ie, bind up the pitch so that it is retained in the sheet, to minimize pitch deposition on machine surfaces and fabrics (35,36). Alum is used commonly in newsprint operations (34). The addition of a nonionic surfactant with a hydrocarbon solvent to the wet end has shown some utility in preventing deposits of adhesive recycled furnish contaminants from forming on the paper... 

Gas turbine fuels can contain natural surfactants if the cmde fraction is high in organic acids, eg, naphthenic (cycloparaffinic) acids of 200—400 mol wt. These acids readily form salts that are water-soluble and surface-active. Older treating processes for sulfur removal can leave sulfonate residues which are even more powerful surfactants. Refineries have installed processes for surfactant removal. Clay beds to adsorb these trace materials are widely used, and salt towers to reduce water levels also remove water-soluble surfactants. In the field, clay filters designed as cartridges mounted in vertical vessels are also used extensively to remove surfactants picked up in fuel pipelines, in contaminated tankers, or in barges. 

Adventitious surfactants also have a marked effect on the mechanism of coalescence. In studying the coalescence of curved water surfaces, Lindblad (L8) used aged distilled water that was stored for about 30 h in a polyethylene bottle opened to the air through a narrow polyethylene tube inserted in the water. He found that if fresh distilled water (water exposed not longer than 1 h to the air) was used, the delay time in coalescence was approximately half as long. Consequently, he concluded that this difference is due to some form of contamination which settled into the water or onto the water surface. 

Davies et al. (D9) have recently measured the rates of absorption of various gases into turbulently stirred water both with carefully cleaned surfaces and with surfaces covered with varying amounts of surfactants. That hydrodynamic resistances, rather than monolayer resistances, are predominant in their work is consistent with the high sensitivity of kL to very small amounts of surface contamination and also with the observation that a limit to the reduction in kL is found (D7, D9). This is in agreement with the results of Lindland and Terjesen (L9), who found that after a small concentration of surfactant had been used further additions caused but little change in terminal velocity (L9). 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

In summary, intratracheal instillation of CNTs has shown that their potential in eliciting adverse pulmonary effects is influenced by exposure time, CNT dose, CNT biopersistence, surface defects, and metal contamination [71, 72]. Despite the use of surfactants, all studies showed that intratracheal instillation caused major difficulties due to the agglomerative nature of CNTs in a biological environment. More realistic exposure methods, namely inhalation rather than intratracheal administration, are therefore needed for determining the pulmonary toxicity [59, 65, 73]. Several investigations have been performed by using administration different from intra-... 

Due to their unique surface-active properties, surfactants possess the capacity to remobilize non-polar contaminants, such as polycyclic aromatic hydrocarbons or heavy metals, which have accumulated in... 

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