Ethylene oxide extended surfactants

It was shown in the early 1990s that nanoscale porosity of silicas can conveniently be generated in a predictable way using smfactant micelles as templates." This approach can be used to form cylindrical pores (diameter 2-30 nm), " spherical pores (diameter 3-27 nm), and other periodic porous structures. Surfactants that are suitable as mieellar templates include alkylammonium surfactants, oligomeric alkyl-poly(ethylene oxide) surfactants, and block copolymers with poly (ethylene oxide) block(s). " The micelle-templating approach has been extended to some other compositions relevant for the manufacture of on-chip insulations, including polymethylsilsesquioxane (formula unit SiOi 5-./2(CH3)(0H),) and... 

The problem of the interaction between polymers and surfactants was laid initially in the study of proteins associated with natural lipids, and later extended to their association with synthetic surfactants [1,2]. More recently, the interaction of water-soluble synthetic polymers such as poly(ethylene oxide) with ionic and non-ionic surfactants [3-7] has attracted the interest of researchers because of its scientific and technological implications. 

Non-ionic surfactants by definition carry no charge and with these surfactants stabilisation is mainly by volume reaction. Again the hydrophobic portion is adsorbed on the polymer surface while the hydrophilic portion, usually long ethylene oxide chains, extends into the water phase. Because of the volume occupied by these ethylene oxide chains the polymer particles cannot easily approach each other, i.e. there is an energy barrier to coalescence due to the spatial presence of the adsorbed surfactant. Stabilisation by this means is termed steric stabilisation . The energy barrier to coalescence can be reduced by reducing the proportion of the ethylene oxide chains, e.g. either by salt addition or by heating the latex. 

Surfactant templating chemistry can be extended to many nonsilicate compositions after modifications to the synthesis route. These materials are less structurally stable than the mesoporous silicates, which is attributed to the thinness of the amorphous pore walls ( 1 to 2 nm). Stucky and coworkers [85,86] showed that this problem could be mitigated by preparing the materials with thicker walls. To prepare mesoporous WO3, they dissolved a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer and WCle salt in ethanol, and dried the resulting solution in open air. The tungsten salt reacted with moisture to undergo hydrolysis and condensation reactions. These chemical reactions caused the eventual formation of amorphous WO3 around triblock copolymer micelle-like domains, and after calcination at 400 C, a mesoporous WO3 with thick, nanocrystalline walls ( 5 nm) and surface area of 125 m /g was formed. 

Amphiphilic polymers, mainly block copolymers, may self-assembly in aqueous medium rendering structures similar to micelles of conventional surfactants (polymeric micelles) or vesicles that resemble liposomes (polymersomes). The hydro-phobic regions of the polymer chains form the core, while the hydrophilic blocks extend towards the aqueous phase as a shell. The resultant polymeric micelles can host drugs of diverse polarity in the core or in the core-shell interface, enhancing the apparent solubility of the drug up to several orders of magnitude [36], A variety of amphiphilic polymers have been synthetized. Common examples of hydrophilic blocks are poly(ethylene oxide) (PEO), poly(N-vinyl pyrrolidone), poly(N-isopropylacrylamide) or poly(acrylic acid) (PAA). Suitable hydrophobic blocks may be PLA, PCL, poly(propylene oxide) (PPO), poly(trimethylene carbonate), polyethers, polypeptides, and poly(P-aminoester)s [37-39]. 

A similar procedure was used to produce PPy-poly(ethylene-covinyl acetate) [PEVA] composites.47 The host polymer can be dissolved in a toluene solution with pyrrole. A concentrated dispersion is then formed by adding it to an aqueous solution containing a surfactant. An aqueous solution of the oxidant (FeCl3) is then introduced to form the polymer. The conductivity of the resultant materials is approximately 5 S cm-1. The PEVA-based composites can be processed into films and other shaped articles by hot pressing at approximately 100-150°C and 15-20 MPa pressure for 1 h. The mechanical properties are determined by the PEVA content. For example, for composites of PPy-PEVA containing 20% (w/w) PPy, soft flexible films that can be extended up to 600% were produced. For pure PPy films, elongations of less than 5% are achievable. 

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