The surfactant tetra(ethylene oxide) n-dodecyl amide (TEDAd) was compared with the poly(ethylene oxide) n-alkyl ethers C12E5, C10E5, and C12E4. The adsorption to hydrophobic liquid-vapor and solidliquid interfaces, as well as the wetting behavior on a hydrophobic surface, was investigated. The amide group is more hydrophilic than the ethylene oxide group, raising the cloud point and critical micelle concentration (cmc). The incorporation of an amide group decreases the adsorbed amount at a fixed surfactant concentration. For all studied surfactants, the adsorbed amount was significantly lower on the solidliquid interface than on the liquid-vapor interface at a fixed concentration below the cmc, but the maximum adsorbed amount was only slightly lower on the solid-liquid interface. The surface pressure vs area/ molecule isotherms reveal attractive interactions between the amide groups in the adsorbed layer, which reduces the surface pressure at a fixed area/molecule. The advancing contact angles were only dependent on the surface tension at the liquid-vapor interface for C12E5 and TEDAd. The calculated adsorbed amount from the advancing contact angle agreed with the adsorbed amount on the liquid-vapor interface, while the adsorbed amount calculated from the receding contact angle was closer to the equilibrium value obtained with ellipsometry on the solid-liquid interface. The experimental results are supported by mean-field lattice model calculations, and due to the unfavorable interaction between the hydrocarbon region and the amide group in the adsorbed layer, the boundary between the hydrophobic and hydrophilic regions in the adsorbed layer becomes better defined in the presence of an amide group. This might be one of the explanations for the differences found in surface force measurements, and this will be described in part 2 of this investigation.

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The internal structure of the solid phase formed in mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and a range of oppositely charged polyelectrolytes with different side chains and charge density has been investigated using small-angle X-ray scattering. Polyelectrolytes with short side chains ([3-(2-methylpropionamido)propyl]trimethylammonium chloride, MAPTAC, and poly{[(2-propionyloxy)ethyl]trimethylammonium chloride}, PCMA) form a 2-dimensional hexagonal structure with SDS, whereas a polyelectrolyte without side chains (poly(vinlyamine), PVAm) forms a lamellar structure. The hexagonal structure of MAPTAC is retained either when a neutral monomer (acrylamide, AM) is included in the polymer backbone to reduce the charge density or when a nonionic surfactant is admixed to the SDS/polyelctrolyte complex. The unit cell length of AM-MAPTAC increases with decreasing charge density from a = 47.7 Å (MAPTAC, 100% charge density) to 58.5 Å (AM-MAPTAC, 30% charge density). The unit cell length in the lamellar SDS/PVAm complex (a = 36.1 Å) is significantly smaller than for the different hexagonal structures. It is conjectured that the cylinders in the hexagonal structure and the bilayers in the lamellar structure are based on self-assembled surfactant aggregates with the polyelectrolyte mainly located in the aqueous region adjacent to the charged surfactant headgroups.

Three different types of sugar surfactants, octyl-β-glucoside, maltose 6′-O-dodecanoate, and Ndodecyllactobionamide have been investigated to examine the effect of the structure of the sugar headgroup on the adsorption to liquid/vapor and solid/liquid interfaces using a number of techniques (surface tension, surface force apparatus, MASIF, and wetting). It was found that all the surfactants form monolayers when adsorbed to a hydrophobic interface at high concentrations. Increased headgroup flexibility leads to the adsorption of higher amounts on both the liquid/vapor and solid/liquid interfaces, resulting in a higher van der Waals attraction between two such monolayers. Increased hydrogen bonding within layers of more flexible surfactants is suggested to explain this difference. The most flexible surfactant, N-dodecyllactobionamide, is the least efficient wetting agent with the highest γSL. The behavior of the receding contact angles indicates the importance of intralayer hydrogen bonds between larger and more flexible sugar headgroups. LA001309Z