Physico-chemical characterisation of novel surfactants

Abstract: The aim of this thesis has been to investigate thephysico-chemical behaviour of novel surfactants based onnatural raw materials. Micellization properties, adsorptionatinterfaces and dynamic aspects have been studied. In additioncomplex formation of surfactants with enzymes and polymers hasbeen evaluated.Two different surfactant series have been studied. The firstseries consisted of a phytosterol hydrophobe with varyingpolyoxyethylene headgroup chain length. The dilute region wasstudied by means of tensiometry,1H-NMR self-diffusion, light scattering andrheology. This region was found to behave as a micellar phasefor the surfactants with short polyoxyethylene chains while forthe more hydrophilic surfactants polymeric behaviour wasobserved. The liquid crystalline phase behaviour wascharacterised in general terms and the structure and dynamicsof the cubic phase of the most hydrophilic sterol ethoxylatewas analysed in more detail using1H-NMR self-diffusion. It was observed that thewater diffusion through the poly(ethylene glycol) phase ismerely dependant on the water binding to the poly(ethyleneglycol) matrix while no effect was observed from obstruction bythe hydrophobic cores.The second surfactant series studied consisted of fatty acidmonoethanolamide ethoxylates. The effect of the amide bond wasstudied as well as effects of variations in unsaturations inthe hydrocarbon chain and the length of the polyoxyethyleneheadgroup. Adsorption at the air / water interface and at thewater / solid interface were studied by means of tensiometryand ellipsometry, respectively. It was found that atconcentrations below the CMC the most hydrophobic surfactantsare selectively adsorbed at the air / water interface leadingto effects from the unsaturations in the hydrocarbon chain onthe surfactant adsorption area. At the water / solid interfacewhere measurements were made at concentrations above the CMC noeffects of the unsaturations were observed. The amide bond wasfound to increase the adsorption area. Micellization wasstudied by means of1H-NMR self-diffusion. The amide group was found tolower the CMC and to favour packing into spherical micelles.The micelle structure was somewhat affected by unsaturations inthe hydrophobe.Complex formation of an amphoteric surfactant with an enzymewas studied at different pH values. It was found that at lowpH, when the surfactant is positively charged, complexformation occurs, even though the enzyme is below itsisoelectric point. A known interaction model forsurfactant-polymer complex formation was used to study foamingand thin film stability. It was found that when the complexconcentration at the air / water interface is low, a decreasein foam and thin film stability occurs. This stability isincreased when the surfactant concentration at the interfaceincreases.Key words: natural raw materials, novel hydrophobes,physico-chemical characterisation, micelles, interfacialadsorption, liquid crystals, enzymes, polymers, complexformation, foam.