ABSTRACT
I. INTRODUCTION Surfactants based on natural products are currently attracting much industrial and academic interest. Some of the more common surfactants in use today are questioned with regard to their biodegradability and toxicity. A well-known example are ethoxylated alkylphenols, which have been found to have severe impact on the environment and biological functioning of rats and fish [1-3]. Due to their good surfactant properties, it has not been straightforward to find a replacement. Alcohol ethoxylates of the same hydrophilic-lipophilic balance (HLB) do not always give satisfactory results. For instance, in the stabilization of dispersed systems, emulsions, or suspensions, it is often found that nonylphenol ethoxylates are superior to alcohol ethoxylates [4]. It is believed that one cause of this is the bulkiness of the hydrophobe of the nonylphenol ethoxylates as compared with that of the alcohol ethoxylates. The nonylphenol consists of a highly branched nonyl group attached via a nonterminal carbon to the para position of the aromatic ring, whereas the hydrophobic part of the alcohol ethoxylate is either a straight hydrocarbon chain or a methyl branched chain normally in the C10_ 16 range. Due to the different degrees of bulkiness of the hydrophobic groups of the alcohol ethoxylate and the nonylphenol ethoxylate, the surfactants will aggregate differently when dissolved in water or at an interface. The very bulky nonylphenol ethoxylate cannot spontaneously form as highly curved micelles or oil-in-water structures as the alcohol ethoxylates. Since most surfaces and interfaces have a low curvature on the scale of the surfactant, nonylphenol ethoxylates generally align better than alcohol ethoxylates at boundaries. Furthermore, good packing properties can be expected for the nonylphenol ethoxylates due to interactions of the 'IT electrons in the benzene rings with the neighboring aromatic rings.
