Surface Activity of Ethoxylated Methyl Dodecanoate

摘要

Surface-tension isotherms were determined for ethoxylated methyl dodecanoate with various degrees of ethoxylation, and different adsorption parameters were estimated. These ethoxylates exhibit interfacial activity similar to that of typical alcohol ethoxylates. The effectiveness of the surface-tension reduction decreases with increasing length of the hydrophilic ethylene oxide chain. Micellization is observed at log critical micelle concentration (CMC) = 4.5 10~(-5)-10~(-4) M increasing slightly with an increase of the ethylene oxide chain length. A minimum of A_(min)/N_(av)~(0.5) is obtained for N_(av) = 8, where A_(min) denotes the minimal molecular area at teh saturated interface and N_(av) stands for the average degree of ethoxylation. The interface becomes saturated at pC_(20)=-6.00-5.35, where pC_(20) denotes the logarithm of ethoxylate concentration for which a decrease of the surface tension is equal to 20 mN m~(-1). The highest and lowest values of the surface excess at saturation and the free energy of adsorption are obtained for the average degree of ethoxylation equal 8.