Influence of the Hydro/Fluorocarbon Chain Length on CMC and HLB of Surface-Active Nonionic Surfactants Containing Polyethylene Glycol Groups

Series of cyclic polyethylene glycol succinates based surfactants bearing a hydro- or fluorocarbon group was synthesized and characterized. Evaluation of the surface-active properties of the obtained compounds reveals, (i) the surface tension decreases gradually when is the length of the lipophilic chain increased (ii) the critical micelle concentration (CMC) increases with the number of ethylene oxide unit present in the polar head and (iii) surface tension follows the increasing pattern of hydrophilic-lipophilic balance (HLB) number.

Synthesis and Monolayer Behaviors of Novel Hybrid Corynomycolic Acids Containing Semifluoroalkyl Groups

In this work, novel hybrid-type corynomycolic acids [hybrid-OH and hybrid-COOH, with semifluoroalkyl groups (Rf-(CH2)n-: Rf = C4F9, n = 6 and Rf = C6F13, n = 3) located on the carbon atoms attached to the hydroxyl and carboxylic acid groups (C-OH and C-COOH), respectively] were successfully synthesized. The behaviors and formation of hybrid corynomycolic acid monolayers at the air-water interface were investigated by surface tension and surface pressure-area (π-A) measurements to clarify the effects of the Rf chain length, position of the semifluoroalkyl group, and surfactant molecule stereochemistry. Compared to dialkyl corynomycolic acid, both the critical micelle concentration (CMC) and the surface tension at the CMC (γCMC) of hybrid corynomycolic acids were reduced by the presence of the Rf group. With respect to the surface tension versus log concentration (γ vs. log C) isotherms, all syn-isomers of the hybrid-OH and hybrid-COOH acids showed two break points, while the anti-isomers showed only one break point. These different isotherms can be explained in terms of the steric repulsion between the two hydrophilic groups (OH and COO(-)), which depend on the stereochemistry of the surfactant. No effect of the location of the semifluoroalkyl group was observed. With respect to the formation of a monolayer film, four parameters-the lift-off area (AL), zero-pressure molecular area (A0), maximum of the Gibbs elastic modulus [EG (max)], and monolayer collapse pressure (πc)-were measured. Both AL and A0 of all hybrid corynomycolic acids were larger than the corresponding dialkyl acids due to the bulky and rigid Rf groups. Interestingly, syn- and anti-hybrids had almost identical isotherms on compression, although the values of πc of anti-hybrids were higher than those of syn-isomers. In addition, the values of EG (max) of hybrid-COOHs were slightly larger than those of the corresponding hybrid-OHs. Using the nascent soap method (agent-in-oil method), we found that anti-F4C6-OH (a hybrid corynomycolic acid) is a promising emulsifier for a ternary system comprising octane, water, and perfluoropolyether oil.

Hybrid Biosurfactant: Syntheses of Hybrid Corynomycolic Acid and its Monolayer Formation

Corynomycolic acids have two hydrophilic heads (OH and COOH) and two hydrophobic tails on adjacent carbon atoms. In this work, hybrid type corynomycolic acids (syn- and anti-isomers) were synthesized via the following three steps: 1) crossed Claisen condensation of t-butyl tridecanoate with ethyl per fluorooctanoate, 2) reduction of C = O to OH, and 3) conversion of COO-t-Bu to COOH using CF3COOH. Both hydrophilic groups (OH and COOH) of hybrid corynomycolic acid would dissociate to –O– and –COO– at alkaline condition (pH = 12) while they remain unchanged at acidic condition (pH < 3). The effect of hybrid structure on the surfactant properties was investigated by the surface tension and surface pressure-area (π-A) measurements. Hybrid type corynomycolic acid gave smaller cmc and γcmc than dialkyl type one due to fluoroalkyl chain. With respect to the stereochemistry, the anti-isomer attained a smaller γcmc value than the syn-isomer. In π-A measurements, the monolayer of the syn-isomer showed a lower collapsing pressure (∼15 mN m– 1) than that of the anti-isomer.