Pegylated surfactants based on fatty acids: 12-hydroxystearic acid versus stearic acid

[Display omitted] •Mono and di-functionalization of Poly(ethylene glycol) with biosourced fatty acids.•SANS structural analysis of associative polymers in water.•Demonstration of the presence of star micelles for mono modified PEG.•Demonstration of the presence of flower micelles for di-functionalized PEG.•Crystallization of flower micelles ate high concentration for di-functionalized PEG.•Importance of interactions through hydrogen bonds for telechelic PEG. We describe the aqueous behavior of short Polyethylene glycol (PEG) chains of Mw 4 kDa that are either mono-functionalized or di-functionalized by 12-hydroxy stearic acid (HSA), and stearic acid (SA), respectively. The end capping of the chains by the fatty acids is achieved by Steglich esterification, after a step of protection of the 12-OH functional group in the case of HSA. Small Angle Neutron Scattering (SANS) shows that mono-functionalized chains with both SA or HSA sticky ends self-assemble in star micelles in aqueous solution, and interact through repulsive steric interactions. The di-functionalized telechelic chains self-assemble in flower micelles that interact through interactions that are attractive on average due to the formation of bridges by chains that share their both ends in two different micelles. Solutions of telechelic chains undergo a phase separation between a dilute solution of micelles and a dense hexagonal crystalline network of flower micelles above a given polymer concentration threshold. This threshold is lower for SA-PEG-SA than for HSA-PEG-HSA. We postulate that this difference of behavior arises from the formation of hydrogen bonds between the OH groups at the C12 of the alkyl chain in case of HSA that increase the stability of the hydrophobic core of the micelles.