The polymerisation of aqueous sodium undecenoate mesophases

Abstract

Sodium 10-undecenoate is a polymerisable surfactant having a double bond in the ω position of its chain. This surfactant has been polymerised by McGrath, both in lamellar and hexagonal mesophases by thermal and photochemical initiation, and she obtained relatively low conversions. She could not obtain the polymerisation kinetics. We have polymerised both liquid crystals by irradiation by γ-rays, and we obtained higher conversions: 91.6±0.7% in 50 wt% of surfactant in water (hexagonal mesophase), while McGrath obtained 56% by thermal and 20.6% by photochemical polymerisation; and a maximum of 59.5% in 75 wt% of surfactant in water (lamellar liquid crystal). McGrath obtained conversion values of 24% (thermal initiation) and 19.2% (photochemical initiation) for this mesophase. We could not obtain the polymerisation kinetics of the 50 wt% sample. Even at the lowest irradiation dose the conversion rendered the maximum value. The 75% sample showed a measurable polymerisation increase with γ-radiation dose until 60 kGy, but a large decomposition was observed at 80 kGy. This decomposition, caused by an excess of radiation, is not exceptional. The Fourier transform IR study of the different kinds of water in the system (bulklike water, water related to surfaces and water molecules trapped in the interstices of the microstructures) indicates that there was no significant transformation of the structure during the irradiation; the values of the nonirradiated liquid crystal remained almost unchanged.