The Determination of the Structure and Coverage of Nonionic Surfactant Monolayers at the Air-Water Interface Using Neutron Reflection Technique

ABSTRACTThe coverage and structure of the monododecyl ethers of oligoethylene glycols, C12Em where m = 2, 4, 6 and 8, adsorbed at the air-water interface have been studied by neutron reflection. At their c.m.c.s, the area per molecule is 33 ± 3 Å2 for C12E2, 44 ± 3 Å2 for C12E4 55 ± 3 Å2 for C12E6 and 62 ± 3 Å2 for C12E8. In terms of the width of a Gaussian distribution at 1/e of its height the thicknesses of the dodecyl chains are found to be constant at 16 ± 2 Å and those of the heads to vary from 11 to 19±2Å from m = 2 to 8. There is also found to be some overlap between the two chains at the interface.