Langmuir 1992,8, 1501
1501
Comments Relationship between Chain Protrusions and Surfactant Critical Micelle Concentration Values
Parsegian and Randl recently criticized a new theory2 for the “protrusion” force between amphiphilic bilayers on the grounds that it “misrepresentsmuch of the data on lipids”. They calculated that chain protrusion predicts a criticalmicelle concentration (cmc)for dilaurylphosphatidylcholine (DLPC) of approximately (e-l5/?)2= 3.1 X 10-7 M,and stated that “molecular protrusion then will lead to a predicted lo-’ to lo+ M concentration of DLPC in the excesswater phase that coexistswith multilayers. This (I) Parsegian, V. A.;Rand, R. P. Langmuir 1991, 7, 1299. (2) Ieraelachvili, J. N.; Wennemtr6m, H. Langmuir 1990, 6, 873.
is at least FOUR orders of magnitude too high a predicted solubility”. Interested readers should note that the literature value for the cmc of DLPC is close to 2.8 X 10-7 M? in remarkably good agreement with Parsegian and Rand‘s calculation based on the protrusion model. Jacob Israelachvili
Department of Chemical & Nuclear Engineering and Materials Department, University of California, Santa Barbara, California 93106 Registry No. DLPC,92312-24-8. (3) Cevc, C.;Marsh,I).PhospholipidBilayers; John Wiley: New York, 1987; p 39.
0743-7463/92/2408-1501$03.00/00 1992 American Chemical Society
