TY - JOUR
T1 - Stripes of partially fluorinated alkyl chains
T2 - Dipolar Langmuir monolayers
AU - Schneider, Matthias F.
AU - Andelman, David
AU - Tanaka, Motomu
N1 - Funding Information:
The authors thank E. Sackmann for helpful comments, C. Gege and R. R. Schmidt for synthesis of lipids, and P. K. J. Kinnunen for the surface potential measurements. This work was supported by Deutsche Forschungs Gemeinschaft (Grant No. DFG Ta 259∕2), Fonds der Chemischen Industrie, the Israel Science Foundation (ISF) under Grant No. 210∕01 and the US-Israel Binational Foundation (BSF) under Grant No. 287∕02. M.T. is thankful to DFG for a habilitation fellowship (Emmy Noether Program, Phase II), and D.A. thanks the Alexander von Humboldt Foundation for a research award. FIG. 1. Chemical structures of (a) F-alkyl lipid ( FL ‐ 8 ‐ 8 ) and (b) alkyl lipid ( AL ‐ 16 ) used as a reference. Note that only the lipid tails in (a) are fluorinated. FIG. 2. Langmuir isotherms of (a) AL ‐ 16 and (b) FL ‐ 8 ‐ 8 monolayers at T = 20 ° C . In addition, fluorescence microscopy pictures are shown in (a) for 39, 43, and 61 Å 2 , and in (b) for 85, 89, 92, and 97 Å 2 . AL ‐ 16 monolayers form spherical domains (bubbles), which are similar to those formed by other alkyl lipids. In contrast, FL ‐ 8 ‐ 8 monolayers at an area per molecule between 85 and 97 Å 2 form stripelike microdomains with an average stripe thickness ranging from 2 to 8 μ m . These domains disappear near the onset of the surface pressure increase, corresponding to area per molecule of 85 Å 2 . FIG. 3. The surface potential of a FL-8-8 monolayer (right axis, solid line) plotted as a function of the area per F-alkyl molecule measured at 20 ° C . The isotherm with the same area per molecule is also given (broken line, left axis). The onset of the transition from the gas to liquid phase as observed by fluorescence microscopy is connected to an abrupt decrease in surface potential. An average surface potential close to the gas-liquid coexistence ( ≈ 90 Å 2 per molecule) was between − 420 and − 390 mV . FIG. 4. Fluorescence image of a FL-8-8 monolayer with 0.1 mol % cholesterol, taken at 90 Å 2 per molecule [same area as in Fig. 2(b) ] and 20 ° C . The doping of cholesterol leads to a decrease in the stripe periodicity from 2 – 8 to 1 – 2 μ m .
PY - 2005
Y1 - 2005
N2 - Stripelike domains of Langmuir monolayers formed by surfactants with partially fluorinated lipid anchors (F-alkyl lipids) are observed at the gas-liquid phase coexistence. The average periodicity of the stripes, measured by fluorescence microscopy, is in the micrometer range, varying between 2 and 8 μm. The observed stripelike patterns are stabilized due to dipole-dipole interactions between terminal- CF 3 groups. These interactions are particularly strong as compared with nonfluorinated lipids due to the low dielectric constant of the surrounding media (air). These long-range dipolar interactions tend to elongate the domains, in contrast to the line tension that tends to minimize the length of the domain boundary. This behavior should be compared with that of the lipid monolayer having alkyl chains, and which form spherical microdomains (bubbles) at the gas-liquid coexistence. The measured stripe periodicity agrees quantitatively with a theoretical model. Moreover, the reduction in line tension by adding traces (0.1 mol %) of cholesterol results, as expected, in a decrease in the domain periodicity.
AB - Stripelike domains of Langmuir monolayers formed by surfactants with partially fluorinated lipid anchors (F-alkyl lipids) are observed at the gas-liquid phase coexistence. The average periodicity of the stripes, measured by fluorescence microscopy, is in the micrometer range, varying between 2 and 8 μm. The observed stripelike patterns are stabilized due to dipole-dipole interactions between terminal- CF 3 groups. These interactions are particularly strong as compared with nonfluorinated lipids due to the low dielectric constant of the surrounding media (air). These long-range dipolar interactions tend to elongate the domains, in contrast to the line tension that tends to minimize the length of the domain boundary. This behavior should be compared with that of the lipid monolayer having alkyl chains, and which form spherical microdomains (bubbles) at the gas-liquid coexistence. The measured stripe periodicity agrees quantitatively with a theoretical model. Moreover, the reduction in line tension by adding traces (0.1 mol %) of cholesterol results, as expected, in a decrease in the domain periodicity.
UR - http://www.scopus.com/inward/record.url?scp=22944441288&partnerID=8YFLogxK
U2 - 10.1063/1.1858852
DO - 10.1063/1.1858852
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AN - SCOPUS:22944441288
SN - 0021-9606
VL - 122
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 9
M1 - 094717
ER -