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1 Polish Journal of Chemistry

1 2004

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Properties of Langmuir Monolayers from Perfluorohexyl-n-alkanes

Broniatowski M., Dynarowicz-Łątka P.

Polish Journal of Chemistry

2004

Vol.78 /nr 11-12

2149-2162

A series of semifluorinated n-alkanes (SFAs), of the general formula: F(CF2)m(CH2)nH, (in short FmHn), where m = 6 and n = 16-20, have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were obtained under a variety of experimental conditions. The Langmuir monolayer experiments have been complemented with Brewster angle microscopy results, which enabled both a direct visualization of the monolayers structure and the estimation of their thicknesses at different stages of compression. Our results show, that these "non-classical" film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are capable of monolayer formation at the air/water interface. The negative sign of the measured surface potential, DeltaV, proves that SFA molecules are oriented at the air/water interface with their perfluorinated parts directed towards the air, independently on the length of hydrogenated moiety. The change of electric surface potential achieves the minimum value of ca. -0.75 V for all the investigated SFA. The minimum effective dipole moment is achieved for a molecule oriented at the angle of about 35 graduate to the surface normal. The relative intensity measurements allow one to conclude, that film molecules are oriented vertically in respect to the surface normal at the vicinity of collapse.