DOI: 10.1140/epje/e2003-00015-0
Controlling wettability by light: illuminating the molecular mechanism
C. Radüge, G. Papastavrou, D.G. Kurth and H. MotschmannMax-Planck-Institute of Colloids and Interfaces, Am Mühlenberg 1, 14424 Golm/Potsdam, Germany hubert.motschmann@mpikg-golm.mpg.de
(Received 5 September 2002 Published online: 16 April 2003 )
Abstract
The functionalisation of a surface with an organic monolayer
containing photoactive moieties such as the azobenzene
chromophore opens an elegant route for controlling its
wettability by light. In this paper we investigate the
microscopic
origin of the macroscopic change in
wettability upon photo-induced cis-trans isomerization of
a copolymeric diphenyl-diazene Langmuir-Blodgett monolayer.
Polarised UV-Vis and FTIR
spectroscopy have been used to monitor the orientational order of
various functional groups, Atomic Force Microscopy and Imaging
Ellipsometry is employed for the quantification of the surface
roughness and morphology, contact angle and surface potential
measurements are carried out for a characterisation of the polar ordering.
The data analysis is further supported by semi-empirical and
ab-initio
calculations of the molecular dipole moments and the
normal IR-modes of the fluorinated chromophore.
The combination of all these techniques provides a detailed
molecular picture. The data suggest that changes in the
projection of the dipole moment onto the surface normal caused by
isomerization of the azobenzene are responsible for the observed
changes in the surface energy. This knowledge allowed us to
predict guidelines for the synthesis of molecules in order to
maximize the wetting contrast upon photo-irradiation.
68.08.Bc - Wetting.
68.35.Md - Surface thermodynamics, surface energies.
82.50.Hp - Processes caused by visible and UV light.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003
