SELF-ASSEMBLED MONOLAYERS OF ALKANETHIOLATES ON THIN GOLD-FILMS AS SUBSTRATES FOR SURFACE FORCE MEASUREMENTS - LONG-RANGE HYDROPHOBIC INTERACTIONS AND ELECTROSTATIC DOUBLE-LAYER INTERACTIONS
T. Ederth et al., SELF-ASSEMBLED MONOLAYERS OF ALKANETHIOLATES ON THIN GOLD-FILMS AS SUBSTRATES FOR SURFACE FORCE MEASUREMENTS - LONG-RANGE HYDROPHOBIC INTERACTIONS AND ELECTROSTATIC DOUBLE-LAYER INTERACTIONS, Langmuir, 14(17), 1998, pp. 4782-4789
Surfaces prepared by self-assembly of alkanethiolates onto thin (10 nm
) gold films supported on glass have been used as substrates for surfa
ce force measurements between macroscopic surfaces. Surface roughness,
the order in the monomolecular film, wetting properties, and their st
ability in aqueous electrolyte solutions have been investigated using
atomic force microscopy, infrared absorption spectroscopy, and contact
angle measurements. Direct force measurements have been performed wit
h a noninterferometric bimorph surface force apparatus, using surfaces
with differently functionalized thiolates; measurements were made in
air, water, and aqueous electrolyte solutions. Results from force meas
urements between hydrophobic and neutral hydrophilic surfaces in air a
nd water are presented and discussed, as well as some results from mea
surements with surfaces exposing carboxylic groups in various aqueous
electrolyte solutions. It is demonstrated that alkanethiol monolayers
self-assembled onto thin gold films on macroscopic surfaces are well-s
uited as substrates for direct measurements of long-range surface forc
es. The utility of these surfaces as substrates for investigations of
short-range phenomena is limited until the effect of the roughness on
the adhesion between the surfaces has been properly quantified and the
contribution of the van der Waals force to the total interaction has
been calculated. The latter is difficult to assess due to the large nu
mber of layers in the system and the presence of conducting surfaces.