Speaker
Description
The common definition of “surface” includes surface atoms and molecules,
practically extending at the most three layers – typically up to one
nanometer. This definition is justified by the fact that many surface
properties such as chemistry, wettability or charge density are determined by
the top most surface layer. Far less explored are effects due to interactions
with deeper subsurface layers, i.e. the region extending over several
nanometers underneath the “surface”. This subsurface region, however,
might significantly contribute to molecular adsorption at the surface via
long-range (i.e. >10 nm) interaction forces.
To make use of such subsurface effects, plasma polymer films (PPFs) with
defined architecture in the nanoscale were deposited comprising a
hydrophobic-to-hydrophilic vertical chemical gradient structure. The
organic/inorganic thin films were generated by depositing 1-15
nm-thick layers of plasma-polymerized HMDSO on a hydrophilic, nanoporous base
layer of SiOx (with O2/HMDSO in the plasma). Diffusion of water through the
hydrophobic terminal layer is still enabled despite the hydrophobic surface
properties yielding hydration of the hydrophobic/hydrophilic subsurface
structure as demonstrated by neutron reflectometry measurements. The hydrated
films were found to strongly affect protein adsorption at the surface thanks
to long-range interaction forces induced by oriented water molecules.
Thereby, additional control over adsorption processes and modulation of
protein adsorption is enabled which is relevant, e.g., for tissue
engineering, wound dressing etc.
Adjusting the thin film architecture of plasma polymer films thus provides an
additional parameter to modulate surface properties of materials.
