Biomedical Engineering Reference
In-Depth Information
possess both micro- and nanopapillae with water CA of 166 ı . In addition to the
low-surface energy of the FPU, the high CA and low sliding angle of the surface
was also due to the lotus-like micro-nano binary structure.
Yabu and Shimonura [ 133 ] have cast block copolymers consisting of equimolar
fluorinated acrylate and methyl methacrylate monomers on a substrate by a blade
to prepare superhydrophobic surfaces. A honeycomb film is eventually achieved
through the control of the condensation of water droplets as well as ultimate
evaporation of the solvent and water. After peeling off the top layer of the
honeycomb film, pin cushion structures can be acquired, where the sizes of both the
honeycomb and pincushion structures can be readily adjusted by tuning the volume
of casting polymer solution. The pincushion surface deriving from honeycomb films
with 1.6 m pores exhibits superhydrophobicity with the contact angle maximizing
at 170 ı .
Wessling's group has fabricated superhydrophobic surfaces possessing two-
scale roughness by membrane casting with Hyflon AD solution on a silicon
template patterned by photolithography [ 134 ], denoted as the phase separation
micromolding (PS M). This method supplies the surface with roughness on both
the microstructure level originating from the template and pore-size level arising
from the phase inversion, which can be controlled independently.
In conclusion, membrane casting is comparatively easy to perform and the
roughness can be controlled during the film formation process, by tuning parameters
such as the choice of solvents, nonsolvents, the concentration of the solution, and the
environmental conditions for membrane casting. Nevertheless, membrane casting
with the PS M[ 134 ] stands as promising technique in preparing superhydrophobic
surfaces.
9.3.3.3
Micelles
Micelles are termed as the aggregates of colloidal dimensions formed by the
association colloids which are in equilibrium with molecules or ions. Micelles are
formed by the microscale phase separation. Block copolymers form micelles due to
the different solubility of the blocks in the particular solvent [ 135 , 136 ]. The cast
micelles formed by block polymer will generate films with different morphologies
when exposed to environments with varied relative humidity.
Micelle solutions stemming from PS- b -PDMS block copolymer were used in
preparing superhydrophobic surface through phase separation induced by vapor
[ 135 ]. Surfaces with different wetting properties are generated according to different
solvents and environment humidity. Enrichment of PDMS block in the outmost
surface shows superhydrophobicity with CA of 163 ı , owing to the rearrangement
of PDMS block to the surface in the period of phase separation process.
Block copolymer of PtBA- b -PDMS- b -ptBA micelle solution was used by Han
et al. [ 137 ] to produce superhydrophobic surfaces with WCA reaching 163 ı .When
incorporating silica nanoparticles into the micelle solution, the surface will exhibit
a contact angle of 170 ı and a sliding angle less than 2 ı .
Search WWH ::




Custom Search