Because the review article “Progress in Superhydrophobic Surface Development” specifically outlines the major methods of creating superhydrophobicity, we will refrain from repeating a list of specific methods
and focus on unifying themes and methods of fabrication as well as the
most salient features of each major method. One such feature belongs to
the first method described by this article—fibrous hydrophobic surfaces.
These surfaces can range from carbon nanotubes bound to cotton fibers to
nanoscale polymer structures created by electrospinning. Fibrous hydrophobic surfaces are versatile, as fibrous materials are inherently rough, and
coating with hydrophobic materials or nanorods can increase this roughness. Very high contact angles have been reported for fibrous hydrophobic surfaces. Some researchers have even reported surfaces having selfcleaning properties that are dirt- and oil-resistant while producing high
contact angles and low hysteresis. This technology appears to be promising
for the development of water- and contamination-resistant clothing that
would essentially wash itself and is already in use in a variety of spill- and
stain-resistant clothing brands.
Another interesting feature that is unique to a specific fabrication method
is the ability of certain hydrophobic semiconductors to be crystallized into
a superhydrophobic surface that exhibits superhydrophobicity in the
dark but superhydrophilicity in the light. One likely explanation for this
phenomenon is that superhydrophilicity is generated by the excitation of
electrons on the surface, which suggests that there are surface properties
that can be changed by applying a voltage. Instead of excitation due to
ultraviolet (UV) radiation, a voltage could be used, thus allowing for
materials that can be dried instantly at the flick of a switch or wetted
completely with another flick.
Several overarching themes appear in this article as well. One of the
most notable is the generation of fractal solids as superhydrophobic
surfaces, which may be achieved in many ways. One common approach
is crystal growth, in which a material is cooled or condensed into a fractal
solid. Fractal solids can be formed from both organic and inorganic
materials. Another common method is the diffusion-limited growth
process, in which a material deposits so quickly onto a substrate that the
growth of the film is limited by the flow of material over the substrate.
This method, by randomness, creates small disturbances on the surface of
the flat substrate, which then cause more particles to attach to these
perturbations. The process continues until large bumps form, which then
have small disturbances on their surfaces that create subbumps, and so
on. The greatest benefit of these kinds of assemblies is that being fractal,
CHAPTER 7: Fundamentals of Surface Nanoscience
228
and focus on unifying themes and methods of fabrication as well as the
most salient features of each major method. One such feature belongs to
the first method described by this article—fibrous hydrophobic surfaces.
These surfaces can range from carbon nanotubes bound to cotton fibers to
nanoscale polymer structures created by electrospinning. Fibrous hydrophobic surfaces are versatile, as fibrous materials are inherently rough, and
coating with hydrophobic materials or nanorods can increase this roughness. Very high contact angles have been reported for fibrous hydrophobic surfaces. Some researchers have even reported surfaces having selfcleaning properties that are dirt- and oil-resistant while producing high
contact angles and low hysteresis. This technology appears to be promising
for the development of water- and contamination-resistant clothing that
would essentially wash itself and is already in use in a variety of spill- and
stain-resistant clothing brands.
Another interesting feature that is unique to a specific fabrication method
is the ability of certain hydrophobic semiconductors to be crystallized into
a superhydrophobic surface that exhibits superhydrophobicity in the
dark but superhydrophilicity in the light. One likely explanation for this
phenomenon is that superhydrophilicity is generated by the excitation of
electrons on the surface, which suggests that there are surface properties
that can be changed by applying a voltage. Instead of excitation due to
ultraviolet (UV) radiation, a voltage could be used, thus allowing for
materials that can be dried instantly at the flick of a switch or wetted
completely with another flick.
Several overarching themes appear in this article as well. One of the
most notable is the generation of fractal solids as superhydrophobic
surfaces, which may be achieved in many ways. One common approach
is crystal growth, in which a material is cooled or condensed into a fractal
solid. Fractal solids can be formed from both organic and inorganic
materials. Another common method is the diffusion-limited growth
process, in which a material deposits so quickly onto a substrate that the
growth of the film is limited by the flow of material over the substrate.
This method, by randomness, creates small disturbances on the surface of
the flat substrate, which then cause more particles to attach to these
perturbations. The process continues until large bumps form, which then
have small disturbances on their surfaces that create subbumps, and so
on. The greatest benefit of these kinds of assemblies is that being fractal,
CHAPTER 7: Fundamentals of Surface Nanoscience
228