Microporous surface coating

FIGURE 38.4 Composite membrane with a dense skin coated on the microporous surface. 

M. Takemoto, S. Fujibayashi, M. Neo, J. Suzuki, T. Kokubo, and T. Nakamura. Bone-bonding ability of a hydroxyapatite coated zirconia-alumina nanocompopsite with a microporous surface. J. Biomed. Mater. Res. A, 78, 693-701 (2006). 

The opposite of super-hydrophobicity, the Lotus Effect, is super-oleophobicity, the Pitcher Plant Effect. A natural example of super-oleophobicity involves the Nepenthes Pitcher Plant, which has microtextured surfaces in which an aqueous liquid fills the spaces within the texture and forms a continuous overlying film to cause insects to slip into the plant s digestive juices. Here, the plant s super-oleophobic surface essentially repels the oils on the insects feet. This is termed the Pitcher Plant Effect. Microporous, microfibre coatings have been developed to mimic this effect and be highly repellent to oils while remaining permeable to water. 

As in dust collection, where surface coatings have been available for many years, the treatments are designed to present a microporous structure to the slurry which effectively restricts the penetration of particles to all but a few micrometres in depth. Consequently, a filter cake quickly forms on the surface of the coating and by restricting the particles to the surface, the same cake can be easily discharged at the end of the filtration cycle. Unlike the coatings in dust collection, however, the microporous structure in liquid applications has to withstand much higher pressures. Failure to do so will result in structural collapse and premature pressurisation of the filter. 

Fig. 1.14 Fractal coated electrode. Above The electrode surface is covered with hemispheres, thus increasing its surface area. These hemispheres are again coated and the process repeated many times. The eventual surface area is thousands times larger than the original surface. Below A scanning electron microscope picture of the fractal microporous surface. (Permission for use Biotronik.)...

Surface coatings applied to filter fabrics can enhance one or more of the filtration properties of the fabric. The coating may be sprayed on as a liquid or laid down as a sheet which is then bonded to the fabric. Microporous polymer coatings may be used to provide a smoother and fine aperture size to the fabric surface, which may enable easier detachment of the cake and prolong the lifetime of the medium. 

A potential problem that could result from this system of corrosion control would be the undermining of the chromium and the possibility that the brittle chromium deposits could flake off the surface. This potential problem was prevented by the development of a microcracked or microporous chromium coating. These coatings contain microcracks or micropores that do not detfact from the bright appearance of the chromium. They are formed very uniformly over the... 

The SEM is used for study of the surface and bulk structures of membranes. Membranes are prepared by attaching them to the specimen stub and applying a conductive surface coating. Bulk structures are observed for membranes fractured in air or liquid nitrogen, sectioned or critical point dried. Figures 5.24 and 5.25 are examples of the varied structures of typical membranes which can be imaged by this technique. An experimental HDPE microporous membrane has... 

Darbandi, M. et al (2013) Blocked-micropores, surface functionalized, biocompatible and silica-coated iron oxide nanocomposites as advanced MRI contrast agent. /. Nat Res, 15 (5), 1-9. 

Kim, J.H., Sotto, A., Chang, J., Nam, D., Boromand, A., and Van der Bruggen, B. 2013. Embedding and surface coating by layer-by-layer deposition of Ti02 nanoparticles on nanoporous polymeric films. Micropor. Mesopor. Mater. 173, 121-128. 

HoUow fibers are usuaUy on the order of 25 p.m to 2 mm in diameter. They can be made with a homogeneous dense stmcture, or preferably with a microporous stmcture having a dense permselective layer on the outside or inside surface. The dense surface layer can be integral, or separately coated onto a support fiber. The fibers are packed into bundles and potted into tubes to form a membrane module. More than a kilometer of fibers may be requited to... 

---