Ultra-Thin Silicone Films

Fig. 5. SE images of bulk-impregnated gypsum samples broken perpendicularly, a, b Overview Gypsum microstructure of samples with high water-gypsum ratio (WGR = 1.0), overdosing with H-siloxane at 2 wt%. TTie loosely packed gypsum microstructure, which depends on the water-to-gypsum ratio, exhibits free polymethylsilicic acid films in crystal interstices only when silicone is present in excess, c The usual market H-siloxane dosage of < 0.5 wt% is found to produce ultra-thin silicone films on gypsum crystals, as shown in non-carbon-coated samples the presence of silicone is indicated by menisci (see arrow).

R.J. Kee, W. Yang, N. Sullivan, A.M. Dean, A. Zojaji, M. Hall, and M. Williams. The Formation of Ultra-Thin Silicon-Oxide Films Using H2-N2O Mixtures. Proc. Combust. Inst., 29 In press, 2002. 

Development work has also investigated alternative asymmetric membrane systems, including (a) an ultra thin nonporous film laminated to a much thicker microporous backing (which may be a different material) and (b) a very thin nonporous film applied as a coating to a thicker microporous substrate (Stem, 1986). A complex membrane structure reportedly used in the Monsanto Prism separator is a skinned asymmetric hollow fiber of polysulfone coated with a thin film of silicone mbber (about 1 micron thick). The polysulfone skin (about U. 1 micron thick) is the active separator, while the silicone mbber serves to. seal any defects in the base membrane without affecting the intrinsic permeability of the membrane (Koros and Chem, 1987). 

Nanostructures are objects with at least one dimension in the nanoscale (0.1-100 nm). SiUcones are inert synthetic materials which have found a variety of apphcations, including those in the biomedical area. The aim of this chapter is to present some aspects of the current state of knowledge on silicone nanostructures. In the following sections, we will review the studies on the development of nanostructured materials composed of silicone. The chapter focuses mainly on the structures such as soUd nanoparticles, empty nanocapsules, and ultra-thin polymeric films. The methods of preparation and characterization of these objects are presented. Some aspects concerning the application of the nanostructures are also mentioned. 

Nanostructures are objects with at least one dimension on a nanometric scale. Typically, the size of objects is in the range of 1-100 nm. However, structures with dimensions of several hundred nanometers can also be considered as the nanostructures. This chapter deals with three types of silicone nanostructures, namely solid particles, nanocapsules, and ultra-thin nanostructural films (see Figure 4.2). 

Ultra-thin polymeric film is a polymer layer of the thickness in a nanometric scale deposited on a substrate (see Figure 4.2C). Such silicone films are of great interest due to their use in many areas of scientific and technical applications. Polydimethylsiloxane (PDMS) is one of the most popular silicone-based polymers used in the preparation of silicone films. This polymer has a unique molecular structure and physicochemical properties, which make it suitable for a wide range of applications such as lubricants, sealants, adhesives, eye contact lenses, and microfluidic devices [48]. 

Ultra-thin Hquid films of PDMS or poly(methyl-hydrodimethyl)siloxane on siHcon substrates were also prepared [50], The silicon wafers were cleaned by immersion in a freshly prepared piranha solution (a mixture of 70% sulfuric acid and 30% hydrogen peroxide), rinsing with deionized water, followed by etching in HF solution. Then the wafers were rinsed with deionized water and blown dry under a stream of nitrogen. The uniform thin films were spread by dipping the clean substrates in dilute solutions of silicone polymers in hexane and withdrawing the wafers at a constant speed. It was shown that solution concentration and withdrawal speed affected the final film thickness. Typical thickness was in the range of 3-8 nm. 

The chapter presents the current state of knowledge on silicone nanostructures such as solid nanoparticles, empty nanocapsules, and ultra-thin polymeric films. The methods of their preparation and characterization, as well as their application are presented. It has been shown that the silicone nanostructures are mainly fabricated in the sol-gel processes from silicone precursors containing groups, which are reactive under acidic or basic conditions. These reactive groups include alkoxysilyl (=Si-0-R), silanol (=Si-OH), or Si-H bonds. The silicone materials are formed in the polymerization and/or polycondensation processes. The process of precursor transformation to silicone polymeric materials is often described as solidification. ... 

The silicone resin network (polymethylsilicic acid) coats the surfaces of both large calcite grains and small titanium dioxide particles with an ultra-thin veil-like film. Clear evidence of an existing network coating is the apparent rounding and void filling just a few nanometers thick (Figs. 3b,d) between the mineral phases (white arrows). 

Yu B, Zhou F, Mu ZG et al (2006) Tribological properties of ultra-thin ionic liquid films on single-crystal silicon wafers with functionalized surfaces. Tribol Int 39 879-887... 

STRUCTURAL AND LIGHT-EMITTING PROPERTIES OF ULTRA THIN ANODIC SILICON FILMS FORMED AT THE... 

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