Silicon/water interactions

Zelisko, P. Bartzoka, V. Brook, M. A. Exploiting Favorable Silicone-Protein Interactions Stabilization Against Denaturation at Oil-Water Interfaces. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 212-221. 

Example 9.3. Plot the estimated adsorption isotherm for water vapor on silicon oxide at 20°C. First we need to estimate the constant C. From Chapter 6 we know that it is related to the Hamaker constant AH (Eq. 6.16) C = TtpBCABl = Ah/3ttpa. Here, pA and pB are the number densities of molecules in liquid water and silicon oxide, respectively. The Hamaker constant for water interacting with silicon oxide across air is Ah = 10-20 J (Table 6.3). With a density of water of 1000 kg/m3, a molecular weight of 18 g/mol, and a molecular radius of Do 1 A we get Vr% = 0.018 kgmoU1 /(1000 kgm-3) = 18 x 10 6m3moU1 and... 

Chemical etching is a process for removal of silicon dioxide films through dissolution in solutions. Dissolution of silicon oxides, in the context of this book, is related to the anodic behavior of silicon electrodes. However, the dissolution of anodic oxides is not well studied. In contrast, there is a wealth of information on the dissolution of other types of oxides. Much of this information must also be applicable, at least the qualitative and mechanistic nature, to that of anodic oxides. Also, because oxides of different types are commonly used in device fabrication, compiling the etch rate data of these oxides and those of silicon (presented in Chapter 7) in the same volume would be useful in practice. Additionally, because silica-water interaction, which has been extensively investigated in the geological field, is fundamental to the etching of silicon oxides, some of the results from the investigations on the dissolution of rocks and sands are also included. 

S. Zangooie, R. Bjorklund, and H. Arwin, Water interaction with thermal oxidation porous silicon layers, J. Electrochem. Soc. 144, 4027, 1997. 

The aim of this book is to serve as a centralized information source for anyone who is interested in the surface and electrochemical properties of silicon and its oxides. It will be most useful to the scientists who study the surface phenomena of silicon and to the engineers who design and fabricate silicon-based electronic devices. It can also serve as a general reference for researchers working in the fields of semiconductor electrochemistry and surface science, in which silicon is commonly used as a model material. In addition, it can be useful to the geologists who study rock-water interactions and to the people who work on etching and surface treatment of glasses. 

Ducker, W. A. and Clarke, D. R., Controlled modification of silicon nitride interactions in water via zwitteri-onic surfactant adsorption. Colloid Surf., A, 93, 275-292 (1994). 

Glass remains the preferred material for parenteral pharmaceutical packaging. Glass requires lubrication, cuid silicone oil due to its physicochemical properties fulfills the criteria of a preferred material. External lubricants inherently are hydrophobic and the substitute for siheone oil can also denature the protein at the lubricant/water interface. Additionally, if similar amount of lubricant (as for siheone oil) would be needed to get optimum lubrication, shedding of the particles may still remain a problem. Therefore, until glass is used as a container with silicone lubrication, it is important to understand the protein-silicone oil interactions cuid find solutions to minimize them. 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

As shown in Table 5.5.1,15% of the silicone surfactants annually used were disposed of via wastewater treatment plants [6], but no studies have addressed their fate or persistence in this environmental compartment. Due to the hydrolytic instability and tendency for sorption to surfaces, it is generally thought that limited persistence of the parent molecule in aqueous systems should occur. Consequently more attention has been focused on interactions with solid media such as that resulting from direct application as agricultural adjuvants, and in re-use of sludge. Increased water solubility for the degradation products of trisiloxane surfactants has, however, been observed [10,12,15], demonstrating the need to also monitor the... 

In regard to the potential effects of silicone membrane or film thickness (e.g., polydimethylsiloxane [PDMS]) on partition coefficients, Paschke and Popp (2003) have shown that that at equilibrium an SPME fiber with a 7 xm thick film of PDMS had about a 6-fold higher ATpw than a similar fiber with a 100 xm thick film. However, this could be the result of interactions with the silica core. Recent research (Smedes, 2004) has shown that silicone sheeting with PRCs can be employed for water sampling with good results. 

The first observation of depletion flocculation by surfactant micelles was reported by Aronson [3]. Bibette et al. [4] have studied the behavior of silicone-in-water emulsions stabilized by sodium dodecyl sulfate (SDS). They have exploited the attractive depletion interaction to size fractionate a crude polydisperse emulsion [5]. Because the surfactant volume fraction necessary to induce flocculation is always lower than 5%, the micelle osmotic pressure can be taken to be the ideal-gas value ... 

The Mobility of Silica in Steam. The reactivity of silica and silica-containing materials to steam has been assumed in the literature to explain several phenomena, a few of which are the sintering of silica (35), the aging of amorphous silica alumina cracking catalysts (36) and the formation of ultrastable molecular sieves (37). The basis of all these explanations is the interaction of siliceous materials with water to form mobile, low molecular weight silicon compounds by hydrolysis (38) such as ... 

It is generally accepted that the only important polar adsoiption sites on the silica surface are the silanol functions, i.e., hydroxyl groups, that are attached to silicon atoms (2). They can interact with the sample molecules by hydrogen bonding and various physical observations ctAi be used to prove this statement. Complete dehydration of silica by beating, i.e., removal of all surface hydroxyl groups, yields a hydrophobia silica which no longer shows adsorption for unsaturated and polar molecules and is no more wetted by water (15). Chemical modification of the surface hydroxyls such as used in the preparation of chemically bonded phases also eliminates the selective adsorption properties of the silica. ... 

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