Silicone surfactants based

Study on the effects of nonelectrolyte additives, 2-butoxyethanol, poly(eth-ylene glycol), and glucose, on various physicochemical aspects of aqueous solutions of two nonionic silicone surfactants based on poly(dimethylsiloxane)-gra/f-... 

The unique surface characteristics of polysiloxanes mean that they are extensively used as surfactants. Silicone surfactants have been thoroughly studied and described in numerous articles. For an extensive, in-depth discussion of this subject, a recent chapter by Hill,476 and his introductory chapter in the monograph he later edited,477 are excellent references. In the latter monograph, many aspects of silicone surfactants are described in 12 chapters. In the introduction, Hill discusses the chemistry of silicone surfactants, surface activity, aggregation behavior of silicone surfactants in various media, and their key applications in polyurethane foam manufacture, in textile and fiber industry, in personal care, and in paint and coating industries. All this information (with 200 cited references) provides a broad background for the discussion of more specific issues covered in other chapters. Thus, surfactants based on silicone polyether co-polymers are surveyed.478 Novel siloxane surfactant structures,479 surface activity and aggregation phenomena,480 silicone surfactants application in the formation of polyurethane foam,481 foam control and... 

Industrially, silicone surfactants are used in a variety of processes including foam, textile, concrete and thermoplastic production, and applications include use as foam stabilisers, defoamers, emulsifiers, dispersants, wetters, adhesives, lubricants and release agents [1]. The ability of silicone surfactants to also function in organic media creates a unique niche for their use, such as in polyurethane foam manufacture and as additives to paints and oil-based formulations, whilst the ability to lower surface tension in aqueous solutions provides useful superwetting properties. The low biological risk associated with these compounds has also led to their use in cosmetics and personal care products [2]. 

The most common polymeric silicone surfactants are based on polyoxyalkylene groups. The structures of graft-type (rake-type) and ABA structures are illustrated in Figures 6.17 and 6.18. It should be noted that there are many possible variants of these basic structures. The actual structure of graft-type silicone copolymers is a random copolymer of m and n rather than the blocky structure suggested by the diagram. 

Many small-molecule silicone surfactants have been made and their properties (especially wetting) characterized [7-11]. The best known small-molecule silicone surfactants are the trisiloxane surfactants based on 1,1,1,3,5,5,5-heptamethyltrisiloxane, shown in Figure 6.19. 

Silicone surfactants are specialty surfactants that are primarily used in applications that demand their unique properties. Most applications are based on some combination of their (a) low surface tension, (b) surface activity in nonaqueous media, (c) wetting or spreading, (d) low friction or tactile properties, (e) ability to deliver silicone in a water-soluble (or dispersible) form, (f) polymeric nature or (g) low toxicity. The major applications will be discussed briefly in following sections. 

Surface treatments are often necessary for aesthetic and performance reasons. This can involve printing or lacquering, using both solvent and non-solvent based inks, which are applied to the surface using rollers, pads, silk screen, inkjet or lasers. Waterborne coatings are environmentally more desirable and silicone surfactants are claimed to give the best performance to improve substrate wetting (456). 

The combination of both the biodegradability and the stability towards hydrolysis is unique in the field of well known silicone surfactants and will ensure the widespread application of trimethylsilane based surfactants. Considering all these facts all applications for which trisiloxane surfactants are already used or at least recommended are opened up in general for the new silane surfactants. Furthermore, applications now can be taken into consideration for which the hydrolytically unstable trisiloxane derivatives failed in the past. 

Sorbitol Polyol-Modified Isocyanurate Foam (71). This foam was prepared according to the following procedure. Potassium 2-ethylhex-anoate containing 4% water was used as the catalyst (soluble in polyether polyols). 94 g of sorbitol-based polyether polyol having a hydroxyl number of 490, 8.5 g of the potassium 2-ethylhexanoate, 120 g of tris(chloroethyl) phosphate, 5 g of silicone surfactant, and 90 g of... 

The silicone surfactants can be viewed as PDMS-polyether-copolymers which are mainly based on a combination of just three structural units the methyl substituted siloxane backbone as well as a sophisticated ratio and arrangement of ethylene oxide and/or propylene oxide forming the attached polyethers and, in some cases, additional modifications. 

Not taking cyclic molecules into account, the general structures of industrial silicone surfactants for flexible slabstock foam production can be seen in Figure 2.13. The main building blocks of these materials are a PDMS backbone and attached polyethers based on ethylene oxide and propylene oxide addition products. The siloxane backbones can either be linear or branched and can have their polyether substituents attached in an either pendant or terminal location. These four general structures are outlined in Figure 2.13). 

To make a surface-active molecule, one needs to have both a water-soluble and an oil-soluble portion in the molecule. The traditional oil-soluble portion of the molecule is fatty. The silicone surfactants substitute or add on silicone-based hydrophobicity. This results in materials that are more easily formulated into detergent systems and have the improved substantivity, lower irritation, improved softening, and other attributes of silicone and properties one expects from the fatty surfactant. In molecules where silicone is predominate, the functional attributes of silicone will predominate. If the molecule has both a silicone and fatty hydrophobe present, it wiU function with attributes of both of the materials. This allows for the formulation of a wide variety of products, which have oil, water, silicone, or variable solubility. 

Silicone-based materials are an important class of polymeric surfactants that are commonly used in the cosmetic industry. They consist of poly(dimethyl siloxane) (PDMS) that is modified by incorporation of specific groups for special applications. For example, dimethicone copolyol (used as emulsifier or dispersant) is typically a copolymer of PDMS and polyoxyalkylene ether. Aminofunctional silicones provide excellent hair-conditioning benefit. Polyether-modified silicones, including terpolymers containing an alkyl or polyglucoside moiety, are very effective emulsifiers for water-silicone emulsions. These silicone surfactants act as defoamers, depending on the amount and type of glycol modification. They are also used to reduce skin irritation. 

The hydrophobic interaction also occurs in other solvents. Solvophobic interactions have been exploited in nonaqueous media using surfactants based around silicone oils or fluorocarbons. The expulsion of both of these molecular groups by bulk liquids leads to adsorption at air-solution interfaces and to the formation of stable, nonaqueous foams, that are used in the production of both rigid and flexible isocyanate-based polymeric foams for insulation and cushioning applications [3]. 

Jaeger, D.A. Ward, M.D. Dutta, A.K. Preparation and characterization of cleavable surfactants based on a silicon-oxygen bond. J. Org. Chem. 1988, 53, 1577-1580. 

The choice of reactions to be carried out in the presence of hydrophobic material-supported platinum catalysts was based on the practical importance of reaction products. Epoxy functional silanes are among the most important adhesion promoters applied to create bonds between filler and polymer matrix, thus improving physicochemical and strength parameters of composites. Of practical importance are also epoxy functional siloxanes that are applied to the modification of epoxy resins, thus making them more flexible, less susceptible to water sorption, and more resistant to heat. Moreover, epoxy functional siloxanes find application to the manufacture of ionic silicone surfactants. 

The theories of antifoam action are complex. Typical antifoam agents for silicone surfactants contain a silicone polymer and finely powdered silica [169]. A low surface tension of an antifoam agent, lower than that of the surfactant solution, is a necessary but insufficient condition. A siloxane surfactant solution cannot be defoamed by conventional siloxane antifoaming agents but is readily defoamed by an antifoam agent based on poly(methyl-3,3,4,4,5,5,6,6,6-nonafluo-rohexylsiloxane), [ CH3[CF3(CF2)3(CH2)2]SiO ], which has a low surface ten-... 

Surfactants based on block copolymers of dimethylsiloxane with poly(ethylene oxide) are unique in regulating the cell size in polyurethane foams. One route to such polymers uses reaction I.E in Table 17.6 between a polysiloxane and an allyl ether of polyethylene oxide [11], Increasing the silicone content makes the surfactant more lipophilic (oil-loving), whereas increasing the poly(ethylene oxide) content makes it more hydrophilic (water-loving). 

Y Sela, S Magdassi, N Garti. Release of markers from the inner water phase of W/O/W emulsions stabilized by silicone based polymeric surfactants. J Control Release 33(1) 1-12, 1995. 

The coal-water mixture fed to the boilers has to be formulated to a certain specification. This is done with the proper inclusion of additives to facilitate combustion. The recommended additives include a petroleum-based surfactant (polysulfones or polycar-boxylates), a stabilizing (e.g. xanthan gum), a biocide and an anti-foaming agent (such as a silicone base). 

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