Fluorocarbon and Silicone Surfactants

Speciality Suijactants - Fluorocarbon and Silicone Surfactants 113 The most interesting sugar surfactants are the alkyl polyglucosides (APG) (1.12). 

These surfactants can lower the surface tension of water to below 20 mN (most surfactants described above lower the surface tension of water to values above 20 mN m typically in the region of 25-27 mN m ). Fluorocarbon and silicone surfactants are sometimes referred to as superwetters as they cause enhanced wetting and spreading of their aqueous solution. However, they are much more expensive than conventional surfactants and are only applied for specific applications whereby the low surface tension is a desirable property. 

It is a common misunderstanding that silicones and silicone surfactants are incompatible with hydrocarbon oils this is only partly correct. Small silicone surfactants, such as the trisiloxanes, are very compatible with organic oils. For example, aqueous solutions of the trisiloxane surfactants give very low interfacial tension against alkane oils. The incompatibility between polymeric silicones and some hydrocarbon oils is due more to the polymeric nature of the silicone block rather than to strong phobicity such as that between fluorocarbon and hydrocarbon groups. The compatibility between two species, such as a polymer and a... 

In aqueous systems, the range of surface tensions that will be encountered using common surfactants and practical concentrations is somewhat limited. In most practical cases, one might expect ctlv to be reduced to the range of 40 mN m"l a change of a factor of 2 from that of pure water (72.8). Lower values are normally attained only with very high surfactant concentrations (which can introduce foaming problems), with purer, more expensive surfactants, or with special materials such as fluorocarbon or silicone surfactants. 

If S is positive (or zero) spreading is spontaneous. If S is negative (nonzero 0), spreading is limited. To achieve spontaneous spreading of spray droplets on leaf surfaces a zero contact angle is required and this is achieved in most case by the so-called superwetters such as fluorocarbon or silicone surfactants. 

In the prepolymer method for one-shot polyether flexible urethane foams the primary role of the silicone surfactant is to lower surface tension and to provide film (cell-wall) resilience. Resilient films prevent the collapse of the foam during foam rise and continue to stabilize it until the foam is self-supporting. A secondary, but nevertheless important role of the silicone surfactant is cell-size control. The silicones can be added to the formulation in any of the 2 to 6 streams usually fed to the mixing head in the one-shot process. Usually, however, the silicone is metered separately, in combination with the polyol, or added as a wa-ter/amine/silicone mixture. It can also be added in the fluorocarbon blowing agent (52). 

Most elements have NMR-active nuclei, i.e., nuclei possessing a magnetic moment. For surfactant systems, the situation is very good in that H and C nuclei, which occur in most surfactant molecules, have good NMR properties. For relaxation work, however, it is often advantageous to use NMR on selectively deuterated compounds. F NMR is very useful for the study of fluorocarbon surfactants, P NMR for phospholipids, and Si NMR for silicon surfactants. For studies of water molecules we have a choice between three good alternatives H, H, and NMR. Many common counterions, e.g., Na, Li, Rb, Cs, F, Cl, Br, and I, have highly sensitive nuclei, whereas others, such as K" ", Mg " ", Ca ", and SO ", have lower sensitivity and are more difficult to study. 

To increase the surface activity, Owen and Groh [135] increased the fluorocarbon content of the side chains while maintaining the ethylene link between the fluorocarbon group and the silicon atom. Nonafluorohexyl (3,3,4,4,5,5,6,6,6-nonafluorohexyl) disiloxane and trisiloxane surfactants have equilibrium surface tensions in water at the cmc of 20 niN/m [142]. However, the response of their surface tension to dynamic changes is impeded by bulkiness of the flouroalkyl group [142]. The surface tension of the fluorosilicones is shown in Table 1.8. 

As surfactants silicones can be used. As blowing agents liquids with a low boiling point and a low heat of vaporization are used. The agent must volatilize at the moment when the viscosity increases mixture under exothermic crosslinking. As blowing agents, volatile fluorocarbons... 

Solid-Phase Components. Dispersed sohds are vital ingredients in commercial antifoam formulations. Much of the cmrent theory on antifoaming mechanism ascribes the active defoaming action to this dispersed solid phase with the liquid phase primarily a carrier fluid, active only in the sense that it must be surface-active in order to carry the solid particles into the foam films and cause destabilization. For example, PDMS, despite its considerable effectiveness in nonaqueous systems, shows little foam-inhibiting activity in aqueous surfactant solutions. It is only when compounded with hydrophobic silica [7631-86-9] to give the so-called silicone antifoam compounds that highly effective aqueous defoamers result. The three main solid-phase component classes are hydrocarbons, silicones, and fluorocarbons. 

A stable foam possesses both a high surface dilatational viscosity and elasticity (21). In principle, defoamers should reduce these properties. Ideally a spread duplex film, one thick enough to have two definite surfaces enclosing a bulk phase, should eliminate dilatational effects because the surface tension of an insoluble, one-component layer does not depend on its thickness. This effect has been verified (22). Silicone antifoams reduce both the surface dilatational elasticity and viscosity of crude oils as illustrated in Table 2. The PDMS materials are Dow Coming Ltd. polydimethylsiloxane fluids, SK 3556 is a Th. Goldschmidt Ltd. silicone oil, and FC 740 is a 3M Co. Ltd. fluorocarbon profoaming surfactant. 

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]. 

Nonionic surfactants with sugar hydrophilic groups -alkylpolyglucoside surfactants - are highly hydro-philic, and form temperature-insensitive microemulsions upon addition of alcohol (47, 48), as do sucrose ester surfactants (49). Zwitterionic surfactants such as lecithins also form microemulsions upon the addition of cosurfactant (50-52). In addition, trisiloxane surfactants microemulsify silicon oils (53), and fluorocarbon-tailed surfactants microemulsify fluorinated oils (54, 55). 

The polyol is a mixture of chemicals of which the main component is called the polyol. This is a compound containing several alcohol groups. The alcohol is the functional group on the compound. The polyol contains a blowing agent usually a Chloro Fluorocarbon, a surfactant usually a silicone compound, a catalyst (a tertiary amine), and a... 

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