Polydimethylsiloxane, surfactants

The use of neutron reflectivity at liquid interfaces, which is a method sensitive to both surface roughness and surfactant layer thickness, was reviewed with the examples of polydimethylsiloxane-surfactant layers.633 Sum-frequency generation (SFG) vibrational spectroscopy was applied to study surface restructuring behavior of PDMS in water in an attempt to understand antifouling properties of silicones.6 ... 

Walderhaug, H., Structures in a Microemulsion System of an Ethoxylated Polydimethylsiloxane Surfactant, Water, and Oil Studied by NMR Self-Diffusion Measurements. J. Phys. Chem. B 2007, 111, 9821-9827. 

It has been shown (16) that a stable foam possesses both a high surface dilatational viscosity and elasticity. 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 iasoluble, one-component layer does not depend on its thickness. This effect has been verified (17). SiUcone antifoams reduce both the surface dilatational elasticity and viscosity of cmde oils as iUustrated ia Table 2 (17). The PDMS materials are Dow Coming Ltd. polydimethylsiloxane fluids, SK 3556 is a Th. Goldschmidt Ltd. siUcone oil, and FC 740 is a 3M Co. Ltd. fluorocarbon profoaming surfactant. 

Miscellaneous compounds. Other materials used include FC-171, fluorocarbon surfactant, 3M Industrial Chemical Products Division, St. Paul MN 55144-1000 Byk 306, Bykchemie USA, Wallingford, CT 06492 Polyol (poly-caprolactonetriol a polyester polyol), and Silwet L-7602 (polyalkylene oxide modified polydimethylsiloxane), both from Union Carbide Chemicals and Plastics Co., Inc., Danbury, CT 06817-0001. 

Inhibition of polydimethylsiloxane hydrolysis on soils [52,60] and clays [25] by high moisture levels has been described, which is in general attributed to their low water solubility. This is not expected to be applicable to the more soluble surfactant analogues, however, which show increased water solubility with degradation [10,12,15], and which are used at concentrations much lower than are required for the formation of hydrophobic degradation products. 

The interfacial tension is a key property for describing the formation of emulsions and microemulsions (Aveyard et al., 1990), including those in supercritical fluids (da Rocha et al., 1999), as shown in Figure 8.3, where the v-axis represents a variety of formulation variables. A minimum in y is observed at the phase inversion point where the system is balanced with respect to the partitioning of the surfactant between the phases. Here, a middle-phase emulsion is present in equilibrium with excess C02-rich (top) and aqueous-rich (bottom) phases. Upon changing any of the formulation variables away from this point—for example, the hydrophilie/C02-philic balance (HCB) in the surfactant structure—the surfactant will migrate toward one of the phases. This phase usually becomes the external phase, according to the Bancroft rule. For example, a surfactant with a low HCB, such as PFPE COO NH4+ (2500 g/mol), favors the upper C02 phase and forms w/c microemulsions with an excess water phase. Likewise, a shift in formulation variable to the left would drive the surfactant toward water to form a c/w emulsion. Studies of y versus HCB for block copolymers of propylene oxide, and ethylene oxide, and polydimethylsiloxane (PDMS) and ethylene oxide, have been used to understand microemulsion and emulsion formation, curvature, and stability (da Rocha et al., 1999). 

Most dispersion polymerizations in C02, including the monomers methyl methacrylate, styrene, and vinyl acetate, have been summarized elsewhere (Canelas and DeSimone, 1997b Kendall et al., 1999) and will not be covered in this chapter. In a dispersion polymerization, the insoluble polymer is sterically stabilized as colloidal polymer particles by the surfactant that is adsorbed or chemically grafted to the particles. Effective surfactants in the dispersion polymerizations include C02-soluble homopolymers, block and random copolymers, and reactive macromonomers. Polymeric surfactants for C02 have been designed by combining C02-soluble (C02-philic) polymers, such as polydimethylsiloxane (PDMS) or PFOA, with C02-insoluble (C02-phobic) polymers, such as hydrophilic or lipophilic polymers (Betts et al., 1996, 1998 Guan and DeSimone, 1994). Several advances in C02-based dispersion polymerizations will be reviewed in the following section. 

Surfactants. Silicone surfactants lower the surface tension and emulsify incompatible ingredients. Copolymers of polydimethylsiloxane and polyoxyalkylene were the originally used surfactants. Surfactants with Si—O—C bonds are hydrolysable, but those with only a Si—C bond are non-hydrolysable. Several non-hydrolysable alkyl pendant silicone copolymers are used as surfactants for specific formulations (Seymour, 1992). 

Others sweeteners, flavors, colors, surfactants, antifoaming agents (polydimethylsiloxane). 

Surfactants. Silicone surfactants, which are used in rigid urethane foams, can be used as surfactants for pyranyl foam jn-eparation. The silicone surfactants are block copolymers of polydimethylsiloxane-polyoxyalkylene ether in either linear or pendant structures. 

The most extensive group of ether surfactants is that of polyethoxylated long-chain alcohols and related ethoxylated products considered, in view of their practical importance, in a separate section. Other ether nonionics of importance are polypropylene glycols, propoxylated alcohols, block-copolymers of ethylene oxide and propylene oxide, block-copolymers of ethylene oxide and butylene oxide [8, 16-20], block-copolymers having a hydrophobic polydimethylsiloxane moiety [19, 21], as well as alkyl polyglycerides, alkyl polyglycosides, derivatives of maltose and other saccarides. 

CAS 64365-23-7 68937-54-2 68938-54-5 Synonyms Dimethylmethyl (polyethylene oxide) siloxane Dimethylsilox-ane/glycol copolymer Polyoxyethylene-grafted polydimethylsiloxane Polysiloxane polyether copolymer Siloxanes and silicones, dimethyl, hydroxy-terminated, ethoxylated propoxylated Classification Silicone glycol surfactant... 

From the results presented in Table 3.27 and in accordance with the results of [157, 158], for oirr case at 333 K, the surface layer at maximum adsorption (surfactant mass fractions from 2.25 x 10 to 7.5 X 10 is an extremely compressed monolayer, whereas the majority of dimethylsiloxane units lie on the surface of the liquid. At higher temperatures (343—353 K) but in a narrower concentration range (from 5 x 10 to 7.5 x 10 ) the polydimethylsiloxane chain tears off the sirrface, forming spiral turns of 6—8 elements, as witnessed by a single element area of 0.09-0.11 nm, which may be referred to one spiral turn [157]. From the concentration and tempera-... 

A polyethyleneoxide-Z)-polydimethylsiloxane-polyethyleneoxide surfactant, (EO)i5-(DMS)i5-(EO)i5, was studied with freeze-fracture transmission electron microscopy and pulsed-field gradient nuclear magnetic resonance speetroseopy, in order to establish the effeet of glyeerol on the permeability of vesiele membranes. Small vesicles with diameters of less than 25 run and multilamellar vesicles with diameters larger than 250 nm were observed in pure water, which were modified when water was gradually replaced with glycerol [47]. 

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