Polydimethylsiloxane viscosity

Figure 9.18 Shear-rate dependence of the shear stress ( ), first normal stress difference (Q), shear viscosity (A), and normal viscosity (A) for a 1 1 mixture (by weight) of polydimethylsiloxane (viscosity = 9.74 Pa-s), and Genelite 4050S (hydrocarbon-formaldehyde resin with viscosity =10.1 Pa-s), at25°C. (From Takahashi et al. 1994, with permission ftom the Journal of Rheology.)...

Joint Assessment of Commodity Chemicals No. 26, Linear Polydimethylsiloxanes (viscosity 10-100,000 centistokes). European Centre for Ecotoxicology and Toxicology of Chemicals, Brussels, 1994 (and references therein). 

FIGURE 6.10 Effect of polydimethylsiloxane viscosity on rate of deactivation of hydro-phobed silica-polydimethylsiloxane antifoams. Foam half-lifetimes are measured after shake cycles made with graduated cylinder. Surfactant solution 0.06 M SDS, total antifoam concentration 0.2 g dm . Polydimethylsiloxane viscosities 0> 5 mPa s , 20 mPa s , -1000 mPa s , -12,500 mPa s A, -60,000 mPa s. (Adapted from J. Colloid Interface ScL, 166, Koczo, K., Koczone, J., Wasan, D., 225. Copyright 1994, with permission from Elsevier.)... 

Silicone Fluids. Sihcone fluids are used in a wide variety of appHcations, including damping fluids, dielectric fluids, poHshes, cosmetic and personal care additives, textile finishes, hydraiflic fluids, paint additives, and heat-transfer oils. Polydimethylsiloxane oils are manufactured by the equihbrium polymerisation of cycHc or linear dimethyl silicone precursors. Trifunctional organosilane end groups, typically trimethylsilyl (M), are used, and the ratio of end group to chain units (D), ie, M/D, controls the ultimate average molecular weight and viscosity (112). Low viscosity fluids,... 

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. 

Dilatational Elasticities and Viscosities of Crude Oil at 1 mHz with Polydimethylsiloxanes (PDMS) [300]... 

This has been verified for polydimethylsiloxanes added to crude oils. The effect of the dilatational elasticities and viscosities on crude oil by the addition of polydimethylsiloxanes is shown in Table 21-1. Under nonequilibrium conditions, both a high bulk viscosity and a surface viscosity can delay the film thinning and the stretching deformation, which precedes the destruction of a foam. There is another issue that concerns the formation of ordered structures. The development of ordered structures in the surface film may also stabilize the foams. Liquid crystalline phases in surfaces enhance the stability of the foam. 

Ito,Y., Shishida,S. Critical molecular weight for onset of non-newtonian flow and upper newtonian viscosity of polydimethylsiloxane. J. Polymer Sci., Polymer Phys. Ed. 10,2239-2278 (1972). 

Fig. 23. Variation of surface layer thickness with molecular weight of the stabilizing polydimethylsiloxane (PDMS) chain. Hydrodynamic thickness <5109) PMMA particles (O), PS particles ( ), micellar dispersions (A) from viscosity data x, thickness h from surface coverage data of PMMA particles assuming a prolate ellipsoid model for the...

Example 7.7. Cazabat et al. observed the spreading of polydimethylsiloxane (PDMS) on a cleaned silicon wafer [283], PDMS is a nonvolatile polymer which is liquid at room temperature. The PDMS used had a mean molecular weight of 9.7 kg/mol and a viscosity of 0.2 Pa s. Spreading was observed by an ellipsometer which had a lateral resolution of of 30 fim. In Fig. 7.16 we can clearly see that, in front of the drop, there is a precursor film of 0.7 nm thickness. 

Inoue T, Okamoto H, Osaki K (1991) Birefringence of amorphous polymers. 1 Dynamic measurements on polystyrene. Macromolecules 24 5670—5675 Isayev AI (1973) Generalised characterisation of relaxation properties and high elasticity of polymer systems. J Polym Sci A-2 116 2123—2133 Ito Y, Shishido S (1972) Critical molecular weight for onset of non-Newtonian flow and upper Newtonian viscosity of polydimethylsiloxane. J Polym Sci Polym Phys Ed 10 2239— 2248... 

At present there are several brands of SKTN A, B, C, D and E, which differ in their viscosity and molecular weight. Similarly to SKTN, one can obtain low-molecular polydimethylsiloxane elastomers which also contain methylphenylsiloxy elements, SKTNPh, SKTNPh-50, etc. 

Fig. 19. The steady-shear rheological behavior for a series of delaminated nanocomposites ol polydimethylsiloxane with dimethyl ditallow montmorillonite at 25 °C. The steady-shear viscosity shows an increase with respect to that of the pure-polymer at low shear rates but still obeys Newtonian type behavior, even at the highest silicate loadings examined. From Ref. [5].

In our studies of the polymerization of cyclic siloxane monomers we observed anomalies in the kinetics of the process and in the viscosity changes of the medium. The growing polydimethylsiloxane chain ends were found to associate... 

FIG. 18. Plot of bulk viscosity vs. average chain length (DP) as measured by Si NMR for hydroxy-terminated polydimethylsiloxanes. (89)... 

For higher molecular weight polydimethylsiloxanes (M > 2500), the number-average molecular weight is related to the bulk viscosity by the following formula, where the viscosity units are mm /s(=cSt). 

For an unvulcanized polydimethylsiloxane, the biaxial viscosity was approximately six times the shear viscosity over the biaxial extensional rates from 0.003 to 1.0 s (Chatraei et al., 1981), a result expected for Newtonian fluids, that is, the relationship between the limiting value of biaxial extensional viscosity (j, ) at zero strain rate and the steady zero-shear viscosity (i o) of a non-Newtonian food is ... 

The state-of-the-art silicone systems used in label stock application are normally solventless and thermal curing. Base polymers for these systems are vinyl-functionalized polydimethylsiloxanes having viscosities of around 200 - 600 mPa.s. Cross-linkers normally are hydride-functionalized polydimethylsiloxanes with a viscosity of around 25 mPa.s. These two components are cross-linked by a platinum catalyst, which can be the Karstedt catalyst. Additionally an inhibitor is added to the silicone mixture to prevent curing before it is applied on the substrate. These inhibitors ate... 

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