Viscosity of silicone oils

Fig. 10.13 Calculated mass transfer coefficients k and regression coefficient, r2, for each condition of agitation rate, viscosity of silicon oil and presence of Triton (0.25 CMC). White columns, water based medium gray columns. Triton X-100 medium void columns 10 cSt silicone oil striped columns 20 cSt silicone oil dotted columns 50 cSt silicone oil...

The conditions that most favored mass transfer of anthracene (250 and 300 rpm and presence of Triton X-100) were evaluated in terms of enzyme inactivation as well as all viscosities of silicone oil. Inactivation coefficients, kd, were calculated according to first-order kinetics (Fig. 10.14). The increase of the agitation rate to 300 rpm did not have a remarkable effect on the inactivation in presence of Triton, whereas in aqueous medium inactivation coefficients slightly increased. The viscosity of solvent does not seem to affect inactivation, except for 10 cSt, which led to the highest values. 

By comparison with mineral oils, the viscosity of silicone oils changes little with temperature. They are thermally stable, low volatility products (from ca. 50 mPa s) exhibiting long term stability at 150°C in air and even up... 

The wettabilty measurements, according to the Stevens test, and the study of the viscosity of silicon oil /silylated silica mixes, corroborate perfectly the IGC results and therefore confirm the validity of the proposed model. 

Summarizing the findings presented, it can be concluded that both the molecular weight and the viscosity of silicone oils could be determined — after calibration — with the help of a less critical... 

Table 21.5 Shear viscosity of silicone oils and the corresponding emulsions with silicone oil and PEG20,000 as well as the viscosity ratios at 25 °C and 1000 s ...

Figure 5.12. Effect of viscosity of silicone oil on its release properties based on measurement of fracture energy. [Data from Briscoe, B. J. Panesar, S. S., J. Adhesion Sci. TechnoL, 2, 4, 287-310,1988.]...

Figures 8.27 and 8.28 show the critical velocity differences describing the onset of KHI for silicone oil 10 and 100, respectively. The results shown with open circles were determined by using both the measured values of Vicr and 2, while open triangles were determined by using the measured values of and calculated value of Vicr based on (8.25). For every salt water layer depth, the two sets of results (i.e., the two symbols) agree with each other in Fig. 8.27. As the kinematic viscosity of silicone oil was increased from 10 to lOOmm /s, a discrepancy appears between the two symbols as seen in Fig. 8.28, but it is limited to about 15%. A number of researchers [27, 30, 32] have also observed a critical velocity difference of approximately 20 cm/s for water-siUcone oil systems shown in Fig. 8.17a.

Figure 8.31 demonstrates that all the measured values of the critical salt water velocity can be predicted by (8.27) regardless of the kinematic viscosity of silicone oil. Yamasaki et al. [30] and Komai et al. [42] also observed that the critical velocity difference is a weak function of the kinematic viscosity of silicone oil. 

Figure 8.32 shows that the wavelength decreases with an increase in the salt water layer depth. When the kinematic viscosity of silicone oil is low, say 2 mm /s, the measured values of wavelength A can be approximated by (8.30). As the kinematic viscosity of silicone oil increased, the wavelength increased (see Table 8.5), and (8.30) overestimated the A. Yamasaki et al. [30] observed that the diameter of a liquid paraffin droplet became large with an increase in the kinematic viscosity, which is consistent with the above finding on the wavelength behavior. 

The amplitude of KHI is a function of the depth ratio H2/H1 and the kinematic viscosity of silicone oil, as shown in Table 8.6. Figure 8.33 shows that (8.32) cannot predict the amplitude. 

The wavelength X increases with an increase in the kinematic viscosity of silicone oil. The analytical equation for A (8.30) agrees with the measured values of A for vi = 2 mm /s, but overestimates A as vi exceeds lOmm /s. The amplitude of the interfacial instability is also measured. 

Silicones exhibit an apparently low solubility in different oils. In fact, there is actually a slow rate of dissolution that depends on the viscosity of the oil and the concentration of the dispersed drops. The mechanisms of the critical bubble size and the reason a significantly faster coalescence occurs at a lower concentration of silicone can be explained in terms of the higher interfacial mobility, as can be measured by the bubble rise velocities. 

A. Crisp, E. de Juan, J. Tiedeman, Effect of silicone oil viscosity on emulsification. Arch. Ophthalmol. 105 (1987) 546-550. 

The advantage of the partially fluorinated compounds lies more in their potential to mix with silicone oil. Various groups started activities to diversify the portfolio of silicone oils used as long-term endotamponades to enable a reattachment of a detached retina. Dimethylsiloxanes of different viscosities are well established but their use is limited to the treatment of the upper quadrants of the retina. This is because a 100% filling of the vitreous cavity cannot be achieved, which means that because of their specific gravity, which is 0.97 g/ml, they float on top of the aqueous material present in the vitreous... 

Figure 3.6 Flow behavior of silicone oils of different viscosities as a function of time period as indicated. The blue line connects flow statuses corresponding to ri t...

Figure 3.22 Measurement of the extensional viscosities of the PEO solution and of silicone oil Baysilone M 1000.

This scaling law, Eq. (9-48), implies that all components of the stress tensor are linear in the shear rate. Consider for example, a constant-shear-rate experiment. At steady state, not only is the shear stress predicted to be proportional to the shear rate, but so also is the first normal stress difference N This prediction has been nicely confirmed in recent experiments by Takahashi et al. (1994), who studied mixtures of silicon oil and hydrocarbon-formaldehyde resin. Both these fluids are Newtonian, and have the same viscosity, around 10 Pa s. Figure 9-18 shows that both the shear stress o and the first normal stress difference N = shear rate, so that the shear viscosity rj = aly and the so-called normal viscosity rjn = N /y are constants. The first normal stress difference in this mixture must be attributed entirely to the presence of interfaces, since the individual liquids in the mixture have no measurable normal stresses. A portion of the shear stress also comes from the interfacial stress. Figure 9-19 shows that the shear and normal viscosities are both maximized at a component ratio of roughly 50 50. At this component ratio, the interfacial term accounts for roughly half the total shear stress. 

Aqueous silicone oil emulsions can be produced from silicone oils, as well as polymethylhydrogensiloxttnes with trimethylsiloxy-end groups, in the viscosity range tiround 1000 mPa s in emulsifying equipment (e.g. baffle-ring pumps), preferably using nonionic emulsifiers. The amounts of silicone oil in these emulsions vary between 3... 

We have compared these theoretical predictions of the low-frequency modulus to experimental measurements on compressed emulsions and concentrated dispersions of microgels [121]. The emulsions were dispersions of silicone oil (viscosity 0.5 Pas) in water stabilized by the nonionic surfactant Triton X-100 [102, 121]. The excess surfactant was carefully eliminated by successive washing operations to avoid attractive depletion interactions. The size distribution of the droplets was moderately polydisperse with a mean droplet diameter of 2pin. The interfacial energy F between oil and water was 4mJ/m. The contact modulus for these emulsions was thus F 35 kPa. The volume fraction of the dispersed phase was easily obtained from weight measurements before and after water evaporation. Concentrated emulsions have a plateau modulus that extends to the lowest accessible frequencies, from which the low-frequency modulus Gq was obtained. Figure 11 shows the variations of Gq/E"" with 0 measured for the emulsions against the values calculated in the... 

Fig. 17 Flow curves measured at steady state for microgel pastes (a) and concentrated emulsions of silicone oil in water (b). In (a) the data for microgel pastes are presented for varying particle concentration (wt%), crosslink density, salt concentration, and solvent viscosity. Symbols are the same as used in (c). Rl and R5 refer to two different crosslink densities, A x = 128 and A x = 28, where A x is the average number of monomers between two crosslinks. In (b), data for emulsions are presented for varying packing fractions. Symbols are the same as used in (d). The solid lines in (a) and (b) are the best fits to the Herschel-Bulkley equation. Plots (c) and (d) show collapse of the different data sets when the shear stress is scaled by <7y and the shear rate by tis/Gq. The equations of the solid lines in (c) and (d) are of the form (26), where m = 0.47 and K = 280 for microgel pastes (c) and m = 0.50 and K = 160 for emulsions (d)...

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