Silicone gels

GELSIL Gel, silicone Gel spinning Gel spun fibers Geltabs... 

In an attempt to determine the applicability of JKR and DMT theories, Lee [91] measured the no-load contact radius of crosslinked silicone rubber spheres in contact with a glass slide as a function of their radii of curvature (R) and elastic moduli (K). In these experiments, Lee found that a thin layer of silicone gel transferred onto the glass slide. From a plot of versus R, using Eq. 13 of the JKR theory, Lee determined that the work of adhesion was about 70 7 mJ/m". a value in clo.se agreement with that determined by Johnson and coworkers 6 using Eqs. 11 and 16. 

Currently, breast cancer is the most frequently diagnosed cancer in both white and African-American women. According to latest reports, of the 662,870 cancer cases reported for women in 2005, 32% were breast cancer. The incidence of breast cancer increased from 1 in 20 in 1960 to 1 in 8 today. More than 100,000 women per year require mastectomy for treatment, and every year 75% decide to have reconstmction. About half the number of these women select prostheses made of silica-reinforced silicone-rubber shell filled with silicone gel, while the other half have the same shell filled with physiological saline. Reportedly, gel-fiUed prostheses feel more natural, but are associated with true or perceived health problems and remain highly controversial. 

In 1992, the FDA issued a moratorium on silicone-gel-filled implants, and restricted their use to reconstmction and clinical smdies. In 2000, they approved saline-filled implants. In 2003, the General and Plastic Surgery Devices (GPSD) Advisory Panel recommended reapproval of gel-filled implants, but the FDA decided to wait for more clinical evidence of safety. In late 2005, the Panel recommended conditional approval of Mentor s and Inamed s gel implants. In October 2006, Health Canada approved the use of sUicone-gel-filled implants, with a warning that no medical device is 100% safe. ... 

In November of 2006, the FDA lifted its 14-year ban of silicone gel filled implants. 

Draft Guidance for Industry and FDA Staff Saline, Silicone Gel and Alternative Breast Implants. Washington DC, January 13, 2004. 

Figure 1. Solvent Fractionation Scheme Using Silicon Gel Column for Crude Oil and Shale Oil.

Figure 3. Content of Fractions of Crude Oil and Shale Oil by Silicon Gel Column.

Fig. 7. Effect of volume fraction of dispersed particles in a gel on the shear modulus of the gel under electric fields. The sample used was a silicone gel containing PMACo particles. The particles were dispersed at random in the gel...

The dynamic viscoelasticity of particulate gels of silicone gel and lightly doped poly-p-phenylene (PPP) particles has been studied under ac excitation [55]. The influence of the dielectric constant of the PPP particles has been investigated in detail. It is well known that the dielectric constant varies with the frequency of the applied field, the content of doping, or the measured temperature. In Fig. 11 is displayed the relationship between an increase in shear modulus induced by ac excitation of 0.4kV/mm and the dielectric constant of PPP particles, which was varied by changing the frequency of the applied field. AG increases with s2 and then reaches a constant value. Although the composite gel of PPP particles has dc conductivity, the viscoelastic behavior of the gel in an electric field is qualitatively explained by the model in Sect. 4.2.1, in which the effect of dc conductivity is neglected. 

The elastic modulus of laminated composite plate in which an ER silicone gel of carbonaceous particles is sandwiched between two PVC sheets also changed under the influence of an electric field. It was found that an electric field of 1.17 kV/mm caused a gain in the elastic modulus of the gel of 13% [57]. 

The entrance window is a relevant part of the sensor. Common glasses as well as most transparent plastics block UV radiation. Standard UV-transmitting materials like quartz and sapphire are expensive. For UVA and to some extent the UVB special glasses but also plastics like some PMMA-derivatives or some silicon gels are available with a reasonable transmittance down to about 330 nm. For UVC applications with the important 254 nm line of Hg, quartz remains the standard solution. 

Many women who have received silicone-fluid-filled breast implants have claimed to suffer from implant-related diseases, apparently caused by small leakages of the fluid into the body tissue. Successful lawsuits on those grounds in the United States have driven Dow Corning, the principal manufacturer of the implants, to file for bankruptcy protection. Food and Drug Administration Commissioner David A. Kessler, however, has reported to a congressional subcommittee that, as of July, 1995, there was no scientific evidence that silicone implants are a significant cause of disease. See M. S. Reisch and R. L. Rawls, Silicone gel breast implants. Chem. Eng. News, December 11, 10-17 (1995). 

Solvates may be readily detected and desolvation may be readily distinguished from a phase change using thermomicroscopy. The appearance of turbidity within the crystal upon heating is a sign of solvent being driven off, but a much more conclusive test involves covering the crystal with silicone gel or paraffin oil, which trap the bubbles of released solvent, as shown in Fig. 4.6. 

Fig. 4.6 Bubbles of solvent evolved from a crystal heated in a silicone gel preparation. (From Kuhnert-Brandstatter 1971, with permission.)...

The protection of electronic devices has been a key application for specialty silicones, and this application continues to keep pace with the rate of device development (5). Silicones are used in various ways, ranging from resinous circuit board coatings to encapsulants, with the silicone gels representing a unique solution to a diflScult problem, stress relief These dielectric gels are prepared by hydrosilation and are lightly cross-linked poly(dimethylsiloxane)s. Their modulus is extremely low, but they are elastic in their behavior. They have the stress-relief characteristic of a liquid but the nonflow property of an elastomer. These jellylike materials maintain their physical profile over the broad temperature range of-80 to 200 °C. 

Chromatography was done using a Waters model 510 pump, a Waters model 712 WISP injector, and a single Toyasoda TSK300W silicon gel column. The same column was used for all solvents it was flushed for 12 h with a new solvent before making measurements. 

Silver RM, Sahn EE, Allen JA, Sahn S, Greene W, Maize JC, Garen PD. Demonstration of silicon in sites of connective-tissue disease in patients with silicone-gel breast implants. Arch Dermatol 1993 129(l) 63-8. 

Brown SL, Silverman BG, Berg WA. Rupture of silicone-gel breast implants causes, sequelae, and diagnosis. Lancet 1997 350(9090) 1531-7. 

Sanger JR, Matloub HS, Yousif NJ, Komorowski R. Silicone gel infiltration of a peripheral nerve and constrictive neuropathy following rupture of a breast prosthesis. Plast Reconstr Surg 1992 89(5) 949-52. 

Teuber SS, Reilly DA, Howell L, Oide C, Gershwin ME. Severe migratory granulomatous reactions to silicone gel in 3 patients. J Rheumatol 1999 26(3) 699-704. 

Viscosity-increasing agent in silicon gels (cosmetics) 1.0-15.0 Viscosity-increasing agent in w/o or o/wemulsions 1.0-5.0 (cosmetics)... 

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