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New Organic – Inorganic Siloxane Hybrid Technology
Siloxanes are one of the most rapidly expanding areas of materials research and coating development. The versatility of siloxane chemistry allows the formation of siloxane hybrids with a large range of organic polymers. The versatility of siloxane chemistry extends to adhesives, sealants and composites.
Polydimethylsiloxane (PDMS) is viscoelastic, meaning that at long flow times (or high temperatures), it acts like a viscous liquid, similar to honey.
However, at short flow times (or low temperatures), it acts like an elastic solid, similar to rubber. In other words, if some PDMS is left on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface imperfections.
However, if the same PDMS is rolled into a sphere and thrown onto the same surface (short flow time), it will bounce like a rubber ball.
Although the viscoelastic properties of PDMS can be intuitively observed using the simple experiment described above, they can be more accurately measured using dynamic mechanical analysis.
This involves using a specialized instrument to determine the material's flow characteristics over a wide range of temperatures, flow rates, and deformations. Because of PDMS's chemical stability, it is often used as a calibration fluid for this type of experiment.
The shear modulus of PDMS varies with preparation conditions, but is typically in the range of 100 kPa to 3 MPa. The loss tangent is very low (tan δ ≪ 0.001).
Polymers containing silicon in the main chain are noteworthy as high-performance and functional materials.
Polysiloxanes with excellent low-temperature flexibility and high-temperature stability derived from their siloxane bonds have been used widely as elastomers and plastics in various industries.
Polysiloxanes have also been studied as useful materials for medical applications, photolithography, and polymer supports for liquid crystal compounds, since these polymers have further attractive characteristics such as good transparency, oxygen permeability, flexibility, resistance to oxygenreactive ion etching, and so on.
Polysiloxanes have been ordinarily synthesized by the anionic ring-opening polymerization of cyclic siloxane monomers.
Due to their versatility in chemistry, siloxanes can be included in polymeric structures having a large variety of molecular architectures: cycles, linear, segmented, block and graft copolymers, telechelic or side-functionalized oligomers and polymers, crosslinked or branched structures etc.
The siloxane polymers have, beside many useful properties, two major drawbacks: poor mechanical strength and high cost.
By combining siloxane units with different organic backbones, in different architectures, improved materials can be obtained.
Thus, siloxane-containing copolymers found a large area of applications, such as; surfactants, membranes, lubricants, photoresists, adhesives, agents to improve blood compatibility, water repellency, flow or heat resistance, etc.
Continuous efforts are focused nowadays to find new synthetic routes for siloxane-organic copolymers or to obtain new structures by “classical” methods, to investigate their properties, and find applications according to the most up-to-date knowledge.
Synthetic techniques have advanced to the point where almost any conceivable block copolymer architecture can be made, and furthermore that the chemical composition of each block can be selected as desired.
Activated dimethicone, a mixture of polydimethylsiloxanes and silicon dioxide (sometimes called simethicone), is used in Over-the-counter drug as an anti-foaming agent and carminative.
Dimethicone is also used widely in skin-moisturizing lotions, listed as an active ingredient whose purpose is "skin protection." Some cosmetic formulations use dimethicone and related siloxane polymers in concentrations of use up to 15%. The Cosmetic Ingredient Review's (CIR) Expert Panel, has concluded that dimethicone and related polymers are "safe as used in cosmetic formulations."
PDMS has been used in the aerospace industry as a heat tile on reentry vehicles.
PDMS is commonly used as a stamp resin in the procedure of soft lithography, making it one of the most common materials used for flow delivery in microfluidics chips.
The process of soft lithography consists of creating an elastic stamp, which enables the transfer of patterns of only a few nanometers in size onto glass, silicon or polymer surfaces.
With this type of technique, it is possible to produce devices that can be used in the areas of optic telecommunications or biomedical research. However, this process still cannot be used for the industrial production of electronic components. In fact, the patterns are obtained by the process of stamping thanks to a shape (or stamp).
This stamp is produced from the normal techniques of photolithography or electron-beam technology. The resolution depends on the mask used and can reach 6 nm.
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