Understanding More What is PDMS

Polydimethylsiloxane or shortly known as PDMS belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological or flow properties. PDMS is optically clear, and, in general, inert, non-toxic, and non-flammable. It is also called dimethicone and is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos as dimethicone makes hair shiny and slippery, food antifoaming agent, caulking, lubricants, kinetic sand , and heat-resistant tiles.

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 method requires determination of 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.

PDMS can be used to fabricate a myriad of structures through soft lithography. The process of soft lithography consists of creating an elastic stamp which enables the transfer of patterns only a few nanometers in size. Furthermore a single master mold can be used to fabricate numerous PDMS devices.

The process of fabricating a microfluidic device from PDMS is relatively simple. To start, the PDMS two-part kit, consisting of the base and the cross-linking agent are mixed. The mixing ratios and curing procedures used determine the mechanical, chemical and optical properties of the final device. Upon mixing, the PDMS must be degassed under vacuum. Next the liquid pre-polymer is poured over a previously fabricated master mold. The master molds used to fabricate PDMS devices are most commonly made from SU-8. However metal, plastic and even 3D printed maters are now gaining popularity. Once the PDMS is poured into the mold, the liquid pre-polymer conforms to the shape of the mold, replicating the features.