Glossary of surface technology


Polydimethylsiloxane, or PDMS for short, is a polymer of the silicones type; it is used very often and for many different purposes. All silicones are characterised by the repeating siloxane unit which consists of one Si-O group each. A wide range of side groups can be bound to the silicon atom. With PDMS, they are methyl groups CH3. Various chain ends can be coupled to the polymer. können unterschiedliche Kettenenden angekoppelt sein. Often, this is the trimethylsiloxyl group Si-SH3. The shortest molecule consisting only of the two end groups without dimethysiloxane monomer units is hexamethyl disiloxane HMDSO; it is very important as a process gas for hydrophobic plasma coating. PDMS are linear polymers which are liquid up to very high molecular weights. But they can be crosslinked, which gives them elastomeric properties. PDMS is an almost inert polymer which is highly resistant to oxidation, but it can also be used as an electric insulator in organic electronics (micro-electronics or polymer electronics) or in biological micro-analytics. One of the most frequent applications of low-pressure plasma with PDMS is in the field of micro-fluidic systems; here, a certain polydimethysiloxane (such as Sylgard 184) is structured by the customer to match the respective application. Next, a plasma treatment is carried out and the PDMS chip can be irreversibly attached to a glass plate, a silicon surface or another substrate. Benefits of plasma pre-treatment of micro-fluidic systems:

  • Short process time
  • Irreversible connections of PDMS to the substrate surface, thus formation of impermeable channels in the micro-fluidic component
  • Hydrophiling of the PDMS and the substrate surface for complete wetting of the channels
  • Formation of hydrophilic-hydrophobic areas

Applications for micro-fluidic systems:

  • Research of chemical reactions and flow of liquids in the micro-range
  • Detection of biological organisms
  • Fast clinical diagnoses and drug tests in medical examinations

Process parameters for the pre-treatment of PDMS

  • Process gas: Oxygen (O2) or ambient air
  • Pressure: 0.1 – 1.0 mbar
  • Generator: 13.56 MHz with a power of 50 – 300 W
  • Process time: 10 – 60 seconds

References of customers using Diener electronic GmbH + Co. KG units for pre-treating micro-fluidic systems made of PDMS:

  • Olaf Dössel, Wolfgang C. Schlegel. “World Congress on Medical Physics and Biomedical Engineering September 7 - 12, 2009 Munich, Germany: Vol. 25/IX Neuroengineering, Neural Systems, Rehabilitation and Prosthetics (IFMBE Proceedings)”
  • Alain Carra(c), Kash L. Mittal (Author). Superhydrophobic Surfaces 

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