Basic Silicone Chemistry II Silicone Classifications by Physical

Basic Silicone Chemistry (II)

Silicone Classifications by Physical Form (1) Fluids (hydraulic, release agents, cosmetics, heat transfer media, polishes, lubricants, damping, dry cleaning) Polymer chains of difunctional units (D) terminated with monofunctional (M) units OR cyclics (Dx) (2) Gums (high temperature heat transfer fluids, lubricants, greases, cosmetic and health care additives) Same structure as PDMS fluids, but much higher molecular weight (viscosities >1, 000 c. St). (3) Resins (varnishes, protective coatings, release coatings, molding compounds, electronic insulation) Rigid solids based on trifunctional (T) and tetrafunctional (Q) units. Surface modification with (M) units (4) Elastomers (Heat cured and RTVs: tubing and hoses, medical implants, sealants, adhesives, surgical aids, electrical insulation, fuel resistant rubber parts, rollers, etc) Soft solids based on crosslinked Si. H Fluids

Elastomers

Elastomers: RTV

Sylgard 184® PDMS Elastomer

Microfluidics Technology Applications: • Genome Mapping • Rapid Separations • Novel Sensors • Nano-scale Reactions • Ink-Jet Printing • Drug Screening http: //www. fluidigm. com/about. htm#

Microfluidics Technology A microfabricated cell sorter with integrated valves and pumps. This is a two-layer device; the bottom layer is a T-shaped fluidic channel, and the top layer contains pneumatic control lines for pumps and valves, as well as cavities to smooth out oscillations. Scale bar, 1 mm. [Photograph courtesy of Felice Frankel/Steve Quake Caltech]

Microfluidics Technology Optical image showing bead sorting in action. A red bead is being sorted to the collection channel.

Device Fabrication Thin Layer Thick Layer 100 mm Photoresist 100 mm 50 mm 12 mm Si Wafer 1) Spin Coat 2) Partial Cure 100 mm 1) Cast into Mold 2) Partial Cure PDMS 5 mm PDMS 12 mm 20 mm 50 mm

Device Fabrication Continued… 1) Peel off thick layer, rotate 90 o, Place onto top of thin layer 2) Cure completely (adheres two layers while maintaining features)

Valve Actuation Cross sectional view of valve actuation Thick layer Thin Layer Open Valve Air 20 psi Thin Layer Closed Valve

Challenges Dow Corning’s Sylgard 184® PDMS Elastomer • Currently the most widely used material in microfluidic device fabrication • Flexible, non-toxic, easily cured, low surface energy Chemical Nature of PDMS allows for significant swelling in common organic solvents • Swelling greatly disrupts micron-scale features of microfluidic devices… • Severely limits the versatility of microfluidics technology! Strong Demand for solvent-resistant materials with mechanical properties of PDMS Elastomers !

PFPE Elastomers

CH 2 Cl 2 Swelling Data Immersion Time (h) % Swelling Sylgard 184 % Swelling PFPE 48 74 % 1% 72 103 % 3% 94 109 % 3%

Two-Layer PFPE Device “Top-down view of PFPE Device” Thin Channel Thick Channel 100 mm

Organic Solvents in Devices: PFPE vs. PDMS Dye Solution of Methylene Chloride, Acetonitrile, Methanol PFPE channel • Solvent moves into channel PDMS channel • Solvent swells material, cannot get into channel