basic silicone chemistry (ii). (1)fluids (hydraulic, release agents, cosmetics, heat transfer media,...
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Basic Silicone Chemistry (II)
(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 >1,000,000 cSt).
(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 SiH Fluids
Silicone Classifications by Physical Form
Elastomers
Peroxide Cure
Si
CH2
CH3
O
Si
CH3
CH2
O
.
.
O Si O Si
Me
Me
n
R
R
RSi
R
R
R
High MW PDMS
Si
CH2
CH3
O
Si
CH3
CH2
O
Elastomers
Si O Si
Me
Men
Me
HC
O High MW PDMS
CH2
Si O Si
Me
Men
Me
H2C
O
CH2
OR
.
Network
Peroxide
Elastomers: RTV
O Si O
Me
O
C
C
C
O
H3C
O
CH3
O
CH3PDMS OHHO
O Si
Me
O
C
C
O
H3C
O
CH3
Acetic Acid
PDMS Si
Me
O
O
C O
CH3
C
O
CH3
Acetic Acid
H2O
Silanols Network
Sylgard 184® PDMSElastomer
CH2 CH
Si
CH3
CH3
O Si O
CH3
CH3
Si
CH3
CH3
CH
CH2n Si
CH3
CH3
O Si O
CH3
Si
CH3
CH3
n
CH2
CH2
Si CH3CH3
O
Si
O
CH3CH3
Si CH3CH3
n
Si
CH3
CH3
OSiO
CH3
Si
CH3
CH3
n
CH2
CH2
CH3 Si
CH3
CH3
O Si O
CH3
Si
CH3
CH3
CH3n
H
+Pt Catalyst
70 oC, 3 h
PDMS Network
Microfluidics Technology
http://www.fluidigm.com/about.htm#
Applications:
• Genome Mapping• Rapid Separations• Novel Sensors• Nano-scale Reactions• Ink-Jet Printing• Drug Screening
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 beadsorting in action. A red bead is being sorted to the collection channel.
Device Fabrication
Thin Layer Thick Layer
1) Spin Coat
2) Partial Cure
1) Cast into Mold
2) Partial Cure
Photoresist
Si Wafer
12 m
20 m
5 mm
PDMS
PDMS
50 m12 m
50 m
100 m
100 m
100 m
Device Fabrication Continued…
1) Peel off thick layer, rotate 90o, Place onto top of thin layer
2) Cure completely (adheres two layers while maintaining features)
Valve Actuation
Thick layer Thick layer
Thin Layer Thin Layer
Cross sectional view of valve actuation
Open Valve Closed Valve
Air 20 psi
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 significantswelling 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 materialswith mechanical properties of PDMS Elastomers !
PFPE Elastomers
OHCH2CF2CF2OCF2CF2OO CF2CH2OH CH2 C
CH3
C O
O
CH2
CH2
NCO
OCH2CF2CF2OCF2CF2OO CF2CH2O C
O
NH
CH2
C CH3C
O
OCH2CH2C
O
NH
CH2
CCH3 C
O
O CH2 CH2
C
O
C
O
CH3
O
CH3
Dibutyltin DiacetateHexafluoroxylenesRT 24h
+Mn = 3,800 g/mol
UV-light 5 min
5 wt%
Crosslinked PFPE Network
CH2Cl2 Swelling Data
ImmersionTime (h)
% SwellingSylgard 184
% SwellingPFPE
48 74 % 1 %
72 103 % 3 %
94 109 % 3 %
Two-Layer PFPEDevice
“Top-down view of PFPE Device”
Thin Channel
Thick Channel
100 m
Organic Solvents in Devices:PFPE vs. PDMS
PFPE channel• Solvent moves into channel
Dye Solution of Methylene Chloride, Acetonitrile, Methanol
PDMS channel• Solvent swells material, cannot get into channel
Entropy Driven Ring Opening Polymerization
O O
CC
O
Cl
O
Cl
HO OH
phosgene
O O
CC
O
O
O
O
H2O, CH2Cl2Bisphenol A
C
CH3
CH3
O C
O
O
n
ROLi
Ring Opening Metathesis Polymerization
C C
R1
R2
R3
R4
C C
R1
R2
R3
R4
Metathesis: Greek “meta” meaning “change” and “titheme” meaning “place”
C
C
R2R1
R2R1
C
C
R4R3
R4R3
+
Ring Opening Metathesis Polymerization
C
M
R2R1
CR1R2
CR3R4
R2R1C CR3R4
C
M
R2R1
M = Ru, W, etc
C
M
R2R1
CR3R4
CR1R2
Transition metal catalyzed process
M
R2R1C CR1R2
CR3R4
MCR1R2 CR1R2 + CR3R4
Metallocyclobutane4-membered intermediate
No polymer formation….
Ring Opening Metathesis Polymerization
C
M
R2P
C
C
C
M
R2R1
C
C
But what if….
Polymer formation…
Ring Opening Metathesis Polymerization
C
M
R2PC
M
R2P
C3
C2
C1
C
M
R2P
C
CC3
C2
C1
Ring Opening Metathesis Polymerization
C
M
R2P
C
CC3
C2
C1
C
M
R2P
C
CC3
C2
C1
C3'
C2'
C1'
C
M
CH2CH2CH2 CH CH CH2CH2CH2 CH C
3' 2' 1' 3 2 1
Ring Opening Metathesis Polymerization