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
>1,000,000 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
Elastomers
Me
R
R
Si
O
R
Si
O
Si
R
High MW PDMS
n
R
R
Me
Peroxide Cure
CH3
CH3
Si
O
Si
CH2
CH2
CH2
CH2
.
.
Si
CH3
O
Si
CH3
O
O
Elastomers
Me
Me
Si
O
Si
CH2
HC
Me
High MW PDMS
O
n
Peroxide
Me
Si
Me
O
Si
.
H 2C
Me
O
CH2
n
OR
Network
Elastomers: RTV
Me
O
H 3C
C
O
Si
O
O
C
HO
CH3
PDMS
OH
O
C
O
Acetic Acid
CH3
Me
O
H3C
C
O
Me
Si
PDMS
Si
O
C
O
O
C
CH3
O
H2O
O
CH3
C
O
CH3
Acetic Acid
Silanols
Network
Sylgard 184® PDMS
Elastomer
CH3
H2C C Si O
H
CH3
CH3
CH3
Si O
Si C CH2
H
CH3
Pt Catalyst
n
CH3
H3C Si O
CH3
O
CH3
CH3
Si O
n
Si
CH3
CH2
CH2
O
70 oC, 3 h
CH3
CH3
Si O
Si CH3
H
Si
CH3
H3 C Si CH3
+
CH3
CH3
n
H3 C Si CH3
O
n
H3 C Si CH3
CH3
CH2
CH3
Si
CH3
CH2
O Si
CH3
CH3
n
O Si
CH3
PDMS Network
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 90o, 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
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
HO CH2 CF2 O
CF2 CF2O
CF2O CF2 CH2 OH
+
CH3
H2 C C
C O
Mn = 3,800 g/mol
O
Dibutyltin Diacetate
Hexafluoroxylenes
RT 24h
CH2
CH2
NCO
CH2
H3 C C C O CH2 CH2
O
N C O CH2 CF2 O
H
O
CF2 CF2O
CF2O CF2 CH2 O C N
H
CH2
CH2 CH2 O C C CH3
O
O
CH3
O O
C C
UV-light 5 min
O
CH3
5 wt%
Crosslinked PFPE Network
CH2Cl2 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
Entropy Driven Ring Opening Polymerization
O
O
O
OH
HO
phosgene
C
C
O
O
O
H2O, CH2Cl2
Bisphenol A
ROLi
O
O
O
C
C
O
C
Cl
O
CH3
O
C
O
Cl
CH3
n
Ring Opening Metathesis Polymerization
Metathesis: Greek “meta” meaning “change” and “titheme” meaning “place”
R1
R3
C
C
R2
R4
R2
R1
R4
R3
C
C
+
R1
R3
C
R2
C
R1
R4
C
C
R2
R3
R4
Ring Opening Metathesis Polymerization
Metallocyclobutane
4-membered intermediate
Transition metal catalyzed process
R2
R1
R2
R1
C
C
R2R1C
R2
R1
C
CR1R2
M
CR3R4
CR3R4
CR1R2
M
M
CR3R4
M = Ru, W, etc
R2R1C
CR1R2
CR1R2
+
M
CR1R2
CR3R4
M
No polymer formation….
CR3R4
Ring Opening Metathesis Polymerization
But what if….
R2
P
C
R2
R1
C
C
C
M
C
M
C
Polymer formation…
Ring Opening Metathesis Polymerization
R2
P
R2
P
C
C1
C2
C
R2
P
C
C
C1
C2
M
M
C3
C
M
C3
Ring Opening Metathesis Polymerization
R2
P
C
C1
C
C2
R2
P
C
C
C1
C
M
C3
C2
M
C
C3
C1'
C3'
C2'
M
C
CH2CH2CH2 CH
3'
2'
1'
CH CH2CH2CH2
3
2
1
CH C
Ring Opening Metathesis Polymerization