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