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Hydrophilizationof Fluoropolymers and Silicones

Wei ChenMount Holyoke College

2017 Adhesive and Sealant Council Spring Meeting

Aknowledgements:• NSF, NIH, Dreyfus, ACS-PRF, MHC• Bryony Coupe, Mamle Quarmyne, Lien Nguyen, Akchheta Karki, Yan Yan

Introduction• Low surface tensions of fluoropolymers and silicones

18-20 mN/m poor wetting and weak adhesion

• Common surface modification methods

aggressive treatments surface degradation and mixed functionalities

• Biopolymers spontaneously adsorb to fluoropolymers

hydrophobic interactions “fouling”

I. Hydrophilization of Fluoropolymers

Our Approachl Adsorption of amphiphilic, synthetic polymers to FEP/water interface

FEP

PolymerAdsorption

XX

XX

XX

H2O

( )n( )n

CO2H NH3+ Cl-

PAA PAH PVOH

( )n

OH

Variables studied-kinetics-concentration-ionic strength-number of steps

Coupe, B.; Chen, W. Macromolecules 2001, 34,1533.Chen, W. U.S. Patent 2007, 7179506.

Contact Angle Analysis

1763PVOH (cast film)

1967FEP-PVOH 89 h

1763FEP-PVOH 24 h

1965FEP-PVOH 5 h

2071FEP-PVOH 2 h

2074FEP-PVOH 1 h

2283FEP-PVOH 30 min

2083FEP-PVOH 10 min

93117FEP

θR (°)θA (°)

Kinetic StudiesXPS Analysis

Polymer

OHOH

OHOH

OHOH

H2O

FEP: -(CF2-CF2)m-(CF2-CF)n-CF3

PET: -(C(O)-Ph-C(O)-OCH2CH2O)n-

PMP:( )n

PVOH Adsorption: A General Approach to Hydrophilize Polymer Surfaces

PVOH

( )n

OH

Driving forces: • hydrophobic interactions • PVOH crystallization

117/9363/17

115/8958/16

77/55 40/13

PVOH Thickness and Film Morphology

AFM: 3 x 3 μm; 10 nmθA/θR : 60-70°/10-20°Γ: 25-30 Å, continuous

Kozlov, M.; Quarmyne, M.; Chen, W.; McCarthy, T. J. Macromolecules 2003, 36, 6054.

PVOH Stability Studies

FEP-PVOH

180o

Pressure-sensitive adhesive tape(3M no. 810)

XPS analyses indicated cohesive failure in FEP substrate

• Mechanical Integrity

• Hydrolytic Stability

Lightly crosslinked PVOH is stable in water and organic solvents.

Derivatizations of -OH groups

PET

-OH

PET -O-C(O)-NH-S(O)2-Ph

O=C=N-S(O)2-Ph

+ [CH3(CH2)10-CO2]2SnBu2

O=C=N-CH2CH2Cl

+ [CH3(CH2)10-CO2]2SnBu2

O=C=N-(CH2)17CH3

[CH3(CH2)10-CO2]2SnBu2

x

x PET

-O

PET -OH

S=O-O

-Cl

SOCl2 (Major product)

(Minor product)

-OH groups in PVOH are 2°alcohols

CF3CF2CF2CF2I

+ Et3N

x

PET

-O

-OCHR

RCHO/H+

Cl-C(O)-CF2CF2CF3

PET

-O-C(O)-CF2CF2CF3

PET

-O-C(O)-C16H33

CH3(CH2)16-C(O)-Cl

+ pyridine

PVOH to SiO2 and TiO2

Quarmyne, M.; Chen, W. Langmuir 2003, 19, 2533.

SiO2

II. Hydrophilization of Silicones

- low Tg = -123 °C- hydrophobicity, γ = 20 mN/m- good gas permeability- excellent thermal stability- reactivity toward acids and bases- nontoxicity- low cost- optical transparency- “hydrophobic recovery”

Hydrophobic Recovery

CH3 CH3 CH3 CH3

SiOx

Silicone

CH3 O CH3OH OH OH

O2 Δt

Hydrophobic Recovery: spontaneous- reorientation of surface hydrophilic groups- condensation of surface silanol groups- migration of low molecular weight (LMW) species from the bulk to the surface- in-situ generated surface cracks facilitating migration of LMW

Solvent extraction?

OH

Fritz, J. L.; Owen, M. J. J. Adhesion 1995, 54, 33.Kim, J.; Chaudhury, M. K.; Owen, M. J.; Orbeck, T. J. Colloid Interf. Sci. 2001, 244, 200.

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35Dyn

amic

con

tact

ang

le (°

)

Time (day)Adv (DVDH) Rec (DVDH) Adv (Sylgard) Rec (Sylgard)

CH3 CH3 CH3 CH3

SiOx

OH OH

O2

CH3CH3 CH3 CH3 CH3

Vacuum extraction

Vacuum Extraction: Reduce Hydrophobic Recovery

56°/39°

51°/38°

Nguyen, L.; Hang, M. et al. ACS Appl. Mater. Interfaces 2014, 6, 22876.

PVOH Adsorption to Hydrophilize Silicones?

Wu, D.; Luo, Y.; Zhou, X.; Dai, Z.; Lin, B. Electrophoresis 2005, 26, 211.

OHOH

OHOH

OHOH

PVOHH2O

PDMS

• Contact angle and IR analyses: PVOH does NOT adsorb to PDMS

• Thickness analysis?

• AFM imaging?

X

PDMS Substrates

Krumpfer, J. W.; McCarthy, T. J. Langmuir 2011, 27, 11514.

React PDMS (2 kDa, 9 kDa, 17 kDa, 49 kDa, 116 kDa) to Si wafers

Experimental Protocols1. Clean wafers with O2 plasma

2. Drop cast PDMSon wafers

3. React PDMSat 100 °C for 24 h

5. Adsorb PVOHat r. t. for 24 h

4. Dissolve PVOHat 95 °C

• Contact Angle Goniometry• Ellipsometry• Optical Microscopy• Atomic Force Microscopy• Transmission Electron Microscopy

Si/SiO2

OHOHOHOH

Si(CH3)2Si(CH3)2Si(CH3)2Si(CH3)2

OHOHOHOH

O2 PDMS PVOHPDMS

PVOH

PDMS

RMS(nm) 0.2 0.3 0.3 0.4 0.5

θA/θR (°) 101/79 107/102 109 /104 109/95 113/98

AFM Images (size: 2.5 x 2.5 μm; height: 10 nm):

y = 0.5695x - 1.7781R² = 0.9636

0

0.2

0.4

0.6

0.8

1

1.2

3 3.5 4 4.5 5 5.5

Log

(thic

knes

s (n

m))

Log (molecular weight (Da))

PDMS Thickness α (MW)0.57

(1 to 11 nm)

PDMS2k PDMS9k PDMS17k PDMS49k PDMS116k

PDMS Substrates: thickness, roughness, hydrophobicity

Karki, A.; Nguyen, L.; Sharma, B.; Yan, Y.; Chen,W. Langmuir 2016, 32, 3191.

PVOH99% Thin Film Morphologies on PDMS

500 μm

PDMS2k PDMS9k PDMS17k PDMS49k PDMS116k

AFM images (size: 20 x 20 μm):

Optical micrographs (scale bar: 500 μm):

20 nm 30 nm 40 nm 100 nm 400 nm

continuous honeycomb fractal (small to large)

Film Formation Mechanism: In situ Optical Microscopy

19

In-situ Time Lapse Movie:

PVOH dewetting on higher MW PDMS: higher contact angles, more surface defects, more liquid-like.

PVOH99%-PDMS49kPVOH99%-PDMS2k

Dried Films:

PVOH88% Thin Film Morphologies on PDMS

PDMS2k PDMS9k PDMS17k PDMS49k PDMS116k

AFM images (size: 20 x 20 μm):

Optical micrographs (scale bar: 200 μm):

20 nm 20 nm 30 nm 100 nm 100 nm

200 μm

continuous honeycomb droplets

ZnO PSS with added salt PEO

Spin cast

Adsorption (collagen on PS)

Crystallization is requiredto form fractal features?

Chen, L. et al. J. Phys. Chem. C 2008, 112, 14286–14291.Haberko, J. et al. Synth. Met. 2010, 160, 2459–2466.Bi, W.; Teguh, J. S.; Yeow, E. K. L. Phys. Rev. Lett. 2009, 102, 048302.Jacquemart, I.et al. J. Colloid and Interface Sci. 2004, 278, 63–70.

Morphologies of Dewetted Thin Films: Fractals

TEM Electron Diffraction of PVOH99% and PVOH88%

(200)(010)

(110) (010)

Crystallization of PVOH99% fractal morphology PVOH88% common droplets

SiO2

PVOH-PDMS2k

PVOH99% PVOH88%

Karki, A.; Nguyen, L.; Sharma, B.; Yan, Y.; Chen,W. Langmuir 2016, 32, 3191.

Minimize PVOH Dewetting

• Minimized PVOH dewetting• Improved wettability

I. Light plasma oxidation of PDMSnm to create pinning sites

PVOH99%-PDMS49k PVOH88%-PDMS49k

plasma treated

PDMS49k: 109°/95° to 101°/80° (1 s O2 plasma), similar to PDMS2k.

native plasma treated native

Karki, A.; Nguyen, L.; Sharma, B.; Yan, Y.; Chen,W. Langmuir 2016, 32, 3191.

Minimize PVOH DewettingII. Attach PDMS2k to PDMSμm films

SiO2

OHOHOHOH

O2Spin castDVDH

PVOH

PDMS

PDMS

OHOHOHOH

PDMS2k

100 °C

PDMS

OHOHOHOH

PVOH

PDMS

118°/97° 27°/12°

111°/91° 93°/20°

Hydrophobic Recovery of PDMS-PVOHs?

• Negligible hydrophobic recovery• Vacuum extraction is not necessary PVOH is a good barrier layer

PVOH (continuous)on PDMS2k

PVOHon PDMS2k-PDMSμm

0

20

40

60

80

100

120

0 40 80 120 160Dyn

amic

Con

tact

ang

les

(°)

Time (h)0 40 80 120 160

Time (h)

PVOH (honeycomb)on O2-PDMS49k

0 20 40 60 80 100 120Time (h)

w/o vac extraction w/ vac extraction

Conclusions

• PVOH spontaneously adsorbs to hydrophobic substrates from aqueous solution• hydrophobic interactions• crystallization of PVOH

• PVOH adsorption can be used to hydrophilize and functionalize fluoropolymers and silicones

• Hydrophilization of silicones has additional challenges: dewetting and hydrophobic recovery• light plasma oxidation and attachment of PDMS2k

• Vacuum extraction• PVOH layer is an effective barrier

OHOH

OHOH

OHOH

H2O

( )n

OH

Thank you!

Questions?