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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?