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B. Poaty1, B. Riedl1, P. Blanchet2, V. Blanchard2, L. Stafford3
EIGHTH INTERNATIONAL SYMPOSIUM ON CONTACT ANGLE, WETTABILITY
AND ADHESION, June 13-15, 2012, Québec City
1 Université Laval, Centre de recherche sur le bois 2 FPInnovations, Nanotechnologies for Wood Products 3 Université de Montréal, Département de Physique
Improved water-repellency of black spruce wood surfaces after treatment in carbon
tetrafluoride plasmas
2
I- STUDY CONTEXT
- Plasma definition - Objective - Principle of the surface modification II- MATERIALS AND METHODS
II.1- Substrates II.2- Plasma device and treatments II.3- Evaluation of plasma-treated wood surfaces III- RESULTS
III.1- Influences of operating time and distance on the contact angle III.2- Impact of the CF4 concentration on the wettability III.3- Evolution of water-repellency vs the coating thickness and the fluorine percentage IV- CONCLUSION
PRESENTATION PLAN
3
Plasma
Plasma definition - Objective - Principle of the modification
- Can be considered as the fourth state of matter (99% of visible matter in universe) - Defined as a partially ionized gas whose global charge is neutral, and containing : → ions (positive)
→ electrons
→ neutrals
→ free radicals
→ electromagnetic radiation
that may interact physically or chemically with organic and inorganic matter
I- STUDY CONTEXT
4
Plasma definition - Objective - Principle of the modification
- Classification of plasmas :
→ hot plasma: very high-temperature electrons
→ cold plasma: low temperature and degrees of ionization interesting for organic substrates, wood for instance
- Interests about wood modification :
→ to make the surface hydrophilic / adhesion of water-based coatings
→ to make the surface hydrophobic / alternative to common coatings
I- STUDY CONTEXT
Man-Made Plasma
5
Plasma definition - Objective - Principle of the modification
Aim of study
impact of the treatment condition variation for black spruce wood surfaces in cold carbon tetrafluoride plasmas, using a parametric approach:
- moderate vacuum - low power input plasma - influence of the plasma exposure time - CF4 concentration in the Ar/CF4 plasma - influence of the plasma source-to-substrate distance
The interest
= to find the set of experimental conditions leading to efficient hydrophobic coatings on wood
I- STUDY CONTEXT
6
Plasma definition - Objective - Principle of the modification
Modification of wood surface
Method: plasma-enhanced chemical vapor deposition (PECVD)
Principle: deposition of a very thin solid layer from chemical reactions implying gaseous precursors
I- STUDY CONTEXT
ionisation (Ar) recombination CF4 F + CFx very thin layer
7
I- STUDY CONTEXT
II- MATERIALS AND METHODS
II.1- Substrates II.2- Plasma device and treatments II.3- Evaluation of plasma-treated wood surfaces III- RESULTS
IV- CONCLUSION
PRESENTATION PLAN
8
Substrates – Plasma device – Evaluation of surfaces
II- MATERIALS & METHODS
II.1- Substrates
Crystalline silica wafers 15 x 15 x 1 mm
(exposed to the same plasma conditions as the wood samples)
Samples of black spruce wood (Picea mariana)
- 46 x 35 x 3 mm (LxTxR) - conditioning: 20 °C et 65 % RH - sanded with 150 grit abrasive paper
9
Substrates – Plasma device – Evaluation of surfaces
II- MATERIALS & METHODS
II.2- Plasma device and treatment
Matching
Network
Generator
gas flowcontrollers
mechanicalvacuum pump
wood sample
stainless steelinsulatingenclosure
adjustable carrier-sample
cylindrical gas
mixing chamber
pressure
gauge
ArCF4O2
stainless steel
vacuum chamber
plasma
source
Matching
Network
Generator
gas flowcontrollers
mechanicalvacuum pump
mechanicalvacuum pump
mechanicalvacuum pump
mechanicalvacuum pump
wood sample
stainless steelinsulatingenclosure
adjustable carrier-sample
cylindrical gas
mixing chamber
pressure
gauge
ArCF4O2
stainless steel
vacuum chamber
plasma
source
10
Substrates – Plasma device – Evaluation of surfaces
II- MATERIALS & METHODS
CF4/Ar plasma treatment :
Fixed conditions for a simple realization :
- moderate injected power and operating gas pressure
(75 W and 0.53 mbar respectively)
Various conditions :
- concentration of CF4 in the Ar/CF4 plasma
- distance between the substrate and the plasma source
- time of plasma exposure
11
Substrates – Plasma device – Evaluation of surfaces
II- MATERIALS & METHODS
II.3- Evaluation of plasma-treated wood surfaces
Water contact angle measurements (Contact Angle Analyzer)
appreciation of hydrophobicity
X-ray photoelectron spectroscopy (XPS)
Survey of the chemical composition % fluorine on the treated wood surface
Thickness measurement of the deposited layers (on crystalline silica)
(stylus profilometry)
12
I- STUDY CONTEXT
II- MATERIALS AND METHODS
III- RESULTS
III.1- Influences of operating time and distance on the contact angle
III.2- Impact of the CF4 concentration on the wettability
III.3- Evolution of water-repellency vs the coating thickness and the fluorine percentage IV- CONCLUSION
PRESENTATION PLAN
13
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
III.3- Influence of operating time and distance on the contact angle
Conditions : → fixed: % CF4 in Ar/CF4 = 50% → variations: exposure time and distance ‘‘D’’
0
20
40
60
80
100
120
140
5 15 30 45
Co
na
tct a
ng
le (°)
Treatment time (min.)
D 15
D 7.8
D 3.4
Untreated
Static contact angle
- Improve of contact angle after plasma treatment
- better contact angle up to 130° after 45 min
- better results when D= 7.8 cm; hydrophobicity plateau begins from 15 min
14
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
Dynamic contact angle
Conditions : → fixed: % CF4 in Ar/CF4 = 50% and D =7.8 cm → variations: exposure time from 5 to 60 min
0 5 10 15 20 25 30 35 40 45 50
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
60 minutes
45 minutes
30 minutes
15 minutes
5 minutes
Untreated
Co
nta
ct an
gle
(°)
Time (s)
- No water incorporation on wood for plasma treatment which time > 45 min
- For time <45 min, little and gradual water absorption on wood following the plasma exposure time partial coverage of hydrophobic coating on wood
15
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
III.3- Impact of CF4 concentration on the wettability
Conditions :
→ fixed: D =7.8 cm → variations: % CF4 in Ar/CF4 at 40, 50, 60 and 70 % exposure time of 15, 30 and 60 min
Data designation:
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60
Time (s)
Co
nta
ct a
ng
le (
°)
: indication of water incorporation on treated surfaces at a choosen time (45 s)
0
45
= 0 - 45
16
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
0 1 40 50 60 700
35
70
105
1400
10
20
30
40
50
60
(b)
a)
CF4 concentration in Ar/CF
4 (%)
15 min
30 min
60 min
efficient and less costly plasma treatment using 50 % fo CF4
- For 30 and 60 min, CF4 set to 50% leads to minimal better water-repellency
17
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
III.3- Evolution of water-repellency vs coating thickness and fuorine percentage
XPS survey spectra from wood before and after CF4 plasma treatment
1000 800 600 400 200 0
0
100000
200000
300000
400000
500000
600000
700000
C 1s
O 1s
N(E
)/E
Binding energy (eV)
1000 800 600 400 200 0
0
100000
200000
300000
400000
500000
600000
700000
C 1sO 1s
N(E
)/E
Binding energy (eV)
F 1s
from untreated wood from plasma-treated wood
appearence of a new peak can be attributed to fluorine on wood surface
18
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
Coating thickness vs % fluorine after deposition
0 10 20 30 40 50 60
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
Linear extrapolation
Thickness
Fluorine
atomic
concentration
Co
atin
g t
hic
kn
ess (
nm
)
Treatment time (min.)
0
5
10
15
20
25
30
35
40
45
50
F c
on
ce
ntr
atio
n (
%)
Fluorine saturation and confirmation of a more compact and fluorinated layer
Exposure of 40 min leading to 63 nm can be enough to reach saturation
- Fluorine increase following the exposure time until a plateau of 47%
Deposition rate of 1.8 nm.min-1
19
Time & distance – CF4 concentration – Coating thickness & % fluorine
III- RESULTS
decreases following the increase of coating thickness
0 20 40 60 80 100 120
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
0
Conta
ct angle
(°)
Coating thickness (nm)
compatibility between hydrophobicity increase and film growth
a minimun coating of about 80 nm is required to do real hydrophobic surfaces
20
IV- CONCLUSION
- Study having allowed variation of some parameters of CF4 plasma treatment on black spruce wood surface
- Made hydrophobic surfaces by deposition of a thin fluorinated layer on wood
- From moderate conditions, improvement treatments by adjusting distance, CF4 concentration in Ar/CF4 and plasma exposure time
- Performances highlighted by the increase of contact angle, the film growth and the fluorine proportion on surface
- Prospect of a relative use of these results in atmospheric plasmas for possible industrial applications
21
BIBLIOGRAPHY
- Becker KH, Belkind A (2003) Introduction to plasmas. Vac Technol Coat 5: 31-36 - Blanchard V, Riedl B, Blanchet P, Evans P (2009) Modification of sugar maple booard surface by plasma treatments at low pressure. Contact Angle, Wettability and Adhesion 6: 311-323
- Chen X, Pfender E (1983) Behavior of small particles in a thermal plasma flow. Plasma Chem Plasma Proc 3: 351-366
- Denes AR, Tshabalala MA, Rowell R, Denes F, Young RA (1999) Hexamethyldisiloxane-plasma coating of wood surfaces for creating water repellent characteristics. Holzforschung 53: 318-326
- Milella A, Palumbo F, d’Agostino R (2008) Fundamentals on Plasma Deposition of Fluorocarbon Films. In: d’Agostino R, Favia P, Kawai Y, Ikegami H, Sato N, Arefi-Khonsari F (Eds) Adv Plasma Technol. Wiley, Weinheim (Germany), pp 175-195
- Zanini S, Riccardi C, Orlandi M, Fornara V, Colombini MP, Donato DI, Legnaioli S, Palleschi V (2008) Wood coated with plasma-polymer for water repellence. Wood Sci Technol 42: 149-160
22
ACKNOWLEDGMENTS
23
Thank you for your attention