2012 sympo contact angle_poaty

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

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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


- 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

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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


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

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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

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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

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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





wood sample

stainless steelinsulatingenclosure

adjustable carrier-sample

cylindrical gas

mixing chamber

pressure

gauge

ArCF4O2

stainless steel

vacuum chamber

plasma

source

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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

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ACKNOWLEDGMENTS

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Thank you for your attention

2012 sympo contact angle_poaty

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