atmospheric pressure plasma sources suitable for...
TRANSCRIPT
Atmospheric pressure plasma
sources suitable for
modification of wood surfaces
Gheorghe Dinescu National Institute for Laser, Plasma and Radiation
Physics, Bucharest, Romania
(Acknowledgments: Dana Ionita, Max Teodorescu, Rosini Ionita, Cristian
Stancu, Claudia Stancu)
NILPRP
PHYSICS RESEARCH - ROMANIACAMPUS MAGURELE, BUCHAREST-
NATIONAL RESEARCH INSTITUTES
• National Institute for Physics and Nuclear Engineering (~800 pers)
• National Institute for Laser, Plasma and Radiation Physics (NILPRP) (~400 pers)
• National Institute of Materials Physics (~200 Pers)
• National Institute for Earth Sciences
• National Institute for Optoelectronics
• Faculty of Physics
UNIVERSITY OF BUCHAREST
Group on Plasma Processes, Materials and Surfaces
Low Temperature Plasma Physics Department
NILPRP
Group on Plasma Processes, Materials and
Surfaces
NILPRP
Topics:
- plasma sources;
- nanomaterials;
- thin films and surface
modification;
- plasma diagnostics
and material
characterization;
Outline
• Motivation
• How plasma works
• Peculiarities of wood processing by plasma
• Plasma sources suitable for wood processing
- low pressure versus atmospheric pressure
- plasma jet sources for material processing
• Examples of processing with atmospheric
pressure plasma sources (polymers)
• Conclusions and perspectivesNILPRP
WOOD: limited service lifetime
• Physical factors:
moisture, temperature
fluctuations, UV-light;
• Chemical factors:
attack by cleaners, acids,
bases, strong oxidants;
• Biological factors:
bacteria, fungi, mold;
dry-rot wood
(humidity, UV)
insufficient wet
adhesion of the
coating
Need of techniques to
protect wood surfaces
moldy wood
due to exposure
to humidityApproaches by plasma techniques
How plasma works
Initial gas +precursor (HMDSO, TEOS)
Radical
flux
Ions
flux
Photon
flux
Ions, e
flux
Bombardment, chemistry:
bond scissions, group attachment
wood piece
Initial gas: Ar, air, N2, O2, He, H2O
Electrons (e) , Ions (Ar+, N2+,O2+), Excited species (Ar*, N2*, O2*, O3);
Radicals, photons (OH, O, N, CN, h )
Radicals: SiOx, C-Si-, -Si-CH3
Electrons (e) , Ions (Ar+, N2+,O2+), Excited species (Ar*, N2*, O2*, O3);
Radicals, photons (OH, O, N, CN, h )
Radical
flux
Ions
flux
Photon
flux
Ions, e
flux
Bombardment, chemistry:
bond scissions, atom removal
wood piece
polar groups, dangling bonds, polar groups, dangling bonds, Coating with a thin film
Wettability increase, etching, reactive
surface for grafting, adhesion, bonding
Film deposition: protective coating,
hydrophobic surface
Plasma processing of wood
Aims:
• Improve the resistance of wood to weathering, erosion under
exposure to UV and moisture conditions; barrier anti-
microorganisms; durability increase.
• Add new functionalities to surface: color, adhesion, glue
ability, or keep natural appearance.
•Solutions:
1. - Surface functionalization by treatment (Ar, N2, O2,
He or mixture): change of roughness, morphology, topography,
chemical moieties at surface, hydrophilic/hydrophobic character;
2. - Surface coating with a thin film (precursors: gaseous
(SF6, C2H2F4), vapor phase (HMDSO), nanoparticles(SiO2);
The problem: to ensure the compatibility of plasma
processing with wood
Peculiarities of wood material and objects
Material peculiarity:- Sensitive to thermal damage;
- Porous and water absorbing;
- Partially conducting.
Size of objects:- Usually large size: specially length, width – meters scale;
- Small features may be present: holes, nuts, gaps –size from a few
millimeters to centimeters.
Shape: flat, but also could be complex: -3D convex surfaces (curved surfaces : plates, rods, bars, etc. );
-3D convex-concave surfaces (objects with inner curvatures).NILPRP
Requirements for plasma sources
Problems related to wood treatment:
- Non-thermal or cold plasmas use (prevent bulk material
degradation, as example by heating);
- Uniform treatment (coat) on large planar surface, or on
complex shape surfaces;
- Ensure the desired properties;
Choices:- Low pressure cold plasma;
- Atmospheric pressure plasma.
Sources design:-In agreement with the
application in view
NILPRP
Low pressure versus atmospheric pressure
plasmas
Low pressure plasma
• Advantages
- plasma is naturally cold, thus reduced
danger of heat damage;
-extends on large volumes;
-plasma generation technology: well-
known.
• Disadvantages
- vacuum technology – difficult with water containing or porous
materials – expensive!
- cannot penetrate in small features as gaps, or holes of the objects;
- processing chambers have limited volume.
Atmospheric pressure - problems
Solutions
• Use of dielectric barriers;
• Keep the system cold:
- Gases with high efficiency of
heat transfer, like helium;
- Use of high gas mass flow rates;
- Control of the power injected in
plasma (ultra short pulsed high
voltages, high frequency, corona,
low RF, DC powers);
-Active cooling of electrodes.Plasma contraction occurs
Appearance of instabilities
High pressure: tendency to arcing (arc discharge);
Pressure
increase
Low pressure: cold plasma
FOCUS ON ATMOSPHERIC
PRESSURE
Plasma sources suitable for wood processing –
atmospheric pressure
Peculiarities:
-Expanding plasmas, or plasma jets:
use of the gas activated in discharge outside
of the inter-electrodic space;
-Remote processing
the sample is placed outside the discharge;
- Radiofrequency generated (13.57 MHz);
- Working gas: argon or nitrogen;
Approach proposed here:
Radiofrequency plasma jet
sources
High
voltage plasma
needle
electrodes
wood
electrode
Corona discharge
High
voltage plasma
wood
Wood as electrode
Dielectric Barrier Discharge
dielectric
electrode
electrode
woodplasma
Type 1 : RF plasma jet sources based on
Discharges with Bare Electrodes (DBE jets)
- principle of operation;
- models;
- some characteristics.
NILPRP
Principle of operation and design
gas in
RF
plasma out
Dielectric
enclosure
nozzledisk
D: 2-10 mm
d: 1- 3 mm
- Argon
- Nitrogen
NILPRP
Surface
Plasma jet
Model 1: hand held, flexible plasma jet source
(20 mm diameter)
- stainless steel body,
- hand held, flexibility for mounting on
robotic arm;
-couplings realized to the back end: RF
power, gas feeding, active water
cooling (2 circuits, inside the RF
electrode and external jacket)
Operation: both in argon an nitrogen
much larger size-length and diameter - in nitrogen
ARGON
NITROGEN
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000
50
100
150
200
250
300
350
400
450
500
550
600
650
argon, 2mm interelectrodic distance
Po
we
r (W
)
Mass flow rate (sccm)
Schematic visualization
of the operation domains
nitrogen, 3mm interelectrodic distance
- Higher power values are possible in nitrogen without arcing;
- Longer jets in nitrogen;
-Increased powers ask for increased mass flow rates.
Model 2: Small size, plasma jet source (8 mm
diameter (designed for low power, no cooling)
Requirements:AIM: surface
modification
of polymers
-Small size
-Flexible
-Low power
-Low temperature
Temperature (thermocouple)
PARAMETERS:
• RF power: 15-25 W
• Gas : Ar, Ar/O2
• Mass flow rates: 2000-4000 sccm
• Plasma jet diameter: 0.5 -1mm
(depends on conditions)
• Plasma jet length (1-10 mm),
depends on gas, power, flow rate
OTHERS:
• Breakdown at atmospheric pressure
• Grounded, not danger of electric
shock
14 15 16 17 18 19 20 21 22 23 24 2530
40
50
60
70
80
90
100
110
Te
mp
era
ture
[oC
]
Power RFfwd
[W]
Dependence of gas temperature upon
forwarded power , for the settings: argon
gas, 4000 sccm, 1 mm from nozzle
Type 2: Expanding RF jet sources based on
dielectric barrier discharges (DBD jets)
designs and models
DBDs jet sources designs
CERAMIC
MATERIAL
GAS
TEFLON
ADAPTER
TEFLON
SPACERS
UPPER
ELECTRODE
RF
GROUNDPLASMA
L=60
mm
a)two
barrie
rs
d=1mm
TEFLON ADAPTER
GAS
TEFLON
SPACERS
UPPER
ELECTRODE
RF
GROUNDPLASMA b)
d=1mm
CERAMIC
MATERIAL
GROUND
GAS
TEFLON
ADAPTER
GROUND
ELECTRODE
DISCHARGE
SPACE
UPPER
ELECTRODE
CERAMIC
MATERIAL
RF
PLASMA
d1=1mm
L=60
mm
c)
d)
UPPER
ELECTRODE
(RF)GAS
CERAMIC
SPACERS
RF
PLASMA
d=1mm
LOWER
ELECTRODE
(GROUND)
CERAMIC
BARRIER
a) parallel rectangular double-barrier configuration, b) parallel rectangular single-barrier
configuration, c) non-parallel double-barrier configuration and d) parallel trapezoidal
single-barrier configuration.
Images of various DBD jet configurations
Single barrier plan parallel
rectangular configuration,
expansion through mesh
Angled parallel single
barrier configuration
Double barrier plan
parallel rectangular
configuration
Single barrier plan
parallel rectangular
configuration
Reactive species - expansion
in open atmosphere
200 300 400 500 600 700 800 900 10000
500
1000
1500
2000
2500
3000
3500
4000
4500
ArI
OI
OH
2ndOrder NO
2nd OrderN
2
N2
N2
N2, NH
OH
Wavelength (nm)
Ar 500sccm, Prf=50 W
NO
OI
Optical emission spectrum recorded
in the front of the parallel DBD
(Ar lines, N2, NH, OH molecules)
Plasma rich in active species-
radicals: oxygen, hydroxyl, etc.
304 305 306 307 308 309 310 311 312 313 314 315
0
2000
4000
6000
8000
10000
12000
14000
16000
Trot=364K
OH
A2 +
-X2
Inte
nsity [a.u
.]
Wavelength [nm]
Experimental spectrum
Simulated spectrum
Simulation of OH bands (small size
jet at 15W and 5200 sccm gas flow, 1
mm from nozzle)
Temperatures (by thermocouple)
0 1 2 3 4 5
30
40
50
60
70
80
90
100
Tem
per
atu
re [
0C
]
d [mm ]
Temperature distribution
perpendicular on the flow
axis ( 2 mm from nozzle)
0 2 4 6 8 10 12 14 16 1830
40
50
60
70
80
90
100
Tem
per
atu
re [
0C
]
d [mm]
Temperature distribution
along the flow plane
(central position)
Cleaning: organic or carbon residuals
removal from surfaces at atmospheric
pressure
- Surface scanning;
-Carbon layers removal from flat surfaces
Plasma cleaning: removal of carbonic
(organic layers) from flat surfaces
Layer thickness: 1 m
Number of scans: 1
Power: 350 W
Nitrogen, mass flow rate: 7500
sccm
Carbon films, thickness: 1-10 m
Substrate: silicon, 2 m
Modification of wettability of polymeric
surfaces at atmospheric pressure
- scanning the surface with the cold plasma jet
A) - measurement of the contact angle after various number of scans;
B) - Illustration of the wettability change: different drop shapes of water by
vapor condensation on the cooled treated PET surface;
C) -patterning surfaces with wettable traces
A. Decrease of the contact angle on PET
surface after scanning
gas: Ar
mass flow: 3000 sccm
power: 16W
temperature : 42oC
scanning speed: 5mm/s
0 2 4 6 8 10
30
40
50
60
70
80
conta
ct
angle
[deg]
number of scans
10 mm
1
0
m
m
1 mm
The scanning path on
the probe
B. Water vapor condensation
In the marked square half of the area
is treated and half is untreated
Cold substrate
holder (Peltier)
PET foil
Detailed view of the border between
untreated and treated zones
B. Water vapor condensation
treated untreated
Cold substrate
holder (Peltier)
PET foil
Detailed view of the border between
untreated and treated zones
Adhesion test (scotch test) on plasma
modified surfaces
0 100 200 300 400 5000.0
0.5
1.0
1.5
2.0
2.5 PET
PTFE
PE
F [
N]
Numar scanari
Results of the adhesion test Measurement of the detachment
force
F=mg
Foil surface
Scotch tape
Detachment force: dependence
upon the number of scans
Modification of wettability of polymeric
surfaces with a DBD jet
Procedure - scanning the surface with the cold
expanding DBD plasma
A) - measurement of the contact angle after various number of scans;
B) - Illustration of the wettability change: different drop shapes of water
by vapor condensation on the cooled treated PET surface;
C) -patterning surfaces with wettable traces
Treatment of polymeric surfaces
10 mm
10
mm
1 mm
The scanning path on
the probe
RF
Computer
interface
Travel stage X-Y
Y Movement
X MovementPlasma source
holder
Sample
DBD
Plasma
Source
Gas
PET and PVC foils of 10 by
30mm have been scanned
on a area of 10x10mm.
Image of the plasma jet
during PET treatment
Wettability improvement and ageing study
0 10 20 30 40 5020
30
40
50
60
70
80
90
100
110
120
Co
nta
ct a
ng
le [
deg
rees
]
Number of scans
in 1'st day
after 9 days
after 21 days
PE
0 10 20 30 40 5010
20
30
40
50
60
70
80
90C
onta
ct a
ng
le [
deg
rees
]
Number of scans
in 1'st day
after 22 days
after 34 days
PET
0 10 20 30 40 5020
30
40
50
60
70
80
90
100
110
120
Co
nta
ct a
ng
le [
deg
rees
]
Number of scans
in 1'st day
after 17 days
after 29 days
PVC
0 10 20 30 40 5020
40
60
80
100
120
Co
nta
ct a
ng
le [
deg
rees
]
Number of scans
in 1'st day
after 4 days
PTFE
Patterning of surfaces
Drops array: condensation of the
water is enhanced on the treated
surface of the polymer
Image of mask, which is placed
between plasma and surface
(holes: 100 microns).
Conclusions and perspectives
NILPRP
• Versatile RF plasma jet sources at atmospheric pressure of various sizes, powers are available;
•Operation in argon and nitrogen;
•Temperature controlled by power, mass flow rate;
•They are sources of reactive species;
•Effective surface modification of polymers at atmospheric pressure;
• Treatment of gaps and voids possible;
•Suitable for downstream precursor injection: deposition;
•Up-scale easily possible for the DBD jets
Thank you for your attention !