Permeation in Flexible Electronics
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Transcript of Permeation in Flexible Electronics
Water Vapor and Oxygen Permeation in Flexible Electronics
Relevance, Test Methods
& the Future
Copyright © 2014 MOCON Inc.
Created by: Michelle Stevens for MOCON Inc.
Mass transfer review
Application of mass transfer concepts to permeation measurement
Oxygen Transmission Rate Measurement (OTR) – ultra barrier
Water Vapor Transmission Rate Measurement (WVTR) – for Ultra Barriers
Mass Transfer Review
Permeation: The flux of molecules through a material normalized to the partial pressure gradient (driving force) and material thickness
Transmission rate: The flux of molecules through a material.
Partial Pressure Gradient: Driving force
Diffusion: Process by which matter is transported from one part of a system to another as a result random molecular motions.
xCDF
F is the permeation flux through a membrane of thickness
C is the concentration of permeant in the membrane at position x
D is the diffusion coefficient
Diffusion follows , it
by factors such as:
The surface area available
The distance the gas molecules must diffuse across
The concentration gradient
Gases must first dissolve in a fluid in order to diffuse across a membrane therefore
all gas exchange systems require a moist environment
xCDF
0 l x
z
y
∞
∞
1) Area is infinite with respect
to thickness transfer in the
x-direction only
2) Constant temperature
Initial and Boundary Conditions
c=0 x=0 t<0
c=0 x=l t
c=ci x=0 t
c=ci(l-x)/l 0<x<l t
0 l x
z
y
∞
∞
c=ci x=0 t
0 l x
z
y
∞
∞
c=ci
c=0 x=l t≥0
0 l x
z
y
∞
∞
c=0
ci
Constant test gas
concentration
Constant sweep across film to
maintain concentration at 0
NORM
ALI
ZED F
LUX ΔF/Δ
F∞
1/X2 = (4D/t2) - t
Pasternak, et. al, 1970
F =Dci
l+D c f - ci( )
l1+ 2 -1( )
nexp -
n2p 2Dt2
ìíî
üýþ
¥
åé
ëê
ù
ûú
Area is infinite with respect to thickness – transfer in the x-direction only
Constant temperature
Constant test gas concentration
Constant sweep across film to maintain concentration at 0
Leaks
Measure only what you intend to measure
Ambient air (72.6 F, 70% RH)
17930 ppm H2O
over 100 g/m2 day
TruSeal®
ELIMINATE
Leaks
Calibration Most sensors are comparative or concentration-based and require
calibration. It is important that sensors be calibrated in the range which they are
used. 10 ppm +/- 10% WVTR = 0.1 g/(m2day)
WVTR = 1 x 10-6 g/(m2day) 0.1 ppb water vapor
Factors that play a role in typical permeation such as temperature, flow
control and repeatability, are only compounded by calibration.
(Lowest NIST traceable calibration gas)
ELIMINATE Calibration
0.1 ppb
Absolute Sensors
Absolute or Intrinsic measurement
Theoretical sensitivity is 2 X 10-6 g/(m2 day) Coulometric Technology not affected by Temperature, Pressure, Flow
or Vibration.
No Calibration Required!
1. Area is infinite with respect to thickness – transfer in the x-direction only
2. Constant temperature
3. Constant test gas concentration
4. Constant sweep across film to maintain concentration at 0
5. Eliminate leaks
6. Eliminate calibration
OTR Data
OTR Data
0
0.002
0.004
0.006
0.008
0 50 100 150 200 250
OTR
(cc
/(m
2 d
ay))
Time (hours)
MOCON OX-TRAN® Model 2/21 10x
OX-TRAN L sensitivity
OX-TRAN 10x data
OX-TRAN 10x sensitivity
WVTR Data
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 100 200 300
WVTR
(m
g/(
m2day))
Time (hours)
AQUATRAN
AQUATRAN Model 2
AQUATRAN 1 SENSITVITY
AQUATRAN MODEL 2
SENSITIVITY
Summary By going back to the basics and relying on 50+ years of permeation
experience, we were able to ‘build a better wheel’ Area is infinite with respect to thickness – transfer in the x-direction only Constant temperature Constant test gas concentration Constant sweep across film to maintain concentration at 0 Eliminate leaks Eliminate calibration
Capable of measuring: OTR at 0.0005 cc/(m2day) WVTR at 0.00005 g/(m2day)
BASED ON THE FUNDAMENTALS OF PERMEATION
References
Pasternak, R.A., Schimscheimer, J.F., and Heller, J. (1970). “A Dynamic Approach to Diffusion and Permeation Measurements.” Journal of Polymer Science Part A-2, 8.3 (1970): 467-479. Print.
Crank, J. The Mathematics of Diffusion. Oxford,: Clarendon, 1975. Print.