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.