Calibrated Permeation Standards
Permeation generally occurs by a three-step process. The analyte (e.g., water vapor, oxygen, carbon dioxide, hydrogen, hydrocarbon, or another gas) is absorbed into the surface of a permeable material. The analyte then diffuses through the permeable material and outgases from the other side. A permeation standard has a unique transmission rate for a particular analyte under specified testing conditions, such as temperature and relative humidity, so that the detection equipment may be calibrated for accurate sample analysis.
Materials useful for flexible electronics and thin film applications are currently being developed that resist moisture permeation in the range of 10-4 to 10-7 g/m2/day. However, calibrating these materials using a known water vapor transmission rate (WVTR) standard is not possible using conventional methods. The normal limit of detection for commercially available instruments is typically a WVTR of approximately 5x10-4 g/m2/day, and custom instruments have lower limits of detection from about 10-4 to 10-7 g/m2/day. However, no standards currently exist that are capable of calibrating any instruments below a WVTR of approximately 10-3 g/m2/day at a suitable temperature and relative humidity.
Further, barriers that utilize thin film inorganic layers cannot be used as standards. A barrier may limit the permeable surface area by masking with a metallic foil or by coating with an oxide coating. However, any oxide or inorganic thin film coating is limited by its defects, including pinholes, grain size, and cracks. Further, these layers are easily cracked or damaged. Barriers may also easily be damaged by mishandling, resulting in a change of the WVTR.
Scientists at the National Renewable Energy Laboratory (NREL) have developed a WVTR standard below 10-3 g/m2/day using calibrated pinholes. An impermeable (to the limits of the testing instrumentation) film such as a metal foil with a single hole in the range of (100 nm to 10 mm) is used and the size and/or number of the holes determines the permeation by altering the effective diffusivity through the film, limited by molecular/viscous flow through the hole(s). Other variations include filling the hole(s) with a permeable material; and/or staggering the holes thereby creating a circuitous path for the analyte.
Additionally, a polymer material with a higher solubility is laminated onto the testing side of the foil and used to spread the incoming water out away from the single defect over the entire area of the film. These standards can also be used to calibrate transmission of gasses other than water.
Calibrated WVTR standard below 10-3 g/m2/day at a suitable temperature & relative humidity
Applications and Industries
· Qualification of measurement instrumentation
· Cross referencing two or more same/different types of measurements
· Water vapor transmission rate (WVTR) standards
· Qualifying barrier requirements (e.g., PV modules)
· Flexible electronics
· Thin films
Patents and Patent Applications
|Title and Abstract||
CALIBRATED PERMEATION STANDARDS
A permeation standard is provided. The permeation standard may include a substrate that is impermeable to an analyte, an orifice disposed in the substrate, and a permeable material filling the orifice. The orifice and the permeable material are configured to provide a predetermined transmission rate of the analyte through the permeation standard. Also provided herein are methods for forming the permeation standard.
|National Renewable Energy Laboratory||02/27/2015
|Technology ID||Development Stage||Availability||Published||Last Updated|
|NREL ROI 13-01||Proposed||Available||02/03/2016||02/03/2016|