New test measures properties polymer thin films membranes

New test measures properties of polymer thin films and membranes

1:35 PM, 30th July 2011
New test measures properties of polymer thin films and membranes
Nanomechanical measurements (microimage of specimen). a) Thin rigid film on elastic substrate b) Initial strain induces surface wrinkles parallel to stress c) Additional strain induces regular pattern of cracks in the film d) Typical specimen imaged with optical profilometre (280 X 210 micrometre).

GAITHERSBURG, US: Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a measurement technique that reliably determines three fundamental mechanical properties of near-nanoscale films. The technique, which highlights the challenge of making mechanical measurements on an object with at least one dimension comparable to the size of a virus, should enable better design and engineering for a variety of thin-film technologies, particularly reverse-osmosis membranes for water purification.

Reverse-osmosis membranes, explained NIST, Researcher Chris Stafford, are an interesting challenge for the materials scientist. The membranes are used in water purification systems - a polyamide film no more than 200 nanometre thick backed by a thicker, porous support layer. Water holding dissolved salts or other contaminants is forced against one side of the membrane at substantial pressures up to about a thousand psi (roughly 7 megapascal) and comes out the other side leaving most of the impurities behind.

The mechanical integrity of the membrane is obviously essential - it can’t tear or develop pinhole leaks under the pressure - but engineers lacked a good way to measure the strength and breaking point, under stress, of these extremely thin films.

The NIST technique builds on earlier work by the team that demonstrated that you can reliably determine Young’s modulus, a measure of stiffness or elasticity, for thin and ultrathin films by bonding it to a piece of silicon rubber. In the new work, they basically pull harder until the film starts developing minute cracks crosswise to the tension.

Applying their technique to study the effect of chlorine on reverse-osmosis membranes, the team uncovered a puzzle. Chlorine in the water is known to cause a progressive deterioration in membrane performance, generally thought to be the result of prolonged chemical attack by the chlorine. Not so, according to the NIST team. “Chemically the chlorine attack is pretty quick,” said Stafford. Spectroscopic chemical analysis showed that all the chemical damage from chlorine exposure happens in the first few hours. Tests using the wrinkle-crack method, however, show that the mechanical properties degrade continuously, up to the longest duration tested - 10 days. “It may be an aging effect in polymers,” said Stafford.

The project is part of a broader NIST programme to study materials issues related to sustainable technologies like water purification, but the research team notes that the wrinkle-crack method itself would be broadly applicable to mechanical studies of almost any nanoscale thin film in fields as diverse as artificial skin, flexible electronics, thin-film sensors, fuel cells and photovoltaics.

(C) National Institute of Standards and Technology News




Your Comments (Up to 2000 characters)
Please respect our community and the integrity of its participants. WOC reserves the right to moderate and approve your comment.

Related News

OSU pigment discovery expanding to new colours

CORVALLIS, US: Chemists at Oregon State University have discovered that the same crystal structure they identified two years ago to create what may be ...

Read more
New X-ray camera to reveal big secrets about how chemistry works

SWINDON, UNITED KINGDOM: Designed to record bursts of images at an unprecedented speed of 4.5 million frames per second, an innovative X-ray camera be ...

Read more
New spin on friction-stir

OAK RIDGE, US: Researchers Zhili Feng, Alan Frederic and Stan David in Oak Ridge National Laboratory’s Materials S&T division have made si ...

Read more
Dow agrees with US EPA to pay $2.5 million to settle violations

  MIDLAND, US: The Dow Chemical Company’s Michigan operations has reached a comprehensive settlement agreement with the United States Envi ...

Read more
ACS enables new subject-based categorization of content

WASHINGTON, US: The ACS Publications and Chemical Abstracts Service (CAS) divisions of the American Chemical Society (ACS) announced jointly the integ ...

Read more
LyondellBasell posts higher income but diluted earnings per share

• Net income of $804 million; Diluted earnings per share of $1.38. • Quarterly EBITDA of $1,553 million; 11 per cent increase fro ...

Read more uses cookies to ensure that we give you the best experience on our website. By using this site, you agree to our Privacy Policy and our Terms of Use. X