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Potsdam team's optical analyzer improves paints and polymers

07 Jun 2016

Collaboration between PDW Analytics and local Fraunhofer Institute for Applied Polymer Research uses novel spectroscopy technique to investigate complex, turbid liquids.

A new optical technique is able to analyze complex liquids like paints, varnishes and glues in situ, giving manufacturers a way to ensure quality control in real time and potentially improve their processes without the need to extract samples.

Called photon density wave spectroscopy, it has been developed by Potsdam company PDW Analytics, then tested and refined by researchers at the nearby Fraunhofer Institute for Applied Polymer Research (IAP).

IAP’s Antje Lieske said: "Our collaboration with PDW Analytics GmbH has given us access to a process development station that for the first time allows us to record important process steps in the production of paints, varnishes and adhesives continuously and directly in-line.”

The technique is able to yield information like average particle sizes, heat flow and viscosity in turbid media – typically a very difficult task for optical technologies because of the high level of scattering and absorption.

“It also allows us to follow and understand the exact course of polymerization – and to design more efficient processes and develop feedback strategies,” Lieske added.

New process understanding
Spun off from the Innovative Fiber-Optical Spectroscopy and Sensing (innoFSPEC) technology center in October 2013, PDW Analytics is managed by business partners Roland Hass and Oliver Reich.

Hass explained: “Photon density wave spectroscopy offers a new possibility to monitor highly concentrated and viscous emulsions or suspensions directly during processing.”

“Together with the experts from Fraunhofer IAP, we can develop a totally new understanding of the processes in such complex materials,” he said, adding that the approach had “enormous potential” for developing far more efficient and robust manufacturing processes for paints, varnishes and adhesives in the future.

The novel spectroscopy technique is based around low-power laser sources operating in the visible and near-infrared ranges that are intensity-modulated at rates up to 1 GHz and beyond. By closely analyzing the scattering properties of a complex liquid emulsion, the fiber-optic equipment is able to determine the average droplet size in such mixtures.

According to PDW, the technique is based on a combination of radiation transport, Mie scattering, and other similar theoretical approaches.

Particle sizing
The technique has previously been shown to work in milk, where it can probe the changing light-scattering properties of fat droplets and other species.

“Detection and analysis of photon density waves in terms of amplitude and phase, with respect to modulation frequency and source-detector distance allow for the precise determination of fundamental optical properties of the material under investigation, namely the absorption and reduced scattering coefficients,” PDW says.

“Whereas [absorption] provides access to chemical concentrations, [reduced scattering] allows for the determination of concentrations or particle and droplet sizes of the dispersed phase without any dilution or calibration.”

The company adds that the technique provides readings at a rate of two per minute, yielding particle sizes of between 50 nm and 500 µm - although the IAP collaboration has extended that range to 2 mm. “Typically we investigate liquid suspensions or emulsions with a content of particles or droplets [from] 0.1 per cent to [more than] 50 per cent,” adds the team, indicating that highly turbid media can still be probed.

Unique technique
Lieske, who describes the technology as “globally unique”, said that PDW’s approach gives polymer experts a much better understanding of the processes going on in the manufacture of complex liquids.

Her IAP team has now developed reference systems using the photon density wave spectroscopy technique to measure various samples with particles of a given size, using them to reconstruct and analyze production processes for customers.

The particle-sizing equipment is combined with IAP’s existing analytical system, and an infrared sensor that is able to pick up changes caused by chemical reactions.

As well as choosing to have their processes analyzed at the IAP, industry customers can install one of the systems on their own premises. Typical uses include working out whether polymerization time can be reduced, or improving material properties - for example ensuring that adhesives stick better, or that a new kind of paint gives better wall coverage.

Printing, textiles and biotechnology applications are also envisaged, ranging from the production of heat-resistant clothes to fermentation processes and manufacture of cosmetics.

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