Abstract-Glassy dynamics of sorbitol solutions at terahertz frequencies

http://pubs.rsc.org/en/content/articlelanding/2013/CP/C3CP51936H

Juraj Sibik, Evgenyi Y. Shalaev and J. Axel Zeitler

The absorption spectra of D-sorbitol and a range of its concentrated aqueous solutions were studied by terahertz spectroscopy over the temperature interval of 80 K < T < 310 K. It is shown that the slow-down of molecules at around the glass transition temperature, T_g, dramatically influences the thermal dependence of the absorption at terahertz frequencies. Furthermore, two different absorption regimes are revealed below T_g: at temperatures well below T_g the absorption resembles the coupling of terahertz radiation into the vibrational density of states (VDOS); above these temperatures, between 160 K and T_g, in the sample of pure sorbitol and the sample of a solution of 70wt% sorbitol in water, another type of absorption is observed at terahertz frequencies. Several possibilities of the physical origin of this absorption are discussed and based on the experimental data this process is tentatively assigned to the Johari-Goldstein β-relaxation processes shifting to lower frequencies at temperatures below T_g leaving behind a spectrum largely dominated by losses into the VDOS.

Dr Axel Zeitler- Terahertz Technology

http://www.scienceomega.com/article/882/terahertz-technology
Measuring through multiple coating layers without physically slicing the sample
One of the biggest challenges for the pharmaceutical industry is to manufacture tablets with consistent quality. Existing measurement technologies struggle to provide the necessary information for effective process control. Part of our research is to apply terahertz radiation to non-destructively image film coatings that are traditionally applied on tablets to change their appearance, but, more recently, have been developed to control the drug release. By exploiting the short pulse duration and the ability to penetrate most polymers, used as excipients for film coating, we are able to resolve spatially the thickness and density of the coating.

Terahertz radiation can propagate more than 3mm into the tablet and, hence, it is possible to measure through multiple coating layers without physically slicing the sample. Recently, we have developed a robust in-line system to quantitatively measure the coating thickness of randomly moving tablets. This development allows terahertz sensors to make their way from research to manufacturing control applications successfully. We are now in a position to start using the information provided by the terahertz sensor to better understand the film coating process. We hope we will be able to develop a more robust control of the process leading to safer and better products for patients.

The aim of our research in this field is to link the coating properties as measured by terahertz imaging with the performance of controlled release dosage forms. Through a better understanding of the physical properties of the film coating and the tablet dissolution, we open new opportunities for improved process understanding for applications in process analytical technology (PAT) and quality by design (QbD).

In addition to our diverse interests in pharmaceutics, we also study nanostructured materials such as carbon nanotubes (CNTs) and carbon nanofibres (CNFs) that have applications as heterogeneous catalysts as well as in many other fields. Ultimately, our goal is to relate catalytic activity and selectivity to both electronic and physical characteristics of the catalysts.

Dr Axel Zeitler
Lecturer
Terahertz Applications Group
Department of Chemical Engineering and Biotechnology
University of Cambridge
+44 (0)1223 334783
www.ceb.cam.ac.uk/thz.php


Read more: http://www.scienceomega.com/article/882/terahertz-technology#ixzz2O5gy5pO5

Grant to develop Terahertz sensor to measure paint quality on automobiles

http://www.vision-systems.com/articles/2012/08/terahertz-imager-to-measure-paint-quality-on-automobiles.html
Researchers at the Department of Chemical Engineering at Cambridge University(Cambridge, UK) led by Dr. J. Axel Zeitler have been awarded a grant of over £240,000 to develop a terahertz sensor that can be used to measure the quality of paint coatings on automobiles.

Painting is an integral part of the manufacturing process in the automotive industry. The paint coats that are applied to modern cars comprise a complex structure of layers, with the integrity of each layer being of critical importance to the overall performance of the coating.

However, the current quality control strategy that is used to ensure the final integrity of the paint coat is a slow manual process that can only cover a limited number of sampling points on a few select automobiles per test cycle. The main bottleneck behind this lack of real-time testing capability is that there is no non-contact measurement technology presently available that is fast and accurate enough for the task.

Dr. Zeitler and his team plan to eliminate this bottleneck by developing a terahertz sensor that is capable of performing real-time measurements of the paint quality and layer integrity in real-time on a six-axis robot that can be directly employed in the spray booth of existing manufacturing lines.

Terahertz systems have already been deployed in a number of pharmaceutical and semiconductor inspection applications where they have been used to penetrate materials to reveal the contrast of the internal microstructures of materials.

In previous work at the university, Dr. Zeitler developed a new in-line measurement technique to determine the coating thickness of individual pharmaceutical tablets during film coating in a pan coating unit using pulsed terahertz technology. Details of that work can be found here.

Dr. Zeitler's new project, which has been funded by the UK-based Engineering and Physical Sciences Research Council(EPSRC; Swindon, UK), will start on September 1 this year.

-- Dave Wilson, Senior Editor, Vision Systems Design