In-Situ Characterisation of Photo-actuating and Photo-rheological Polymers
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In-Situ Characterisation of Photo-actuating and Photo-rheological Polymers Chris J. Sabey, M. Moniruzzaman, Gerard F. Fernando, Rodney A. Badcock, Darren Winter, Jackie Akhavan, Esam Kronfli and A. Bandara1 Cranfield University, RMCS Shrivenham, Swindon, United Kingdom 1 Kingston University, Kingston-upon-Thames, Surrey, United Kingdom ABSTRACT This paper reports on the design and validation of three in-situ measurement techniques for characterisation of photo-rheological and photo-actuation phenomena. Results from these in-situ techniques are presented and used to investigate isomerisation and recovery effects in azobenzene and spiropyran polymer systems with and without flexible spacer groups. A new in-situ technique for the measurement of photo-viscosity effects in polymer solutions has been developed using a cone and plate rheometer. The new technique permits simultaneous irradiation of the photo-responsive polymer solutions and continuous measurement of its viscosity in a controlled environment. An additional benefit of the technique is the greatly reduced sample volume compared to traditional capillary viscometers. Techniques for the in-situ measurement of the photo-actuation effect in polymer systems are discussed, including image analysis and interferometric methods. The effects of environmental factors such as temperature are considered and steps taken to minimise them. The resulting measurement techniques provide an accurate means of measuring the effect of irradiation on the photo-actuating polymers in solution and as solids. A range of polymers with photo-responsive azobenzene and spiropyran groups in the polymer side chains have been synthesised and evaluated using these three techniques. The photoviscosity and photo-actuation effects under irradiation have been measured in a variety of solvents. The effect of incorporating a flexible spacer group in the side chain of the azobenzene polymers is examined and its effect on the photo-rheology mechanism is discussed. INTRODUCTION The photo-responsive behaviour of various azobenzene and spiropyran based polymer systems have been examined in the past [1]. In this paper, the phenomena of interest are the photo-viscosity effect in solutions and the shape or volume changes in solid films upon UV/visible light irradiation. In addition to these previously reported effects, this study aims to measure the effect of irradiation on the volume of photo-responsive polymer solutions. The photo-viscosity effect was first reported by Lovrien in 1967 [2]. Since then many more studies have reported photo-viscosity effects in a wide range of polymers [3]. However, the range of measurement techniques has been restricted, almost exclusively, to the use of capillary flow type viscometers. Viscosity measurements performed using capillary flow type viscometers are not continuous, requiring the flow to be reversed between measurements. The geometry of the capillary viscometers makes homogeneous irradiation of the sample solution difficult, requiring the addition of stirring
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