Transport of Matter Phenomena in Polymers
Permanent research personnel
M. Sanopoulou (Chemist, PhD), principal researcher
K.G. Papadokostaki (Chemist, PhD) principal researcher
J. H. Petropoulos (Chemist, PhD)
V. Dimos (Chemical Engineer, PhD)
A. Stavropoulou (Chemist, MSc)
The Laboratory of Transport of Matter Phenomena in Polymers is concerned with the study of micromolecular sorption and diffusion in polymeric materials by a combination of theoretical and experimental approaches. The aim of the work is to help create the basic scientific background for the optimization of the design of polymeric materials for important applications (controlled release systems, permselective membranes, packaging, microchip manufacture, etc).
Current Research Activities
A. Polymer-based Controlled Release Systems
Development of controlled release devices aims at the regulated, prolonged delivery of drugs, agrochemicals or other bioactive agents. Matrix-type controlled release devices consist of a swellable polymer matrix incorporating the requisite bioactive solute and are activated by the ingress of water when placed in an aqueous environment. These devices, although they have a low manufacturing cost due to their structural simplicity, are commonly characterized by a continuous decline of dose rate. The latter constitutes a substantial drawback for most practical applications. Research of our group in this area aims at the optimization of the functioning of these devices by a combination of modeling and experimental work. In particular, we have developed an advanced, realistic model, simulating the strongly interacting fluxes of solvent and solute and, hence, capable of predicting the resulting rate and kinetics of release. Theoretical work is supported by experimental studies on the effect of various system parameters (such as solute solubility, polymer degree of hydration, osmotic effect of solvent) on the kinetics of release and concurrent uptake of water. In addition, methods for approaching the desired constant dose rate are investigated (e.g. multilaminate systems).
B. Mechanisms of Micromolecular Non-Fickian Transport Kinetics in Glassy Polymers
Sorption and diffusion of micromolecular substances in glassy polymer films is of great importance in many technological applications (e.g. polymer film drying, lithographic step of integrated circuit production, polymeric controlled release systems, food packaging materials). Sorption kinetics in these systems exhibit a variety of deviations from normal Fickian behaviour, attributable to (a) slow viscous relaxations of the swelling polymer or (b) differential swelling stresses generated by the constraints imposed on local swelling during sorption. Our group has developed macroscopic models based on both mechanisms, capable of simulating all basic features of observed non_Fickian kinetic behaviour, including Case II kinetics. Experimental work includes
(i) sorption from the vapour phase. Carefully designed experimental protocols, consisting of series of successive integral or interval sorption kinetic experiments, supplemented by measurement of longitudinal swelling kinetics of the polymer film enable us to study various types of non-Fickian behaviour. On the basis of the models mentioned above, we developed general diagnostic criteria for distinguishing between the underlying mechanisms responsible for the observed behaviour and applied this methodoly to particular cellulosic or methacrylic polymer systems.
(ii) sorption from the liquid phase. Various optical techniques are used in order to obtain information not only on the rate and kinetics of penetration but also on penetrant concentration profiles and parallel deformation and structural relaxation of the swelling polymer. Combination of these techniques enables us to study in detail various types of non-Fickian penetration such as stress-dependent diffusion and Case II kinetics.
C. Molecular Dynamics Simulation of Structure and Transport Properties of Poly(dimethylsilamethylene) Polymers
The project aims at the development of novel membrane materials for the separation of hydrocarbons in the petroleum and natural gas industry. Molecular Dynamics is used for computer simulation of hydrocarbon sorption and diffusion properties in polysilamethylene polymers. In addition, experimental evaluation of the transport properties is performed in collaboration with Topchiev Institute of the Russian Academy of Sciences.
D. Characterization of Transport and Thermal properties of polymer systems for specific applications.
In collaboration with the Institute of Microelectronics in Demokritos, we evaluate the swelling and/or dissolution behaviour of thin supported polymer films exposed to different vapour or liquid environments for the development of lithographic systems and silicon bilayer chemical sensors.