[nanoPost] Nano-hybrids with optimized mechanical, rheological, optical and thermal properties

University Greece

The group is concerned with the fundamental understanding of the behavior of the composites in order to optimize the final properties of the hybrid materials. They have been involved with the development of nano-hybrids with optimized mechanical, rheological, optical and thermal properties and high added value with applications in the field of automotive industry, food packaging, agriculture, as well as in that of optoelectronics and random lasers.

The area of polymer/layered silicate nanocomposites has been of special interest. In these systems three different types of structure can be observed: the phase separated structure, where the polymer and the inorganic material are highly immiscible, the intercalated structure, where the polymeric chains reside between the layers of the silicate, and the exfoliated structure, where the platelets are well dispersed in the polymeric matrix. A central objective of the group’s involvement is the understanding of the interactions between the polymer chains and the surfaces of the inorganic material in order to be able to control the miscibility and thus the structure of the hybrid material by modifying the interactions.

The control of the structure in each case is correlated with the final properties, which is the main interest of the end user. This optimization of the structure and the properties is especially important in the case of widely-utilized commodity polymers like polyethylene or polypropylene, which, however, are not particularly miscible with the layered silicates due to their non-polar character.

Polyethylene is used in films for food packaging or agricultural applications and it is clear that products with lower permeability in gases and better mechanical and surface properties are important. One of the major applications of polypropylene is in the car industry, where it is very important that the final product possesses both stiffness and toughness, is easily processable and shows high scratch and flame resistance. It has been anti-cipated that optimized polymer/layered silicates hybrids can significantly improve these properties. The understanding of the interactions between the polymer and the surfaces as well as of the mechanism of intercalation can also provide the opportunity to develop responsive systems by appropriately tuning these interactions.

A second area of interest has been the development of nano-hybrids for optoelectronic applications and, more specifically, for random lasers. In this case, the existence of dispersed inorganic material (e.g., nanoparticles, nanotubes, nano- or micro-porous inorganic additives) in a polymeric matrix causes multiple scattering of the incident light. In the presence of a gain medium and for pumping intensities above a threshold value, the effectively-trapped radiation in the “microcavities” (due to the multiple scattering) can lead to the amplification of the light and in the appearance of laser effect. This has been demonstrated in a system of ZnO particles dispersed in poly (dimethyl phenyl siloxane) matrix, where excitation of the nano-hybrid by a pulse with duration shorter than the ZnO photoluminescence lifetime leads to a dramatic increase in the emitted light intensity accompanied by a significant spectral and temporal narrowing. Optimal use of this phenomenon can find applications in bar coding, in cryptographic coatings as well as in special coatings for airplanes in order to assist “search and rescue” operations.

A subject of great scientific interest has been lately that of the effect of confinement and surfaces on the dynamics of polymers. The intercalated polymer/layered silicates nanocomposites provide a unique opportunity to study the static and/or dynamic behaviour of macromolecules in nanoconfinement: one can utilize conventional analytical techniques on macroscopic samples and nevertheless investigate the properties of 1-3 nm films. They are very interested on how this confinement affects the different dynamics of polymer chains, i.e. the local, global or side group motion.