I would like to thank prof. Stephen J. Picken and Dr. Henk Schut from the Technical University of Delft for their great hospitality and help during my staying at the Interfaculty Reactor Institute for the PALS measurements. Also, many thanks to Dr. Louise Nobel for the supply of the acrylic resin emulsion.I deeply thank prof. Josef Breu for his invitation and excellent hospitality at the University of Bayreuth in Germany. His high level scientific team and work was an important experience for me. Also many thanks to Dr. Daniel Kunz for his support and for the supply of the hectorite powder.I am gratefull to prof. Dionysios Mantzavinos of the Environmental Engineering Department for the ultrasound device. Also I thank prof. Georgios Kostakis of the Mineral Resources Engineering Department for the X-ray measurements and Ms. Maria Stratigaki for conducting the PALS measurements of the hectorite samples.I would like to deeply thank prof. Spiridon Anastasiadis, prof. Dimitrios Vlasopoulos, Dr. Emmanuel Stratakis and Mr. Lampros Papoutsakis of the University of Heraclion and Foundation of Research and Technology (F.O.R.T.H.) for the X-ray and TGA measurements and for the supply of the organo-modified montmorillonite powders. Their hospitality and willingness to help are the most obvious examples that explain why these research foundations are considered to be the best in Greece.Finally, I thank all seven members of the advisory committee for their thoughtful comments on this dissertation.xi xii