• Increase font size
  • Default font size
  • Decrease font size
Home Publications
Investigation of binary polar solvent mixtures, solubilized ferroelectric salts and paraffin-based derivatives using dielectric spectroscopy
Research Area: thesis Year: 2007
Type of Publication: Phd Thesis  
  • Dana Daneshvari
Water properties are the subject of investigations in physics, chemistry, biology and different applied fields of natural science. Liquid dosage forms, generally based on aqueous solutions, take an important role in drug administration e.g. as parenteral preparations, ophthalmic formulations or as oral solutions for children and elderly patients. Sufficient drug solubility in water is a prerequisite for orally administrated solid dosage forms such as tablets, capsules, etc. to show a sufficient bioavailability. The solubility of a drug is determined by intermolecular forces. While these can be reasonably well characterized in gaseous and solid material, no satisfying description has yet been found for liquid systems, especially for nonideal solutions. The presence of several types of intermolecular interactions let water show rather a complex associated structure due to which it has a number of its abnormal properties. In part A of this work, the intermolecular forces in pure solvents and binary mixtures at 298.2 K (25?C) are investigated, using quasistatic low-frequency and AC highfrequency broadband (0.2-20 GHz) dielectric spectroscopy. The data were interpreted using for the low frequency measurements the modified Clausius-Mossotti-Debye equation according to Leuenberger and Kirkwood-Fr?hlich equation. For the description of the dielectric relaxation in the high frequency range there are different models available which describe the relaxation behaviour of a polar liquid. The most simple equation is the Debye equation, which will be described and will be compared with the other models in the theory chapter. It has to be kept in mind that the resulting relaxation times (??) depend on the mathematical model applied. If the mean corrected R2 coefficient does not differ significantly for the mathematical models used, it is not possible to make an unambiguous choice of model. In part A of this work, we collect a wide study of percolation phenomena in DMSO and its analogues (DMAC, DMF & NMP) in binary mixtures with water, to investigate any similarity in their behaviour. In addition, we investigated these solvents in 1,4- dioxane binary mixtures to study their behaviour in a nonpolar environment. Furthermore, we studied Formamide and its mono and dimethylated form in binary mixtures with water to investigate the effect of adding a methyl group to a molecular structure using percolation phenomena. In pharmaceutical science the polymorphism of the Active Pharmaceutical Ingredients (APIs) is of an important interest. More than 50% of all APIs show polymorphism. However, it is very difficult to predict in which condition, which type of polymorph is formed. In part B of this work we try to detect pre-formation of crystalline order in the liquid and to investigate the different polymorphism during this process at different temperature and different concentrations. As a model compound, Seignette salt was chosen due to its ferroelectric activity and high solubility in water. The binary mixtures of Salt-water and ternary mixtures of Salt-water-1,4-dioxane were the subject of the investigation. The relaxation behaviour of these mixtures was studied using Debye model and percolation phenomena. Furthermore, any sudden increase or decrease in their complex permittivity (real and imaginary part) was studied at temperatures between 10-70?C and at different concentration from low salt content to saturated and supersaturated solutions. To have a broader investigation, aqueous binary mixtures of KDP and ADP which both posses a ferroelectric activity with high water solubility were studied. Part C of this work is collaboration with ?Swiss Federal Institute for Materials Science & Technology Research and Testing, EMPA?. Paraffin based PEG derivatives were the subject of the investigation. These labeled polymers with different PEG number were studied to find which one is more appropriate to use as a binder in ceramic production. Dipolar losses in the microwave range are used in modern technology for accelerating thermal processing of polymers (tempering, curing etc...). In the other hand, the importance of removing binders in pharmaceutical and material science is well known. The results of this part will be presented in ?International symposium HES-07, Padua, Italy? on June 2007 with the title of ?Effect of PEG Derivative Number on Dielectric Properties of Paraffin Based-PEG Polymers at Microwave Frequencies?. In addition, ?The Cole-Cole plot analysis of dielectric behavior of paraffin labeled with different PEG-chains? has been submitted to the Polymer International, Journal (www3.interscience.wiley.com) on 16.05.2007.
Digital version