Panagiotis Klonos

Interfacial effects in polymer nanocomposites studied by dielectric and thermal techniques

DSC and dielectric DRS and TSDC measurements in PDMS/silica and PDMS/titania nanocomposites reveal the presence of several contributions to segmental dynamics and the corresponding glass transition. Further work is needed to clarify as to whether this behavior is common to rubber nanocomposites, in relation to the high flexibility of the polymer backbone.

Applying Broadband Dielectric Spectroscopy (BDS) for the Biophysical Characterization of Mammalian Tissues under a Variety of Cellular Stresses

The dielectric properties of biological tissues can contribute non-invasively to a better characterization and understanding of the structural properties and physiology of living organisms. The question we asked, is whether these induced changes are effected by an endogenous or exogenous cellular stress, and can they be detected non-invasively in the form of a dielectric response, e.g., an AC conductivity switch in the broadband frequency spectrum. This study constitutes the first methodological approach for the detection of environmental stress-induced damage in mammalian tissues by the means of broadband dielectric spectroscopy (BDS) at the frequencies of 1–106 Hz. Firstly, we used non-ionizing (NIR) and ionizing radiation (IR) as a typical environmental stress. Specifically, rats were exposed to either digital enhanced cordless telecommunication (DECT) radio frequency electromagnetic radiation or to γ-radiation, respectively. The other type of stress, characterized usually by high genomic instability, was the pathophysiological state of human cancer (lung and prostate). Analyzing the results of isothermal dielectric measurements provided information on the tissues’ water fraction. In most cases, our methodology proved sufficient in detecting structural changes, especially in the case of IR and malignancy. Useful specific dielectric response patterns are detected and correlated with each type of stress. Our results point towards the development of a dielectric-based methodology for better understanding and, in a relatively invasive way, the biological and structural changes effected by radiation and developing lung or prostate cancer often associated with genomic instability.

Bifunctional Silicas with Immobilized Lignin

Silica/lignin biocomposites were obtained by impregnation of the modified pyrogenic silicas with water solutions of polymer. Modification of silica surface was carried out using liquid-phase and gas-phase treatment with alkoxyorganosilanes and hexamethyldisilazane, respectively. The silicas with methyl, amine, and silicon hydride groups in a mono- or bifunctional (methyl-hydride, methyl-amino, amino-hydride) surface layers were impregnated with kraft lignin and characterized using differential scanning calorimetry (DSC), attenuated total reflectance (ATR), Fourier transform infrared (FT-IR), and UV spectroscopies. The influence of nature and amount of silica surface functional groups on physicochemical properties of immobilized lignin has been studied. The data on the structure of the polymer layer and the nature of silica/lignin interactions are discussed.