| Abstract |
Mixing polymers with inorganic materials leads to the synthesis of composites, which have improved properties with respect to the original materials. An important category among them, are the nanohybrids in which the inorganic component has at least one dimension at the nanometer scale. This category includes hybrids that are formed by mixing polymers with layered silicate clays. Such materials exhibit (depending on their structure) high thermal resistance and improved mechanical properties, whereas they retain the advantages of the initial polymers, such as the transparency or the easy processability.
The purpose of the present project is the synthesis and the study of the interactions and the properties of nanocomposite materials which consist of layered silicate clays and poly(ethylene oxide)-b-poly(styrene) (PEO-b-PS) diblock copolymers. The clay used is a natural hydrophilic sodium montmorillonite (Na+) whereas the copolymers were synthesized in the lab, in the framework of this work, utilizing controlled radical polymerization. It is well known from the literature that the PEO homopolymer has the ability to intercalate between the layers of the clay, as it is hydrophilic molecule, therefore has favorable interactions with the surface of the clay. On the other hand, the PS homopolymer is hydrophobic molecule and has unfavorable interactions with the clay, leading to phase separated structures. This study is focalized in the case of PEO-b-PS amphiphilic copolymers. The total interactions of the copolymers with the natural montmorillonite as well as the structure of the resulted nanocomposite materials are investigated. Especially, the influence of the molecular weight and the concentration of the copolymers to the final structure of the nanocomposite materials is examined in detail.
Seven PEO-b-PS copolymers with varying molecular weight and composition were synthesized utilizing controlled Atom Transfer Radical Polymerization (ATRP). Their molecular weight and their polydispersity were evaluated with Size Exclusion Chromatography (SEC) whereas their composition was measured with 1H Nuclear Magnetic Resonance (1H NMR). The thermal properties and the thermodynamic condition of the polymers were also studied with Differential Scanning Calorimetry (DSC) and Small Angle X-ray Scattering (SAXS) respectively.
For the preparation of the nanocomposite materials, the polymer melt intercalation method was used and hybrids with composition that varied from pure polymer to pure clay were synthesized. Following the synthesis, X-ray diffraction (XRD) was utilized to study the structure and to determine the interlayer distance. It was found that all nanohybrids have intercalated structure with interlayer distances that are similar to the ones that correspond to the respective of PEO homopolymer when it is mixed with the same inorganic material. There is, thus, a strong indication that in every case the final structure is determined by just the Na+/PEO ratio in the copolymer hybrids. In order to investigate the role of the PS block in the system, the interactions between the blocks of the copolymer and the inorganic surface were studied by infrared spectroscopy (FTIR).
Finally, the fluorescence of the PS block as well as the way it is affected by whether the polystyrene is intercalated or not was studied. It was proved that the intrinsic fluorescence of PS is vanished when it is intercalated between the inorganic layers. In the case of the Na+/PEO-b-PS nanocomposites the PS fluorescence is measurable, evidencing that the PS block is outside of the inorganic galleries and only the PEO block of the copolymer intercalates.
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Σύνθεση και μελέτη των αλληλεπιδράσεων σε νανοϋβρίδια δισυσταδικών συμπολυμερών με ανόργανα υλικά
