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Synthesis and Characterization of Smart Silica Nanocomposites via Reversible Addition−Fragmentation Chain-Transfer (RAFT)Polymerization

Rahemipoor, Sahand | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52734 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Pourjavadi, Ali
  7. Abstract:
  8. Photochromism is defined as a reversible transformation of a chemical species between two forms having different absorption spectra induced in one or both directions by photoirradiation. Numerous photochromic molecules were investigated such as spiropyrans (SP), spirooxazines (SO), fulgides, diarylethenes, and azobenzenes. Recently, spirooxazines have been attracted more attention due to their more sensitivity towards photo, pH, heat, pressure, solvent polarity, and high fatigue resistance. Spirooxazine moieties are one of the most popular photochromic groups that can be transformed from colorless closed ring form (SO from) to blue color open ring form by UV irradiation that so-called; merocyanine (MC form). Merocyanine is photochromism, polar and hydrophilic, which its stability is strongly dependent on the solvent and it could be stable in highly polar or acidic solvents due to H-bonding, which demonstrates Vis adsorption in about 580-630 nm. In the closed structure of molecule (spiro structure), conjugation disturbs and a colorless, non-polar, hydrophobic, and stable structure is formed, which has adsorption peak in UV region. The reversible transformation of MC to SO structure takes place by heat or visible irradiation. In this study, photochromic monomer of spirooxazine was synthesized through six steps. Then, the macro-raft agent was synthesized with NIPAM and SOM as monomers and DDMAT as a RAFT agent which a purple powder was obtained. In the next step, SiO2 nanoparticles were synthesized using TEOS in ethanol. Then, the surface of SiO2 nanoparticles was modified by 3- (trimethoxylsilyl) propyl methacrylate (MPS). Then, photochromic nanocomposite was synthesized in presence modified SiO2 or SiO2@MPS, macro-RAFT agent and DMAEMA. The product was centrifuged in which the free block copolymer in the solution was separated from the nanocomposite. The free block copolymer was precipitated which produced a gray powder. Size istribution of the smart polymeric nanparticles, their surface charge and thermal properties were analyzed by DLS and TGA analyses, respectively. Photochromic properties of these compounds were investigated by UV-Vis spectroscopy. FTIR analyses, SEM and TEM images were used to characterize chemical structure and surface morphology of the smart nanocmposite, respectively. Finally, application of this nanocmposite in chemical sensors were investigated by three external stimuli of UV irradiation, pH and temperature
  9. Keywords:
  10. Photochromism ; Nanocomposite ; Silica Nanoparticles ; Reversible Addition-Fragmentation Chain-Transfer (RAFT) ; Spirooxazines

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