PhD thesis defense of Svitlana Railian
Oct 29, 2019 - 15.00 uur
Agoralaan Gebouw D
Lokaal auditorium H5
Mevrouw Svitlana RAILIAN
Svitlana Railian invites you to the public defense of her doctoral thesis entitled:
"Graphene oxide modification towards advanced polymer nanocomposites".
Promoter: Prof. Dr. Tanja Junkers
Copromoter: Prof. Dr. Ir. Wim Deferme
Development of novel polymer nanocomposites has been widely investigated by scientists. The important factors of designing nanocomposites with value-added properties include type and size of nanofiller and its dispersion in a polymer matrix. Polymer reinforcement can be obtained by incorporation of graphene sheets. It improves the mechanical strength, enhances electrical and thermal conductivity, influences thermocalorimetric transitions, reduces gas permeation and improves thermal stability. Despite those outstanding properties and great potential in a variety of applications, graphene sheets have low interfacial interaction with polymers that reduces this synergistic effect.
To improve the dispersion of nanofiller in a polymer phase, graphene oxide (GO) and reduced graphene oxide (rGO) were pre-modified with polymer brushes. For this, surface-initiated photo-induced copper-mediated polymerization (SI-photoCMP) was employed to grow acrylate polymers under mild reaction conditions: UV irradiation instead of elevated temperatures. The use of reduced catalyst concentration was demonstrated to potentially reduce waste. Transferring the polymerization from batch reactor to continuous-flow reactor allows for enormous decrease of reaction time (from 24 hours to 1 hour) without losing the grafting efficiency and potentially upscale the system. The poly(methyl methacrylate) (PMMA) grafted rGO showed improved dispersibility in chloroform, compare to initial rGO. Presence of poly(di(ethylene glycol) ethyl ether acrylate) (PDEGA) chains on rGO surface improves its dispersibility in ethanol.
The PMMA grafted GO sheets (prepared via SI-photoCMP) were further tested in polymer nanocomposites applications. A good dispersion was obtained after solution mixing of poly(methyl methacrylate-stat-n-butyl acrylate) (P(MMA-stat-nBA)) matrix with GO-PMMA. The polymer nanocomposites films have smoother surface, compared to bare GO as nanofiller. After thermal treatment (160 °C, 24 hours) the insulating properties of the films were observed, presumably due to the enwrapping and isolation of the single GO-PMMA sheets by the polymer matrix. An increased glass transition temperature (Tg) was obtained in polymer latex with incorporation of the GO-PMMA filler content without presence of conventional surfactant.
Since grafted polymers on GO or rGO surfaces can influence its properties, the GO was modified with polyethylene glycol (PEG) chains for improved solubility and long-term stability of the sheets in water-content systems. Formed GO-PEG was used as ink in the inkjet printing application. The GO-PEG-based ink contains a solvent mixture of water and ethylene glycol in a 1/3 volume ratio as a close fit to the required printing-compatible physical properties. The concentration of GO-PEG in the ink was 3.4 mg/mL, allowing reducing the number of printing cycles. The ink was printed on a glass substrate and irradiated under NIR light. It allows for efficient solvent evaporation with preserving the layer uniformity of the film. The following thermal treatment (280 °C for 20 hours in vacuum oven) restored the aromatic structure of GO sheets and resistance approx. 4 MΩ was obtained only after three printing cycles. It allows the fabrication of printed electronics, such as electronic circuits and devices.