In this thesis the design and synthesis of surface functionalized nanoparticles is central. ‘My main work was on low density nanocellular polymer nanocomposite foams,’ says Shanqiu Liu. ‘This is a promising class of materials with many potential applications, especially in high performance thermal insulation.
Nanoparticles in these foams act as energetically favorable heterogeneous nucleation sites. ‘However, the currently reported cell nucleation efficiency is very low,’ thus Shanqiu who used Poly(methyl methacrylate) (PMMA) as a foam matrix polymer. As a comparison, polystyrene (PS) was used.
The influence of nanoparticles size, surface chemistry and surface texture on foam cell nucleation, are discussed in detail. Also presented is the investigation of interfacial interactions between individual nanoparticles and CO2 swollen polymer matrices.
One of Shanqiu’s main conclusions: Decoration of silica nanoparticles with a low surface energy and high CO2-philic thin polymer shell, e.g. PDMS, is found to be an efficient strategy to increase the nucleation efficiency of silica nanoparticles.
Shanqiu: ‘We succeeded in achieving heterogeneous nucleation. The PDMS particles outperformed all currently known nanoparticles. The impressive results open new avenues for the fabrication of highly efficient nucleation agents. The low surface energy and relatively high CO2-sorption in the PDMS shell, appeared favorable for heterogeneous nucleation. ’
One of the new key theoretical concepts in this thesis research is ‘line tension’, says Shanqiu. ‘It contributes to a higher nucleation energy. In theoretically defining this concept, as a member of the Materials Science & Technology of Polymers (MTP) Group I collaborated with the Mesa+ Physics of Fluids (PoF) Group, incorporating interfacial interactions into our considerations. Both Groups benefitted from the collaboration. Experimental setups and theoretical work alternated well and strengthened one another. The PhD work resulted in seven papers. Polymer, European Polymer Journal and ACS Applied Materials & Interfaces, were among those.’
Also Sabic Petrochemicals, based in Geleen, was interested in Shanqiu’s work. ‘At conferences colleagues showed eager to hear my results,’ he says. ‘The results emphasize the need for the development of new particle designs, to further enhance the nucleation efficiency of nanoparticles in polymer nanocellular foaming.’
During the PhD work Shanqiu learned to synthesize the nanoparticles. ‘This was totally new to me,’ he says. ‘I learned to work in an independent manner, helped by the collaboration opportunities between Mesa+ Groups, making use of the vast amount of equipment available and due to the open working atmosphere. Experts of different groups are always willing to help you out.’
Shanqiu also enjoyed supervising master students during his PhD working period. ‘It is great helping them, to develop their experimental and scientific skills,’ he says. ‘I got inspired by their commitment and clever questions. Also they were of great help by performing my experiments.'
In his future work Shanqui hopes to combine academic work and application oriented research. ‘After my Defense I hope to find a post-doc position, preferably involving polymer science and surface modification,’ he says. ‘Be it in academics or in industry, I want to perform research projects aimed at application. I don’t like the idea of my research only staying in the lab and not being used in daily life. My PhD work is fundamental in nature, but application potential is most certainly present. I now possess more skills, developing new projects and ideas on this cutting edge.'