Marcella Cabrera Berg

A thesis submitted  November, 2017 for the degree of Doctor of Philosophy and defended December, 2017.

Nano-Science Centre, Niels Bohr Institute, University of Copenhagen, 2 Department of Odontology, Faculty of Health and Medical Sciences, University of Copenhagen

Supervisors:
Heloisa Nunes Bordallo and Ana Raquel Benetti

 

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Dynamics of Liquids Confined in Porous Materials: A Quasi-Elastic Study

Oral health is an integrated part of the public wellbeing, and does not only affect the quality of life, but also the healthcare system through related economic costs. Despite great global progress in oral health related issues, dental caries is still a major problem that affects both children and adults. Indeed, dental restorative work in industrialized countries is very costly, thus developing and improving restorative materials can beneficially impact the public health system. Among dental restorative materials glass ionomer cements (GIC) are of great interest, since they have the ability to bond to the tooth structure without the need for preconditioning the surface with an acid or unnecessary removal of tooth substance. Furthermore, fluoride is slowly released during setting adding to the anticariogenic benefits of the material. GIC’s poor mechanical strength is however a disadvantage, and improved knowledge on this subject can bring potential development. One possibility is to advance our understanding of the dynamics of the aqueous solution used to prepare the GIC.

Under these lines, in this work I have combined neutron spectroscopy and calorimetric analysis to understand the nanoscale mobility of the hydrogen atoms, mostly from water, present in conventional GIC. Water plays a big part in the setting process in GIC. It is the reaction medium in which the cations leach to crosslink. Furthermore, water also hydrates the siliceous hydrogel and the metal polyacrylate salts. In matured GIC, water occupies coordination sites around cations in a hydration shell of the cation-polyacrylate, hydration regions around the polymer chain or still remains unbound in its bulk state. Neutron spectroscopy was chosen since the high incoherent scattering cross section of the hydrogen atom makes this technique ideal for assessing the dynamics of water in the material. Water is furthermore also easily detected by thermogravimetric analysis coupled to Fourier transform infrared spectroscopy and differential scanning calorimetric methods, which were also employed in this thesis. However understanding water dynamics in such complex hierarchical structure, where different motions occur in a broad range of time scales and simultaneously, can be difficult. So in this Ph.D. thesis, the experimental data was combined with preliminary classical molecular dynamics simulations (MD), aiming to investigate the different nanoscale water dynamics in the GIC. This unique approach opens new possibilities to better explore all the information contained in the neutron spectroscopy data.

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