The objective of this thesis was to systematically investigate the two dimensional assembly of cellulose-based materials and the two dimensional response to various external stimuli. The motivation of studying such materials is the ever increasing trend in materials science to substitute synthetic polymers for greener materials. Studies such as the one presented here are essential to understand the fundamental behaviours and characteristics of bio-based polymers and to be able to utilize them in new functional materials. Trimethylsilyl cellulose (TMSC), cellulose triacetate (CTA), cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) were extensively studied by means of Langmuir-Schaefer deposition. The formation of nanostructures on the surface of solid substrates as a result of monolayer transfer from the air/water interface was investigated using substrates of varying total surface free energy. It was established that for TMSC, a decrease in substrate surface energy resulted in progressive dewetting of the transferred film, which eventually led to the formation of dendritic fractals. A similar pattern was not detected in the films of CTA, CAP and CAB however, it was found that the acetate and residual hydroxyl group content of the cellulose esters played a key role in the morphologies of the ultrathin films. The morphology of the cellulose derivative films could be tuned by regeneration, exposure to water or by altering film deposition surface pressure. The behaviour of the cellulose esters upon compression at the air/water interface was also thoroughly scrutinized by monitoring surface pressure-area Langmuir isotherms with a fast and slow compression. Results revealed the behavioural differences in monolayer assembly as a function of compression rate. The intricate relationship between cellulose-based materials and water was also studied using cellulose in its native form. The water vapour sorption behaviours of ultrathin films of cellulose nanocrystals (CNCs) and regenerated amorphous cellulose (from TMSC) along with films with a combination of both were studied using a quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry (SE). Quantitative analysis of the results showed that hydration of CNC networks occurs through the envelopment of the individual crystals by three monolayers of water. The water vapour response of the cellulose films became unexpectedly complex when CNCs were mixed with amorphous cellulose. Relative humidity studies showed that the crystalline/amorphous ratio of films containing both types of cellulose played a critical role in water vapour adsorption. Adsorption in films with a similar ratio to that prevalent in the woody plant cell wall (~50/50) was promoted by the addition of CNCs, whereas in predominantly amorphous films it was inhibited.
|Translated title of the contribution||Selluloosapohjaisten materiaalien kaksiulotteinen järjestyminen|
|Publication status||Published - 2016|
|MoE publication type||G5 Doctoral dissertation (article)|
- cellulose derivatives
- cellulose nanocrystals