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Functional Nanocomposite Hydrogels Based on Cellulose Nanocrystals

dc.contributor.advisorZhang, Kai Prof. Dr.
dc.contributor.authorWang, Xiaojie
dc.date.accessioned2020-11-03T15:12:20Z
dc.date.available2021-01-31T23:50:02Z
dc.date.issued2020-11-03
dc.identifier.urihttp://hdl.handle.net/21.11130/00-1735-0000-0005-14D9-0
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-8277
dc.language.isoengde
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject.ddc634de
dc.titleFunctional Nanocomposite Hydrogels Based on Cellulose Nanocrystalsde
dc.typecumulativeThesisde
dc.contributor.refereeZhang, Kai Prof. Dr.
dc.date.examination2020-07-31
dc.description.abstractengHydrogels are ubiquitous in nature, which are three-dimensionally (3D) crosslinked polymer networks with amounts of water inside. Naturally, they can be regarded as semi/solid showing intermediate properties of solid and liquid. Hydrogels have attracted growing interest in diverse applications, due to their excellent biocompatibility, permeability, and 3D network. With the development of polymer synthesis, great progress in tough hydrogels, and continuous emerging of advanced fabrication methods, hydrogels become promising functional materials. To further broaden their practical usages, great efforts have made to hydrogel functionalization, which mainly focused on both polymer network and architectures within hydrogels. Normally, functional hydrogels were fabricated from stimuli-responsive polymers, cleavable bonding, inhomogeneous or aligned microstructures, especially, functionalization by diverse nanoparticle composites. In this study, cellulose nanocrystals (CNCs) as one of the bio-based natural nanoparticles were investigated in hydrogel functionalization owing to their excellent mechanical properties, facile surface modification and unique optical properties. CNCs and surface modified CNCs were introduced into synthetic hydrogels to ensure the implementation of specific functions of hydrogels. CNCs and surface modified CNCs with methyl acrylamide groups (CNCs-MAm) were incorporated into thermal-responsive and solvent-driven bilayer hydrogel actuators (BHAs). The introduction of CNCs and CNCs-MAm significantly improved the mechanical properties of BHAs and ensured largely promoted lifting capability for them. The weight-lifting capability of BHAs was promoted from ~800 wt% to ~1800 wt% of their own polymer weight. Furthermore, the CNCs with numerous carboxyl groups on the surface can apparently increase the spatial distinction of dynamic hydrogels. When ferric ions were introduced along with diffusion from outside to inside of hydrogels, the carboxyl groups would complex with ferric ions. This additional crosslinking retarded the penetration of ferric ions, increasing the spatial crosslinking difference. This promoted spatial distinction assisted in fabricating closed hollow hydrogels with tunable microstructures of the inner and outer walls. CNCs can accelerate the process of spatial separation to form the hollow interior in around 9 days of dialysis, whereas, about 20 days of dialysis for non-composite hydrogels. Distinguished from typical thermal controlled release system, this hollow hydrogel showed unique sustained release of hydrophilic small molecules at higher temperature. It would reach release equilibrium after only ~24 h at 25 oC, while the release equilibrium was largely retarded to ~200 h at 37 oC as comparison. In addition, as one-dimensional nanomaterials, CNCs and gold nanorods (GNRs) are widely used in optical materials due to their respective inherent natures: birefringence with accompanying light retardation in aligned CNCs and surface plasmon resonance (SPR) of GNRs. These properties of both nanorods were combined to generate synergistic and readily tunable structural colors of polymer films. The CNCs and GNRs are embedded either in the same hybrid composite films or in separated films after their unidirectional alignment from dynamic precursor hydrogels. By synergistically leveraging the optical features of CNCs and GNRs with diverse amounts in hybrid films or in stacked individual films, wide-ranging structural colors were realized, which is far beyond the limitation of the same films solely with aligned CNCs or GNRs. Increasing GNRs contents leads to promoted color red with enhanced light absorption at 520 nm and CNCs influence the overall phase retardation, giving distinctively structural colors. Furthermore, with angle adjustment between CNCs films and GNRs films using stacking/rotating technique, we further achieve facile and continuous color manipulation easily for color combinations. In one set of stacked films, light absorption wavelengths can traverse from roughly 500 nm to 650 nm solely by rotating GNRs film (0-180°). Tuning the adjustable synergism of the birefringence of CNCs and SPR of GNRs in one film or separate films provides great potential for structural colors, which enlightens new avenue for optical applications. This thesis is a cumulative work including 3 publications. One of them was already published and two are under submission. The background, the objective of the study, results and discussion of these three publications and the conclusion are presented in Sections 1-4.de
dc.contributor.coRefereeRehfeldt, Florian Dr.
dc.subject.enghydrogelde
dc.subject.engcellulose nanocrystalsde
dc.subject.engactuatorde
dc.subject.engStructural color filmde
dc.subject.enghydrogel containerde
dc.identifier.urnurn:nbn:de:gbv:7-21.11130/00-1735-0000-0005-14D9-0-1
dc.affiliation.instituteFakultät für Forstwissenschaften und Waldökologiede
dc.subject.gokfullForstwirtschaft (PPN621305413)de
dc.description.embargoed2021-01-31
dc.identifier.ppn1737715929


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