Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Mechanical Engineering | en_US |
| dc.contributor.advisor | Yao, Haimin (ME) | en_US |
| dc.creator | Zhang, Zijing | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14356 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Moisture-responsive behavior of hygroscopic membranes : from mechanistic understanding to rational regulation | en_US |
| dcterms.abstract | Moisture-responsive membranes have attracted increasing attention in the fields of actuators and energy harvesting due to their lightweight and high flexibility. For instance, bilayer membranes are often employed in humidity sensors because of their rapid and precise hygroscopic deformation. However, the underlying mechanical mechanisms and regulation strategies governing hygroscopic deformation remain largely unexplored, and this lack of fundamental understanding limits further development of such materials. To address these challenges, this thesis systematically investigates the mechanics of hygroscopic membrane deformation under humidity stimuli, aiming to establish a comprehensive theoretical framework and propose rational regulation strategies. | en_US |
| dcterms.abstract | This thesis is organized into three core research chapters (Chapters 4-6), focusing on two distinct types of membrane system and their corresponding mechanical insights. In Chapter 4, the deformation of bilayer membranes under different humidity fields was systematically investigated by extending a classical thin-film mechanics model to derive analytical solutions for the curvature-humidity relationship. Bilayer systems composed of MXene/NP as the active layer and PVC as the inert layer were fabricated, and the theoretical predictions were validated through both finite element simulations and experiments. The results demonstrate that our model not only predicts the deformation configuration but also assesses the stability of free-standing membranes under arbitrary humidity fields, while clarifying their dependence on the physical properties of each layer. These findings provide a robust mechanical foundation for predicting bilayer hygroscopic deformation and hold great potential for their applications in sensors and actuators. | en_US |
| dcterms.abstract | In Chapter 5, monolayer stacked nanoflake assemblies (SNA) membranes were found to exhibit more complex hygroscopic responses. Unlike the static bending observed in bilayers, SNA membranes placed in humidity fields above a hot water bath exhibited autonomous oscillatory behavior. Comparative experiments revealed that this oscillation originates from the coupling between humidity gradients along the height and the reversible hygroscopic expansion of the membrane. Theoretical analysis, integrating water diffusion with beam vibration theory, uncovered the fundamental mechanics of this phenomenon. Furthermore, dimensional analysis established quantitative relations between oscillation characteristics, intrinsic material properties, and external humidity fields. These results provide valuable insights for understanding and predicting the oscillatory behavior of SNA membranes, which is crucial for their application in actuators and energy harvesting. | en_US |
| dcterms.abstract | In Chapter 6, the practical implications of such autonomous oscillations are explored. Inspired by biological propulsion, a fluke-inspired propulsion system driven by SNA membranes was demonstrated, along with a hand-moisture-powered nanogenerator based on electromagnetic induction. These proof-of-concept demonstrations further confirm the functional importance of our findings. Additionally, systematic experiments revealed the failure mechanisms of SNA membranes under prolonged humid operation, including oxidation in MXene/NP membranes and hygroscopic saturation in GO/SA membranes. Importantly, the theoretical framework also successfully explains the disappearance of oscillatory behavior after decay, providing guidelines for improving the durability and performance of SNA membranes. | en_US |
| dcterms.abstract | Overall, this thesis establishes a systematic and in-depth framework for understanding and regulating the hygroscopic deformation of membranes. By bridging theoretical modeling, finite element simulations, and experimental validation, it not only develops a solid mechanical foundation for both bilayer and monolayer systems but also proposes strategies to achieve controlled, predictable, and durable deformation responses. The results provide valuable guidance for the structural design and optimization of hygroscopic membranes, with broad application prospects in soft actuators and energy harvesting devices. Ultimately, the framework developed herein is expected to accelerate the development of multifunctional hygroscopic membrane systems and their integration into next-generation smart devices. | en_US |
| dcterms.extent | xxiv, 139 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Membranes (Technology) | en_US |
| dcterms.LCSH | Moisture | en_US |
| dcterms.LCSH | Actuators | en_US |
| dcterms.LCSH | Energy harvesting | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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