Elastocapillary self-assembly: theoretical and experimental investigations of dynamic liquid-lamella systems

Li, Chengzhang

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https://hdl.handle.net/2142/127465 Copy

Description

Title

Elastocapillary self-assembly: theoretical and experimental investigations of dynamic liquid-lamella systems

Author(s)

Li, Chengzhang

Issue Date

2024-12-05

Director of Research (if dissertation) or Advisor (if thesis)

Tawfick, Sameh H

Doctoral Committee Chair(s)

Tawfick, Sameh H

Committee Member(s)

• Hilgenfeldt, Sascha
• Feng, Jie
• Vella, Dominic

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Elastocapillarity, surface tension, capillary effect, fluid-structure interaction, elastic deformation, lubrication theory, Bond number, self-assembly, dynamics

Abstract

In biological systems, animals find strategies to deal with elastocapillary effects that could lead to the unintentional collapse of elastic structures at liquid interfaces. These effects arise when the elastic forces due to the deformation of slender solid structures are comparable to the capillary forces of a small drop or meniscus. For example, water-breathing animals, which use flexible high surface area gills, carefully interact with the liquid-air interface, such as when fish float near the surface. In air, fish gill lamellae tend to collapse, leading to fish suffocation due to oxygen depletion. However, some amphibious fish have evolved strategies to prevent elastocapillary-induced lamellae collapse, while others allow their lamellae to deform and develop a different morphology to adapt to capillary forces when near the water surface. Understanding elastocapillarity offers insights into the behavior of these animals and could help develop strategies to extend the survival time of fish in air during or after fishing. In engineering systems, elastocapillarity has initially been considered a detrimental collapse mechanism of microscale systems triggered by liquid wetting. However, later, scientists exploited capillary self-assembly to form geometrically complex structures across scales, particularly at the sub-mm scales. Such structures can be fabricated into their final shape by elastocapillarity, or can dynamically and reversibly morph their shape due to fluid structure interactions involving capillarity. Self-directed capillary forces can change the geometry of nanostructured materials after synthesis to enable their precise self-assembly from the nano- to the macro-scale. Despite these proof-of-concepts, process control and repeatability remain challenges towards their industrial-scale applications. This can be explained by the important role of dynamics of elastocapillarity which had not been systematically studied experimentally or theoretically. Many studies have studied the static equilibrium configurations of elastic structures under the effect of capillarity. However, integrating dynamic factors, such as time-varying forces or changes in liquid volume, into these models presents a considerable challenge. For instance, existing models do not explain phenomena such as the impact of dynamic drainage flow, the possibility of various self-assembly modes, the meniscus development under liquid volume constraints, or the effect of gravitational forces. In my thesis, I present experiments and reduced-order models that investigate the dynamic self-assembly of flexible lamellae dominated by elastocapillary effects. Several millimeter-scaled systems, comprising vertically placed elastomeric lamella and lamellae arrays, are designed and fabricated using 3D-printed molds. By dynamically controlling drainage flow, it is possible to control the self-directed capillary forces to reversibly change the geometry of slender lamellae. Each system is tested to characterize the significance of certain factors and to serve as a prototype for practical application. This is enabled by focusing on lamellae that have a thickness of a fraction of a millimeter and a height of a few millimeters, a size scale that cannot be achieved by traditional microfabrication. The reduced-order models represent each lamella as a discrete rigid element connected to the substrate by a torsional spring. I begin by analyzing the static equilibria of single and multi-lamella fixed to a submerged substrate as they emerge from the liquid interface, identifying the significant role of the developing meniscus in maintaining the equilibrium of the self-assembled morphology, as well as the relationship between stability and the liquid volume remaining in the system. Later, I integrated fluid flow using lubrication theory and the effects of liquid gravity into my analysis, formulating comprehensive dynamic models for each system. For single-lamella systems, my simulations successfully predict bimorphic behavior based on external drainage flow rates. For the multi-lamella system, I modeled the spontaneous coalescence due to the elastocapillary effect, where the gaps between the elastic lamellae are filled with liquid while the tips of the lamellae are initially fixed and then released. Accordingly, I derived a universal scaling law for maximum cluster size based on the model, which shows strong agreement with experimental and simulation results. Additionally, I study the morphology of multi-lamella systems under dynamic drainage, where I experimentally observe a unidirectional collapse pattern, termed the “dominos pattern,” under specific initial conditions or dynamic excitation, such as gradient drainage. The existence of the dominos pattern, suggested by my static equilibrium study, has been replicated by my comprehensive dynamic model under the same drainage conditions. The findings of this thesis have implications for biology and engineering. In biology, it can be used for studies of the evolution of lamellae in amphibian fish. In engineering, my analysis enables the design of polymorphic fins and lamellae devices, capillary self-folding structures, and capillary origami in engineering. Particularly, the analysis emphasizes the critical role of dynamic process modeling, and the possibility of reversible bi- and polymorphic assembly based on the rate of self-assembly.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127465

Copyright and License Information

Copyright 2024 Chengzhang Li

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