Abstract
The ability of liquid interfaces to shape slender elastic structures provides powerful strategies to control the architecture of mechanical self assemblies. However, elastocapillarity-driven intelligent design remains unexplored in more complex architected liquids – such as foams. Here we propose a model system which combines an assembly of bubbles and a slender elastic structure. Arrangements of soap bubbles in confined environments form well-defined periodic structures, dictated by Plateau's laws. We consider a 2D foam column formed in a container with square cross-section in which we introduce an elastomer ribbon, leading to architected structures whose geometry is guided by a competition between elasticity and capillarity. In this system, we quantify both experimentally and theoretically the equilibrium shapes, using X-ray micro-tomography and energy minimisation techniques. Beyond the understanding of the amplitude of the wavy elastic ribbon deformation, we provide a detailed analysis of the profile of the ribbon, and show that such a setup can be used to grant a shape to a UV-curable composite slender structure, as a foam-forming technique suitable to miniaturisation. In more general terms, this work provides a stepping stone towards an improved understanding of the interactions between liquid foams and slender structures.
Highlights
Combination of soft materials and fluids offer a rich physics in which both elasticity and capillarity come into play [1], opening an area of opportunity for novel materials and fabrication strategies in the case of slender elastic structures [2] and of bulk systems [3]
The question of complex deformation of an intruder in an architected medium has been widely studied in the case of granular media [15, 16] with applications in the context of root growth [17], a limited number of studies on model systems exist in the case of liquid foams, such as the analysis of simple arrangements of soap films interacting with rigid solids [18], and simulations of flexible fibres in foam under shear [19]
We focus on the dependence of the equilibrium shapes of ribbon-foam couples as a function of the competition between elasticity and capillarity in such systems, by introducing into the foam PDMS ribbons of 10 different thicknesses, ranging from 35 μm to 359 μm
Summary
Combination of soft materials and fluids offer a rich physics in which both elasticity and capillarity come into play [1], opening an area of opportunity for novel materials and fabrication strategies in the case of slender elastic structures [2] and of bulk systems [3]. Nature provides numerous examples such as the aggregation of wet hair [5] or the spooling of spider web in liquid droplets [6], serving progressively as a source of inspiration for the design of innovative materials [7] Turning catastrophic events such as capillarity-induced collapse [8] into robust microfabrication techniques [9, 10] has promissing impacts in electronics and energy harvesting, soft robotics, or even drug encapsulation and delivery [11, 12]. Further confinement of bubbles in columns of square-cross section results in welldefined ordered structures, provided that the enclosure dimensions are comparable to the bubble diameters [14] Such systems form periodically ordered liquid film architectures into which an elastic ribbon can be introduced. The question of complex deformation of an intruder in an architected medium has been widely studied in the case of granular media [15, 16] with applications in the context of root growth [17], a limited number of studies on model systems exist in the case of liquid foams, such as the analysis of simple arrangements of soap films interacting with rigid solids [18], and simulations of flexible fibres in foam under shear [19]
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