Feeling through a film

Touch a liquid surface with a sharp needle and pull it gently – the force you exert is essentially determined by the surface tension of the liquid. This classical capillary phenomenon was revisited in a recent paper, published in Physical Review Letters, when a thin elastic film floats on the liquid surface. The presence of a film increases the force that is needed to poke the interface, as might be expected. Surprisingly, however, it is not the 3POKING newmechanical properties of the film that stiffen the interface, but rather the interplay between surface tension, hydrostatic pressure and the finite size of the sheet. This universal, material-independent response, is attributed to a novel geometrical concept that the authors call “asymptotic isometry”: Continue reading

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Drop deforms a thin solid

Imagine a liquid drop resting on the surface of a solid material. The classical picture, due to Young and Laplace, assumes that the drop rests on the substrate without deforming it. However, if the solid is sufficiently thin, the capillary forces affect its shape dramatically, yielding a pattern of wrinkles that emanate from the liquid-solid contact line (see attached figure). Continue reading

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A sheet on a drop presents: wrinkle-to-crumple transition

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Smooth wrinkles and sharply crumpled regions are familiar motifs in biological or synthetic sheets, such as rapidly growing plant leaves and crushed foils. Nevertheless, the generic route whereby a featureless sheet develops a complex shape remains elusive. Think for instance … Continue reading

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The curtain problem

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The question underlying pattern formation theory is how a complex shape emerges under featureless forces and constraints. The basic paradigm here relies on a fundamental principle in modern condensed matter theory: A spontaneous breaking of continuos symmetry. In a previous … Continue reading

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Smooth cascades

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How does one make a rippled sheet terminate at a straight edge? If the sheet is sufficiently thin, such as a piece of paper or fabric, then the obvious solution of stretching it out flat will induce large stresses near … Continue reading

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Understanding Wrinkling

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Wrinkling patterns are ubiquitous in elastic sheets of various types: plastic wraps, metallic foils, human skins, or plant leaves. Yet, the strong dependence of these patterns on physical parameters, such as the thickness of the sheet and the stretching forces, … Continue reading

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Elastic building blocks

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The cusp topography of a crumpled paper appears markedly different from a smooth wrinkled skin. Nevertheless, a work that was published recently in Phys.Rev.Lett. suggests that both morphologies may simply reflect different coexistence forms between a few common “elastic building blocks”. … Continue reading

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