Bending, Twisting, and Snapping of Thin Films    

D.P. Holmes, M. Roche, T. Sinha, and H.A. Stone, In Preparation, 2010

Soft biological tissues exhibit complex patterns due to their nonlinear responses to large stresses and strains.  These behaviors become increasingly significant when observing the instabilities that occur during the growth of soft tissues.  In this paper, we present the dynamic instabilities that occur by anisotropically swelling an elastic gel.  We examine how thing elastic plates can undergo rapid bending, buckling, and twisting when swollen with a favorable solvent.

Geometry Controlled Vesicle Adsorption and Formation   

M. Staykova, D.P. Holmes, and H.A. Stone, In Preparation, 2010.

Lipid membranes have been prepared on various substrates, including: flat, wrinkled, porous, rigid, and compliant.  In our experiments, lipid membranes are prepared on an elastic substrate, allowing us to study their to geometric constraints. A biaxial increase in the surface area of the underlying substrate placed the membrane under tension and facilitated the fusion of vesicles onto it. Accordingly, the compression of the supported membrane led to lipid jamming that resulted in the formation of nano-tubes anchored to the membrane.

Draping Films: A Wrinkle to Fold Transition    

A polymer film draping over a point of contact will wrinkle due to the strain imposed by the underlying substrate.  The wrinkle wavelength is dictated by a balance of material properties and geometry; most directly the thickness of the draping film.  At a critical strain, the stress in the film will localize, causing hundreds of wrinkles to collapse into several discrete folds.  In this paper, we examine the deformation of an axisymmetric sheet and quantify the force required to generate a fold.   The onset of folding, in terms of a critical force or displacement, scales as the thickness to the four-ninth power, which we predict from the energy balance of the system.  The folds increase the tension in the remainder of the film causing the radial stress to increase, thereby decreasing the wavelength of the remaining wrinkles.  

Folded Polymer Films     

D.P. Holmes, A. Davis, A.J. Crosby, In Preparation, 2010.

The folding of ultrathin films in confined geometries will provide insight to the material's properties, as well as insight into controlling the next generation of nanoscale feature morphology and structure.  In this paper, we present scaling relationships to predict the sharpness of deformed features, ranging from macroscopic to nanoscopic.  The sharpness ratio of the features achieved on the polystyrene films is near unity for adequately high uniaxial compressive strains.  The film thickness of the polystyrene films presented in this chapter are on the order of the material length scale, leading to the fabrication of sharply folded nanostructures.  While the width of these structures vary from tens to hundreds of nanometers, their lengths are typically several hundred microns to many millimeters.

Crumpled Surface Structures    

D.P. Holmes, M. Ursiny, and A.J. Crosby.  Soft Matter, 4, 82, 2008. [PDF]

The topographic control of pattern features is of great interest for a range of applications including the generation of ultrahydrophobic surfaces, microfluidic devices, and the control and tuning of adhesion.  In these areas, surface patterning is achieved by a variety of techniques including: photolithography, imprint lithography, and surfaces wrinkling.  In this paper, we present a scalable patterning method based on surface plate buckling, or crumpling, to generate a variety of topographies that can dynamically change shape and aspect ratio in response to stimuli.

Snapping Surfaces    

The responsive mechanism of the Venus flytrap has captured the interest of scientists for centuries.  Although a complete understanding of the mechanism controlling the Venus flytrap movement has yet to be determined, a recent publication highlights the importance of geometry and material properties for this fast, stimuli-responsive movement.  Specifically, the movement is attributed to a snap-through elastic instability whose sensitivity is dictated by the length scale, geometry, and materials properties of the features.  Here, we use lessons from the Venus flytrap to design surfaces that dynamically modify their topography.  We present a simple, biomimetic responsive surface based on an array of microlens shells that snap from one curvature to another when a critical stress develops in the shell structure.