One-Step Nanoscale Assembly of Complex Structures via Harnessing of an Elastic Instability

Laboratory for Research on the Structure of Matter, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104, USA.
Nano Letters (Impact Factor: 13.59). 05/2008; 8(4):1192-6. DOI: 10.1021/nl0801531
Source: PubMed


We report on a simple yet robust method to produce orientationally modulated two-dimensional patterns with sub-100 nm features over cm2 regions via a solvent-induced swelling instability of an elastomeric film with micrometer-scale perforations. The dramatic reduction of feature size ( approximately 10 times) is achieved in a single step, and the process is reversible and repeatable without the requirement of delicate surface preparation or chemistry. By suspending ferrous and other functional nanoparticles in the solvent, we have faithfully printed the emergent patterns onto flat and curved substrates. We model this elastic instability in terms of elastically interacting "dislocation dipoles" and find complete agreement between the theoretical ground-state and the observed pattern. Our understanding allows us to manipulate the structural details of the membrane to tailor the elastic distortions and generate a variety of nanostructures.

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Available from: Pei-Chun Lin, Jan 28, 2014
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    • "Surface wrinkling is a form of instability occurring in mechanical systems [1] [2] [3] [4] [5] [6]. Similar to buckling, surface wrinkling is also caused by a bifurcation in the solution of the equations of static equilibrium. "
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    ABSTRACT: We report on the development of a PDMS-SMA composite whose surface micro wrinkles can be dynamically programmed by an electrical current supplied to the SMA wire. It is advantageous over other techniques for surface topographical modulation, including portability, real-time programmability, no requirement for specific surface chemistry, operability under ambient conditions, and relative ease of control. A simplified mechanical model is also developed to describe the force-deflection balance of the PDMS-SMA composite. The wavelengths and amplitudes of the wrinkles when different currents applied to the SMA are characterized, and the experimental results agree with the theoretical model. The developed composite device can be applied to programmable modulations of surface adhesion, friction, wettability, etc.
    Full-text · Article · Oct 2014 · Smart Materials and Structures
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    • "When gel is immersed in solvent, the characteristic time for the swelling process of a gel film depends mainly on its thickness [Durning and Morman, 1993; Klein et al., 2007]. Besides the rapid responses, a thin polymeric gel film can develop a great variety of off-plane deformation patterns during swelling or deswelling, while part of it is constrained [Cerda and Mahadevan, 2003; Sharon et al., 2002; Klein et al., 2007; Zhang et al., 2008; Trujillo et al., 2008; Brochard-Wyart and de Gennes, 2003; Southern and Thomas, 1965; Sidorenko et al., 2007; Mullin et al., 2007]. In this deformation process, not only the overall shape and morphology can be changed, but the curvature on each material point of the gel film can be modified on the fly [Klein et al., 2007]. "
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    ABSTRACT: One of the unique properties of polymeric gel is that the volume and shape of gel can dramatically change even at mild variation of external stimuli. Though a variety of instability patterns of slender and thin film gel structures due to swelling have been observed in various experimental studies, many are not well understood. This paper presents the analytical solutions of swelling-induced instability of various slender and thin film gel structures. We have adopted the well developed constitutive relation of inhomogeneous field theory of a polymeric network in equilibrium with a solvent and mechanical load or constraint with the incremental modulus concept for slender beam and thin film gel structures. The formulas of buckling and wrinkle conditions and critical stress values are derived for slender beam and thin film gel structures under swelling-induced instability using nonlinear buckling theories of beam and thin film structures. For slender beam structure, we construct the stability diagram with the distinct stable and unstable zones. The critical slenderness ratio and corresponding critical stresses are provided for different dimensionless material parameters. For thin film gel structures, we consider the thin film gel on an elastic foundation with different stiffness. The analytical solutions of critical stress and corresponding wrinkle wavelength, as well as buckling condition (or critical chemical potential) are given. These analytical solutions will provide a guideline for gel structure design used in polymeric gels MEMS and NEMS structures such as sensors and actuators. More importantly, the work provides a theoretical foundation of gel structure buckling and wrinkle, instability phenomena are different from normal engineering or material buckling.
    Full-text · Article · Apr 2012 · International Journal of Applied Mechanics
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    • "Experimental studies have shown complex material behaviors of gels (Li and Tanaka, 1992; Tokarev and Minko, 2009). Subject to geometric confinement and/or mechanical constraint, a variety of instability patterns have been observed in gel-like materials (Southern and Thomas, 1965; Tanaka et al., 1987; Matsuo and Tanaka, 1992; Tirumala et al., 2005; Mora and Boudaoud, 2006; Sultan and Boudaoud, 2008; Trujillo et al., 2008; Zhang et al., 2008). Of particular interest, surface wrinkling of swollen rubber vulcanizates was observed by Southern and Thomas (1965), who reported a critical swelling ratio of about 2.5 due to the effect of substrate constraint. "
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    ABSTRACT: In response to external stimuli, polymeric hydrogels can change volume and shape dramatically. Experimental studies have observed a variety of instability patterns of hydrogels, due to swelling or shrinking, many of which have not been well understood. The present paper considers swell-induced surface instability of a hydrogel layer on a rigid substrate. Based on a recently developed theoretical framework for neutral polymeric gels, a linear perturbation analysis is performed to predict the critical condition for the onset of the surface instability. Using a nonlinear finite element method, numerical simulations are presented to show the swelling process, with the evolution of initial surface perturbations followed by the formation of crease-like surface patterns. In contrast to previously suggested critical conditions for surface creasing, the present study suggests a material-specific condition that predicts a range of critical swelling ratios from about 2.5 to 3.4 and quantitatively relates the critical condition to material properties of the hydrogel system. A stability diagram is constructed with two distinct regions for stable and unstable hydrogels depending on two dimensionless material parameters.
    Full-text · Article · Oct 2010 · Journal of the Mechanics and Physics of Solids
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