Microstructuring of polystyrene surfaces with nonsolvent sessile droplets

Herein, we study the microstructuring of toluene-vapor-softened polystyrene surfaces with nonsolvent sessile droplets. Arrays of microvessels are obtained by depositing non-evaporating droplets of ethylene glycol/water on the original polystyrene surfaces and subsequently exposing them to saturated toluene vapor. The droplets act as a mask on the polymer, thereby impeding the toluene vapor to diffuse and soften the polystyrene surface below them. Alternatively, the formation of microcraters at random positions-with an average depth-to-width aspect ratio of 0.5 and a diameter as small as 1.5 mu m-is achieved by condensing water droplets on a softened polystyrene surface. The cross-sections of the microvessels and the contact angle of the sessile water droplets suggest that the structures are formed by the combined action of the Laplace pressure at the bottom of the droplet and the surface tension acting at the three-phase contact line of the droplets. As a support, the rim height and the depth of the microvessels are fitted with an elastic theory to provide Young's modulus of the softened polystyrene surface

Soft Cells for Programmable Self-Assembly of Robotic Modules

Programmable self-assembly of chained robotic systems holds potential for the automatic construction of complex robots from a minimal set of building blocks. However, current robotic platforms are limited to modules of uniform rigidity, which results in a limited range of obtainable morphologies and thus functionalities of the system. To address these challenges, we investigate in this paper the role of softness in a programmed self-assembling chain system. We rely on a model system consisting of “soft cells” as modules that can obtain different mechanical softness presettings. Starting from a linear chain configuration, the system self-folds into a target morphology based on the intercellular interactions. We systematically investigate the influence of mechanical softness of the individual cells on the self-assembly process. Also, we test the hypothesis that a mixed distribution of cells of different softness enhances the diversity of achievable morphologies at a given resolution compared to systems with modules of uniform rigidity. Finally, we illustrate the potential of our system by the programmable self-assembly of complex and curvilinear morphologies that state-of-the-art systems can only achieve by significantly increasing their number of modules

Interaction forces and molecular adhesion between pre-adsorbed poly(ethylene imine) layers

Interaction forces between pre-adsorbed layers of branched poly(ethylene imine) (PEI) of different molecular mass were studied with the colloidal probe technique, which is based on atomic force microscopy (AFM). During approach, the long-ranged forces between the surfaces are repulsive due to overlap of diffuse layers down to distances of a few nanometers, whereby regulation of the surface charge is observed. The ionic strength dependence of the observed diffuse layer potentials can be rationalized with a surface charge of 2.3 mC/m(2). The forces remain repulsive down to contact, likely due to electro-steric interactions between the PEI layers. These electro-steric forces have a range of a few nanometers and appear to be superposed to the force originating from the overlap of diffuse layers. During retraction of the surfaces, erratic attractive forces are observed due to molecular adhesion events (i.e., bridging adhesion). The frequency of the molecular adhesion events increases with increasing the ionic strength. The force response of the PEI segments is dominated by rubber-like extension profiles. Strong adhesion forces are observed for low molecular mass PEI at short distances directly after separation, while for high molecular mass weaker adhesion forces at larger distances are more common. The work of adhesion was estimated by integrating the retraction force profiles, and it was found to increase with the ionic strength. (c) 2005 Elsevier Inc. All rights reserved

Miniature curved artificial compound eyes.

International audienceIn most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories

Atomic force microscopy study of the adsorption and electrostatic self-organization of poly(amidoamine) dendrimers on mica

The adsorption behavior of poly(amidoamine) dendrimers to mica surfaces was investigated as a function of ionic strength and pH. The conformation and lateral distribution of the adsorbed dendrimers of generations G8 and G10 were obtained ex situ by tapping mode atomic force microscopy (AFM). The deposition kinetics of the dendrimers was found to follow a diffusion-limited process. Fractional surface coverage and pair correlation functions of the adsorbed dendrimers were obtained from the AFM images. The data are interpreted in terms of the random sequential adsorption (RSA) model, where electrostatic repulsion due to overlapping double layers is considered. Although the general trends typical for an RSA-determined process are well-reproduced, quantitative agreement is lacking at low ionic strengths

Vision Tape - a flexible compound vision sensor for motion detection and proximity estimation

In this paper, we introduce Vision Tape (VT), a novel class of flexible compound-eye-like linear vision sensor dedicated to motion extraction and proximity estimation. This novel sensor possesses intrinsic mechanical flexibility that provides wide-range adaptive shape, allowing adjustable field of view as well as integration with numerous substrates and curvatures. VT extracts Optic Flow (OF) of the visual scene to calculate the motion vector, which allows proximity estimation based on the motion parallax principle. In order to validate the functionality of VT, we have designed and fabricated an exemplary prototype consisting of an array of eight photodiodes attached to a flexible PCB that acts as mechanical and electrical support. This prototype performs image acquisition and processing with an integrated microcontroller at a frequency of 1000 fps, even during bending of the sensor. With this, the effect of VT shape on motion perception and proximity estimation is studied and, in particular, the effect of pixel-to-pixel angle is discussed. The results of these experiments allow estimating an optimal configuration of the sensor for OF extraction. Subsequently, a method that enhances the quality of extracted OF for non-optimal configurations is proposed. The experimental results show that, by applying the proposed method to VT in a suboptimal curvature, the quality of the OF can be increased by up to 176% and proximity estimation by 178%

Effective Charge of Adsorbed Poly(amidoamine) Dendrimers from Direct Force Measurements

Interaction forces between silica surfaces with adsorbed poly (amidoamine) (PAMAM) dendrimers were measured with the colloidal probe technique based on the atomic force microscope (AFM). At small separations, attractive non-DLVO forces are observed. These forces likely originate from interactions between oppositely charged patches on the surfaces, resulting from the heterogeneous distribution of the adsorbed positively charged dendrimers on the negatively charged surface. At large separation distances, the interaction forces are repulsive and consistent with DLVO theory. These forces can be interpreted quantitatively as originating from the overlap of diffuse layers of positively charged surfaces in terms of the Poisson-Boltzmann theory. From the resulting diffuse layer potentials, one can extract the effective charge of the dendrimers in the adsorbed state. This effective charge is about half of the ion condensation value given by Poisson-Boltzmann theory for a charged spherical macromolecule in solution for the different dendrimer generations investigated. This reduction probably originates from the smaller volume available for the diffuse layer of adsorbed macromolecules, but charge neutralization may also play an essential role