Search

Micrograph analysis and characterization is a key function of many materials laboratories supporting manufacturing, quality control, and R&D. While classic methods are subjective and resource intensive, advancements in capture technology [...]

Penrose's pentagonal P2 quasi-crystal.sup.1-4 is a beautiful, hierarchically organized multiscale structure in which kite- and dart-shaped tiles are arranged into local motifs, such as pentagonal stars, which are in turn arranged into various close-packed superstructural patterns that become increasingly complex at larger length scales. Although certain types of quasi-periodic structure have been observed in hard and soft matter, such structures are difficult to engineer, especially over large areas, because generating the necessary, highly specific interactions between constituent building blocks is challenging. Previously reported soft-matter quasi-crystals of dendrimers.sup.5, triblock copolymers.sup.6, nanoparticles.sup.7 and polymeric micelles.sup.8 have been limited to 12- or 18-fold symmetries. Because routes for self-assembling complex colloidal building blocks.sup.9-11 into low-defect dynamic superstructures remain limited.sup.12, alternative methods, such as using optical and directed assembly, are being explored.sup.13,14. Holographic laser tweezers.sup.15 and optical standing waves.sup.16 have been used to hold microspheres in local quasi-crystalline arrangements, and magnetic microspheres of two different sizes have been assembled into local five-fold-symmetric quasi-crystalline arrangements in two dimensions.sup.17. But a Penrose quasi-crystal of mobile colloidal tiles has hitherto not been fabricated over large areas. Here we report such a quasi-crystal in two dimensions, created using a highly parallelizable method of lithographic printing and subsequent release of pre-assembled kite- and dart-shaped tiles into a solution-dispersion containing a depletion agent. After release, the positions and orientations of the tiles within the quasi-crystal can fluctuate, and these tiles undergo random, Brownian motion in the monolayer owing to frequent collisions between neighbouring tiles, even after the system reaches equilibrium. Using optical microscopy, we study both the equilibrium fluctuations of the system at high tile densities and also the 'melting' of the pattern as the tile density is lowered. At high tile densities we find signatures of a five-fold pentatic liquid quasi-crystalline phase, analogous to a six-fold hexatic liquid crystal. Our fabrication approach is applicable to tiles of different sizes and shapes, and with different initial positions and orientations, enabling the creation of two-dimensional quasi-crystalline systems (and other systems that possess multiscale complexity at high tile densities) beyond those of current self- or directed-assembly methods.sup.18-20. We anticipate that our approach for generating lithographically pre-assembled monolayers could be extended to create three-dimensional Brownian systems of fluctuating particles with custom-designed shapes through holographic lithography.sup.21,22 or stereolithography.sup.23.A lithographic patterning and release method is used to create a dense, fluctuating, Brownian system of mobile colloidal kite- and dart-shaped Penrose tiles over large areas that retains quasi-crystalline order., Author(s): Po-Yuan Wang [sup.1] [sup.2] , Thomas G. Mason [sup.1] [sup.3] Author Affiliations:(1) Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, USA(2) Department of Materials Science and [...]

The impulse acoustic microscopy method was applied to observe the bulk microstructure and to measure sonic velocities and elastic moduli in the carbon nanocomposite specimens prepared by a traditional method and with the use of a vacuum mixer. It is shown that carbon nanoparticles tend to cluster and form micron-sized aggregates. The impulse acoustic microscopy technique makes it possible to visualize a nonuniform distribution of carbon nanofillers over the specimen bulk. Both nanotube and nanoplatelets conglomerates are visible most likely due to the air containing. Results of the elastic measurements demonstrate homogeneity of elastic properties over the material bulk and a weak dependence of sonic velocities and elastic moduli on the filler content. Reduction of the air content and enhancement of elastic properties are observed when increasing the nanofiller content and employing the vacuum mixing technology in nanocomposite fabrication., INTRODUCTION Essential changes in material properties of nanocomposites result from formation of extensive networks of contacting nanoparticles with high values of the aspect ratio--nanotubes, nanoplatelets, nanoflakes, and so forth. A [...]

Non-destructive inspection of carbon fiber-reinforced (CFR) composites applied to aerospace industry attracts wide attention. In this article, high frequency (50-100 MHz) focused ultrasound has been applied to study defects and destruction processes in the bulk microstructure of the CFR material and constructions under the mechanical loading. It has been shown that the impulse acoustic microscopy provides detecting areas of structural failures and adhesion losses at the millimeter and micron level. Behavior of the CFR laminate structure fabricated by prepreg or infusion technology has been investigated under the tensile and impact loading., INTRODUCTION Application of fiber-reinforced polymers (FRP) is extensive in aviation industry due to their excellent strength-to-weight ratio. The sufficient strength is achieved by reinforcement of polymer matrix by regular packaging [...]