Direct observation of a buckling transition during the formation of thin colloidal crystals (original) (raw)
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Thin colloidal crystals : a series of structural transitions
Journal de Physique, 1983
2014 Nous étudions des couches minces de cristaux colloïdaux formés de billes de polystyrène de diamètre 1,1 03BCm en suspension aqueuse. Ces couches minces sont produites par le confinement des cristaux colloidaux entre deux plaques de verre rapprochées, lesquelles, aux échelles colloïdales, se comportent comme des parois répulsives et parfaitement lisses. Dans le cas où les deux plaques de verre forment un dièdre, nous réalisons le passage continu entre deux et trois dimensions. L'observation directe au microscope optique révèle que ce passage est caractérisé par une série de transitions structurelles consistant en un changement du nombre de couches cristallines mais aussi en un changement de structures dans les couches. Abstract. 2014 We study thin layers of colloidal crystals made of polystyrene balls (1.1 03BCm diameter) in aqueous suspension. These thin layers are produced by confining colloidal crystals between two glass planes, which act as repulsive and perfectly smooth boundaries at colloidal scales. When the two planes form a wedge, a continuous passage from 2 to 3 dimensions is realized. Direct observation with an optical microscope reveals that this passage is characterized by a series of structural transitions consisting of changes in the number of layers and also in the structure of each layer.
Layering transitions in confined colloidal crystals: The hcp-like phase
Physical Review E, 2007
This paper investigates the sequence of morphological transitions in a nearly hard sphere arrangement confined in a wedge cell. A model that shows smooth transitions between the different particle orderings for a small number of layers is proposed. In this model, both the buckling and the ͑100͒ hexagonal close packed ͑hcp͒ phases are particular cases of a much more general particle arrangement tendency that we call hcp-like ordering. This phase, which does not correspond to any known close packed ordering, is able to adopt packing arrangements commensurate with the cell thickness. More striking, the hcp-like phase adapts itself to the progressive changes of the cell thickness by a smooth change in the interlayer spacing. We present hcp-like orderings up to six layers and a complete sequence of transformations between two and four layers. Finally, a packing model of the transition from two to three layers is also presented.
Liquid-like behavior in colloidal crystals
Physica B: Condensed Matter, 1996
The van der Waals approach to predict liquid vapor coexistence, becomes exact in the limit of weak, long-ranged attractive forces. However, for shorter-ranged attractions, the liquid range shrinks and eventually disappears altogether. When the width of the attractive well becomes very small (less than 7% of the diameter of particles), an iso-structural solid-solid transition, reminiscent of the liquid-vapor transition, appears in the crystalline phase. This transition, that should be experimentally observable in certain colloidal suspensions, ends in a critical point. In quasi-two-dimensional systems (e.g. confined colloids), this critical point induces the formation of a stable hexatic phase.
Journal of Physics: Condensed Matter, 2006
We study the phase behaviour of hard spheres confined between two parallel hard plates using extensive computer simulations. We determine the full equilibrium phase diagram for arbitrary densities and plate separations from one to five hard-sphere diameters using free energy calculations. We find a first-order fluid-solid transition, which corresponds to either capillary freezing or melting depending on the plate separation. The coexisting solid phase consists of crystalline layers with either triangular () or square () symmetry. Increasing the plate separation, we find a sequence of crystal structures from • • • n → (n + 1) → (n + 1) • • •, where n is the number of crystal layers, in agreement with experiments on colloids. At high densities, the transition between square to triangular phases is interrupted by intermediate structures, e.g., prism, buckled, and rhombic phases.
Construction and stability of a close-packed structure observed in thin colloidal crystals
Physical Review E, 2007
We have characterized a close-packed structure of confined charged colloidal spheres, which has been recently discovered. Using different microscopy experiments, the vertically arranged hexagonal planes of n-hcpЌ are found to continuously evolve from the horizontally oriented stacks of n hexagonal planes ͑n⌬͒ following the maximum packing criterion, but discontinuously transform to a stack of n + 1 square planes ͓͑n +1͒ ᮀ ͔. Large mechanically stable domains with threefold twin structures are regularly observed in the suspended state at packing fractions between 0.4 and 0.58.
Anisotropic colloids through non-trivial buckling
The European Physical Journal E, 2008
We present a study on buckling of colloidal particles, including experimental, theoretical and numerical developments. Oil-filled thin shells prepared by emulsion templating show buckling in mixtures of water and ethanol, due to dissolution of the core in the external medium. This leads to conformations with a single depression, either axisymmetric or polygonal depending on the geometrical features of the shells. These conformations could be theoretically and/or numerically reproduced in a model of homogeneous spherical thin shells with bending and stretching elasticity, submitted to an isotropic external pressure.
Formation of two-dimensional colloid crystals in liquid films under the action of capillary forces
Journal of Physics: Condensed Matter, 1994
When two similar small particles are attached to a liquid interface they attract each other due to a lateral capillay force. This force appears because the gravitational potential energy of the floating particles decreases when they are approaching each other. This force is proportional to R6 ( R is the particle radius), so it decreaxs very fast with panicle size and becomes negligible for R c 10 Km. We found that the situation is quite different when ihe particles (instead of being freely floating) are panidly immersed in a liquid layer on a substrate. In this case the energy of capillary attraction is propaltional to R2 and "s out to be much larger than kT even with particles of diameter about 10 nm. The effect is related to the particle three-phme contact angle, i.e. to the intermolecular forces, rather than to gravity. The experiments show that the lateral capillary forces can bring about the formation of a twodimensional anay (20-crystal) h m both micrometre-size and submicrometre particles: latex spheres. protein globules. etc.
Stress-free production and effective medium model of colloidal crystals
Journal of Materials Chemistry, 2007
Colloidal crystals of silica spheres functionalized with N-trimethoxysilylpropyl-N,N,Ntrimethylammonium chloride have been formed by the Langmuir-Blodgett methodology (LB). Monolayers at the air/water interface of functionalized silica spheres have been characterized by surface pressure-area and surface potential-area isotherms and by Brewster angle microscopy (BAM). In order to control and optimize the production of such a colloidal crystal we have measured the diameter and order of spheres in the films, their defects and the density of spheres in each film. Morphologies of the Langmuir-Blodgett films were analyzed by scanning probe ellipsometric microscopy (SPEM) and by scanning electron microscopy (SEM). The results of SPEM are in agreement with the SEM results. The density distribution of colloidal crystals was evaluated using the ellipsometric data by means of the three-layer Brueggemann effective medium approach. The Langmuir-Blodgett methodology was successful for the synthesis of colloidal crystals without cracks. { Electronic supplementary information (ESI) available: range of color seen under different angles of a glass plate coated with a Langmuir-Blodgett film of silica spheres. See
Structure and dynamics of two-dimensional colloidal crystals in confined geometry
Progress in Colloid & Polymer Science
The properties of two-strongly dominated by the shape of R. Bubeck. S. Ncser Dr. C. Bechinger (m). P. Leidercr dimensional (2D) colloidal crystab those regions and anisotropic Fakultat fiir Physik have been wide1 y investigated during diffusion coefficients, indicating University of Konstanz the last 20 years, but only little a reduced mobility perpendicular to