Stress-free production and effective medium model of colloidal crystals (original) (raw)
Related papers
Structure and physical properties of colloidal crystals made of silica particles
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012
The relationship between the particles size distribution of colloidal crystals and the structure and physical properties of the resulting 2D colloidal crystals is presented in this work. The colloids were constituted of silica sub-micron spheres with different size distributions comprised between 150 and 520 nm, synthesized by the Stöber method and assembled in one monolayer through the Langmuir-Blodgett technique. Optical and wetting properties of the resulting crystals were studied by different techniques -UV-visible spectrometry, spectroscopic ellipsometry and contact angle measurements. They were related to the crystal structure which was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The conservation of orientational and translational orders over a large area is found for crystals with narrow particle size distribution. Optical interference bands in the transmittance spectra are linked to the crystal periodicity and the presence of optical anisotropy is attributed to distortions in the film generated by the deposition process. Moreover, large particle size distribution results in the most hydrophobic crystals. Thus the physical properties of the colloidal crystals can be tailored or tuned by controlling the particle size distribution and the deposition parameters.
Soft Matter, 2008
Discussions of the Structural and Mechanical Properties of the Langmuir Monolayer of the 1.5-µm Silica Particles For in situ imaging of the silica colloid monolayer at the air-water interface under various compression conditions, the miniaturized Langmuir trough equipment (Kibron Microtrough X-LB) was staged on a Leica DMIRB inverted microscope. All in situ imaging was performed in a vibration-controlled environment within a plexiglass chamber which prevents any disturbance of the silica monolayer at the air-water interface by air flow in the room and contamination of the interface due to dust accumulation. The representative images shown in Figure E1 were taken at an objective lens magnification of 40×. At low compression, the mean particle separation distance is sufficiently large (i.e., in the gas limit) (Figures E1(A) and E1(B)), and the dependence of π on A is almost unnoticeable in the linear presentation of the π vs. A plot. With further compression (i.e., when the interparticle distance is significantly decreased), the increase of π becomes slightly pronounced even though the system is still in the fluid phase (Figure E1(C)). At A ≈ 2.4 µm 2 per particle, further compression of the monolayer causes an abrupt increase of π, indicating the onset of formation of dense hexagonal close-packed structures (Figures E1(D) through E1(F)) due to the hard-core repulsive interaction among the silica particles. From the π-A isotherm data, the monolayer collapse pressure is estimated to be about 10 mN/m for the hydroxy silica particles used in this study; this value is considerably lower than those reported in the literature for hydrophobically surfacemodified silica particles (> 15 mN/m), 1-5 indicating a weaker interaction between adjacent particles in the solid phase in the hydroxyl functionalized case. The limiting area A o (the x-intercept of the extrapolated linear regression of the steepest section of the solid portion of the isotherm curve) is estimated to be approximately 1.97 µm 2 per particle. This limiting area can be interpreted as the theoretical onset of the hard-spherelike repulsion, and the estimated value is consistent with the theoretical surface area that would be occupied by a particle when the particles are packed into an HCP lattice (= 2 3 r 2 where r is the particle radius), i.e., 1.95 µm 2 per particle for the 1.5-µm silica, indicating that the actual range of the hard core exclusion is quite comparable to their physical diameter. We performed optical microscopy imaging under the identical sequence of compression conditions or in real time simultaneously to the measurements of the π-A isotherms, and identified the exact structures of the Langmuir monolayer which characterize the various states in the π-A isotherm that occur during the lateral compression of the particle monolayer; the results are shown in Figure E1. From the images taken from the fluid regime (Figures E1(A) through E1(C)), it was estimated that approximately 7% of the particles were lost from the water surface due to sedimentation into the subphase during the initial spreading process; however, it was confirmed that at least in the fluid regime and in the early stage in the development of the solid phase during the compression, no additional sedimentation occurred during the course of compression. It should be mentioned that in constructing the π-A isotherm shown in Figure 2 of the main text, we used the surface area per particle values corrected for the amount of the sedimented particles. As shown in Figures E1(A) though E1(D), we found that the transitions from the gaseous state (A and B) to the condensed liquid state (C) to the solid state (D) are rather smooth and continuous; we observed no evidence for a
Langmuir, 2001
This paper describes a convenient approach to the fabrication of fluidic cells to be used for crystallizing spherical colloids into three-dimensionally periodic lattices over large areas. The major component of the fluidic cell was a rectangular gasket sandwiched between two glass substrates. Here we demonstrate that these gaskets could be simply cut out of commercial Mylar films. Three non-photolithographic methods were also demonstrated to create shadow channels between the Mylar film and two glass substrates: (i) by wiping (along one single direction) both sides of the Mylar film with a piece of soft paper (Kimwipes EX-L); (ii) by coating both surfaces of the Mylar film with polymer beads whose size was smaller than those to be packed in the cell; and (iii) by patterning the surface of the bottom glass substrate with an array of gold channels using a combination of microcontact printing and selective etching. When an aqueous dispersion of monodispersed spherical colloids was injected into this packing cell, a crystalline lattice nucleated and grew from the edge(s) of the cell as a result of solvent depletion through the channels between the Mylar film and the glass substrates. The capability and feasibility of this new approach have been demonstrated by the fabrication of uniform opaline lattices of polystyrene beads and silica colloids over areas as large as several square centimeters. Because Mylar films with thicknesses in the range 20-100 µm are commercially available in large quantities and at reasonably low costs, the present approach offers a flexible tool to those who want to explore the use of large crystals of spherical colloids but have no access to clean room facilities.
Three-dimensional colloidal crystals with a well-defined architecture
Journal of colloid and interface science, 2004
Monodisperse silica spheres with diameters of 220-1100 nm were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in an alcoholic medium in the presence of water and ammonia. By grafting vinyl or amino groups onto silica surfaces using the coupling agents allyltrimethoxysilane and aminopropyltriethoxysilane, respectively, amphiphilic silica spheres were obtained and could be organized to form a stable Langmuir film at the air-water interface. The controlled transfer of this monolayer of particles onto a solid substrate gave us the ability to build three-dimensional regular crystals with a well-defined thickness and organization. These colloidal crystals diffract light in the UV, the visible, and the near-infrared (NIR) spectral regions, depending on the size of the silica spheres and according to Bragg's law. The depth of the photonic stop band can be tuned by varying the number of deposited layers of particles. By using successive depositions, we could prepare multilayered films with silica spheres of different sizes. The thickness of each slab in the binary crystals can be tuned at the layer level, while the crystalline order of each layer is well preserved.
Colloidal photonic crystals obtained by the Langmuir–Blodgett technique
Applied Surface Science, 2005
Monodispersed silica spheres with diameters of 220-1100 nm were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in an alcoholic medium in the presence of water and ammonia. By grafting vinyl or amine groups on silica surfaces using the coupling agents allyltrimethoxysilane and aminopropyltriethoxysilane, respectively, amphiphilic silica spheres were obtained and could be organized to form a stable Langmuir film at the air-water interface. The control led transfer of this monolayer of particles onto a solid substrate gave us the ability to build three-dimensional regular crystals with well-defined thickness and organization. These colloidal crystals diffract light in the UV, visible and the near-infrared (NIR) spectral regions, depending on the size of the silica spheres and according to the Bragg's law.
Colloidal crystallization of monodisperse and polymer-modified colloidal silica in organic solvents
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002
The formation of colloidal crystals from polymer-modified silica in organic solvent was studied. The colloidal crystallization of poly(maleic anhydride-styrene)-, polystyrene-and poly(methyl methacrylate)-modified silica took place in organic solvents, which were good solvents for the grafted polymer. It is, however, observed that there is a matching or a mismatching between the grafted polymer and solvent for the crystallization. The critical volume fraction ( o ) of the silica particles for the colloidal crystallization depended on the modified polymer, the extent of grafting, and molecular weight of the polymer. From the fact that o in the crystallization of poly(malic anhydride-styrene)-modified silica in acetonitrile decreased with the addition of a salt, NH 4 PF 6 , the crystallization occurred in the organic solvents due to the electrostatic repulsion between the particles, as well as those in aqueous solution. The neighboring inter-sphere spaces agreed well with the calculated values, which were obtained by the assumption of the close packing under electrostatic repulsion between the particles. It is suggested that the grafted polymer contributes to the enhancement of the elecrostatic interaction through electric double layer between the particles in the colloidal crystallization in organic solvent.
Colloid and Polymer Science, 2006
Thermo-sensitive colloidal crystals are prepared simply by mixing colloidal silica spheres and large thermosensitive gel spheres. The thermo-reversible change in the lattice spacing of colloidal crystals of monodisperse silica spheres (CS82, 103 nm in diameter) depends on the size of the admixed temperature-sensitive gel spheres. For spheres with sizes less and greater than that of the silica spheres, the lattice spacing upon temperature increase above the lower critical solution temperature of poly(N-isopropyl acrylamide) decreases (cf. Okubo et al. Langmuir 18:6783, 2002) and increases, respectively. A mechanism, which is able to explain these experimental findings, is proposed. Moreover, crystal growth rates and the rigidities of the thermosensitive colloidal crystals are studied.
Fabrication and characterization of colloidal crystal thin films
European Journal of Physics, 2011
We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained from the crystallization of a latex colloidal solution in a wedge cell. Depending on the thickness of the sample, microcrystals with different structures and orientation are obtained. Colloidal arrangements are studied by scanning electronic microscopy images of the top and edge views of several areas of the crystals.
Journal of Colloid and Interface Science, 2009
This short communication reports the observation that in contrast to most previously reported procedures, it is possible to prepare 3D photonic crystal structures from silica particles that have not been deliberately treated with surfactant molecules, using the Langmuir-Blodgett method. We find that colloidal particles prepared simply via the Stöber method with diameters in the range 180-360 nm and dispersed in ethanol, may be effectively floated at the air/water interface and compressed into close packed layers prior to depositing the layers on a substrate. We also find, by comparing structures made with both particles treated with the surfactants 3-(trimethoxysilyl) propyl methacrylate or (3aminopropyl)triethoxysilane and particles which have not been treated with any surfactant species, that the position of the Bragg peak and the reflectivity of the sample does not appear to be influenced by the presence of the surfactant molecules.
Journal of Colloid and Interface Science, 2004
Opalescent starburst patterns were formed on a convex surface by sedimenting colloidal silica spheres with a low silica volume fraction. The opalescent starburst patterns were also formed by the radial expansion of the meniscus when sedimented samples were slowly dried. The dependence of starburst formation on the rate of sedimentation and drying was experimentally investigated. Self-assembled opals fabricated from colloidal silica spheres grew vertically along the [100] direction of the face-centered cubic lattice. Elongated single-crystal crystallites nearly 1 cm wide and a few centimeters long formed in the curve at the bottom of an ordinary laboratory beaker from sedimenting 200-and 290-nm colloidal silica spheres. The elongated crystallites appear to be the result of an increased sedimentation rate, which creates favorable growth conditions. This is caused by the presence of the curve in the beaker and the spheres' inability to expand into the interior of the beaker before being sedimented. A narrowing of crystallites is shown to result from the competition between neighboring crystallites and large crystallites are shown to result from a lack of competition during their formation.