Monodisperse polymer spheres

F. Caruso uses monodisperse polymer spheres and their colloidal crystals only as templates to create hollow capsules or extended opal arrays with the layer-by-layer technique. Again this is a typical colloid chemistry tool which is unparalleled in low molecular weight organic chemistry, and hollow mesostruc-tures systems with astonishingly high complexity and chemical function can be generated. 

Polymer Colloids Emulsion polymerization produces monodisperse polymer spheres 50 to 500 nm in diameter by the scheme shown in Figure 11.9. Water-immiscible vinyl monomers such as styrene, acrylic esters, and methacrylic... 

Coating PANI onto various matrixes has been studied for a long time [38,39]. In particular, monodispersed particles with a perfect spherical shape are generally preferred as model ER materials to investigate ER effect since the morphology of the dispersed phase is one of the critical parameters. However, PANI particles synthesized by conventional oxidization polymerization are often of irregular shape. Therefore, to obtain monodispersed PANI ER particles, researchers have used monodispersed polymer spheres as core to develop various PANI-coated ER particles. For example, Jun et al. [40,41] have used monodisperse micron-sized porous... 

Thermoreversible polymer hydrogels also represent a medium for synthesis of nanosized zeolite crystals. This support is recyclable and stable in the temperature range of interest for zeolite synthesis. In aqueous media, the voids between monodisperse polymer spheres can serve as a nanoreactor for controlled growth [157]. Recycling of the support can be done via dissolution of... 

An important step in tire progress of colloid science was tire development of monodisperse polymer latex suspensions in tire 1950s. These are prepared by emulsion polymerization, which is nowadays also carried out industrially on a large scale for many different polymers. Perhaps tire best-studied colloidal model system is tliat of polystyrene (PS) latex [9]. This is prepared with a hydrophilic group (such as sulphate) at tire end of each molecule. In water tliis produces well defined spheres witli a number of end groups at tire surface, which (partly) ionize to... 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

Recent experimental studies (1-3), on systems of sterically stabilized colloidal particles that are dispersed in polymer solutions, have highlighted the role played by the free polymer molecules. These experiments are particularly relevant because the systems chosen are model dispersions in which the particles can be well approximated as monodisperse hard spheres. This simplifies the interpretation of the data and leads to a better understanding of the intcrparticle forces. DeHek and Vrij (1, 2) have added polystyrene molecules to sterically stabilized silica particles dispersed in cyclohexane and observed the separation of the mixtures into two phases—a silica-rich phase and a polystyrene-rich phase—when the concentration of the free polymer exceeds a certain limiting value. These experimental results indicate that the limiting polymer concentration decreases with increasing molecular weight of... 

As for the preparation of colloidal crystals using polymer spheres, the monodispersity of the cells strongly influences the order of the material. Hence yeast cells were carefully grown to form spherical cells of similar diameter. These cells were dip coated with a silica sol on a microscope slide [39]. A mono-layer of the cells arranged in a hexagonal close packing form on the microscope slide. The interstitial sites between the cells contained silica, an SEM image of the film is shown in Fig. 4. The cells remain alive and such films have potential applications in catalysis and as sensors. 

Ikawa T, Mitsuoka T, Hasegawa M, Tsuchimori M, Watanabe O, Kawata Y. 2001b. Azobenzene polymer surface deformation due to the gradient force of the optical near field of monodispersed polystyrene spheres. Phys Rev B 64 195408. 

Monodisperse latex spheres of a controlled size can be arranged into three-dimensional arrays and are used as templates to prepare well-defined cavities and structures once the latex sphere template has been removed. These latex spheres are identical to one another in size and shape and are often prepared from colloidal clusters resulting from the aggregation of sol-gel colloids (Section 5.6). The spherical polymer clusters can be fabricated by the slow addition of an aqueous solution into a reservoir of hydrophobic silicone liquid, forming emulsion droplets. This produces a highly structured porous matrix with a well-defined structure upon polymerisation. The size of the droplets is controlled by the concentration of the aqueous latex, the speed at which the suspension is stirred and the ratio between the silicone liquid and latex. As the concentration of the latex spheres increases to its critical concentration, i.e. the concentration at which the colloidal spheres start to order themselves into a close-packed structure, the balls are filtered off and are dried, ready to be used as templates. 

In the introductory chapter we saw that many systematic depletion studies were performed on mixtures of spherical colloids plus non-adsorbing or free polymers. The reason is obvious spherical colloids are of industrial and fundamental relevance, and can be prepared in a relatively controlled way (rather monodisperse, hard-sphere like), while polymers are ubiquitous, and are efficient depletants. 

The phase behaviour of mixtures of monodisperse hard spheres and polydisperse ideal polymers has been investigated using original FVT [67]. At fixed mean... 

Iridescence due to Bragg diffraction of visible light is exhibited by electrolyte-free monodisperse polymer latexes, and also by redispersions of the polymer spheres in certain polar organic media. The center-to-center particle separation D, the particle diameter D, and the volume fraction ( ) are related by < >(D/D =... 

Both linear and cross-linked monodisperse latexes of polystyrene in the size range 0.1 - 1.2y have been prepared by persulfate-initiated emulsion polymerization (6,7,8), and the size and size distributions of the polymer spheres detennined by electron microscopy. Free electrolyte was removed by a mixed-bed ion exchange resin, and surface charge measured by conductometric titration against standard base. Redispersion in organic media was effected by successive dialyses, first with methanol and finally against the desired solvent. 

Ahnog Y, Reich S, Levy M. Monodisperse polymeric spheres in the micron size range by a single step process. Braz Polym J 1982 14 131-136. 

A monodisperse hard sphere is packed in a faee-centered cube with the porosity of 0.295 and orthorhombic system with the porosity of 0.395. The porosities of dry superabsorbent polymers are generally 0.40 to 0.75, and are higher than a hard sphere, for example, a glass bead. However, the permeability of superabsorbent polymers is much lower than glass bends of a similar thiekness. 

The scaling exponent a can be related to the particle shape. One finds a = 2,0, 0.5, and 0.8 for a thin rod, solid sphere, ideal chain, and swollen chain, respectively. For most polymers K and a have been tabulated [23]. For a monodisperse sample Equation (36) can be used for a crude determination of the molar mass ... 

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