Colloidal crystalline

Similarly, charged solid particles (such as latex spheres) —kinetically stable lyophobic colloids —may exist in colloidal crystalline phases (with body-centered or face-centered cubic structures) as a consequence of thermodynamically favored reduction in free energies (see Chapter 13). Even neutrally charged spherical particles ( hard spheres ) undergo a phase transition from a liquidlike isotropic structure to face-centered cubic crystalline structures due to entropic reasons. In this sense, the stability or instability is of thermodynamic origin. 

Figure 2.1 The hard-sphere phase diagram. Below volume fraction < (f>] = 0.494, the suspension is a disordered fluid. Between <) >i = 0.494 and 02 = 0.545, there is coexistence of this disordered phase with a colloidal crystalline phase with FCC (or HCP) order the colloidal crystalline phase is the equilibrium one up to the maximum close-packing limit of 0cp = 0.74. Nonequilibrium colloidal glassy behavior can also occur between

Figure 4.20 Normalized intermediate scattering function versus time at a wavenumber near the peak in the static scattering function, for suspensions of hard, noninteracting, spherical particles. The curves are labeled by the volume fraction. The curve for 0 = 0.565 is in the glassy state where the relaxation is arrested after a short time of relaxation. Above the concentration 0 = 0.494 the equilibrium structure would be colloidal crystalline. (From van Megen and Pusey 1991, reprinted with permission from the American Physical Society.)...

Colloidal Crystalline Arrays Colloidal spheres of silica and of polymers can be made relatively monodisperse, with standard deviations of 4% of the mean diameter for silica and 1% for polymer latexes. The spheres pack as shown in Figure 11.22a from fluid dispersions into fee (sometimes hep or bcc) colloidal crystals (CC) by gravity, by membrane filtration, or by capillary forces at the surface of an evaporating dispersion (80-82). The crystalline order of the materials is strictly at the length scale of the packed colloidal particles the packing of the atoms and molecules within the silica and polymer particles is totally amorphous. The CCs diffract... 

Modification of the surfaces of coUoidal silica spheres with silane coupling agents enables transfer of the particles to nonpolar solvents. With 3-methacryloxypropyltri-methoxysilane bonded to the surface, the particles have been transferred from water to the polymerizable monomer, methyl acrylate. Electrostatic repulsion due to a low level of residual charge on the particle surfaces cause the dilute dispersions of particles to form a non-close packed colloidal crystalline array (CCA). Polymerization of the methyl acrylate with 200 nm diameter silica spheres in a CC fixes the positions of the spheres in a plastic film by the reactions shown in Figure 11.14. The difriaction... 

Precipitates have often been placed in one of three different categories based on their macroscopic appearance. A precipitate can be colloidal, crystalline, or curdy gelatinous. The kind of precipitate given by a specific salt has no correlation to its degree of insolubility but is determined by the particle size distribution of the precipitate, and its affinity toward the water molecules and ions of the surroimding solution. 

Definition Isolated, colloidal crystalline portion of cellulose fibers partially depolymerized acid hydrolysis prod, of purified wood cellulose... 

Synonyms Cellulose gel MCC Dehnition Isolated, colloidal crystalline portion of cellulose fibers partially depolymerized acid hydrolysis prod, of purified wood cellulose Properties Wh. fine cryst. powd., odorless partly sol. with swelling in dil. alkali insol. in water, dil. acids, and most org. soivs. bulk dens. 18-19 Ib/ft ref. index 1.55 pH 5-7 Toxicology LD50 (oral, rat) > 5 g/kg, no significant hazard irritant by inhalation (dust) may be damaging to lungs TSCA listed... 

Figure 28 Preparation of the photonic structural sensors from colloidal crystalline arrays (CCAs) is performed by in situ copolymerization of the polymerizable receptor to yield polymerized colloidal crystalline arrays (PCCAs). A receptor-analyte recognition process can affect the changes in the CCA periodicity, and, following Bragg s law, the wavelengths of diffracted and transmitted light, which serve as a signal for the sensing event.

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