Comment of »Theory of the Formation of Colloidal Crystals« by Mirnik

Recently Mirnik discussed colloidal crystals1 on the basis of our experimental findings.2 He claimed that the hexagonal structure of one particle surrounded by six others is in reality impossible and what we observed is a not true apparent hexagonal packing. His argument was based on a simple cubic lattice (See Figure 2 in Ref. 1.), which he incorrectly presumed to exist in colloidal dispersions. It should be pointed out that a simple cubic lattice structure has never been observed for colloidal systems. Our micrographic study ,3 X-ray scattering4 and Kossel line analyses5 have established that the crystals belong to a face-centered-cubic (fee) or body-centered cubic (bcc) symmetry, depending on the latex concentration. The (111) plane of an fee structure provides a strictly hexagonal arrangement while the (110) plane of a bcc symmetry shows a slightly deformed hexagonal packing. Thus, his claim that 2Z)exp is apparent interparticle distance is unwarranted, particularly for the fee symmetry, it is actually the center-to- center distance between particles

Viscosity of Dilute Solutions of Polyelectrolytes

The viscosity measurements were performed with poly (vinyl alcohol) partially acetalized with glyoxylic acid, in solutions of a simple electrolyte, and Pals and Hermans' method of dilution was used. It was found that the extension of a macro-ion on the dilution line was kept constant over the polymer concentration range covered, utilizing our treatment as previously reported. A parameter, m, introduced in the method of dilution was known to be not far from the ratio of activity coefficients of polymeric and simple electrolytes. The “effective ionic strength” proposed by Pals and Hermans was suggested to be a significant quantity in dilute solutions of polyelectrolytes

»Ordering« Phenomena of Ionic Solutes in Dilute Solutions

In 1965 we carried out the determination of the mean activity coefficient of polyelectrolytes (r), curiously enough for the first time.\u27 Shortly thereafter we realized that In r showed the cube-root dependence on polymer concentration for hydrophylic macroions, instead of the square-root dependence

Potentiometric Titrations of a Polyelectrolyte

A study was carried out on the potentiometric titrations of poly(vinyl alcohol) partially acetalized with glyoxylic acid (PVAG). The titration curves were known to fulfil the relation proposed already by Pals and Hermans and the dissociation exponents were determined thereby. The radius of this polyacid was estimated from the electro-static free energy change by means of our theoretical treatment of polyelectrolyte solutions : it was found that the size decreased with the concentration, consistently with the well-known variation of the viscosity. Moreover, a potential potentiometrically obtained was shown not to be in agreement with the surface potential electrophoretically determined. This could be understood by referring the former to an average potential inside the spherical macro-ion

Electrophoresis of Polyelectrolytes : II. Electrophoretic Study of Poly (vinyl alcohol) Partially Acetalized with Glyoxylic Acid

Electrophoretic behaviors of a synthetic polyelectrolyte, poly(vinyl alcohol) partially acetalized with glyoxylic acid (PVAG), were studied. The mobility was found to be almost independent of the degree of polymerization. The mobility-polymer concentration curve appears to have a minimum for materials of high charge density, whereas it is steadily decreasing for those of low charge density. Moreover the mobility variation with the ionic strength of buffer solution showed a tendency of decreasing under our experimental condition. The number of charges of this polyacid was estimated by means of Debye-Henry's relation from the observed (descending) mobility and found to be in a fairly good agreement with the value determined by conductomentric titration with an exception at the very low ionic strength

Recent Study of Counterion-mediated Attraction between Colloidal Particles and between Particles and Interface Studied by the Ultra-small-angle X-ray Scattering

The application of the 1D- and 2D-ultra-small-angle X-ray scattering (USAXS) methods to the structural study of dilute colloidal silica particle dispersions is reviewed. A single colloidal crystal showed 22 sharp diffraction peaks, which allowed us to uniquely determine the lattice symmetry (body-centered-cubic), lattice constant (around 0.3–0.4 μm) and crystal orientation. In dilute dispersions, the closest interparticle spacing was confirmed to be smaller than the average spacing, pointing to the important role of a counterion-mediated attraction between the particles. The scattering profile had six-fold and four-fold symmetries with [111] and [001] directions being parallel to the axis of the capillary (dispersion container), respectively. In both cases, the (110) planes, the most densely packed planes of bcc, were in contact with and parallel to the capillary surface, confirming the presence of a possibly counterion-mediated attractive interaction between negatively charged interface and particles. After the capillary was shaken, only the six-fold symmetry was found, which is reasonable in the light of larger contact between the capillary surface and the (110) planes (and hence greater stabilization of the system) than for the four-fold symmetry

コウブンシ デンカイシツ ヨウエキ ニ カンスル ケンキュウ

京都大学0048新制・課程博士工学博士工博第18号新制||工||10(附属図書館)UT51-44-P2421京都大学大学院工学研究科繊維化学専攻(主査)教授 桜田 一郎, 教授 堀尾 正雄, 教授 岡村 誠三学位規則第5条第1項該当Kyoto UniversityDFA