Kunio Furusawa

Colloid chemical studies of polystyrene latices polymerized without any surfaceactive agents: I. Method for preparing monodisperse latices and their characterization

SummaryPolystyrene latices were polymerized in the absence of any emulsifiers using potassium persulphate as an initiator. The latex dispersions obtained consisted of particles having high monodispersity and their diameters could be varied within a wide range (350 to 1400 mμ) in response to the preparing conditions.The electrophoretic mobilities of the latices were measured according to a microelectrophoretic technique and their zeta-potential was obtained as 70–80 mV in the standard state.Average molecular weights and the distributions of the latices were determined by use of the Gel Permeation Chromatography and the mechanism of the particle growth was discussed.The critical flocculation concentrations for the latex dispersion were determined with the various salts (KCl, BaCl2 and LaCl2) by measuring sedimentation rates. These results were discussed byVerwey-Overbeeks analytical expression for the flocculation concentration.ZusammenfassungDie Polystyrol-Latices wurden ohne Emulgatoren mit Kaliumpersulfat als initiator polymerisiert. Die erhaltenen Polystyroldispersionen waren monodispers; der Durchmesser der Partikel konnte im großen Bereich (350 to 1400 mμ) variiert werden.Die elektrophoretische Beweglichkeit der Latices wurde mikroelektrophoretisch gemessen; das Zetapotential lag zwischen 70 und 80 mV. Die mittleren Molekulargewichte und die Verteilungskurven wurden durch Geldurchdringungschromatographie bestimmt. Die kritische Auflockerungskonzentration für die Polystyroldispersion wurde mit verschiedenen Salzen (KCl, BaCl2 und LaCl3) bestimmt. Die Ergebnisse werden mit der Verwey-Overbeek-Theorie diskutiert.

Synthetic process to control the total size and component distribution of multilayer magnetic composite particles

A new synthetic process to prepare composite particles with multilayers, comprised of usual polymer latices, ultra-fine magnetic particles, and a polystyrene layer was examined under various solution conditions.First, the synthetic conditions of heterocoagulates, consisted of polystyrene latices (2a=180∼900 nm) and NiO·ZnO·Fe2O3 particles (2a=20 nm), were investigated as a function of medium pH, particle concentration, and particle size ratio, based on the concept of the heterocoagulation theory as applied by Harding et al. Regular heterocoagulates were generated under suitable medium and mixing conditions, and that their total size can be controlled by selecting the size of the original polymer latices used as the core.Second, the best encapsulation condition of the heterocoagulates via emulsion polymerization with polystyrene monomer was surveyed. The encapsulation of the heterocoagulates was greatly promoted by pretreatment with oleate molecules, although there is no tendency for the encapsulation when the surfactant-free bare heterocoagulates are used as the core.

Heterocoagulation behaviour of polymer latices with spherical silica

Abstract The heterocoagulation behaviour of amphoteric polymer latices (2 a = 250 nm) on large spherical silica (2 a = 240–1590 nm) was studied as a function of pH, particle size ratio, and of electrolyte and aqueous polymer concentrations in the medium. Under suitable conditions, the adhesion isotherms are all of the high affinity type with well-defined plateaus and the heterocoagulates generated from the mixed suspensions are comprised of uniform composite particles composed of lots of latex particles adhering to the silica particle in the core. Removal experiments show that the adhesion of latex particles is essentially irreversible except for adhesion occurring in a highly alkaline solution. Furthermore, it is found that addition of polymer or electrolyte to the medium is very useful in controlling the contents of organic and inorganic materials in the heterocoagulate particles. These conditions for forming the regular heterocoagulates and the properties of the products have been analysed using the theories of DLVO and heterocoagulation.

Colloid chemical studies of polystyrene latices polymerized without any surface-active agents

SummaryThe influence of “secondary minimum” for the stability of spherical colloid has been studied using a series of “soap-free” polystyrene latices from 350 mμ to 1400 mμ in diameter.The critical flocculation concentration (c. f. c.) and the zeta-potential at the c. f. c. for each latex were determined with several salts of different ionic valencies. The values of c. f. c. varied with the particle size, reaching a maximum value at 750 mμ and then decreasing gradually with the diameter.Another phenomenon detected in the experiment was the complete reversibility of coagulation which was observed only in the cases of large size latices, i. e., the coagulates of large size particles were fully redispersed in the solution by stirring. The time-dependence of their sedimentation curves was reproducible.These experimental results could not be explained by the simple theoretical consideration for stability of suspension. The satisfactory explanation is given only using the term of “secondary minimum” of interaction potential, i. e., the origin of coagulation was shifted from the ordinary primary minimum to the shallow “secondary minimum” at about 750 mμ of the particle diameter.ZusammenfassungDer Einfluß des “Sekundär-Minimum” auf die Stabilität von Kolloiden wurde an seifenfreien Polystyrol-Latex-Suspensionen mit einem Durchmesser von 350 mμ bis 1400 mμ untersucht. Die kritische Flockungskonzentration (c. f. c.) und das Zeta-Potential bei c. f. c. wurde mit verschiedenen Salzen bestimmt.Der Wert von c. f. c. ändert sich mit der Teilchengröße.Ein weiterer wichtiger experimenteller Befund ist die vollständige Reversibilität der Flockung bei größeren Latices.Derartige Versuchsergebnisse können durch das Sekundär-Minimum befriedigend erklärt werden.

Syntheses of composite polystyrene latices with silica particles in the core

Abstract A study of the synthesis of composite polystyrene latices with silica particles in the core has been performed under various conditions. It was apparent that the dense adsorption layer of hydroxyl propyl cellulose (HPC), which was formed on the silica particles at the lower critical solution temperature, plays a part in the preparation of the composite. When the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of the silica particles and, indeed, new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were prepared. Furthermore, in the high concentration runs of the SDS, a new type of composite with a raspberry shape was generated with a high product yield. It is assumed that nucleation of new polymer particles would occur above the critical micelle concentration of the surfactant and that one portion of the new polymer particles would coagulate heterogeneously with the HPC-coated silica particles after some period of the seeded polymerization.

Preparation of composite fine particles by heterocoagulation

To prepare regular composite particles comprised of organic and inorganic compounds, based on heterocoagulation theory, the properties of the mixture of small amphoteric latices (2a=250 nm) and large spherical silica (2a=240–1590 nm) were investigated as a function of pH, particle number ratio, particle size ratio and electrolyte concentration in the medium. It is apparent that under suitable conditions, we may prepare a stable mixed suspension comprising uniform composite particles, which are made up of many latices regularly adsorbed on silica surfaces, and each composite particle is undergoing Brownian motion as an isolated unit. This new composite particle is very stable for electrolyte, base and acid medium, and its surface charges (sign and magnitude) can be controlled by changing the pH of the medium.

Adsorption of monodisperse polystyrene onto porous glass. I. preference adsorption and displacement of high-molecular-weight species

Abstract The effect of the molecular weight of a polymer on the maximum adsorption, the adsorption rate, the competitive adsorption of two or three species simultaneously, and the displacement process of adsorbed polymer was measured at the theta condition of the solution using polystyrene samples of narrow molecular weight distribution. The analyses for these measurements were carried out quantitatively by the gel permeation chromatography technique. It is apparent that the preferential adsorption of large-sized molecules over small ones can be detected in many kinds of adsorption, but the preferential adsorption is not very pronounced and is greatly dependent on the concentration of each component at which the corresponding adsorption is carried out. These effects could be explained mainly by the difference of the adsorption/desorption rate of the small component, because at the beginning the adsorption layer of the mixture is occupied entirely by the small-sized component due to its rapid adsorption rate.

Flocculation behavior of egg phosphatidylcholine liposomes caused by Ca2+ ions

Abstract The interaction between bilayer phospholipid membranes has been studied through flocculation phenomena of phospholipid liposomes. Unlike liposomes composed of other phospholipids, liposomes made of egg phosphatidyl-choline (PC) have a strong resistance against aggregation. This phenomenon can be attributed to the hygroscopic nature of the choline group, i.e. the repulsion force that is the so-called “hydration force” or the “steric force” with hydration is the origin of the phenomenon. By changing the diameter of the PC liposomes, we observed a different flocculation behavior of the liposomes when the electrostatic surface potential of the liposomes is zero. For diameters above 320 nm, a weak flocculation occurred, but liposomes with diameters below 200 nm are stable as colloidal dispersions. This diameter dependency of flocculation has been explained by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory together with hydration forces.

Adsorption behavior of poly-l-lysine and its conformation at the latex—water interface

Abstract Adsorption behavior of poly- l -lysine (PLL) on negatively charged polystyrene latices was examined systematically using various experimental techniques. It was realized that the conformation of PLL in the bulk persisted in adsorbed state and large structure change have not occurred upon adsorption, i.e., highly charged PLL which held in an extended conformation in the bulk, built up a flat adsorption layer on the latex surface. On the other hand, the PLL molecule taking a helical conformation in the bulk gave a thick adsorption layer and the thickness was influenced extensively by the molecular mass of adsorbate. These results suggest that the helical rods of PLL are adsorbed partly on the ends of the rods.

Adsorption of monodisperse polystyrene onto porous glass: II. Study of the exchangeability of adsorbed polymer layer

Abstract Exchangeability in the adsorption layer of one polymer by another was analyzed for different molecular weight combinations of polystyrene using gel permeation chromotography. The adsorption layers formed by small molecules are exchanged effectively by the solution of large molecules and the degree of exchange is dependent on the difference in their molecular weights. Furthermore, the degree of exchange extensively influences the solution concentration at which the corresponding adsorption is carried out, i.e., the polymer layer formed at the higher concentration is exchanged more easily than the layers at lower concentrations. This can be explained as follows: the polymer molecules in the dilute solution arrive at the sparsely populated surface, adopting a flat conformation, but the polymer molecules in the concentrated solution, especially when later arrivals come to the surface, occupy a smaller number of sites and make an extended loop conformation, which is exchanged more easily than are molecules in a flat conformation.