Takuji Okaya

Hydrogen particles and supersaturation in alkaline water from an Alkali-Ion-Water electrolyzer

The hydrogen content in alkaline water obtained from an electrolytic flow cell was examined by measuring the diameter distribution of hydrogen microbubbles (hydrogen particles) in electrolyzed alkaline water using the dynamic light scattering (DLS) method. The influence of electrolysis conditions on the hydrogen content and the diameter distribution of hydrogen particles were also examined. The diameter of hydrogen particles changes rapidly with elapsed time after electrolysis, indicating that hydrogen particles grow to form large particles. The distribution of the particle diameter shows two peaks. The mean diameter of hydrogen particles is distributed mainly between 20 and 300 nm. The mean diameter decreases with an increasing current density up to 0.03 Ad m −2 . The diameter of hydrogen particles is smaller than the equilibrium diameter obtained by the concentration of dissolved hydrogen, suggesting that the electrolyzed water is a transition state from supersaturated to saturated solutions. Hydrogen exists in particles as a colloidal solution in a region of hydrogen content in electrolyzed water above 0.75 mM, which represents the saturation concentration of the dissolved hydrogen.

Dissolution of hydrogen and the ratio of the dissolved hydrogen content to the produced hydrogen in electrolyzed water using SPE water electrolyzer

Concentration of dissolved hydrogen in electrolyzed water using a solid polymer electrolyte (SPE) water electrolyzer was investigated using a DH-meter. A ratio of the dissolved hydrogen content to an amount of hydrogen concentration calculated from charge passed during electrolysis was estimated. The ratio increased from 10 to 20% with a decrease in current density from 3.0 to 0.3 A dm−2. The effect of the linear velocity of water on the ratio of dissolved hydrogen was studied. The cross-sectional area of the water channel was changed to change the linear velocity of water. The ratio of dissolved hydrogen increased with increasing the velocity. Due to the fast mass transport by high velocity, the small hydrogen bubbles are fast transferred by the diffusion into the bulk water and dissolved. The population density of the small hydrogen bubbles is found to have an effect on the ratio of the dissolving hydrogen.

IMPORTANCE OF GRAFTING IN THE EMULSION POLYMERIZATION OF MMA USING PVA AS A PROTECTIVE COLLOID. EFFECT OF INITIATORS

Abstract To clarify the initial stage of particle formation in the emulsion polymerization of methyl methacrylate (MMA) using poly(vinyl alcohol) (PVA) as a protective colloid, a model experiment with a low concentration of MMA (1 ml/100 ml H2O) was carried out in the presence of various initiators, ammonium persulfate (APS), 2,2′-azobis(2-amidinopropane)dihydrochloride (V-50) and 2,2′-azobis (isobutyronitrile) (AIBN). In the experiments using a large amount of PVA (1 g) at 70°C, the polymerization proceeded without any flocculation with all kinds of initiators, yielding stable emulsions with a diameter of approx. 90 nm and number of particles of 2×1013/ml H2O. The polymers in the emulsions were fractionated into three parts, acetone-soluble, water-soluble, and insoluble in both solvents. The amount of insoluble part was the largest in the APS system and the smallest in the AIBN system. The absence of the acetone-soluble part showed the high efficiency of grafting onto PVA in the initial stage of polymerization. In the experiments using a small amount of PBA (0.1 g) at 70°C, the emulsion polymerization occurred at a very early stage. With the increase in conversion, much coagulation took place due to the shortage of PVA. In this case, the ratio of PVA to monomer was 1:10, similar to the conventional emulsion polymerization of vinyl acetate (VAc). In the experiments without PVA, stable emulsions could not be obtained in all kinds of initiators. These results show the importance of the grafting in this emulsion system.

Hydrogen concentration in water from an Alkali–Ion–Water electrolyzer having a platinum-electroplated titanium electrode

The supersaturated concentration of hydrogen in electrolyzed water obtained from a flow-type electrolytic cell was studied under various electrolysis conditions. The degree of supersaturation was found to decrease as the solution supply rate to the cell increased. The ratio of observed hydrogen concentration to the theoretical hydrogen concentration obtained from the electrochemical equivalent, as calculated from the transfer of charge in the cell, was found to increase with the solution supply rate. The concentration of hydrogen in solution has a maximum at a current density of approximately 0.3 A dm−2. This maximum was found to be independent of the flow rate, indicating that the hydrogen concentration is related to both the diffusion of dissolved hydrogen from the electrode surface to the bulk solution and hydrogen bubble growth.

Physical properties of acrylic copolymer emulsions using poly(vinyl alcohol) as a protective colloid in comparison with those using surfactants

Properties of copolymer emulsions of methyl methacrylate and butyl acrylate prepared using poly(vinyl alcohol) (PVA) as a protective colloid have been studied and compared with those prepared using anionic and anionic/non-ionic surfactants. The emulsions with PVA revealed a Newtonian flow, while those with surfactants had a thixotropic flow. Cast films of the emulsions with PVA afforded much larger tensile strengths, higher Youngs moduli, and poorer resistance to water compared with those with surfactants. Adhesive layer composed of the copolymers with PVA revealed markedly higher creep resistance to shearing stress, while that with surfactants had poor resistance; these phenomena appear to arise from the canal-like morphology of PVA in the former cast films, while the surfactants in the latter existed in island morphology. © 2000 Society of Chemical Industry

Functional modification of poly(vinyl alcohol) by copolymerization : IV. Self-crosslinkable poly(vinyl alcohol)s

Abstract An investigation has been made on the copolymerization of vinyl acetate with N-(methoxymethyl)-acrylamide, N-(n-butoxymethyl)-acrylamide or N-methylol-acrylamide, and or the alcoholysis of copolymers and crosslinking properties of the resulting modified poly(vinyl alcohol)s (PVALs). The former two comonomers, N-(alkoxymethyl)-acrylamides, have been found useful for producing self-crosslinkable PVALs where timing of crosslinking is controllable: no crosslinks are included in the powder or in aqueous solution, and crosslinked materials having high water-resistance can be produced in the dry state with the aid of ammonium chloride. The following crosslinking reaction can be assumed: From a modified PVAL containing 1.0 mol% of N-(n-butoxymethyl)-acrylamide units, a crosslinked film showing high resistance to boiling water, 0.8% of the sol fraction and 2.4% (w/w) of the swelling degree, has been obtained. Modification with N-(methoxymethyl)-acrylamide also shows a similar performance. In contrast, N-methylolacrylamide cannot be used for this purpose because crosslinking occurs in alcoholysis. The monomer reactivity ratios for the copolymerization of N-(n-butoxymethyl)-acrylamide (monomer-1) and vinyl acetate (monomer-2) have been determined as r1 = 8 and r2 = 0.095.

Effect of poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group as a steric stabilizer on dispersion polymerization of styrene

In dispersion polymerization of styrene in ethanol, effects of a reactive steric stabilizer, poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group (P(VAc/VA)-SH), were investigated. In the absence of the thiol end group, the dispersion coagulated at the middle stage of the polymerization, while in the presence of the thiol end group, the polymerization proceeded successfully to result in close to monodisperse particles. The reactive thiol group acts as a site of formation of the block copolymer, that is, polystyrene-b-P(VAc/VA), which is utilized as an effective dispersant. From the measurement on molecular weights during the course of polymerization, two polymerization loci were realized. Addition of butyl methacrylate to styrene affected markedly not only rate of polymerization but also particle size.

Study on chain transfer reaction of poly(vinyl acetate) radical with poly(vinyl alcohol) in a homogeneous system

The first purpose of this study is to obtain effectively the graft copolymer of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc). Polymerization of VAc in the presence of PVA in dimethyl sulfoxide (DMSO) was investigated. The second purpose of the study is to obtain a PVA having a long branch whose properties have not been clarified yet. By hydrolyzing the PVAc portion in the graft copolymer, the PVA having a long branch might be obtained. The polymerization system was thought to be homogeneous since DMSO is a common solvent for PVA and PVAc at 60°C. Prior to the experiment, solution polymerization of VAc in DMSO was carried out in the absence of PVA to know the chain transfer constant (C S) to DMSO. The C S value was determined to be 0.7×10-4. Then the chain transfer constant to PVA (C P) on the basis of monomer unit was measured to be 9.9×10-4. The C P value was much smaller than the value we had expected, since the C S to isopropanol, whose structure resembles that of the vinyl alcohol unit in PVA, had been reported to be about 5-times larger than this. The reason of the rather smaller value of C P appeared arise from the substantial decrease in concentration of the reactive sites that are buried in the polymer coil. The aimed graft copolymer of PVA and PVAc, as well as the PVA having a long branch, was proved to be rather difficult to obtain, since the reactivity of PVA molecule in the chain-transfer reaction is much lower than that of isopropanol.

Surface sulfate groups on poly(methyl methacrylate) and poly(vinyl acetate) particles from soap-free emulsion polymerization

Abstract The amounts of sulfate groups on the particle surfaces of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) obtained in soap-free emulsion polymerization were determined. Polymerization was carried out at low monomer concentration using ammonium persulfate as an initiator. After the ionexchange procedure, conductometric titration was carried out. Amounts of surface sulfate groups were lower and particle diameter was larger in the PMMA system compared with PVAc. A large and remarkable difference appeared in the ratio of surface sulfate groups to decomposed sulfate radicals, viz. 90% for the PVAc system and 50% for PMMA. The ratios of sulfate groups per polymer molecule on PMMA and PVAc particles (functionality) were calculated. The functionality of the PMMA system was 70% of the theoretical value, while it was close to 100% in the PVAc system. This large difference might arise from the weak reactivity of the sulfate radical with MMA compared with that of VAc, due to the strong electrophilic nature of the radical. A side reaction of the sulfate radical with MMA is assumed. On the basis of these experimental results, the instability of the emulsion polymerization of acrylic monomers using poly(vinyl alcohol) (PVA) as a protective colloid is discussed in terms of the instability of the soap-free particles formed after the consumption of free PVA in water by the grafting reaction.

Fabrication of YSZ Thin Films by Chemical Vapor Infiltration Using NiO as Oxygen Source

A yttria-stabilized zirconia (YSZ) film was successfully fabricated by a modified chemical vapor infiltration process at 1000-1200°C on a NiO substrate that also served as an oxygen source. ZrCl 4 and YCl 3 were used as metal sources. The growth rate of the YSZ film was independent of deposition time but was influenced by the carrier gas flow rate. The oxygen contained in the Ar carrier gas also served as an oxygen source. This oxygen, which adsorbed on the YSZ film surface immediately after the gas supply was turned on, reacted with the metal source gases. The large fluctuation in pressure during each a chemical vapor infiltration cycle was found to enhance the growth rate of YSZ films dramatically.