Yukishige Kondo

Enhanced Hydrolytic Stability of Dental Composites by Use of Fluoroalkyltrimethoxysilanes

The hydrolytic stability of a group of experimental composite materials was evaluated. Seven distinct composites were formed by the mixing of a resin monomer mixture with silica filler that had been pre-treated with one of 7 different ethanol solutions. In one case, the filler was treated with an ethanol solution that contained only 3-methacryloyloxypropyltrimethoxysilane. In 5 cases, it was treated with solution containing a mixture of 3-methacryloyloxypropyltrimethoxysilane and one of the following hydrophobic fluoroalkyltrimethoxysilanes: trifluoropropyl-, nonafluorohexyl-, tridecafluorooctyl-, heptadecafluorodecyl-, and henicosafluorododecyl-trimethoxysilane. The tensile strength, after being immersed in water for 1800 days, of 2 of the experimental composites, whose pre-treatment regimen had included a fluoroalkyltrimethoxysilane, was significantly higher than that of the composite whose pre-treatment regimen had not included a fluoroalkyltrimethoxysilane. Moreover, there was no significant difference between the tensile strength of fresh samples of these 2 composites and the tensile strength of identically produced samples that had remained under water for 1800 days or that had been subjected to 30,000 cycles of thermal stress.

Plaque-Controlling Surface Modifier Containing Fluorocarbon Chain

Abstract A silane coupling agent, CF 3 (CF 2 ) 9 CH 2 CH 2 Si(NCO) 3 , prepared by hydrosilylation of trichlorosilane with CF 3 (CF 2 ) 9 CHue5f8CH 2 in the presence of hydrogen hexachloroplatinate(IV), followed by reaction with silver cyanate, was used for glass and bovine tooth surface modification. In ESCA of the modified glass surfaces, nitrogen atoms in the silane coupling agent bound to the surfaces were detected only at contamination levels. This ESCA revealed that neither urethane bonds nor NCO groups were present on the modified glass surfaces. Clear AFM images of the modified glass surfaces were also obtained. Though the contact angles of water on the modified glass surfaces were independent of the modification time (20 min or 4 h), the AFM images obtained show that the original glass-surface patterns of unevenness remained on the surfaces in the case of the short modification time (20 min), whereas they disappeared from the surfaces in the case of the long modification time (4 h). In the latter case (4 h), the silane coupling agent reacted sufficiently over the entire glass surface, and no region of unmodified glass surface was detected. The surfaces of bovine tooth specimens were modified with this silane coupling agent by spreading of the agent on the surfaces with a small brush followed by brief drying with a hair drier. The amounts of plaque adhering to the modified and unmodified bovine tooth surfaces after wearing of the specimens in a human oral cavity for five days were compared. The amounts of plaque adhering to these specimens in in vitro tests as determined from SEM images were also compared. It is expected that this silane coupling agent will be useful as a plaque-controlling surface modifier for enhancement of oral health.

Structures and photoisomerization of the polyion complex Langmuir-Blodgett films of an amphiphile bearing two azobenzene units

Abstract The structures and the photoisomerization of polyion complex Langmuir-Blodgett (LB) films of an amphiphile bearing two azobenzene units were studied. The anionic amphiphile was spread on the aqueous subphases with and without polycations. The area per molecule depended on the polycation species and was larger than that of pure amphiphile for three polycations out of four. It was suggested that the area per molecule is determined by the compromise between the various intermolecular interactions involved in the formation of the monolayer. The LB transfer was possible for all the polyion complex systems and reversible photoisomerization was observed for all the LB films by alternate UV and visible light irradiation. As the area per molecule where the LB transfer was conducted increased, the fraction of the cis isomer at the photostationary state with UV light irradiation increased, suggesting the role of free volume in the trans-to-cis photoisomerization.

Thermoresponsive viscoelasticity of concentrated solutions with a fluorinated hybrid surfactant

Abstract Temperature-dependent viscosity of an aqueous solution of sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate (FC6-HC4), a fluoro-hybrid type surfactant, which has a fluorocarbon chain and a hydrocarbon chain in a molecule, was examined. The FC6-HC4 solution showed viscoelastic behavior at concentrations around 10 wt.%. Further study on the temperature dependence of the viscosity of a 10 wt.% solution revealed that the viscosity increased about 10 2 times, showing a maximum as temperature rose from 6 to 36°C, and then decreased about 10 −4 times with further rising at temperatures up to 64°C. Moreover, tanxa0 δ , a parameter for visoelasticity, exhibited a minimum at 36°C. The phenomenon found in this work was reversible with respect to temperature change. The study revealed the importance of the chemical structure in which the numbers of carbon atoms are 6 and 4 in the fluorocarbon and hydrocarbon chains, respectively, for the hybrid surfactant to show the thermoresponsive viscoelastic behavior. Temperature-dependent visicosity increase was found to be observed during the process where the size of assemblies of surfactant molecules decreased with rising temperature and when the probability of collision is highest between small and large molecular assemblies.

Effects of fluoroalkyl chain length and added moles of oxyethylene on aggregate formation of branched-tail fluorinated anionic surfactants

Abstract The effects of fluorocarbon chain length and oxyethylene chain length were examined on the aggregate formation of newly synthesized double chain-type fluorinated anionic surfactants. The solution properties of double chain-type fluorinated anionic surfactants with two moles of added oxyethylene ( n FS(EO) 2 ) were found to depend on the fluorocarbon chain length. Thus, the Krafft temperature rose abruptly as the length of fluorocarbon chain increased, while the concentration at which the lowest surface tension is attained or aggregates are formed lowered with increasing chain length. In contrast, for double chain-type fluorinated anionic surfactants with two more moles of added oxyethylene ( n FS(EO) 4 ), their solution properties were almost inaffected by fluorocarbon chain length. That is, almost no change was seen in the concentration that indicates the lowest surface tension or aggregate formation when the chain length was altered, whereas the Krafft temperature was below 0°C for all members, providing them with a high solubility in water. In addition, spontaneous vesicle formation was observed in solution of n FS(EO) 4 and the size distribution of the vesicles thus formed had plural peaks (discrete size distribution).

Syntheses and reactions of metal organics. XXL Syntheses of (1H,1H,2H,2H-polyfluoroalkyl)triisocyanate silanes and surface modification of glass

Abstract Four silane coupling agents having a fluorocarbon chain and three isocyanate groups as reactive centers, i.e. CF 3 (CF 2 ) 3 CH 2 CH 2 Si(NCO) 3 ( 1 ), CF 3 (CF 2 ) 5 CH 2 CH 2 Si(NCO) 3 ( 2 ), CF 3 (CF 2 ) 7 CH 2 CH 2 Si(NCO) 3 ( 3 ) and CF 3 (CF 2 ) 9 CH 2 CH 2 Si(NCO) 3 ( 4 ), were prepared by the hydrosilylation reaction of trichlorosilane with the corresponding 1 H ,1 H ,2 H -polyfluoro-1-alkene [CF 3 (CF 2 ) n CH=CH 2 , n = 3, 5, 7 and 9 in the presence of hydrogen hexachloroplatinate(IV), followed by reaction with silver cyanate. Their application to the surface modification of glass was attempted. From measurements of the contact angles θ for water and oleic acid against a modified glass surface, it was found that the isocyanate-type silane coupling agents have a higher surface modification ability toward glass than those of methoxy-type silane coupling agents. The highest contact angle on the glass surface modified by each silane coupling agent was obtained employing both a shorter modification time (1/6) and a lower concentration (1/10) of the silane coupling agent solution in comparison with those of methoxy-type silane coupling agents. The oxidation and acid resistance of the modified glass surface were investigated, and the results of the resistance abilities assessed by measuring the contact angle reduction of water and oleic acid were also higher than those of methoxy-type silane coupling agents.

VOLATILITY AND SOLUBILIZATION OF SYNTHETIC FRAGRANCES BY PLURONIC P-85

ABSTRACT The volatility of synthetic fragrances (benzyl formate, benzyl acetate, benzyl propionate) from pluronic P-85 aqueous solution has been investigated by the dynamic headspace method The experimental results showed that the volatility of a more hydrophobic fragrance was strongly controlled by pluronic P-85. This volatile behavior was explained by the solubilization constants of fragrances between the micelle and bulk phase by semiequilibrium dialysis method.

Stability of surfactant vesicles formed from cationic didodecyldimethylammonium bromide

Abstract The solution properties of didodecyldimethylammonium bromide (DDAB) vesicles, including their relative stability, were estimated by measuring the vesicular diameter, the trapping efficiency of glucose, the aggregation number, and the ζ potential. DDAB vesicles with diameters in the range 17–40 nm were stable for long periods of time. However, 50 nm vesicular solutions were unstable and showed phase separation after 4 days. The DDAB vesicles were observed to have positive ζ potential values independent of diameter. The stability of vesicles may be attributed to electrostatic repulsive forces between the vesicles. Also, the glucose trapping efficiency for the 17 nm vesicle solution was 0.57%, and increased with an increase in vesicular diameter up to 2%. The results indicate that DDAB vesicles with small diameters (17 nm) have an inner phase. Further, the surface charge density calculation showed that 8–13% of DDAB molecules constituting the outside of the vesicles are charged, preventing the vesicles from fusing or flocculating in the aqueous solution and stabilized vesicle solution.

Electrochemical control of solubilization using a ferrocene-modified nonionic surfactant

Abstract An investigation was conducted on the control of solubilization making use of changes in the surface properties caused by the electrochemical redox reaction of 11-ferrocenylundecyl polyoxyethylene ether (FPEG), a ferrocene-modified nonionic surfactant, in aqueous solutions. Examinations through surface tension measurement of the effect of the redox reaction of the ferrocenyl group on the critical micelle concentration (cmc) of FPEG showed that the oxidation produces an increase in the cmc from 6×10 −6 to 5×10 −5 mol l −1 and the re-reduction causes the cmc to decrease from 5×10 −5 to 9×10 −6 mol l −1 . The effect of the redox reaction of the ferrocenyl group was then examined on the solubilization equilibrium constant, K , for solubilization of benzene, ethylbenzene and 2-phenylethylalcohol in FPEG micelles. The equilibrium constant was found for all solubilizates to decrease when the ferrocenyl group is oxidized and increase again if the group is re-reduced, indicating that oxidation of the ferrocenyl group releases portions of the solubilizate from the micelles into the bulk and the re-reduction gives rise to re-solubilization of the released solubilizate.

Syntheses of novel fluorocarbon surfactants with oxyethylene groups

Abstract Three anionic fluorocarbon surfactants with oxyethylene groups, sodium bis[2-{2-(perfluoroalkyl)ethoxy}ethyl] 2-sulfosuccinate C n F 2 n +1 -CH 2 CH 2 OCH 2 CH 2 OCOCH 2 CH(SO 3 Na)COOCH 2 CH 2 OCH 2 CH 2 C n F 2 n +1 ( n FEOS; n = 4, 6, or 8), were prepared from ethylene carbonate, maleic anhydride, corresponding alcohols having a polyfluoroalkyl chain, and sodium hydrogensulfite. The surfactants were highly water-soluble, and their Krafft points ( K p ) were below 0°C. The K p values of n FEOS were lower than those of conventional fluorocarbon surfactants, sodium bis[2-(perfluoroalkyl) ethyl] 2-sulfosuccinate C n F 2 n +1 CH 2 CH 2 OCOCH 2 CH(SO 3 Na)COOCH 2 CH 2 C n F 2 n +1 ( n FS; n = 4, 6, or 8). The surface tension at cmc ( γ cmc ) of n FEOS showed very low values, and the cmcs of 4FEOS and 6FEOS were smaller by about one order of magnitude than those of n FS surfactants at the same fluorocarbon chain length n . It should be noted that the introduction of oxyethylene groups enhances the hydrophilicity and micellar forming ability of n FEOS compared to n FS.