Noboru Takisawa

Binding of hexadecylammonium surfactants to water-soluble neutral polymers

The binding of hexadecyltrimethylammonium bromide and hexadecyldimethyl-2-hydroxyethylammonium bromide to neutral polymers was measured by a potentiometric titration method using surfactant selective electrodes. Binding to poly(vinyl alcohol) was slightly cooperative, while that to poly(ethylene oxide) lacked the co-operativity. Poly(vinyl pyrrolidone) did not bind them at all. Binding affinity as estimated by a distribution coefficient of the cationic surfactants between the bulk and polymer phases is about 2 orders of magnitude smaller than that of anionic sodium dodecyl sulfate. The heat of binding was estimated from the temperature dependence of the distribution coefficient and found to be endothermic. It is imagined that the cationic surfactants are simply partitioned between the aqueous bulk phase and the polymer coil phase which is regarded as aqueous organic mixed solvent.

Interactions of amphiphilic drugs withα-,β-, andγ-cyclodextrins

The association of several amphiphilic drugs with α-, β-, and γ-cyclodextrins has been measured by use of drug-sensitive electrodes. Drugs investigated are hydrochlorides of chlorpromazine, dibucaine, tetracaine, and procaine, and valethamate bromide. Each drug forms the drug:cyclodextrin=1∶1 complex with α- and β-cyclodextrin, and both the 1∶1 and 2∶1 complex with γ-cyclodextrin, except valethamate which only forms the 1∶1 complex. The strength of the 1∶1 complex formations is in the order of βCyD>α-CyD>γ-CyD. The association constant of the 2∶1 complex in drug-γ-CyD is larger than that of 1∶1 complex. The free energy change of the conplex formation has a positive correlation with that of the micelle formation of drugs. The deviation from this relation is explained in terms of fittability of the bulky hydrophobic group of drugs into the cyclodextrins cavity. The free energy change for the complex formation between chlopromazine or valethamate and β-CyD is governed by the enthalpy term and not by the entropy term which controls the surfactant-β-CyD interactions.

Interaction between poly(styrene sulfonate) and dodecylpyridinium chloride in ethanol-water mixed solvents

Abstract Binding of dodecylpyridinium chloride to poly(styrene sulfonate) in ethanol-water mixed solvent was measured by a surfactant-selective electrode which consists of polymeric materials only and thus shows a good electrode performance even in mixed solvent. It was found that both intrinsic binding and the cooperative effect were reduced by added ethanol. This is ascribed to replacement of water molecules hydrophobically hydrated around the hydrophobic moieties of the polymer and the surfactant with ethanol molecules. This tendency is correlated with the free energy change of a surfactant molecule when transferred from water to an ethanol-water mixed solvent, which was also measured by the same surfactant electrode as used in the binding study.

The interaction of mixed surfactants with polyelectrolytes

Abstract The interactions between a linear polymer, sodium poly(2-acrylamide-2-methylpropane sulfonate), and two cationic surfactants, dodecylpyridinium chloride and tetradecylpyridinium chloride and their mixtures with different ratios, were studied by a potentiometric titration method using a surfactant-selective electrode. The ideal mixing/ideal cooperative binding model we had proposed previously was applied to successfully predict the binding isotherms of the mixed surfactant systems and the critical aggregation concentrations of the binding. The binding of surfactant mixtures to polymers is similar to the ideal mixed micelle formation and a sort of synergetic effect was found during the binding process.

Interaction of surfactant with polymer gel binding isotherm and swelling ratio

Abstract Binding of a cationic surfactant, dodecylpyridinium chloride, to three kinds of anionic polymer gels (copolymers of N-isopropylacrylamide(NIPA) and sodium 2-acrylamide-2-methylpropane sulfonate (AMPS) cross-linked by 1 mol.% N,N′-methylene bis(acrylamide)) is determined in 10 mM NaCl by using a surfactant-selective electrode at 25°C, where the polymer compositions are AMPS:NIPA=100:0, 50:50, and 25:75 in mole ratio. The binding behavior is compared with three linear polymers with the same monomer composition as the polymer gels. Binding to both polymer gels and linear polymers is highly cooperative, being stronger for a polymer with a higher charged group content. Linear polymers bind the surfactants stronger than polymer gels, but the difference gets smaller as the charged group content decreases. These results imply that the extent of interaction between bound surfactant is larger than the average cross-linking distance in the 100:0 gel, but at least comparable in 25:75. The gel volume is measured in the presence of a surfactant by a microscope and found to drastically shrink when surfactant binding exceeds about 20% of binding sites (sulfonate groups). A plot of the swelling ratio vs the degree of binding gives a curve around which all the experimental points scatter showing that the swelling ratio is uniquely determined by surfactant binding, irrespective of the copolymer composition.

Interaction between cationic surfactants and poly(vinyl alcohol)

Abstract The binding of four cationic surfactants (tetradecylpyridinium chloride and bromide, dodecylpyridinium chloride and dodecylammonium chloride) to poly (vinyl alcohol) (10% acetylated) was measured in aqueous solution by potentiometry using a surfactant-selective electrode and complementarily by equilibrium dialysis. The amount of binding was very small at low equilibruim concentrations (Cf), but increased markedly as the Cf approached the critical micelle concentration (c.m.c) of each surfactant. By comparing the effect of cationic head groups, counter-ion, and alkyl chain length at low Cf, it was inferred that the alkyl chain plays a minor role, while the polar head groups, especially a monoalkylammonium group, contribute very much to the binding affinity. As for the effect of added electrolyte, it was very little at low Cf, but at higher Cf binding increased sharply near the c.m.c. The amount of binding was replotted against a reduced equilibrium concentration, Cf/c.m.c. and then all the binding isotherms came together on a single isotherm showing that ordinary micellization has an intimate connection with the binding at higher Cf.

Improvement of solvent affinity for graphene derivatives by solution plasma process

A solution plasma (SP) process was employed to obtain hydrophilic graphene derivatives. Three different SP treatment time durations of 5, 10, and 15 min were applied as the experimental parameter to a sample solution including graphite in 9% hydrogen peroxide (H2O2) aqueous solution. The prepared graphene derivatives showed high dispersibility in contrast to that from natural graphite. The average particle size and absolute value of zeta potential of the obtained samples decreased as the SP treatment time increased. The particle size of SP-treated graphene derivatives in the supernatant linearly decreased depending on the SP treatment duration. The required particle size between 1.6 and 2.5 ?m was obtained by SP treatment (i.e., reaction control was achieved). It was clearly shown that the necessary reaction time for graphene treatment using SP processing was much shorter than that by the modified Hummers method.

Effect of the protonation equilibrium on the interaction of mixed micelles with their counterions

Abstract Ionic/nonionic mixed micelle formation of dodecyldimethylamine oxide (DDAO) was studied by measuring the activities of DDAO+ ions and Cl− ions using surfactant-selective electrodes and Ag/AgCl electrodes at three pH values in the absence of added salt. DDAO monomer exists as either a nonionic or a cationic species depending on the pH of the aqueous solution and hence the two species are not independent of each other. A new relation between the activity of the surfactant ions and that of the counterions is presented which differs from the corresponding relation valid for ionic/nonionic mixed micelles consisting of independent components.

Diverse actions of added alkanols on the binding of dibucaine cation to an anionic polymer

The binding of dibucaine cation to a polyanion [poly(acrylamide 2-methylpropane sulfonate)] in the presence of various alkanols(C1C3, C5, and C7) is measured by using an electrode responsive to dibucaine cation. The binding is characteristic of cooperative interaction. The binding affinity is enhanced by added pentanol and heptanol, and is well correlated with thermodynamic activities of these alkanols. In contrast, methanol and ethanol reduce the binding affinity, which is well correlated with the free energy of transfer of dibucaine cation from water to mixed solvent. The effect of added propanol lies between the medium- and the small-chain alkanols. The significance of the present results is briefly referred to in relation with the solution state of dibucaine in a body fluid.