Shuji Saito

Solubilization properties of polymer-surfactant complexes

Abstract Complexes of polymer and surfactant which are formed in aqueous solution have different solubilization properties from those of the surfactant solution alone. The solubilization properties of the complexes were extensively studied with aliphatic and aromatic compounds as the solubilizates. It was found that the solubilization properties of the complexes depend mainly on the compatibility of polymer with the solubilizate. For example, aromatic compounds are more readily solubilized by the complexes of hydrophilic polymers with no proton donor, such as polyvinylpyrrolidone, than aliphatic compounds. Naphthol, which reacts with polymers and causes precipitation, is also solubilized to yield a clear solution in the complexes of anionic surfactants. Some complexes of polymer and cationic surfactant are broken by solubilization of aromatic compounds. The role of charge of cationic surfactants in such cases is discussed from the viewpoint of polymer structure.

Effect of nonionic surfactants on aqueous polyacrylic acid solutions

Abstract The interaction of polyacrylic acid (PAA) and nonionic surfactants (polyethylene oxide alkylethers) was studied with respect to pH and viscosity changes. As a result of hydrogen bonding between the acid units and ether oxygen atoms of the nonionic surfactants, the pH rises. The interaction is enhanced above the critical micelle concentration of the surfactants, and also becomes greater with increase in chain length of polyethylene oxide of the surfactants. At a certain degree of hydrogen bonding by the nonionic surfactants, PAA molecules are closely folded, and by a further surfactant binding they are again unfolded. The interaction is weakened by rising pH. The degrees of hydrogen bonding to PAA by the surfactants in various degrees of neutralization by NaOH were estimated.

Interactions of anionic surfactants with nonionic polymers. Comparison of guanidinium, tetraalkylammonium, and alkali metal ions as counterions

Abstract The interactions of anionic surfactants with nonionic polymers such as polyvinyl pyrrolidone (PVP), polyvinyl alcohol-acetate copolymers (PVA-Ac), and polyvinyl alcohol (PVA) in aqueous solution were studied with respect to guanidinium, four tetraalkylammoniums, sodium, and potassium as the counterions by means of electrical conductivity, dye solubilization, viscosity, and cloud point measurements. With sodium salts as the reference, guanidinium, a strongly water structure-breaking cation, lowers the critical micelle concentration (emc) of the long-chain alkylsulfates, and in the presence of PVP and PVA-Ac it promotes the binding of the anions to them and enforces the attraction between the bound anions by ion-pairing, exhibiting such phenomena as shrinking of the polymer chains or depression of the cloud points. Similar phenomena have been observed and discussed previously in the interactions of these polymers and long-chain alkylammonium or symmetrical tetraalkylammonium ions with thiocyanate or iodide as counterions, both also strongly water structure-breaking anions. Sodium and potassium dodecylsulfates interact with PVP and polyvinyl acetate to a similar extent because both counterions are of weak effect on water. On the other hand, for the quaternary ions, which promote the water structure, as the counterions to dodecylsulfate, the cmc lowers with increase in size of the quaternaries but the polymer interactions weaken, and tetrabutylammonium dodecylsulfate in particular barely interacts with PVP and PVA in the presence of the micelles, and only weakly with PVA-Ac. Thus, in comparison with the sodium salts, only the strongly water structure-breaking counterions enhance the binding of the long-chain anions to the polymers. The role of the quaternary counterions has been discussed in terms of the effect on the equilibria between micelle formation and complex formation with the polymer.

Counterion effect of tetraalkylammonium and long-chain alkylammonium salts in the interaction with nonionic polymers

Abstract In the interaction of nonionic polymers and hydrophobic cations, such as tetraalkylammoniums and alkylammoniums, in aqueous solution, counterions play a significant role. Compared to counterions such as bromide, chloride, and fluoride, those of the so-called strongly water structure-breaking type (thiocyanate > iodide > nitrate) induce a stronger attraction or binding between the polymers and the alkylsubstituted cations accompanied by ion pairing, leading to a decrease of the polymer solubility or viscosity at low salt concentrations; this irregular counterion effect is more pronounced the more both the polymers (polyvinyl alcohol-acetate copolymer > polyvinylpyrrolidone) and the cations (tetrabutylammonium > tetrapropylammonium; octylammonium > hexylammonium) are hydrophobic. Such an irregular salt effect is supposedly caused both by the binding of the hydrophobic cations to the polymers and by an extraordinary counterion fixing to the polymer complex by thiocyanate, iodide, and nitrate ions. The irregular counterion effect appears more remarkable for long-chain alkylammonium ions because of their strong ability to bind to the polymers. As counterions, organic anions with small hydrophobic groups are quite similar to the chloride ion in the interaction of the polymers and the long-chain cations.

Interactions of polymers and cationic surfactants with thiocyanate as counterions

The interactions of deodecylammonium ions with nonionic polymers such as polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyvinylalcohol-acetate copolymer (PVA-Ac) were strengthened by changing the counterion from chloride to thioeyanate. For example, whereas the specific viscosity of a PVP solution underwent little change by addition of dodecylammonium chloride, addition of dodecylammonium thiocyanate (DASCN) decreased it at low concentrations and raised it remarkably at high concentrations. Such a viscosity change by DASCN is of a different type from that by sodium dodecylsulfate (NaDS) and may be attributed to a concurrent binding of the dodecylammonium ion with SCN− to the hydrophobic parts of the polymers. Therefore, the mechanism of binding of DASCN to the polymers is different from that of NaDS, whose dodecylsulfate ion is itself bound directly to many nonionie polymers. The binding of DASCN to the polymers was also exhibited by the higher solubilization power of the mixed solutions of DASCN wih the polymers than that of the DASCN solution alone for an oil-soluble dye Yellow OB. The binding of the dodecylammonium cation to PVP with the aid of the inorganic counterion was in the order of SCN− > I− > Br− > CI−, and as for small organic anions such as ethylsulfate, butyrate, and caproate the effect was very poor or insignificant. Dodeeylpyridinium thiocyanate did not show an interaction with PVP and PEO, but interacted strongly with hydrophobie PVA-Ac. The polymer-cationic interaction in the presence of thiocyanate ion thus depends specifically on the polymer and cationic head group of the surfactant.

Critical surfactant concentration in the interaction between nonionic surfactants and polymeric acids. effects of temperature, pH and salts

AbstractsCritical surfactant concentrations at which the binding of nonionic surfactants to polyacrylic acid, or complex formation, abruptly occurred in aqueous solution were lower than the CMC and were temperature-independent. The complex was precipitated by pH lowering or salt addition. At low pH, precipitation limit surfactant concentration (PLC) existed, below which no precipitation of the complex took place, and the PLC coincided with the critical concentration mentioned above. In this case the PLC did not change with temperature either. In the precipitation caused by A1C1```3`` addition, the PLC was a little higher than that at low pH, because Al ions induced not only shrinking and agglomeration of the complex but at the same time blocked the sites on the polymeric acid for hydrogen bonding with the surfactant. By NaCl or CaCl```2`` addition no PLC was found, because in both cases the salting-out effect dominated.

Dissolution of some polymers in aqueous solutions of urea, of its related compounds, and of tetraalkylammonium salts

Abstract Some water-insoluble polymers, such as polyvinylpyrrolidone-acetate copolymer, polyvinylalcohol-acetate copolymer, and polypropylene glycol dissolved in aqueous solutions of urea, alkylureas, amides, guanidine hydrochloride, and also of tetrabutylammonium bromide (Bu 4 NBr) have been studied. The intrinsic viscosities and clouding points of the polymer solutions rise with increase of concentration of these substances. Aqueous urea dissolves these hydrophobic polymers by breaking the ordered water structure around the hydrophobic parts. The effects of alkylureas and acetamide are complex because these substances include in the same molecules groups that break, and groups that form water structure. Aqueous Bu 4 NBr dissolves the polymers by association in a manner similar to that of surfactants but far less efficiently for dissolution. Me 4 NBr is nearly ineffective for dissolution of these polymers.

Precipitation of nonionic surfactants by polymeric acid

Nonionic surfactants of the polyethylene oxide type are precipitated by carboxy vinyl polymer (CVP) in its acid form. While the reduced viscosity of the CVP solution is affected more markedly by a surfactant with a longer polyethylene oxide chain, the binding to CVP of the nonionic surfactants with the same hydrophobic parts occurs more effectively with shortening of the polyethylene oxide chain or with lowering of the critical micelle concentration. The structure of the complexes formed is discussed.

Precipitation of non-ionic surfactants with poly(acrylic) acid and cationic polymers

Abstract Ethoxylated non-ionic surfactants were precipitated together with poly(acrylic) acid (PAA) and cationic polymers (chitosan hydrochloride and a cationized cellulose derivative) from aqueous mixtures. A precipitation limit surfactant concentration (PLC) existed, below which no more surfactant was separated with the agglomerates of both types of polymer. The PLC was dependent upon the hydrophobic moiety, and was independent of the polyoxyethylene chain length of the surfactants, of the temperature and of the cationic polymers employed, and was lower than the respective CMC. The PLC was equal to the critical surfactant concentration for binding to PAA in the absence of cationic polymer. Although the ratio of PAA to cationic polymer was the major factor governing the precipitation of surfactants from the three-component systems, surfactants with shorter polyoxyethylene chains were more easily precipitated.

Precipitation of nonionic surfactant-polymeric acid complexes solubilizing oil-soluble substances

Abstract The complex formed between the polyoxyethylene-type nonionic surfactant and polycarboxylic acid in aqueous solution has a solubilization ability different from that of the surfactant alone. As the complex is precipitated by the addition of acid or salt, so is the complex containing a solubilized oil-soluble substance. The complexes of the nonionic surfactant and polyacrylic or polymethacrylic acid containing solubilized yellow OB, azobenzene, or naphthalene were precipitated almost intact. The solubilizates in the dried matrix of the complexes were hardly extractable with such solvents as benzene, carbon tetrachloride, and n -hexane, and therefore, it is considered that the solubilizates are contained in a cross-linked structure of multiple hydrogen bonds between the polyoxyethylene chain of the surfactant and polycarboxylic acid.