Masako Koyama

Effect of Arginine as a Counterion on Surfactant Properties of Fatty Acid Salts

Arginine (Arg) is considered to be useful as a counterion with its large hydration radius and high bulkiness due to high dissociation constant compared to other organic bases, the presence of a ganido group, and its high molecular weight. The effects of Arg as a counterion on the surfactant properties of fatty acids were studied in comparison to triethanolamine (TEA), ammonia (NH3), and sodium ions (Na). The critical micelle concentrations (CMCs) and the degree of counterion binding to the micelles were determined based on electrical conductivity measurements. The degree of binding of argininium (Arg) counterions to micelles of fatty acids was the same as for triethanolammonium (TEA) counterions, and greater than that of ammonium (NH4) and Na counterions, attributed to the bulkiness of the Arg counterion. The CMCs of aqueous solutions of fatty acid Arg salts and fatty acid TEA salts were smaller than the CMCs of the corresponding aqueous solutions of fatty acid NH4 salts and fatty acid Na salts. The effect of the different counterions on the change in Gibbs hydrophilic energy was not investigated. Surface adsorption was determined through surface tension measurements, and it was found that when the bulk concentration was lower than the CMC, without micelle formation, the surface adsorption of fatty acid Arg salts was the same as for fatty acid Na salts and less than that for TEA and NH4 salts. This adsorption trend is attributed to the large hydration radius of the Arg counterion.

Effect of Amino‐Acid‐Based Polar Oils on the Krafft Temperature and Solubilization in Ionic and Nonionic Surfactant Solutions

Abstract The Krafft temperature and solubilization power of ionic and nonionic surfactants in aqueous solutions are strongly affected by added polar oils such as amino‐acid‐based oils (e.g., N‐acylamino acid esters, AAE), because they tend to be solubilized in the surfactant palisade layer. The Krafft temperatures of 5 wt.% sodium dodecyl sulfate (SDS)‐water and octaoxyethylene octadecyl ether (C18EO8)‐water systems largely decreases upon addition of AAE and 1‐hexanol, whereas it decreases very slightly in isopropyl myristate (IPM) and n‐dodecane. The lowering of the Krafft temperature can be explained by the same mechanism as the melting‐temperature reduction of mixing two ordinary substances. Namely, the polar oils are solubilized in the surfactant palisade layer of micelles and reduce the melting temperature of hydrated solid‐surfactant (Krafft temperature). On the other hand, non‐polar oil such as dodecane is solubilized deep inside micelles and makes an oil pool. The solubilization of non‐polar oil is enhanced by mixing surfactant with AAE due to an increase in micellar size.

Quantification of the Sensation on Using Cleansing Oil

化粧品の使用感評価は人による官能評価を主体として 行われているが,より客観的かつ定量的な方法として, 機器測定による評価方法の開発が進められている。例え ば,小松らは,化粧水の使用感の機器評価方法を報告し ている。一方で,同じスキンケア化粧品であるクレン ジング化粧品においては,洗浄という明確な機能があ り,さらにリンスオフすることから,その他の使い心地 についてはあまり触れられてこなかった。そこで本研究 ではクレンジングオイルをターゲットとし,その使用感 を機器測定で評価した。 クレンジングオイルの使用感に関して,本来の機能で ある洗浄性は,これまで様々な評価報告がなされてき た。しかし,クレンジングオイルによるメイク除去の 行為は,クレンジングを手に取ってから,顔へ塗布し, メイクと馴染ませ,最終的に水で洗い流すといった一連 の動作であり,手触りやすすぎ性といった洗浄性以外の 部分についても,総合的な使用感に大きく影響すると考 えられる。そこで,洗浄性に限らず,クレンジングオイ ルの様々な使用感について官能評価を行い,一連の動作 のなかで試料間同士の識別に重要な感覚を抽出した。そ して,その感覚を機器測定により数値化する方法を考案 した。

Behavior of a Metastable Gel of Sodium N‐Stearoyl‐l‐Glutamate/Water System

Gel formation was observed at 25°C in a mono sodium N‐stearoylglutamate (C18GS)/water system by quick cooling (quenching, 15°C/minute), whereas coagel was formed by slow cooling (annealing, 1°C/minute). Two kinds of phase transition temperatures, Tgel (coagel‐gel) and Tc (gel‐liquid crystal or micelle), were detected in the annealing system using a differential scanning calorimeter (DSC). On the other hand, only Tc was observed in the quenching system. Since the phase transition entropies at Tc in both the quenching and annealing systems are similar, both gels are considered to be in the same structure, and the gel observed in the quenching system at low temperature is in the metastable, supercooled state. Judging from the 1H‐NMR data and microscopic observation, a homogenous gel is formed above 7 wt% of C18GS. With an increase in surfactant concentration, the thixotropic tendency of the gel increases due to the decrease in free‐water. Since it was difficult to show gel formation with the shorter chain homologs, C14GS and C12GS, the hydrocarbon chain length of the surfactant appears to be very important in the formation of a metastable, supercooled gel.