Amphoteric surfactants are amino acid derivatives; their net charge varies with the pH in solution (Table 7). At pH below the isoelectric point they are positively charged in aqueous
Table 7 Surfactants
Nonionics polyhydric alcohol esters sucrose esters methyl glucose esters glucose ethers fatty acid alkanolamides
Amphoterics ampholytes propionates imidazoline derivatives Anionics phosphoric acid esters and salts acyl amino acids and salts acyl peptides acyl glutamates sarcosinates taurates sulfonic acids and salts sulfosuccinates isethionates sucrose laurate or cocoate PEG-120 methyl glucose dioleate PEG-80 methyl glucose laurate alkyl polyglucosides cocodiethanolamide cocamidopropyl betaine olivamidopropyl betaine sesamidopropyl betaine oleamidopropyl betaine isostearamidopropyl betaine cocamidopropyl hydroxysultaine cocamidopropyldimethyl aminohydroxypropyl hydrolyzed collagen alkylamino propionates alkyliminodipropionates acylamphoacetate
C9-C15 alkyl phosphate PPG-5 ceteth-10 phosphate Oleth-3 phosphate sodium cocoyl hydrolyzed protein sodium lauroyl oat amino acids
TEA or sodium lauroyl animal collagen amino acids sodium cocoyl glutamate sodium cocoyl or lauroyl sarcosinate sodium methyl cocoyl taurate disodium laneth-5 sulfosuccinate disodium ricinoleamido MEA-sulfosuccinate disodium laureth sulfosuccinate disodium PEG-8 palm glycerides sulfosuccinate sodium cocoyl isethionate
Abbreviation: INCI, international nomenclature for cosmetic ingredients.
solution and can consequently adsorb more easily onto the skin. Alkyl chain length can also significantly act on the skin feel; some betaines based on C16/C18 cuts provide more greasy, refattened feel but also have detrimental effect on foam.
Polydimethylsiloxane grafted with a betaine moiety leads to an amphoteric surfactant combining substantivity, refattening properties as well as silicone typical skin feel profile.
Some nonionics are used for their emollient properties and excellent afterfeel; e.g., sucrose and methyl glucose esters as well as sucrose ethers. Fatty acid alkanolamides are often referred to as refatteners; these are not lipids but they confer a greasy slippery feel to the foam and impart a particular afterfeel on the skin that subjectively compares with refatting. Several mild anionic surfactants are known to provide improved skin feel (afterfeel) by themselves, e.g., sarcosinate, taurate, acylglutamate, and isethionate. Fatty acids-protein condensates salts also act as conditioning aids, imparting a pleasant, smooth feel to the skin. The inclusion of fatty acids in soap and syndet bars contributes to enhance skin feel during and after use, and produces creamier lather. Phosphoric acid fatty esters deliver soap-like skin feel: slipperiness during use, and very good rinseability leaving skin feeling ''clean'' and powdery.
Benefits brought by additional skin conditioning agents are sometimes hidden by a mild or very mild cleaning-surfactant system delivering by itself very good skin feel properties; the sensorial baseline is high to start with and the increment in performance brought by skin feel agent is leveled off, and sometimes not even perceivable. It is, however, important to notice that several mild anionic and most of the nonionic surfactants, if they provide a pleasant afterfeel, are characterized by a ''water feel'' (feel in solution) that is often unpleasant, with rough and drag feel sensations.
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