Adsorption Behavior of Surface-Chemically Pure N-Alkyl-N-(2-Hydroxyethyl)aldonamides at the Air/Water Interface

摘要

N-alkyl-N-(2-hydroxyethyl)aldonamides (alkyl:nCeH_13,n-C_8H_17,n-C_10H_21,n-C_12H_25,and n-C_14H_29 were obtained in the reaction of long-chain N-alkyl-N-(2-hydroxyethyl)amines with D-glucono-l,5-lactone and D-glucoheptono-l,4-lactone.The adsorption isotherms were obtained from surface tension measurements of aqueous solutions of surface-chemically pure surfactants.The experimental equilibrium surface tension versus concentration isotherms were evaluated by the Frumkin adsorption equation to get the adsorption parameters,namely,standard free energy of adsorption,DELTAG _(ad)deg,saturation adsorption,GAMMA_infinity,minimum surface area demand per molecule adsorbed,A_min,and interaction parameter,H~s.The investigated functionalized alkylaldonamides show improved solubility in comparison with the corresponding sugar derivatives of the primary amines.The introduction of the -CHOH moiety into the saccharide headgroup causes a noticeable increase of the hydrophobic character of surfactant.The minimum surface area demand,A_min,is slightly greater for glucoheptonamides than for the corresponding gluconamides.The practically constant A_min value within the homologue series of the aldonamides indicates that the obtuse hydroxyethyl residue is the determining factor for the arrangement of the adsorbed surfactants in the interfacial layer.