Aggregation behavior of derivatives of sodium alginate and N-octyl-β-d-glucopyranoside in aqueous solutions

•We obtained sodium alginate derivative through hydrophobic modification.•A competitive absorption between CSAD and OGP exists in the gas–liquid interface.•Four conformations of complexes were found with the increasing of OGP concentration.•The mechanism explains the formation of polymer–surfactant complexes.

In this study, the aggregation of N-octyl-β-d-glucopyranoside (OGP) and cholesteryl grafted sodium alginate derivative (CSAD) in solutions was investigated by surface tension method, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. Results showed that cholesteryl of CSAD and OGP were adsorbed competitively to the gas–solution interface. Four different conformations of complexes were found with the increasing of OGP concentration (C). When C < critical aggregation concentration (CAC), the OGP stimulates CSAD association. When CAC < C < critical micelle concentration (CMC), the OGP was stimulated by hydrophobic interaction, then it compounded CSAD to form polymer–surfactant complexes and some pearl-chain structure complexes. When CMC < C < adsorbed saturation concentration (C2), the quantity of pearl-chain structure complexes increases, they interact to form core–shell structure complexes, and several core–shell structure complexes formed short string-structures by association of CSAD molecule. When C > C2, adsorption amount of OGP to CSAD reached saturation, OGP molecules formed small single OGP micelles, while the string-structures were dissolved because the cholesteryl among the micelles were replaced by the single OGP micelles.

Graphical abstractIn gas–liquid interface, a competitive absorption exists between CSAD and OGP. When the concentration of OGP is low, OGP and CSAD form polymer–surfactant complexes. When the concentration of OGP exceeds CAC, polymer–surfactant complexes convert into pearl-chain structure and core–shell structure complexes, and two core–shell structure complexes can be jointed to form the short string-structures. When the concentration of OGP exceeds C2, single OGP micelles form and destruct the string-structures.Figure optionsDownload full-size imageDownload as PowerPoint slide