A study on the conformation transition of polyacrylic acid in its aqueous solution by fluorescence correlation spectroscopy

• 1、Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an, Shaanxi 710127, China
• 2、Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

Abstract：In this paper, the conformation transition of an annealed polyelectrolytes, polyacrylic acid (PAA), was studied by fluorescence correlation spectroscopy in its aqueous solution. The influence of pH, counterions concentration and valence on the conformation transition was investigated. The results revealed that PAA undergoes a continuous conformational transition between pH 6 and 3 from an extended coiled structure to a collapsed globule conformation. The conformational transition can also be achieved by increasing the counterions concentration. The dependence of hydrodynamic radius on the Debye screening length are determined. The results were compared with quenched polyelectrolytes. "Ion-bridging effect" was founded when added multi-valent counterion. A series about the interaction ability of multivalent counterions and PAA was founded: La3+>Ba2+>Sr2+≈Ca2+>Mg2+. An evidence of re-entrant transition of PAA with Mg2+ ion was also discovered.

keywords： polyacrylic acid conformation transition Fluorescence Correlation Spectroscopy

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