Effect of the concentration on sol-gel transition of telechelic polyelectrolytes.

Telechelic polyelectrolytes, bearing short hydrophobic blocks at both ends, will ionize into polyions and their counterions when dissolved in water. With the variation of concentration, the interplay between short range attraction and the long range electrostatic interaction as well as the counterion distribution exerts a major influence on the chain conformations (two basic conformations: loop and nonloop, the latter can be subdivided into three association types: free, dangling, and bridge), the cluster structure and the forming of a physical gel. For weak hydrophobic interaction, the relative strong electrostatic interaction dominates the gelation progress; sol-gel transition occurs at higher concentrations due to electrostatic screening and mainly involves the forming of stretched nonloop conformations such as dangling and bridge. While for strong hydrophobic interaction, the hydrophobic interaction dominates and the electrostatic interaction provides a contribution to the formation of gels by maintaining a spatial swelling structure, resulting in a much lower concentration region of sol-gel transition; besides, the sol-gel transition is characterized by the competition of the forming of loop and bridge chains.