Morphological, structural and rheological properties of beta-cyclodextrin based polypseudorotaxane gels

Supramolecular self-assembled gels of polypseudorotaxane (PPR) were made through sequential inclusion complexations between beta-cyclodextrin (β-CD) and reverse Pluronic^® (RPL, or PPG-PEG-PPG). This study aimed to disclose the differences in morphological, structural and rheological properties of the PPR gels made in citric acid and other conditions. β-CD/RPL mixture in citric acid solution incubated at 25 °C (β-CD/RPL-C-25) had the most homogeneous, fine and continuous structure, the lowest crystallite size, and the highest gel strength and thixotropy. It was hypothesized that the citric acid partially interfered with the crystal growth of PPR, and thus led to high degree of crosslinking which explained its largest gel strength and thixotropy. β-CD/RPL mixtures in water incubated at 65 °C (β-CD/RPL-W-65) underwent PPR rearrangement, resulting in larger crystallites and a more integrate net-like structure, therefore yielding higher gel strength as compared with β-CD/RPL mixture in water incubated at 25 °C.