Dendritic nano- and microhydrogels fabricated by triethoxysilyl focal dendrons

Abstract

Nano- and microhydrogels were fabricated in water by first to third generation triethoxysilyl focal poly(amido amine) dendrons with hexyl spacer. The focal points of dendrimers were hydrolyzed and covalent-bonded through the simple sol–gel process at an acidic or basic catalytic condition. The growth of aggregates and the following gel formation were determined by rapid increase and convergent steady value in light scattering of dendron solutions. The sol–gel reaction was also confirmed from the disappearance of an infrared absorption band of Si–O(C₂H₅) stretching vibration mode (1080 cm⁻¹) and the appearance of Si–O–Si stretching bands (1136 and 1049 cm⁻¹). The resultant gels were transparent and rather fluid. Transmission electron microscopic images of the gels showed three-dimensional dendritic growing of fine fibrils. The nanogel nuclei grew up favourably to nanogels in acidic conditions and to microgels in basic conditions, and the growth was more remarkable at higher generation of dendrimers. At high concentration of dendrimer, macrogels with fiber-like texture were formed. It was supported that siloxane-linked focal groups constructed main chains and branches of fibrils, and dendron side chains coated polysiloxane backbones. The hydrogels emitted fluorescence, which was stronger at base-catalyzed condition than at acid-catalyzed condition. This indicates that crowded circumstances or large amount of fluorescence-inducing moieties intensify the fluorescence. Fluorescent images of such architectures were visualized on a fluorescent microscope.