Dependence of the dispersion behavior of [60]fullerene in aqueous media on the chain length of poly (N-isopropylacrylamide) as a dispersing agent

摘要

We have investigated the effect of the chain length of temperature-sensitive poly(N-isopropylacryla-mide) (PIPAAm) on the dispersion of [60]fullerene (C_(60)) in aqueous media through an interaction between PIPAAm and C_(60) below the lower critical solution temperature (LCST) of PIPAAm. UV-vis absorption spectral measurements showed that the saturated amount of the dispersed C_(60) increased in proportion to the chain length of the PIPAAm. Additionally, an absorption band at around 430 nm was observed in the dispersed C_(60) solution and was assigned to a C_(60)/PIPAAm complex. The complex formed an amorphous molecular assembly between C_(60) molecules and PIPAAm chains, the structure of which was confirmed in a transmission electron microscopy image. Dynamic light scattering measurements indicated that the particle size of the C_(60)/PIPAAm complex increased with the chain length of the PIPAAm. From electrophoretic laser light scattering measurements, the zeta potential of the C_(60)/ PIPAAm complex was found to be shifted from a negative value to zero with an increase in the chain length of PIPAAm. Longer PIPAAm chains, however, gave rise to a higher dispersion stability of the complex. Similar to the dispersion behavior of PIPAAm-C_(60) conjugates in aqueous solutions, the aqueous C_(60) dispersion with PIPAAm exhibited rapid, and reversible dispersion-aggregation changes in response to temperature alternation across the LCST.