Phase transition of silver nanoparticles from aqueous solution to chloroform with the help of inclusion complexes of p-sulfonated calix[4] arene and alkanethiol molecules and its application in the size sorting of nanoparticles

Silver nanoparticles were synthesized in aqueous solution and capped with an inclusion complex of octadecanethiol (ODT) and p-sulfonated calix[4] arene (pSC4). By vigorous shaking of a biphasic mixture of the pSC4-threaded ODT-stabilized silver hydrosol and chloroform, the phase transition of the silver nanoparticles could be observed in the course of the transition of colour from the aqueous phase to the organic phase. The procedure of phase transition was independently verified by UV-vis spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectra, and H-1 nuclear magnetic resonance (NMR). In shaking the biphasic mixture, it was believed that pSC4 molecules were desorbed from the inclusion complex and the protective layer of silver nanoparticles shifted from hydrophilic to hydrophobic, which drove the phase transition of silver nanoparticles from aqueous solution into chloroform. More interestingly, the efficiency in the phase transition of aqueous silver nanoparticles rigidly depended on their sizes, which maybe used in the size sorting of nanoparticles.