Visualizing spontaneous physisorption of non-charged π-conjugated polymers onto neutral surfaces of spherical silica in nonpolar solvents

Abstract

In this study, we demonstrated that the non-charged π-conjugative polymeric fluorophore poly(di-n-octylfluorene; PF8) spontaneously physisorbs onto the neutral surface of μm-sized spherical silica (SiO2) in suspension within several hours at room temperature using chloroform, benzene, toluene and carbon tetrachloride as solvents. This process was observed by photoluminescence and photoluminescence excitation spectra, as well as observation with the naked eye. The level-off amount of physisorption was controlled by the choice of dispersion solvent and physisorption time. Surprisingly, the highest fraction (51-56%) of β-phase was spontaneously deposited at the surface without thermal treatment. Similarly, two other non-charged π-conjugated polymers (i.e., poly[(9,9-dioctyl-fluorenyl-2,7-diyl)-alt-bithiophene]; PF8T2) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]; MEH-PPV) spontaneously physisorbed onto surfaces of several μm-sized SiO2, Al2O3, ZnO and TiO2 (anatase and rutile) particles in chloroform over several hours. Attractive van der Waals interactions between these non-charged polymers and ceramics are assumed to be the driving force for spontaneous solution-phase physisorption. Our experimental results may provide an alternative approach that enables hybridization of various π-conjugative polymers with ceramics in addition to the conventional chemisorption and physisorption approaches (i.e., grafting-from, grafting-to and layer-by-layer deposition due to Coulombic forces).