Susan Kelleher

To test the stability of the dipodal activation verses the monopodal activation, zeta potential experiments were undertaken. Figure x outlines the results of DLS tests looking at the zeta potential of amine-coated NPs monopodal and Dipodal activation, prepared over different reaction times. The zeta potential of the amine-coated particles, if stable in solution, should be positive (>10). As hydrolysis of the silane occurs, the positively charged amines “fall off” and a reduction in zeta potential can be seen. The negative charges correspond to the silica shell, which is abundant in hydroxyl groups and hydroxide ions. As can be seen in Graph 3, attaching the monopodal amines for three hours results in a nanoparticle which over time loses its amine functionality and a drop in zeta potential (from +5mV to -35mV) takes place.

On the other hand, the Dipodal activation is seen to be very stable and that this stability depends on the reaction time giving for attachment of the amines to the nanoparticle surface. After a short reaction time (1 hour), it is shown that the resulting NPs lose their amine functionality over time (12mV to -10mV). The longer the Dipodal APTMS is allowed to react, the more stable the resulting the amine-coated NPs are. After three hours reaction time however, equilibrium is reached and further reaction time doesn’t increase the stability of the functional groups. After three hours reaction, the amines on the NPs are secure and little reduction in the zeta potential occurs (20mV to 10mV).