Effect of pH Conclusion

The pH of the 50 nm sphere solution was tested and found to be roughly 4.5.  From the literature, at 8.5 pH silica has a negative charge which hinders the adsorption of anionic surfactants (1).  Because our pH is much lower than this value we can say that the surface of the silica has a slightly positive charge which would increase the adsorption of the SDS (anionic) in the sphere solution.  The theory that this would increase the sphere adsorption as well would require further experimentation which is not the primary focus of this project. Therefore, we will conclude that the pH effect on the sphere adsorption is not a factor to be explored in enhancing the monolayer coverage for this project. 

However, the SDS adsorption to the silica as a result of the low pH may be a factor is creating a sharp relief.  It has been recommended that the samples be soaked in methanol to loosen the SDS on the surface of the silica.  To make sure that this soaking step does not affect the sphere monolayer, SEM will be performed prior to the soak and then again after the soak to determine the effect, if any, on the already deposited spheres.