Adsorption variation due to pH effects

Depending on the pH of the solution in which the substrate(silica) is immersed the surface charge of the substrate tends to vary.  A higher pH will lead to a more negative charge on the silica surface.  The polystyrene sphere solution has SDS, an anionic surfactant, and surface sulfate groups from the synthesis of the of the spheres.  These sulfate groups lead to an overall anionic charge in the sphere solution prior to the addition of the SDS surfatant.  Yesterday I was able to discuss with a colleague  the possibility of the pH of the sphere solution causing a slight repulsion between the spheres and the substrate, due to the negative charge attached by the sulfate groups and the hydrophilic nature of the silica.  It seems a simple task to check the pH of a sample solution and test the effect of it's variation on the surface coverage of the substrate.  I will note that I feel as though speaking with a peer who is extraordinarily familiar with the effect of pH on adsorption, although the conditions are different for their project, was extremely helpful in making assumptions as to the nature of it's effect and whether or not considering the pH a factor was a major necessity.  

On a personal not, the frustration of not knowing if all of this work and produce the surface we need and whether or not what these small considerations are going to make any difference in the end is a little dis-hearting at times.  However, what worries me most is the time spent on this part of the project if we have to change methods.  I do not feel that it is time wasted because I am definitely learning a lot about how all of the little things affect adsorption.  That being said, I feel that research is exciting once you get results that tell you something new and I am excited and anxious for that part of the project to be here!  It's even more exciting because you know that you didn't cut corners and all that trial and error and work made a difference!  It's like a Christmas that comes early!