I was wondering about the surface chemistry of borosilicate glass capillary. If we dig it into buffer solution (low concentration of KCl for example), how can be sure about the charge of the surface? As far as I know they can be charged positively or negatively. Can we say in low pH5-6 it can be negatively charged due to..?
I worked with the bulk of the glasses, and rarely with surfaces, so this might be a bit of guesswork on my part. Given that positively charged Na+ can dissolve away, leaving behind a negatively charged oxide network (think dissociated sodium silicate), I would guess that the surface would be negatively charged. When adjusting for pH, a factor to consider would be the pKa of the borate/silicate network. Since silicic and boric acids are weak acids, and have fairly high pKa, I would guess that lowering the pH would introduce more H+ ions that would bind to the negatively charged oxide groups, thus lowering the surface charge. I'm not sure if the surface charge could ever become positive. I hope this helps.
I agree with Pavel. The source of negative charges are slightly dissociated silanol groups, similar to those in silica nanoparticles (SNP). The charges in SNP can be directly evaluated by zeta-potential measurements, see for example the recent paper of K.-M. Kim et al. Surface treatment of silica nanoparticles: Int. J. Nanomedicine 9(S2) (2014) 29. The charges are clearly negative in the pH range you are interested in.
- Badges
- Science topic
- Similar topics
- Geoscience
- Asia
- India