Same old, same new. Right now, it’s just repetition of what I’m familiar with and what I’m still unfamiliar with. I’ve got the hang of running the RO system and using the goniometer to measure contact angles, but I’m still learning how ATRP (remember atom transfer radical polymerization?) works. It’s a lot of chemistry and science at a molecular level because initiators, buffers, attachments of copolymers, etc. are involved. In case you don’t remember from my last report, it is one of the most commonly employed techniques for the development of new materials due to the ability to control molecular weight and polymer structure throughout the process.
We decided to reduce the salinity concentration of the feed water for the RO system because the first modified membrane’s permeability was negatively affected by the polydopamine phase (which acts as the initiator) and therefore it’s flux was low relative to the commercial BW30 membranes. Lowering the salinity allows us to better characterize the surface, especially since the concentration will be at a saturation index of less than one (because at an index of greater than one, crystallization is going to occur regardless of the surface chemistry of the membrane). The concentration at the membrane surface also has to be taken into account because it is always greater than the concentration of the feed. There was a reduced appearance of scaling on the membrane surface after 48 hours in the RO system, but, again, the flux was lower at the same pressures and cross flow as the commercial membranes. Just to give you an idea, the commercial membrane produced a flux of approximately 1.7 mL/min at 350 psi while it took a pressure of about 400 psi to reach the same flux with the modified membrane.
There is a lot of room for error throughout the ATRP procedure, so non-homogeneity is expected, but a lack of uniform coverage of the membrane surface with the copolymers is an issue when it comes to reducing scaling. We were measuring contact angles the other day and the first strip of the newly modified membrane was giving us very low angles with drops of water, which is exactly what we wanted because it indicates that the surface is more hydrophilic. Then, we tried another strip of a membrane from the same modified batch and the angles were almost twice as large. When the membrane was examined more closely, there was a varying level of dullness on the surface, which could be evidence that the modifications are not taking place throughout the entire surface evenly.
This week has been a race against time, with my work ending this Friday and Humberto’s conference taking place a week later. We’re hoping that by performing more ATRP on membranes and having a better handle on the process and consistency of modification, we can gather more agreeable data on the effects of ATRP on scaling. My next post will detail the end of my research here at Yale, and hopefully I’ll have conclusive results by then. Wish me luck!