This week I sulfidized a lot of coupons, I digested coupons, I brainstormed protocols, and I presented preliminary data.
Oh, I just realized I need to make a comment about the previous sentence. A long time ago, before I was a teacher, I worked in a factory that made circuit boards. We made huge 3’x2′ sheets with lots of layers and lots of individual small circuit boards to cut out later. To prove the boards were good, we cut out small rectangles from the sheet, next to the circuit boards, to check the inside layers. Everyone called those cutouts coupons. I guess the sheet did look like a newspaper spread with holes where someone cut out coupons. So when we have a membrane and I cut out a piece to analyze, I call it a coupon. And “digesting coupons” means dissolving them, or at least dissolving everything except the plastic backing. So let me start again.
This week I sulfidized a lot of 1″ circular cutouts from membranes, I digested said cutouts, I brainstormed protocols, and I presented preliminary data.
The first thing I discovered is that my quest for efficiency produced inconsistent results. In processing things quickly (and efficiently I might add – I would still be running
coupons 1″ circular cutouts today otherwise) the process turned anaerobic (no oxygen) and produced colors different from previous work. I also had 3x the standard deviation in silver loading. So I am rethinking (with my mentor’s help) the protocol to produce silver membranes and sulfidized membranes. Again for my quest for efficiency, I am building a frame this weekend to try and triple the membrane throughput. I’ll post a picture if it works.
So I got to present my data. It shows that partially sulfidized silver nano particles do stay in membranes longer. Perhaps a lot longer, like months instead of weeks. Not only was it good to present a positive outcome, I now know that even if everything else breaks down, I have data for the poster. This photo shows the digested
coupons 1″ membrane cutouts. The dark color hints that maybe even 2% nitric acid is inadequate to remove sulfidized silver nano particles. I’ll find out this week.
The goal this week was to make more nano-silver laced membranes, react them with sulfur, and destructively test coupons to see how fast the sulfur-modified silver nano-particles leach. So, just like that one team playing for the world cup (yes, that one), I was close but missed my goal. I also had an unexpected set of data and a you-should-have-listened moment.
In week one I created a membrane and we sent off coupons to see how consistent the silver nano particle concentration was across the surface. We got the data back. We found a large (200%) difference between the center and the edge of the membrane. Well that changes things. I had observed while creating the membranes that sometimes during the agitation, the center of the coupon had a very thin amount of solution above it. So I modified the process to have a slightly deeper well of reactants (25mL instead of 20mL – with mentor permission). Maybe the center and corner coupons will be closer now. To make sure, I cut our 8 coupons (4 corner and 4 center) and we will test those. That took 24 hours.
I needed to make many more membranes, especially if the silver loading varies. How many? 8 coupons per membrane, with 5 different sulfur concentrations, with 6-8 timed leaching samples, and possibly 2-3 coupons per reading – that’s a lot of membranes. So I started Monday after the RET meetings. And the first membranes – failed. I should have listened. Previously someone mentioned that they thought one of the chemicals (NaBH4) had failed the day after they made the solution. The solution I used was even older. I should have listened. Do over on Tuesday.
Tuesday I created a fresh solution of NaBH4 and created 10 membranes. That took all day. The picture above was membrane #3 or 10.
I then cut out 40 coupons.
I then created the sulfidation chemicals – lots of stoichiometry, solubility, molarity, and -ty’s.
I then reacted everything which took another 24 hours. Note the black speckled lines on the coupons – that’s the silver sulfide. The picture is 16 of the 40 coupons.
So Tuesday this next week I will be doing the leaching. I will have to bring cookies for the mass spec person who will analyze the dozens of samples.
Then we decide what to do next.
The first week: three things accomplished, waiting on mass spec, and I got to push the button.
Dr. Perreault was very patient this week, showing me around his lab space, describing the research I will be working on, and answering my totally naive-sounding questions. As a side, I mentioned that I had produced nano particles with high school students at SMHS. I said how difficult it is to produce evidence that they produced nano particles when limited to high school lab equipment. A few minutes later, I had a test for the presence of nano-particles using a laser pointer (which Dr. Perreault even demonstrated in his office) that I can do in my classroom. He also described a dynamic light scattering test and a UV-VIS test for nano particle size that I might try out here and use in my classroom as well.
Doug Rice, my mentor, and Diane (REU) walked me through the steps to create nano-silver laden membranes. I created my first one, and I got the the membrane to turn yellow. YAY! I t means I did the steps right and my stoichiometry was good too. So now I can make infinite numbers of membranes. Or at least a few dozen.
I also determined efficient ways to cut coupons out of the membrane. Best use of material and such. They let me use a hammer. In a lab.
Also, I set up samples for ICP-MS (inductively coupled plasma mass spec). The initial data will let us know if our procedures produces results similar to a previous study.
Next week I will be reacting the silver with sulfur. The idea is that silver nano particles leach too fast from the membrane, so an incomplete reaction with sulfur will bridge together all of the silver nano particles keeping them in place longer while retaining most of their antibiotic capabilities.
But the highlight this week was when Doug showed me how to use an autoclave. He let me push the button.