This week was spent mostly in the lab. I worked on finding the Cp* of bentonite clay and then taking pictures of back scatted light from solutions with different Cp values. To find the Cp* of the bentonite clay I used data collected by Wayne and Alina last week along with data I collected this week. I used the LISST to find the Cp of four different concentrations. The graph below shows the results.

I found the slope of the linear regression line formed by the points above. I forced the regression line through the origin of the graph because if there are zero particles, the Cp should be zero. The regression line is not on the graph above because I could not figure out how to force it through the origin in matlab. So I graphed it in excel to find the slope. I came up with a slope (Cp*) of 238936 mL/m*g or 0.24 m^2/g. Wayne's measurements after salt had been added to form aggregates was 0.4-0.5 m^2/g. So i believe my value to be reasonable and accurate enough for my purposes.

Next I attempted taking pictures using the mirror set up, having the laser shine through a hole in a mirror positioned at a 45 degree angle. Back scatted light should hit the mirror and be reflected to the camera lens. It seemed like i good idea, but i could not get it to work properly. The hole in the mirror was purposely smaller then the laser beam, this forced the laser beam to be a round beam. However this illuminated the inside of the hole in the mirror, the camera was picking up this light and ruining the picture. So i tried using a pinhole in a piece of paper to shrink the laser beam before it went through the mirror. This reduced the light to almost nothing. Next i tried drilling the hole in the mirror larger and making the pinhole larger. This worked to some extent, but the reflected light off the surface was still illuminating the hole in the mirror. After trying to get everything positioned just right for hours, I abandon the mirror idea.

Next up was our other idea of putting the laser pointer in the center of the camera frame. This way the camera looked down on the solution with the laser pointing directly in the center of the picture. The light reflected off the waters surface should be reflected directly back at the laser pointer and never make it to the camera lens. I tried using the polarized lens with this setup and found that it was eliminating the back scattered light. I went into a completely dark room to take the pictures and coated the inside of a beaker with black rubber to reduce reflection off the sides. I tried using a pinhole again but it made the pictures much darker and placed more unwanted objects in the picture. The pictures looked much better without it. Next I made the solutions and took some pictures. On the camera I used an iso of 1600 and an exposure time of 13 seconds. For the 0.5 1/m solutions I used pure water and could not see any back scattered light. For the rest i got reasonable pictures. Here are the pictures, from top to bottom the C total values are: 2 1/m, 8 1/m, and 32 1/m.

I am still kicking myself for the first picture. It looked great on the camera screen, but once i got it on the computer, i realized i must have moved it during the 13 second picture. I don't have a picture for pure water because the camera picked up very little light and the pictures looked terrible. The only thing i don't like about the above pictures is the ring formed at the edge of the beaker. I need a larger beaker that the edges will be out of the camera frame, or a lens that can focus over smaller distances. Given more time I don't see why I won't be able to get excellent pictures now that I have experimented.

Don't expect a post next week, because I will be relaxing and BBQing in the mountains of Vermont!