Cloud Point Versus Procedures/NaCl Concentration for 1% HTB Solution:
Procedure and Results
The test started with a 1 mL sample of 1 mL HTB solution that had been prepared 13 days previous and kept refrigerated. Because of the long storage time, there is some risk that the polymers had hydrogenated in the water solvent.
In order to test for a cloud point, a continuously stirred boiling water bath was prepared, and the test tube containing the solution and a stir bar was submerged in the boiling water. With no salt added, no cloud point was observed.
To find the initial cloud point, 5 M Procedures/NaCl solution was prepared, and added to the test tube 10 microliters at a time. An initial cloud point was found at .045 M Procedures/NaCl at 94 C. During this initial testing it was found that enough water had evaporated from the sample that no additional HTB needed to be added.
For a more thorough investigation, a 10% HTB solution was made was added with a
5 M Procedures/NaCl solution to the initial sample at a 9:1 ratio, to preserve a 1% HTB concentration. The added solution (High Concentration Solution, HCS) was thus 4.5 M Procedures/NaCl.
The salinity of the cloud point sample increased according to the following equation:
C¬new = (Cold*Vold+CHCS*VHCS)/(Vold+VHCS)
For example after the first addition of 20 microliters of 1% HTB .45 M Procedures/NaCl the salinity of the test sample was: (.045*1+4.5*.02)/(1.02) = .132 M Procedures/NaCl
For each trial an addition of 4.5 M Procedures/NaCl and 1% HTB solution was added to the test solution, the test solution was immersed into the boiling water bath until a cloud point was observed, the solution was removed from the boiling water bath and immersed into a room temperature water bath, with continuous stirring, until the cloud disappeared. The temperature when the cloud disappeared was measured with a K-type thermocouple and thermometer.
4 trials of 20 microliter additions of HCS were done, followed by 2 trials of 40 microliters, 3 trials of 80, 3 trials of 160, 11 trials of 320 microliters, and finally 4 trials adding 640 microliters of HCS.
At trial 15, a clearly separated layer formed on top of the test tube with a very persistent cloud. It was assumed that this was due to a very high Procedures/NaCl and HTB concentration in the layer because of poor mixing. The test solution was transferred to a 25 mL flask, and the test continued with no further separation of cloud layer.
If re-done, considering the math of how concentration changes with each addition of HCS, fewer of the 320 microliter additions would need to be performed before the added volume is increased to 640 microliters.
The results were a linear relationship as shown:
An extrapolation of this relationship shows a 20 C cloud point at 5.82 M Procedures/NaCl.
