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I dissolved PEO 10K - PLLA 14K in toluene at the concentration of $\pu{50 mg/ml}$, $\pu{25 mg/ml}$, and $\pu{5 mg/ml}$ including $\pu{30 min}$ of sonication.

When I sonicated them at room temperature, only $\pu{5 mg/ml}$ was clear solution but others were cloudy.

However, when I did at $\pu{50 ^\circ C}$, all the solutions were clear initially, but only $\pu{50 mg/ml}$ solution became cloudy as it naturally cooled to room temperature.

I measured and compared water/solution interfacial tensions, and I found that solutions sonicated at room temperature showed relatively higher surface tension than those sonicated at $\pu{50 ^\circ C}$. I think this means some of polymers are not dissolved or highly aggregated so that they did not effectively act as surfactants.

My questions are:

  1. What does clear/unclear solution mean? Is it not dissolved? Or is it highly aggregated?
  2. Solutions of $\pu{25 mg/ml}$ and $\pu{5 mg/ml}$ were clear in both cases but have different interfacial tension. How can I explain this?
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