I performed a DSC measurement on hydrogen-bonded ionic liquid crystal materials type to determine the temperature of transition from crystal solid to LC state.
I get an endothermic peak (transition to mesophase) which is considerably broad (over 100°C range). Can anyone suggest why the transition is so broad and what may be the cause of this broadening?
How fast is the scan? Sometimes if the thermal conductivity is low, thermal capacitance high,or sample is large it could be kinetic effect as the sample does not heat fully.
Wow, could you present the curve?
In polymers the breadth of the transition has to do with crystalline size ditriibution. But that is not 100 degC broad. Are you sure that this is a single transition? Can you use mlodulated DSC? Did you perform other temperature dependent measurments?
The heating rate seems appropriate. I agree with Marina Makarova. If we use a large amount of sample, a broad endothermic peak is likely observed due to some kinetic effect. have you seen such breadth in the corresponding peak on heating- cooling cycle run?
In the file attached are the corresponding DSC curves of my compounds.(sample weight between 6 to 9 mg) scan rate 10°C/min. first heating-cooling cycle (black line) and second heating-cooling cycle (red line)
the broad endothermic peak seen in the first heating segment is attributed to a transition from solid crystal to liquid crystal state of the corresponding compounds.
Dear Dr. Ciobanu,
As the others mentioned the peak is quite broad for a solid-liquid transition in such a material. I don't believe that this can be related to the sample mass, heating rate or low thermal conductivity. There might be a strange explanation (might be right or wrong). Please cross-check the sample weight immediately after the test (in case you have used open or pierced crucibles). It might be that there is some humidity inside the sample and what you see is evaporation during the first heating run. The temperature range would fit. In such a case the sample weight should slightly decrease during the test.
Please do the following checks
1. Check the purity of the sample.
2. Crip the cell perfectly
3. Run the instrument with a standard sample.
4. Check the base line
5. Clean the heating chamber, if required
after a heating-cooling cycle, try another cycle with the same sample in the same crucible. Your signal indeed looks like a loss of moisture. On cooling no exothermic signal appears. One should expect some crystallization to occur, maybe with some hysteresis.
I agree with Alberto Schiraldi. There may be a moisture loss in your sample.
I also agrre with Alberto.
You observe this broad peak only during the first heating. Not during the second heating cycle. We can also add that the two cooling curves are almost the same.
The temperature of this peak (close to 90°C) would correspond to the moisture loss.
Is it possible that you have three peaks overlapping?
Something like I draw?
- Badges
- Science topic
- Similar topics
- Linguistics
- Composition Studies
- Publication