Greetings everyone,
I am developing a formulation based on poloxamer (15% - 20%) in phosphate buffer. I used some methodologies from the literature to obtain the DSC profile, but I didn't get any satisfactory results (the attached image).
Methodology: PL hydrogels (35 mg) were placed in sealed aluminum pans and submitted to three successive thermal cycles of heating-cooling from 0 °C to 50 °C at a rate of 5 °C/min, using a TA Instruments (USA) Q200 DSC apparatus. An empty pan was used as reference. All analyzes were performed in triplicate and thermograms represented by heat flux (kJ·mol−1 ) versus temperature (°C).
I even used two different equipment and had similar results, far from what is expected (Tg of approximately 30ºC). Could anyone give me any thoughts on this?
Cheers!
Hi Matheus. I am not quite sure about the poloxamer behavior exactly, but if you need to see a Tg from DSC results, maybe by varying the heating ramp (using a slower heating ramp) you will be able to see something. Another option to see the Tg, if possible, is using DMTA or rheology experiments I wonder.
Good luck!
Hi Matheus!
The hydrogel (Poloxamer diluted in phosphate buffer) does not show glass transition; instead, there is the micellization temperature, which is the temperature in which the poloxamer self-assembly into micelles. In most of your compositions, this is the peak you observe in the third graph over 10-30 °C.
If you want to see the gelation temperature, I recommend you perform a rheology analysis, fixing the frequency, varying the temperature, and recording elastic and viscous moduli.
As far as I know, the glass transition is only observed in dried poloxamer. The hydrogel does not show glass transition below 100 °C, which is the maximum temperature you can work since you have water in the hydrogels. So then, only the dried poloxamer pellets show glass transition due to the degree of freedom of PEO-PPO-PEO chains.
I hope I have helped you.
Best regards,
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