Phase Changes, Cholesteryl Myristate

Sample

Cholesteryl myristate, fine platelets

Conditions

Measuring cell: DSC821^e with IntraCooler

Pan: Aluminum 40 µl, hermetically sealed

Sample preparation: As received, no preparation

DSC measurement: Heating from 40 °C to 110 °C at 10 K/min, then cooling down to 40 °C.  Second heating run from 40 °C to 110 °C.  All steps with a heating/cooling rate of 5 K/min.

Atmosphere: Nitrogen, 50 cm³/min

Interpretation

Cholesteryl myristate is an example of a substance whose melting process exhibits intermediate liquid crystal stages: On heating, the substance is not directly transformed from the crystalline state to an isotropic melt; the melting process includes a smectic and a cholesteric intermediate stage (mesophases). On cooling at 5 K/min, rapid mesophase transitions and a crystallization process (effect D) can be observed. In the second heating run a slight shift of peak A to lower temperature is noticeable. This is possibly due to better thermal contact between the sample and the pan.

Evaluation

Onset temperature determination and integration of the individual peaks.

Conclusion

Even mesophase transitions with very low transition enthalpies can be characterized with DSC. Additional information concerning the different mesophases can be gained by the use of thermomicroscopy with polarised light.

_{Phase Changes, Cholesteryl Myristate | Thermal Analysis Application No. HB827 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals}