Is there a reliable way to investigate liquid-liquid phase separation in glasses using thermal analysis techniques such as DSC or DTA/TGA? Can anyone provide references?
Due to the low mobility in glass phase phase separation may be hidered, and frequently non-equilibrium structures are formed, especially casting used to prepare the samples. If you heat such samples above the glass trantion temperature and repeat the DSC run you may get two glass transitions. In an earlier paper written with the scentists of UMASS we have observed such a phenomenon in polyimide-polybenzimidazole systems. Ithink that SC is not always sensitive enough to detect such a phase separation, DMA or dielectric spectorscopy may be better, TSC (thermaly stimulated current) is especially sensitivedue to itslow effective frequency.
I agree with Gyorgy; I have never seen a paper dealing with a study of liquid-liquid phase separation by classical thermal analysis methods.
Merry Xmas!
EDZ
Just an update. There are many papers now known to me where two Tg's are shown due to supposed liquid-liquid phase separation. For instance, DOI: 10.1016/j.jnoncrysol.2008.10.016 Fig 3.
Its is true that in some special cases of liquid-liquid phase separation (LLPS) one can detect two Tgs by DTA or DSC, but quite often one of the liquid phases is very rich in SiO2, hence a clear inflexion in DSC/DTA traces is not seen. Therefore, many phase separated systems only show one Tg!
In general it is quite hard to obtain relevant kinetic and microstructural information about the LLPS process by DSC and TDA methods (other than Tg). In order to follow the kinetics and micro - nanostructural evolution of LLPS it is much better to use SEM, TEM or SAXS as shown, for instance, in a classical article: THE EFFECTS OF AMORPHOUS PHASE-SEPARATION ON CRYSTAL NUCLEATION KINETICS IN BaO-SiO2 GLASSES .3. ISOTHERMAL TREATMENTS AT 718C TO 760C - SMALL-ANGLE X-RAY-SCATTERING RESULTS - Journal of Materials Science 21(1986) 3050-3064.
Thanks Edgar. Of course, there is always a danger in doing quenched studies that fugitive phases or other phenomena have not been arrested and the nanostructure is different than it was at temperature. That being said, there are many in-situ high temperature techniques available now. One which we are considering is small angle neutron scattering.
Thanks for your note that absence of two Tg's does not necessarily rule out LLPS. My understanding is that it depends also on heating rate in the DSC/DTA, and that at least 20K/min is required to see these..
Thanks, John
SANS could indeed be excellent, and I agree that in-situ high temperature studies are, in principle, better that ex-situ studies! Although, for in-situ work one should always be aware of and continuously check for unwanted surface crystallization that might happen during thermal treatment. In ex-situ studies, on the other hand, one can always grind off the crystallized surface layer before doing microscopy, SAXS or any other type of measurement.
Good luck in your research!
Edgar
I try to use DSC to capture the phase separation of cellulose in water, but it seems the thermal change is too small to be recorded with the machine
any new method suggested?
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