I would like to have an idea of the value of the glass transition of my polymeric nanoparticles before performing DSC analysis. As the Tg is dependent on the nanoparticles' morphology, I believe Fox' equation cannot be used in this case.
Anyhow, I'd also expect to obtain two different Tgs, because I am working with a hard core and a soft shell, but DSC analysis (and literature) suggest that the Tg is mainly dependent on the Tg of the shell. How does that work?
Thank you!
Dear Madam;
if both blocks forming the core and the shell have distinct Tg Transition, than in a DSC thermogram you will get both separate second order transitions relative to each block. Slow heating rate is needed to allow for distinct responses. Regards
Usually, the Tg of your CSNPs will lie between the Tg of the core and Tg of the shell. The reason of otherwise would be the direct reaction between the core and shell material giving rise to distinct materials property. If you are using a bridging chemical/ cross-linker then the Tg would be in between the two.
For your point, the reason Tg would depend on the shell is because the thermal gradient start from shell to the core, with shell surface having maximum temp. If the Tg of Shell is low then core materials, it will be reflected in the peak. Usually, the Tg depends on the shell thickness , core : shell ratio, as well as thermal properties of your materials.
Also, the DSC is default characterization technique to obtain the Tg of a given materials. For unknown materials, multiple scans at multiple heating rates are performed to obtain a Tg. Back calculation is an mathematically exhaustive process which would be time consuming. Hope this helps
You seem to have some good advice from the others who have posted already. I would, however, add some missing details. First, aside from the complexity and rate dependence of DSC, the structure and make-up of your particles can also cause problems.
First, if you have not read about it already, many material properties can change when a material is confined to a small dimension. This is a particularly big problem for polymers, for example, a free-standing thin film of polystyrene can have its glass transition change by over 50 degrees when reduced to thicknesses below 50 nm. In a spherical geometry the changes are amplified because it is related to the surface of the sample. In fact, depending on the surface the glass transition temperature may also be increased in comparison to bulk measurements. Prediction of what may happen is essentially an open problem in the physics of polymers.
Also, because Tg is surface dependent, Tg can really change depending on what is used as 'core' or 'shell'. At best one can make a rough guess of Tg and then try to measure it. I would look for 1.) the dimensions of the core and shell 2.) try to guess at the interaction between the two. If the shell and core are both large, then I would simply use the bulk values for Tg estimation - if they are close to one another then DSC will show a 'blur' of the two (think of an average). If they are far apart DSC should resolve each. If the core and shell are small (
For polymer nanoparticle there is some modification of orientation of chains. The Tg may be shifted.
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