Did you know that interfacial and mixed polymer content in structured (sometimes called core-shell) latex particles comes about naturally during the second stage polymerization in the latex particles as phase separation and late-stage ripening takes place to create the final morphology of the particles? Depending upon the reaction kinetics and polymer chain diffusion conditions during the polymerization, we know that the amount of this mixed polymer can be very different from one set of conditions to another. Therefore, many times the particles will contain three phases of material; two pure (well, not always so pure) polymer phases and a mixed, or interfacial, phase. Each has certain volumes (masses) and these can be readily measured in the differential scanning calorimetry (DSC). Note that the interfacial polymer is not effectively seen in TEM images, even when chemical staining is applied.
Differential scanning calorimetry is the well-known and widely used technique to measure the glass transition temperatures (Tgs) of polymers. Of course, it also measures the degree of crystallinity in polyolefins, etc. By extension, the DSC thermal signal is also sensitive to mixtures of polymers that have different Tgs. Noting that the glass transition is not a first order thermodynamic change (as are vaporization and freezing – large enthalpic changes at a fixed temperature) thermal analysis of polymers results in significant changes in heat capacity as the temperature increases through the transition region. Thus, the DSC generates a signal that, when differentiated, results in a transitional “peak”. The maximum in the peak signal is, by common practice, taken as the Tg.