In this work, the phase diagram of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends is measured by means of standard and modulated temperature differential scanning calorimetry. Blends were made by solvent-casting from chlorobenzene, as blends cast from toluene or 1,2-dichlorobenzene prove to retain effects of phase segregation during casting, hindering the determination of the phase diagram. The film morphology of P3HT/PCBM blends cast from chlorobenzene results from a dual crystallization behavior, in which the crystallization of each component is hindered by the other component. A single glass transition is observed for all compositions. The glass transition temperature (Tg) increases with increasing concentration of PCBM: from 12.1 degrees C for pure P3HT to 131.2 degrees C for pure PCBM. The observed Tg defines the operating window for the thermal annealing and explains the long-term instability of both the morphology and the photovoltaic performance of the P3HT/PCBM solar cells.

The heat capacity signal from modulated temperature DSC can be used to measure the onset of phase separation in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions, showing a type II LCST demixing behavior. Quasi-isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity, caused by demixing and remixing heat effects on the time scale of the modulation. These excess contributions and their time-dependent evolution are useful to describe the kinetics of phase separation and to follow the related morphology development. Partial vitrification of the polymer-rich phase slows down the remixing kinetics.

The effect of additives on the LCST phase behavior of aqueous solutions of either poly(N-isopropylacrylamide) (PNIPAM) or poly(vinyl methyl ether) (PVME) has been investigated using high-resolution ultrasonic spectroscopy (HR-US) and modulated temperature differential scanning calorimetry (MTDSC). Both techniques revealed that the addition of salt causes a decrease in demixing temperature (T demix) due to the water-structuring capacity of salt ions. This salting-out effect becomes more pronounced at high polymer concentration, causing an asymmetric shape of the LCST demixing curve. Conversely, adding a surfactant results in an increase of T demix because of the increased solubilization of the polymer chains. In addition, HR-US provides supplementary information on a molecular level, illustrating that both types of additives dissimilarly affect the polymer−water hydration structure; i.e., salt ions primarily dislocate the structured water molecules, whereas surfactants interact with the polymer itself.

The heat capacity or reversing heat flow signal from modulated-temperature differential scanning calorimetry can be used to measure the onset of phase separation in a poly(vinylmethylether)/water mixture, clearly showing the special type III lower critical solution temperature demixing behavior. Characteristic of this demixing behavior is a three-phase region, which is detected in the nonreversing heat flow signal. Stepwise quasi-isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity signal, caused by demixing/ remixing heat effects on the timescale of the modulation (fast process). These excess contributions and their time-dependent evolutions (slow process) are useful in understanding the kinetics of phase separation and the morphology (interphase) development. Care has to be taken, however, in interpreting the heat capacity signal derived from the amplitude of the modulated heat flow because nonlinear effects lead to the occurrence of higher harmonics. Therefore, the raw heat flow signal for quasi-isothermal demixing and remixing measurements is also examined in the time domain.

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