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Thermodynamics of Polymer Mixtures
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
Spinodal decomposition occurs when a homogeneous (single phase) mixture is thrust into the unstable region of a phase diagram. The resulting morphology is a complex bicontinuous structure that finds interesting and useful applications. Certain membranes (e.g., reverse osmosis) are produced this way using polymer–solvent mixtures. Your CEO wants to make money in the membrane business using excess company capacity to make M = 2 × 105 g/mol poly(vinyl acetate) membranes. Choose a solvent and specify the composition range that can be used for this purpose if the phase separation temperature is 27 °C. (Hint: Place the critical temperature at about 100 °C by choosing an appropriate solvent. You may blend two solvents and assume that the associated solubility parameter and molar volume are simple averages, provided the solvents don't phase separate. Table 7.1 may be helpful.)
Thermoset/Thermoplastic Blends with a Crosslinked Thermoplastic Network Matrix
Published in Boris A. Rozenberg, Grigori M. Sigalov, Marina Z. Aldoshina, Yurii B. Scheck, Heterophase Network Polymers, 2020
Ying Yang, Tsuneo Chiba, Takashi Inoue
It is well known that the formation of phase-separated morphology via spinodal decomposition can be well characterized by light scattering profiles. The appearance of a scattering peak and the continuous increase of the scattering intensity are indications of the development of a regular phase-separated morphology as schematically shown in Fig. 3. After the intensity of the scattered light reaches the maximum value, the change of the scattering profile will be different depending on the further development of the morphology. When the phase-separated morphology is arrested by gelation or vitrification, the peak intensity will level off [5].
Electrospinning and Electrospun Nanofibers
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
In the electrospinning process, polymer solution jet solidifies during the travel from orifice to collector. If two or more polymers exist in solution, polymer-polymer phase separation occurs with the evaporation of solvent. Due to fast evaporation of solvent, polymer-polymer phase separation mechanism is not thermodynamic. There are two kinds of phase separation mechanism: nucleation and growth mechanism and spinodal decomposition mechanism. The former happens when the solution is in metastable state, i.e. the solution may stay for a long time and during this time period, the phase separation happens via nucleation and growth. The individual droplets of the minor phase that are formed in the early state of the process grow slowly. They are dispersed in the matrix of the corresponding coexisting phase and can become rather large in the end. The latter happens when the solution is in unstable state, i.e. phase separation takes place spontaneously and fast because any fluctuation in polymer concentration will inevitably lead to a reduction in the Gibbs free energy right away, which is a more stable state. For spinodal decomposition, the size of the coexisting phases is usually at least one order of magnitude smaller than the other mechanism and the phase-separation morphology tends to be co-continuous, i.e. for each phase, it is possible to find paths through the entire system. In the process of electrospinning, solvent evaporation is superfast and fibers solidify very quickly after ejecting from the electrospinning orifice. In this case, spinodal decomposition is preferred and phase-separated domains may not have enough time to become as large as they are in equilibrium state as described by Gibbs free energy [16,78,79]. Therefore, fine phase morphology should be observed.
Concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in ferritic steel containing copper during aging
Published in Philosophical Magazine, 2022
Weiming Lin, Wei Wang, Shijuan Zhu, Zishan Chen, Chuanwei Fan
In this study, modulated (Fe,Mo)2C carbides associated with spinodal decomposition were observed by transmission electron microscopy (TEM) in as-aged ferritic steel containing copper. In contrast to a conventional nucleation process, spinodal decomposition is initiated by concentration fluctuations. It is generally agreed that spinodal decomposition is affected by the concentration of alloy, aging temperature and the prior cold work [17–19]. Choo et al. have already shown that Fe-Mn-Al-C alloys go through spinodal decomposition only in the composition range enriched carbon and manganese and at the same time where there is enough aluminium [20].
Insights into photovoltaic properties of ternary organic solar cells from phase diagrams
Published in Science and Technology of Advanced Materials, 2018
Mohammed Makha, Philippe Schwaller, Karen Strassel, Surendra B. Anantharaman, Frank Nüesch, Roland Hany, Jakob Heier
Finding the ideal three-component composition by trial and error is a cumbersome process. Phase diagrams are a fundamental tool to better understand and control the morphology of multi-component mixtures and are common in polymer science. Phase diagrams also give valuable insights into the composition of a phase (solubility of minority components in the majority component) [36]. However, they have been employed only recently to explain the morphology of a BHJ-blend in a solar cell device [37]. A couple of reasons can be made accountable for this. First of all, BHJs are typically fabricated by solution casting, where the final morphology is the result of a fast solvent quench that can hardly follow thermodynamic equilibrium. Strictly spoken, a system with three solid components and a common solvent is punctiliously described by a quaternary phase diagram. During solvent evaporation the composition and consequently the thermodynamic driving forces change continuously and most frequently a particular morphology freezes in before thermodynamic equilibrium is reached as represented by a phase diagram. Still, the ternary phase diagram can be a good approximation when looking at the final film. Second, different competing mechanisms lead to the structure formation in BHJs. Crystalline materials may form nanostructured morphologies when crossing the liquidus [38]. A competing mechanism is spinodal decomposition when unfavorable interactions between the components bring the system into the thermodynamically unstable region of the phase diagram [39]. However, spinodal decomposition is a spontaneous process and phase separation will start instantly when entering the unstable region (solvent quench) [40], while crystallization requires the formation of nuclei [38]. BHJ samples are often subjected to annealing, which alters the film morphology.
Stability limits and consolute critical conditions for liquid mixtures
Published in Chemical Engineering Communications, 2018
Naif A. Darwish, Fahad M. Al Sadoon, Muhammad Qasim
Phase stability limits and the critical phenomena are subjects of special importance in the physical chemistry science of materials. Beside the basic fundamental significance, these subjects are important to many industrial processes. Phase stability limits are important in separation processes to determine the phase splitting conditions and to decide on the downstream processing equipment required for further purification (Sánchez et al., 1996). The concept of phase splitting is also of great significance in the petroleum industry where precipitation of asphaltenes and the resulting plugging of the flow lines is a major concern (Wu et al., 1998). The conditions at which asphaltene precipitates can be predicted using phase stability criterion, which will consequently lead to better design of oil flow lines. In polymer science, phase splitting of polymer solution can take two paths; either spinodal decomposition or nucleation and growth (Cahn, 1961; Hashimoto, 1988). Spinodal decomposition occurs when the system is inside the spinodal curve, while nucleation and growth occur when the system is between the spinodal and the binodal curves. Thus, determination of spinodal locus is essential to understand how phase splitting occurs. Also, knowledge of stability limits of fluid systems is practically important, especially in the cases of safety engineering and material handling. This is because stability limits represent conditions beyond which spontaneous and abrupt phase change must occur. Sometimes, situations that can give rise to reaching these stability limits are unavoidable. For example, an erupting fire in close proximity to chemical substances storage areas can result in reaching stability limits and consequently undergoing an abrupt phase change transition concomitant with disastrous consequences (Bubbico and Salzano, 2009; Darwish and Al-Muhtaseb, 1996; Koopman and Ermak, 2007).