Phase Separation In Ternary System Research Articles

Investigation of process–structure–property relationship in ternary organic photovoltaics

Organic photovoltaics (OPVs) have held on to the race for providing a sustainable source of energy for more than two decades, and ternary OPVs have emerged as a promising candidate for harnessing solar energy. While the ternary OPVs have potential, optimization of the process parameters, particularly for deriving active-layer morphologies with high efficiencies, is non-trivial as the parameter space is large and a theoretical framework is necessary. This is specifically important for determining the appropriate compositions of the ternary blend which, upon phase-separation, lead to the formation of the heterogenous active layer with a distribution of three phases. In this paper, we present an approach for deriving both the process–structure and structure–property correlations based on the diffuse-interface approach. Herein, we derive process–structure correlations using phase-field simulations based on the Cahn–Hilliard formalism for modeling phase-separation in ternary systems where a third component that acts as an acceptor is added to a binary OPV. This leads to structures that can be classified as donor–acceptor–acceptor. Thereafter, we derive the structure–property correlations again using a diffuse interface approach for deriving the electronic properties such as the efficiency, fill-factor, short-circuit current, and the open-circuit voltages for the simulated microstructures involving the three phases in the active layer. Thus, using a combination of the process–structure and structure–property correlations, optimal compositions can be determined. Further, in order to expedite the theoretical prediction, a robust and elegant data analytics model is built using dimensionality reduction techniques.

Rheological characteristics of nitrate glycerol ether cellulose gel based on phase separation in ternary system

By non-solvent-induced phase separation, nitrate glycerol ether cellulose (NGEC) gels were formed in ternary NGEC/acetone/ethanol system. The rheological behaviors of NGEC gels were investigated using dynamic rheological measurements. The final compositions and morphologies of NGEC gels were influenced by the initial solvent/non-solvent (acetone/ethanol) ratios and NGEC concentrations. In addition, the effect of initial acetone/ethanol ratios on the characteristics of NGEC gels is different from the effect of NGEC concentrations. The critical strain of NGEC gels decreased almost with increasing NGEC concentration of gels by increasing initial acetone ratio, but it increased with increasing NGEC concentration of gels by increasing NGEC concentration beyond a certain concentration in 2/3 (w/w) acetone/ethanol solution. For all gels, the storage modulus (G′) and loss modulus (G′′) of NGEC gels rapidly increased with increasing NGEC concentration of gels. In addition, the curves for G′ and G′′ were temperature sensitive throughout the entire temperature sweep, which implied that the interactions between NGEC/solvent could be disrupted upon heating to higher temperatures.

Sol–gel transition and phase separation in ternary system of gelatin-water–poly(ethylene glycol) oligomer

The phase behaviors are studied in the ternary system of gelatin-water–poly(ethylene glycol) oligomer. It is found that both the phase separation and the sol–gel transition occur simultaneously when the poly(ethylene glycol) oligomers are added to the aqueous gelatin solution. The phase separation boundary is found to shift in the higher temperature than the sol–gel transition line when the higher molecular weight oligomers of poly(ethylene glycol) coexist in the solution. The competition of these two transitions creates two new phases in the system, the phase separated solution of gelatin and poly(ethylene glycol) and the opaque gelatin gel in which the density fluctuation due to the phase separation is frozen in.

Modeling morphology evolution during solvent-based fabrication of organic solar cells

Solvent-based thin-film deposition constitutes a popular class of fabrication strategies for manufacturing organic electronic devices like organic solar cells. All such solvent-based techniques usually involve preparing dilute blends of electron-donor and electron-acceptor materials dissolved in a volatile solvent. After some form of coating onto a substrate to form a thin film, the solvent evaporates. An initially homogeneous mixture separates into electron-acceptor rich and electron-donor rich regions as the solvent evaporates. Depending on the specifics of the blend, processing conditions, and substrate characteristics different morphologies are typically formed. Experimental evidence consistently confirms that the resultant morphology critically affects device performance. A computational framework that can predict morphology evolution can significantly augment experimental analysis. Such a framework will also allow high throughput analysis of the large phase space of processing parameters, thus yielding considerable insight into the process–structure–property relationships governing organic solar cell behavior.In this paper, we formulate a computational framework to predict evolution of morphology during solvent-based fabrication of organic thin films. This is accomplished by developing a phase field-based model of evaporation-induced and substrate-induced phase-separation in ternary systems. This formulation allows most of the important physical phenomena affecting morphology evolution during fabrication to be naturally incorporated. We discuss the various numerical and computational challenges associated with a three dimensional, finite-element based, massively parallel implementation of this framework. This formulation allows, for the first time, to model three-dimensional nanomorphology evolution over large time spans on device scale domains. We illustrate this framework by investigating and quantifying the effect of various process and system variables on morphology evolution. We explore ways to control the morphology evolution by investigating different evaporation rates, blend ratios and interaction parameters between components.

Effect of nanoclay dispersion on liquid–liquid phase separation in a ternary system of segmented polyurethane/dimethylformamide/water system

AbstractThis paper reports a study on liquid‐liquid phase separation in an isothermal ternary system of segmented polyurethane/dimethylformamide/water system with and without the presence of nanoclay dispersion in the system. Isothermal ternary phase diagrams for three different grades with varying shore A hardness of thermoplastic polyurethane (TPU)/solvent/nonsolvent system were constructed based on the cloud point measurement that was carried out by the titration method. The effect of temperature on phase diagrams has also been studied. The binary interaction parameters between TPUs and water were estimated by water sorption experiments. The effect of organoclay dispersion concentration in the TPU solution on isothermal ternary phase diagrams has also been studied. This understanding of phase separation characteristics would be very helpful in correlating the final morphology developed in wet‐spun TPU as well as polyurethane/clay nanocomposite fibres. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Statistical thermodynamics of liquid-liquid phase separation in ternary systems during complex coacervation

Liquid-liquid phase separation leading to complex coacervation in a ternary system (oppositely charged polyion and macroion in a solvent) is discussed within the framework of a statistical thermodynamics model. The polyion and the macroion in the ternary system interact to form soluble aggregates (complexes) in the solvent, which undergoes liquid-liquid phase separation. Four necessary conditions are shown to drive the phase separation: (i) (σ{23}){3}r/Φ{23c}≥(64/9α{2})(χ{23}Φ{3}){2} , (ii) r≥[64(χ{23}Φ{3}){2}/9α{2}σ{23}{3}]{1/2}, (iii) χ{23}≥(2χ{231}-1)/Φ{23c}Φ{3}, and (iv) (σ{23}){2}/sqrt[I]≥8/3α(2χ{231}-1) (where σ{23} is the surface charge on the complex formed due to binding of the polyelectrolyte and macroion, Φ{23c} is the critical volume fraction of the complex, χ{23} is the Flory interaction parameter between polyelectrolyte and macroion, χ{231} is the same between solvent and the complex, Φ{3} is the volume fraction of the macroions, I is the ionic strength of the solution, α is electrostatic interaction parameter and r is typically of the order of molecular weight of the polyions). It has been shown that coacervation always requires a hydrated medium. In the case of a colloidal macroion and polyelectrolyte coacervation, molecular weight of polyelectrolyte must satisfy the condition r≥10{3} Da to exhibit liquid-liquid phase separation. This model has been successfully applied to study the coacervation phenomenon observed in aqueous Laponite (macroion)-gelatin (polyion) system where it was found that the coacervate volume fraction, δΦ{23}∼χ{231}{2} (where δΦ{23} is the volume fraction of coacervates formed during phase separation). The free energy and entropy of this process have been evaluated, and a free-energy landscape has been drawn for this system that maps the pathway leading to phase separation.

Phase equilibria at various temperatures in ternary liquid systems consisting of thorium(IV) and lanthanide(III) nitrate solvates with tri-n-butyl phosphate and of isooctane

The phase diagrams of ternary liquid systems (TLSs) [Th(NO3)4(TBP)2]-[Ln(NO3)3(TBP)3] (Ln = Nd, Gd, Ho; TBP = tri-n-butyl phosphate)-isooctane at 298.15–333.15 K were studied. The TLSs are characterized by the fields of homogeneous solutions and of two-phase liquid systems (systems with phase separation) in which one of the phases (I) is enriched in [Th(NO3)4(TBP)2] and [Ln(NO3)3(TBP)3], and the other phase (II), in isooctane. The temperature (298.15–333.15 K) does not noticeably affect the mutual solubility of [Th(NO3)4(TBP)2] and isooctane but decreases the field of phase separation in ternary systems. In two-phase systems, [Ln(NO3)3(TBP)3] is predominantly distributed into phase I, despite the fact that binary systems [Ln(NO3)3(TBP)3]-isooctane are single-phase at all the examined temperatures. The distribution of [Ln(NO3)3(TBP)3] into phase I results in the redistribution of [Th(NO3)4(TBP)2] into phase II and of isooctane into phase I. The critical composition points of the TLSs at various temperatures were determined; they depend on particular lanthanide(III).

Domain growth in ternary fluids: A level set approach

We analyze phase separation in ternary systems in the asymptotic hydrodynamic regime when the volume fractions and concentrations are constant. The multiphase Navier-Stokes equations are solved using a level set method. A new projection method was developed to treat multiple junctions for systems with more than two phases. It is found that surface tension ratios can alter the growth mechanism of a minority phase in the presence of two majority phases. When the minority phase wets the interface of the majority phases the domain growth rate of all three phases is initially similar to that of a symmetric binary fluid but slows down at later times.

Formation of Percolated Structure During Solvent Casting of Polymer Blend-solvent Systems.

The development of phase separation in ternary systems composed of polybutadiene-poly(styrene-co-butadiene)-good solvent was studied by time-resolved light-scattering during the solvent casting process. Double percolated structures with two different periodic distances were observed for the thick film. The structure with the smaller periodic distance was formed at the surface of films and the larger one was formed inside the film. It was found that the periodic distance for the larger percolated structure was proportional to (tP – tS)0.6, where (tP – tS) is the lapse of the time from the start of phase separation to fixation of the structure. The time dependence of the wave number, qm, at which the light-scattering intensity reaches maximum, was correlated by a similar relationship. The intensity of light scattering at qm was proportional to qm3.3 irrespective of the solvent-casting conditions. The development of the percolated structure was qualitatively interpreted by numerical analysis of an equation describing spinodal decomposition and an equation expressing the time dependence of the polymer concentration in the cast solution.