scholarly journals Computational study of comprehensive methods of initiating phase separation within metastable regions and obtaining some notable patterns in unstable region

2021 ◽  
Author(s):  
Viet-Nhien Tran Duc
Keyword(s):  
Phase Separation ◽  
Spinodal Decomposition ◽  
Thermal Noise ◽  
Complex Geometry ◽  
Activation Barrier ◽  
Computational Study ◽  
Polymeric Materials ◽  
Mixed Solution ◽  
Flat Panel Displays ◽  
Energy Behavior

Binary phase polymer solution is interesting in that they expresses double-well local energy behavior, which means phase separation is preferred when condition is right. It is a feature that has been used to fabricate functional polymeric materials such as PDLC films for electro-optical devices (e.g. flat-panel displays and switchable windows). A uniformly mixed solution may be in one of three state: unstable, stable, or metastable. If the solution is unstable, then phase separation is spontaneous and proceeds by spinodal decomposition. If the solution is metastable, then the solution must overcome certain activation barrier for phase separation to proceed spontaneously. The activation barrier is usually the thermal noise or the fluctuation created by some external influence. This mechanism is called nucleation-and-growth. Manipulating morphology of phase separation has been of some great research interest because of its practical use. While spinodal decomposition has been well-studied, there are several other methods to further control morphology. For this thesis, the following methods are considered: double quench, anisotropic quenching with varying temperature or polymerization, surface-directed wetting, and concentration gradient. The methods are carried out within metastable or unstable regions or both. To numerically model, Cahn-Hilliard theory and FloryHuggins’ theory are used. This thesis is to also demonstrate that, present numerical method is very efficient and can work on complex geometry.

scholarly journals Computational study of comprehensive methods of initiating phase separation within metastable regions and obtaining some notable patterns in unstable region

2021 ◽  
Author(s):  
Viet-Nhien Tran Duc
Keyword(s):  
Phase Separation ◽  
Spinodal Decomposition ◽  
Thermal Noise ◽  
Complex Geometry ◽  
Activation Barrier ◽  
Computational Study ◽  
Polymeric Materials ◽  
Mixed Solution ◽  
Flat Panel Displays ◽  
Energy Behavior

Binary phase polymer solution is interesting in that they expresses double-well local energy behavior, which means phase separation is preferred when condition is right. It is a feature that has been used to fabricate functional polymeric materials such as PDLC films for electro-optical devices (e.g. flat-panel displays and switchable windows). A uniformly mixed solution may be in one of three state: unstable, stable, or metastable. If the solution is unstable, then phase separation is spontaneous and proceeds by spinodal decomposition. If the solution is metastable, then the solution must overcome certain activation barrier for phase separation to proceed spontaneously. The activation barrier is usually the thermal noise or the fluctuation created by some external influence. This mechanism is called nucleation-and-growth. Manipulating morphology of phase separation has been of some great research interest because of its practical use. While spinodal decomposition has been well-studied, there are several other methods to further control morphology. For this thesis, the following methods are considered: double quench, anisotropic quenching with varying temperature or polymerization, surface-directed wetting, and concentration gradient. The methods are carried out within metastable or unstable regions or both. To numerically model, Cahn-Hilliard theory and FloryHuggins’ theory are used. This thesis is to also demonstrate that, present numerical method is very efficient and can work on complex geometry.

scholarly journals A computational study of surface-directed phase separation in polymer blends under temperature gradient

2021 ◽  
Author(s):  
Mohammad Tabatabaieyazdi
Keyword(s):  
Growth Rate ◽  
Phase Separation ◽  
Temperature Gradient ◽  
Long Range ◽  
Spinodal Decomposition ◽  
Surface Potential ◽  
Short Range ◽  
Computational Study ◽  
Polymeric Materials ◽  
Partial Wetting

To apprehend the real industrial behavior of polymeric materials phase separation phenomenon, the nonlinear Cahn-Hilliard theory incorporating the Flory-Huggins-de Gennes free energy theory was used to study the non-uniform thermal-induced phase separation phenomenon in a symmetric binary polymer blend in which surface(s) with short- and long-range attraction to one polymer component compete with temperature gradient effects. The numerical results indicate that an increase of diffusion coefficient value will increase the rate of phase separation in the bulk but will decrease the growth rate of the wetting layer on the surface regardless of the surface potential strength. Also, the morphology transition from complete to partial wetting of the surface with short range surface attraction is successfully demonstrated. However, no partial wetting is observed for the surface with long-range potential. For shallow quenches, first, a growth rate of t 0.5 is observed in the early stage of spinodal decomposition phase separation at the surface and then a decline in the growth rate to t 0.13 in the intermediate stage occurred. For short- and long-range surface potential, the growth rate value of t 0.33 obtained in the bulk. The morphology results of temperature gradient effect on surface directed spinodal decomposition in short-range, long- range and multiple-surface attraction cases have been presented for the first time. It is realized that regardless of surface potential magnitude, surface enrichment is increased by higher temperature gradient (deep quenches on the side with no surface attraction). The studied models would provide more in depth understanding of polymer blendiprocesses.

scholarly journals A computational study of phase separation in polymer solutions under a concentration gradient

2021 ◽  
Author(s):  
Baitao Jiang
Keyword(s):  
Phase Separation ◽  
Polymer Solution ◽  
Spinodal Decomposition ◽  
Concentration Gradient ◽  
Computational Study ◽  
Polymeric Materials ◽  
Polymeric Membranes ◽  
Separation Processes ◽  
Initial Concentration ◽  
Linear Concentration

Anisotropic porous polymeric materials fabricated from the phase separation method via spinodal decomposition are used in various practical engineering applications. Examples include anisotropic porous polymeric membranes for separation processes and holographic polymer dispersed liquid crystal films for electro-optical devices. We have studied numerically the formation of anisotropic porous polymeric materials by imposing an initial linear concentration gradient across a model polymer solution. The mathematical model is composed of the non-linear Cahn-Hilliard theory to describe spinodal decomposition dynamics, the Flory-Huggins theory for polymer solution thermodynamics, and the slow mode theory combined with the Rouse law for polymer diffusion. The computer simulations include uniform (no gradient) and non-uniform (with an initial concentration gradient) cases. For the non-uniform cases, the initial concentration gradient is placed at three different regions of polymer sample for the purpose of comparison. All the simulation results are in good agreement with published experimental observations which are reported from the applications of porous polymeric membranes. The structure development shows that an anisotropic porous morphology forms when an initial linear concentration gradient is applied to the model polymer solution.

scholarly journals A computational study of phase separation in polymer solutions under a concentration gradient

2021 ◽  
Author(s):  
Baitao Jiang
Keyword(s):  
Phase Separation ◽  
Polymer Solution ◽  
Spinodal Decomposition ◽  
Concentration Gradient ◽  
Computational Study ◽  
Polymeric Materials ◽  
Polymeric Membranes ◽  
Separation Processes ◽  
Initial Concentration ◽  
Linear Concentration

Anisotropic porous polymeric materials fabricated from the phase separation method via spinodal decomposition are used in various practical engineering applications. Examples include anisotropic porous polymeric membranes for separation processes and holographic polymer dispersed liquid crystal films for electro-optical devices. We have studied numerically the formation of anisotropic porous polymeric materials by imposing an initial linear concentration gradient across a model polymer solution. The mathematical model is composed of the non-linear Cahn-Hilliard theory to describe spinodal decomposition dynamics, the Flory-Huggins theory for polymer solution thermodynamics, and the slow mode theory combined with the Rouse law for polymer diffusion. The computer simulations include uniform (no gradient) and non-uniform (with an initial concentration gradient) cases. For the non-uniform cases, the initial concentration gradient is placed at three different regions of polymer sample for the purpose of comparison. All the simulation results are in good agreement with published experimental observations which are reported from the applications of porous polymeric membranes. The structure development shows that an anisotropic porous morphology forms when an initial linear concentration gradient is applied to the model polymer solution.

scholarly journals A computational study of surface-directed phase separation in polymer blends under temperature gradient

2021 ◽  
Author(s):  
Mohammad Tabatabaieyazdi
Keyword(s):  
Growth Rate ◽  
Phase Separation ◽  
Temperature Gradient ◽  
Long Range ◽  
Spinodal Decomposition ◽  
Surface Potential ◽  
Short Range ◽  
Computational Study ◽  
Polymeric Materials ◽  
Partial Wetting

To apprehend the real industrial behavior of polymeric materials phase separation phenomenon, the nonlinear Cahn-Hilliard theory incorporating the Flory-Huggins-de Gennes free energy theory was used to study the non-uniform thermal-induced phase separation phenomenon in a symmetric binary polymer blend in which surface(s) with short- and long-range attraction to one polymer component compete with temperature gradient effects. The numerical results indicate that an increase of diffusion coefficient value will increase the rate of phase separation in the bulk but will decrease the growth rate of the wetting layer on the surface regardless of the surface potential strength. Also, the morphology transition from complete to partial wetting of the surface with short range surface attraction is successfully demonstrated. However, no partial wetting is observed for the surface with long-range potential. For shallow quenches, first, a growth rate of t 0.5 is observed in the early stage of spinodal decomposition phase separation at the surface and then a decline in the growth rate to t 0.13 in the intermediate stage occurred. For short- and long-range surface potential, the growth rate value of t 0.33 obtained in the bulk. The morphology results of temperature gradient effect on surface directed spinodal decomposition in short-range, long- range and multiple-surface attraction cases have been presented for the first time. It is realized that regardless of surface potential magnitude, surface enrichment is increased by higher temperature gradient (deep quenches on the side with no surface attraction). The studied models would provide more in depth understanding of polymer blendiprocesses.

scholarly journals A computational study of phase separation in polymer solutions under a double quench

2021 ◽  
Author(s):  
Ehsan Hosseini
Keyword(s):  
Phase Separation ◽  
Polymer Solution ◽  
Spinodal Decomposition ◽  
Computational Study ◽  
Stable State ◽  
Thermal Quenching ◽  
Nucleation And Growth ◽  
Two Dimensions ◽  
Numerical Work ◽  
Binary Polymer

Polymer-dispersed liquid crystals (PDLCs) are a relatively new class of materials used for many applications ranging from switchable windows to projection displays. PDLSs are formed by spinodal decomposition induced by thermal quenching or polymerization. The objective of the present study is to introduce a new mechanism of phase separation in a binary polymer solution and develop a mathematical model and computer simulation to describe the phase separation during the early and intermediate stages of nucleation and growth and spinodal decomposition induced by thermal double quenching. The growth equilibrium limits of phase separation as well as phase transition are calculated by taking into consideration the Flory-Huggins theory for the free energy of mixing. A two step quench is modeled using Cahn-Hilliard theory for asymmetric binary polymer solution which is quenched from a stable state in the one-phase region to a metastable region where nucleation and growth occurs. The solution is allowed to coarsen for different time periods before a second quench was applied to a point further inside the phase diagram. The numerical results in two dimensions replicate the experimental and numerical work that has been recently done and published.

scholarly journals A computational study of phase separation in polymer solutions under a double quench

2021 ◽  
Author(s):  
Ehsan Hosseini
Keyword(s):  
Phase Separation ◽  
Polymer Solution ◽  
Spinodal Decomposition ◽  
Computational Study ◽  
Stable State ◽  
Thermal Quenching ◽  
Nucleation And Growth ◽  
Two Dimensions ◽  
Numerical Work ◽  
Binary Polymer

Polymer-dispersed liquid crystals (PDLCs) are a relatively new class of materials used for many applications ranging from switchable windows to projection displays. PDLSs are formed by spinodal decomposition induced by thermal quenching or polymerization. The objective of the present study is to introduce a new mechanism of phase separation in a binary polymer solution and develop a mathematical model and computer simulation to describe the phase separation during the early and intermediate stages of nucleation and growth and spinodal decomposition induced by thermal double quenching. The growth equilibrium limits of phase separation as well as phase transition are calculated by taking into consideration the Flory-Huggins theory for the free energy of mixing. A two step quench is modeled using Cahn-Hilliard theory for asymmetric binary polymer solution which is quenched from a stable state in the one-phase region to a metastable region where nucleation and growth occurs. The solution is allowed to coarsen for different time periods before a second quench was applied to a point further inside the phase diagram. The numerical results in two dimensions replicate the experimental and numerical work that has been recently done and published.

scholarly journals Long-Range Surface-Directed Polymerization-Induced Phase Separation: A Computational Study

Polymers ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 256
Author(s):  
Shima Ghaffari ◽  
Philip K. Chan ◽  
Mehrab Mehrvar
Keyword(s):  
Phase Separation ◽  
Long Range ◽  
Spinodal Decomposition ◽  
Surface Potential ◽  
Computational Study ◽  
Polymer Mixture ◽  
Condensation Polymerization ◽  
Wetting Layer ◽  
Polymerization Induced Phase Separation ◽  
Directed Polymerization

The presence of a surface preferably attracting one component of a polymer mixture by the long-range van der Waals surface potential while the mixture undergoes phase separation by spinodal decomposition is called long-range surface-directed spinodal decomposition (SDSD). The morphology achieved under SDSD is an enrichment layer(s) close to the wall surface and a droplet-type structure in the bulk. In the current study of the long-range surface-directed polymerization-induced phase separation, the surface-directed spinodal decomposition of a monomer–solvent mixture undergoing self-condensation polymerization was theoretically simulated. The nonlinear Cahn–Hilliard and Flory–Huggins free energy theories were applied to investigate the phase separation phenomenon. The long-range surface potential led to the formation of a wetting layer on the surface. The thickness of the wetting layer was found proportional to time t*1/5 and surface potential parameter h11/5. A larger diffusion coefficient led to the formation of smaller droplets in the bulk and a thinner depletion layer, while it did not affect the thickness of the enrichment layer close to the wall. A temperature gradient imposed in the same direction of long-range surface potential led to the formation of a stripe morphology near the wall, while imposing it in the opposite direction of surface potential led to the formation of large particles at the high-temperature side, the opposite side of the interacting wall.

scholarly journals Phase Separation by Spinodal Decomposition in Polymer Blends Under a Single and Double Quench: a Computational Study

2021 ◽  
Author(s):  
Tuyet Tran
Keyword(s):  
Phase Separation ◽  
Polymer Blends ◽  
Spinodal Decomposition ◽  
Computational Study ◽  
Early Stage ◽  
Critical Factor ◽  
Domain Size ◽  
Secondary Structures ◽  
Numerical Results ◽  
Numerical Work

A mathematical model and computer simulations are used to describe the dynamics of thermally induced phase separation (TIPS) by spinodal decomposition for polymer blends (single quench and double quench) using the nonlinear Cahn-Hilliard theory and the Flory-Huggins-de Gennes free energy. The importance of TIPS is to enhance material properties such as toughness, impact resistance and elasticity. Therefore, controlling the morphology is a critical factor in optimizing performance. The numerical results for the single quench are consistent with known characteristics of phase separation by spinodal decomposition observed in polymer blends. The numerical results for double quenching replicate recently published experimental and numerical work. Under a double quench the numerical work shows that a critical quench depth exists before secondary phase separation occurs, the growth rate of the primary and secondary structures are dependent on domain size and early stage dynamics for the secondary structures, after the second jump, appears to follow the linear Cahn-Hilliard theory.

scholarly journals Using the Cahn–Hilliard Theory in Metastable Binary Solutions

2019 ◽  
Vol 3 (3) ◽  
pp. 75 ◽  
Author(s):  
Viet-Nhien Tran Duc ◽  
Philip K. Chan
Keyword(s):  
Phase Separation ◽  
Spinodal Decomposition ◽  
Activation Barrier ◽  
Binary Solution ◽  
Functional Materials ◽  
Nucleation And Growth ◽  
Unstable Region ◽  
Unstable Phase ◽  
Spinodal Line ◽  
Model Phase

A solution may be in one of three states: stable, unstable, or metastable. If the solution is unstable, phase separation is spontaneous and proceeds by spinodal decomposition. If the solution is metastable, the solution must overcome an activation barrier for phase separation to proceed spontaneously. This mechanism is called nucleation and growth. Manipulating morphology using phase separation has been of great research interest because of its practical use to fabricate functional materials. The Cahn–Hilliard theory, incorporating Flory–Huggins free energy, has been used widely and successfully to model phase separation by spinodal decomposition in the unstable region. This model is used in this paper to mathematically model and numerically simulate the phase separation by nucleation and growth in the metastable state for a binary solution. Our numerical results indicate that Cahn–Hilliard theory is able to predict phase separation in the metastable region but in a region near the spinodal line.

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