Kinetics of pressure-induced phase separation (PIPS) in polystyrene+methylcyclohexane solutions at high pressure

Xiong, Yan; Kiran, Erdoǧan

doi:10.1016/s0032-3861(99)00592-3

Cited by 17 publications

(20 citation statements)

References 45 publications

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“…The kinetics of phase separation in polymers is an area of intense research activity. The interest is both theoretical and practical. − Among the reasons is the desire to understand the time evolution of microstructure development so that practical methodologies can be developed for pinning the nonequilibrium transient structures for specific end uses. The majority of the studies reported in the literature have been on the kinetics of phase separation in “polymer + polymer” blend systems where structure development and morphology control are of great importance. ,,− Relatively little work has been done in phase separation kinetics in “polymer + solvent” systems.…”

Section: Introductionmentioning

confidence: 99%

Pressure-Induced Phase Separation in Polymer Solutions: Kinetics of Phase Separation and Crossover from Nucleation and Growth to Spinodal Decomposition in Solutions of Polyethylene in n-Pentane

Liu

Kiran

2001

Macromolecules

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The kinetics of pressure-induced phase separation (PIPS) in solutions of polyethylene (M w = 108 000, PDI = 1.32) in n-pentane has been studied using time- and angle-resolved light scattering. Controlled pressure quench experiments were conducted at different polymer concentrations (0.49, 0.97, 2.07, 2.8, 4.1, 5.0, and 10.8% by mass) to determine both the binodal and spinodal envelopes and the critical polymer concentration. At each concentration, a series of rapid pressure quenches with different depths of penetration into the region of immiscibility were imposed, and the time evolutions of the scattered light intensities were followed to determine the pressure below which the mechanism changes from “nucleation and growth” to “spinodal decomposition”. The crossover is identified from the characteristic fingerprint scattering patterns associated with each mechanism. The spinodal decomposition process is characterized by the formation and evolution of a spinodal ring during phase separation that leads to a maximum in the angular variation of the scattered light intensity. The nucleation and growth mechanism is characterized by the absence of such a maximum and the continual decrease of the scattered light intensities with increasing angles. The time scale of new phase formation and growth is shown to be relatively short. The late stage of phase separation is entered within seconds. For quenches leading to spinodal decomposition, the characteristic wavenumber q m corresponding to the scattered light intensity maximum I m is observed to be nonstationary, moving to lower wavenumbers after a very short elapsed time. The growth of domain size is observed to follow power-law-type scaling with q m ∼ t -α and I m ∼ t β with β ≈ 2α. In the intermediate and late stages, the domain size is found to grow from 4 to 14 μm within 5 s. Analysis of the early stage of phase separation according to Cahn−Hilliard theory shows that the diffusion coefficients are in the range of (1−9) × 10-12 m2/s and depend on the quench depth.

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Section: Introductionmentioning

confidence: 99%

Pressure-Induced Phase Separation in Polymer Solutions: Kinetics of Phase Separation and Crossover from Nucleation and Growth to Spinodal Decomposition in Solutions of Polyethylene in n-Pentane

Liu

Kiran

2001

Macromolecules

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“…1,2,[16][17][18][19] The technique combines the notion of multiple repetitive pressure-drop (MRPD) with timeand angle resolved light scattering. Figure 7 illustrates the basic methodology and the essential components of the system.…”

Section: Kinetics Of Phase Separationmentioning

confidence: 99%

“…The scattered light intensity profiles shown in Figures 8 and 10 correspond to the intermediate or late stage of spinodal decomposition and the maximum of scattered light intensity I, and the peak wave number qmshow power law relationship of the type qm t and Im t b that are typical of later stages of spinodal decomposition. 3,[17][18][19] The maximum value of the wave number qmis related 20 to the dominant size scale through L = 2 /qm. In these systems the characteristic domain size grows rapidly and reaches a size of about 4 microns within about 1 s after the quench is initiated.…”

Section: Kinetics Of Phase Separationmentioning

confidence: 99%

Polymer Solutions at High Pressures: Pressure-Induced Miscibility and Phase Separation in Near-critical and Supercritical Fluids

Kiran

Liu

Bayraktar

2002

Computational Studies, Nanotechnology, and Solution Thermodynamics of Polymer Systems

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Pressure-induced miscibility and phase separation constitute the integral steps in a wide range of applications that use supercritical or near-critical fluids as a process or processing medium for polymers. Thermodynamic aspects of miscibility, and the kinetic aspects of the phase separation both play a very important role. Pressure becomes the practical tuning parameter that transforms a fluid or a fluid mixture from behaving like a solvent to one behaving like a non-solvent, thereby inducing miscibility or phase separation. Dynamics of phase separation becomes particularly important if transient (non-equilibrium) structures are to be pinned by proper matching of the process conditions with the onset of transitions in material properties such as the vitrification or crystallization in polymers. This paper provides an overview of factors that influence miscibility and presents the consequences of pressure-induced phase separation in terms of the time scale (kinetics) of new phase formation, the domain growth and structure development in polymer solutions. A time-and angle-resolved light scattering technique combined with controlled pressure quench experiments with different depth of penetration into the region of immiscibility is used to document the kinetics of phase separation and domain growth and identify the crossover from "metastable" to "unstable" region of the phase diagram. This crossover that represents the experimentally accessible spinodal boundary is demonstrated with recent data on pressure-induced phase separation in "poly(dimethylsiloxane) + supercritical carbon dioxide" and "polyethylene + npentane" solutions. The paper also describes a unique application of polymer miscibility and phase separation concepts in the preparation of novel polymerpolymer blends that is based on impregnating a host polymer that is swollen in a fluid with a second polymer that is dissolved in the same fluid at high pressures. The dissolved polymer is in-situ precipitated and entrapped in the host polymer matrix by pressure-induced phase separation. blending of otherwise incompatible polymers, and is demonstrated for blending of polyethylene with poly(dimethylsiloxane) in supercritical carbon dioxide .

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“…All angles are scanned every 3.2 ms. The system has been used in recent years to study the kinetics of pressure-induced phase separation in "polystyrene + methyl cyclohexane" [41,42], "polydimethylsiloxane + supercritical carbon dioxide" [43,44], and "polyethylene + n-pentane" binary solutions [43,44], and in the ternary mixture of "polyethylene + n-pentane + carbon dioxide" [45].…”

Section: Kinetics Of Pressure-induced Phase Separation Crossover Fromentioning

confidence: 99%

“…The scattered light intensity profiles shown in Figures 19 and 21 correspond to intermediate or late stage of spinodal decomposition and the maximum of scattered light intensity 1m and the peak wave number qm follow the power law relationship of the type qm = f a 1m = til. The scaling exponents that characterize the time-evolution of the phase growth in these systems show a 13= 2a dependence [42,43,44]. This is different then polymer-polymer blends undergoing spinodal decomposition for which the literature reports 13= 3a, which may come about from the low viscosity and hence greater hydrodynamic influence in the phase separation process in polymer solutions.…”

Section: Kinetics Of Spinodal Decompositionmentioning

confidence: 99%

Polymer Miscibility and Kinetics of Pressure — Induced Phase Separation in Near-Critical and Supercritical Fluids

Kiran

2000

Supercritical Fluids

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Kinetics of pressure-induced phase separation (PIPS) in polystyrene+methylcyclohexane solutions at high pressure

Cited by 17 publications

References 45 publications

Pressure-Induced Phase Separation in Polymer Solutions: Kinetics of Phase Separation and Crossover from Nucleation and Growth to Spinodal Decomposition in Solutions of Polyethylene in n-Pentane

Pressure-Induced Phase Separation in Polymer Solutions: Kinetics of Phase Separation and Crossover from Nucleation and Growth to Spinodal Decomposition in Solutions of Polyethylene in n-Pentane

Polymer Solutions at High Pressures: Pressure-Induced Miscibility and Phase Separation in Near-critical and Supercritical Fluids

Polymer Miscibility and Kinetics of Pressure — Induced Phase Separation in Near-Critical and Supercritical Fluids

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