Phase separation in mixtures of poly(ethylene glycol monomethylether) and poly(propylene glycol) oligomers

Time-resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two-phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time-evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensity I_m and the corresponding peak wavenumber q_m was found to follow the power-law {I_m(t)? t^α, q_m(t)? t^-β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self-similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted for off-critical mixtures.     

Spinodal decomposition and phase separation kinetics in nanoclay–biopolymer solutions

Intensity of light, I(q,t), scattered from homogeneous aqueous solutions, of nanoclay (Laponite) and protein (gelatin‐A), was studied to monitor the temporal and spatial evolution of the solution into a phase‐separated nanoclay–protein‐rich dense phase, when the sample temperature was quenched below spinodal temperature, T_s (=311 ± 3 K). The zeta potential data revealed that the dense phase comprised charge‐neutralized intermolecular complexes of nanoclay and protein chains of low surface charge. The early stage, t < 500 s, of phase separation could be described adequately through Cahn‐Hilliard theory of spinodal decomposition where the intensity grows exponentially, I(q, t) = I₀ exp.(2R(q)t). The wave vector, q dependence of the growth parameter, R(q) exhibited a maxima independent of time. Corresponding correlation length, 1/q_c = ξ_c was found to be ≈75 ± 5 nm independent of quench depth. In the intermediate regime, anomalous growth described by I(q, t) ～ t^α with α = 0.1 ± 0.02 independent of q was observed. Rheological studies established that there was a propensity of network structures inside the dense phase. Isochronal temperature sweep studies of the dense phase determined the melting temperature, T_m = 312 ± 4 K, which was comparable with the spinodal temperature. The stress‐diffusion coupling prevailing in the dense phase when analyzed in the Doi‐Onuki model yielded a viscoelastic correlation length, ξ_v determined from low‐frequency storage modulus, G ′₀ ≈ k_B T/ξ, which was ξ_v ≈ 35 ± 3 nm indicating 2ξ_v ≈ ξ_c. It is concluded that the early stage of phase separation in this system was sufficiently described by linear Cahn‐Hilliard theory, but the same was not true in the intermediate stage. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 555–565, 2010     

UNMIXING KINETICS AND ITS MORPHOLOGY OF POLY ( ETHYLENE OXIDE) WITH POLYETHERSULPHONES BLENDS

Unmixing kinetics in a binary polymer mixture of polyethersulphones with poly (ethylene oxide) by spinodal decomposition has been investigated with time-resolved light scattering and microscope methods. The results showed that time evolution of scattered light intensity is of an exponential growth The maximum growth rate R(qm) of phase separation has been obtained. The experimental data did not satisfy the condition that the plot of R(q)/q~2 vs q~2 should be linear For unmixing system annealing at 30℃for three hours, its morphology manifested dish structure The experimental data of the Bragg spacing D_m can be correlated with a straight line which expresses the power-law relation, D_m=bl~α     

A light-scattering study of phase separation kinetics in polystyrene/poly(2-chlorostyrene) blends

The angular dependence of the intensity of scattered light from polystyrene/poly(2-chlorostyrene) blends was measured as a function of time in early and late stages of phase separation. The results were discussed in terms of Cahn's theory and scaling law for the late stage. Some distinctive behaviors which had not been found in other polymer blends were observed: the intensity of low-angle scattering increased significantly during phase separation, possibly because of inhomogeneities in density. In the power laws k_m α t_? and I_m α t_θ for the time (t) evolution of the peak position k_m and peak heigh I_m of the structure function in the late stage; the value of ? was around ?1, almost independent of composition and temperature; the ratio |θ/?| was less than the theoretical value 3. Possible explanations for these behaviors are discussed in relation to the glass transition.     

Investigation on LCST behavior of a new amorphous/crystalline polymer blend: Poly(n‐methyl methacrylimide)/poly(vinylidene fluoride)

The liquid–liquid phase‐separation (LLPS) behavior of poly(n‐methyl methacrylimide)/poly(vinylidene fluoride) (PMMI/PVDF) blend was studied by using small‐angle laser light scattering (SALLS) and phase contrast microscopy (PCM). The cloud point (T_c) of PMMI/PVDF blend was obtained using SALLS at the heating rate of 1 °C min^?1 and it was found that PMMI/PVDF exhibited a low critical solution temperature (LCST) behavior similar to that of PMMA/PVDF. Moreover, T_c of PMMI/PVDF is higher than its melting temperature (T_m) and a large temperature gap between T_c and T_m exists. At the early phase‐separation stage, the apparent diffusion coefficient (D_app) and the product (2Mk) of the molecules mobility coefficient (M) and the energy gradient coefficient (k) arising from contributions of composition gradient to the energy for PMMI/PVDF (50/50 wt) blend were calculated on the basis of linearized Cahn‐Hilliard‐Cook theory. The kinetic results showed that LLPS of PMMI/PVDF blends followed the spinodal decomposition (SD) mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1923–1931, 2008     

Non‐linear dynamics of spinodal decomposition

A new approach is proposed to describe the spinodal decomposition, in particular, in polymer binary blends. In the framework of this approach, the spinodal decomposition is described as a relaxation of one‐time structure factor S(q,t) treated as an independent dynamic object (a peculiar two‐point order parameter). The dynamic equation for S(q,t), including the explicit expression for the corresponding effective kinetic coefficient, is derived. In the first approximation this equation is identical to the Langer equation. We first solved it both in terms of higher transcendental functions and numerically. The asymptotic behaviour of S(q,t) at large (from the onset of spinodal decomposition) times is analytically described. The values obtained for the power‐law growth exponent for the large‐time peak value and position of S(q,t) are in good agreement with experimental data and results of numerical integration of the Cahn‐Hilliard equation.     

羧化聚苯醚与聚苯乙烯共混体系相分离初期分子量影响的光散射研究

 本文用激光光散射方法研究了具有特殊相行为[(低临界溶解温度(LCST),高临界溶解温度(UCST)共存]共混体系羧化聚苯醚和聚苯乙烯在UCST域内的不稳相分离初期分子量对动力学参数的影响。结果表明:相分离初期动力学过程与Cahn理论吻合;随着分子量增加,表现扩散系数D_app明显减小;该体系的表现扩散系数为10^-14 cm²s^-1数量级。deGennes管子模型可很好地描述不稳相分离初期大分子扩散行为。     

聚甲基丙烯酸甲酯/(苯乙烯-丙烯腈)共聚物混合体系的早期分离

本文用激光光散射技术研究了高分子混合体系聚甲基丙烯酸甲酯/(苯乙烯-丙烯腈)共聚物(PMMA/PSAN)不稳相分离(Spinodal decomposition)过程,结果指出,相分离前期符合Cahn理论预言的结果;首次用光散射技术在高分子混合体系相分离研究中得到了不稳相分离增长速率最大值R(q_m);只(q)的实验结果与理论值相吻合;证实了界面自由能对相分离增长速率的影响是不可忽略的。     

Light scattering and image analysis studies in polymer blends

Various optical techniques have been investigated as potential candidates for characterization of multiphase polymeric materials. The model calculations and corresponding experiments (time‐resolved light scattering and image analysis) have been conducted to investigate the kinetics of phase dissolution of polymer blends. The blends studied were polystyrene/poly (methyl methacrylate) mixtures with diblock copolymer composed of the corresponding homopolymers. The time evolution of the spinodal peak position q_m(t,T) and the scattered intensity maximum I_m(t,T) at q_m have been compared with theoretically predicted values of exponents for distinct time scales of the phase dissolution in various temperature regimes.     

Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). II. Morphology and mechanical properties

The effects of the phase‐separation temperature and time on the mechanical properties and morphology of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride with 10 wt% ethyl acrylate) (SMA) blends were studied. Two compositions (20/80 and 40/60 w/w SMA/PMMAe) were prepared with a miniature twin‐screw extruder. Compared with those of the miscible blends, the Young's modulus values of the blends increased after the phase separation of the 40/60 SMA/PMMAe blend and within the early stage of spinodal decomposition of the 20/80 SMA/PMMAe blend. The mechanical properties, in terms of the tensile strength at break and the elongation, were better for the miscible blends than for the phase‐separation blends. This was believed to be the result of changes in the composition and molecular reorganization. The changes in the phase‐separating domains of both compositions, as observed by transmission electron microscopy, had no significant influence on the tensile moduli. Detailed studies of the morphology revealed a cocontinuous structure, indicating that the blends underwent spinodal decomposition. A morphological comparison of the two compositions illustrated the validity of the level rule. The growth rate of the droplet size was determined by approximation from the light scattering data and by direct measurements with transmission electron microscopy. The discrepancies observed in the droplet size growth rate were attributed to heat variations induced by the different sample thicknesses and heat transfer during the investigation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 886–897, 2004     

Morphology and Dynamics of Phase‐Separating Fluids with Viscosity Asymmetry

Summary: The effects of viscosity asymmetry of the components on morphology and dynamics of phase‐separating AB fluids are investigated numerically based on a modified Model H. For critical mixtures, in the early stage of phase separation the co‐continuous morphology with droplets of A in B and B in A is observed. In the late stage of phase separation, the viscosity asymmetry leads to morphological change from co‐continuous structure to completely dispersed structure where the less viscous component forms droplet. The pathway of this transformation is accompanied by the breakdown of balance of volume fraction between droplets with different viscosity. Domain growth is characterized by a crossover from a faster growth at intermediate time under the influence of hydrodynamics to Lifshitz–Slyozov behavior at late times. For off‐critical mixture, viscosity asymmetry only plays an important role for domain growth in the intermediate stage of phase separation and the domain growth depends on whether the more viscous phase is dispersed or continuous, and the late stage of domain growth follows Lifshitz–Slyozov power law independent of which phase is dispersed.

Result for the evolution of phase‐separating domains for critical fluid mixtures = 0.5 for t = 1 500 with viscosity asymmetry: η_A = 0.8, η_B = 0.2. A‐rich regions and B‐rich regions are represented by white and black, respectively.     

Morphology development and crystallization behavior of poly(ethylene terephthalate)/phenoxy blend

The morphological development and crystallization behavior of a poly(ethylene terephthalate)/poly(hydroxyl ether of bisphenol A) (phenoxy) blend were studied with time‐resolved light scattering, optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering (SAXS). During annealing at 280 °C, liquid–liquid phase separation via spinodal decomposition proceeded in the melt‐extruded specimen. After the formation of a domain structure, the blend slowly underwent phase homogenization by the interchange reactions between the two polymers. Specimens annealed for various times (t_s) at 280 °C were subjected to a temperature drop and the effects of liquid‐phase changes on crystallization were then investigated. The shifts in the position of the cold‐crystallization peaks indicated that the crystallization rate is associated with the composition change of the separated phases as well as the change of the sequence distribution in polymer chains during annealing. The morphological parameters at the lamellar level were determined by a correlation function analysis on the SAXS data. The crystal thickness (l_c) increased with t_s, whereas the amorphous layer thickness (l_a) showed little dependence on t_s. Observation of a constant l_a value revealed that a large number of noncrystallizable species formed by the interchange reactions between the two polymers were excluded from the lamellar stacks and resided in the interfibrillar regions, interspherulitic regions, or both. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 223–232, 2008     

Viscoelastic phase separation in polyethersulfone modified bismaleimide resin

The polymerization-induced phase separation process of polyethersulfone (PES) modified bismaleimide resin, 4,4′-bismaleimidodiphenylmethane (BDM), was investigated by time resolved light scattering (TRLS) and scanning electronic microscopes (SEM). At the blends with 10 wt% and 12.5 wt% PES, a phase inversion structure was found by SEM. TRLS results displayed clearly the spinodal decomposition (SD) mechanism and the exponential decay procedure of scattering vector q_m, which followed Maxwell-type relaxation equation. The characteristic relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in these PES modified bismaleimide blends were affected by viscoelastic effect.     

Characteristic lengths and the structure of salt free polyelectrolyte solutions. A small angle neutron scattering study

We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chainS ₁(q) and the structure factorS ₂(q). Two lengths are deduced from these two factors: the persistence lengthb _t which characterizes the electrostatic interactions along the chain by a fitting ofS ₁(q) with calculation of the scattering function for a wormlike chain, and fromS ₂(q),q _m ^–1 which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions (b _t C _p ^–1/2 ,q _m ^–1 C _p ^–1/2 ) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range.Laboratoire Commun CEA-CNRS.     

Investigation of phase separation mechanisms of thermoset polymer blends by time-resolved SAXS

Phase separation induced by crosslinking was studied by time-resolved small angle X-ray scattering in thermoset blend based on unsaturated polyester, styrene and low molar weight saturated polyester as low profile additive. The scattering intensities were analyzed using the Cahn-Hilliard-Cook theory. Combining DSC and DMA experiments allowed us to conclude that phase separation proceeded via spinodal decomposition frozen in the early stage. Apparent diffusion coefficients D_app were estimated.     

Phase Behavior and Morphology of Poly(Methyl Methacrylate)/Poly(α‐Methyl Styrene‐co‐Acrylonitrile) Blends Under Quiescent and Shear Flow

The kinetics of spinodal decomposition (SD) for the binary blend poly(methyl methacrylate), PMMA, and Poly(α‐methylstyrene‐co‐acrylonitrile), PαMSAN, with 31 wt% AN content (LCST‐type phase diagram) has been thoroughly studied using a time‐resolved light scattering technique. The early stage SD was dominated by a diffusion process and can be well described within the framework of the linearized Cahn‐Hilliard theory. The spinodal temperature could be evaluated from the analysis of the early stage SD based on the Cahn theory. In addition, viscoelastic properties of this system have been systematically investigated at temperatures below and above the LCST phase diagram. The linear viscoelastic properties of the blends were found to be greatly changed by phase separation in the two‐phase regime. This change in the linear viscoelastic properties attributed to an additional contribution of concentration fluctuations to the material functions at the phase separation temperatures. The phase diagram of the blends was also estimated rheologically through the dynamic temperature ramps of G′, G″ and η*. Furthermore, the phase behavior and morphology of this system has been studied under different shear rates using simple shear apparatus and transmission electron microscopy (TEM), respectively.     

Dynamic aspects of phase decomposition in reactive blends of polycarbonate and syndiotactic polymethyl methacrylate

Dynamics of phase separation in bisphenol-A polycarbonate (PC)/syndiotactic polymethyl methacrylate (sPMMA) blends has been investigated by means of time-resolved light scattering. Solvent-cast films of the PC/sPMMA blends were transparent, suggestive of miscible character. Several temperature jumps were carried out at a 50/50 PC/sPMMA composition from a homogeneous state (room temperature) into a two-phase regime. The process of phase separation first occurred for some considerable period, then it was followed by phase dissolution driven by chemical reaction. The thermodegradative reaction of sPMMA triggered the dissolution process by probably forming PC/sPMMA graft or random copolymers at the interface, which eventually resulted in a single phase. However, annealing at elevated temperatures for an extended period could lead to cross-linking, and thus a two-phase structure could be fixed permanently. The early stage of spinodal decomposition was interpreted in terms of the linearized Cahn-Hilliard theory. In the late stages of spinodal decomposition, the relationship between scattering peak wavenumber and time was found to obey a power law, but the exponents showed a strong dependence on temperature jumps. The temporal universal scaling failed due to the influence of the chemical reaction. © 1995 John Wiley & Sons, Inc.     

Concentration fluctuation dynamics of concentrated aqueous hydrophobicallymodified acrylic copolymer solutions

The dynamics of concentration fluctuation in concentrated aqueous solutions of a poly(hexaethylene glycol monomethacrylate-co-acrylic acid/allyl glycidyl ether) copolymer were studied by means of the timeresolved low angle laser light scattering (LALLS). Concentrated aqueous solutions in the range 30–55% w/w showed a lower critical solution temperature behaviour (LCST). A peak was observed in the scattered light profile with time,I(q,t), when a temperature jump above the coexistence curve was performed. The peak shifted to lowerq values with time in a logarithmic mode. Only at lowq values and very short times did the solutions obeyed Cahn's linear spinodal decomposition kinetics, subsequently slowing down.     

SMALL ANGLE LIGHT SCATTERING MEASUREMENT OF THE ISOTROPIC TO NEMATIC TRANSITION OF A SIDE CHAIN NEMATIC POLYMETHACRYLATE*

The kinetics of I→N transition of a side chain nematic polymethacrylate has been studied by small angledepolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer showsthe transition temperatures K52N79I in ℃. The H_v scattering intensity J(q,t) during the transition I (at 80.2℃)→N (at75.8℃) shows that J(q) is independent of q for all t, and during the initial stage (in 6 s) J(t) increases exponentially with t.In the later stage of the transition J(t) approaches a saturation value in 2 min. This experimental result indicates that the I→Ntransition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.