Phase Diagram Of Poly Research Articles

Prediction and phase segregation in thin‐film of conjugated polymer blends

AbstractBlending conjugated polymers is an efficient method to improve the properties of the films. The phase diagram of poly(9,9‐dihexylfluorene) (PF) and poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxyl)‐p‐phenylene vinylene) (MEHPPV) was predicted by a modified Flory–Huggins theory based on the topological method (graph theory) for the structure‐property correlations. It shows that the two polymers have a strong trend to separate. Atomic/friction force microscopy (AFM/FFM) measurements show there exist microphase separations in film prepared at room temperature. After annealing at 160 °C, serious phase segregations took place in both the lateral and vertical direction. The photoluminescence of the thin films was also measured by a fluorophotometer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1382–1391, 2005

Selective Solubility of E7 Components in Poly(n-butylacrylate)

Recently, the phase diagram of poly(n-butyl acrylate) and the nematic liquid crystal (LC) mixture E7 has revealed an anomalous behaviour that was attributed to the multicomponent nature of the LC which is made of four cyanoparaphenylenes. The anomalous emergence of a nematic phase at relatively low LC concentration above 60°C cannot be rationalized in terms of standard meanfield models commonly used to calculate phase diagrams of analogous systems. It was then suspected that the only possibility to explain this observation is to invoke the hypothesis of a selective solubility of the LC components with respect to the polymer. A detailed analysis of the composition of the LC within droplets as a function of the E7 concentration in the samples was made by HPLC. The corresponding measurements indicate unambigously that E7 undergoes a phase separation in the presence of poly(n-butylacrylate) and exhibits a selective miscibility that is reminiscent of the preferential solvation phenomenon. HPLC chromatograms exhibit peaks that correspond to the four single compounds included in the E7 mixture and can precisely identify those present in the sample droplets. We find that both nature of components and composition depend upon samples under consideration. The overall analysis of data enables us to understand the anomalies revealed by the complete phase diagram.

Effects of the Method of Preparation on the Molar Mass of Polymer and Phase Diagrams of Poly(2-ethylhexylacrylate)/5CB Systems

Effects of the Method of Preparation on the Molar Mass of Polymer and Phase Diagrams of Poly(2-ethylhexylacrylate)/5CB Systems

Onset and End of Transitions in PDMS/5CB Blends as Revealed by Static Light Scattering

The phase diagram of poly(siloxanes) and low molecular weight liquid crystals as obtained by polarized optical microscopy have shown a peculiar behavior : Transitions from a nematic to an isotropic and from an isotropic miscibility gap to a single isotropic phase take place in two steps interpreted as onset and end of transitions. This behavior has been observed in various systems and particular in those involving poly(dimethylsiloxane) (PDMS) and 4-cyano-4′- n -pentyl-biphenyl (5CB). In order to confirm this behavior we performed static light scattering on blends of PDMS ( M w =45000g/mol) and 5CB at different compositions. These experiments covered a temperature range from 20 to 115°C and several scattering angles.

Phase behavior of (polyacrylamides + water) solutions: concentration, pressure and isotope effects

Phase diagrams of poly( N-isopropylacrylamide) (PNIPAAM) as well as of hydrophilically-modified copolymers in aqueous solution were determined. A high-accuracy He–Ne Laser scattering technique was used for the detection of operational spinodal (sp) and cloud-point (cp) curves. Polymer concentration was varied from 0.5 to 20 wt.%. In the case of copoly(PNIPAAM/vinylsaccharide) several different chain lengths were considered. Pressure (up to 400 bar) and solvent isotope effects were studied. We predict a closed-loop type phase diagram for the copolymers, which presents an estimated hypercritical point in H 2O solutions at M w∼0.5×10 5, although only lower critical solution temperature (LCST) is experimentally accessible. At lower molecular weights, the solutions are always in the one-phase region.

Phase diagrams of poly(dimethylsiloxane)/E7 mixtures

The phase behavior of blends of poly(dimethylsiloxane) and the eutectic mixture of liquid crystals E7 is investigated. Experimental phase diagrams are established by polarized optical microscopy for two systems with widely different polymer molecular weights. Surprisingly, we find a very slight loss of miscibility of the mixture as a result of an increase of the polymer molecular weight by almost an order of magnitude. This unexpected phase behavior is in contrast with the results reported so far on other systems.

Phase diagrams of poly(dimethylsiloxane) and 5CB blends

The phase diagrams of poly(dimethylsiloxane) (PDMS) and 4-cyano-4′-n-pentyl-biphenyl (5CB) mixtures are studied for two systems of different molecular weights of the polymer. The experimental diagrams are established by polarized optical microscopy (POM), and analyzed using a combination of the Flory–Huggins theory of isotropic mixing and the Maier–Saupe theory of nematic order. The results are compared with those of polystyrene (PS) and 4-cyano-4′-n-octyl-biphenyl (8CB) with analogous molecular weight of the polymer. This investigation could be useful for the choice of systems in electro-optical devices. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 581–588, 2001

Phase diagrams of poly(dimethylsiloxane) and 5CB blends

The phase diagrams of poly(dimethylsiloxane) (PDMS) and 4-cyano-4′-n-pentyl-biphenyl (5CB) mixtures are studied for two systems of different molecular weights of the polymer. The experimental diagrams are established by polarized optical microscopy (POM), and analyzed using a combination of the Flory–Huggins theory of isotropic mixing and the Maier–Saupe theory of nematic order. The results are compared with those of polystyrene (PS) and 4-cyano-4′-n-octyl-biphenyl (8CB) with analogous molecular weight of the polymer. This investigation could be useful for the choice of systems in electro-optical devices. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 581–588, 2001

Phase behavior of a water/2-propanol/poly(methyl methacrylate) cosolvent system

A phase diagram of poly(methyl methacrylate) in mixtures of water and 2-propanol, individually nonsolvents for the polymer, was studied at 25 °C. For this system, there were two liquid–liquid demixing regions separated by a miscible region. This cosolvent phenomenon was thought to be a joint effect of the nonsolvents. The phase behavior was modeled according to modified Flory–Huggins chemical-potential equations, which accounted for the possible contribution from a ternary interaction in terms of a lumped parameter, χ123. The calculated phase-equilibrium curves (binodals) agreed well with the measured results. By contrast, if only binary interaction parameters were considered, computations yielded binodals whose compositions departed significantly from the measured data. Using the wet phase inversion method with casting dopes selected on the basis of the phase diagram, we prepared membranes with microporous structures in various coagulation baths. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 747–754, 2000

Aqueous polymer two-phase systems formed by new thermoseparating polymers.

A set of new polymers that can be used as phase forming components in aqueous two-phase systems is presented. All polymers studied have thermoseparating properties i.e. form one separate polymer enriched phase and one aqueous solution when heated above the critical temperature. This property makes the polymers attractive alternatives to the polymers used in traditional aqueous two-phase systems such as poly(ethylene glycol) (PEG) and dextran. The thermal phase separation simplifies recycling of the polymers, thus making the aqueous two-phase systems more cost efficient and suitable for use in large scale. Thermoseparating polymers studied have been copolymers of ethylene oxide and propylene oxide (EO-PO), poly (N-isopropylacrylamide) (poly-NIPAM), poly vinyl caprolactam (poly-VCL) and copolymers of N-isopropylacrylamide and vinyl caprolactam with vinyl imidazole (poly(NIPAM-VI) and poly(VCL-VI), respectively). In addition, the copolymer poly(NIPAM-VI) has the property to be uncharged at pH above 7.0 and positively charged at lower pH. This allows the partitioning of protein to be directed by changing the pH in the system instead of the traditional addition of salt to direct the partitioning. Hydrophobically modified EO-PO copolymer (HM-(EO-PO)) with alkyl groups (C14) at both ends forms two-phase system with for example poly(NIPAM-VI). The phase diagram for poly(NIPAM-VI)/HM-(EO-PO) was determined and the model proteins lysozyme and BSA were partitioned in this system. For BSA in poly(NIPAM-VI)/HM-(EO-PO) system a change in pH from 8.0 to 5.4 results in a change of partition coefficient from K = 0.8 to K = 5.1, i.e. BSA could be transferred from the HM-(EO-PO) phase to the poly(NIPAM-VI) phase. BSA partitioning in poly(NIPAM-VI)/HM-(EO-PO) system allows quantitative BSA recovery, and recoveries of poly(NIPAM-VI) and HM-(EO-PO) were 53% and 92%, respectively, after the thermoseparation step.

Phase Diagram of Poly(4-vinylphenol)−N,N-Dimethyloctadecylamine Mixture

The phase diagram of poly(4-vinylphenol)−N,N-dimethyloctadecylamine (PVPh−NDOA) mixture is investigated by X-ray diffraction measurements and optical microscopy. In the low-temperature region PVPh−NDOA mixtures take the mesoscopically ordered phase like a comb-shaped polymer above the melting temperature of the crystal of PVPh−NDOA aggregates. With elevating temperature PVPh−NDOA mixtures undergo an order−disorder phase transition that is a characteristic phase transition in block- or comb-shaped polymers and take homogeneous single phase. Furthermore, at higher temperatures PVPh−NDOA mixtures show the LCST-type phase transition and macroscopically separate into two homogeneous phases. These complex phase behavior in the PVPh−NDOA mixture is explained in relation to the balances of association between the hydroxyphenyl group of PVPh and the dimethylamino group of NDOA, repulsion between PVPh and the octadecyl group of NDOA, and the variation of the entropy contribution with varying temperature.

A high-pressure cell for optical microscopy and measurements on the phase diagram of poly(diethylsiloxane)

A new high-pressure cell as useful equipment for a polarizing microscope is described. Measurements in a temperature range between −40 and +270 °C under hydrostatic pressures up to 300 MPa allow for example the observation of polymer morphology and phase transitions. In addition to a documentation on video and photograph, respectively, the computer-controlled light intensity measurement offers the possibility of a quantitative analysis. Investigations on the phase diagram of poly(diethylsiloxane) have been carried out and show, that the transition temperature from mesophase to isotropic melt decreases with increasing pressure for pressures above 160 MPa.

Cocrystallization of poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoroethylene copolymers: 2. Thermodynamic study

The phase diagrams of poly(vinylidene fluoride) (PVF 2; KF and KY) and vinylidene fluoride-tetrafluoroethylene (VF 2–VF 4) copolymers (Cop-1, Cop-2) have been reported. They are the KF/KY, Cop-1/Cop-2, KF/Cop-1 and KY/Cop-1 systems. The head to head (H-H) defect structures of KF, KY, Cop-1 and Cop-2 are 3.5, 5.3, 15.8 and 21.3 mol%, respectively. The KF/KY and Cop-1/Cop-2 blends exhibit linear variation of apparent melting points with composition but the KF/Cop-1 and KY/Cop-1 blends show a bifurcation of melting point-composition diagram at the Cop-1 rich regions. The crystallization temperature ( T c)-composition plots are linear except for the KF/Cop-1 system. The anomaly of the KY/Cop-1 system in this regard has been explained. The equilibrium melting points ( T m 0) of the blends were determined using the Hoffman-Weeks procedure. The KF/KY blends show a slightly concave upward T m 0 vs. composition curve indicating weak interaction of the components. The Cop-1/Cop-2 blends exhibit a linear plot over the same composition due to ideal mixing. Both the KF/Cop-1 and KY/Cop-1 blends exhibit a concave upward curve with some concave downward portion for the T m 0 vs. composition plots at the Cop-1 rich regions. Further, at the Cop-1 rich regions ( W Cop-1 = 0.75), three melting peaks of isothermally crystallized KF/Cop-1 and KY/Cop-1 blends were observed when melted from the T c s. Liquid-liquid phase separation in the melt for the KF/Cop-1 and KY/Cop-1 systems at Cop-1 rich compositions has been attributed to the different behaviour rather than observed from the other pairs. The cocrystallization of this system is complicated by both the crystalline phase segregation and the liquid-liquid phase segregation.

Shear flow and the phase behaviour of polymer blends

The effect of simple shear flow on the phase diagram of partially miscible polymer blends has been analysed through the use of a generalised Gibbs energy of mixing, modified by a stored energy term. The latter is defined as the energy stored by the polymeric molecules during flow, and is seen to have a significant influence on the magnitude and direction of the change in the phase boundary caused by shear. Computer simulations indicate that flow induces mixing when the excess stored energy is negative and phase separation when the excess stored energy is positive. The dependence of the stored energy on the viscosity of the polymer blend was investigated for seven model blends exhibiting different viscosity-composition behaviours. A negative deviation of the viscosity-composition curve from the linear mixing rule was found to be a sufficient condition for a negative excess stored energy, resulting in shear-induced mixing. This prediction is in qualitative agreement with the experimental results on the effect of shear on the phase diagram of poly(styrene-co- acrylonitrile) poly(methymethacrylate) blends. In contrast, a positive deviation of the viscosity-composition curve from additivity was found to be a necessary but not sufficient condition for a positive excess stored energy which would cause shear-induced phase separation. This analysis seems to indicate that the viscosity-composition behaviour of a polymer blend could be used to qualitatively anticipate the change in the phase diagram of a polymer blend upon flow.

The crystallization behaviour and phase diagram of extended-chain crystals of poly(vinylidene fluoride) under high pressure

In order to obtain the pressure-temperature ( P—T) phase diagram of poly(vinylidene fluoride) (PVDF), the melting and crystallization behaviours under high pressure were investigated as a function of temperature and pressure. A corrected P—T phase diagram, in which the triple point (orthorhombic, hexagonal and melt) exists at 320 MPa and 300°C, is proposed. A film mainly consisting of extended-chain lamellar crystals of β-form can be obtained by crystallization in the metastable hexagonal phase, which appears when increasing pressure is applied on the melt. This crystallization method provides good-quality β-form films without thermal degradation.

Miscibility between components of acrylic pressure‐sensitive adhesives: Phase diagrams of poly(butyl acrylate‐co‐acrylic acid) and esterified rosins

AbstractA series of acrylic copolymers, poly(butyl acrylate‐co‐acrylic acid), were blended with tackifiers and dehydroabietic acid esters, and the miscibility between the components was investigated. The phase diagram of the blends changed from an LCST type to a UCST type as acrylic acid content increased, and the miscibility region in the phase diagrams decreased as the tackifier became bulkier. It was found that some of the trends can be accounted for on the basis of mean field approximation. © 1995 John Wiley & Sons, Inc.

Light-Scattering Studies on Hydrogen-Bonded Polymer Blends

Phase diagrams for poly(n-hexyl methacrylate) blends with a series of styrene-co-vinylphenol polymers have been mapped using light-scattering techniques. These are compared to theoretical phase diagrams calculated using an association model that incorporates the various interactions in hydrogenbonded polymer systems. The thermodynamics of these blends is strongly affected by the competition between the self-associating and interassociating hydrogen bonds and the unfavorable dispersive interactions. The balance of these competing factors controls the temperature and composition of phase separation. The results of the theoretical predictions are found to be in good accord with the experimental phase diagrams

Measurements of the complex shear modulus of polymers under hydrostatic pressure usina the quartz resonator method

Abstract The quartz resonator method measures the complex shear modulus or compliance of viscoelastic materials in the frequency range from 50 kHz to 140 MHz at temperatures between −150°C and 300°C and pressures up to 1 GPa. This method can be applied to viscous fluids or polymer melts -even in their glassy or seminystalline regime. The phase diagram of poly(diethylsiloxane) PDES (a mesophase polymer) was determined for two samples with different molecular weight at pressures up to 400 MPa and temperatures between 20°C and 100°C. Phase transitions are indicated by a sharp bend in the shear compliance although the volume effect of the mesophase-isotropic transition vanishes around 80 MPa. The pressure dependence of the glass relaxation process (in PVAc), was studied by measuring the change of the complex shear modulus with pressure at constant temperatures between 95°C and 145°C and pressures up to 600 MPa. Additionally to the relaxation process, also the pressure dependence of the real part of the shear ...

Molecular modeling of micelle formation and solubilization in block copolymer micelles. 2. Lattice theory for monomers with internal degrees of freedom

A self-consistent mean-field lattice theory of the micellization and solubilization properties of poly(ethylene oxide)-poly(propylene oxide) block copolymers is described. The polymer segments are allowed to assume both polar and nonpolar conformations (corresponding to the gauche and trans rotations of the C-C and C-O bonds), which permits the dependence of the segment-segment interactions on temperature and composition to be accounted for in a physically realistic manner. The phase diagrams of poly(ethylene oxide) and poly(propylene oxide) in water, both of which exhibit lower critical solution temperatures, can be reproduced semiquantitatively. The predictions of the theory compare favorably with published light scattering results on the aggregation behavior of block copolymers and with the authors experimental results for the solubilization of naphthalene in these micelles as a function of polymer composition and molecular weight. The dependence of the micelle-water partition coefficient on polymer composition is not simply related to the proportion of the hydrophobic constituent but depends on the detailed micelle structure. The strong effect of the molecular weight and PPO content of the polymer on the amount of naphthalene solubilized observed experimentally was interpreted in terms of the model results.

Gelation of poly(vinyl alcohol)-vanadate aqueous solutions

A phase diagram of poly(vinyl alcohol) (PVA) and vanadate ions was constructed as a function of PVA and sidium vanadate concentrations as well as pH. It was found that PVA aqueous solutions became a gel in the presence of H 2 V 10 O 28 4- vanadate ions, which are exclusively formed in the pH range 2-3. It was found that only H 2 V 10 O 28 4- ions among more than 10 kinds of vanadate ions were responsible for the complex formation with PVA molecules. The viscosity of PVA/vanadate aqueous solutions increased with time when the PVA concentration was larger than the chain overlap concentration