Binary Polymer Mixtures Research Articles

Kinetics of the Isotropic‐Ordered Phase Transition in Binary Mixtures of Mesogenic Monomers and Polymers

Kinetics of the nematic phase growth in the melted liquid crystalline azomethine monomer, siloxane‐azomethine polymer, and their mixtures was studied under a deep cooling using polarizing optical microscopy. The nematic droplets revealed in the optical images across the phase transition were treated statistically and the resulting statistical size distributions were described using principles of irreversible thermodynamics. Analysis of the mean droplet diameter as a function of time allowed recognition of two regimes involved to the nematic phase evolution: (1) nucleation and rapid nucleus growth and (2) nucleus coarsening. Both regimes were quantitatively described with the universal law of the cluster growth.

Kinetic Study of the Aggregation of Colloids Immersed in a Binary Mixture of Polymers

AbstractSummary: We consider an assembly of colloidal particles, which are immersed in a binary mixture of polymers. At temperatures close to the critical point of the free mixture, the fluctuations of the composition induce a critical Casimir force between colloids. This force naturally depends on their distance and it is responsible for the colloidal aggregation. In this paper, we propose to study the kinetics of such a transition leading colloids from a dispersed phase (gas) to a dense one (liquid). This kinetics is studied through the relaxation rate, which is a function of the transfer wave‐vector.

Investigations on mixed micelles of binary mixtures of zwitterionic surfactants and triblock polymers: A cyclic voltammetric study

Cyclic voltammetry has been employed to investigate the mixed micellar behavior of the binary mixtures of different zwitterionic surfactants such as 3-( N , N -dimethylhexadecylammonio)propane sulfonate (HPS), 3-( N , N -dimethyltetradecylammonio)propane sulfonate (TPS) and 3-( N , N -dimethyldodecylammonio)propane sulfonate (DPS) with three triblock polymers (L64, F127 and P65) by using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as an electroactive probe at 25 °C. Critical micellar concentration ( cmc) has been determined from the plots of variation in peak current ( i p ) versus the total concentration of surfactant/triblock polymer. Diffusion coefficient of the electroactive species has also been reported. The regular solution theory approximation has been used to determine various micellar parameters of ideal systems. The variation in micellar mole fraction ( X 1 ) of the zwitterionic surfactant supports the formation of mixed micelles, which are rich in triblock polymer component in the surfactant rich region of the mixture and vice versa. The regular solution interaction parameter ( β) suggests the formation of mixed micelles due to the synergistic interactions in case of HPS/TPS/DPS + F127/P65 systems and gets affected by EO/PO ratio of triblock polymers.

Surface-Directed Phase Separation via a Two-Step Quench Process in Binary Polymer Mixture Films with Asymmetry Compositions

Surface-directed phase separation via a two-step quench process in asymmetry polymer mixtures is numerically investigated by coupling the Flory-Huggins-de Gennes equation with the Cahn-Hilliard-Cook equation. Two distinct situations, i.e., the minority component is preferred by the surface and the majority component is preferred by the surface, are discussed, respectively. The morphology and evolution dynamics of the phase structure, especially the secondary domain structure, are analyzed. The wetting layer formation mechanisms during the two-step quench process are examined. The simulated results demonstrate that different secondary domain structures in these two situations can be induced by the second quench with deeper quench depth, which can be used to tailor phase morphology. It is also found that, in the second quench process, the evolution of the wetting layer thickness can cross over to a faster growth when the preferential component is the minority component. In this situation, the formation mechanism of the wetting layer will change and is eventually determined by the second quench depth. However, when the preferential component is the majority component, a deeper second quench depth corresponds to a slower growth of the wetting layer thickness. The chemical potential is calculated to explain the difference regarding the growth dynamics of the wetting layer thickness between these both situations.

Kinetic Pathway of Pattern-Directed Phase Separation in Binary Polymer Mixture Films

The phase separation of polymer blend films on the stripe patterned surface is numerically investigated by coupling the Flory-Huggins-de Gennes equation with the Cahn-Hilliard-Cook equation. The kinetic pathway and its mechanisms are analyzed in both real space and reciprocal space. Compared to experimental measurements, the simulated results exhibit more complete kinetic pathways of pattern-directed phase separation. It is found that the extreme fluctuation of the chemical potential at the edges of stripes leads to the formation of the branch structure. Our simulated results indicate that the phase inversion, occurring not only in the polymer/ air interface but also in the bulk, can extensively affect the relations between the isotropic phase separation and the periodic structure. The analysis in reciprocal space shows that the evolution of the phase morphologies in the polymer/air interface obeys a 1/3 power law for a thick film, consistent with the experimental results. It is also found that the amplitude change of the first diffraction peak can reflect the kinetic pathway of the phase structure in the polymer/air interface very well. A narrower strip periodicity corresponds to an earlier phase inversion and an earlier appearance of the droplet arrays in strips.

Lamellar morphology induced by two-step surface-directed spinodal decomposition in binary polymer mixture films

A novel process for obtaining ordered morphology on the basis of two-step surface-directed spinodal decomposition is numerically investigated. The formation mechanism and evolution dynamics of this process are also discussed in detail. The calculated results of the chemical potential demonstrate that the equilibration state at the first quench affects the competition between the surface potential and the chemical potential in the bulk, leading to a surprising lamellar structure at the second further quench. It is also found that the lamella formation obeys the logarithmic growth. These results could provide a new approach for fabricating ordered structure of polymer materials and stimulate experimental studies based on this subject.

Novel Combination of Anionic and Cationic Polymethacrylate Polymers for Sustained Release Tablet Preparation

The objectives of this study were to prepare and evaluate a novel sustained release tablet formulation using a binary mixture of polymethacrylate polymers: Eudragit E-100 (EE) and Eudragit L-100 (EL) in their salt forms. Tablets prepared using EE-citrate and EL-Na showed the highest degree of swelling among other combinations of EE and EL. The drug release rates were independent of the pH of the dissolution medium as the release profiles exhibited a continuous release pattern with no burst effect when changing the pH of the medium. These results, along with other test results, indicated the presence of an ionic interaction between both polymers when combined in the salt forms.

Chemically Produced Toner Containing a Binary Polyester Binder

The fuser roller is commonly used in electrophotograhic machines such as copiers, laser printers and multifunctional printers to fix toner image on paper. For improving printing speeds, image gloss and energy consumptions, an increasing number of printers are designed to adopt polyester toner. Polyester toner, with its low fusing temperatures, is aimed to accommodate fuser rollers operated at low temperatures to reduce energy consumption. Although polyester toner has the above advantages, low fusing temperatures on the other hand can cause hot-offset defects on the fuser roller. This paper reports the study of chemically produced toner (CPT) consisting of a binary polyester binder. The toner was prepared by phase-separation/aggregation (PSA) method. It was found a balance of low-temperature fixing and anti-offset characteristics can be achieved by incorporating a binary polymer mixture of low- and high-molecular weight polyesters. The addition of wax was also used to provide an option to tune the fixing and anti-offset characteristics. Wax content, however, was found to exhibit some threshold value, above which wax tends to separate from the toner and the resultant wax leaks can contaminate associated printer parts to cause streaking defects.

A Predictive Group-Contribution Simplified PC-SAFT Equation of State: Application to Polymer Systems

A group-contribution (GC) method is coupled with the molecular-based perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) to predict its characteristic pure compound parameters. The estimation of group contributions for the parameters is based on a parameter database of 400 low-molecular-weight compounds estimated by fitting experimental vapor pressures and liquid densities. The method has been successfully used for estimating the PC-SAFT parameters for common polymers. Specifically, using the new polymer parameters as calculated from the proposed GC scheme, the simplified PC-SAFT yields rather good predictions of polymer densities and gives promising modeling results of various binary polymer mixtures exhibiting both vapor—liquid and liquid—liquid phase equilibria. In summary, the data required for calculating polymer phase equilibria with the proposed method are the molecular structure of the polymer of interest in terms of functional groups and a single binary interaction parameter for accurate mixture calculations.

Effect of polymer size and chain length on depletion interactions between two colloids

A density functional theory based on the weighted density has been developed to investigate the depletion interactions between two colloids immersed in a bath of the binary polymer mixtures, where the colloids are modeled as hard spheres and the polymers as freely jointed tangent hard-sphere chain mixtures. The theoretical calculations for the depletion forces between two colloids induced by the polymer are in good agreement with the computer simulations. The effects of polymer packing fraction, degree of polymerization, polymer/polymer size ratio, colloid/polymer size ratio on the depletion interactions, and colloid-colloid second virial coefficient B2 due to polymer-mediated interactions have been studied. With increasing the polymer packing fraction, the depletion interaction becomes more long ranged and the attractive interaction near the colloid becomes deeper. The effect of degree polymerization shows that the long chain gives a more stable dispersion for colloids rather than the short chain. The strong effective colloid-colloid attraction appears for the large colloid/polymer and polymer/polymer size ratio. The location of maximum repulsion Rmax is found to appear Rmax approximately sigmac+Rg2 for the low polymer packing fraction and this is shifted to smaller separation Rmax approximately sigmac+sigmap2 with increasing the polymer packing fraction, where sigmap2 and Rg2 are the small-particle diameter and the radius of gyration of the polymer with the small-particle diameter, respectively.

Tuning Supramolecular Structuring at the Nanoscale Level: Nonstoichiometric Soluble Complexes in Dilute Mixed Solutions of Alginate and Lactose-Modified Chitosan (Chitlac)

Two oppositely charged polysaccharides, alginate and a lactose-modified chitosan (chitlac), have been used to prepare dilute binary polymer mixtures at physiological pH (7.4). Because of the negative charge on the former polysaccharide and the positive charge on the latter, polyanion-polycation complex formation occurred. A complete miscibility between the two polysaccharides was attained in the presence of both high (0.15 M) and low (0.015 M) concentrations of simple 1:1 supporting salt (NaCl), as confirmed by turbidity measurements; phase separation occurred for intermediate values of the ionic strength (I). The binary solutions were further characterized by means of light scattering, specific viscosity, and fluorescence quenching measurements. All of these techniques pointed out the fundamental role of the electrostatic interactions between the two oppositely charged polysaccharides in the formation of nonstoichiometric polyelectrolyte soluble complexes in dilute solution. Fluorescence depolarization (P) experiments showed that the alginate chain rotational mobility was impaired by the presence of the cationic polysaccharide when 0.015 M NaCl was used. Moreover, upon addition of calcium, the P values of the binary polymer mixture in 0.015 M NaCl increased more rapidly than that of an alginate solution without chitlac, suggesting an efficient crowding of the negatively charged alginate chains caused by the polycation.

Synergistic Effects in Semidilute Mixed Solutions of Alginate and Lactose-Modified Chitosan (Chitlac)

The present study specifically aimed at preparing and characterizing semidilute binary polymer mixtures of alginate and chitlac which might find an application in the field of cell encapsulation. A polyanion, alginate, and a polycation, a lactose-modified chitosan, were mixed under physiological conditions (pH 7.4 and NaCl 0.15) and at a semidilute concentration avoiding associative phase separation. The mutual solubility was found to be dependent on the charge screening effect of the added NaCl salt, being prevented below 0.05 M NaCl. A comparison with the behavior of the polyanion (alginate) under the same experimental conditions revealed that both the viscosity and the relaxation times of the binary polymer solutions are strongly affected by the presence of the polycation. In particular, the occurrence of electrostatic interactions between the two oppositely charged polysaccharides led to a synergistic effect on the zero-shear viscosity of the solution, which showed a 4.2-fold increase with respect to that of the main component of the solution, i.e., alginate. Moreover, the relaxation time, calculated as the reciprocal of the critical share rate, markedly increased upon reducing the alginate fraction in the binary polysaccharide solution. However, the formation of the soluble complexes and the synergistic effect are reduced upon increasing the concentration of the 1:1 electrolyte. By containing a gel-forming polyanion (alginate, e.g., with Ca(2+) ions) and a bioactive polycation (chitlac, bearing a beta-linked D-galactose), the present system can be regarded as a first step toward the development of biologically active scaffold from polysaccharide mixtures.

Critical adsorption of crosslinked polymer blends

The purpose of this paper is a quantitative investigation of the critical adsorption of crosslinked polymer blends in the molten state or in solution. These mixtures are assumed to be in contact with a wall that strongly attracts one connected polymer, at the spinodal temperature, where a microphase separation takes place. This is the so-called critical adsorption. The latter is studied through the composition fluctuation profile. Using an extended de Gennes theory, we find that, at criticality, the equilibrium profile obeys a universal scaling law, which depends only on two kinds of lengths, namely the perpendicular distance from the wall and the mesh size (microdomains size). For critical crosslinked binary polymer mixtures, we show that the composition fluctuation profile is given by: ϕ ( z ) = ( σ N / ξ * ) f ( z / ξ * ) , where σ is the monomer size, N the common polymerization degree of connected chains, z the perpendicular distance, ξ * ∼ σ n the mesh size ( n being the number of monomers of the section of a chain between two neighboring crosslinks), and f ( x ) a known universal scaling function. For critical crosslinked polymer blends in solution, using the blob model, we show that the composition fluctuation profile, δ x ( z ) , is governed by the scaling law: δ x ( z ) = ( σ N Φ - 1 / 8 / ξ ^ * ) f ^ ( z / ξ ^ * ) , with the new mesh size ξ ^ * ∼ σ n Φ - 1 / 8 and the known universal scaling function f ^ ( x ) . Here, Φ accounts for the overall monomer fraction. Extension of these results, away from the spinodal temperature, is also discussed. Finally, the present work must be considered as a generalized study of the critical adsorption of uncrosslinked polymer blends.

Phase Separation of Binary Polymer Mixtures under an Electric Field

Time evolution of phase separation under an AC electric field was studied for poly(2-chlorostyrene)/poly(vinyl methyl ether) blends containing 0.5 wt % lithium perchlorate (LiClO4) near the critical point. We observed anisotropic morphologies with the interfaces aligned parallel to the direction of the field between two electrodes. The degree of anisotropy (D) was quantitatively evaluated by image analysis of the resulting morphology observed with an optical-phase contrast microscope. We found that D increased at the beginning of the phase separation and tended to reach an equilibrium state, while the characteristic length scale ξ of the morphology increased monotonically with time according to a power law ξ − tα.

Athermal models for diblock copolymer self-assembly

Recent work on coarse-grained representations of interacting homopolymers and diblock copolymers in solution is briefly reviewed. Long homopolymer chains are modelled as ‘ultrasoft colloids’, with the effective interaction between their centres of mass (CM) determined by averaging over polymer conformations for fixed CM–CM distances. Diblock copolymers are modelled as ‘ultrasoft dumbells’, with the CMs of the two strands tethered by an anharmonic intramolecular potential. Monte Carlo simulations of these coarse-grained models allow the self-assembly of model diblock copolymers into lamellar and micellar microphases to be investigated. We show that the onset of clustering of two athermal models of diblock copolymers can be predicted within the ‘reference interaction site model’ (RISM) integral equation theory for the pair structure, using the simple random phase closure assumption. This analytic formulation highlights the natural link between bulk phase separation of binary polymer mixtures and microphase separation of the corresponding diblock copolymer in the same selective solvent.

Blend Miscibility and the Flory−Huggins Interaction Parameter: A Critical Examination

The Flory−Huggins interaction parameter, χ, is often used in the literature to describe the binary interactions of polymer blends, yet to what extent does this widespread analysis yield valuable thermodynamic insight? In this work we think critically about χ and creatively about alternatives. Making use of a simple lattice theory to model binary polymer mixtures, we follow a different, less ambiguous route and show connections between the microscopic characteristic parameters of a system and its macroscopic thermodynamic behavior. To this end we analyze experimental data, including results from neutron scattering experiments, cloud point curves, and pressure−volume−temperature (PVT) surfaces for a series of blends, including deuterated polystyrene/poly(tetramethyl bisphenol A polycarbonate) (dPS/TMPC), deuterated polystyrene/poly(vinyl methyl ether) (dPS/PVME), polystyrene/polybutadiene (PS/PB), deuterated polystyrene/poly(p-methylstyrene) (dPS/PpMS), polypropylene/deuterated head-to-head polypropylene (PP/dhhPP), polystyrene/deuterated polystyrene (PS/dPS), polystyrene/polychlorostyrene (PS/PCS), deuterated poly(methylbutylene)/poly(ethylbutylene) (dPMB/PEB), and poly(ethylmethylsiloxane)/deuterated poly(dimethylsiloxane) (PEMS/dPDMS). We conclude by suggesting that there is a temperature- and concentration-independent parameter which may prove to be a more characteristic indicator of blend behavior than χ.

Mixed micelles of binary triblock polymer mixtures in pure water at 30 °C

This is the first report on the mixed micelles of binary triblock polymer (TBP) mixtures. The steady-state fluorescence and viscosity measurements have been carried out for the various binary combinations of TBP (i.e., P103 + F127/P84/L64/P104/P123) in pure water at 30 °C. All the TBP components selected for the study show clear micelle formation process. The pyrene fluorescence has been used to determine the critical micelle concentration. As micelle-forming TBP can also be termed as nonionic surfactants; therefore, their mixed micelle formation has been evaluated by applying the regular solution theory. It has been observed that this theory very well predicts the nature of mixed micelles. The P103 + F127/P84/L64 binary mixtures undergo mixed micelle formation due to the synergistic interactions while P103 + P104/P123 show antagonistic behavior. The results clearly show that the mixtures with greater number of poly(ethylene oxide) units undergo favorable mixing.

Numerical Simulation of Surface Effects on Spinodal Decomposition in Polymer Binary Mixture: Quench Depth Dependence

The surface-directed spinodal decomposition (SDSD) in binary polymer mixture with different quench depths is investigated by numerical simulations, combining Cahn−Hilliard−Cook (CHC) theory with Flory−Huggins−de Gennes theory. The formation mechanisms of the wetting layer with different quench depths are discussed. The simulated results demonstrate that the growth of the wetting layer can exhibit pure diffusion-limited growth law, logarithm growth law, and Lifshitz−Slyozov (LS) growth law with the increasing quench depth, which reproduces experimental observations. Furthermore, the detailed ranges of these three regimes are determined on the basis of simulated results. The growth law of the wetting layer is pure diffusion-limited growth law when χN < 2.01. In the case of 2.08 ≤ χN, the growth of the wetting layer obeys LS growth law. However, when 2.01 ≤ χN < 2.08, the logarithm growth law of the wetting layer is favored. The simulated results also demonstrate that the evolution of the polymer morphology ...

Simulation of phase separation of polymer–liquid-crystal mixtures and the effect of confining external surfaces

A Monte Carlo simulation is performed on a lattice model of a binary mixture of nematogenic liquids and polymers to study the main aspects of phase separation including the influence of external surfaces. The system was investigated at various temperatures, concentrations, and degrees of polymerization. The results seem to fit well within Flory-Huggins theory predictions. It is also shown that in some cases the anisotropy plays an important role in structure formation. The influence of the external surfaces on the condensation of one of the phases was studied on systems that experience the separation by nucleation and growth. It has been noticed that the surfaces that prefer nematogenic molecules act as better condensation nuclei, especially if they are ordered.

Soft core fluid in a quenched matrix of soft core particles: A mobile mixture in a model gel

We present a density-functional study of a binary phase-separating mixture of soft core particles immersed in a random matrix of quenched soft core particles of larger size. This is a model for a binary polymer mixture immersed in a cross-linked rigid polymer network. Using the replica "trick" for quenched-annealed mixtures we derive an explicit density functional theory that treats the quenched species on the level of its one-body density distribution. The relation to a set of effective external potentials acting on the annealed components is discussed. We relate matrix-induced condensation in bulk to the behavior of the mixture around a single large particle. The interfacial properties of the binary mixture at a surface of the quenched matrix display a rich interplay between capillary condensation inside the bulk matrix and wetting phenomena at the matrix surface.