Phase Separation Of Polystyrene Research Articles

Thin microporous polydimethylsiloxane membrane prepared by phase separation and its applications for cell culture

Animal experiments are often required for biological studies. However, in vitro cell culture models, such as cell-culture inserts and microphysiological systems, can provide a suitable alternative, making them essential tools in cell biology research, including the simulation of an organ environments closely related to the human body. Cell-culture inserts with porous membranes assist in recreating in vivo cell culture environments to study and process cell-culture assays. However, conventional cell culture membranes typically made of polyethylene terephthalate or polycarbonate cannot accommodate cell types that require deformable substrates. As such, this paper introduced a novel approach using spin-casting-assisted polymer-blend phase separation to create thin, flexible, and highly porous membranes for cell culture applications. Polydimethylsiloxane (PDMS) was selected as the material for the porous membrane, and polystyrene (PS) was used as a counter pair to induce phase separation with PDMS. PDMS facilitated the necessary reversible deformations during cell culture owing to its low elastic modulus. The thickness of the membrane and connectivity of the phase-separated PS domains can be adjusted, facilitating the fine-tuning of the pore size and density to improve the membrane performance. Therefore, this study successfully fabricated thin microporous PDMS membranes with improved performance over standard membranes for cell-culture inserts, namely a higher porosity, flexibility, and softness. The results of this study can enhance cell culture methodologies and contribute to a deeper understanding of cellular processes.

Enhanced performance of organic light-emitting diodes by integrating quasi-periodic micro-nano structures

To integrate a quasi-periodic micro-nano structure (PMS) to the organic light-emitting devices (OLEDs) is an efficient way to enhance the performance of OLEDs. In this paper, the PMS prepared by the phase separation of Polystyrene and Poly (methyl methacrylate) was integrated to the OLEDs with the structures of Glass/PMS/Ag (30 nm)/MoO3 (5 nm)/(NPB) (40 nm)/(Alq3) (60 nm)/LiF (0.5 nm)/Al (150 nm). The maximum luminance intensity and external quantum efficiency increased to 10700 cd/m2 and 1.11 %, which is 48 % and 44 % higher than that of 7209 cd/m2 and 0.77 % of the planar reference device. The enhanced performance of OLEDs was ascribed to the attenuation of surface plasmon polariton loss caused by the PMS, which was testified by the Finite-Difference Time-Domain (FDTD) simulation. The PMS was also transferred to the hole transfer layer (PEDOT: PSS) of OLEDs by nano-imprinting lithography with the structure of Glass/(ITO) (100 nm)/PEDOT: PSS (100 nm) (with PMS)/NPB (10 nm)/Alq3 (50 nm)/LiF (0.5 nm)/Al (100 nm). The performance was also improved by the optimized PMS and the light out-coupling efficiency increased to about 49.5 %, which is much higher than that of 28.8 % in the OLEDs with PMS Ag anode and 20 % in the planar reference devices. This suggests that the PMS can improve the OLED device performance regardless of the functional layer in which the PMS is integrated.

Visualizing Surface Phase Separation in PS-PMMA Polymer Blends at the Nanoscale.

Phase-separated polymer blend films are an important class of functional materials with numerous technological applications in solar cells, catalysis, and biotechnology. These technologies are underpinned by the precise control of phase separation at the nanometer length-scales, which is highly challenging to visualize using conventional analytical tools. Herein, we introduce tip-enhanced Raman spectroscopy (TERS), in combination with atomic force microscopy (AFM), confocal Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), as a sensitive nanoanalytical method to determine lateral and vertical phase-separation in polystyrene (PS)-poly(methyl methacrylate) (PMMA) polymer blend films. Correlative topographical, molecular, and elemental information reveals a vertical phase separation of the polymers within the top ca. 20 nm of the blend surface in addition to the lateral phase separation in the bulk. Furthermore, complementary TERS and XPS measurements reveal the presence of PMMA within 9.2 nm of the surface and PS at the subsurface of the polymer blend. This fundamental work establishes TERS as a powerful analytical tool for surface characterization of this important class of polymers at nanometer length scales.

Anisotropic phase-separated morphology of polymer blends directed by electrically pre-oriented clay platelets.

We describe a general pathway to prepare an anisotropic phase-separated polystyrene (PS) - poly(vinyl methyl ether) (PVME) blend morphology by using electrically pre-orientated clay platelets. The clay platelets were oriented in a PS/PVME blend by means of an externally applied AC electric field while the blend is in one phase. Following orientation step, phase separation of the blends was induced by a temperature jump above their lower critical solution temperature (LCST) in the presence of the oriented clay platelets. In this process, an early stage co-continuous PS/PVME morphology coarsened and turned anisotropic phase-separated morphology parallel to the direction defined by clay planes oriented by AC electric field. The degree of anisotropy of PS/PVME phase-separated morphology was characterized by image analysis and that was found to be linearly proportional to the degree of orientation of clay platelets obtained by a 2D Wide Angle X-ray Scattering (WAXS). Transmission Electron Microscope (TEM) image of the blend morphology revealed that clay platelets oriented to AC field direction were located in a PVME phase. The electrically ordered column structures of clay platelets in the PVME phase yielded anisotropic PS diffusion during the phase separation. This process provides a unique new way to develop directionally organized phase-separated morphology from partially miscible binary blends using nanoparticles in combination with an external electric field.

High transparent mid-infrared silicon "window" decorated with amorphous photonic structures fabricated by facile phase separation.

High transparency in the infrared (IR) region is desirable for most common IR materials and devices, due to their high interfacial reflectance, resulting from the high refractive indices of constituent substances. Herein, a new strategy, with using phase-separated polystyrene (PS)/polymethylmethacrylate (PMMA) blends as masks, is proposed to fabricate subwavelength structures for Si with significantly enhanced mid-IR transmission. Maximum transmittance approaching to 70% and 90% are achieved with single and double- side structured Si respectively. The fabricated subwavelength structures are short-range ordered amorphous photonic structures (APSs). By using different spin-coating speeds and molar ratios of PS to PMMA and by adjusting the etching duration time, tunable enhanced transmission are also obtained. The good performance of high transmission is confirmed by mid-IR thermal imaging experiments. Furthermore, the enhanced transmission is effective over a wide range of incident angles up to 50° and well maintained at high temperatures up to 600 °C.

Macromol. Rapid Commun. 12/2017

Front Cover: The cover image corresponds to phase-separated polystyrene (PS) and polymethylmethacrylate (PMMA) blend film that is optically blue in color. Temperature-induced phase-separation in PS/PMMA blend film offers control over lateral scale of phase separation and surface roughness. Furthermore, this study demonstrates that control on specular and diffuse reflectance of incident UV-visible light can be achieved by controlling the rough area, which is determined by the product of lateral scale of phase separation and surface roughness. Further details can be found in article number 1600803 by A. Nallapaneni, M. D. Shawkey, and A. Karim.

Direct Characterization of In-Plane Phase Separation in Polystyrene Brush/Cyclohexane System

The phase behavior of polystyrene (PS) brushes in cyclohexane (CHX) was investigated, for the first time, by environmental atomic force microscopy as a function of the graft density and temperature. The polystyrene brushes of three different graft densities exhibited island-, bicontinuous-, and hole-shape microdomains in the direction parallel to the substrate. The size of such “in-plane” microdomains is close to the end-to-end distance of PS brush chain due to the anchoring of one of the chain ends of PS brushes to the substrate. The microdomain structure disappeared as the temperature increased, and new structure with same morphological features reappeared by lowering temperature. This reversible temperature response corresponds to the in-plane phase separation of the PS brush/CHX system. The UCST type binodal line shifted toward slightly lower temperature in the PS brush/CHX system compared to that of the corresponding nongrafted polymer solution, i.e., PS/CHX system, in excellent agreement with our pr...

A New Strategy of Lithography Based on Phase Separation of Polymer Blends.

Herein, we propose a new strategy of maskless lithographic approach to fabricate micro/nano-porous structures by phase separation of polystyrene (PS)/Polyethylene glycol (PEG) immiscible polymer blend. Its simple process only involves a spin coating of polymer blend followed by a development with deionized water rinse to remove PEG moiety, which provides an extremely facile, low-cost, easily accessible nanofabrication method to obtain the porous structures with wafer-scale. By controlling the weight ratio of PS/PEG polymer blend, its concentration and the spin-coating speed, the structural parameters of the porous nanostructure could be effectively tuned. These micro/nano porous structures could be converted into versatile functional nanostructures in combination with follow-up conventional chemical and physical nanofabrication techniques. As demonstrations of perceived potential applications using our developed phase separation lithography, we fabricate wafer-scale pure dielectric (silicon)-based two-dimensional nanostructures with high broadband absorption on silicon wafers due to their great light trapping ability, which could be expected for promising applications in the fields of photovoltaic devices and thermal emitters with very good performances, and Ag nanodot arrays which possess a surface enhanced Raman scattering (SERS) enhancement factor up to 1.64 × 108 with high uniformity across over an entire wafer.

Control of Rubrene Polymorphs via Polymer Binders: Applications in Organic Field-Effect Transistors

In this report, the crystallization mechanisms in solution-processed, annealed thin films of semiconducting small molecule 5,6,11,12-tetraphenylnaphthacene (rubrene) blended with three different amorphous polymers (polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(4-vinylpyridine) (P4VP)) are investigated. The results show that the degree of phase separation, the exact crystal structure, and the electronic properties of the blend films depend strongly on the choice of polymer binder. While rubrene films crystallized from blends with PS and P4VP consist of crystalline spherulites in a mostly orthorhombic crystal structure, rubrene in PMMA blends contains a significant fraction of triclinic phase and is generally more disordered. Structural characterizations also reveal a high degree of vertical phase separation in PS and P4VP films, which is attributed to residual solvent effects in the case of rubrene/PS films and a preferential hydrophilic interaction with the Si/SiO2 interface for rubrene/P4VP films. This type of phase separation is shown to be critical for crystallization and lead to improved field-effect mobilities. Finally, this processing technique easily allows for patterning of transistors using chemically modified substrates, which is useful for large-scale device fabrication.

Influence of the molecular weight of a modifier on the phase separation in an epoxy thermoset modified with a thermoplastic

The effect of varying the molecular weight of a thermoplastic modifier on the phase separation in polystyrene (PS)-modified epoxy/amine blends was investigated by comparing blends with PS of different molecular weights. A thermodynamic analysis of polymerization-induced phase separation was performed using a model based on the Flory–Huggins theory, from which the phase diagram and species distribution in the separated phases were calculated. Morphologies developed by the blends were studied in terms of concentration and molecular weight of modifier. Trends in morphologies and thermodynamics of phase separation were exposed and discussed. An increase in the molecular weight of modifier caused a decrease in the miscibility of blend affecting phase diagram, molecular fractionation between the separated phases and morphologies developed showing that molecular weight is a tool to control the final materials.

Directed phase separation of PFO:PS blends during spin-coating using feedback controlled in situ stroboscopic fluorescence microscopy

Uniform thin-films of polymer blends can be produced through spin-coating, which is used on an industrial scale for the production of light emitting diodes, and more recently organic photovoltaic devices. Here, we present the results of the direct observation, and control, over the phase separation of polystyrene and poly(9,9′-dioctylfluorene) during spin-coating using high speed stroboscopic fluorescence microscopy. This new approach, imaging the fluorescence, from a blend of fluorescent + non-fluorescent polymers allows for intensity to be directly mapped to composition, providing a direct determination of composition fluctuations during the spin-coating process. We have studied the compositional development and corresponding structural development for a range of compositions, which produce a range of different phase separated morphologies. We initially observe domains formed by spinodal decomposition, coarsening via Ostwald Ripening until an interfacial instability causes break-up of the bicontinuous morphology. Ostwald ripening continues, and depending upon composition a bicontinuous morphology is re-established. By observing compositional and morphological development in real-time, we are able to direct and control morphological structure development through control of the spin coating parameters via in situ feedback.

Phase separation of polymer-functionalized SWNTs within a PMMA/polystyrene blend

Phase separation of polystyrene (PS) and poly(methyl methacrylate) (PMMA) blends was used as a means to segregate PS- or PMMA-functionalized single-walled carbon nanotubes (SWNTs) in thin films. Dilute solutions (5 wt % in THF) of 1:1 PS/PMMA blends containing the functionalized nanotubes were spin cast and annealed at 180 °C for 12 h. Two different polymer molecular weights were used (Mn = 8000 or Mn = 22,000), and were of approximately equivalent molecular weight to those attached to the surface of the nanotubes. Nanotube functionalization was accomplished using the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition, in which alkyne-decorated nanotubes were coupled with azide-terminated polymers, resulting in polymer-SWNT conjugates that were soluble in THF. Characterization of the annealed films by scanning Raman spectroscopy, which utilized the unique Raman fingerprint of carbon nanotubes, enabled accurate mapping of the functionalized SWNTs within the films relative to the two phase-separated polymers. It was found that nanotube localization within the phase-separated polymer films was influenced by the type of polymer attached to the nanotube surface, as well as its molecular weight. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 450–458, 2009

Evaporative Organization of Hierarchically Structured Polymer Blend Rings

We report the first study of the controlled, evaporative self-organization of a polymer blend from a restricted geometry comprised of a spherical lens upon a Si substrate (i.e., a sphere-on-flat geometry). This geometry facilitated the control over the evaporation rate of solvent, thereby eliminating the temperature gradient and the possible convective instabilities. In this study, a drop of polystyrene (PS) and poly(methyl methacrylate) (PMMA) toluene solution evaporated in the sphere-on-flat geometry. The combination of controlled, consecutive pinning−depinning cycles (i.e., “stick−slip”) of the contact line at the edge of the geometry, spontaneous phase separation of incompatible polymers at the microscopic scale, and a dewetting process in the late stage of phase segregation led to the formation of gradient, hierarchically structured polymer blend rings composed of phase-separated PS and PMMA. The topographic distribution of PS and PMMA phases on the ring surface were revealed after removal of the PS ...

Effect of Molecular Weight on the Morphology of Polystyrene/Poly(methyl methacrylate) Composite Particles Prepared by the Solvent Evaporation Method

The effect of molecular weight on the morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles was investigated. PS/PMMA composite particles with different molecular weights (M*=MwPS+MwPMMA)/2 approximately 2x10(4)-1x10(6) g.mol(-1)) were prepared by the release of toluene (T) from PS/PMMA/T (1/1/24, w/w/w) droplets dispersed in an aqueous solution of polyoxyethylene nonylphenyl ether nonionic surfactant (Emulgen 911). As T evaporated, the spherical droplets phase separated, resulting in snowmanlike composite particles with Janus morphology. The nonspherical shape was closely related to the morphology, which depended on M*. The interfacial tension between the phase-separated PS and PMMA phases increased with an increase in M*, and this would allow the formation of the snowmanlike shape to decrease the interfacial area between the PS and the PMMA phases.

Highly porous polyacrylonitrile/polystyrene nanofibers by electrospinning

The concept of phase separation was coupled with electrospinning to induce polyacrylonitrile (PAN) and polystyrene (PS) bicomponent electrospun fibers that, upon removal of the phase-separated PS domains by solvent extraction, became nanoporous. Electrospinning of PAN (Mw 150 kDa) with 5 % w/w PS (Mw 250 kDa) at a 10 % w/w total concentration in N,N-dimethylformamide (DMF) produced fibers with stable morphology and average diameters from 1130±680 to 890±340 nm by FESEM. The nanoporous fibers made from a 95/5 w/w PAN/PS bicomponent precursor had internal pores of about 20∼110 nanometers. Pore sizes of the porous PAN fibers were decreased to approximately ∼25 nm after oxidation and carbonization thermal treatment because of fiber shrinkage during the thermal treatment. The fibers retained a high density of pores after the thermal treatment.

Uniform Nonspherical Colloidal Particles with Tunable Shapes

Colloidal particles are ubiquitous for a broad spectrum of applications. Many current applications require nonspherical particles. They have been used for modifying optical properties and as a building block for self-assembled biomaterials. They are also beneficial for controlling suspension rheology and for engineering colloidal composites. In general, synthesizing uniform nonspherical particles is difficult because surface tension favors spherical shapes in overall length scales. This limitation may be overcome with advanced techniques such as microfluidics and clusterization separations; these precision processes generally produce small yields, severely limiting their utility for practical applications. Recently, several methods that can produce nonspherical particles such as dimers and higher-order clusters have produced larger yields. These methods all rely on random coagulation of single particles or on the formation of clusters by using emulsification techniques. However, a common limitation of these synthesis techniques is that a single batch contains many particle types, requiring a sorting process to produce homogeneous samples, thus limiting the yield for any given sample type. Thus, there exists a need for flexible and robust techniques to generate nonspherical particles with well-defined shapes and high yields. One method of controlling particle shapes is to use a controlled phase separation in the seeded polymerization technique. This technique can produce extremely high yields of uniform particles. In the typical technique, seed particles are first swollen with a polymerizable monomer-based solution, and subsequent polymerization induces phase separation. Depending on thermodynamic and kinetic factors, the phase separation results in a variety of particle shapes. Shapes of higher aspect ratio may be obtained by crosslinking the seed particles before the phase separation. The crosslinking makes the seed particles more elastic. The elastic forces can impart greater directionality to the formation of the newly polymerizing phase. This suggests that seed particle crosslinking might be used to control the shapes of nonspherical particles. In this Communication, we introduce a new seeded-polymerization technique that uses the crosslinking forces to synthesize a variety of uniform nonspherical particles in large synthesis scales. Our technique involves controlling the directionality of phase separations in the seeded-polymerization technique by manipulating the crosslinking density gradients of the seed particles. This enables us to generate a variety of particle shapes, including “rod”, “cone”, “triangle”, and “diamond” particles (Fig. 1). The uniform placement of the individual bulbs in nearly all of the particles in each batch is achieved solely by tuning the crosslinking properties of the seed particles. To illustrate how crosslinking controls particle morphology, we compare the synthesis of two different types of trimer particles: “rods” and “triangles” (Fig. 1a and b, respectively). Rods and triangles both result from the seeded polymerization performed on dimers. The difference is the degree of crosslinking in the two bulbs of the seed dimer. Dimers that contain two bulbs with slightly different degrees of crosslinking become rods when swollen and polymerized. By contrast, dimers that contain two bulbs with equal crosslinking become triangle particles (Fig. 2). This is demonstrated by a series of experiments in which we synthesized trimers from different types of dimers. First, we synthesized spherical crosslinked polystyrene (PS) particles from linear PS template particles by swelling them with styrene monomers containing a crosslinker, divinylbenzene (DVB). In this swelling step, step a, the concentration of DVB, [DVB]a was fixed at 1 vol % relative to the total monomers. After polymerizing the spherical particles, we performed another swelling step, step b, to produce dimers. In step b, [DVB]b was varied from 0.5 to 1.1 vol %. Polymerization after swelling step b resulted in symmetrical phase-separated PS dimers. The size and appearance of the dimers produced were identical for all samples. Finally, in step c, the dimers were again swollen with a similar mixture, and polymerized following the same procedure. This resulted in trimer particles of various shapes. The shape of the trimers depends only on [DVB]b. High values of [DVB]b produced triangle particles, intermediate values of [DVB]b produced triple rod particles, and the lowest value of [DVB]b gave rise to snowman particles. To understand this behavior, we examine how changing [DVB]b changes the internal network properties of the seed C O M M U N IC A IO N

Kinetics of pressure-induced phase separation in polystyrene + acetone solutions at high pressures

The kinetics of pressure-induced phase separation in solutions of polystyrene ( M w = 129,200; PDI = 1.02) in acetone has been studied using time- and angle-resolved light scattering. A series of controlled pressure quench experiments with different quench depths were conducted at different polymer concentrations (4.0%, 5.0%, 8.2% and 11.4% by mass) to determine the binodal and spinodal boundaries and consequently the polymer critical concentration. The results show that the solution with a polymer concentration 11.4 wt% undergoes phase separation by spinodal decomposition mechanism for both the shallow and deep quenches as characterized by a maximum in the angular distribution of the scattered light intensity profiles. Phase separation in solutions at lower polymer concentrations (4.0, 5.0 and 8.2 wt%) proceeds by nucleation and growth mechanism for shallow quenches, but by spinodal decomposition for deeper quenches. These results have been used to map-out the metastable gap and identify the critical polymer concentration where the spinodal and binodal envelops merge. The time scale of new phase formation and growth as (accessed) from the time evolution of scattered light intensities is observed to be relatively short. The late stage of phase separation is entered within seconds after a pressure quench is applied. For the systems undergoing spinodal decomposition, the characteristic wave number q m corresponding to the scattered light intensity maximum I m was analyzed by power–law scaling according to q m ∼ t − α and I m ∼ t β . The results show β ≈ 2 α . The domain size is observed to grow from 4 μm to 10 μm within 2 s for critical quench, but about 9 s for off-critical quenches. The domain growth displays elements of self-similarity.

Assessment of morphology in transient and steady state regimes resulting from phase separation in polystyrene/poly(vinyl methyl ether) blend

Morphology development after phase separation in polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend was assessed both in transient and in steady state regimes. Phase segregation was evaluated by various techniques including optical microscopy, light transmission, dynamic scanning calorimetry and rheological analyses. The steady state particle size resulted from phase separation was determined experimentally and then compared to the predictions of both the emulsion models that assume zero-thickness interfacial boundaries and to the asymptotic value of the Cahn–Hilliard theory that assumes rather a diffuse interphase.

Phase Separation of Polystyrene/Poly(vinylmethylether)/Organoclay Nanocomposites

The effect of addition of organically modified montmorillonite (OMMT) on the phase separation of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend was examined. Using two types of OMMT modified with two different kinds of surfactants, the effect of organic modification on nanocomposites was investigated by focusing on three major aspects: phase transition, morphological study, and melt rheological behavior both below and above the critical transition temperature. X-ray diffraction (XRD) patterns revealed the formation of intercalated nanocomposites and transmission electron micrographic (TEM) observations showed that the ordering of silicate layers in blend matrix is well matched with the XRD patterns. The addition of clay was found to affect both the mechanism of phase separation and the final morphology. Such effects resulted in uncommon rheological behavior of the blend both below and above the critical transition temperature. Surface phase separation of thin films for virgin blend and nanocomposites was also examined by atomic force microscopy (AFM). Morphology resulting after phase separation was found to be dependent on the nature and the amount of OMMT added to the polymer blend.

Small-angle X-ray scattering study of modified porous suspension-poly(vinyl chloride) particles

Small-angle X-ray scattering (SAXS) was ap- plied to investigate the microstructure of unmodified and modified porous commercial suspension-type poly(vinyl chloride) (PVC) particles. The modified PVC particles were prepared by an in situ stabilizer-free polymerization/ crosslinking of particles absorbed with a monomer/ crosslinker/peroxide solution. The modifying polymers in- clude styrene with or without divinyl benzene (DVB) as a crosslinker and methyl methacrylate (MMA) with or with- out ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The SAXS method was used to highlight the effect of polystyrene (PS) on the microstructure of PVC particles and to evaluate the characteristic lengths, both in the PVC/PS and the PVC/XPS (PS crosslinked with 0 and 5% DVB, respectively) systems. A model is suggested, where during the synthesis modification process, swelling of PVC by styrene and styrene polymerization occur simulta- neously. PVC swelling by styrene causes destruction of the PVC subprimary particles, whereas styrene polymerization leads to phase separation resulting from incompatibility of the polymers. It was further suggested that because of PVC swelling by styrene, structure of the subprimary particles is lost. Therefore the characteristic lengths of PVC/PS and PVC/XPS, as calculated from the SAXS measurements, were attributed to the size of the phase-separated PS and XPS inclusions, respectively. The SAXS method also shows that PMMA and XPMMA do not influence the PVC microstruc- ture. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1024 -1031, 2005