Reptation in polymer blends

Forward recoil spectrometry (FRES) was used to measure the tracer diffusion coefficients D*_PS and D*_PXE of deuterated polystyrene (d-PS) and deuterated poly(xylenyl ether) (d-PXE) chains in high molecular weight protonated blends of these polymers. The D*s were shown to be independent of matrix molecular weights and to decrease as M⁻², where M is the tracer molecular weight, suggesting that the tracer diffusion of both species occurs by reptation. These D*s were used to determine the monomeric friction coefficients ζ_0,PS and ζ_0,PXE of the individual PS and PXE macromolecules as a function of ф, the volume fraction of PS in the PS:PXE blend. Since ζ_0,PSζ_0,PXE at each ф, the rate at which a PS molecule reptates is much greater than that of a PXE molecule, even though both chains are diffusing in identical surroundings. Part of this difference may be due to the difficulty of backbone bond rotation of the PXE molecule. However, even when measured at a constant temperature increment above the glass transition temperature, ζ_0,PS and ζ_0,PXE were observed to be markedly composition dependent. In addition the ratio ζ_0,PS/ζ_0,PXE varied from a maximum of 4 × 10⁻² near ф=0.85 to a minimum of 5 × 10⁻⁵ for ф=0.0. These results show that intramolecular barriers do not solely determine the ζ₀s of the components in this blend. Clearly, the interactions between the diffusing chains and the matrix chains also influence ζ₀.     

Morphological evolution of thin PS/PMMA films: Effects of surface energy and blend composition

We systematically compare the morphological evolution of thin PS/PMMA films, with varying compositions, during thermal annealing on preferential and non-preferential surfaces. On native silicon oxide surfaces, the phase evolution in the films was dictated by the preferential substrate-wetting of PMMA. However, the resulting PS relief structures on the PMMA wetting layer varied with the blend composition, and transitioned from capillary-fluctuation-mediated breakup to random nucleation with increased PS concentration. In contrast, the morphological evolution of the PS/PMMA films on non-preferential surfaces was also dictated by the coarsening of PMMA domain, but proceeded without the formation of a PMMA wetting layer. Both the PS and PMMA domains maintain direct contact with both the substrate and free surfaces throughout the evolution of the morphology. The morphologies at the interfaces were highly correlated, but with distinctive length scales. A variety of dispersed and continuous phase-separated structures can thus be obtained.     

Inhibition of thin polystyrene film dewetting via phase separation

By addition of a small amount of poly(methyl methacrylate) (PMMA) into polystyrene (PS), we present a novel approach to inhibit the dewetting process of thin PS film through phase separation of the off-critical polymer mixture (PS/PMMA). Owing to the preferential segregation of PMMA to the solid SiO_x substrate, a nanometer thick layer, rich in PMMA phase, is formed. It is this diffusive PMMA-rich phase layer near the substrate that alters the dewetting behavior of the PS film. The degree of inhibition of dewetting depends on the concentration and molecular weight of PMMA component. PMMA with low (15.9k) and intermediate (102.7k) molecular weight stabilizes the films more effectively than that with a higher molecular weight (387k).     

The characteristic properties of poly(methyl methacrylate)/polystyrene core‐shell composite polymer latex

In this study, the poly(methyl methacrylate/polystyrene (PMMA/PS) core‐shell composite latex was synthesized by the method of soapless seeded emulsion polymerization. The morphology of the PMMA/PS composite latex was core‐shell structure, with PMMA as the core and PS as the shell. The core‐shell morphology of the composite polymer latex was found to be thermally unstable. Under the effect of thermal annealing, the PS shell region first dispersed into the PMMA core region, and later separated out to the outside of the PMMA core region. This was explained on the basis of lowing interfacial tension between the PMMA and PS phases owing to the interpenetration layer. The interpenetration layer, which was located at the interface of the core and shell region, contained graft copolymer and entangled polymer chains. Both the graft copolymer and entangled polymer chains had the ability to lower the interfacial tension between the PMMA and PS phases. Also, the effect of thermal annealing on the morphology of commercial polymer/composite latex polymer blends was examined. The result showed that the core‐shell composite latex had the ability to enhance the compatibility of the components of polymer blends. The compatibilizing ability of the core‐shell composite latex was better than that of a random copolymer. Moreover, the effect of the amount of core‐shell composite latex on the morphology of the polymer blend was investigated. The polymer blends, which contained composite latex above 50% wt, showed the morphology of a double sea‐island structure. In addition, the composite latex was completely dissolved in solvent to destroy the core‐shell structure and release the entangled polymer chains, and then dried to form the entangled free composite polymer. The entangled free composite polymer had the ability to enhance the compatibility of the components of the polymer blend as usual. The weight ratio 3/7 commercial polymer/entangled free composite polymer blend showed the morphology of the phase inversion structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 312–321, 2003     

External normal pressure prevents preferential wetting of PS/PMMA blend thin films

Substrate wetting of the component(s) of thin polymer blend films strongly dictates their phase evolution during thermal annealing. In the case of wetting by one component being preferential than the other, a continuous wetting layer at the substrate will form. Here, we report that the preferential wetting of PMMA within a PS/PMMA thin film can be prevented under normal pressure. Moreover, the external pressure drives the PMMA wetting layer at the substrate (or a PMMA cushion layer intentionally placed between the blend film and the superstrate) into the isolated PMMA domains within the blend film. This results in a film morphology normally observed on neutral surfaces, revealing that normal pressure can potentially be used to effectively control the blend film morphology by preventing the hydrodynamic wetting.     

Investigation on particular morphology of immiscible polyamide 12/polystyrene blends

In this article, a particular phase morphology of immiscible polyamide 12/polystyrene (PA12/PS) blends prepared via in situ anionic ring-opening polymerization of Laurolactam (LL) in the presence of PS was investigated. SEM and FTIR were used to analyze the morphology of the blends. The results showed that PS is dispersed as small droplets in the continuous matrix of PA12 when PS content is less than 5 wt %. When the PS content is higher than 10 wt %, two particular phase morphologies appeared. First, dispersed PS-rich particles with the spherical inclusions of PA12 can be found when PS content is between 10 wt % and 15 wt %. Then, the phase inversion (the phase morphology of the PA12/PS blends changes from the PS dispersed/PA12 matrix to PA12 dispersed/PS matrix system) occurred when PS content is higher than 20 wt %, which is completely different from traditional polymer blends prepared by melt blending. The possible reason for the particular morphology development was illuminated through phase inversion mechanism. Furthermore, the stability of the phase morphologies of the PA12/PS blends was also investigated. SEM showed that the particular morphology is instability, and it will be changed upon annealing at 230°C for 30 min. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

拉曼Mapping成像研究聚苯乙烯/聚甲基丙烯酸甲酯共混体系的相态结构

利用拉曼光谱成像技术研究了聚苯乙烯/聚甲基丙烯酸甲酯（PS/PMMA）共混薄膜体系及其增容体系（增容剂为PS-b-PMMA嵌段共聚物）的相态结构及化学成分分布。实验结果表明,拉曼Mapping成像技术不仅可以得到PS/PMMA共混体系化学成分的精确分布图,同时也可以获取共混体系中分散相、界面相和连续相的分子指纹光谱。研究发现,共混体系中分散相和连续相组分分布与体系的组成紧密相关,当PS/PMMA质量比30/70时,分散相为PS,连续相为PMMA;当PS/PMMA质量比为50/50时,分散相为PS,但PS分子链仍存在于PMMA连续相中;当PS/PMMA质量比为70/30时,分散相为PMMA,连续相为PS。当增容剂PS-b-PMMA加入到PS/PMMA共混体系中后,分散相粒径减小、分布更加均匀、共混体系相容性指数（N_c）增大,说明PS/PMMA共混体系由完全不相容体系趋向变成半相容性体系,这是因为增容剂能增加PS和PMMA之间的相互作用,降低了体系的相分离程度,改善了共混体系的相容性。     

A study on weld line morphology and mechanical strength of injection molded polystyrene/poly(methyl methacrylate) blends

In this work, the mechanical strength and weld line morphology of injection molded polystyrene/poly(methyl methacrylate) (PS/PMMA) blends were investigated by scanning electron microscopy (SEM) and mechanical property test. The experimental results show that the tensile strength of PS/PMMA blends get greatly decreased due to the presence of the weld line. Although the tensile strength without the weld line of PS/PMMA (70/30) is much higher than that of the PS/PMMA (30/70) blend, their tensile strength with weld line shows reversed change. The viscosity ratio of dispersed phase over matrix is a very important parameter for control of weld‐line morphology of the immiscible polymer blend. In PS/PMMA (70/30) blend, the PMMA dispersed domains at the core of the weld line are spherically shaped, which is the same as bulk. While in the PS/PMMA (30/70) blend, the viscosity of the dispersed PS phase is lower than that of the PMMA matrix, the PS phase is absent at the weld line, and PS particles are highly oriented parallel to the weld line, which is a stress concentrator. This is why weld line strength of PS/PMMA (30/70) is lower than that of PS/PMMA (70/30) blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1856–1865, 2002; DOI 10.1002/app.10450     

Submicrometer-scale heterogeneous surfaces by PS-PMMA demixing

Patterned surfaces were created using two polymers: polystyrene (PS) on the one hand, and either poly(methyl methacrylate) (PMMA) or poly(methyl methacrylate)-poly(methacrylic acid) (PMMA-PMAA) on the other hand. PMMA was dissolved in a solvent of PS; this solution was then spin-coated on a PS support that partially dissolved during the process. The materials were analyzed by water contact angle measurement, XPS, ToF-SIMS and AFM. The effect of the solvent on the final surface morphology was strongly marked. With chloroform, the acrylic polymer was the major surface constituent, possibly because of the high evaporation rate of this solvent. With toluene, which is a better solvent for PS compared to PMMA, the obtained surface was almost exclusively constituted of PS. The use of chlorobenzene provided inclusions of acrylic polymer in PS, both polymers being exposed at the outermost surface. The surface morphology presented rings, the interior of which consisted of the acrylic polymer, while the rest of the surface was made of PS.     

Ordered porous polymer films via phase separation in humidity environment

A transition of morphology from island-like structure to disordered and ordered holes on the surface of polystyrene (PS) and poly(2-vinylpyridine) (PVP) blend films were observed with the increase of humidity. At appropriate weight ratio of PS/PVP and PS molecular weight, when humidity reached to a critical value, the hexagonal arrays of holes formed for PS/PVP blend films due to ‘breath figures’ stabilized by PVP with its strong hygroscopic characteristics during phase separation.     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Janus-like polymer particles prepared via internal phase separation from emulsified polymer/oil droplets

Poly(methylmethacrylate) (PMMA) and polystyrene(PS)/PMMA particles with Janus-like morphology were prepared via the internal phase separation followed by extraction of hexadecane (HD) template. The internal phase separation was triggered by evaporation of dichloromethane (DCM) from the polymer/HD/DCM-in-water emulsion droplets, which led to the formation of HD/PMMA or HD/PMMA/PS microparticles. After extraction of HD with hexane, PMMA or PS/PMMA particles with different morphologies were produced. Poly(vinyl pyrrolidone) (PVP), sodium dodecyl sulfonate (SDS) or sodium dodecyl benzylsulfate (SDBS) was chosen as the emulsifier. The morphology depended on the HD/polymer ratio and the interfacial tensions, which were adjusted by changing the type of the emulsifier and its concentration. With poly(vinyl pyrrolidone) (PVP) emulsifier, PMMA hollow spheres were observed; while with SDS emulsifier, the particles changed from bowl-like particles to hemispheres and truncated spheres with the increase of SDS content. The morphology of PS/PMMA composite particles depended on the ratio of the two polymers. Scanning electron microscopy observation, selective etching and X-ray photoelectron spectroscopy results confirmed that PMMA tended to engulf PS component. With the increase of PMMA/PS ratio, the particles changed the morphology from capped acorn to ‘ball in bowl’ morphology. Furthermore, the particle morphology was simulated via a theoretical model based on the minimum interfacial energy of the system. The simulation results agreed with the experimental observations. Our results indicate that internal phase separation is an effective method to obtain Janus-like microparticles. Via adjusting the composition of the system and the corresponding interfacial tensions, we could tailor the polymer particles with different morphologies.     

Molecular weight effects on the phase morphology of PS/P4VP blend films on homogeneous SAM and heterogeneous SAM/Au substrates

The effects of the molecular weight of polystyrene (PS) component on the phase separation of PS/poly(4-vinylpyridine) (PS/P4VP) blend films on homogeneous alkanethiol self-assembled monolayer (SAM) and heterogeneous SAM/Au substrates have been investigated by means of atomic force microscopy (AFM). For the PS (22.4k)/P4VP (60k) system, owing to the molecular weight of PS component is relatively small, the well-aligned PS and P4VP stripes with good thermal stability are directed by the patterned SAM/Au surfaces. With the increase of the molecular weight of PS component (for the PS (582k)/P4VP (60k) system), the diffusion of P4VP is hindered by the high viscosity of PS during the fast spin-coating process. The phase separation behavior of PS/P4VP on the SAM/Au patterned substrates is similar to that on the homogeneous SAM and cannot be easily directed by the patterned SAM surfaces even though the characteristic length of the lateral domain morphology is commensurate with the stripe width. This indicates that the relative viscosity of the PS is one of the dominant factors in obtaining well-aligned pattern by the phase separation of polymer blends.     

Temperature dependence of surface composition and morphology in polymer blend film

Thin films of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) blend can phase separate upon heating to above its critical temperature. Temperature dependence of the surface composition and morphology in the blend thin film upon thermal treatment was studied using in situ X-ray photoelectron spectroscopy (XPS) and in situ atomic force microscopy (AFM). It was found that in addition to phase separation, the blend component preferentially diffused to and aggregated at the surface of the blend film, leading to the variation of surface composition with temperature. At 185 °C, above the critical temperature, the amounts of PMMA and SAN phases were comparable. At lower temperatures PMMA migrated to the surface, leading to a much higher PMMA surface content than in the bulk. The migration and preferential segregation of a blend component in thin films demonstrated here are responsible for the great difference between in situ and ex situ experimental (not real quenching or annealing) results of polymer blend films, and help explain the slow kinetics of surface phase separation at early stage for blend thin films reported in literature. This is significant for the control of surface properties of polymer materials.     

Morphology of polystyrene/poly(dimethyl siloxane) blends compatibilized with star polymers containing a γ-cyclodextrin core and polystyrene arms

A star polymer with a γ-CD core and PS arms is used to compatibilize blends of the immiscible polymers PS and PDMS. The mechanism of compatibilization is threading of the CD core by PDMS and subsequent solubilization in the PS matrix facilitated by the star arms. Spun-cast films of this blend are examined with optical microscopy, scanning electron microscopy and atomic force microscopy. Blends without CD-star exhibit large-scale phase separation, whereas those containing CD-star exhibit very homogeneous morphologies in the optical microscope and nanometer-sized phase domains in the AFM. The effect of PDMS molecular weight on the blend morphology is insignificant. The morphology of the compatibilized films does not change significantly after annealing at 125 °C for 3 days, indicating that the CD-star polymer effectively stabilizes these blends at temperatures where both polymers are mobile and could otherwise undergo large-scale phase separation. The degree of compatibilization in these blends is correlated with the molar ratio of PDMS repeat units to CD-star molecules.     

Fracture toughness of interfaces between glassy polymers in a trilayer geometry

We studied the fracture behavior of trilayer A/B/A assemblies based on polystyrene (PS) and poly(methylmethacrylate) (PMMA) where the central layer of the A polymer was confined (0.5–200 μm) between two thick plates of the B polymer (1– 3 mm). Diblock and random P(S-MMA) copolymers were used to provide a good stress transfer across the interfaces. Fracture experiments were performed with the double-cantilever beam method and the fracture mechanisms were observed by optical microscopy on microtomed slices of the damaged zone. The measured _c of the A/B interface fractured during the test was dependent on the molecular structure at the interface (random copolymer, diblock copolymer or no copolymer), on the crazing stress of the bulk materials and on the interfacial shear stresses. When the phase angle of the loading was even slightly positive, oblique crazes were observed in the PS increasing greatly _c. If PS was the central layer, this resulted in a very marked dependence of _c on the thickness of the central layer for a thickness range 10–200 μm which was not observed when the PMMA was the central layer. Thermal treatments modifying the interfacial shear stresses were also found to have a very strong effect on _c.     

The effect of incorporation of POSS units on polymer blend compatibility

In this work, the compatibility of poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers with their polyhedral oligomeric silsesquioxane (POSS) copolymers combined by solution blending is investigated, to determine the effect of incorporation of the POSS unit on polymer compatibility. The morphology of these tethered POSS copolymer/polymer blends was studied by electron microscopy, thermal analysis, and density. Although the basic PS/PMMA blend was clearly immiscible, it was also found that the incorporation of POSS into the PS chain led to incompatibility when the POSScoPS copolymer was blended with PS homopolymer. However, conversely, in the case where the POSS moiety was included as part of a copolymer with PMMA, the copolymer was miscible with the PMMA homopolymer. The presence of isobutyl units on the corners of POSS cage is clearly sufficient to encourage miscibility with PMMA. Interestingly, blends of the two different POSS copolymers led to an immiscible structure, despite having the common POSS units, the interactions between the POSS moieties clearly not being sufficient to drive compatibility. The POSS copolymers have also been used as interfacial agents in immiscible PS and PMMA blend, and it has been found that the appearance of the interface bonding is improved, although the phase morphology is only slightly changed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of organically modified layered silicates on the morphology of symmetrical blends of polystyrene and poly(methyl methacrylate)

The changes in morphology caused by the addition of organically modified layered silicate on equal volume fraction blends of polystyrene and poly(methyl methacrylate) are investigated. In thin films supported on silicon, without layered silicates, the PMMA forms a layer on the silicon, while the PS tend to minimize contact with both the hydrophilic silicon substrate and the PMMA phase, and tend to form discrete domains on top of the PMMA layer. With the introduction of layered silicates, the characteristic length scale of the structure decreases. On the other hand, in bulk samples, without the layered silicates, the equal volume fraction blend has the PS domains in a PMMA matrix. At 0.6 wt% of added silicate, in both thin film and bulk, the blend morphology converts from discrete to co-continuous. Electron micrographs reveal well dispersed silicate sheets locating at the interface between small PS domains in the PMMA phase. The change in morphology is conjectured to be the result of the interfacial location of the layered silicates rather than the change in viscosity ratio between the two phases.     

Effect of composition on the linear viscoelastic behavior and morphology of PMMA/PS and PMMA/PP blends

Here, the effect of concentration on the morphology and dynamic behavior of polymethylmethacrylate/polystyrene (PMMA/PS), for PS with two different molecular weight, and polymethylmethacrylate/polypropylene (PMMA/PP) blends was studied. The blends concentrations ranged from 5% to 30% of the dispersed phase (PS or PP). The dynamic data were analyzed to study the possibility of inferring the interfacial tension between the components of the blend from their rheological behavior using Palierne [Palierne JF. Rheol Acta 1990;29:204-14] [1] and Bousmina [Bousmina M. Acta 1999;38:73-83] [2] emulsion models. The relaxation spectrum of the blends was also studied. The dynamic behavior of 85/15 PS/PMMA blend were studied as a function of temperature. It was possible to fit both Palierne and Bousmina's emulsion models to the dynamic data of PMMA/PS blends, to obtain the interfacial tension of the blend. This was not the case for PMMA/PP. The relaxation spectrum of both blends was used to obtain the interfacial tension between the components of the blends. The values of interfacial tension calculated were shown to decrease when the concentration of the blends increased. It was shown using morphological analysis that this phenomenon can be attributed to the coalescence of the dispersed phase during dynamic measurements that occurs for large dispersed phase concentration. When the ‘coalesced’ morphology is taken into account in the calculations the interfacial tension inferred from rheological measurement did not depend on the concentration of the blend used. The values of interfacial tension found analyzing the dynamic behavior of one of the PMMA/PS blend were shown to decrease with temperature.     

An application of micro-thermal analysis to polymer blends

Micro-thermal analysis (micro-TA) is a new subsurface thermal analysis technology. The average of the DC signal is a function of the thermal conductivity, and the response to the AC modulation signal is a function of the thermal diffusivity of the subsurface. Using this technique, three images based on topography, thermal conductivity, and thermal diffusivity are obtained simultaneously. Specific areas and domains in these images can then be characterized by simply positioning the probe and performing a localized thermal analysis experiment. The technique has been used to study the phase separation process in a 50:50 (by weight) polystyrene (PS)–poly(vinyl methyl ether) (PVME) blend and natural rubber–nitrile rubber blends. For these polymer blends, considerable contrast between phases is obtained, based on thermal conductivity, whereas optical and electron microscopy would show them as being very similar. For example, it is difficult to image the morphology of natural and nitrile rubber blends by means of transmission electron microscopy, because of their similar chemical structures. Micro-TA gives an excellent image of the morphology of these natural–nitrile rubber blends. This opens a new way for rubber industries to study morphologies of rubber–rubber blends in general. In the 50:50 PS–PVME blend, annealed at 125°C, spinodal decomposition occurred. With increasing time, the domain size and the glass transition temperature of PS-rich domains increased, indicating that the concentration of PVME in the PS-rich phases decreases. The results imply that micro-TA can be used to image the composition in the near-surface or surface regions in multicomponent materials, if the resolution is high enough. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2136–2141, 2001