Immiscible Polystyrene Research Articles

Heterogeneous nucleation of polyethylene crystals on binary hexagonal nanoplatelets

Crystal nucleating agents offer an effective strategy for controlling the morphology, dimensional stability and rate of solidification of polymers during processing. Molecular dynamics (MD) simulation can shed light on nucleation behavior at the nanoscopic length and time scales over which nucleation occurs. In this work, crystal nucleation of a polyethylene oligomer, n-pentacontane, on three graphene-like substrates, hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), and tungsten disulfide (WS2), was simulated, and the thermodynamic efficiencies of these substrates as nucleating agents were determined. Experimental measurements of heterogeneous nucleation of a high-density polyethylene on nanoparticles of these three graphene-like materials were performed using the method of dispersed microdroplets in an immiscible polystyrene matrix. Qualitative agreement between simulations and experiments was observed for trends in nucleation rate, J, and interfacial free energy difference, Δσ, with JhBN>JMoS2>JWS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J_{\ ext{hBN}} > J_{\ ext{MoS}_{2}} > J_{\ ext{WS}_{2}}$$\\end{document}. The simulations are then used to gain additional insight into the mechanisms of nucleation. Epitaxy is confirmed in all systems, with small mismatches in lattice spacing being accommodated by strain in the oligomer crystal. However, epitaxy alone is insufficient to explain the observed trends. The strength of interaction between the nucleating agent and the polyethylene oligomer is found to be the strongest predictor of nucleating agent efficiency. The strength of interaction is in turn related to the density of interaction sites at the interface: hBN has the highest density, and thus the fastest nucleation rate.

How nucleating particles migration affects the fractionated crystallization of isotactic polypropylene/polystyrene immiscible blends

We investigate the inter-phase migration of nucleating particles and their effect on the fractionated crystallization of polypropylene droplets dispersed in an immiscible polystyrene matrix by preparing melt-mixed 90/10 wt% PS/PP blends with selected nucleating agents. Different concentrations of nucleating agents (NAs): Phtalocianene Blue, NA11, Talc, and sodium benzoate, were initially incorporated either in neat PP or in neat PS. Then the different PS/PP/NAs blends were prepared. Contact angles were determined for the neat polymers and the NAs, and the results indicated that, from a thermodynamics point of view, all NAs should remain or migrate to the PS phase. According to SEM observations, a sea-island morphology was obtained that did not vary with NA addition. Hence the results should be independent of differences in the morphology.PP droplets crystallized in neat blends in three well-differentiated crystallization peaks (i.e., fractionated crystallization). The NAs induce a concentration-dependent increase in the high-temperature crystallization peak at the expense of reducing the low-temperature peaks, as droplets become in contact with or contain the NAs. When compared at a constant concentration in one of the phases, the nucleating agents have efficiencies that decrease in the order: Pht Blue ≈NA11>Talc>Sod Benz. Surprisingly, for the three most effective NAs, it was found that adding them initially to the PS phase led to a much higher nucleation efficiency (evaluated in terms of increases in peak crystallization temperature) than adding them to PP. This indicates that these NAs, initially present in the PS phase, migrate to the interface or to the bulk of the PP phase (against thermodynamics). Sod Benz was the only exception, as it shows a higher thermodynamic affinity to the PS phase. We explain the migration of most particles from the PS phase to the phases’ boundary or to the bulk of the PP droplets by considering that kinetic factors dominate the behavior, as, from a rheological perspective, the minor component (PP) always displays a lower viscosity than the matrix component (PS) under the chosen mixing conditions.

Preparation of Nanofiber Bundles via Electrospinning Immiscible Polymer Blend for Oil/Water Separation and Air Filtration.

Nanofiber bundles with specific areas bring a new opportunity for selective adsorption and oil/water or air separation. In this work, nanofiber bundles were prepared by the electrospinning of immiscible polystyrene (PS)/N-trifluoroacetylated polyamide 6 (PA6-TFAA) blends via the introduction of carbon nanotubes (CNTs) or a copolymer of styrene and 3-isopropenyl-α, α'-dimethylbenzene isocyanate (TMI), which was denoted as PS-co-TMI. Herein, CNT was used to increase the conductivity of the precursor for enhancing the stretch of PS droplets under the same electric field, and PS-co-TMI was used as a reactive compatibilizer to improve the compatibility of a PS/PA6-TFAA blend system for promoting the deformation. Those obtained nanofiber bundle membranes showed an increase in tensile strength and high hydrophobicity with a water contact angle of about 145.0 ± 0.5°. Owing to the special structure, the membranes also possessed a high oil adsorption capacity of 31.0 to 61.3 g/g for different oils. Moreover, it exhibits a high potential for gravity-driven oil/water separation. For example, those membranes had above 99% separation efficiency for silicon oil/water and paraffin wax/water. Furthermore, the air filtration efficiency of nanofiber bundle membranes could reach above 96%, which might be two to six times higher than the filtration efficiency of neat PS membranes.

Finely Modulated LDPE/PS Blends via Synergistic Compatibilization with SEBS-g-MAH and OMMT

Melt blending is an effective way to prepare new composite materials, but most polymers are incompatible. In order to reduce the interfacial tension and obtain fine and stable morphology with internal symmetric micro-textures, suitable compatibilizers should be added to the blend. The two immiscible polymers, low-density polyethylene (LDPE) and polystyrene (PS), were compatibilized by styrene/ethylene/butylene/styrene block copolymers grafted with maleic anhydride (SEBS-g-MAH) and organomontmorillonite (OMMT). The scanning electron microscope results indicated that the size of the PS phase decreased with increasing the content of SEBS-g-MAH. By introducing OMMT into LDPE/PS/SEBS-g-MAH composites, the compatibility of composites was further improved. The rheological analysis and Cole–Cole plot analysis indicated that the addition of SEBS-g-MAH and OMMT increased the interaction between the two phases. The tensile strength, elongation at break, and impact strength of the LDPE/PS/SEBS-g-MAH (70/30/7, wt%) composite increased by 64%, 255%, and 380%, respectively, compared with the LDPE/PS (70/30, wt%) composite. A small amount of OMMT could synergistically compatibilize the LDPE/PS composite with SEBS-g-MAH. After adding 0.3% OMMT into the LDPE/PS/SEBS-g-MAH system, the tensile strength, elongation at break, and impact strength of the composite were further increased to 18.57 MPa, 71.87%, and 33.28 kJ/m2, respectively.

Competing crystallization of α- and β-phase induced by β-nucleating agents in microdroplets of isotactic polypropylene

Crystallization of heterogeneously nucleated isotactic polypropylene microdroplets in an immiscible polystyrene matrix allows the estimation of intrinsic nucleating efficiency of nucleating agents promoting the formation of different polymorphs.

Reversible humidity-driven tuning of the light scattering properties of PS:PEG-based porous polymer films: Understanding derived from the cross-sensitivity of a luminescent oxygen sensor

We analyze and explain the reversible humidity-responsive behavior of porous structured luminescent oxygen (O2) sensing films in terms of O2 permeability and optical light scattering. The luminescent O2 sensing films are composed of an O2-sensitive dye within porous polymer matrices, where the porous structure is formed via phase separation between immiscible polystyrene (PS) and polyethylene glycol (PEG). A comparison of the sensing film with a porous polymeric film without an O2-sensitive dye by in situ measurement of both the photocurrent signal and diffused reflectance under different relative humidity (RH) levels reveals the origin of the optical variations in the luminescent O2 sensing film as a function of RH. Here, the hygroscopic PEG surrounded by the PS matrix swells and fills up the pores as the RH increases, which mainly tunes the optical scattering property of the porous polymeric films, and the variation in light scattering of the porous polymeric films is explained by Mie scattering theory. By considering and analyzing the humidity response in luminescent O2 sensing films in the aspects of fabrication processes and experimental systems as well as the hydration property of the materials, this study can provide fundamental insights into the cross-sensitivity of optical O2 sensors to humidity. Moreover, the fully reversible humidity-driven tuning of the light scattering properties in porous polymeric films allows various applications, such as dual monitoring of O2 and RH in wearable sensors, responsive coating or smart windows, that require optical tuning without extra energy.

Inversion of Dispersion: Colloidal Stability of Calixarene-Modified Metal-Organic Framework Nanoparticles in Nonpolar Media.

Making metal-organic frameworks (MOFs) that are stabilized in nonpolar media is not as straightforward as making their inorganic nanoparticle counterparts, since surfactants penetrate through the porous structures or dissolve the secondary building units (SBUs) through ligand-exchange linker modulator mechanisms. Herein, we report that calixarenes stabilize UIO-66 nanoparticles effectively by remaining outside the grains through size exclusion, without pores becoming blocked, all the while providing amphiphilicity that permits the formation of stable colloidal dispersions with much narrower size distributions. Using the UIO-66 dispersed solutions, we show that smooth films from an otherwise immiscible polystyrene can be made feasibly.

Optical and structural approaches for improved luminance distribution and enhanced efficiency of organic light emitting diodes

We combined cavity based optical method and polymer based structural approach to achieve efficiency enhancement and widened luminance distribution of organic light emitting diodes. Cavity method was implemented by adjusting the thickness of the hole transport layer and using a ITO-Metal-ITO transparent electrode. Utilizing the lateral phase separation of immiscible polystyrene/ polyethylene glycol binary system, we have fabricated an aperiodic protruding structure. The application of the two methods yielded two fold efficiency enhancement and widened luminance distribution. To be specific the external quantum efficiency increased from 8.9% to 17.9%.

Effect of the selective localization of carbon nanotubes in polystyrene/poly(vinylidene fluoride) blends on their dielectric, thermal, and mechanical properties

The selective localization of multiwalled carbon nanotubes (MWNTs) in immiscible polystyrene (PS)/poly(vinylidene fluoride) (PVDF) blends (volume ratio of both components is 1/1) and its effect on composites’ dielectric, thermal, and mechanical properties are systematically studied. Employing two-step mixing process can make MWNTs localize in PS or PVDF phase successfully. When three components are simply mixed together by one-step processing, the MWNTs are selectively distributed in PVDF phase, which is supported by the dielectric measurements and the SEM observations and is consistent with the wetting coefficient evaluation. For the two-step mixing, when the fillers are first mixed with PS in the first step, some of them will migrate into PVDF phase in the second step although the migration is very slow. When the overall volume fraction of MWNTs is 3.9vol%, the selective localization of MWNTs in PVDF phase produces higher dielectric constant (ε′, ca. 485) than the case when the fillers are only in PS phase (ε′ of ca. 16) at 100Hz and room temperature of 25°C. Differential scanning calorimetry (DSC) measurements and mechanical tests show that the selective localization of all the fillers in PVDF phase produces little change of the melting point and crystallinity of PVDF component but slightly higher tensile strength. In contrast to the one-step mixing process, the two-step mixing to selectively localize the fillers in their favorite phase could be used to control the dielectric and mechanical properties of the materials.

Compatibilization Mechanism of Nanoclay in Immiscible PS/PMMA Blend Using Unmodified Nanoclay

Organically modified nanoclays have been reported to play the role of a compatibilizer for immiscible polymer blends. However, the mechanism of compatibilization by nanoclay has been reported differently. In this work, we investigated the exact mechanism of compatibilization of nanoclay in immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend in the presence of sodium-montmorillonite (Na-MMT) through selective dispersion of clay in the matrix phase. Through a detailed investigation of the morphology of PS/PMMA/Na-MMT blend nanocomposites, the plausible mechanism behind the compatibilization effect of clay in immiscible blends has been proposed.

Tuning the Dielectric Properties of Polystyrene/Poly(vinylidene fluoride) Blends by Selectively Localizing Carbon Black Nanoparticles

In this work, the dielectric properties of immiscible polystyrene (PS)/poly(vinylidene fluoride) (PVDF) blends are tuned by selectively localizing carbon black (CB) nanoparticles in different phases. The PS/PVDF blends have a wide window of cocontinuity (ca. 30-80 vol % in terms of the volume fraction of PS component (v(PS))). The selective localization of CB nanoparticles is achieved by using the masterbatch process during melt mixing. For the volume ratio PS/PVDF 1/1 and the volume fraction of CB nanoparticles (v(CB)) below but close to the percolation threshold (v(c)(CB)), the selective localization of CB nanoparticles in PVDF phase produces higher dielectric constant (ε) than that in PS phase, whereas the ε of the ternary mixtures without selective localization of fillers is in the middle. For the volume ratios PS/PVDF 1/2 and 2/1, the selective location of CB nanoparticles in different phases can be used to easily tune the system from conductive to insulating or inverse, which might have potential applications in industry. The fillers are found to be "fixed" in the masterbatch of PS or PVDF component and there is no migration of the fillers to another phase occurring during the further mixing process for the mixing time up to 30 min. Furthermore, the addition of CB nanoparticles to the polymer matrix is found to induce the brittle-ductile transition in the system and increase the compatibility between the immiscible PS and PVDF components, which should benefit the mechanical properties.

Effect of polystyrene mixing on mechanical properties and structural changes in melt spinning

To increase the spinning speed of poly(trimethylene terephthalate) (PTT) fibers, polystyrene (PS) was selected as an additive polymer in the PTT matrix. Mixing of the immiscible PS with PTT led to an increase in spinning speed up to 5,500 m/min. PS was employed to improve the extensibility of the matrix PTT in the spinning process as it can prevent PTT molecular orientation. Experimental results show that the mixing of PS achieved this. The elongation at break of spun fibers increased with the amount of PS. PS addition prevented fiber orientation, especially amorphous orientation, and improved drawability, and as such, increased spinning speed up to 5,500 m/min.

Probing polymer deformation profiles at varying depths in nanoimprint lithography

We use immiscible polystyrene (PS)/polyacrylic acid (PAA) bilayer films as resist materialsfor nanoimprint lithography to probe the deformation profiles of the resist after the cavityfilling process. By systematically varying the composition of the bilayers, we determinedthe deformation profiles of the bilayer resists at different depths after filling the 240 and480 nm wide cavities. A single-peak deformation mode was observed for the bilayerfilms when the thickness of the top PS layer is less than the minimum thickness (Hc) needed to completely fill the cavities. This is in good agreement with simulations basedon pressure-driven viscous flow. However, for bilayers with a PS layer thickness close toHc, a dual-peak deformation mode was observed near the entrance of the cavities, which isattributed to the stronger shear thinning of the polymer resist around these corners.

Percolation network of organo-modified layered double hydroxide platelets into polystyrene showing enhanced rheological and dielectric behavior

A hybrid organic inorganic layered double hydroxide incorporating 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) is characterized by means of XRD, FTIR, and XPS. The in situ polymerization is scrutinized by 13C CPMAS as well as by a set of XRD experiments with varying temperature. It is found that the in situ polymerization is complete at 200 °C, and the hybrid framework sustains temperatures as high as 350 °C. Direct incorporation of poly(AMPS) is reported and the resulting hybrid LDH phases studied. Subsequently, all generated hybrid platelets are used as organo-modified 2D-type filler dispersed into polystyrene (PS). An immiscible PS composite structure with salient gel-like viscoelastic properties is obtained after bulk polymerization. In the low-frequency region, the typical Newtonian flow behaviour of PS is found to change progressively against filler loading into a shear-thinning behaviour evidenced by a pseudo-plateau in the elastic and loss modulus curves and associated with a shift of the glass transition temperature of PS to higher temperature. It is interpreted by hybrid LDH platelet domains presenting a large interface with the polymer, thus having the effect of restricting the plastic deformation by obstructing polymer chain motion. Such dispersed hybrid LDH tactoids forming a three-dimensional percolated network are indirectly evidenced by the enhancement of the dielectric properties illustrated by an increase in bulk dc conductivity of about one order at room temperature and in the dissipation factor. The study shows that hybrid LDH assembly is of relevance in topical applications regarding mechanical reinforcement as well as electrostatic energy dissipation.

Guided phase separation of polymer blend thin films on ion beam-induced pre-patterned substrates

A technique for fabricating pre-pattern induced phase-separated polymer blend films is presented. The gold layer coated silicon substrates were bombarded with focused ion beams (FIB) to sputter away Au grains in the irradiated regions and expose silicon oxide surface underneath, thereby creating pre-patterns of relatively hydrophobic (Au)/hydrophilic (silicon oxide) regions. In the pre-patterned regions, the spin-coated films consisting of immiscible PS (polystyrene) and PtBA (poly-tert-butyl acrylate) blend exhibited phase separation induced by the underlying pre-patterns and formed two distinct ordered morphologies with periodicities much smaller than that of the pre-patterns. The influence of varying periodicities of the pre-patterned structures, blending ratios and spin-coating parameters on the resulting morphologies are presented.

The effect of incorporation of POSS units on polymer blend compatibility

AbstractIn 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

Domain Structures on PS-PMMA Mixture Films

We studied the domain structures in immiscible polystyrene poly(methyl methacrylate) (PS/PMMA) lms by using atomic force microscopy, lateral force microscopy and force spectroscopy. As previously known, circular PS bumps are formed on the PMMA layer after annealing, which was con rmed by the topographic image. We found that lateral force image showed substructures on the PS bumps. The sub-structures (or domains) have circular shapes on the centers of the PS bumps. Because the lateral forces on the domains have similar values on the PMMA layer, the domains are thought to have the chemical composition of PMMA. This estimate is supported by the force spectroscopy result, which shows that the pull-o force between the domain and a cantilever tip also has values similar to that for the PMMA layer.

Rheology-morphology relationship in polystyrene/poly(methyl methacrylate) blends

The relationship between rheological properties and morphology of immiscible polystyrene(PS)/poly(methyl methacrylate)(PMMA) blends was studied. The blends were prepared using a twin screw extruder. A single screw extruder equipped with a slit die was used to perform shear flow measurements of PS/PMMA blends. Morphological examinations were conducted on the cryogenically fractured and extracted samples by scanning electron microscopy. The results show that the melt viscosity of PS/PMMA blend decreases with increasing shear stress, which is attributed to not only the disentanglement of macromolecules but also the reduction in the domain size and the resultant increase of the interfacial area. The power-law index of the blend melt is lower than any of its component melt, suggesting that deformation and breakup of the dispersed phase increase the dependence of the melt viscosity on the shear stress. The blend whose domain size decreases at a faster rate with increasing shear stress, exhibits a strong shear rate dependence on the melt viscosity. The comparison of the morphologies of samples before and after the slit section of the die indicates that the morphology of the blend has a quick response to shear flow, the coalescence of the dispersed drops is predominant for blends at low shear rates.

Effects of vibration force field on the interfacial interaction and morphology of polystyrene/poly(methyl methacrylate) blends

Immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends were extruded using an electromagnetic dynamic plasticating extruder. Effects of vibration force field on the interfacial interaction and morphology of PS/PMMA blends were studied by differential scanning calorimetry (DSC), IR spectra, scanning electron microscope (SEM) and small angle X-ray scattering (SAXS). Results show that the introduction of a vibration force field into the extrusion process increases the solubility of the two components of PS/PMMA blends, which seems to be a physical compatibilization as indicated by the IR spectra. The enhanced interfacial interaction and the increased shear effect caused by vibration improve the dispersion of the dispersed phase. With application of vibration, the PS/PMMA blends exhibit a smaller drop size and a narrower particle size distribution. The morphologies of PS/PMMA blends with different compositions have a different response to vibration forces; the mean domain size of 25/75 PS/PMMA blends has a higher speed of decrease with increase of vibration amplitude or frequency. The Porod invariant data as determined by SAXS indicate that introduction of vibration improves the homogeneity of the PS/PMMA system.

Effect of Density Fluctuating Supercritical Carbon Dioxide on Polymer Interfaces

We investigated an effect of CO2 sorption on the compatibility of immiscible polystyrene (PS) and polybutadiene (PB) bilayers by using in situ neutron reflectivity. By labeling either polymer with deuterium, we found that the excess CO2 molecules were adsorbed to both top PS and bottom PB layers when the bilayers were exposed to CO2 at the narrow T and P regime near the critical point of pure CO2. Furthermore, we clarified that this excess sorption of CO2 molecules increased the interfacial width between the layers up to 100 angstroms even near room temperature, while the interfacial width without CO2 exposure has been reported to be at most 40 A even at the highest temperature (T congruent with 175 degrees C).