Volume Fraction Of Polystyrene Research Articles

The Micellization of Well-Defined Single Graft Copolymers in Block Copolymer/Homopolymer Blends.

A series of well-defined (polyisoprene)2(polystyrene), I2S, single graft copolymers with similar total molecular weights but different compositions, fPS, were blended with a low molecular weight polyisoprene homopolymer matrix at a constant concentration 2 wt%, and the micellar characteristics were studied by small-angle x-ray scattering. To investigate the effect of macromolecular architecture on the formation and characteristics of micelles, the results on the single graft copolymers were compared with those of the corresponding linear polystyrene-b-polyisoprene diblock copolymers, SI. The comparison reveals that the polystyrene core chains are more stretched in the case of graft copolymer micelles. Stretching turned out to be purely a result of the architecture due to the second polyisoprene block in the corona. The micellization of a (polystyrene)2(polyisoprene), S2I, graft copolymer was also studied, and the comparison with the results of the corresponding I2S and SI copolymers emphasizes the need for a critical core volume rather than a critical length of the core-forming block, in order to have stable micelles. Finally, the absence of micellization in the case of the I2S copolymer with the highest polystyrene volume fraction is discussed. For this sample, macrophase separation occurs, with polyisoprene cylinders formed in the copolymer-rich domains of the phase-separated blends.

Fluorescence and photon transmission techniques for studying film formation from PS/GO nanocomposites

Steady-state fluorescence and UV–Vis techniques were used to study the film formation behavior of composites consisting of pyrene (P)-labeled polystyrene (PS) latex and graphene oxide (GO) in terms of PS latex/GO volume fraction. PS/GO composite films were prepared on glass substrates with different volume fractions of PS and GO using the drop casting method at room temperature. The film formation behavior of these composites was studied by annealing them at a temperature range of 100–300 °C and monitoring the scattered light intensity (Isc), fluorescence intensity (IP) from P and transmitted light intensity (Itr) through the films after each annealing step. The optical results indicate that PS/GO composites showed complete film formation independent of GO volume fraction. The morphological changes in the films were also found to be in consistent with these results.

Asymmetric polystyrene-polylactide bottlebrush random copolymers: Synthesis, self-assembly and nanoporous structures

Control of polymer architecture can be a powerful strategy to refine the structure and properties without changing the chemical structure of the monomers. Here, we exploit a highly branched bottlebrush architecture to access tailored self-assembled morphologies and nanoporous structures. To this end, a series of well-defined bottlebrush random copolymers are synthesized by macromonomer approach, where polystyrene (PS) and poly(D,L-lactide) (PLA) side chains of non-equal molecular weights are grafted to the polynorbornene backbone. These bottlebrush copolymers exhibit microphase-separated structures including lamellar, hexagonal cylinders and disordered structures with the domain sizes of 13–20 nm depending on the relative volume fraction (f) of PS and PLA side chain. Due to highly asymmetric nature, these bottlebrush copolymers exhibit cylinders at fPS = 41–50% and lamellar at fPS = 67–70%, unlike the case of linear diblock copolymers. The selective degradation of PLA from these bottlebrushes allows for nanoporous structures to be created of which size, distribution and connectivity of pores are dictated by the composition of bottlebrush precursors. The ability to exploit the bottlebrush architecture to manipulate self-assembled morphologies and nanoporous structures may be a useful way to design materials for adsorptions, separations, catalysis and gas storages.

Morphology and linear rheology of comb-like copolymer melts with high grafting density: Ⅱ. Heterografted PVSt-g-(PS/PE) comb-like copolymer with short backbone and mixed side chains

A series of heterografted PVSt-g-(PS/PE) based on polystyrene (PS) backbone with mixed PS and polyethylene (PE) side chains was obtained, in which the branching density of PVSt-g-(PS/PE) was above 72%. Because of the extremely short backbone, long side chains and high branching density in these comb-like copolymers, the topological structure of PVSt-g-(PS/PE) was similar to asymmetrical star copolymers. By adjusting the molar ratio of PS and PE side chains, the total PS (PVSt backbone + side chain PS) volume fraction in the graft copolymers could be adjusted. PVSt-g-(PS/PE) showed a microphase-separated structure at the melt state, depending on the composition of the copolymers. When the volume fraction of PS changed from 42.7% to 76.9%, the microphase-separated structures changed from lamellar phase structure to cylindrical morphology. Furthermore, all the PVSt-g-(PS/PE) samples with the microphase-separated structure showed a typical rheological behavior of cross-linked network-like structure, but the change trend of melt elasticity of the copolymer with increasing temperature depended on the microphase-separated structure.

Orienting Block Copolymer Thin Films via Entropy

Controlling the orientation of nanostructured thin films of block copolymers (BCPs) is essential for next-generation lithography using BCPs. According to conventional wisdom, the orientation of BCP thin films is mainly determined by molecular interactions (enthalpy-driven orientation). Here, we show that the entropic effect can be used to control the orientation of BCP thin films. Specifically, we used the architecture of star-block copolymers consisting of polystyrene (PS) and poly(dimethylsiloxane) (PDMS) blocks to regulate the entropic contribution to the self-assembled nanostructures. The study unequivocally demonstrate that for star-block copolymers with the same volume fractions of PS and PDMS, perpendicularly oriented BCP nanostructures could be induced via an entropic effect regulated by the number of arms. Also, the feasibility of using the star-block copolymer thin films for practical applications is demonstrated by using the thin film as a mask for nanolithography or as a template for the fabri...

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

A nanocomposite with ultra-low percolation threshold and high dielectric performance is prepared by controlling the localization of multiwalled carbon nanotubes (MWNTs) in one phase of a ternary continuous polymer blend system through melt processing. Polystyrene (PS), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) can form a ternary continuous structure when the volume fractions of PS, PVDF and PMMA are 70 vol%, 20 vol%, and 10 vol%, respectively. The PS is a continuous matrix (sea-phase) whereas the other two phases are interconnected threads (the PVDF is situated as the core while the PMMA is the shell, and the thickness of the PMMA shell is about 1 μm). Adding PMMA could improve the compatibility between the PS and PVDF components. Selective distribution of MWNTs in the PMMA shell is achieved through a combination of PMMA modified MWNTs and appropriate processing procedures. The composite shows an ultra-low percolation threshold of ca. 0.3 wt%. When the weight fraction of PMMA modified MWNTs is 0.4 wt%, the dielectric constant of the composite is as high as 182 (at 100 Hz), which is about 60 times higher than that of a pure PS matrix. The composite’s dielectric properties have excellent temperature stability. This approach can provide a new and low-cost route to design high-performance dielectric materials with ultra-low percolation thresholds.

Direct Visualization of Three-Dimensional Morphology in Hierarchically Self-Assembled Mixed Poly(tert-butyl acrylate)/Polystyrene Brush-Grafted Silica Nanoparticles

Three-dimensional (3D) morphology of hierarchically self-assembled mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brush-grafted 67 nm silica nanoparticles cast from chloroform on a carbon-coated transmission electron microscopy (TEM) grid was directly visualized using electron tomography (i.e., 3D TEM). The number-average molecular weights for PtBA and PS were 22.2 and 23.4 kDa, and their grafting densities were 0.51 and 0.34 chains/nm2, respectively. For a dense monolayer of mixed brush-grafted silica particles, a rippled phase structure was observed, and the monolayer consisted of protruded top portions from large nanoparticles and a bottom continuous film. In the top protruded part of large nanoparticles, isolated cylindrical PS microdomains were formed in the PtBA matrix due to the low PS volume fraction (i.e., 37%). The morphology in the lower continuous film was strongly influenced by interparticle interactions via mixed polymer brushes. As a result, bicontinuous nanostructures instead of i...

Measurement of normalised radar cross‐section of polystyrene foam at 60 GHz

The backscattering measurement of a rectangular solid volume of polystyrene foam (width: 0.92 m; height: 0.9 m; depth: 1.82 m) carried out at frequencies ranging from 59 to 60 GHz is described with horizontal polarisation for both transmission and reception antennas. The volume fraction of polystyrene in the measured material is about 0.01. The normalised radar cross-section of the measured polystyrene foam sample is estimated as 2.9 × 10 − 3(±3 × 10 − 4) m2/m3 by using the range-resolved data of the backscattered power arising from inside of the polystyrene foam volume. When using polystyrene foam as a support for radar targets in radar measurements, this result is considered useful for quantitatively estimating the intensity of the unwanted backscattered waves due to the foam.

Effect of Macromolecular Architecture on the Morphology of Polystyrene–Polyisoprene Block Copolymers

The impact of block connectivity on the morphologies of four block copolymers of varying architecture containing polystyrene (PS) and polyisoprene (PI) has been studied. The volume fraction of PS and molecular weight are held constant while varying the architecture from a linear PS–PI diblock copolymer to three different miktoarm star architectures: PS2PI, PSPI2, and PS2PI2. Morphologies of the PS2PI and PSPI2 miktoarm stars are different from those observed for the linear copolymer and dependent on the connectivity of the copolymer blocks. The change in morphology with connectivity indicates that combining two chains at a junction point leads to chain crowding, where subsequent excluded volume effects drive the change in morphology for each sample. The PS2PI2 miktoarm star exhibits the same morphology as the linear diblock but with a reduction in the size of the domains. The extent of the decrease in domain size indicates that chain stretching impacts the formation of this morphology. Experimentally obse...

Viscoelastic behaviors of shell‐crosslinked core–shell nanoparticles suspended in polystyrene solutions

AbstractShell‐crosslinked core–shell nanoparticles (SCCSNs) were prepared via miniemulsion polymerization of styrene in the presence of silane‐modified inorganic silica. The polystyrene (PS) shell of 58.6% in weight fraction was crosslinked using divinylbenzene. SCCSNs were spherical with a diameter distribution from 32 to 98 nm determined by dynamic light scattering. Dynamic rheology of SCCSNs suspended in PS/toluene solution was compared with that of suspensions of naked silica. The critical strain for onset of rheological nonlinearity was independent of SCCSN concentration above a concentration threshold, which differs from the silica suspensions. Linear dynamic rheological investigation revealed that SCCSN suspensions with a PS volume fraction of 20% were fluid‐like at low particle concentrations while suspensions containing 4.2 vol% SCCSNs formed a gel‐like structure. On the contrary, the silica suspensions with 20.0 vol% PS underwent a fluid‐to‐solid‐like transition with increasing silica concentration. Reasons for the different rheological behaviors of the naked silica and SCCSN suspensions are discussed. Copyright © 2012 Society of Chemical Industry

Preparation of spherical macroporous silica in an aerosol phase

Macroporous silica (MS) and macro/mesoporous silica (MMS) were prepared by spray drying a polystyrene (PS) latex sol containing a silica source, followed by calcination. As a silica source, 3-aminopropyl triethoxysilane (APS) was used for MS while either silica sol (SS) or tetraethoxyothosilicate using P123 templating (P123-TEOS) was used for MMS. Spray drying and calcination could also take place in a once-through aerosol reactor. The transformation of the silicon alkoxides to silica and decomposition of PS occurred at similar temperatures. Therefore, for APS-originated MS, the metal additives such as silver and nickel were required to accelerate the former. In addition, the nickel was well dispersed in the silica matrix during calcination even at 800 °C, in turn to thermally stabilize the porous structures. The wall-preforming additives were unnecessary for PS/SS and PS/P123-TEOS, since the SS drying and P123 templating, respectively, took place at lower temperature than PS decomposition. The porosities of all the porous silica prepared ranged from 0.54 to 0.57, which were close to the volume fraction of PS in the PS-alkoxides mixture solidified right after spray drying.

Interphase development in a three-component polymer system with asymmetric mobility

We report a study on the interphase evolution in a system composed by three polymeric components with markedly different mobility distributed between two layers. One of the layers is a low-Tg blend containing a low molecular weight polystyrene (PS) as a plasticizer (low-M PS) and PS chains with much higher molecular weight (high-M PS). The counterpart is a high-Tg layer composed by polyphenylene oxide. The system was annealed at several temperatures between Tg of the polymer layers and the subsequent interphase development probed by optical sectioning with confocal Raman microspectroscopy. The profiles obtained revealed the existence of two diffusion fronts that advance in opposite directions, both showing a similar response with time and temperature. These fronts act as well-defined boundaries that structure the interphase into three well-defined regions with almost constant PS volume fraction. We discuss this particular phenomenology proposing a simple diffusion model that describes the main interphase features. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 627–633, 2010

Effect of Homopolymer Molecular Weight on Nanophase-Separated Structures of AB Block Copolymer/C Homopolymer Blends with Hydrogen-Bonding Interactions

We describe morphological variations in binary mixtures of a poly(styrene-b-2-vinylpyridine) diblock copolymer (SP) (Mw = 151K) and poly(4-hydroxystyrene)s (Mw = 8K, 14K, 52K) (H8, H14, H52) as a function of molecular weight of homopolymer H and as a function of blend ratio. Transmission electron microscopy reveals ordered nanophase-separated structures for all samples regardless of molecular weight and the amount of homopolymer added. As much as 28-fold homopolymer H52, which has a Mw higher than that of the P block, can be added to the SP block copolymer without inducing macrophase separation. This unusual miscibility is apparently due to the affinity of P for H via hydrogen-bonding interactions. Furthermore, at a constant volume fraction of polystyrene (ϕs of 0.48) and an H/P ratio of 3.2, a structural transition from hexagonally packed cylinders to lamellae occurs upon increasing the Mw of the homopolymer. The small-angle X-ray scattering (SAXS) data obtained for these blends show that the intercylind...

Synthesis and self-assembly in bulk of six-arm star-block copolymers with a C60 core

This study focuses on the synthesis and the structural characterization of various branched star-block copolymers (polyisoprene-block-polystyrene)6C60 with a fullerene C60 as a core. Well defined 6-arm stars (PI-b-PS)6C60 with a low polydispersity and a precise control of the number of branches were prepared by grafting PI-b-PS diblock copolymers through the polystyrene block onto the C60 core. The self-assembled structures formed in bulk were studied by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS) for both symmetric and asymmetric polystyrene-block-polyisoprene (PS-b-PI) diblock arms in the strong-segregation regime (65≤χN≤115). Various microstructures including lamellae, hexagonal packings of PS and PI cylinders as well as a gyroid phase were obtained by varying the volume fraction of polystyrene (fPS) of the branches, leading to the formation of ordered, periodic and localized nanoscale dispersions of the C60 in a polymer matrix including planes, threads and a 3D bicontinuous network of C60.

Self-assembly of colloidal crystals from polystyrene emulsion at elevated temperature by dip-drawing method

The self-assembly of colloidal crystal arrays from polystyrene (PS) sphere emulsion at elevated temperature by dip-drawing method was investigated. The dependence of effective sphere transfer in the meniscus of emulsion on temperature was discussed. The results show that the assembled arrays formed at 50 °C have fewer defects than those at room temperature. The elevated emulsion temperature during the ordered arrangement of colloidal crystals causes quicker solvent evaporation, hence quicker sphere transfer. However, exceeding solvent flux and crystal growth induced by over high temperatures result in more fracture lines displayed in arrays. At 50 °C, the effective sphere transfer by the solvent flux to the array edge can also be enhanced by increasing the PS volume fraction of emulsion, which obviously reduces fracture lines on the surface of multilayer.

Influence of Ionic Complexes on Phase Behavior of Polystyrene-b-poly(methyl methacrylate) Copolymers

The influence of ionic complexes on phase behavior of PS-b-PMMA copolymers over a wide range of molecular weights and PS volume fractions was investigated by small-angle X-ray scattering (SAXS), grazing incidence small-angle X-ray scattering (GISAXS), transmission electron microscopy (TEM), and neutron reflectivity (NR). The disorder-to-order transition (DOT) in both symmetric and asymmetric copolymers indicates that the overall Flory−Huggins segmental interaction parameter, χeff, between polystyrene (PS) and poly(methyl methacrylate) (PMMA) blocks with lithium−PMMA complexes is increased compared to that of the neat copolymers. This enhanced χeff further results in an order-to-order transition (OOT), from spheres to cylinders, and an increase in the ordering and spacing of microdomains. Moreover, transitional metal ionic complexes, such as copper−PMMA complexes, are found to have the similar influence on phase behavior of PS-b-PMMA copolymers. The formation of ionic complexes in the copolymers not only offers a parameter to tune the degree of microphase separation of PS-b-PMMA copolymers but also provides a way to fabricate multifunctional materials.

Polystyrene thin films in CO(2).

In air, or vacuum environments, liquid polystyrene (PS) thin films (thickness, h<100 nm ) supported by SiOx /Si substrates are structurally metastable or unstable, depending on film thickness. They rupture and eventually form droplets on the SiOx /Si substrates (dewet) due to the influence of destabilizing long-ranged van der Waals dispersion forces. We used scanning force microscopy to examine the structural stability of liquid PS films in the thickness range 5 nm<h<100 nm in liquid and in supercritical carbon dioxide ( CO2 ) environments. All films in this thickness range were metastable; holes developed throughout the films and over time these holes grew, impinged, and eventually formed droplets. The rate of destabilization is controlled by three factors: film thickness, temperature, and CO2 pressure (which dictates CO2 volume fraction in the films). Calculations of the effective interface potentials suggest that the energy barrier for nucleation and growth of holes in CO2 is larger than that in air, and in the limit of vanishingly low PS volume fraction the films should be stable.

Effect of Composition Distribution on Microphase-Separated Structure from BAB Triblock Copolymers

The effects of composition distribution on microphase-separated structures formed by monodisperse BAB triblock copolymers were investigated. Monodisperse nine parent BAB triblock copolymers consisting of polystyrene for A and poly(2-vinylpyridine) for B were prepared by anionic living polymerization. These nine copolymers were designed such that polystyrene volume fraction, φs, ranged from 0.1 to 0.9, and they were blended to produce samples with various composition distributions but with constant average composition at φs of 0.5. Periodic simple alternating lamellar structures were observed for solvent cast and well-annealed blend films as long as composition distribution is relatively low. It has been found that microdomain spacing increases with increasing composition distribution of copolymer samples up to 1.25 in terms of Mw(S)/Mn(S), where Mw(S) and Mn(S) are weight-average and number-average molecular weights of polystyrene blocks, respectively, as was the case of the AB diblock copolymer system, t...

Thermodynamic analysis of the phase separation during the polymerization of a thermoset system into a thermoplastic matrix. I. Effect of the composition on the cloud‐point curves

AbstractThe cloud‐point curves of polystyrene (PS) mixed with reactive epoxy monomers based on diglycidyl ether of bisphenol A with stoichiometric amounts of 4,4′‐methylenebis(2,6‐diethylaniline) were experimentally studied. A thermodynamic analysis of the phase‐separation process in these epoxy‐modified polymers was performed that considered the composition dependence of the interaction parameter, χ(T,Φ2) (where T is the temperature and Φ2 is the volume fraction of polystyrene), and the polydispersity of both polymers. In this analysis, χ(T,Φ2) was considered the product of two functions: one depending on the temperature [D(T)] and the other depending on the composition [B(Φ2)]. For mixtures without a reaction, the cloud‐point curves showed upper critical solution temperature behavior, and the dependence of χ(T,Φ2) on the composition was determined from the threshold point, that is, the maximum cloud‐point temperature. During the isothermal reactions of mixtures with different initial PS concentrations, the dependence of χ(T,Φ2) on the composition was determined under the assumption that, at each conversion level, the D(T) contribution to the χ(T,Φ2) value had to be constant independently of the composition. For these mixtures, it was demonstrated that the changes in the chemical structure produced by the epoxy–amine reaction reduced χ(T,Φ2). This effect was more important at lower volume fractions of PS. Nevertheless, the decrease in the absolute value of the entropic contribution to the free energy of mixing was the principal driving force behind the phase‐separation process. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1351–1360, 2004

Thermodynamic analysis of the phase separation during the polymerization of a thermoset system into a thermoplastic matrix. II. Prediction of the phase composition and the volume fraction of the dispersed phase

AbstractA thermodynamic simulation of the phase‐separation process of an off‐critical blend, based on a thermoplastic matrix with a reactive epoxy system undergoing polycondensation at a constant temperature, was performed. The model considered the composition dependence of the interaction parameter, χ(T,Φ2) (where T is the temperature and Φ2 is the volume fraction of polystyrene), along with the polydispersity of both polymers. For every level of conversion, the simulation provided the amount, composition, stoichiometric ratio, and conversion of each phase present. The accuracy of the model was proved by the good agreement between the experimental and predicted glass‐transition temperatures and heat capacity changes at the glass‐transition temperatures for both phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1361–1368, 2004