Amorphous Polystyrene Research Articles

Nanocomposite synthesis by thermolysis of [Ag(hfac)(COD)] in amorphous polystyrene

AbstractLightfast color filters (intensively and brightly colored) can be easily produced by dying optical plastics with the surface plasmon resonance (SPR) of metal nanoparticles such as silver and gold. Here, color filters based on silver nanoparticles embedded in amorphous polystyrene have been prepared by dissolving and thermally decomposing (1,5-cyclooctadiene)(hexafluoro-acetylacetonate)silver(I) in amorphous polystyrene. The metal precursor quickly decomposes (10 s, at 180°C), leading to silver atoms that clusterize and produce a non-aggregated dispersion of silver particles in the polymer matrix. The intensity of the yellow coloration due to the SPR of nanoscopic silver can be widely tuned simply by varying the cluster numerical density in the polymer matrix that depends on the silver precursor concentration. The obtained nanocomposite films have been characterized by X-ray power diffraction, transmission electron microscopy, and UV-Vis spectroscopy.

On the formation of topological entanglements during the contact of glassy polymers

Fracture energy (G) of the symmetric amorphous polystyrene (PS)–PS interfaces that were partially healed at temperatures (T) below the glass transition temperature of the bulk (\( T_{\text{g}}^{\text{bulk}} \)) has been measured at ambient temperature and compared with those reported in the literature (G 0) for the symmetric PS–PS interfaces that were fully healed at T > \( T_{\text{g}}^{\text{bulk}} \). It has been shown that G developed at T < \( T_{\text{g}}^{\text{bulk}} \) corresponds to G 0 for the polymers having the molecular weight larger than the entanglement molecular weight. This behaviour indicates that topological entanglements can be formed across the contact zone of the polymers with glassy bulk via the interdiffusion of the chain segments located in the viscoelastic contact layer.

Diffusivity of alcohols in amorphous polystyrene

AbstractGravimetry is used to study the diffusion of a homologous series of alcohols (Cn, with n = 1, 2, 3, 4, 6, 10, and 16) in amorphous polystyrene at temperatures from 35 to 145°C, that is both below and above the polymer glass transition temperature of 100°C. All the mass uptake results are well described by a simple Fickian model (for t &lt; t1/2) and are used to calculate the corresponding diffusion coefficients using the thin‐film approximation. At any particular temperature, the alcohols Cn with n = 3, 4, and 6 possess very similar diffusivities despite the fact that the chain length doubles from C3 to C6. This peculiar diffusivity behavior is explained based on the variation of the polymer–solvent chemical affinity along the homologous series. As expected, at any particular temperature, the diffusivity decreases considerably from C6 to C10 and from C10 to C16. For each alcohol, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Nanocomposite preparation by thermal decomposition of [Ag(hfac)(COD)] in amorphous polystyrene

AbstractA simple technique to prepare plastic color filters based on the surface plasmon resonance of silver nanoparticles has been developed. In particular, silver/polystyrene nanocomposite has been prepared by dissolving silver 1,5‐cyclooctadiene‐hexafluoroacetylacetonate in amorphous polystyrene, and the obtained solid solution was heated for ca. 10 s at a convenient temperature (180°C). In these conditions, the metal precursor decomposes and produces silver atoms that diffuse into the polymeric matrix and clusterize, leading to the formation of a contact‐free dispersion of silver nanoparticles. The resulting films have been characterized by large‐angle X‐ray powder diffraction, transmission electron microscopy, and UV–vis spectroscopy. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 31: 242–245, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21278

Dynamic measurement of stress optical behavior of three amorphous polymers

In the present study, rheo-optical and mechanical properties of three amorphous polymers, i.e., PS (polystyrene), PC(polycarbonate) and COC(cyclo olefin copolymer), widely used for optical products have been investigated. Accurate measurement of stress optical coefficients and elastic modulus data across the glass transition region are essential for predicting optical anisotropy in many injection molded optical products like pickup lenses and waveguide in LCD module since the final products have both flow and thermal history from the melt to glass. To obtain stress optical behavior in wide range of frequency and temperature including rubbery, glassy and glass transition regime, frequency sweep tests with extensional bar and shear sandwich tools were undertaken. As a result, glassy and melt extreme values of stress optical coefficient of PS and PC were evaluated as well as master plots in wide frequency region. The sign change of stress optical coefficient was shown clearly for PS as the frequency increased. On the other hand, the sign of stress optical coefficient over the whole frequency region is always positive for PC. For COC’s of different composition, even though the glass transition temperature can vary, the stress optical coefficient of COC’s with different composition stays almost constant at two extremes.

Diffusivity of alkanes in polystyrene

Gravimetry is used to study the diffusivity of a homologous series of linear alkanes (Cn, with n = 8, 10, 12, 14 and 16) in amorphous polystyrene at temperatures ranging from 45 °C to 145 °C, i.e. both below and above the polymer glass transition temperature (100 °C). All the mass uptake results obtained are well described by a simple Fickian model (for t 0.993, for all temperatures) with respect to the number of carbon atoms (n) in the alkyl chain, log(D) decreasing when n increases. For each liquid penetrant, over the temperature intervals considered, its log(D) also increases linearly (R2 > 0.996 for all the systems) with the decrease in the penetrant’s liquid viscosity.

Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene

Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (Cn, with n=2, 6–16) in amorphous polystyrene at temperatures from 35°C to 165°C, that is, both below and above the polymer glass transition temperature of 100°C. All the mass uptake results are well described by a simple Fickian model (for t<t1/2) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n2D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.

Activity of Antimicrobial Silver Polystyrene Nanocomposites

A simple technique based on doping polymers with in situ generated silver nanoparticles (Ag/PS films) has been developed. In particular, an antiseptic material has been prepared by dissolving silver 1,5‐cyclooctadiene‐hexafluoroacetylacetonate in amorphous polystyrene, and the obtained solid solution has been heated for ca. 10 s at a convenient temperature (180°C). Under such conditions the metal precursor decomposes producing silver atoms that diffuse into the polymer and clusterize. The antimicrobial characteristics of the resulting polystyrene‐based material have been accurately evaluated toward Escherichia coli (E. coli) comparing the cytotoxicity effect of 10 wt.% and 30 wt.% (drastic and mild annealing) silver‐doped polystyrene to the corresponding pure micrometric silver powder. Two different bacterial viability assays were performed in order to demonstrate the cytotoxic effect of Ag/PS films on cultured E. coli: (1) turbidimetric determination of optical density; (2) BacLight fluorescence‐based test. Both methods have shown that silver‐doped polystyrene (30 wt.%) provides higher antibacterial activity than pure Ag powder, under similar concentration and incubation conditions.

Hierarchical modelling of polystyrene surfaces

We present hierarchical simulations of amorphous polystyrene surfaces: first, we use a systematically coarse-grained description of atactic polystyrene that allows for efficient equilibration of polystyrene chain conformations and chain packing at the surface. This approach is followed by an inverse-mapping procedure that reintroduces the atomistic degrees of freedom in the coarse-grained structures and provides a detailed atomic-scale picture of the polymer surface characteristics and a direct comparison with experimental data, as the orientation of the rings at the surface. At the level of the coarse-grained modelling, several system specific properties, closely related to the molecular architecture such as the chain tacticity, can already be studied. We investigate how amorphous polystyrene surface properties depend on the molecular weight of the polymer, on the temperature and on the chain tacticity.

Dependence of dielectric properties on the crystallinity of ceramic/polymer composites

Effects of ZnNb(2)O(6) content and crystallinity of polymers on the dielectric properties of ZnNb(2)O(6)/polytetrafluoroethylene (PTFE), polypropylene (PP), and polystyrene (PS) composites were investigated at microwave frequencies. With increasing ZnNb(2)O(6) content, the dielectric constant (K) of the composites increased, whereas the dielectric loss (tanδ) and temperature coefficient of resonant frequency (TCF) decreased. The tanδ of the composites with amorphous PS was lower than those of the composites with semi-crystalline PP and PTFE. For the composites with semi-crystalline PTFE and PP, the tanδ was strongly dependent on the degree of crystallinity of composites. Several types of theoretical models were applied to predict the effective dielectric properties of the composites. Typically, K of 5.73, tan δ of 1.45 x 10(-3), and TCF of 2.66 ppm/°C were obtained for the PP composites with 0.5 volume fraction V(f) of ZnNb(2)O(6).

Nanocomposites Based on Metal and Metal Sulfide Clusters Embedded in Polystyrene

Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)x, where R is a linear aliphatic hydrocarbon group, –CnH2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal sulfide species and an organic by-product, disulfide (RSSR) or thioether (RSR) molecules, respectively. Alkane-thiolates are non-polar chemical compounds that dissolve in most techno-polymers and the resulting solid solutions can be annealed to generate polymer-embedded metal or metal sulfide clusters. Here, the preparation of silver and gold clusters embedded into amorphous polystyrene by thermolysis of a dodecyl-thiolate precursor is described in detail. However, this chemical approach is quite universal and a large variety of polymer-embedded metals or metal sulfides could be similarly prepared.

Experimental study of melting of LDPE/PS polyblend in an intermeshing counter‐rotating twin screw extruder

AbstractAn experimental study is presented of the melting mechanism in a starve‐fed closely intermeshing counter‐rotating twin screw extruder of a modular Leistritz design. Various polymeric materials, semicrystalline low density polyethylene (LDPE), amorphous polystyrene (PS), and (LDPE/PS) polyblend were investigated at various operating conditions. A “screw pulling‐out” technique was used to investigate polymer behavior along the screw axis. In particular, the solid conveying, melting positions, the extent of starved character along the screw, and the fully filled regions were observed. Polymer samples were stripped off from each screw which was removed from the machine to investigate melting mechanism. Generally, it has been concluded that the melting mechanism revealed by White and Wilczyński for polyolefines has been proved for other polymeric materials under study. This mechanism consists of pellets being dragged into the calendering gap where they are melted due to calendering action. The molten polymer is expelled from the gap and pushes against the pellet bed which is continuously dragged into the gap. The composite modeling of an intermeshing counter‐rotating twin screw extrusion of polyblends has also been discussed. POLYM. ENG. SCI., 52:449–458, 2012. © 2011 Society of Plastics Engineers

The Evolution of Interfacial Strength as a Way to Characterize a Low-Temperature Limit of the Surface Glass Transition of an Amorphous Polymer

The evolution of autoadhesive strength, σ, with healing temperature, T h, at the symmetric amorphous polystyrene (PS)−PS interfaces of the samples with vitrified bulk has been used to characterize a low-temperature limit of the surface glass transition temperature T g surface(low). The existence of a linear relationship between the square root of σ and T h has been found for both polydisperse and monodisperse polymers. By the extrapolation of straight lines σ 1/2 − T h to σ 1/2 = 0, the values of T g surface(low) have been determined and compared with those of a high-temperature limit of T g surface, T g surface(high), measured earlier. The differences between T g surface(low) and T g surface(high) have been found to be insignificant, 10–20°C. Using an average value of the shift of T g surface(low) with healing time, t h, the quasi-equilibrium value of the surface glass transition temperature of amorphous PS T ∞ surface has been estimated to be 10–15°C.

Testing the minimum thermal conductivity model for amorphous polymers using high pressure

Pressure dependence of thermal conductivity provides a critical test of the validity of the model of the minimum thermal conductivity for describing heat transport by molecular vibrations of an amorphous polymer. We measure the pressure dependence of the thermal conductivity \ensuremath{\Lambda}($P$) of poly(methyl methacrylate) using a combination of time-domain thermoreflectance and SiC anvil-cell techniques. We also determine \ensuremath{\Lambda}($P$) from a computational model of amorphous polystyrene. In both cases, \ensuremath{\Lambda}($P$) is accurately predicted by the minimum thermal conductivity model via the pressure dependence of the elastic constants and density.

Stimulus-Responsive Self-Assembly: Reversible, Redox-Controlled Micellization of Polyferrocenylsilane Diblock Copolymers

In depth studies of the use of electron transfer reactions as a means to control the self-assembly of diblock copolymers with an electroactive metalloblock are reported. Specifically, the redox-triggered self-assembly of a series of polystyrene-block-polyferrocenylsilane (PS-b-PFS) diblock copolymers in dichloromethane solution is described. In the case of the amorphous polystyrene(n)-b-poly(ferrocenylphenylmethylsilane)(m) diblock copolymers (PS(n)-b-PFMPS(m): n = 548, m = 73; n = 71, m = 165; where n and m are the number-averaged degrees of polymerization), spherical micelles with an oxidized PFS core and a PS corona were formed upon oxidation of more than 50% of the ferrocenyl units by [N(C(6)H(4)Br-4)(3)][SbX(6)] (X = Cl, F). Analogous block copolymers containing a poly(ferrocenylethylmethylsilane) (PFEMS) metalloblock, which has a lower glass transition temperature, behaved similarly. However, in contrast, on replacement of the amorphous metallopolymer blocks by semicrystalline poly(ferrocenyldimethylsilane) (PFDMS) segments, a change in the observed morphology was detected with the formation of ribbon-like micelles upon oxidation of PS(535)-b-PFDMS(103) above the same threshold value. Again the coronas consisted of fully solvated PS and the core consisted of partially to fully oxidized PFS associated with the counteranions. When oxidation was performed with [N(C(6)H(4)Br-4)(3)][SbF(6)], reduction of the cores of the spherical or ribbon-like micelles with [Co(η-C(5)Me(5))(2)] enabled full recovery of the neutral chains and no significant chain scission was detected.

Self Assembling and Coordination of Water Nano-Layers On Polymer Coated Long Period Gratings: Toward New Perspectives for Cation Detection

In this work, polymeric coated Long Period Gratings (LPGs) working in transition mode have been used to monitor the coordination and self assembling of water nano-layers (typical thicknesses range in few tens of nanometers) providing new scenarios in chemical sensing applications. In particular, nano-scale layers (∼320 nm) of semicrystalline syndiotactic and amorphous atactic polystyrene (sPS and aPS), have been deposited by dip-coating onto LPGs to tune the devices at the transition point. Experimental results demonstrate the polymers capability to orient water molecules in proximity of their surfaces. The sPS and aPS interactions with water have been continuously monitored and then compared demonstrating the higher capability of the crystalline phase of sPS to orient water nano-layers. Moreover, the high sensitivity of the coated LPGs was used to monitor the effect of disorder induced on the interfacial water molecular arrangement by different cations (sodium, Na+, potassium, K+, and calcium, Ca2+, ions) depending on their size and electrical charge. Experimental results show for the first time that, thanks to the water-polymer interaction, sPS coated LPGs could be successfully employed as high sensitivity cation sensors. In fact, the monitoring of the disorder induced by cations on the coordinated water layer leads to high sensitivities, in terms of detected RI change for unitary variation of concentration (∼ for Na+ ions, ∼ for K+ ions, and ∼ for Ca2+ ions).

On the scaling law of the evolution of lap-shear strength with healing temperature at amorphous polymer−polymer interfaces and surface glass transition

The evolution of lap-shear strength (σ) with healing temperature Th at symmetric and asymmetric amorphous polymer−polymer interfaces formed of the samples with vitrified bulk has been investigated. It has been found that the square root of the lap-shear strength behaves with respect to healing temperature as σ1/2 ~ Th both at symmetric and asymmetric interfaces. Basing on this scaling law between σ and Th, the values of the surface glass transition temperature \( \left( {T_{\rm{g}}^{\rm{surface}}} \right) \) have been estimated for a number of amorphous polymers by the extrapolation of the experimental curves σ1/2 ~ Th for symmetric polymer−polymer interfaces and, in some cases, for asymmetric, both compatible and incompatible, polymer−polymer interfaces, to zero strength. A significant reduction in surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}} \) with respect to the glass transition temperature of the polymer bulk \( \left( {T_{\rm{g}}^{\rm{bulk}}} \right) \), reported earlier, has been confirmed by the use of the new proposed approach. The quasi-equilibrium surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}} \) of amorphous polystyrene (PS) has been predicted in the framework of an Arrhenius approach using the plot “logarithm of healing time − reciprocal surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}}\prime \prime \) and the activation energy of the surface alpha-relaxation of PS has been calculated.

Two-step micro cellular foaming of amorphous polymers in supercritical CO 2

Microcellular foaming of amorphous rigid polymers, polymethylmethacrylate (PMMA) and polystyrene (PS) was studied in supercritical CO 2 (ScCO 2) in the presence of several types of additives, such as triblock (styrene-co-butadiene-co-methylmethacrylate, SBM and methylmethacrylate-co-butylacrylate-co-methylmethacrylate, MAM) terpolymers. This work is focused in the two-step foaming process, in which the sample is previously saturated under ScCO 2 being expanded in a second step out of the CO 2 vessel (e.g. in a hot oil bath) where foaming is initiated by the change of temperature near or above the glass transition temperature of the glass/polymer glassy system. Samples were saturated under high pressures of CO 2 (300 bar), at room temperature, for 16 h, followed by a quenching at a high depressurization rate (150 bar/min). In the last step, foaming was carried out at different temperatures (from 80 °C to 140 °C) and different foaming times (from 10 s to 120 s). It was found that cellular structures were controlled selecting either the additive type or the foaming conditions. Cell sizes are ranging from 0.3 μm to 300 μm, and densities from 0.50 g/cm 3 to 1 g/cm 3 depending on the polymers considered.

Rheological and conductive percolation laws for syndiotactic polystyrene composites filled with carbon nanocapsules and carbon nanotubes

Semicrystalline syndiotactic polystyrene (sPS) composites with carbon nanocapsule (CNC) and carbon nanotube (CNT) fillers were prepared and good filler dispersion confirmed by electron microscopy. Their rheological and electrical properties were investigated to reveal the effect of filler aspect ratio. Amorphous atactic polystyrene (aPS) was used to prepare composites with a CNT filler to elucidate the effect of matrix tacticity. Percolation scaling laws are applied and the threshold concentration and exponent are determined. Above a threshold, the magnitudes of storage modulus ( G′) and conductivity are related to the level of percolation network as well as the intrinsic properties of the matrix and filler. Master curves are obtained provided that an appropriate percolation function is selected. Different scaling laws are validated for the G′ and conductivity results. Composites with CNTs show a much lower threshold than those with CNCs. A lower threshold is derived from the G′ results compared to that obtained from the conductivity data regardless of the filler aspect ratio and matrix tacticity. Owing to the pronounced nucleating effects of CNT, crystalline sPS composites exhibit a four times larger conductivity threshold compared to their amorphous aPS counterparts, although their rheological thresholds are similar.

Optical limiters based on silver nanoparticles embedded in amorphous polystyrene

A simple technique to prepare plastic color-filters based on the surface plasmon resonance (SPR) of silver nanoparticles has been developed. In particular, silver/polystyrene nanocomposites have been prepared by dissolving silver acetylacetonate in amorphous polystyrene and heating the obtained solid solution at a convenient temperature (ca. 200°C). When the metal precursor decomposes, the produced silver atoms diffuse into the polymeric matrix and clusterize, leading to the formation of a contact-free dispersion of hyperfine silver phase. The obtained films have been characterized by UV-VIS spectroscopy and the optical extinction spectra have been fitted by the Mie’s theory, introducing the limitation of the mean free path due to the collisions of conduction electrons with the boundary of the nanoparticles.