Effect of Temperature and Pressure on Surface Tension of Polystyrene in Supercritical Carbon Dioxide

Utilization of surface-active compounds derived from biosolids to remediate polycyclic aromatic hydrocarbons contaminated sediment soil

In the present study, surface-active compounds (SAC) were extracted from biosolids using an alkaline treatment process. They were tested for their remediation efficiency of crude oil-contaminated sediment soil and was compared with Triton x-100. The SAC exhibited a similar soil washing efficiency to that of the commercial Triton x-100, and under the optimized soil washing parameters, SAC exhibited a maximum of 91% total polycyclic aromatic hydrocarbons removal. Further, on analysing the toxicity of the soil residue after washing, it was observed that SAC from biosolids washed soil exhibited an average of 1.5-fold lesser toxicity compared to that of Triton x-100 on different test models-earthworm, a monocot, and dicot plants. The analysis of the key soil parameters revealed that the commercial surfactant reduced the soil organic matter and porosity by an average of 1.3-fold compared to SAC. Further, the ability of surfactants to induce toxicity was confirmed by the adsorption of the surfactants on the surface of the soil particles which was in the order of Triton x-100 > SAC. Thus, this study suggests that SAC can be applied as an effective bioremediation approach for contaminated soil for a greener and sustainable ecosystem.

Estimation of the Effects of CO2 and Temperature on the Swelling of PS-CO2 Mixtures at Supercritical Conditions on Rheological Testing

The use of supercritical CO₂ as a blowing agent for polymeric foams instead of traditional blowing agents has been a trend in recent years. To achieve the final desired properties of the polymeric foams, the rheological behavior of the material needs to be reliable. The polymer swelling in the samples for rheological testing affects the results of the viscoelastic properties of the material. This study proposes a new testing methodology to control the accuracy and repeatability of the rheological characterization for PS-SCO₂ samples. To develop this methodology, three polystyrene resins with different molecular weight distribution were studied at three temperatures (170, 185 and 200 °C) and three pressures (0.1 MPa, 6.89 MPa and 13.78 MPa). The CO₂ concentration was estimated and used in the Sanchez–Lacombe Equation of State (SLEOS) to determine the polymer swelling, as it affects the dimensions of specimens tested in high-pressure rheometers. The correction factors provided a consistent trend in the viscosity with respect to temperature and a decrease of up to 50% in the standard deviation. The results of this study are crucial for an accurate measurement of viscoelastic properties by parallel-plate rheometry.

Vacuum-Driven Orientation of Nanostructured Diblock Copolymer Thin Films

This work aims to demonstrate a facile method for the controlled orientation of nanostructures of block copolymer (BCP) thin films. A simple diblock copolymer system, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), is chosen to demonstrate vacuum-driven orientation for solving the notorious low-surface-energy problem of silicon-based BCP nanopatterning. By taking advantage of the pressure dependence of the surface tension of polymeric materials, a neutral air surface for the PS-b-PDMS thin film can be formed under a high vacuum degree (∼10^-4 Pa), allowing the formation of the film-spanning perpendicular cylinders and lamellae upon thermal annealing. In contrast to perpendicular lamellae, a long-range lateral order for forming perpendicular cylinders can be efficiently achieved through the self-alignment mechanism for induced ordering from the top and bottom of the free-standing thin film.

Supercritical Carbon Dioxide Impregnation of Gold Nanoparticles Demonstrates a New Route for the Fabrication of Hybrid Silk Materials

How many nanoparticles can we load in a fiber? How much will leak? Underlying is the relatively new question of the “space available” in fibers for nanoparticle loading. Here, using supercritical carbon dioxide (scCO2) as a carrier fluid, we explored the impregnation in four Indian silks (Mulberry, Eri, Muga, and Tasar) with five standard sizes of gold nanoparticles (5, 20, 50, 100 and 150 nm in diameter). All silks could be permanently impregnated with nanoparticles up to 150 nm in size under scCO2 impregnation. Accompanying structural changes indicated that the amorphous silk domains reorganized to accommodate the gold NPs. The mechanism was studied in detail in degummed Mulberry silk fibers (i.e., without the sericin coating) with the 5 nm nanoparticle. The combined effects of concentration, time of impregnation, scCO2 pressure, and temperature showed that only a narrow set of conditions allowed for permanent impregnation without deterioration of the properties of the silk fibers.

Amphilic Water-Lean Carbon Capture Solvent Wetting Behavior through Decomposition by Stainless-Steel Interfaces

A combined experimental and theoretical study has been carried out on the wetting and reactivity of water-lean carbon capture solvents on the surface of common column packing materials. Paradoxically, these solvents are found to be equally able to wet hydrophobic and hydrophilic surfaces. The solvents are amphiphilic and can adapt to any interfacial environment, owing to their inherent heterogeneous (nonionic/ionic) molecular structure. Ab initio molecular dynamics indicates that these structures enable the formation of a strong adlayer on the surface of hydrophilic surfaces like oxidized steel which promotes solvent decomposition akin to hydrolysis from surface oxides and hydroxides. This decomposition passivates the surface, making it effectively hydrophobic, and the decomposed solvent promotes leaching of the iron into the bulk fluid. This study links the wetting behavior to the observed corrosion of the steels by decomposition of solvent at steel interfaces. The overall affect is strongly dependent on the chemical composition of the solvent in that amines are stable, whereas imines and alcohols are not. Moreover, plastic packing shows little to no solvent degradation, but an equal degree of wetting.

Review on the recent development of durable superhydrophobic materials for practical applications

Biomimetic superhydrophobic surfaces show great potential in oil-water separation, anti-icing and self-cleaning. However, due to the instability caused by its fragile structure and non-durable superhydrophobicity, it is difficult to apply them in the actual field. Here, by introducing surface wettability and analysing the mechanism of superhydrophobic failure, it is concluded that the reason for the failure of the superhydrophobic surface comes from the transition of the surface energy and the hysteresis of the contact angle (CA). On the basis of this analysis, it is concluded that the principle of designing a durable superhydrophobic surface is to satisfy one of the following three points: improving the binding force between molecules, introducing durable materials and improving chemical durability. On this basis, a variety of preparation methods are proposed, such as assembly method and spray/dip coating method, and the design and preparation of a self-healing surface inspired by nature will also be included in the introduction. Last but not least, the preparation and application of a durable super-hydrophobic surface in oil-water separation, anti-icing and self-cleaning are also introduced in detail. This review reveals the conclusions and prospects of durable superhydrophobic surfaces, and aims to inspire more researchers to invest in this research.

Mercury, Arsenic and Lead Removal by Air Gap Membrane Distillation: Experimental Study

Synthetic industrial wastewater samples containing mercury (Hg), arsenic (As), and lead (Pb) ions in various concentrations were prepared and treated by air gap membrane distillation (AGMD), a promising method for heavy metals removal. Three different membrane pore sizes (0.2, 0.45, and 1 μm) which are commercially available (TF200, TF450, and TF1000) were tested to assess their effectiveness in combination with various heavy metal concentrations and operating parameters (flow rate 1–5 L/min, feed temperature 40–70 °C, and pH 2–11). The results indicated that a high removal efficiency of the heavy metals was achieved by AGMD. TF200 and TF450 showed excellent membrane removal efficiency, which was above 96% for heavy metal ions in a wide range of concentrations. In addition, there was no significant influence of the pH value on the metal removal efficiency. Energy consumption was monitored at different membrane pore sizes and was found to be almost independent of membrane pore size and metal type.

New trends in cellular silicone: Innovations and applications

The purpose of this article is to provide an overview of manufacturing processes used in the development of cellular silicone for a wide variety of applications. The combination of intrinsic properties of silicone and foam is considered as an attractive solution in many applications. With regard to the long-standing interest of the industry in silicone chemistry, foaming is very common from hydrosilylation/condensation reactions. This well-known technology leads to homogeneous, elastic, low density and biocompatible foams. However, the size of the cells remains large, the reactions are sensitive to humidity and the dangerousness of the hydrogen could be an industrial concern. Many researches are moving towards alternatives to the manufacture of silicone cellular materials such as gas foaming, phase separation, emulsion and sacrificial models, and syntactic charges. In addition, the theories of sorption, diffusion, nucleation and cell growth are detailed to explain the formation of gaseous foam. CO2 is commonly used to physically foam silicone because of its good solubility. However, the diffusive behavior of CO2 is high in silicone as explained by the free volume theory. Silicone–CO2 foaming is essentially triggered by rapid depressurization leading to a cell density around 1 × 109 cells/cm3 in the best case. In addition, templated foams are divided into emulsion polymerization (polyHIPE), sacrificial foams and syntactic foams. These methods are simple because they do not need specific foaming equipments. Pore sizes are also tunable as function of template sizes.

Measurement of nanoscale molten polymer droplet spreading using atomic force microscopy

We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures using atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μm diameters at 115-175 °C on sapphire, silicon oxide, and mica. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The contact angle evolution follows a power law with time with experimentally determined values of -0.29 ± 0.01, -0.08 ± 0.02, and -0.21 ± 0.01 for sapphire, silicon oxide, and mica, respectively. The non-zero steady state contact angles result in a slower evolution of contact angle with time consistent with theories combining molecular kinetic and hydrodynamic models. Monitoring the cantilever phase provides additional information about the local mechanics of the droplet surface. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 °C to 175 °C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means.

Investigation of material characteristics and processing conditions effects on bubble growth behavior in a physical foaming process

Bubble growth during polymeric foam production by a physical nucleating agent is a result of rapid gas phase separation in a polymer/gas solution media. The dynamics of bubble growth is thought to be influenced by the material properties and processing conditions. However, the degree of effectiveness of each parameter has not been evaluated in earlier studies. In this work, a simplified single bubble growth in a polymeric media was modeled to specify the critical parameters affecting the bubble growth phenomenon. The predicted bubble growth profile was compared with some experimental data reported in the literature. The model was able to predict the observed bubble growth profile with acceptable precision. Therefore, it was applied to investigate the effect of each physical property of the polymer, i.e. viscosity, surface tension and diffusion coefficient as well as processing conditions, i.e. temperature and pressure release rate on the bubble growth profile. Furthermore, the impact of each factor was clarified.

Study of volume swelling and interfacial tension of the polystyrene-carbon dioxide-dimethyl ether system

We investigated the interaction of blended carbon dioxide (CO2) and dimethyl ether (DME) with polystyrene (PS) through volume swelling and interfacial tension. The experiments were carried out over a temperature range of 423-483 K, and the pressure was varied from 6.89 MPa to 20.68 MPa. With an incremental concentration of DME in the blend, the volume swelling increased while the interfacial tension between the PS/blend gas mixture and the blend gas decreased. The validity of the Simha-Somcynsky (SS) equation of state (EOS) for the ternary system was established by comparing experimentally measured volume swelling to that obtained via SS-EOS.

Response surface optimization for producing microcellular polymethyl methacrylate foam using supercritical CO2

A regression model constructed by response surface methodology was employed to optimize the relationships between the cell density of microcellular polymethyl methacrylate foam and three independent variables: foaming pressure, temperature, and time. A Box–Behnken Design statistical approach was employed to fit the available response data to a second-order polynomial response surface model. The analysis of variance of the model indicated that the interactions between the foaming pressure and temperature, and that between the foaming temperature and the saturation time, both positively affect the cell density. Experimental verification of the predicted optimum conditions of foaming pressure = 21 MPa, foaming temperature = 313 K, and saturation time = 6.9 h gave an actual maximum cell density of 20.86 × 109 cells/cm3, which is close to the data predicted by the regression model.

Bubble morphological evolution and surface defect formation mechanism in the microcellular foam injection molding process

A multiphase model was established to simulate the bubble morphological evolution in MFIM, and a new phenomenon of surface collapse and pits with the gradient depth was discovered.

Simha-Somcynsky Equation of State Modeling of the PVT Behavior of PP/Clay-Nanocomposite/CO2 Mixtures

The Pressure-Volume-Temperature (PVT) property of polymer nanocomposite (PNC)/gas solutions is an important fundamental property in the foaming of PNC. However, accurate data have not yet been reported. We examined the PVT behaviors of polypropylene (PP) and PP/organoclay polymer nanocomposite (PP-PNC) by monitoring the swelling changes of the polymer melt in supercritical carbon dioxide (scCO2). A model was adopted that describes the PVT behaviors of PP-PNC with and without dissolved gas. Based on the model, a PNC consists of two sections: a hard section (a nanoparticle surrounded by solidified polymer) and a soft section (neat polymer). It was observed that an infusion of nanoparticles decreased the swelling. It seems that the hard section had a minimal free volume in which to dissolve the blowing agents, and that the number of hard sections increased with the infusion of nanoparticles. As a result, the total gas absorption capacity of the system decreased, and consequently, the swelling also decreased.

A semi-empirical model for density gradient in microcellular thermoplastic foams

In microcellular plastics, produced by the solid-state batch method, an integral solid skin and a core with graded porosity can be created by allowing absorbed gas to diffuse from the surface of a saturated specimen prior to foaming. In this article a semi-empirical model is proposed to predict the local density of microcellular foam as a function of dissolved gas concentration. To this end, Henry’s law is applied on available experimental data for polystyrene—nitrogen system. The resultant spatial variation of mass density would be interesting for analyzing engineering structures made of microcellular plastics.

Reduction of polymer surface tension by crystallized polymer nanoparticles

Self-consistent field theory is applied to investigate the effects of crystallized polymer nanoparticles on polymer surface tension. It is predicted that the nanoparticles locate preferentially at the polymer surface and significantly reduce the surface tension, in agreement with experiment. In addition to the reduction of surface tension, the width of the polymer surface is found to narrow. The reduced width and surface tension are due to the smaller spatial extent of the nanoparticles compared to the polymer. This allows the interface to become less diffuse and so reduces the energies of interaction at the surface, which lowers the surface tension. The solubility of the surrounding solvent phase into the polymer melt is mostly unchanged, a very slight decrease being detectable. The solubility is constant because away from the interface, the system is homogeneous and the replacement of polymer with nanoparticles has little effect.

Effect of Temperature on Foaming Behaviors of Homo- and Co-polymer Polypropylene/Polydimethylsiloxane Blends with CO2

Poly(dimethylsiloxane) (PDMS) was blended with two different types of polypropylene (PP). The blends were subsequently batch-foamed with supercritical CO2 at a series of temperatures that varied by a narrow increment of 2°C to investigate the effect of the foaming temperature on foaming. In the case of the random copolymer PP, it was found that the cell density of the blends containing PDMS increased significantly and good cell structures could be obtained across a wide temperature spectrum. PDMS typically generated high CO2 concentration and low surface tension, which positively impacted the cell nucleation. In the case of linear homopolymer PP, the addition of PDMS did not result in any pronounced improvement to cell morphology; however, at very low temperatures, much lower than the melting point, a few very small cells appeared. In both experiments, the addition of maleic anhydride grafted PP (PP-g-MAH) as a compatibilizer promoted the dispersion of PDMS and yielded a better cell morphology within a specific temperature range. Moreover, the presence of a compatibilizer enhanced the melt strength, which in turn served to broaden the processing window.

Origin of change in molecular-weight dependence for polymer surface tension

Self-consistent-field theory is used to reproduce the behavior of polymer surface tension with molecular-weight for both lower and higher molecular-weight polymers. The change in behavior of the surface tension between these two regimes is shown to be due to the almost total exclusion of polymer from the nonpolymer bulk phase. The predicted two regime surface tension behavior with molecular-weight and the exclusion explanation are shown to be valid for a range of different polymer compressibilities.