Solvent Evaporation Temperature Research Articles

A green solvent strategy for the development of piezoelectric poly(vinylidene fluoride–trifluoroethylene) films for sensors and actuators applications

Green chemistry approaches are increasingly relevant for the development of sustainable technologies, but this approach is scarcely being used in the field of piezoelectric polymers. Poly(vinylidene fluoride) (PVDF) based materials are the family of polymers with the larger piezoelectric response and, when processed from solution, are typically prepared using N,N-dimethylformamide (DMF) as solvent. This work demonstrates that poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) films can be prepared by solvent casting using 1,3-dioxolane (DXL) as a solvent. The influence of solvent evaporation temperature has been studied and compared with P(VDF-TrFE) films produced with DMF. It is shown that piezoelectric films with a d33 ~−21 pC·N−1 and suitable for applications can be obtained by this greener approach, opening the way for the development of environmentally friendlier sensors and actuators based on the PVDF family.

Multi-objective Optimization of Preparation Conditions of Asymmetric Polyetherimide Membrane for Prevaporation of Isopropanol

Abstract Multi-objective optimization is used in many chemical engineering fields that have conflict objective functions. Prevaporation is an effective process for removing trace or minor amount of the component of diluting solutions. This process is used for dehydration of alcohols containing small amounts of water. In this process membrane flux and separation factor have conflict with each other. So a multi-objective optimization approach can be used for optimization of the process. In this paper, in first stage a neural network based model was developed for preparation conditions for polyetherimide membrane in isopropanol prevaporation. Four major variables involved in the membrane preparation procedure, including polymer concentration, additive content, solvent evaporation temperature and time was considered. Membrane flux and separation factor were considered as objective functions. Elitist Non-dominated sorting genetic algorithm with jumping gene and altruistic adaptation (Alt-NSGA-aJG) was applied for simultaneous maximization of flux and separation factor. Pareto optimal solutions for membrane preparation conditions and effect of decision variables (four preparation variables) on Pareto front were investigated.

Influence of Solvent Evaporation Rate in the Preparation of Carbon‐Coated Lithium Iron Phosphate Cathode Films on Battery Performance

AbstractIn this work, the drying step for cathodes based on carbon‐coated LiFePO4 prepared in the temperature range of 60–120 °C has been investigated in detail. The microstructure of the cathode shows a homogeneous distribution of the active material and conductive additive particles independent of the drying temperature. However, the results of impedance spectroscopy and cycling voltammetry are affected by the drying temperature. The solvent evaporation temperature, therefore, affects the polymer binder distribution and its characteristics, which include the polar phase content of the polymer and its affinity with the other components of the cathode. The discharge capacity value after 50 cycles is 120 and 81 mAh g−1 for the samples dried at 80 and 60 °C, respectively, which show the best and worst battery performance, respectively. It was concluded that carbon‐coated LiFePO4 cathodes should be prepared at drying temperatures between 80 and 100 °C for optimized performance.

In situ niosome forming maltodextrin proniosomes of candesartan cilexetil: In vitro and in vivo evaluations

The aim of this study is to develop novel proniosomal tablets of candesartan cilexetil. Drug loaded proniosomes were prepared as dry powder by slurry method. The critical parameters of the production process were the type of the carrier (sorbitol, maltodextrin, and lactose), addition of charge inducers, rotation speed of the rotavapor and solvent evaporation temperature. The effects of these parameters on proniosome specifications such as the recovery, drug loading, drug release were investigated and also the influence on the particle size and surface charge of the niosomes derived by the hydration of proniosomes were evaluated. The mean particle size and drug loading of niosomes formed from the hydrated proniosomes were 204±2nm and 99.09±0.04% respectively, with a negative charge −43.65±0.54mV. The proniosomes demonstrated good flowability, compressibility and consolidation properties both alone and together with the tableting agents (microcrystalline cellulose and cross-linked poly vinylpyrrolidone). The niosomes derived by the hydration of proniosomal tablets preserved their initial properties. Compatibly with the increased in vitro drug dissolution rate, the relative bioavailability of drug from proniosomal tablets increased 1.86-fold and 2.75-fold and higher candesartan plasma levels were achieved within shorter time compared to the pure drug.

Tailoring poly(vinylidene fluoride-co-chlorotrifluoroethylene) microstructure and physicochemical properties by exploring its binary phase diagram with dimethylformamide

Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) membranes were prepared by solvent casting from dimethylformamide (DMF). The preparation conditions involved a systematic variation of polymer/solvent ratio and solvent evaporation temperature. The microstructural variations of the PVDF-CTFE membranes depend on the different regions of the PVDF-CTFE/DMF phase diagram, explained by the Flory-Huggins theory. The effect of the polymer/solvent ratio and solvent evaporation temperature on the morphology, degree of porosity, β phase content, degree of crystallinity, mechanical, dielectric, and piezoelectric properties of the PVDF-CTFE polymer were evaluated. In this binary system, the porous microstructure is attributed to a spinodal decomposition of the liquid-liquid phase separation. For a given polymer/solvent ratio, 20 wt %, and higher evaporation solvent temperature, the β phase content is around 82% and the piezoelectric coefficient, d33, is −4 pC/N © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 761–773

Variation of the physicochemical and morphological characteristics of solvent casted poly(vinylidene fluoride) along its binary phase diagram with dimethylformamide

Poly(vinylidene fluoride), PVDF, films and membranes were prepared by solvent casting from dimethylformamide, DMF, by systematically varying polymer/solvent ratio and solvent evaporation temperature. The effect of the processing conditions on the morphology, degree of porosity, mechanical and thermal properties and crystalline phase of the polymer was evaluated. The obtained microstructure is explained by the Flory–Huggins theory. For the binary system, the porous membrane formation is attributed to a spinodal decomposition of the liquid–liquid phase separation. The morphological features were simulated through the correlation between the Gibbs total free energy and the Flory–Huggins theory. This correlation allowed the calculation of the PVDF/DMF phase diagram and the evolution of the microstructure in different regions of the phase diagram. Varying preparation conditions allow tailoring polymer microstructure while maintaining a high degree of crystallinity and a large β crystalline phase content. Further, the membranes show adequate mechanical properties for applications in filtration or battery separator membranes.

Microstructural variations of poly(vinylidene fluoride co-hexafluoropropylene) and their influence on the thermal, dielectric and piezoelectric properties

Polymer films and membranes of poly(vinylidene fluoride co-hexafluoropropylene), PVDF-HFP, have been prepared by thermally induced phase separation (TIPS), allowing the tuning of microstructure and morphology.The obtained microstructure is explained by the Flory-Huggins theory, depending on polymer concentration and solvent evaporation temperature. The formation of a porous membrane is attributed to a spinodal decomposition of the liquid-liquid phase separation. The effect of the processing conditions on the morphology, degree of porosity, degree of crystallinity and crystalline polymorph, thermal, dielectric and piezoelectric properties of the PVDF-HFP polymer were evaluated.The crystalline phase and degree of crystallinity depend on the processing conditions and further influence the dielectric and piezoelectric response. The piezoelectric coefficient is correlated with the β-phase content and decreases with decreasing polymer concentration in the initial solution at a given evaporation temperature.

Electroactive Polymer Based Porous Membranes for Energy Storage Applications

The market of portable batteries will reach $30.5 billion dollars in 2015 with an annual growth rate of 8.5% [1]. This growth is interconnected with advances of the portable electronic products (mobile-phones, computers) and with the development of new products such as e-labels, e-packaging, disposable medical testers and drug delivery patches.Wide ranges of materials properties for cathode, anode and battery separator/electrolyte are being developments for improving characteristics and performance of the battery.The battery separator is essential in electrochemical cells, separating the anode and cathode and controling the number and mobility of the lithium ions.Among the materials most investigated for battery separators are the PVDF and its copolymers poly(vinylidene fluoride-co-trifluoroethylene), PVDF-TrFE, poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, and poly(vinylidene fluoride-cochlorotrifluoroethylene),PVDF-CTFE [2].These materials show strong advantages for their use as separator membranes in comparison to polyolefins due to their high dipolar moment and large dielectric constant for a polymer material, which can assist ionization of lithium salts.In this work, PVDF and its copolymers have been processed by solvent cast technique with varying solvent evaporation temperature and the polymer/solvent ratio with the objective to tailor degree of porosity, mechanical, thermal and electrical properties.Degree of porosity, uptake, tortuosity, degree of crystallinity and ionic conductivity of the different membranes are evaluated and their influence in lithium-ion battery performance presented and discussed. Acknowledgments This work is funded by FEDER funds through the “Programa Operacional Factores de Competitividade—COMPETE” and by national funds from FCT—Fundação para a Ciência e a Tecnologia, in the framework of the Strategic Project PEST-C/FIS/UI607/2011, project F-COMP-01-0124-FEDER-022716 and grant SFRH/BD/68499/2010 (C.M.C.). The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER).The authors thank Celgard LLC, Timcal, Solvay, Arkema and Clariant for kindly supplying their high quality membranes and excellent materials, respectively.

PDMS-modified CaO-SiO2 hybrids derived by a sol-gel process for biomedical applications

Monolithic and crack-free disks of PDMS-modified CaO-SiO2 hybrids were obtained by a hydrolysis and polycondensation of poly (dimethylsiloxane), tetraethoxysilane, calcium nitrate. The bone-forming bioactivity of the as-obtained hybrids was influenced by some parameters, including surface morphology, microstructure and mesophase. It should be mentioned here that the heat treatment temperature plays an important part on the microstructural property and the bioactivity of the hybrids. The bioactivity of the hybrids was also evaluated by immersing the specimen in the simulated body fluid (SBF), and results indicate that it can be significantly improved by the porosity of the hybrids, which can be tuned by controlling the solvent evaporation temperature during the thermal process rigorously. The porous product may be used as a new kind of bioactive bone-repairing material. POLYM. COMPOS., 35:1193–1197, 2014. © 2013 Society of Plastics Engineers

Controlled self-assembly and alignment of organic–magnetic hybrid microrods

Growth control and alignment of rod-like self-assemblies have been studied widely since rod-like particulates have enormous potential as components of modern devices. In this study, size-controlled magnetic microrods were prepared by evaporation-induced self-assembly (EISA) from the self-assembling organic molecule and a magnetic γ-Fe2O3 nanoparticle mixture. Sizes of the magnetic microrods were controlled by adjusting solvent evaporation temperature to produce magnetic microrods in hundreds of micrometers with high aspect ratio. Thin microrods with an aspect ratio of 129.6 were obtained by lowering the temperature to at −20°C. The prepared magnetic microrods showed superparamagnetic properties similar to that of γ-Fe2O3 nanoparticles, while the pristine microrods showed diamagnetism. Unidirectional alignment of the magnetic microrods was achieved by applying an external magnetic field. Further, the prepared magnetic microrods had different refractive indices in the axial and radial directions, which is due to the alignment of chemical bonds of the building block molecules during self-assembly. The practical outcome of this study is that fabricating self-assembled structures into ordered structures with controlled sizes is readily achievable.

Effect of ionic liquid on the properties of poly(vinylidene fluoride)-based gel polymer electrolytes

Poly(vinylidene fluoride)-based polymer electrolytes using ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide as the plasticizer were prepared by solution casting method. The effects of the solvent evaporation temperature (SET) and ionic liquid content (ILC) on the properties and structures of the polymer electrolytes were investigated by characterization of scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry, as well as mechanical and ionic conductivity test. It was confirmed that both SET and ILC had significant influence on the morphology, degree of crystallinity, mechanical properties, and ionic conductivity of the prepared polymer electrolytes. With ILC of 40 %, an excellent polymer electrolyte can be obtained at SET of 60 °C, which exhibited ionic conductivity up to ca. 10−4 S/cm at room temperature, accompanied by excellent tensile strength of 22.8 MPa and elongation at break of 540 %.

Experimental study of nanofiber production through forcespinning

A newly developed method of producing nanofibers, called forcespinning, has proven to be a viable alternative to mass produce nanofibers. Unlike electrospinning, the most common method currently being employed (which draws fibers through the use of electrostatic force), forcespinning utilizes centrifugal forces which allow for a host of new materials to be processed into nanofibers (given that electric fields are not required) while also providing a significant increase in yield and ease of production. This work presents a detailed explanation of the fiber formation process. The study is conducted using high speed photography to capture the jet initiation process at the orifice and to track the trajectories of the resulting jets. The effects that influential controllable parameters have on the fiber trajectories and final fiber diameters are presented. The forcespinning controllable parameters include the spinneret angular velocity and aspect ratio, orifice radius and orientation, fluid viscoelasticity and surface tension, fluid fill level, solvent evaporation rate, temperature, and distance of spinneret orifice to collector.

Formation of Gradient Multiwalled Carbon Nanotube Stripe Patterns by Using Evaporation-Induced Self-Assembly

Gradient stripe patterns of multiwalled carbon nanotubes (MWCNTs) with remarkable regularity over large areas were fabricated by using evaporation-induced self-assembly technique. In this method, a glass coverslip was inclinedly immersed into a suspension of MWCNTs in dichloroethane. By controlling the solvent evaporation temperature, well-defined gradient stripes were formed at the air-solvent-substrate contact line. The effects of several experimental parameters, such as the substrate tilt angle, concentration of MWCNTs, and evaporation temperature, on the regularity of stripes were discussed. A possible stripe formation process was described as a negative feedback of MWCNT concentration caused by a concavely curved shape of the meniscus. Additionally, the strips of MWCNTs on Si/SiO(2) substrate were directly used to fabricate field-effect transistor (FET) devices. The electrical properties of the MWCNT-FET devices were also investigated.

Preparation and Characterization of E7–PMMA Microcapsules by Solvent Evaporation

Nematic liquid crystal E7 (core) was microencapsulated into the poly(methyl methacrylate) (PMMA, shell) via the solvent evaporation method. The morphology of microcapsules depends importantly on the initial PMMA/E7 ratio in oil phase. Solvent evaporation temperature, as well as the co-solvent, could further influence the surface morphology of microcapsules. Results of optical microscope measurements show that microcapsule shells with smooth surface are transparent. The microcapsule core loading is in accordance with the initial E7 content. The final obtained mononuclear microcapsules exhibit transparent shell, high E7 loading, and decent thermal stability.

Insight into Fractal Self-Assembly of Poly(diallyldimethylammonium chloride)/Sodium Carboxymethyl Cellulose Polyelectrolyte Complex Nanoparticles

Poly(diallyldimethylammonium chloride)-sodium carboxymethyl cellulose polyelectrolyte complexes (PDDA-CMCNa PECs) solids were prepared and dispersed in NaOH aqueous solution. Self-assembly of PECs nanoparticles during the solvent evaporation was examined by field emission electron microscopy (FESEM), atomic force microscopy (AFM), and fractal dimension analysis. It was found that tree-shaped fractal patterns formed after the solvent (water) was dried at ambient temperatures, and the fractal pattern is composed of needle-shaped PEC aggregate (PECA) nanoparticles. Time-dependent FESEM observation revealed that the fractal pattern started with the formation of initial nucleon and it is growing, during which the diffusion limited aggregation (DLA) mechanism revealed and made the pattern branched. Physical insight into the DLA mechanism was discussed in detail. Effects of PEC concentrations, PEC compositions, solvent evaporation temperatures, pH of PEC dispersion, and chemical structures of PECs on the formation of self-assembled fractal pattern were studied. Generally, it was found that the morphologies, charge characters of PEC particles, and the solvent evaporation conditions play important roles during the fractal self-assembly process.

The high flux poly (m-phenylene isophthalamide) nanofiltration membrane for dye purification and desalination

The aromatic poly (m-phenylene isophthalamide) (PMIA) nanofiltration (NF) membrane with polyvinyl pyrrolidone (PVP) and LiCl as additives was fabricated by phase inversion. The effects of additive content in the casting solution, solvent evaporation temperature and evaporation time during membrane fabrication on the performance of the PMIA NF membrane were investigated. The rejection of the PMIA NF membrane for dyes Eriochrome black T, Eriochrome blue black B and Alizarine red were all over 98%, with a flux about 80 L/m 2h , while the rejection for NaCl was only about 5.5% when tested at 0.4 MPa. The PMIA NF membrane was applied in the desalination and purification process of Eriochrome black T and NaCl mixed solution. The flux increased largely with the increase of the operation pressure and the temperature, while the rejection for dye remained over 99%. The flux decreased with the increase of the concentration of dye and salt in the feed solution while the rejection for dye and salt remained relative stable. The desalination and purification experiment exhibits that the rejection for the dye remained over 99% throughout the whole experiment which indicated that the PMIA-NF membranes could be successfully applied in the dye purification and desalination process.

Fabrication and Pore Size Control of Large-Pore Mesoporous Silica Particles through a Solvent Evaporation Process

Large-pore mesoporous silica particles were synthesized through a solvent evaporation process using hydrophobic fumed silica particles and tetraethyl orthosilicate (TEOS) as silica sources. The solvent evaporation of an ethanol solution of fumed silica particles, TEOS, HCl and triblock copolymer (F127) resulted in mesoporous silica particles with pores with sizes of about 7 nm. In addition, the interplanar spacing of the mesoporous silica particles can be controlled by changing the solvent evaporation temperatures.

Comparison of epithelial and fibroblastic cell behavior on nano/micro-topographic PCL membranes produced by crystallinity control

In this study, the relationship between the cellular morphology and the material surface topography was investigated. Poly(ε-caprolactone) (PCL) membranes were prepared in a wide range of surface wettabilities by means of crystallinity-controlled solvent casting process. Membrane surfaces were characterized by atomic force microscope (AFM), scanning electron microscope (SEM), and static/dynamic water contact angle measurements. It was found that solvent evaporation and non-solvent (methanol) addition to the solvent (THF) are the most decisive parameters to change the surface topography. The non-solvent addition and the decrease in solvent evaporation temperature from room temperature to −20 °C caused increased polymeric chain mobility and crystallization time. Such changes in crystallization parameters led to the formation of micro/nano-sized features on the membrane. Cell culture studies indicated that in contrast to Madin Darby kidney (MDBK) epithelial cells, L929 mouse fibroblast preferred rough and porous surfaces.

Ordered Honeycomb Microporous Films from Self-Assembly of Alkylated Guanosine Derivatives

Ordered honeycomb microporous films have previously been fabricated from polymeric macromolecules. We report here the successful fabrication of them from the supramolecular self-assembly of small molecules, alkylated guanosine derivatives. The ribbonlike self-assembly of the guanosines in CHCl3 is found to be the intrinsic structure that forms regular microporous structure via Bénard-Maragoni convection. Factors such as substrate, solvents, guanosine concentration, and solvent evaporation temperature are revealed to be able to control the size of the formed micropores, which in turn allows for the wettability of the honeycomb film surface to be modulated. These microporous materials exhibit excellent ability of loading organic dyes that eventually leads to the fabrication of luminescent honeycomb films. As structures of both the small molecules that can assemble and their self-assemblies can be varied and controlled, extended applications of this supramolecular method are expected to lead to microporous films of interesting functions.

Preparation and characterization of polystyrene/polycarbonate composite hollow microspheres by microencapsulation method

Polystyrene/polycarbonate (PS/PC) composite hollow microspheres were successfully prepared via microencapsulation method. Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry, and thermogravimetric analysis were used for the characterization of the obtained hollow microspheres. SEM images showed that there were a big cavity and some small cavities inside the composite hollow microspheres, and the hollow microspheres prepared at 42 °C presented better morphology and smaller size distribution compared with that prepared at higher temperature of solvent evaporation. The tap density of the composite hollow microspheres increased from 0.28 g cm−3 at PS/PC composite concentration of 5 wt% in oil phase to 0.42 g cm−3 at concentration of 11.7 wt%. The mean diameter of the composite hollow microspheres ranged from 13 to 528 μm. It increased with an increase in the concentration of composite in oil phase and decreased with increasing the second rotating speed. Thermal analysis showed that the composite hollow had thermal stability below 358 °C.