Nonsolvent Vapor Research Articles

Enhanced charge transport of conjugated polymer/reduced graphene oxide composite films by solvent vapor pre-treatment

In this study, a facile approach that could provide a significant enhancement of the charge transport properties of the conjugated polymer/reduced graphene oxide (rGO) composite films using a non-solvent vapor treatment is reported. As the methanol vapors were exposed to the poly(3-hexylthiophene) (P3HT)/rGO composite solution, P3HT chains self-assembled to create nanofibrillar structures via favorable π–π interactions. The π–π staking in P3HT occurred by the non-solvent vapor exposure to minimize unfavorable interactions of P3HT chains with the non-solvent vapor molecules. The self-assembly of P3HT chains was chiefly facilitated by the presence of rGO. This is because the surface of rGO can serve as nucleation sites for the growth of P3HT nanowires. Consequently, P3HT/rGO composite films obtained from the methanol vapor treated corresponding solutions exhibited a high charge carrier mobility (1.3 × 10−1 cm2 V−1 s−1), which is approximately 11-times and 6.5-times higher than those of pristine P3HT (1.2 × 10−2 cm2 V−1 s−1) and P3HT/rGO (2.0 × 10−2 cm2 V−1 s−1) composite films, respectively.

Improvement in Mechanical Properties of 3D-Printed PEEK Structure by Nonsolvent Vapor Annealing.

The broad applications of 3D-printed poly-ether-ether-ketone (3D-PEEK) structures are largely hampered by their inadequate mechanical properties that can be improved by post treatments. At present, thermal annealing is generally used to improve the mechanical properties of 3D-PEEK. However, it cannot simultaneously improve strength and ductility. Here, a cost-effective postprocessing method is developed to improve the mechanical properties of 3D-PEEK, based on annealing in nonsolvent vapor at room temperature. The annealing in nonsolvent vapor at room temperature simultaneously improves the strength, ductility, and fracture energy of as-printed 3D-PEEK by 22.6%, 151.3%, and 109.1%, respectively. The improved mechanical properties are attributed to enhanced interfacial bonding, increased crystallinity, decreased pinhole defects, and stress relaxation in the 3D-PEEK. Moreover, the annealing in both polar solvents (such as acetone and chloroform) and nonpolar solvents (such as n-hexane) are demonstrated to be effective for improving the mechanical properties of 3D-PEEK. The nonsolvent vapor-annealed 3D-PEEK can thus have potential applications in the fields of medical implants, automotive, aerospace, and more.

Preparation of a composite coating film via vapor induced phase separation for air purification and real-time bacteria photocatalytic inactivation

Infectious diseases resulted from transmitting of bacteria or virus like COVID-19 via air-borne droplets have brought severe threat to human beings worldwide. Cutting the spreading paths to obtain clean air is one of the promising strategies to prevent people from such dangerous diseases. In this work, we have employed a strategy of spray coating in combination with vapor induced phase separation to prepare a composite coating film to fulfill that purpose. A stable mixture suspension containing micelles of block copolymer of poly(styrene-block-butadiene-block-styrene) and TiO2 nanoparticles was sprayed onto stainless steel mesh to evaporate solvent in non-solvent vapor atmospheres. A water vapor atmosphere and an ethanol vapor atmosphere were in turn employed to improve the mechanical strength of the obtained coating film. The porous microstructure, the porosity, and the superhydrophobicity of the coating film were carefully characterized and analyzed. The air pressure-drop of the coating film was determined to be lower than 100 Pa, indicating a high air permeability. Moreover, a foggy air containing E. coli was pressed through the coating film via a home-made apparatus to simulate the air purification system, where E. coli contained air-borne droplets were intercepted by the film matrix in a physical manner, and the bacteria was photocatalytically inactivated at the meantime. A filtration efficiency of 99.7% and a 99.6% efficiency of real-time photocatalytic inactivation of E. coli demonstrate the promising potential of the coating film.

Controlled self-assembly of polymer semiconductors in solution using a solvent-vapor approach

A facile solution treatment strategy for controlling the microstructure of conjugated polymers using a non-solvent vapor is introduced. The content of well-ordered poly(3-hexylthiophene) (P3HT) aggregates in solution was precisely controlled by varying the non-solvent vapor exposure time. P3HT chains were self-assembled upon exposure to the non-solvent vapor to minimize the unfavorable interactions with the non-solvent molecules. The effect of solvent vapor on the molecular ordering and morphologies of P3HT films was investigated by UV-Vis spectroscopy, atomic force microscopy, and polarized optical microscopy. These studies reveal that the self-assembled P3HT aggregates have well-ordered nanofibrillar structures formed via [Formula: see text]–[Formula: see text] stacking. This strategy paves the way toward fabricating well-ordered polymeric structures, especially in the field of opto-electronic applications including FETs, LEDs, and lasers, where proper alignment or molecular assembly is in great demand.

Controlled Self-Assembly of Conjugated Polymers via a Solvent Vapor Pre-Treatment for Use in Organic Field-Effect Transistors.

A facile solution-processing strategy toward well-ordered one-dimensional nanostructures of conjugated polymers via a non-solvent vapor treatment was demonstrated, which resulted in enhancements to the charge transport characteristics of the polymers. The amount of crystalline poly(3-hexylthiophene) (P3HT) nanofibers was precisely controlled by simply varying the exposure time of solutions of P3HT solutions to non-solvent vapor. The effects of non-solvent vapor exposure on the molecular ordering and morphologies of the resultant P3HT films were systematically investigated using ultraviolet-visible (UV-vis) spectroscopy, polarized optical microscopy (POM), grazing incidence X-ray diffraction (GIXRD), and atomic force microscopy (AFM). The non-solvent vapor facilitates the π–π stacking in P3HT to minimize unfavorable interactions between the poor solvent molecules and P3HT chains. P3HT films deposited from the non-solvent vapor-treated P3HT solutions exhibited an approximately 5.6-fold improvement in charge carrier mobility as compared to that of pristine P3HT films (7.8 × 10−2 cm2 V−1 s−1 vs. 1.4 × 10−2 cm2 V−1 s−1). The robust and facile strategy presented herein would be applicable in various opto-electronics applications requiring precise control of the molecular assembly, such as organic photovoltaic cells, field-effect transistors, light-emitting diodes, and sensors.

Porous poly(vinylidene fluoride) membranes with tailored properties by fast and scalable non-solvent vapor induced phase separation

Hydrophobic and highly porous poly(vinylidene fluoride) (PVDF) membranes with isotropic cross section as well as tunable and narrow barrier pore size distribution in the range from ~0.1 to ~1 µm have been prepared using the non-solvent vapor induced phase separation (VIPS) technique. The process conditions have been tuned to suit an industrial scale up, using a short production time and dimethyl sulfoxide (DMSO) as solvent for PVDF, instead of commonly used hazardous chemicals. Factors like kind of solvent, the relative humidity of air, the exposure time to humid air and the mass fraction of PVDF in the casting solutions have been used to tune membrane characteristics. Interestingly, it was revealed that DMSO as a less common solvent for PVDF shows better qualities regarding upscaling than other more frequently used polar aprotic solvents (e.g. dimethylacetamide) when using VIPS under suited conditions. The phenomenon was explained through investigations of the membrane formation step, in particular by water uptake and cloud point measurements, as well as structure and performance analyses, e.g. by scanning electron microscopy, gas flow/liquid dewetting permpometry, gas and water vapor permeability analyses and liquid water entry pressure measurements. Lab-scale manufactured membranes showed pore characteristics and performance desired for membrane contactor applications. Furthermore, fabrication on a roll-to-roll machine using a nonwoven support and the established VIPS conditions was realized in a short manufacturing time; resulting membranes structure and characteristics were found to be similar to the ones for the lab-scale membranes. Overall, the combination of PVDF with DMSO gives promising opportunities for a more eco-friendly industrial fabrication of porous membranes with advanced properties via VIPS.

Porous flower-like superstructures based on self-assembled colloidal quantum dots for sensing

Quantum dots (QDs) have been envisaged as very promising materials for the development of advanced optical sensors. Here we report a new highly porous luminescent material based on colloidal QDs for potential applications in optical sensing devices. Bulk flower-like porous structures with sizes of hundreds of microns have been produced by slow destabilization of QD solution in the presence of a non-solvent vapor. The porous highly luminescent material was formed from CdSe QDs using the approach of non-solvent destabilization. This material demonstrated a 4-fold decrease in PL signal in the presence of the ammonia vapor. The relationship between the destabilization rate of QDs in solution and the resulting morphology of structural elements has been established. The proposed model of bulk porous flower-like nanostructured material fabrication can be applied to nanoparticles of different nature combining their unique properties. This research opens up a new approach to design novel multi-component composite materials enabling potential performance improvements of various photonic devices.

Octadecylsilyl-bonded silica based novel solid phase extraction membranes

Octadecylsilyl-bonded silica based novel solid phase extraction membranes were fabricated by non-solvent vapor induced phase separation method for the first time, and employed for extraction trace phenol as a model. The effects of membrane fabrication conditions and extraction parameters on the recoveries were explored. Under the optimized fabrication conditions, the extraction recovery of phenol (0.02 mg/L, 100 mL) attains 100% with enrichment factor of 10. The spike recovery of real water samples reaches 97.67%–99.40% with standard deviation of 1.16%–1.42%, demonstrating great potential in solid phase extraction.

Preparation of superhydrophobic porous coating film with the matrix covered with polydimethylsiloxane for oil/water separation

In this work, an organic coating film was designed to have a porous microstructure together with a rough surface, and its matrix was covered with a low surface energy layer, so that it can be employed for oil/water separation based on its superhydrophobicity and superoleophilicity. First, a mixture solution of poly(styrene-block-butadiene-block-styrene) (SBS) and polydimethylsiloxane (PDMS) prepolymer was sprayed onto stainless steel mesh in a non-solvent vapor atmosphere of ethanol. After solvent evaporation, a porous coating film has been obtained. The film matrix was formed from SBS to have a nodular-microstructure, which was covered by the highly flexible PDMS prepolymer. Then, the PDMS prepolymer was cured to cover the nodular microstructure at 60 °C, which was chosen to be far below the glass transition temperature of polystyrene block of SBS in order to maintain the formed nodular microstructure. The microstructures of the obtained coating films were carefully characterized and analyzed. Water and oil contact angles on the coating films were measured to indicate their wetting properties of superhydrophobicity and superoleophilicity. The oil diffusion speed along the coating film and the oil swelling behavior were examined to suggest the advantages of the covering PDMS layer. The coating films have been employed for oil/water separation through self gravity-driven filtration, where oil could penetrate the coating film automatically while water retained. The oil separation rate was found to be higher than 99.0% and the flux was estimated to be greater than 162 L∙h−1 m−2. Moreover, the cycling tests suggest the satisfactory reusability of the coating film, implying its potential applications in oily wastewater treatment or oil spill recovery.

Superhydrophobic paper from conjugated poly(p-phenylene)s: Self-assembly and separation of oil/water mixture

The oil pollution is an increasing threat to nature and human health. Therefore, effective separation of oil from the oily wastewater is a challenging task. Through the nonsolvent vapor method, a superhydrophobic paper can be self-assembled by dropping the conjugated poly-p-phenylenes solution on the commercial filter paper in a nonsolvent vapor atmosphere. The numerous nano-mircostructral particles composed of polymer nanowires covered on the filter paper, just like the morphology of lotus leaves, lead to the excellent superhydrophobic effect. Moreover, the polymer-coated filter paper not only exhibits good mechanical stability, long-term durability, self-cleaning, but also has superhydrophobicity and superoleophilicity. The as-prepared paper possess remarkable oil/water separation ability for a variety of oil/water mixtures, including bromoethane, hexane, cyclohexane, petroleum ether, gasoline, dodecane, and the mixed oil of gasoline and diesel, demonstrating that it can be a good candidate for the treatment of industrial oil-polluted water.

Petal-effect superhydrophobic surface self-assembled from poly(p-phenylene)s

In the nonsolvent vapor atmospheres, the petal-effect superhydrophobic surface was self-assembled from conjugated poly(2,5-dibutoxy-p-phenylene). During the dissolution of the nonsolvent vapor and the evaporation of the solution, the side-chain interactions and the π–π interactions between conjugated backbones induced the formation of polymer particles, which further agglomerated and formed the network structures and radiate spherical-like hierarchical microstructures. The increase in the distribution of microspheres improved the roughness of the surface and increased the contact angles more than 150°. The network of agglomerated polymer particles were easier to be formed and induced a relatively important penetration of the water inside the pores. Therefore, the network of agglomerated polymer particles and radiate spherical-like hierarchical microstructures can form a Cassie-impregnating regime to display the petal-effect. This provides a new strategy for preparing petal-effect superhydrophobic polymer surfaces, which show significant potential for future application in the control of microdroplet and micro-fluidics.

Dewetting-Induced Photoluminescent Enhancement of Poly(lauryl methacrylate)/Quantum Dot Thin Films.

A new method for enhancing photoluminescence from quantum dot (QD)/polymer nanocomposite films is proposed. Poly(lauryl methacrylate) (PLMA) thin films containing embedded QDs are intentionally allowed to undergo dewetting on substrates by exposure to a nonsolvent vapor. After controlled dewetting, films exhibited typical dewetting morphologies with increased amounts of scattering that served to outcouple photoluminescence from the film and reduce internal light propagation within the film. Up to a 5-fold enhancement of the film emission was achieved depending on material factors such as the initial film thickness and QD concentration within the film. An increase in initial film thickness was shown to increase the dewetted maximum feature size and its characteristic length until a critical thickness was reached where dewetting became inhibited. A unique light exposure-based photopatterning method is also presented for the creation of high contrast emissive patterns as guided by spatially controlled dewetting.

Preparation of conjugated poly(p-phenylene) hierarchical microspheres by nonsolvent vapor self-assembly and their fluorescent detection of metal ions

The novel hierarchical microspheres from conjugated poly(p-phenylene)s can be self-assembled by the nonsolvent vapor method. The formation of hierarchical microspheres depends on the choice of polar nonsolvent vapor atmospheres, solvents, and the length of side chains. The intermolecular interactions, including the side-chain interactions and the π–π interactions between conjugated backbones, occur spontaneously to form various conformations and polymeric aggregates, which have an effect on the fluorescence wavelength of the polymer hierarchical microspheres. Our results demonstrate a facile way to prepare polymeric hierarchical microspheres and adjust their optical properties. Moreover, the hierarchical microspheres with rough surface show a highly selective fluorescence “turn-off” sensor for Fe3+ with almost no interference of other metal ions.

Preparation of breathable and superhydrophobic coating film via spray coating in combination with vapor-induced phase separation

Abstract Breathable and superhydrophobic coating film has been successfully prepared in one step by combining spraying technique and non-solvent vapor induced phase separation. Namely, solution of an inexpensive commercially available thermoplastic elastomer, i.e., a star-shaped triblock copolymer of poly (styrene- block -butadiene- block -styrene), was sprayed in an ethanol vapor atmosphere. The sprayed tiny droplets of the polymer solution facilitated the solvent evaporation and the non-solvent condensation, resulting in their fast phase separation and solidification. After complete evaporation of the solvent in a few minutes, a porous and superhydrophobic coating film was thus obtained, with a nanometer to micrometer inter-connected nodular morphology. In order to improve the superhydrophobicity and strengthen the coating film, inorganic nanoparticles of SiO 2 have been added into the polymer solution for spraying fabrication. The obtained coating films were thermally treated to further improve their mechanical properties for practical application. The contact angle, the sliding angle and the abrasion tests results proved all previous methods effective. Moreover, water-vapor permeation through the coating film was checked to indicate its breath ability. Therefore, this paper provides a practical method for the preparation of porous and superhydrophobic coating films, which may have great promise in microfiltration and textile industry.

Self-assembly of poly(p-phenylene)-based flower-like 3D micro-nanostructures

Poly(2,5-dioctyloxy-p-phenylene) was fabricated into Chrysanthemum-like, rose-like, and coil-like micro-nanostructures and porous sponge-like three-dimensional (3D) network via solution-phase self-assembly by two types of phase separations (continuous and dispersed phases) occurred by the dissolution of polar MeOH vapor and nonpolar hexane vapor into the polymer solutions, respectively. Morphological changes of polymers produced significant changes in the optical properties. It was concluded that the choice of a good solvent and nonsolvent vapor for hairy-rod polymers is a facile way to design and fabricate various super-macromolecular architectures.

Blue-emitting poly(1,1′-binaphthol butyl ether) nanospheres via the nonsolvent vapor method

Under nonsolvent vapor atmospheres, poly(1,1′-binaphthol butyl ether) nanospheres can be self-assembled from various good solvent solutions. To obtain the optimized assembling parameters, the factors such as the solvents and the polymer concentrations, on the formation of polymeric nanospheres were investigated. The choice of good solvent and nonsolvent is an important factor. The well-ordered nanospheres with the sizes of hundreds nm can be easily obtained from the preparation combinations such as CH2Cl2/MeOH vapor, CHCl3/MeOH vapor, CHCl3/EtOH vapor, and THF/EtOH vapor. Moreover, the increasing polymer concentration leads to the increasing spherical agglomerations. The static water contact angles of the films with polymeric spheres were measured to be above 130°. With the excitation wavelength of 371 nm, the polymeric nanospheres showed the blue emission with the peak at 480 nm. The nonsolvent vapor method is a facile way to prepare polymeric nanospheres.

A three-dimensional TiO2/graphene porous composite with nano-carbon deposition for supercapacitor

Titanium dioxide/graphene composite is receiving intensive attention because of its potential applications in energy field. Herein, we report the preparation of a three-dimensional TiO2/graphene porous composite prepared by using a sacrificial template strategy, avoiding the usual hydrothermal and freeze-drying processes. Graphene oxide sheets and TiO2 nanoparticles were first dispersed in a block copolymer micelle solution, and then the mixture was exposed to a non-solvent vapor atmosphere to evaporate the solvent. Finally, the resultant intermediate product was calcined in nitrogen to remove polymer template. As a result, the obtained free-standing composite material has a three-dimensional porous microstructure. Scanning electron microscopy and transmission electron microscopy observations indicate that the composite is supported by TiO2-anchored graphene sheets. More interestingly, nano-carbon particles derived from the carbonization of the polymer template are evenly deposited onto both the graphene sheets and the TiO2 nanoparticles. The specific capacitance of the carbon/TiO2/reduced graphene oxide composite has been measured to reach 23.6 mF/cm2. Our results indicate that the enhanced electrochemical properties of the composite are attributed to a synergistic effect of the 3-D porous network and the unique microstructure. The electrochemical stability and the cycle performance of the obtained composite electrode are tested to illustrate its potential applications.

A superhydrophobic film with high water vapor transmission prepared from block copolymer micelle solution via VIPS method

A superhydrophobic film with high water vapor transmission has been prepared via a vapor-induced phase separation process, where a block copolymer micellar solution was exposed to an organic non-solvent vapor atmosphere to evaporate solvent. After complete evaporation of the solvents, the obtained film displays 3-dimentional network with bi-continuous matrices and channels, both of which are at the scale of nanometers to micrometers. Interestingly, the matrix of the film consists of inter-connected sub-micrometer particles. The special hierarchical microstructure results in superhydrophobic and high adhesive properties of the film. Films with this kind of microstructure coating on non-planar substrates have been successfully prepared. The porosity of the film has been determined, and applications of the film in fields such as water vapor transmission and microfiltration separation have been carried out in order to indicate its potential.

Coagulation bath composition and desiccation environment as tuning parameters to prepare skinless membranes via diffusion induced phase separation

ABSTRACTDiffusion Induced Phase Separation (DIPS) is a currently used technique to produce porous membranes for a large variety of applications. A strong limitation is represented by the occurrence of a dense skin, which is formed during the process, highly reducing the membrane permeability. To overcome this issue, two modifications of the standard DIPS protocol were investigated: the use of coagulation baths composed by a solvent/nonsolvent mixture and the desiccation in a controlled environment, by modulating the partial pressure of nonsolvent vapor. An appropriate choice of coagulation bath composition, together with an appropriate desiccation protocol (i.e., the use of a nonsolvent vapor), will produce a skinless membrane, and offers the chance to control the morphology of both membrane surfaces. These results underline the importance of post‐treatment stage in membrane preparation via phase separation, thus suggesting that membrane washing/drying stage will affect the final morphology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42151.

Microstructures of Poly (9'9-Dihexylfluorene) Grown in the Non-Solvent Vapor

In this research, the microspheres of poly (99-dihexylfluorene) were fabricated with dichloromethane as a good solvent by self-assembly methods. The effects of poor solvent vapor, polymer concentration, and the temperature of environment on the formation of the sphere patterns were investigated. It was found that the microsphere could be easily prepared in the ethanol non-solvent vapor atmosphere. Besides, increasing the environment temperatures was advantageous to fabricate microspheres. Furthermore, the property of non-solvent vapor was a key role to the formation of the sphere.