Solvent Evaporation-induced Phase Separation Research Articles

Towards Single-Polymer-Based Fully Printed Textile-Based Flexible Ag2O-Zn Battery for Wearable Electronics

Printed textile-based flexible batteries are gaining attention in several applications, but they are becoming more relevant to the health care industry in terms of realizing wearable and skin-conformable electronic devices. A flexible battery must ideally be deformable along multiple directions. In this work, with an aim to develop a fully printed omnidirectional deformable battery, we report the fabrication process of a novel single-polymer-based flexible non-rechargeable planar Ag2O-Zn battery on a textile substrate using the stencil printing method. Except for the electrolyte, all the components of the battery, including the current collectors, the anode, the cathode, and the separator membrane, are fabricated using a single polymer, namely styrene–ethylene–butylene–styrene (SEBS). To fabricate the SEBS separator, we introduce the solvent evaporation-induced phase separation (SEIPS) process. In the SEIPS method, toluene and dimethyl sulfoxide (DMSO) are selected as the solvent–nonsolvent pair. The SEBS: toluene: DMSO system with a wt% ratio of 6:85:9 showed improved performance regarding the OCV tests. A polyacrylic acid (PAA)-based alkaline polymer gel is used as an electrolyte. The demonstrated process is simple, and, with suitable modifications, it should find its use in the development of digitally printed alkaline batteries.

Nitric Oxide-Releasing Porous Coating with Antibacterial Activity and Blood Compatibility.

Nitric oxide (NO)-releasing coating is promising to enhance the biocompatibility of medical devices. In this study, polyurethane (PU) and S-nitrosated keratin (KSNO) were dissolved with dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF) to prepare a coating solution. This solution is facile to form a porous coating on various substrates based on solvent-evaporation-induced phase separation (SEIPS). The coating could continuously release NO up to 200 h in the presence of ascorbic acid (Asc). In addition, the coating could accelerate endothelialization by promoting the viability of human umbilical vein endothelial cells (HUVECs) while inhibiting the proliferation of human umbilical artery smooth muscle cells (HUASMCs). Furthermore, the coating had good antibacterial activity and blood compatibility. Taken together, this universal coating provides wider potential applications in the field of cardiovascular implants.

Data-Driven Prediction of Janus/Core-Shell Morphology in Polymer Particles: A Machine-Learning Approach.

The majority of research on Janus particles prepared by solvent evaporation-induced phase separation technique uses models based on interfacial tension or free energy to predict Janus/core-shell morphology. Data-driven predictions, in contrast, utilize multiple samples to identify patterns and outliers. Using machine-learning algorithms and explainable artificial intelligence (XAI) analysis, we developed a model based on a 200-instance data set to predict particle morphology. As model features, simplified molecular input line entry system syntax identifies explanatory variables, including cohesive energy density, molar volume, the Flory-Huggins interaction parameter of polymers, and the solvent solubility parameter. Our most accurate ensemble classifiers predict morphology with an accuracy of 90%. In addition, we employ innovative XAI tools to interpret system behavior, suggesting phase-separated morphology to be most affected by solvent solubility, polymer cohesive energy difference, and blend composition. While polymers with cohesive energy densities above a certain threshold favor the core-shell structure, systems with weak intermolecular interactions favor the Janus structure. The correlation between molar volume and morphology suggests that increasing the size of polymer repeating units favors Janus particles. Additionally, the Janus structure is preferred when the Flory-Huggins interaction parameter exceeds 0.4. XAI analysis introduces feature values that generate the thermodynamically low driving force of phase separation, resulting in kinetically stable morphologies as opposed to thermodynamically stable ones. The Shapley plots of this study also reveal novel methods for creating Janus or core-shell particles based on solvent evaporation-induced phase separation by selecting feature values that strongly favor a given morphology.

High‐Performance Biomechanical Energy Harvester Enabled by Switching Interfacial Adhesion via Hydrogen Bonding and Phase Separation (Adv. Funct. Mater. 38/2022)

Biomechanical Energy Harvesters In article number 2204304, William W. Yu, Wen Jung Li, Walid A. Daoud, and co-workers demonstrate a high-performance flexible biomechanical energy harvester by switching its interfacial adhesion via hydrogen bonding interactions and solvent evaporation induced phase separation. This wearable power source can generate a record high peak power density of 20.5 W m−2 Hz−1 under a low biomechanical input of 5 N, and can sufficiently power small electronics through harvesting regular or intermittent human motions.

Complex Suspended Janus Droplets Constructed through Solvent Evaporation-Induced Phase Separation at the Air-Liquid Interface.

Phase separation technology has attracted extensive scientific interest because of its intriguing structure changes during the phase separation process. Phase separation inside emulsion droplets in continuous surroundings has been well studied in recent years. Many investigations have also been conducted to study the droplet phase separation phenomena in noncontinuous surroundings. However, studies on the phase separation phenomena and the spreading behavior of suspended droplets at the air-liquid interface were rarely reported. In this study, PEGDA-glycerol suspended Janus droplets with a patchy structure were produced by utilizing solvent evaporation-induced droplet phase separation at the air-liquid interface. By altering the glycerol/PEGDA volume ratio, the initial proportion of ethanol, and the concentration of surfactants, suspended droplets with different morphologies can be achieved, which include filbert-shaped droplets (FSDs), half lotus seedpod single-phase Janus droplets (HLSDs), lotus seedpod single-phase Janus droplets (LSDs), lotus seedpod-shaped droplets (LSSDs), multiple-bulge droplets (MBDs), and half gourd-shaped droplets (HGSDs). A patchy structure was generated at the air-droplet interface, which was attributed to the Marangoni stresses induced by nonuniform evaporation. Furthermore, a modified spreading coefficient theory was constructed and verified to illustrate the phase separation at the air-droplet interface, which was the first research to predict the phase separation phenomena at the air-liquid interface via spreading coefficients theory. Moreover, we studied the factors that led to the droplets being able to float by designing the combined parameters, including three interfacial tensions and the equilibrium contact angles. Therefore, a simple and versatile strategy for creating suspended Janus droplets has been developed for the first time, which holds significant potential in a variety of applications for material synthesis, such as the electrospinning solution behavior when sprayed from the nozzle into the air.

A surfactant-free approach: Novel one-step ultrasonic nebulizer spray method to generate amphiphilic Janus particles

HypothesisA solvent evaporation-induced phase separation method, which is based on the preferential partitioning of two or more immiscible materials after solvent evaporation on providing heat, has been one of the main strategies for synthesis of Janus particles (JPs). Considering this approach, it should be possible to synthesize surfactant free-JPs in continuous flow by the ultrasonic nebulizer spray method. ExperimentsTwo polymers, polystyrene and polymethylmethacrylate, were dissolved in dichloromethane, and droplets of a precursor solution generated by an ultrasonic nebulizer were then conveyed through a borosilicate glass cylinder with two heating zones. The solvent evaporation-induced phase separation occurred in a single flow process, which resulted in the preferential partitioning of two incompatible polymers in the droplets, leading to the formation of the spherical bicompartmental JPs. FindingsThe successful fabrication of spherical JPs was observed at high polymer concentrations (1.5 and 2.0 wt%), and at elevated temperature (40–75 °C). The fluorescent compartmentalization of JPs was confirmed. Furthermore, the interfacial arrangement of JPs at oil–water interface was studied. A detailed explanation of theoretical prediction of interfacial configurations of JPs was provided. Lastly, the generated JPs were proved as Pickering stabilizers at the oil–water interface.

High‐Performance Biomechanical Energy Harvester Enabled by Switching Interfacial Adhesion via Hydrogen Bonding and Phase Separation

AbstractDramatic advances in wearable electronics have triggered tremendous demands for wearable power sources. To mitigate the impact of CO2 emission on the environment caused by energy consumption, biomechanical energy harvesting for self‐powered wearable electronics offers a promising solution. The output power of devices largely relies on the surface charge density, where adhesion interfaces generate a higher amount than nonadhesion counterparts, yet unfavorable for wearable devices due to the large detachment force required. Thus, sustaining high surface charge density in an adhesion‐free interface represents a major challenge. Herein, by leveraging intermolecular interactions and solvent evaporation induced phase separation, a nonadhesion interface is successfully realized, minimizing the interfacial adhesion from 20 to 0 kPa. Importantly, benefiting from the induced nano/microscale topography upon phase separation, comparable surface charges are generated at the interface. Consequently, a high‐performance flexible biomechanical energy harvester featuring a record high peak power density of 20.5 W m‐2 Hz‐1 at low matching impedance of 1 MΩ is achieved under a low biomechanical input force of 5 N. The device can power small electronics by harvesting regular or intermittent biomechanical energy and illuminate light‐emitting diodes wired/wirelessly. This work provides a facile strategy for interfacial engineering toward efficient energy harvesting.

One-step electrospinning PCL/ph-LPSQ nanofibrous membrane with excellent self-cleaning and oil-water separation performance

The ladder-like phenyl polysilsesquioxane (ph-LPSQ) was synthesized by sol-gel method. Then the Polycaprolactone/ladder-like polysilsesquioxane (PCL/ph-LPSQ) nanofibrous membranes were prepared via one-step electrospinning technique. The addition of ph-LPSQ was proposed to improve the hydrophobic and thermal properties of PCL membranes. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed the PCL/ph-LPSQ composite fibers had porous rough surface structure, which was caused by solvent evaporation induced phase separation, respiration diagram and silicon segment migration. The composition of PCL/ph-LPSQ membranes was characterized by using fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDS). Compared with pristine PCL membranes, the water contact angle and initial degradation temperature for PCL/ph-LPSQ membranes were increased to 158.0° and 355 °C, respectively, from the corresponding 133.6° and 340 °C. The superhydrophobic PCL/ph-LPSQ membranes exhibited excellent self-cleaning, anti-fouling and oil-water separation performance. Driven by gravity alone, the oil-water separation efficiency remained as high as 98% after ten cycles. More importantly, the as-prepared membrane showed good stability in 80 °C, 1 M acid, alkali and salt solutions. Considering the comprehensive properties of PCL/ph-LPSQ membranes, it might be a promising nonwoven fabric material in many fields like textile manufacturing industry. • A facile and ingenious method of preparing super hydrophobic nanofibrous membrane was developed in this paper. • The thermal and hydrophobic properties of the composite membrane were improved with the addition of organo-silicon polymer. • The as-prepared membranes exhibited excellent self-cleaning and oil-water separation performance.

3D Printed Flexible Microscaled Porous Conductive Polymer Nanocomposites for Piezoresistive Sensing Applications

AbstractPorous conductive polymer nanocomposites (CPNCs) have attracted significant attention for developing flexible piezoresistive sensors. In this work, a novel approach is developed by combining direct ink writing (DIW) and solvent evaporation induced phase separation method to synthesize porous CPNC with strain sensing capabilities. CPNC is prepared by dispersing carbon nanotubes (CNTs) at various concentrations in polydimethylsiloxane polymer, followed by mixing with solvent and nonsolvent phases to achieve a homogenous solution. 3D structures with 100% infill density are deposited layer‐by‐layer via DIW, while a microscaled porous network is formed during the curing cycle. The phase separation is induced by solvent evaporation, followed by the nonsolvent phase, while the polymer experiences gelation during the heat treatment procedure. The microstructure of the printed samples is characterized utilizing a scanning electron microscope. The piezoresistive and mechanical behavior of porous CPNC is evaluated to identify the optimum formulation that provides the highest sensitivity and flexibility. The sensors made with 1 wt% CNT loading with the optimum printing conditions are then fully characterized to evaluate the durability and reliability of the 3D printed sample for long‐term piezoresistive applications. The porous CPNCs are successfully employed as a piezoresistive sensor to detect human motion.

Large-Scale and Low-Cost Preparation of Ordered Honeycomb-Patterned Film by Solvent Evaporation-Induced Phase Separation Method

A large-scale and low-cost method for producing highly ordered honeycomb-patterned film using commonly commercialized polymers was proposed. This method provides the ability to prepare honeycomb-pa...

A highly stretchable and biodegradable superamphiphobic fluorinated polycaprolactone nanofibrous membrane for antifouling

A highly stretchable and biodegradable superamphiphobic fluorinated polycaprolactone (PCL-b-PTFOA) nanofibrous membrane with a hierarchical porous surface was prepared via electrospinning. Solvent evaporation-induced phase separation and fluorinated segment migration are the major reasons for the formation of hierarchical porous surface. The introduction of fluorinated segments (PTFOA) greatly improved the superhydrophobic and mechanical properties of the nanofibrous membrane. The superamphiphobic nanofibrous membrane could repel various solutions, including water, acidic, alkaline, coffee, glycol and n-hexane solutions. These solutions were repelled with a small sliding angle of water due to the membrane’s hierarchical pored morphology and low-surface-energy material, as revealed by scanning electron microscopy (SEM), atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) analyses. Studies of tensile testing and enzymatic biodegradation were also performed. The simultaneous reinforcing and toughening effect was achieved by the bonding of PTFOA onto the PCL chains, which breaking elongation increases from 152.97 %–678.15 %, and the tensile strength increases from 4.11 to 5.78 MPa. Additionally, the superamphiphobicity of the membrane was not lost with a strain up to 600 %. More importantly, the PCL-b-PTFOA nanofibrous membranes demonstrated excellent enzymatic degradation with 81.1 % weight loss at 37 °C for 24 h with Aspergillus oryzae in a phosphate buffer solution. These results suggest that compared with non-degradable materials, the prepared PCL-b-PTFOA nanofibrous membrane can be used as an excellent biodegradable material with good adaptability for antifouling and self-cleaning.

Optically Active Janus Particles Constructed by Chiral Helical Polymers through Emulsion Polymerization Combined with Solvent Evaporation-Induced Phase Separation.

Polymer Janus particles (PJPs) have been extensively investigated due to their intriguing features which cannot be achieved in traditional counterparts. Chiral polymer particles also have constituted a unique research area in polymer science. However, how to construct PJPs derived from chiral polymers, especially chiral helical polymers, still remains a significant academic challenge. This contribution reports the first success in preparing optically active PJPs constructed by chiral helical substituted polyacetylene via emulsion polymerization combined with solvent evaporation to induce phase separation. In emulsion polymerization systems, polymethyl methacrylate worked as a template and separated from polyacetylene domains in the course of acetylenic monomers' polymerization and evaporation of the solvent, by which optically active PJPs were formed. The major influencing factors were explored to elucidate their effects on the formation and morphology of PJPs. Mushroom- and bowl-like PJPs were obtained. Scanning electron microscopy (SEM) images ascertain nonspherical morphologies of the obtained PJPs. Circular dichroism and UV-vis absorption spectra demonstrate their optical activity, which originated in the predominantly one-handed helical polyacetylene chains constructing the PJPs. A formation mechanism was then proposed for understanding this unprecedented type of PJPs.

Microfluidic preparation of polymer-lipid Janus microparticles with staged drug release property

This work demonstrated a microfluidic preparation process for novel Janus microparticles with individual drug release properties in each compartment. A flow-focusing microfluidic chip was designed to produce oil-in-water droplets from a mixed solution of poly(lactic-co-glycolic acid) and a triglyceride type lipid. Based on solvent evaporation-induced phase separation, droplets evolved and were solidified into Janus particles, each of which had a polymer compartment and a lipid compartment. The ratio of the two compartments in a particle can be discretionarily regulated, and the particle structure can also be flexibly altered to Janus-patchy, triple, quadruple or core-shell type. Phase transition of the chosen lipid from solid to liquid would occur under physiological temperature, which was applied for rapid release of the loaded drug. The polymer compartment would undergo a slow degradation process in physiological environment, facilitating sustained drug release. Paclitaxel was loaded into Janus particles during preparation, and staged release was achieved, leading to a combination of rapid and sustained release, which is highly desired in target drug delivery. This study would start the application of hybrid Janus particles of polymer-lipid type with novel release kinetics in drug delivery systems.

Preparation of golf ball-shaped microspheres with fluorinated polycaprolactone via single-solvent electrospraying for superhydrophobic coatings

1H,1H,2H,2H-Perfluorooctyl polyacrylate (PTFOA) with a controllable molecular weight was successfully synthesized via atom-transfer radical polymerization (ATRP) followed by condensation with polycaprolactone (PCL) to obtain a new fluorinated block copolymer. Then, the copolymer PCL-b-PTFOA was processed via single-solvent electrospraying in chloroform to fabricate hierarchically porous microspheres. The microsphere size could be controlled from 5.13 ± 0.51 μm to 8.61 ± 0.90 μm, and the pore size on the microsphere surface could be controlled from 282.5 ± 42.0 nm to 603.3 ± 99.6 nm. Solvent evaporation-induced phase separation and fluorinated segment migration are the major reasons for the formation of the golf ball-shaped microspheres. In this study, the influence of electro-spraying parameters on the size and morphology of the porous microspheres was systemically studied. The golf ball-shaped microspheres significantly improved the surface roughness and the CA of their coatings reached 167.3 ± 1.7°. Furthermore, a superhydrophobic fabric was produced by pretreating cotton fabric with adhesive followed by coating with PCL-b-PTFOA via electrospraying. The robust superhydrophobicity can be obtained by the stable binding of PCL-b-PTFOA microspheres onto the fibers, with the CA reaching 155.3 ± 1.1°. Electrospraying of the fluoropolymer microsphere coating was proven to be a very promising technique to produce superhydrophobic coatings on textiles through a simple procedure.

Preparation and characterisation of poly(butylene succinate) microcarriers containing pesticide

Microcarriers containing pesticide have been designed to improve drug stability and increase release efficiency, which is favourable to the environment and agriculture development. In this work, biodegradable poly(butylene succinate) microspheres containing pesticide, λ-cyhalothrin, as an active agent are prepared by the solvent evaporation induced phase separation method. The microspheres show a uniform morphology and a narrow particle size distribution. The pesticide content is measured by high-performance liquid chromatography. The prepared microcarriers demonstrate high-loading capacity, encapsulation efficiency and long release time, which may find potential applications as new pesticide formulations.

One-Step Fabrication of Bioinspired Lubricant-Regenerable Icephobic Slippery Liquid-Infused Porous Surfaces.

Icephobic coating and surfaces are essential for protecting infrastructures such as transmission lines, transportation vehicles, and many others from severe damages of excessive icing. The slippery liquid-infused porous surfaces (SLIPS) are attracting escalating attention because of their low-ice adhesion strength. Despite all of the encouraging laboratory scale results, the SLIPS are still far from being applicable in real environments owing to the key unsolved problem, namely anti-icing durability. Inspired by the functionality of the amphibians’ skin, lubricant regenerability was introduced to conventional SLIPS and realized by a facile and scalable fabrication route. A series of polydimethylsiloxane (PDMS)-based skinlike SLIPS were designed and fabricated by using a one-step method, the solvent evaporation-induced phase separation technique. The obtained skinlike SLIPS were able to regenerate surface lubricant constantly by internal residual stress because of phase separation and survive more than 15 cycles of wiping/regenerating tests. Thanks to the regenerability of the surface lubricant, the new SLIPS demonstrated durable icephobicity, showing a long-term low-ice adhesion strength below 70 kPa, which was only 43% of 160 kPa that for the pristine PDMS (Sylgard 184), even after 15 icing/deicing cycles. This work paves a new and facile way for achieving icephobic durability of SLIPS.

Colloid silica nanoparticles trapped morphology of polymer blends during solvent evaporation

During the solvent evaporation induced phase separation of PS and PMMA blends with silica nanoparticles, the dispersed and bicontinuous morphologies need to be stabilized by the absorption of silica nanoparticles at the interface. In order to accomplish this, the silica nanoparticles need to be chemically neutral to PS and PMMA homopolymers. For this purpose, their surfaces were modified by attaching mono-hydroxyl group terminated polystyrene poly(methyl methacrylate) random (PS-r-PMMA-OH) copolymer via the condensation reaction between the hydroxyl groups of silica particles and copolymer. The resulting morphology was found to be affected by the rate of solvent evaporation, blend compositions, particle loading and size. In the symmetric blend system, the dispersed phase was observed at low evaporation rate and bicontinuous morphology was obtained at high evaporation rate. The silica nanoparticles were found to be densely packed at the interface of PS and PMMA. For asymmetric blend system, only dispersed phase was observed at both low and high evaporation rates. The size of phase separated domains decreases with increasing solvent evaporation rate and particle loading. The silica nanoparticles with smaller size resulted in relatively smaller domain size due to their higher surface area to volume ratio. Porous membranes with partially exposed nanoparticles were fabricated by etching PMMA phase in acetic acid.

A Phase Separation Route to Synthesize α-Fe2O3 Porous Nanofibers via Electrospinning for Ultrafast Ethanol Sensing

A facile and economic procedure was provided to synthesize α-Fe2O3 nanofibers. In this procedure, porous α-Fe2O3 nanofibers were obtained by a single-polymer/binary-solvent system, while solid α-Fe2O3 nanofibers were prepared by a single-polymer/single-solvent system. The crystal structure and morphology of both samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption isotherms. The formation mechanism of porous structure was based on solvent evaporation-induced phase separation by the use of mixed solvents with different volatility. Furthermore, ethanol-sensing performance of the porous α-Fe2O3 nanofibers was evaluated and compared with solid α-Fe2O3 nanofibers. Results from gas-sensing measurements reveal that porous α-Fe2O3 nanofibers exhibit higher sensitivity and slightly longer recovery time than solid α-Fe2O3 nanofibers. Over all, the gas sensor based on porous α-Fe2O3 nanofibers shows excellent ethanol-sensing capability with high sensitivity and ultrafast response/recovery behaviors, indicating its potential application as a real-time monitoring gas sensor.

Elongated phase separation domains in spin-cast polymer blend thin films characterized using a panoramic image.

Polymer thin films with micro/nano-structures can be prepared by a solvent evaporation induced phase separation process via spin-casting a polymer blend, where the elongated phase separation domains are always inevitable. The striation defect, as a thickness nonunifomity in spin-cast films, is generally coexistent with the elongated domains. Herein, the morphologies of polymer blend thin films are recorded from the spin-cast center to the edge in a panoramic view. The elongated domains are inclined to appear at the ridge regions of striations with increasing radial distance and align radially, exhibiting a coupling between the phase separation morphology and the striation defect that may exist. We demonstrate that the formation of elongated domains is not attributed to shape deformation, but is accomplished in situ. A possible model to describe the initiation and evolution of the polymer blend phase separation morphology during spin-casting is proposed.

Electromagnetic interference shielding effectiveness of microcellular polyimide/in situ thermally reduced graphene oxide/carbon nanotubes nanocomposites

A simple and effective method was adopted to fabricate microcellular polyimide (PI)/reduced graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) nanocomposites. Firstly, microcellular poly (amic acid) (PAA)/GO/MWCNTs nanocomposites were prepared through solvent evaporation induced phase separation. In this process, PAA and dibutyl phthalate (DBP) co-dissolved in N,N-dimethylacetamide (DMAc) underwent phase separation with DMAc evaporating, and DBP microdomains were formed in continuous PAA phase. Subsequently, PAA was thermally imidized and simultaneously GO was in situ reduced. After DBP was removed, the microcellular PI/reduced GO (RGO)/MWCNTs nanocomposites were finally obtained. When the initial filler loading was 8wt%, the electrical conductivity of microcellular PI/RGO, PI/MWCNTs and PI/RGO/MWCNTs nanocomposites were 0.05, 0.02 and 1.87S·m−1, respectively, and the electromagnetic interference (EMI) shielding efficiency (SE) of microcellular PI/RGO, PI/MWCNTs and PI/RGO/MWCNTs nanocomposites were 13.7–15.1, 13.0–14.3 and 16.6–18.2dB, respectively. The synergistic effect between RGO and MWCNTs enhanced both the electrical conductivity and EMI shielding performance of the microcellular PI/RGO/MWCNTs nanocomposites. The dominating EMI shielding mechanism for these materials was microwave absorption. While the initial loading of GO and MWCNT was 8wt%, the microcellular PI/RGO/MWCNTs nanocomposite (500μm thickness) had extremely high specific EMI SE value of 755–823dB·cm2·g−1. Its thermal stability was also obviously improved, the 5% weight loss temperature in nitrogen was 548°C. In addition, it also possessed a high Young’s modulus of 789MPa.