Solvent-induced Crystallization Research Articles

A new crystal form of Hx2TNBI·2H2O through solvent-induced crystallization

Polymorphism is universal in energetic materials (EMs), which is originated from the differences of molecular conformers and stacking mode. The polymorphic transition may lead to the change of crystal structure and properties of EMs. In this work, β-Hx2TNBI·2H2O (β-1) was successfully synthesized through solvent-induced conformational transition of Hx2TNBI·2H2O. From the perspective of quantum chemistry and molecular dynamics, the crystal stacking changes caused by different molecular conformations are discussed in detail, which leads to the properties difference of EMs. The results show that β-1 featured wave-like crystal stacking, making it less sensitive to external mechanical stimuli than α-Hx2TNBI·2H2O (α-1) (α-1: IS > 6 J, FS > 288 N; β-1: IS > 20 J, FS > 360 N). α-1 featured better the aromaticity, which gives it higher thermal stability than β-1 (α-1: Td = 186 °C; β-1: Td = 146 °C). Simultaneously, compared with β-1, α-1 has higher crystal density and detonation performance. This work provides a new and effective way to change the safety of EMs.

Upcycling spent lithium-ion battery cathodes into cobalt-polyphenol networks by DES dissolution and solvent-induced crystallization

A strategy is proposed to induce the self-assembly process of metal ions with polyphenol in deep eutectic solvents (DESs) for the generation of metal-polyphenol network particles (MPNPs).

Tough and lightweight polyimide/cellulose nanofiber aerogels with hierarchical porous structures as an efficient air purifier

With the increasing severity of health problems caused by air pollution, the demand for high-quality air filtration aerogel materials is increasing. Aerogels with a hierarchical porous structure are beneficial for filtering dangerous small-sized particles, especially for the removal of nanoparticles in the air. In this study, composite nanofibrous aerogels with clear hierarchical porous structures were successfully prepared by the introduction of cellulose nanofibers (CNF) into a polyimide nanofiber (PINF) system by self-assembly and freeze-drying technology. Notably, solvent-induced crystallization was used to improve the pore structures of the nanofiber aerogels. The resulting aerogel samples exhibited an extremely low density and a hierarchical porous structure. More importantly, the samples exhibited high filtration efficiency (99.69% for PM0.3) and a low pressure drop (230 Pa) at a lower base weight, rendering them promising air filtration materials for the applications in more complex environments.

Effect of crystallinity on the migration of plastic additives from polylactic acid-based food contact plastics

The dependence of swelling and migration on polymer crystallinity was investigated in the case of polylactic acid (PLA)-based plastics. Migration and swelling kinetic experiments were performed at two different temperatures, using plasticized/non-plasticized and annealed/unannealed PLA test specimens. Both swelling and migration proved to be inhibited by the presence of polymer crystals. Crystallization induced clear differences in migration at 40 °C contact temperature, which got more pronounced with the increasing molecular weight (Mw) of additives. At 60 °C the differences diminished, except for Irgafos 168, possibly because of the formation of an inclusion complex type structure. Consequently, to lessen migration, the application of crystallized PLA and high Mw additives in food packaging industry is advantageous. The solvent-induced crystallization of PLA in ethanol 95 v/v% was also confirmed, therefore this alternative food simulant should be used with restrictions in the migration testing of PLA-based plastics.

Atomically precise chiral silver clusters based on non-chiral ligands for acid/base stimulated luminescence response.

Chiral metal nanoclusters synthesized by non-chiral ligands are usually in the form of racemates. Thus, resolving racemic compounds continues to be a great challenge. Herein, we report a case of the racemic compound hexanuclear silver cluster (Ag6-Rac) protected by the non-chiral sulfhydryl ligand sodium 1H-1,2,3-triazole-5-thiolate (SHTT) and 2,6-bis(diphenylphosphino)pyridine (dpppy). The homochiral clusters in Ag6-Rac are able to spontaneously crystallize and undergo chiral resolution to obtain a racemic conglomerate (Ag6-S/Ag6-R) by solvent-induced crystallization. Interestingly, the Ag6-Rac clusters exhibit strong luminescence in solid and solution, which can respond to trifluoroacetic acid (TFA) and reversible cycling over five times using diethylamine (DEA). This work provides a new research model for resolving racemic clusters and constructing stimulus-responsive clusters.

Solvent-induced crystallization and phase-transition phenomena in syndiotactic polystyrene and its relatives

The studies of time-dependent structural changes in the solvent-induced crystallization and phase transition phenomena have been reviewed by focusing mainly on syndiotactic polystyrene (SPS) and its relatives having the functional groups on the phenyl rings. The time-resolved measurement of X-ray diffraction and vibrational spectra has revealed the structural evolution process in the solvent-induced crystallization of SPS, which depends on the type (polarity, bulkiness, etc.) of the solvent molecules. The heating of the SPS-solvent complexes causes the complicated phase transitions from theδform (complex) to theγform and to theα(orβ) form. The introduction of such a polar functional group as OCH3or halogen units on the phenyl rings enhances the interactions between the SPS and the solvent, the strength of which depends on the substitution position of the OCH3units on the phenyl ring. For example, the ortho- or para-substitution dissolves the sample quite easily at room temperature, while the meta-substitution makes it possible to create the solvent complexes. The discussion has been made for the structural relation before and after the formation of the solvent-complexes.

Hydrolytic degradation mechanism of modified polylactic acid in different food simulants

Hydrolytic degradation of non-compatibilized and compatibilized toughened polylactic acid (PLA) blends produced with polyolefin elastomer (POE) at 5 and 15 wt percent were examined in distilled water and both 50 % and 95 % ethanol solutions at 40 °C for up to 180 days and were compared with pure PLA. The change in swelling degree, molecular weight, crystallinity, thermal properties, and lactic acid (LA) release were monitored. All samples demonstrated higher hydrolytic degradation in contact with 50 % ethanol in comparison to 95 % ethanol and distilled water, which were in conformity with the results of the LA release during the exposure time. During the exposure period, the crystallinity degree of samples increased specifically in contact with 50 % ethanol solution. that could be due to amorphous regions degradation and solvent-induced crystallization. Blending PLA with POE and compatibilizing with polyolefin elastomer-graft-maleic anhydride (POE-g-MA) resulted in lower hydrolytic degradation and subsequently restricted polymer chain mobility as highlighted by glass transition temperature and the crystallization change.

Solvent-Induced Crystallization Method for High-Performance and Long-Term Stability Flexible Perovskite Photodetectors

Herein, we report a novel solvent-induced fabrication method to synthesize a perovskite thin film on flexible substrates. The high-quality CH3NH3PbI3 (MAPbI3) thin film is successfully fabricated, which is applied to prepare the stable flexible photodetector (PD). Compared with the reported results, this method achieved a low-temperature and low-cost perovskite thin film fabrication process on a flexible substrate. The constructed MAPbI3 layer possesses the advantages of being highly crystalline, uniform, and compact in a large area. The flexible PD based on the as-prepared perovskite thin film exhibits excellent performance and long-term stability. The EQE and R of the flexible PDs reached 8 × 102% and 3.6 A/W, respectively. At the same time, the flexible PDs still showed superior stability and high performance after 15 days of continuous working. The presented high-quality perovskite thin-film fabrication method and high-performance flexible perovskite PDs are expected for application in the development of novel optoelectronic devices.

Nanofibrous, hierarchically porous poly(ether sulfone) xerogels templated from gel emulsions for removing organic vapors and particulate matters

Emulsion-templated method is an emerging technology for the fabrication of porous polymers, but the conventionally chemical crosslinking still restricts the popularization. Based on the physical gelation, emulsion-templated porous polymers (polyHIPEs) can be possible to break the bottleneck. This work reports gel emulsions and corresponding xerogels solidified by solvent-induced crystallization of the poly(ether sulfone) for removing organic vapors and particulate matters. Gel emulsions showed wide adaptability in the dispersed phase fraction (from 5% to 80%) and high stability over 5 months without change in appearance. Emulsion-templated xerogels were obtained from gel emulsions by atmospheric drying, which represents a facile method for the preparation of emulsion-templated porous polymers. The resulting xerogels exhibited controllable external shapes, low shrinkages, emulsion-templated voids, nanofibrous structures, hierarchically interconnecting pores, robust mechanical properties and the reshape ability, which are much more advantageous than conventional polyHIPEs. The xerogels exhibited high adsorption capacities to the organic solvent vapors from air (1.21 mL g−1 for toluene and 1.45 mL g−1 for chloroform), high reusability (without deterioration after five adsorption-desorption cycles) and enhanced adsorption rate imposed by emulsion-templated structures. Moreover, the xerogels captured a mass of particulate matters from air with high durability. The wide adaptability, facile preparation, unique morphology and high capacity and stability to capture solvent vapors and particulate matters enable the current xerogels to be excellent candidates for cleaning air.

Fabrication of mesoporous crystalline microparticles of poly(ether sulfone) via solvent-induced crystallization

Mesoporous polymer microparticles are promising for energy, environmental, and biomedical applications. A linear polymer microparticle is desirable from the perspective of polymer recycling. In this study, mesoporous crystalline microparticles of a commercially available high-performance polymer, poly(ether sulfone) (PES), were prepared. Solvent-induced crystallization of PES in nitrobenzene resulted in nearly spherical microparticles with an average size of 5 μm and narrow size distribution. The microstructure and mesoporosity of the microparticles were characterized with scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, and nitrogen adsorption/desorption, which gave a pore size distribution peaking at 7 nm with a porosity of 0.44. Fourier-transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis confirmed the cocrystal of PES and nitrobenzene. The formation mechanism of the PES microparticles was elucidated based on the theory of polymer spherulite formation. This study gives an insight on solvent-induced crystallization of rigid high- T g polymers useful for the mesoporous polymer particle fabrication. • Solvent-induced crystallization of poly(ether sulfone) (PES) was investigated. • Nitrobenzene induces crystallization of PES and forms a polymer-solvent cocrystal. • The cocrystal spontaneously makes uniform microparticles with 5 μm diameter. • The microparticles gives large mesoporosity with specific surface area of 200 m 2 /g. • The method is promising as a facile preparation of polymer microparticles.

Facile Preparation of Hydrophobic PET Surfaces by Solvent Induced Crystallization

In this work, Polyethylene terephthalate (PET), one of the most widely consumed polymers, has been used as starting material for the development of non-stick surfaces through a fast, simple and scalable method based on solvent-induced crystallization to generate roughness, followed by a fluorination step. Several solvents were tested, among which dichloromethane was chosen because it gives rise to the formation of a particulate layer with rough topography. This particulate layer was covered by a polymer thin and smooth skin that must be removed to leave the rough layer as surface. The skin has been successfully removed by two strategies based on mechanical and chemical removal, each strategy producing different surface properties. A final treatment with a diluted solution of a fluorinated silane showed that it is possible to obtain PET surfaces with a water contact angle higher than 150° and low water adhesion. The reason behind this behavior is the development of a hierarchical rough profile during the induced polymer crystallization process. These surfaces were characterized by XRD, FTIR and DSC to monitor solvent induced crystallization. Topography was studied by SEM and optical profilometry. Wetting behavior was studied by measuring the contact angles and hysteresis.

Porous Silk Scaffold Derived from Formic Acid: Characterization and Biocompatibility

Silk porous scaffold possesses 3D space structure for cell adhesion and tissue growth and demonstrates promising applications in biomedical engineering. In this study, a porous silk scaffold was prepared from formic acid, and its morphology, structure, mechanical properties, and biocompatibility were characterized. The preparation process involved silk dissolution in formic acid and salt leaching in water, avoiding widely used organic solvent-induced crystallization including methanol or ethanol. The resulting porous silk scaffolds showed good pore structure, stable silk II crystalline structure, good mechanical properties, and enhanced cell biocompatibility. Therefore, these findings demonstrate that porous silk scaffold derived from formic acid has great potential applications as 3D scaffold for cell culture and tissue repair.

Durable fluorinated-SiO2/epoxy superhydrophobic coatings on polycarbonate with strong interfacial adhesion enhanced by solvent-induced crystallization

In this study, we designed mechanically and chemically robust superhydrophobic coatings with strong interfacial adhesion with polycarbonate (PC) substrates by dripping an acetone solution containing fluorinated silica (F-SiO2) nanoparticles and epoxy resin. It was found that the acetone-induced crystallization and roughening of PC leading to a firm bonding of superhydrophobic F-SiO2/epoxy coatings onto the surface of PC substrates. The coatings prepared under the optimal condition showed an excellent superhydrophobic property with a water contact angle (CA) larger than 160° and a sliding angle (SA) smaller than 2°, together with superior anti-icing performance. The coatings retained their excellent superhydrophobicity after various external mechanical damages (such as tape adhesion, knife scratch, finger wiping, and sandpaper wear) and in different corrosive environments (acidic, alkaline, and salinity solutions). Furthermore, the new coatings exhibited outstanding ability against photo-oxidative and hygrothermal aging. Therefore, it is believed that the superhydrophobic coatings prepared have the potential to satisfy the imperative requirements in many harsh outdoor applications based on PC materials.

Temperature and Time Dependence of the Solvent-Induced Crystallization of Poly(l-lactide).

The role of organic solvents in governing the crystallization and morphology of semi-crystalline poly-l-lactide (PLLA) sheets was systematically investigated. Three different organic solvents; ethyl acetate (EA), o-dichlorobenzene (ODCB), and nitrobenzene (NB), with a solubility parameter analogous to PLLA and with a high capability of swelling, were chosen. It has been witnessed that the degree of crystallization and crystal morphology depends highly on the degree of swelling and evaporation rate of the solvent. Besides, the temperature and time of treatment played a significant role in the crystallization of polymers. The effect of different solvents and curing times are reflected by the measured X-ray diffraction (XRD) peaks and the differences are best shown by the unit cell size. The largest variation is observed along the c-axis, indicating shorter bonds, thus, showing better conformation after NB and ODCB treatment. The percentage of crystallinity calculated using the classical relative crystallinity index of XRD shows closer values to those calculated with differential scanning calorimetry (DSC) data, but a huge variation is observed while using the LeBail deconvolution method. The strong birefringence of polarised optical micrograph (POM) and the crystal morphology of scanning electron micrograph (SEM) also evidenced the orientation of polymer crystallites and increased crystallinity after solvent-supported heat treatment.

A mechanistic investigation of the directional entrapping modification on the semicrystalline polypropylene surface

AbstractThis article concerns a detailed mechanistic investigation of the directional entrapping modification on the polypropylene (PP) surface, when stearyl‐alcohol poly(ethylene oxide) ether (AEO) was applied as the modifier. The results of swelling degree and contact angle are found to exhibit similar evolutions as functions of swelling temperatures and swelling time, revealing that the modifier implantation is closely related to the swelling level of swollen PP. A solvent‐induced crystallization (SINC) and a subsequent crystalline collapse are indicated to occur during surface swelling. Both the amorphous regions on PP surfaces and the microvoids induced by SINC are suggested to contribute to surface swelling and to provide embedding sites for modifier implantation. XRD and DSC analyses reveal a considerably homogeneous distribution of the stearyl segments of AEO in modified surfaces and confirm that the stearyl chain is partially compatible with PP. A thermodynamically stable phase‐mixed structure of modified PP is proposed. The mechanistic investigation gives comprehensive insights into the directional entrapping modification and is significant for the extensive applications of the entrapping method for semicrystalline polymers.

Effects of thermal annealing and solvent-induced crystallization on the structure and properties of poly(lactic acid) microfibres produced by high-speed electrospinning

This research concentrates on the marked discrepancies in the crystalline structure of poly(lactic acid) (PLA) nano- and microfibres, achieved by different annealing strategies. PLA nonwoven mats were produced by high-speed electrospinning. The high-speed production technique allowed the manufacturing of PLA microfibres with diameters of 0.25–8.50 µm with a relatively high yield of 40 g h−1. The crystalline content of the inherently highly amorphous microfibres was increased by two methods; thermal annealing in an oven at 85 °C was compared to immersion in absolute ethanol at 40 °C. The morphology of the fibres was examined by scanning electron microscopy; crystalline forms and thermal properties were assessed using X-ray diffractometry, Raman spectrometry, differential scanning calorimetry (DSC) as well as modulated DSC. As a consequence of 45-min heat treatment, the crystalline fraction increased up to 26%, while solution treatment resulted in 33% crystallinity. It was found that only disordered α′ crystals are formed during the conventional heat treatment; however, the ethanol-induced crystallization favours the formation of the ordered α polymorph. In connection with the different crystalline structures, noticeable changes in the macroscopic properties such as heat resistance and mechanical properties were evinced by localized thermomechanical analysis and static tensile test, respectively.

Morphology, Structure, and Properties of Conductive Polylactide Fibers Prepared Using Polyvinyl Acetate and Multiwalled Carbon Nanotubes

Two kinds of conductive polylactide fibers—polylactide pre-oriented yarns (PLA-POY) and PLA-drawn textured yarns (PLA-DTY) are prepared by coating method using ethyl acetate as solvent, multiwalled carbon nanotubes (MWCNTs) as conductive filler, and polyvinyl acetate (PVAc) as dispersing agent and coating agent. The PLA fibers are characterized by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), resistance meter, and tensile test. The results show that PLA-POY and PLA-DTY have been coated successfully by PVAc and MWCNTs. After PLA-POY fibers are treated by ethyl acetate, the highly porous structures form because of swelling and the subsequent solvent-induced crystallization of PLA-POY fibers with low crystallinity. This causes the tensile force to decrease. However, PVAc can improve the tensile force of the treated PLA-POY fibers. For PLA-DTY fibers, the effect of ethyl acetate on surface morphology is small. Therefore, the treated PLA-DTY fibers own higher tensile properties than original PLA-DTY fibers due to the existence of PVAc. With the increase of PVAc and MWCNTs, the conductive properties of the PLA fibers will increase. The electrical conductivity of PLA-POY and PLA-DTY fibers can reach 0.53 and 0.13 µs/cm, respectively.

Nanoporous-crystalline films of PPO with parallel and perpendicular polymer chain orientations

Oriented nanoporous crystalline (NC) phases of poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) are for the first time described. In particular, PPO films with orientations of crystalline chain axes preferentially parallel (c//) or perpendicular (c⊥) to the film plane are obtained by suitable procedures of solution casting or of solvent-induced crystallization, respectively. 2D-WAXD patterns of NC PPO films, exhibiting c// and c⊥ orientations, have allowed indexing of reflections and establishing unit cell parameters of NC modifications (e.g., for the NC modification from carvone an orthorhombic unit cell with a = 1.97 nm; b = 1.24 nm; c = 0.53 nm). FTIR spectra of NC PPO films exhibiting c// or c⊥ orientations, have allowed establishing the direction of transition moment vectors of polymer chain vibrational peaks. NC films with c// and c⊥ orientations, are expected to allow control of guest diffusivities as well as orientation of active guest molecules.

Revealing non-crystalline polymer superstructures within electrospun fibers through solvent-induced phase rearrangements.

The design of nanofibers for biomedical applications requires a deep understanding of the fiber formation process and the resulting internal structure. In this regard, non-crystalline, mesomorphic structures play a central role in the processing of many polymers as precursors in the formation of crystalline superstructures (e.g. shish-kebab) and influence strongly the physical properties of polymers with a low degree of crystallinity. Yet, our ability to probe these relevant features is often greatly limited by their low contrast differences with the amorphous phase. We present an approach to reveal the organization of the mesomorphic superstructures within such polymeric materials, on the example of electrospun poly(l-lactide) nanofibers. Based on solvent-induced crystallization, this method employs fine-tuned solvent/non-solvent systems to enhance the contrast of these structural features by selectively triggering and controlling reorganization of the phases. Hereby, the mesomorphic regions are transformed into an α-crystalline phase, while the nanoscale spatial arrangement of the underlying superstructures is preserved. Combined with X-ray analytical techniques and electron microscopy, our approach provides detailed insights into the nanofiber's inner architecture, allowing for its direct visualization. Thereby, the influence of electrospinning parameters on the fiber formation process is explained as well as the impact of the resulting non-crystalline superstructures on single fiber mechanical properties. The method can be applied to comparable polymers for the development of materials with controlled, tailored properties.

Highly Hydrophobic Conductive Polyester Fabric Based on Homogeneous Coating Surface Treatment

ABSTRACTA highly hydrophobic conductive polyester (PET-HE) fabric was prepared by a simple two-steps method. Firstly, homogeneous coating (the mixture of PET and carbon black (CB)) was uniformly coated on the PET fabric, which through curing in water coagulation bath and electrically conductive (PET-E) fabric was prepared. Then the solvent-induced crystallization process was adopted to PET-E fabric to endow the hydrophobic property. Investigations showed that PET-HE treated fabrics exhibited better hydrophobic and conductivity when the content of PET is 9wt% and the content of CB is the range of 8wt%-10wt%. The prepared polyester fabric proved to have such features as WCA was about 145°and surface resistance was about 300 Ω.GRAPHICAL ABSTRACT