Simple Solvent Exchange Research Articles

Mechanically robust and superhydrophobic aerogels of poly(ether ether ketone)

The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in dichloroacetic acid (DCA) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in DCA up to a weight fraction of 25 wt%. For PEEK solutions within this concentration range, the time required for gelation decreased with increasing temperature up to 80 °C, above which the gelation time increased considerably. Highly porous aerogels of PEEK were prepared through simple solvent exchange and lyophilization of the PEEK/DCA gels. Aerogel density was controlled by varying the PEEK concentration in solution, and shown to be unaffected by PEEK molecular weight (MW). Annealing PEEK aerogels prepared from relatively low concentration gels resulted in aerogels of increased density. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density regardless of preparation method (concentration variation or annealing parameters). Additionally, density-matched aerogels from various MW PEEK showed a correlation between increasing MW and increasing compressive modulus. Contact angle and contact angle hysteresis revealed that PEEK aerogels have a high contact angle, suggesting superhydrophobicity, that decreases with increasing density and a very low contact angle hysteresis that increases with increasing density.

Reagent-free continuous thermal tert-butyl ester deprotection

Continuous processing enables the use of non-standard reaction conditions such as high temperatures and pressures while in the liquid phase. This expands the chemist’s toolbox and can enable previously unthinkable chemistry to proceed with ease. For a series of amphoteric amino acid derivatives, we have demonstrated the ability to hydrolyze the tert-butyl ester functionality in protic solvent systems. Using a continuous plug flow reactor at 120–240°C and 15–40min reaction times, no pH modification or additional reagents are needed to achieve the desired transformation. The method was then expanded to encompass a variety of more challenging substrates to test selectivity and racemization potential. The acid products were generally isolated as crystalline solids by simple solvent exchange after the deprotection reaction in good to high yield and purity.

2-Hydroxyethylcellulose and Amphiphilic Block Polymer Conjugates Form Mechanically Tunable and Nonswellable Hydrogels

Herein, we report a family of mechanically tunable, nonswellable hydrogels that are based on a 2-hydroxyethylcellulose (HEC) scaffold grafted with amphiphilic diblock copolymers. Poly[(oligo(ethylene glycol)methyl ether methacrylate]-b-poly(methyl methacrylate) (POEGMA-b-PMMA) diblock copolymers of different compositions were created via RAFT polymerization using an alkyne terminated macro chain transfer agent (CTA). 2-Hydroxyethylcellulose (HEC) was modified with azide groups and the diblock copolymers were attached to the backbone via the copper-catalyzed click reaction to yield HEC-g-(POEGMA-b-PMMA) graft terpolymers. The resulting conjugates were soluble in DMF and able to form hydrogels upon simple solvent exchange in water. By increasing the concentration of the conjugates in DMF, the storage moduli of the hydrogels increased and the pore size in the gel decreased. After hydrogel formation, the structures were also found to be nonswellable (no macroscopic volume change upon incubation in water), which is an important feature for retaining size and mechanical integrity of the gels over time. Moreover, these materials were able to be electrospun into fibers that, upon hydration, formed fibrous hydrogel structures. The nonswellable and tunable mechanical properties of these materials imply great potential for a variety of applications such as personal care, active delivery, and tissue engineering.

A slurry compounding route to disperse graphene oxide in rubber

In polymer composites, filler dispersion and interfacial adhesion are two critical factors in determining their properties. To date, it still remains a challenge to achieve uniform filler dispersion and implement interfacial tailoring in rubber composites by direct melt mixing. In this study, we prepared graphene oxide (GO) slurry in acetone via a simple solvent exchange method and modified GO in the slurry. Then the slurry was compounded with nitrile rubber on two-roll mill to produce composites. Morphological and interfacial structural studies revealed that GO was dispersed at nano-scale in the composites, and the dispersion of GO and interfacial adhesion were further improved upon the modification of GO with silane. Consequently, the mechanical properties of the composites were remarkably enhanced by adding GO.

Biomass-derived dendritic-like porous carbon aerogels for supercapacitors

Three-dimensional (3D) dendritic-like hierarchical porous carbon areogels (PCAs) have been fabricated via a simple and efficient solvent exchange method followed by an activation process. The natural and renewable biomass material, leonardite fulvic acid (LFA) is used as the carbon source. The hierarchical porous structures are composed of numerous nanospheres with interconnected 3D carbon architectures which are in favor of enhancing the electrical conductivity and facilitating ion transport by providing small resistances and short diffusion pathways. The resultant PCAs are advantageous as electrodes for electrochemical energy storage. For example, the PCAs2 sample exhibits a superior high specific capacitance of 368Fg−1 at a current density of 0.05Ag−1 in 6M KOH electrolyte, which can still remain 228Fg−1 when the current density increases to 100Ag−1. The sample also has outstanding cycling stability with capacitance retention of 98.4% after 10,000 cycles. Remarkably, it is shown that the PCAs2 sample exhibits outstanding electrochemical performance in an organic electrolyte as well. It has an energy density of 43.50Whkg−1 at a power density of 33.85Wkg−1 and still maintains 23.25Whkg−1 at a power density of 5.89kWkg−1. This suggests that the 3D hierarchical PCAs should be a competitive and promising supercapacitor electrode material.

Structural diversity in metal–organic nanoparticles based on iron isopropoxide treated lignin

The magnetic nature of iron-containing nanoparticles enables multiple high-end applications.

Solvent Exchange to Exfoliate Graphene Oxides into Epoxy with Improved Mechanical and Thermal Properties

The dispersion and exfoliation of graphene oxides in polymer matrix remains a challenge for graphene oxides based epoxy nanocomposites fabrication. In the present paper, we reported a simple and facile solvent exchange technique to successfully transfer graphene oxides (GOs) from aqueous solution to ethanol. In addition, we found that GO dispersion in epoxy resins was affected by the curing agents. Good dispersion of GOs in epoxy resin together with enhanced thermal and mechanical properties were observed when epoxy was cured with aliphatic curing agents. For aromatic curing agent, high loading of GOs leaded to GOs aggregation, but well dispersed GOs was observed at low loading of GOs. Especially, a 12 °C increase of glass transition temperature of the epoxy resin was observed with only 0.1 wt% GOs was added to the epoxy resin.

Isotonic sodium bicarbonate-triggered emodin release from borate stabilized emodin nanoparticles-loaded polymeric microgel films.

Hydrosoluble emodin-borate (EmB) nanoparticles (NPs) were fabricated by a simple solvent exchange method to address emodin's poor water solubility. As the result, negative charges were introduced in the surface of EmB NPs. In addition, layer-by-layer assembled multilayer films containing cation-rich polymeric microgels (named PAHD) and sodium carboxymethyl cellulose (NaCMC) were employed as drug carrier. Anionic EmB can be loaded into the PAHD/CMC multilayer films. The influences of various experimental parameters on cargo capacity of the PAHD/CMC film were studied in detail. The loaded EmB can be released in the form of emodin molecule in presence of isotonic sodium bicarbonate (ISB) solution. Gratifyingly, EmB did not almost release in presence of water, PBS buffer solution, 0.9% normal saline, and 5% glucose solution.

Lysozyme binding to tethered bilayer lipid membranes prepared by rapid solvent exchange and vesicle fusion methods

Tethered bilayer lipid membranes (tBLMs) are important tools for studying protein-lipid interactions. The widely used methodology for the preparation of these membranes is the fusion of phospholipid vesicles from an aqueous medium onto an anchored phospholipid layer. The preparation of phospholipid vesicles is a long and tedious procedure. There is another simple method, rapid solvent exchange, for preparing lipid membranes. However, there is a lack of information on the effects of the preparation method of tBLMs on their interactions with proteins. Therefore, we present in this paper a comparative study on the binding of lysozyme onto tBLMs prepared by the abovementioned methods. The prepared tBLMs have either zwitterionic or anionic characteristics. The results show that lysozyme binding onto the prepared tBLMs is unaffected by the preparation method of the tBLMs, suggesting that the tedious fusion method might be replaced by the simple rapid solvent exchange method without altering the level of protein-lipid interactions.

A generic solvent exchange method to disperse MoS2 in organic solvents to ease the solution process

A simple solvent exchange method is presented to suspend monolayers of MoS2 in various organic solvents, which facilitates the phase transformation of MoS2 and preparation of MoS2-filled polymer composites straightforwardly in organic solvents.

A stable silicon/graphene composite using solvent exchange method as anode material for lithium ion batteries

Current research has demonstrated the combination of the high theoretical capacity offered by silicon nanoparticles (Si NPs) with graphene-based matrices in order to produce a high energy density and stable lithium ion battery system. However, Si NPs do not mix well with graphene oxide aqueous suspensions and thus create severe segregation of the materials. In this letter, we propose a simple, cost-effective and commercially-viable solvent exchange process to improve the interaction of the Si NPs in poor solvent environments such as in aqueous media. Using N-methylpyrrolidone (NMP) to disperse the Si NPs and followed by a solvent exchange process, we are able to improve the dispersion and stability of Si NPs in aqueous graphene oxide aqueous suspension. Consequently, this also improves the output and the stability of the lithium ion battery using the aforementioned composite system.

Microbelts and flower-like particles of hexakis-(4-(5-styryl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene: self-assembly and photoreaction

Recently, we have reported the self-assembly of nanobelts and microbelts originating from the organic–inorganic hybrid molecule hexakis-(4-(5-phenyl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene (HPCP) by a simple solution method. Inspired by [2 + 2] photodimerization, our group has further attempted to verify the proposed self-assembly mechanism of oxadiazole-containing cyclotriphosphazene by solid-state photochemical reaction. We modified the molecular structure of HPCP, introducing a vinyl group into it to obtain a new oxadiazole-containing cyclotriphosphazene, hexakis-(4-(5-styryl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene (HSCP). The microbelts and flower-like particles of HSCP were self-assembled through a simple solvent exchange process by exploiting the π–π interactions between neighboring HSCP molecules as the driving force. The as-prepared materials were capable of [2 + 2] photodimerization and shape maintenance, as well as forming insoluble fluorescent materials. The self-aggregating and photoreaction properties of HSCP were characterized by UV-vis, FESEM, TEM, 1H-NMR, etc.

Strong and conductive polybenzimidazole composites with high graphene contents

Graphene has been considered as an ideal reinforcement agent for polymer composites for a long time, however, strong and highly conductive composites have rarely been reported because of the poor dispersion that results when the loading of graphene is increased to a certain level. In this paper, by combining simple solvent-exchange and solution-casting methods, graphene oxide (GO)/polybenzimidazole composites with high GO contents (up to 40 wt%) are initially prepared. SEM and XRD results demonstrate the good dispersion state and alignment of GO in the composites. Tensile testing reveals that the modulus of the composite increases with the addition of GO as a result of the homogenous dispersion and strong interfacial interactions, while the strength shows a maximum value in the composite with 20 wt% GO. To make the composites conductive, chemical treatment with hydroiodic acid or thermal annealing at 220 °C were carried out on the samples. It was found that the chemical reduction is more effective in improving the conductivities of the composites, but slightly detrimental to the mechanical properties. Although the thermally treated composites show relatively lower conductivities, they possess a higher modulus and strength than the corresponding unreduced and chemically reduced ones. By these efforts, composites with diverse properties, but which are generally mechanically strong and conductive, are fabricated. It is expected that these high-performance composites could find applications in a broad range of technical fields.

Gold Nanoparticle Deposition on Silica Nanohelices: A New Controllable 3D Substrate in Aqueous Suspension for Optical Sensing

We describe new methods to prepare gold nanoparticle/silica nanohelix hybrid nanostructures which form a 3D network in the aqueous phase. Nanometric silica helices and tubules obtained by sol–gel polycondensation on organic templates of self-assembled amphiphilic molecules were further functionalized with (3-aminopropyl)triethoxysilane (APTES) or (3-mercaptopropyl)triethoxysilane (MPTES). These helices interact strongly with gold nanoparticles (GNPs) of various diameters (1–15 nm). Small GNPs (1–2 nm) at the surface of silica nanohelices grew to about 5 nm when stored in the appropriate organic solvent, whereas this growth process was not observed in water, allowing the size of GNPs at the surface of silica to be controlled by a simple solvent exchange. Larger GNPs (more than 10 nm) at the surface of nano hybrid fibers were used to produce surface enhanced raman scattering (SERS) using benzenthiol as a probe. This provides a novel sustainable approach for designing nanohybrid systems with photonic applications such as ultrasensitive chemical and biological sensors using a simple aqueous suspension of a 3D network of nanohelices.

Mesostructured Block Copolymer Nanoparticles: Versatile Templates for Hybrid Inorganic/Organic Nanostructures.

We present a versatile strategy to prepare a range of nanostructured poly(styrene)-block-poly(2-vinyl pyridine) copolymer particles with tunable interior morphology and controlled size by a simple solvent exchange procedure. A key feature of this strategy is the use of functional block copolymers incorporating reactive pyridyl moieties which allow the absorption of metal salts and other inorganic precursors to be directed. Upon reduction of the metal salts, well-defined hybrid metal nanoparticle arrays could be prepared, while the use of oxide precursors followed by calcination permits the synthesis of silica and titania particles. In both cases, ordered morphologies templated by the original block copolymer domains were obtained.

New hierarchically porous titania monoliths for chromatographic separation media

Separation media based on hierarchically porous titania (TiO(2)) monoliths for high-performance liquid chromatography (HPLC) have been successfully fabricated by the sol-gel process of titanium alkoxide in a mild condition utilizing a chelating agent and mineral salt. The as-gelled TiO(2) monoliths were subjected to a simple solvent exchange process from ethanol (EtOH) to H(2)O followed by drying and calcination. The resultant monolithic TiO(2) columns consist of anatase crystallites with the typical specific surface area of more than 200 m(2)/g. The resultant monolithic TiO(2) column calcined at 200 and 400°C exhibited a good separation performance for organophosphates as well as for polar benzene derivatives in the normal-phase mode.

Dispersion of graphene in ethanol using a simple solvent exchange method

A dispersion of graphene in ethanol was achieved using solvent exchange from N-methyl-2-pyrrolidone (NMP) that enables broader application of dispersed graphene.

Solvent exchange using hollow fiber prior to separation and determination of some antioxidants by high performance liquid chromatography

This study presents a simple and rapid solvent exchange procedure using a hollow fiber. Antioxidants (Irganox 1010, Irganox 1076 and Irgafos 168) and solvents such as tetrahydrofuran (THF), carbon tetrachloride and toluene were selected as model compounds and sample solvents, respectively. After injection of the sample solution into the hollow fiber and solvent evaporation, the precipitated analytes in lumen and pores of the fiber were washed with methanol (the mobile phase for separation and determination by HPLC-diode array detection) and good chromatographic peaks were obtained. The effect of different parameters such as fiber length, volumes of sample and washing solvents were investigated and the optimum conditions were selected. The repeatability of the method was tested and it was found that the relative standard deviation (R.S.D.) was less than 10% for all analytes. Also enrichment factors of 3.03, 2.21 and 1.19 times were obtained for Irganox 1010, Irganox 1076 and Irgafos 168, respectively, when 200 μL sample and 50 μL methanol (washing solvent) were used.

Kinetics and mechanism of substitution reactions of (dimethylsulfoxide)pentaamminecobalt(III) ion in dimethylsulfoxide solvent: complications due to redox and conjugate base processes

Simple anation and solvent exchange reactions of Co(NH3)5DMSO3+ in DMSO are accompanied by reactions in which the conjugate base of this complex undergoes either internal redox to cobalt(II) or relatively rapid substitution. These conjugate base reactions are eliminated by addition of H+, although a minor redox pathway persists within ion pairs of Co(NH3)5DMSO3+ with chloride or bromide. The latter pathway is evidently not mechanistically related to the solvent exchange or anation reactions, which proceed by dissociative interchange (Id) according to the activation parameters (volume of activation = +10 cm3 mol−1 for DMSO exchange; enthalpy of activation = 123, 121, and ∼126 kJ mol−1 for DMSO exchange and bromide and chloride anation respectively). Enthalpies of activation for solvent exchange and for the limiting anation rate are shown to be better criteria of mechanism than the corresponding rate coefficients.