Low Viscosity Solvents Research Articles

Chemical dual-site capture of NH3 by unprecedentedly low-viscosity deep eutectic solvents.

It is unprecedentedly found that ethylamine hydrochloride (EaCl) and phenol (PhOH) can form a new type of deep eutectic solvent (DES) with quite low viscosity. The strong hydrogen-bond donating abilities of EaCl and PhOH provide two active sites for robust interaction with NH3. Thus, the capacities of EaCl + PhOH DESs for NH3 absorption are notably high even at low pressures.

Restriction of Flip-flop Motion as a Mechanism for Aggregation-Induced Emission.

Although the restriction of intramolecular motion (RIM) has been accepted as a general working mechanism for the aggregation-induced emission (AIE) phenomenon, some new mechanisms, such as suppression of Kasha's rule (SOKR), has also been proposed to explain the AIE of boron difluorohydrazone (BODIHY) derivatives. However, the understanding of the relation and difference between RIM and SOKR mechanisms is limited. To address this issue, we performed a theoretical study on the excited state decay of a series of BODIHY derivatives. Surprisingly, we found that the first excited state of BODIHY derivatives is a bright state and contradicts with the SOKR mechanism. Importantly, we proposed a new mechanism, termed as restriction of flip-flop motion, to explain the AIE of BODIHY derivatives. This mechanism involves the formation of an umbrella-like minimal energy conical intersection through flip-flop motion, which is easily accessible in low-viscosity solvents and will be restricted in high-viscosity solvents.

Solvent viscosity induces twisted intramolecular charge transfer state lifetime tunable of Thioflavin-T

Excited-state deactivation dynamics of Thioflavin-T (ThT) in gradual viscosity solvents were investigated. Femtosecond transient absorption spectra and dynamic decay curves both present significant distinction of ThT in different volume ratios binary mixtures solvents. Dynamics fitting lifetime of twisted intramolecular charge transfer (TICT) state is strongly dependent on solvents viscosity. Compared to rotation corresponding time of ThT in low viscosity solvent (0.6 cp) experimentally coincident well with Stokes-Einstein-Debye (SED) equation, the relation between rotation corresponding time and relatively high viscosity (5.9 cp to 1091.2 cp) is more consistent with fractional SED equation. Combined with optimized geometric structures of ThT by density functional theory and time-dependent density functional theory, further understand TICT state lifetime increases with increasing solvents viscosity. Our work provides a comprehensive understanding of fluorescence molecular rotor (FMR) deactivation process in different viscosity solvents and is helpful to design new FMR.

Computational Estimation of Microsecond to Second Atomistic Folding Times.

Despite the development of massively parallel computing hardware including inexpensive graphics processing units (GPUs), it has remained infeasible to simulate the folding of atomistic proteins at room temperature using conventional molecular dynamics (MD) beyond the microsecond scale. Here, we report the folding of atomistic, implicitly solvated protein systems with folding times τ ranging from ∼10 μs to ∼100 ms using the weighted ensemble (WE) strategy in combination with GPU computing. Starting from an initial structure or set of structures, WE organizes an ensemble of GPU-accelerated MD trajectory segments via intermittent pruning and replication events to generate statistically unbiased estimates of rate constants for rare events such as folding; no biasing forces are used. Although the variance among atomistic WE folding runs is significant, multiple independent runs are used to reduce and quantify statistical uncertainty. Folding times are estimated directly from WE probability flux and from history-augmented Markov analysis of the WE data. Three systems were examined: NTL9 at low solvent viscosity (yielding τf = 0.8-9 μs), NTL9 at water-like viscosity (τf = 0.2-2 ms), and Protein G at low viscosity (τf = 3-200 ms). In all cases, the folding time, uncertainty, and ensemble properties could be estimated from WE simulation; for Protein G, this characterization required significantly less overall computing than would be required to observe a single folding event with conventional MD simulations. Our results suggest that the use and calibration of force fields and solvent models for precise estimation of kinetic quantities is becoming feasible.

Development of a New Antimicrobial Photosensitizer from Brominated Carbon Dots: Metal-Enhanced Phosphorescence and Singlet Oxygen Generation

The ever-growing wave of antibiotic resistance in bacterial strains has placed pressure on the scientific community to develop new, diverse methods for fighting deadly microbials. One such method investigated is antimicrobial photodynamic inactivation (aPDI), whereby photosensitizing compounds or particles that commonly occupy a triplet excited state (T1) may generate toxic species, such as reactive oxygen, when irradiated. Subsequently, these short-lived reactive agents inflict critical damage on nearby microbials. Although numerous photosensitizers have been developed and implemented for this purpose, the need remains to develop more photostable and dynamic photosensitizers. Carbon nanodots are well known to exhibit strong photostability and biocompatibility, are easily synthesized, and may undergo simple structural modification. We report a new singlet oxygen photosensitizer from a carbon nanodot scaffold, termed “Heavy Carbon Nanodots.” These luminescent, quasi-spherical nanoparticles are composed of brominated sheets of oxidized graphene that exhibit phosphorescence (T1→S0) when oxygen diffusion is slowed; however, in oxygenated, low viscosity solvents we show singlet oxygen is readily generated by these particles. Further we explore the potential of silver-coated 96-well plates “Quanta Plates™” to plasmon amplify both the phosphorescent signal and singlet oxygen generation, in processes known as metal-enhanced phosphorescence (MEP) and metal-enhanced generation of singlet oxygen (ME1O2) respectively. We report increased detection of triplet emission and increased generation of singlet oxygen by these metal-coated wells. These phenomena are also observed to be pH-dependent. The data reported here provides the foundation for future development of brominated carbon nanodots as novel agents for antimicrobial photodynamic inactivation. ∗all correspondence: [email protected]

Fabrication of nanorods colloids of copper hexadecafluorophthalocyanine by nanosecond-pulse laser fragmentation in organic solvents

Laser fragmentation in liquids is one of the modern techniques to prepare organic nanoparticles. Here, we reported the fabrication of copper hexadecafluorophthalocyanine (F16CuPc) nanorods in several organic solvents: methanol, ethanol, 2-propanol, and ethyl acetate. A mixture of F16CuPc microcrystals (several-μm size) and a poor solvent was exposed to nanosecond Nd3+:YAG laser pulses at the 140 mJ/cm2 for 10 min, and the sphere-like nanoparticles colloid having a mean diameter of 20–40 nm was generated. After the nanoparticle colloids stood for 1 day or a few weeks at room temperature, the morphology of the nanoparticles changed to nanorods having dimensions of 20–40 nm in width and 200–1000 nm in length, and the absorption spectra of the nanorods colloids changed from those just after laser irradiation. The absorption spectrum of the nanorods was characteristic of β-like phase F16CuPc, and high-resolution transmission electron microscope (HRTEM) observations demonstrated the single crystalline nature of the nanorods having well-aligned, one-dimensional columns of co-facial stacking of F16CuPc molecules. The prepared nanorods dispersed stably in the poor solvents for longer than several months. We examined solvent dependence of the size and the morphology of the nanorods and found that the nanorods having a large mean aspect ratio generated rapidly in a low-viscosity solvent.

Viscoelasticity of poly(ethylene glycol) in aqueous solutions of potassium sulfate: a comparison of quartz crystal microbalance with conventional methods

The viscoelasticity of poly(ethylene glycol) (PEG) in aqueous solutions with different concentrations of potassium sulfate (K2SO4) was studied by quartz crystal microbalance with dissipation (QCM-D), after coating a rigid supported lipid bilayer of 1,2-dioleoyl-sn-glycero-3-phosphocholine on the silicon oxide substrate. The obtained viscoelastic properties of PEG in K2SO4 solutions agree well with the Zimm model predictions for linear polymer chains. With increasing K2SO4 concentration, the excluded volume exponent ν of PEG decreased from 0.565 in water to 0.55 in 0.19 mol/L K2SO4, and 0.50 in 0.43 mol/L K2SO4. The solvent quality gradually worsened for PEG with increasing K2SO4 concentration, which was verified by decreases in the polymer intrinsic viscosity and the corresponding Mark–Houwink exponent. The high-frequency characteristic of QCM-D makes it possible to directly study the viscoelasticity of polymer solutions in a low-viscosity solvent, which is complementary to conventional rheometers working at low frequency. Viscoelasticity of PEG in aqueous solutions containing different concentrations of K2SO4 was studied by QCM-D, after coating a rigid supported lipid bilayer on the silicon oxide substrate. The obtained viscoelastic properties of PEG in K2SO4 solutions agree well with the Zimm model predictions for linear polymer chains. The gradual worsening of solvent quality by adding K2SO4 to aqueous PEG solutions is demonstrated by the obtained excluded volume exponents via QCM-D and the conventional intrinsic viscosity measurements.

Physicochemical compatibility of highly-concentrated solvate ionic liquids and a low-viscosity solvent.

High ionic carrier mobilities are important for the electrolyte solutions used in high-performance batteries. Based on the functional sharing concept, we fabricated mixed electrolytes consisting of solvate ionic liquids (SIL), which are highly concentrated solution electrolyte, and the non-coordinating low-viscosity dilution solvent 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE). We investigated the thermal, transport, and static properties of electrolytes with different ratios of SIL to HFE. In particular, the interactions between the SILs and HFE and static correlations of the coordinating (ether-based molecules), non-coordinating (HFE), and carrier ionic species (lithium salt) were clarified by applying the excess density concept. Ether molecules always formed strong complexes with lithium cations regardless of the absence or presence of HFE. The repulsion force between the SILs and HFE was strongly affected by lithium salt concentration. From our results, we proposed dissociation/association models for these electrolyte systems.

Attempting to Break the 2 GJ/tonne CO2 Barrier; Development of an Advanced Water-Lean Capture Solvent From Molecules to Detailed Process Design

Solvent-based post-combustion CO2 capture is an energy-intensive process primarily driven by the energy required to regenerate the CO2 capture solvent. Researchers are currently focused on developing drop-in solvent replacements for commercial amine solvents with lower regeneration energies. One approach to reducing the regeneration energy of a solvent is to reduce its water content, thereby reducing unnecessary condensing and consequent boiling in the process. There are a number of water-lean solvent formulations currently under development that allow for water contents below 10% by weight, versus more than 60% for commercial aqueous amines. One solvent class, CO2-Binding Organic Liquids (CO2BOLs), shows promise to reduce the parasitic load to a coal-fired power plant but has been impeded by high viscosities at high CO2 loadings. In this paper, we perform a preliminary modeling study of a new low-viscosity CO2BOL solvent and assess the energetics of different process stripper configurations. By tailoring the process configuration with the unique aspects of the solvent reboiler duties below 2 GJ/tonne CO2 could be achievable. Further, this study suggests that there is no one-size-fits-all process optimum configuration for solvents, and therefore optimal configurations will be solvent specific.

The Effect of Solvent Viscosity on Production of Few-layer Graphene from Liquid-phase Exfoliation of Graphite

Abstract:Prior research into the liquid-phase exfoliation of graphite to produce few-layer graphene has focused primarily on the surface energy matching between graphite and solvent; however, the effect of other solvent properties, such as liquid viscosity, have not been systematically explored. In principle, a higher viscosity solvent should enable the production of graphene and other graphitic nanomaterials by liquid-phase exfoliation at lower shear rates than traditionally used organic solvents of low viscosity, such as N-methyl-2-pyrrolidone (NMP). Thus, at a given shear rate, more material should be exfoliated in the higher viscosity solvent. Hence, graphite suspensions in NMP, benzyl benzoate, and propylene glycol were exfoliated at various shear rates in a rheometer. Exfoliant concentrations were measured by ultraviolet- visual (UV-vis) spectroscopy and quality characterization was performed by Raman spectroscopy and scanning electron microscopy (SEM). Graphite exfoliation in the more viscous propylene glycol solvent resulted in a higher exfoliant concentration than in the less viscous NMP and benzyl benzoate solvents across all shear rates. Benzyl benzoate lowered exfoliant levels, likely due to a poor surface energy match, resulting in particle attraction and aggregation. Characterization showed that at least some of our material is few-layer graphene.

Reverse Micelle Encapsulation of Proteins for NMR Spectroscopy.

Reverse micelle (RM) encapsulation of proteins for NMR spectroscopy has many advantages over standard NMR methods such as enhanced tumbling and improved sensitivity. It has opened many otherwise difficult lines of investigation including the study of membrane-associated proteins, large soluble proteins, unstable protein states, and the study of protein surface hydration dynamics. Recent technological developments have extended the ability of RM encapsulation with high structural fidelity for nearly all proteins and thereby allow high-quality state-of-the-art NMR spectroscopy. Optimal conditions are achieved using a streamlined screening protocol, which is described here. Commonly studied proteins spanning a range of molecular weights are used as examples. Very low-viscosity alkane solvents, such as propane or ethane, are useful for studying very large proteins but require the use of specialized equipment to permit preparation and maintenance of well-behaved solutions under elevated pressure. The procedures for the preparation and use of solutions of RMs in liquefied ethane and propane are described. The focus of this chapter is to provide procedures to optimally encapsulate proteins in reverse micelles for modern NMR applications.

Viscosity effects for ion transport in electrochemical systems

Ion transport in a fluid medium is often described by the Poisson-Nernst-Planck (PNP) equation, a time-dependent mean-field theory that ignores the ion excluded-volume effects and electrostatic correlations, and a number of theoretical procedures have been recently proposed to alleviate the mean-field approximation. In this work, we investigate the charging kinetics of an electric double layer (EDL) of organic electrolytes using the dynamic density functional theory (DDFT). Unlike the PNP equation, DDFT predicts a nonlinear dependence of the surface charge density on the charging voltage. For systems with low solvent viscosity, the collective behaviors caused by inertial effects lead to an oscillatory variation of the surface charge density, occurrences in the charging process of the electrochemical system. Both the strength and frequency of charge oscillation are affected by the solvent viscosity and the degree of EDL overlap.

Research on the High-Frequency Electromagnetic Acoustic Heating of an Oil Reservoir with Further Pumping of a Solvent

A method involving high-frequency electromagnetic and acoustic fields (for heating) and subsequent pumping of a low-viscosity solvent is proposed to affect high-viscosity oil reservoirs. The system of heat conduction, peizoconductivity, and diffusion equations is solved with corresponding initial and boundary conditions by the method of finite differences with an implicit scheme. The dependence of the found solutions (oil reservoir temperature fields, bottomhole temperature dynamics, solvent flow rate change) on such parameters as the bottomhole pressure, the initial oil viscosity, and the high-frequency electromagnetic field generator power is considered.

Synthesis of 2′-deoxycytidine and its triphosphate bearing tryptophan-based imidazolinone fluorophore for environment sensitive fluorescent labelling of DNA

We synthesized 2′-deoxycytidine and the corresponding nucleoside triphosphate bearing (indol-3-yl)methylene-2-methyl-5-oxo-4,5-dihydroimidazol-1-yl group (a tryptophan-based fluorophore from cyan fluorescent protein) linked through a propargyl group at position 5. The fluorophore is weakly solvatochromic, sensitive to pH, and, as a molecular rotor, it is highly sensitive to viscosity. In low viscosity solvents, the fluorescence is very weak, whereas in more viscous environment it lights up. Primer extension or PCR using the modified dCTrpTP and KOD XL DNA polymerase was used for construction of labelled oligonucleotides and DNA. Preliminary study showed a 2-fold increase of fluorescence of labelled ON probe in presence of single strand-binding protein indicating a potential of this label for sensing of protein-DNA interactions.

Microfluidics to determine the diffusive mass transfer of a low viscosity solvent into a high viscosity hydrocarbon

In this work, a microfluidic platform along with X-ray computerized tomography were employed to analyze diffusive mass transfer of a low viscosity solvent (hexane) into a high viscosity hydrocarbon (bitumen). T-shaped microfluidic channels were fabricated to measure the diffusion coefficient in significantly shorter times and lower sample volume compared with traditional methods. Semitransparent nature of bitumen facilitates the application of light transmission imaging during the time and relating intensities to solvent concentration. Diffusion mass transfer was studied with respect to Fickian and Single-File mass transfer mechanisms and corresponding equation was applied to calculate both constant and concentration dependent diffusion coefficients. The accuracy of Fickian mass transfer mechanism was confirmed with calculating values of fitting parameter (i.e. nw) in addition to superimposition of data for both techniques. The optimum values of constant diffusion coefficient for T-shaped microchannel and X-ray technique were 2 × 10−10 and 1.8 × 10−10 m2·s−1, respectively. Concentration dependent diffusion coefficients ranged from 1 × 10−12 to 3.6 × 10−10 m2·s−1 for the experiments that reveal constant mutual diffusion coefficient assumption can result in significantly high errors particularly at low and high solvent mass fractions.

Lubricity of High Water Content Aqueous Gels

Aqueous gels such as biopolymer gels, mucus, and high water content hydrogels are often qualitatively described as lubricious. In hydrogels, mesh size, ξ, has been found to be a controlling parameter in friction coefficient. In the tribology of aqueous gels, we suggest that the Weissenberg number (Wi) is a useful parameter to define different regimes, and following the original formulations in rheology, Wi is given by the polymer relaxation time (ηξ3/kBT) multiplied by the shear rate due to fluid shear through a single mesh (V/ξ): Wi = ηVξ2/kBT. At sliding speeds below a Weissenberg number of approximately 0.1, Wi < 0.1, the friction coefficient is velocity-independent and scales with mesh size to the − 1 power, µ ∝ ξ−1. De Gennes’ scaling concepts for elastic modulus, E, give a dependence on polymer mesh size to the − 3 power, E ∝ ξ−3, and following Hertzian contact analysis, the contact area is found to depend on the mesh size squared, A ∝ ξ2. Combining these concepts, the shear stress, τ, and therefore the lubricity of aqueous gels, is predicted to be highly dependent on the mesh size, τ ∝ ξ−3. Studies aimed at elucidating the fundamental mechanism of lubricity in biopolymer gels, mucus, and hydrogels have wrestled with comparisons across mesh size, which can be extremely difficult to accurately quantify. Using scaling concepts relating polymer mesh size to water content reveals that shear stress decreases rapidly with increasing water content, and plots of shear stress as a function of swollen water content are suggested as a useful method to compare aqueous gels of unknown mesh size. As a lower bound, these data are compared against estimates of fluid shear stress for free and bound water flowing through a mesh size estimated by the water content of the gels. The results indicate that the strong dependence on lubricity is likely due to a synergistic combination of a low viscosity solvent (water) coupled to a system that has a decreasing friction coefficient, modulus, and the resulting contact pressure with increasing water content. Although the permeability, K, of aqueous gels increases dramatically with water content (and mesh size), K ≅ ξ2/η, the stronger decrease of the elastic modulus and subsequent decrease in contact pressure due to an increase in the contact length, predicts that the draining time under contact, t, actually increases strongly with increasing water content and mesh size, t ∝ ξ2. Consistent with the finding of extremely high water content aqueous gels on the surfaces of biological tissues, these high water content gels are predicted to be optimal for lubrication as they are both highly lubricious and robust at resisting draining and sustaining hydration.

Lattice Boltzmann simulation of viscoelastic flow past a confined free rotating cylinder

To study the dynamics of rigid body immersed in viscoelastic fluid, an Oldroyd-B fluid flow past an eccentrically situated, free rotating cylinder in a two-dimensional (2D) channel is simulated by a novel lattice Boltzmann method. Two distribution functions are employed, one of which is aimed to solve Navier–Stokes equation and the other to the constitutive equation, respectively. The unified interpolation bounce-back scheme is adopted to treat the moving curved boundary of cylinder, and the novel Galilean invariant momentum exchange method is utilized to obtain the hydrodynamic force and torque exerted on the cylinder. Results show that the center-fixed cylinder rotates inversely in the direction where a cylinder immersed in Newtonian fluid do, which generates a centerline-oriented lift force according to Magnus effect. The cylinder’s eccentricity, flow inertia, fluid elasticity and viscosity would affect the rotation of cylinder in different ways. The cylinder rotates more rapidly when located farther away from the centerline, and slows down when it is too close to the wall. The rotation frequency decreases with increasing Reynolds number, and larger rotation frequency responds to larger Weissenberg number and smaller viscosity ratio, indicating that the fluid elasticity and low solvent viscosity accelerates the flow-induced rotation of cylinder.

Approaches to Complex Electrolyte Formulation Optimization

Lithium ion battery electrolytes are complex formulations of solvents, salts, and additives. Each component can contribute to the battery performance in a unique way. For example, high dielectric constant solvents are necessary to dissolve the lithium salt, but are high viscosity. Therefore, low viscosity solvents are required to reduce the bulk electrolyte viscosity. Salt type and concentration can affect properties such as conductivity and thermal stability. Finally, many additives may be considered for use in formulations – with functions such as anode solid electrolyte interphase (SEI) formers, cathode SEI formers, acid scavengers, thermal stabilizers, and more. Development of optimized electrolyte formulations can require many experiments to find the best components and ratios/concentrations of components. Using Wildcat’s high throughput battery workflow, we can apply combinatorial chemistry approaches to screen hundreds of new electrolyte components and study their interactions for electrolyte formulation development. Combining statistical models for formulation optimization, and component substitution, the function of a single component in a complex electrolyte and its interaction with other components can be elucidated. In this presentation, we will demonstrate the power of these tools to rapidly improve and optimize complex electrolyte formulations.

Ultralight, Recoverable, and High-Temperature-Resistant SiC Nanowire Aerogel.

Ultralight ceramic aerogels with the property combination of recoverable compressibility and excellent high-temperature stability are attractive for use in harsh environments. However, conventional ceramic aerogels are usually constructed by oxide ceramic nanoparticles, and their practical applications have always been limited by the brittle nature of ceramics and volume shrinkage at high temperature. Silicon carbide (SiC) nanowire offers the integrated properties of elasticity and flexibility of one-dimensional (1D) nanomaterials and superior high-temperature thermal and chemical stability of SiC ceramics, which makes it a promising building block for compressible ceramic nanowire aerogels (NWAs). Here, we report the fabrication and properties of a highly porous three-dimensional (3D) SiC NWA assembled by a large number of interweaving 3C-SiC nanowires of 20-50 nm diameter and tens to hundreds of micrometers in length. The SiC NWA possesses ultralow density (∼5 mg cm-3), excellent mechanical properties of large recoverable compression strain (>70%) and fatigue resistance, refractory property, oxidation and high-temperature resistance, and thermal insulating property (0.026 W m-1 K-1 at room temperature in N2). When used as absorbents, the SiC NWAs exhibit an adsorption selectivity of low-viscosity organic solvents with high absorption capacity (130-237 g g-1). The successful fabrication of such an attractive material may provide promising perspectives to the design and fabrication of other compressible and multifunctional ceramic NWAs.

Effect of Using Fluorinated Ether and Sulfone as Electrolyte Solvents for Lithium Ion Batteries with Lithium-Rich Layered Cathodes and Silicon Oxide Anodes

We examined fluorinated ether and sulfone as electrolyte solvents for Lithium (Li) ion batteries with Li-rich layered cathodes and Silicon oxide anodes. We evaluated the mixture of cyclic carbonate, sulfone compound, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropopyl ether (FE1). The gas volume after the initial charge-discharge process increased with the amount of ethylene carbonate (EC) or 4-fluoro 1,3-dioxolane 2-one (FEC). These results show that the reaction between EC or FEC and cathode-active material can be considered to be the cause of gas evolution in the initial charge-discharge cycle. We evaluated sulfone compounds and low-viscosity solvents. By using electrolyte solution with ethyl isopropyl sulfone, FE1, and FEC as electrolyte solvents, the retention capacity after 500 cycles increased to around 67%, which was larger than that of conventional electrolyte solutions such as 1 M LiPF6 EC/diethyl carbonate (30/70 v/v).