Solvent Viscosity Research Articles

Droplet size in the breakup of a viscoelastic filament

The breakup process of a viscoelastic filament is investigated for a range of fluids with different polymer concentrations and solvent viscosities. Images taken by a high-speed camera show that the filament first thins exponentially to a terminal diameter and then generates surface waves, which form drops in a cascade manner, known as beads-on-string structures. The time spent in the exponential thinning stage is proportional to the relaxation time (λr) of the fluid, and it takes about 6λr for the tested fluids to reach the terminal diameter. The Rayleigh–Plateau instability gives reasonable prediction on the wavelength of surface waves but overestimates the growth rate. The sizes of different generations of beads are proportional to the filament diameters at which they form and can be predicted by a model based on the filament thinning rate. The bead size distribution has a Gamma distribution, and increases in polymer concentration and solvent viscosity result in a more uniform bead size distribution.

Solvent effects on static stability and flow characteristics of waste-activated carbon-derived coal water slurry: a numerical simulation study

ABSTRACT This study investigates the impact of various solvents on the static stability and flow characteristics of waste-activated carbon (WAC)-based coal-water slurry for co-gasification. Using the Euler–Euler method, we analyze slurry stability both in stationary conditions and during flow in a horizontal pipeline. Results show that glycerin offers the highest stability during slurry preparation, while acetonitrile provides the lowest. Solvents like glycerin, propanol, and formamide improve stability compared to water. In static conditions, glycerin’s stable height change rate is nearly 0, while acetonitrile peaks at 4.09. During the flow, glycerin-based slurry maintains a stable height of 40 mm with no accumulation, while acetonitrile retains only 88% of its height. The solid volume fraction difference for glycerin slurry is minimal (0.011), whereas acetonitrile slurry shows a much larger difference (0.7). However, glycerin slurry has the highest pressure drop (129 mWc/100 m), indicating higher energy consumption during transportation. This study highlights how solvent viscosity and density influence slurry properties and introduces a numerical approach for predicting slurry stability in preparation and transport.

Kinetic and Thermodynamic Characterization of Human 4-Oxo-l-proline Reductase Catalysis.

The enzyme 4-oxo-l-proline reductase (BDH2) has recently been identified in humans. BDH2, previously thought to be a cytosolic (R)-3-hydroxybutyrate dehydrogenase, actually catalyzes the NADH-dependent reduction of 4-oxo-l-proline to cis-4-hydroxy-l-proline, a compound with known anticancer activity. Here we provide an initial mechanistic characterization of the BDH2-catalyzed reaction. Haldane relationships show the reaction equilibrium strongly favors the formation of cis-4-hydroxy-l-proline. Stereospecific deuteration of NADH C4 coupled with mass spectrometry analysis of the reaction established that the pro-S hydrogen is transferred. NADH is co-purified with the enzyme, and a binding kinetics competition assays with NAD+ defined dissociation rate constants for NADH of 0.13 s-1 at 5 °C and 7.2 s-1 at 25 °C. Isothermal titration calorimetry at 25 °C defined equilibrium dissociation constants of 0.48 and 29 μM for the BDH2:NADH and BDH2:NAD+ complexes, respectively. Differential scanning fluorimetry showed BDH2 is highly thermostabilized by NADH and NAD+. The kcat/KM pH-rate profile indicates that a group with a pKa of 7.3 and possibly another with a pKa of 8.7 must be deprotonated and protonated, respectively, for maximum binding of 4-oxo-l-proline and/or catalysis, while the kcat profile is largely insensitive to pH in the pH range used. The single-turnover rate constant is only 2-fold higher than kcat. This agrees with a pre-steady-state burst of substrate consumption, suggesting that a step after chemistry, possibly product release, contributes to limit kcat. A modest solvent viscosity effect on kcat indicates that this step is only partially diffusional. Taken together, these data suggest chemistry does not limit the reaction rate but may contribute to it.

Inulin Dehydration to 5-HMF in Deep Eutectic Solvents Catalyzed by Acidic Ionic Liquids Under Mild Conditions.

Valorization of carbohydrate-rich biomass by conversion into industrially relevant products is at the forefront of research in sustainable chemistry. In this work, we studied the inulin conversion into 5-hydroxymethylfurfural, in deep eutectic solvents, in the presence of acidic task-specific ionic liquids as catalysts. We employed aliphatic and aromatic ionic liquids as catalysts, and choline chloride-based deep eutectic solvents bearing glycols or carboxylic acids, as solvents. The reactions were performed in a biphasic system, with acetone as a benign extracting solvent, enabling continuous extraction of 5-HMF. We aimed to find the best experimental conditions for this transformation, in terms of catalyst loading, solvent, reaction time and temperature to achieve an economical and energy efficient process. We also analyzed the results in terms of solvent viscosity and structural organization as well as catalysts acidity, to elucidate which structural features mostly favour the reaction. Under optimized conditions, we obtained a yield in 5-HMF of 71 %, at 80 °C in 3 h. Our system can be scaled up and recycled three times with no loss in yield. Finally, comparison with the literature shows that our system achieves a higher yield under milder conditions than most protocols so far reported for the same transformation.

Deciphering the Photophysical Properties of Nonplanar Heterocyclic Compounds in Different Polarity Environments.

Nonplanar (butterfly-shaped) phenothiazine (PTZ) and its derivative's (M-PTZ) photophysical and spectral properties have been tuned by varying the solvents and their polarity and investigated employing spectroscopic techniques such as UV-Vis, steady-state and time-resolved fluorescence, and TDDFT calculations. The UV-Vis absorption studies and TDDFT calculations reveal two distinct bands for both compounds: a strong π-π* transition at shorter wavelengths and a weaker n-π* transition, which displays a little bathochromic shift in polar solvents. The detailed emission studies reveal that such dual emission is a result of the photoinduced excited-state conjugation enhancement (ESCE) process. The band at a shorter wavelength corresponds to the locally excited (LE) state, while the longer wavelength band arises from the planarized excited state resulting from ESCE. With the increase in solvent polarity, the LE band is less affected, whereas strong positive solvatochromism is observed for the ESCE band. As the solvent polarity increases, the ESCE band demonstrates significant positive solvatochromism, while emission intensity decreases with higher solvent polarity, suggesting stabilization of the excited state. The biexponential decay of fluorescence lifetimes further corroborates the dual emission behavior of PTZ and M-PTZ. PTZ exhibits a higher photoluminescence quantum yield (PLQY) than that observed for M-PTZ, and the solvent viscosity influences the PLQY, indicating that nonradiative decay is activated during the planarization of the excited state, also known as excited-state conjugation enhancement. Furthermore, the (time-dependent) density functional theory (TD) DFT calculations performed to understand the geometrical parameters and the electronic transitions of these model molecules further corroborate experimental findings. These findings underscore the significant influence of solvent polarity and molecular structure on the dual emission and excited-state dynamics of PTZ and M-PTZ, which eventually hold substantial implications for advanced photophysical applications.

Unraveling Hydration Shell Dynamics and Viscosity Effects Around Cyanamide Probes via 2D IR Spectroscopy.

Hydration dynamics and solvent viscosity play critical roles in the structure and function of biomolecules. An overwhelming body of evidence suggests that protein and membrane fluctuations are closely linked to solvent fluctuations. While extensive research exists on the use of vibrational probes to detect local interactions and solvent dynamics, fewer studies have explored how the behavior of these reporters changes in response to bulk viscosity. To address this gap, two-dimensional infrared spectroscopy (2D IR) was employed in this study to investigate the ultrafast hydration dynamics around a cyanamide (NCN) probe attached to a nucleoside, deoxycytidine, in aqueous solutions with varying glycerol content. The use of a small vibrational probe on a targeted nucleic acid offers the potential to capture more localized hydration dynamics than alternative methods. The time scales for the frequency correlation decays were found to increase linearly with bulk viscosity, ranging from 0.9 to 11.4 ps over viscosities of 0.96-49.1 cP. Additionally, molecular dynamics (MD) simulations were performed to model the local hydration dynamics around the NCN probe. Interestingly, increasing the glycerol content did not significantly alter the hydration of the deoxycytidine. The MD simulations further suggested that the NCN probe's frequency fluctuations were primarily influenced by the dynamics of water in the second solvation shell. Cage correlation functions, which measure the movement of water molecules in and out of the second solvation shell, exhibited decays that closely matched those of the frequency-fluctuation correlation function (FFCF). These findings offer new insights into hydration dynamics and the impact of viscosity on biological systems.

Amine-Based Solvents and Additives to Improve the CO2 Capture Processes: A Review

The use of amine-based solvents for carbon dioxide (CO2) capture has shown significant promise; however, operational challenges such as high energy requirements, solvent degradation, and equipment corrosion highlight the need for enhanced solutions. This review focuses on identifying amine-based solvents and additives that can improve CO2 capture efficiency while minimizing costs and avoiding substantial modifications to existing industrial facilities. Specifically, the study emphasizes the development of a comprehensive database of additives to optimize CO2 capture processes. A detailed analysis of recent advancements in amine-based solvents was conducted, with a focus on (i) process optimization strategies, (ii) sector-specific CO2 emission profiles, and (iii) equipment issues associated with conventional chemical solvents. The study evaluates these solvents’ kinetic and thermodynamic properties and their potential to address critical operational challenges, including reducing corrosion, solvent viscosity, and evaporation rates. The findings highlight the pivotal role of amino group-containing compounds, particularly alkanolamines, in enhancing CO2 capture performance. The structural versatility of these compounds, characterized by the presence of hydroxyl groups, facilitates aqueous dissolution while offering kinetic and thermodynamic benefits. This review underscores the importance of continued innovation in solvent chemistry and the integration of amine-based solvents with emerging technologies to overcome current limitations and advance the implementation of efficient and sustainable CO2 capture technologies.

Effect of Binary Solvent Mixtures on Ion-Pair Formation and Solvation Dynamics

This study determines the impact of binary solvent mixtures, particularly water and Dimethylformamide (DMF), on the formation of the ion-pair and dynamic solvation. The ion interaction dynamics of halides and nitrates with M²⁺ and M³⁺ have been assessed through conductivity studies and also ion-pair stability in addition to assessing solvation thermodynamics by varying the temperature. Experiments along with theoretical understanding lead the paper to highlight the critical modulatory effect of solvent polarity, hydrogen bonding, and viscosity of the medium affecting ion-ion interactions and finally, structures of solvation.

Wafer-Level Packaging of Microelectromechanical Systems Based on Frame Structure

Modern microelectromechanical systems (MEMS) are devices that incorporate microelectronic components and micromechanical structures on a single chip. Packaging is a mandatory stage in MEMS manufacturing. It ensures mechanical protection, sealing and transmission of electric energy and signals. The present work was aimed at developing a MEMS packaging method as a part of the consolidated manufacturing process. The method is developed on the example of a microwave MEMS switch. The switch manufacturing scheme includes conventional technologies used for producing gallium arsenide integrated circuits: optical lithography, liquid etching, electron-beam and magnetron deposition of metallic, resistive and dielectric films. The work presents a new inter-plate MEMS packaging based on a frame structure with a passivating film. The main purpose of the package frame layer is mechanical support for an upper layer of the sealing material. The frame layer should have the structure allowing for unimpeded removal of the sacrificial photoresist and be impermeable for the sealant. To satisfy the requirements stated, a metallic thin copper-film spatial frame was fabricated by galvanic deposition. The frame structure is a geodesic dome comprised of a complex network of triangle cells arranged in rows. The connected triangles create a self-supporting durable framework. The measurement and modeling results demonstrate that the round frame structure is more durable than a square frame with the same maximum cell dimensions. The stress-strain state for the round framework considerably alters depending on the number of rows of triangle cells. In addition to the mechanical support, the cell structure of the framework – with adequate selection of cell dimensions, solvent and sealant viscosities – allows for unimpeded penetration of the solvent (N-methyl-2-pyrrolidone, NMP) and removal of ma-P1225 photoresist sacrificial layers. At the same time, the layer structure is impermeable for the sealant (benzocyclobutene, BCB). The proposed MEMS switch packaging enables mass fabrication of GaAs integrated circuits in a single process, which expands their frequency range. The new plate-level packaging technology is absolutely compatible with MEMS fabrication technology without specific materials and equipment which reduces the dimensions and cost of MEMS.

Optimizing corncob pretreatment with eco-friendly deep eutectic solvents to enhance lignin extraction and cellulose-to-glucose conversion

Deep eutectic solvents (DES) are an eco-friendly, cost-effective alternative to traditional ionic liquids for biomass pretreatment, with unique characteristics encompassed by hydrogen bond donor (HBD), the molar ratio of hydrogen bond acceptor (HBA) to HBD, temperature, and time affecting efficiency. Despite its potential, a comprehensive study exploring the interplay of these factors is limited. This study explores the optimization of pretreatment variables using choline chloride/lactic acid (1:5) via the response surface method (RSM). It aims to evaluate the effects of time and temperature on lignin extraction, cellulose-to-glucose conversion, and hemicellulose removal. Employing a 22 central composite design with temperature (80–140 °C) and time (2–6 h) as variables, optimal conditions were 123 °C for 6 h. Results include 90.08±1.42 % lignin extraction, 68.77±6.9 % cellulose-to-glucose conversion, and 77.34±0.85 % hemicellulose removal, with 52.52±8.07 % lignin recovery. The fractions of pretreated CC and lignin recovered in the optimal condition found were characterized by X-ray diffraction (XDR), Fourier transform infrared spectroscopy (FTIR), 1H, 13C, 2D-HSQC NMR spectroscopy, Thermogravimetric analysis (TGA/DTG), Gel Permeation Chromatography (GPC) to elucidate chemical characteristics of the materials obtained and facilitate downstream valorization. High efficiency was achieved in lignin extraction and cellulose conversion, and addressing solvent viscosity and DES recycling will further enhance the potential for industrial scalability.

Encapsulation-induced hypsochromic shift of emission properties from a cationic Ir(III) complex in a hydrogen-bonded organic cage: A theoretical study.

Encapsulation of coordination complexes within the confined spaces of self-assembled hosts is an effective method for creating supramolecular assemblies with distinct chemical and physical properties. Recent studies with calix-resorcin[4]arene hydrogen-bonded hexameric capsules revealed that encapsulated metal complexes exhibit enhanced and blue-shifted photoluminescence compared to their unencapsulated forms. The photophysical change has been hypothetically attributed to encapsulation-induced confinement, which isolates the metal complex from the solvent, suppressing stabilization of the excited state of the guest by solvent reorganization and structural relaxation, and altering the local environment, such as solvent polarity and viscosity, around the guest. In this study, density-functional theory calculations were conducted to explore how encapsulation affects the photophysical properties of a cationic iridium complex within a hydrogen-bonded hexameric capsule. The encapsulation-induced emission shift was analyzed by separating it into three factors: suppression of solvent reorganization, suppression of structural relaxation of the complex, and electronic interactions between the complex and the capsule. The findings indicate that the photoluminescence modulation is driven by the electronic interaction between the host and guest, which affects the energy levels of the molecular orbitals involved in the T1 excited state and the suppression of excited-state structural relaxation of the Ir complex due to the presence of the host. This study advances our understanding of the photophysical dynamics of coordination complexes within the confined spaces of hexameric capsules, providing a valuable approach for tuning the excited state properties of guest molecules.

Prediction of the viscosity of green deep eutectic solvents by constructing ensemble model based on machine learning

Deep eutectic solvents (DESs), as novel green and sustainable solvents, play an important role in industrial mass and heat transfer processes due to their viscosity. In this study, four machine learning models (multilayer perceptron, random forest, gradient boosting regressor, extreme gradient boosting) were constructed based on extended-connectivity fingerprints to predict the viscosity of DESs. Grid search and 10-fold cross-validation were employed to optimize the models and enhance their robustness. Additionally, the shapley additive explanations method was utilized to explain the model and analyze the impact of feature descriptors generated by HBDs and HBAs on DESs viscosity. Building upon the optimal model, 11 ensemble learning models were constructed using stacking technology. Comparative analysis with models from the literature demonstrated that stacking technology effectively improves model accuracy. The key factors affecting DESs viscosity were analyzed using quantum chemical methods. This work will facilitate the widespread application and green development of DESs.

Formation of dimer and higher aggregates of methylene blue in alcohol

This study investigates MB aggregation in propanol, ethanol, butanol, and methanol using UV–Visible, steady-state, and time-resolved fluorescence spectroscopy at room temperature. This work reveals the presence of monomers, dimers, and higher aggregates across various concentrations, affecting both the absorption spectra and fluorescence intensity. Characteristic peaks for monomeric, dimeric, and higher aggregates of MB are identified, with shifts in emission peak intensity and lifetime as a function of concentration, solvent polarity, and viscosity. A strong correlation between fluorescence lifetime and solvent properties, such as dielectric constant and viscosity, suggests that solvent polarity and viscosity significantly influence the stabilization of excited states and the deactivation dynamics of methylene blue. The critical concentration for MB aggregation is identified for each solvent and is found to be higher in solvents with a greater dielectric constant, likely due to Van der Waals forces dominating over Coulombic interactions in the aggregation process. The findings indicate that MB aggregation in alcohols differs from that in aqueous solutions, underscoring the importance of the solvent environment in MB’s aggregation and fluorescence behavior, with implications for optimizing its use in laser and photomedicine applications.

Electrolyte Dependence of Li+ Transport Mechanisms in Small Molecule Solvents from Classical Molecular Dynamics

As demands on Li-ion battery performance increase, the need for electrolytes with high ionic conductivity and a high Li+ transference number (tLi) becomes crucial to boost power density. Unfortunately, tLi in liquid electrolytes is typically <0.5 due to Li+ migrating via a vehicular mechanism, whereby Li+ diffuses along with its solvation shell, making its diffusivity slower than the counteranion. Designing liquid electrolytes where the Li+ ion diffuses independently of its solvation shell is of significant interest to enhance the transference number. In this work, we elucidate how the properties of the solvent influence the Li+ transport mechanism. Using classical molecular dynamics simulations, we find that a vehicular mechanism can be increasingly preferred with a decreasing solvent viscosity and increasing interaction energy between the solvent and Li+. Thus, a weaker interaction energy can enhance tLi through a solvent-exchange mechanism, ultimately improving Li-ion battery performance. Finally, metadynamics simulations show that in electrolytes where a solvent-exchange mechanism is preferable, the energy barrier to changing the coordination environment of Li+ is much lower than in electrolytes where a vehicular mechanism dominates.

Application of 1-octanol in the extraction and GC-FID analysis of volatile organic compounds produced in biogas and biohydrogen processes

Information about the volatile organic compounds generated in biogas and hydrogen production bioreactors is essential to elucidate the metabolic routes and varying yields of CH4 and H2 processes. In this work, the determination of 12 compounds (acetone, methanol, ethanol, 1-propanol, 1-butanol, and acetic, propanoic, butyric, isovaleric, valeric, caproic, and lactic acids) was performed by gas chromatography, after a vortex-assisted liquid–liquid microextraction (VALLME) procedure using 1.2 mL of crude sample and 400 µL of 1-octanol. Optimization of the separation process was performed, considering the solvent viscosity. The analytical curves were validated using ANOVA, demonstrating satisfactory precision and accuracy. Selectivity was confirmed by GC–MS analysis, which allowed the detection of glycerol, 1,3-propanediol, and 1,3-butanediol in some samples. Methanol levels exceeded the upper limit of quantification, with acetic acid and ethanol being the predominant compounds in the analyzed reactors. An additional investigation was conducted to assess potential interferences for lactic acid. The developed method employs a biodegradable extraction solvent, without any need for a dispersing solvent, and involves a single chromatographic run, without any derivatization steps.

Multifocal lipid membrane characterization by combination of DAS-deconvolution and anisotropy

Three analog solvatochromic probes, Laurdan, Prodan, and Acdan, are extensively used in the study of biological sciences. Their locations in lipid membranes vary greatly in depth, and their fluorescence responds to their surrounding environment based on their corresponding locations in the membrane. Utilizing the fluorescence lifetimes (τ) and emission peak positions (λ) acquired from the time-resolved emission spectrum, one can effectively determine the local lipid environment using the analytical approach, referred to as τ and λ plots. Herein, a τ and λ plot was created using the aforementioned probes to expand the analytical field according to their location. Furthermore, the solvent modeling method in the τ and λ plot was upgraded to artificially emulate the complex environment in lipid membranes by utilizing liquid paraffin and glycerol to assess the contribution of viscosity to each fluorescence distribution. According to the results from a series of solvent mixtures, the effect of solvent viscosity on lifetime values was confirmed in the short lifetime region (τ < 3 ns). However, it was impossible to emulate the longer than 4 ns lifetime values observed in lipid membranes containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine in the range of viscosity applied in this study. From the insight of the limiting anisotropy (r∞), the τ and λ plot was divided into a solvent-like region with an isotropic environment (r∞ < 0.15) and a region highly ordered enough to define it as an anisotropic environment (0.15 < r∞) at τ = 4 ns. Also, the membrane-specific distribution was illustrated as 4 ns < τ and λ < 460 nm from this work. An updated analytical model was created to visualize multiple fluorescence components of each probe in six types of lipid bilayers, confirming the different distributions between these probes. Our results well illustrate the multiplicity of lipid environments modeled with solvent and ordered environments in each lipid bilayer system.

The Thermodynamic and Kinetic Properties of the dA-rU DNA-RNA Hybrid Base Pair Investigated via Molecular Dynamics Simulations.

DNA-RNA hybrid duplexes play essential roles during the reverse transcription of RNA viruses and DNA replication. The opening and conformation changes of individual base pairs are critical to their biological functions. However, the microscopic mechanisms governing base pair closing and opening at the atomic level remain poorly understood. In this study, we investigated the thermodynamic and kinetic parameters of the dA-rU base pair in a DNA-RNA hybrid duplex using 4 μs all-atom molecular dynamics (MD) simulations at different temperatures. Our results showed that the thermodynamic parameters of the dA-rU base pair aligned with the predictions of the nearest-neighbor model and were close to those of the AU base pair in RNA. The temperature dependence of the average lifetimes of both the open and the closed states, as well as the transition path times, were obtained. The free-energy barrier for a single base pair opening and closing arises from an increase in enthalpy due to the disruption of the base-stacking interactions and hydrogen bonding, along with an entropy loss attributed to the accompanying restrictions, such as torsional angle constraints and solvent viscosity.

Synthesis and Properties of Tris(3‐Pyrrolyl BODIPY) on 1, 3, 5‐Triazine Scaffold

AbstractTris(3‐pyrrolyl BODIPY) on 1,3,5‐triazine scaffold was synthesized over a sequence of steps starting from commercially available cyanuric chloride. The cyanuric chloride was reacted with p‐hydroxy benzaldehyde to afford 1,3,5‐triazine tris(p‐oxybenzaldehyde) which was then reacted with excess pyrrole under acid catalyzed conditions to afford 1,3,5‐triazine‐tris(meso‐p‐oxyphenyl dipyrromethane). Subsequent in situ oxidation of this compound with DDQ to obtain tris(meso‐oxyphenyldipyrromethene) which was then treated with pyrrole followed by the addition of Et3N/BF3 ⋅ OEt2 afforded fluorescent tris(3‐pyrrolyl BODIPY). For comparison, tris(BODIPY) on the triazine scaffold was prepared by oxidizing tris(meso‐oxyphenyldipyrromethane) with DDQ followed by complexation with BF3 ⋅ OEt2. Both compounds were thoroughly characterized and studied by various experimental and theoretical methods. Absorption, steady state fluorescence, time‐resolved fluorescence, and transient‐absorption studies revealed that in tris(3‐pyrrolyl BODIPY), excitonic interactions between two of the three 3‐pyrrolyl BODIPY units resulted in a hypsochromic shift in spectral bands, reducing the quantum yield and singlet state lifetime whereas tris(BODIPY) did not show such excitonic interactions. DFT studies helped in understanding the excitonic interactions in tris(3‐pyrrolyl BODIPY). The tris(3‐pyrrolyl BODIPY) was fluorescent both in solution and solid state. The viscosity studies indicated that the fluorescence of tris(3‐pyrrolyl BODIPY) increases significantly with solvent viscosity, suggesting its potential for measuring cellular viscosity during physiological processes.

Tetraarylpyrrolo[3,2-b]pyrrole-BODIPY dyad: a molecular rotor for FRET-based viscosity sensing.

With the aim to develop a FRET-based viscosity sensor, two dyad molecules, 4 and 5, comprising tetraarylpyrrolo[3,2-b]pyrrole (TAPP) (donor) and naked boron-dipyrromethene (BODIPY) dyes (acceptor), were designed. Dyads were synthesized via acid-catalyzed multicomponent reactions followed by Sonogashira coupling. In both dyads, the BODIPY and TAPP moieties are linked through phenylethynyl groups, which allow free rotation of the BODIPY dyes; that is, they can act as molecular rotors. This was supported by X-ray crystallographic and DFT-optimized structures. Spectroscopic studies also confirmed the presence of both TAPP and BODIPY dyes in dyads with no electronic interactions that are suitable for fluorescence resonance energy transfer (FRET). Very high energy transfer efficiency (ETE >99%) from the donor TAPP moiety to the acceptor BODIPY moiety on excitation at the TAPP part was observed. However, due to the non-fluorescent nature of naked BODIPY dyes, no fluorescence emission was observed from the BODIPY moiety in both dyads. With increasing solvent viscosities, emission from the BODIPY moieties increases due to the restricted rotation of the BODIPY moieties. Plotting the logarithms of the fluorescent intensity of dyad 5 and the viscosity of the solution showed a good linear correlation obeying a Förster-Hoffmann equation. Non-fluorescent dyad 5 in methanol became greenish-yellow fluorescent in a methanol/glycerol (1:1) solvent. Furthermore, with an increase in the temperature of the methanol/glycerol (1:1) system, as the viscosity decreases, the fluorescence also starts decreasing. Thus, dyad 5 is capable of sensing the viscosity of the medium via a FRET-based "Off-On" mechanism. This type of viscosity sensor with a very large pseudo-Stokes shift and increased sensitivity will be useful for advancing chemo-bio sensing and imaging applications.

Novel lattice Boltzmann method for simulation of strongly shear thinning viscoelastic fluids

AbstractThe simulation of viscoelastic liquids using the Lattice–Boltzmann method (LBM) in full three dimensions remains a formidable numerical challenge. In particular the simulation of strongly shear‐thinning fluids, where the ratio between the high‐shear and low‐shear viscosities is large, is often prevented by stability problems. Here we present a novel approach to overcome this issue. The central idea is to artificially increase the solvent viscosity which allows the method to benefit from the very good stability properties of the LBM. To compensate for this additional viscous stress, the polymer stress is reduced by the same amount. We apply this novel method to simulate two realistic cell carrier fluids, methyl cellulose and alginate solutions, of which the latter exhibits a viscosity ratio exceeding 10,000.