Solvent Evaporation Rate Research Articles

Evaporation-Induced Crystal Nucleation and Morphology of Dried Poly(Vinylidene Fluoride) Droplets

The evaporation of a polymer solution droplet is important in solution-based polymer film fabrications, such as inkjet printing, spray coatings, and droplet casting, etc. In this work, we investigated the effect of droplet size, solvent evaporation rate, and concentration on the “coffee-ring” effect, crystal nucleation, polymorphism, and morphology of dried poly(vinylidene fluoride) (PVDF) solution droplets with the atomic force microscopy (AFM) and two-dimensional grazing incidence wide angle X-ray scattering (2D GIWAXS) method. We found that the crystal structure, morphology and crystal distribution in the center and edge regions of dried PVDF droplets were different due to the “coffee-ring” effect. The “coffee-ring” effect of dried PVDF droplets was mainly composited of accumulated crystals at the edge region of a droplet, which was mainly made by the crystallization of migrated chains. The interplay between the migration of chains and the crystallization and solidification of PVDF droplets significantly influenced the formation of the “coffee-ring”. In addition, our results showed that the decrease in droplet size and the controlling solvent evaporation rate were effective ways to improve the electroactive crystalline phases (β and γ-phases) nucleation and decrease the crystal size.

Determination of Dental Adhesive Composition throughout Solvent Drying and Polymerization Using ATR-FTIR Spectroscopy.

The of this study aim was to develop a rapid method to determine the chemical composition, solvent evaporation rates, and polymerization kinetics of dental adhesives. Single-component, acetone-containing adhesives One-Step (OS; Bisco, Anaheim, CA, USA), Optibond Universal (OU; Kerr, Brea, CA, USA), and G-Bond (GB; GC, Tokyo, Japan) were studied. Filler levels were determined gravimetrically. Monomers and solvents were quantified by comparing their pure Attenuated Total Reflectance-Fourier Transform Infra-Red (ATR–FTIR) spectra, summed in different ratios, with those of the adhesives. Spectral changes at 37 °C, throughout passive evaporation for 5 min, then polymerisation initiated by 20 s, and blue light emitting diode (LED) (600 mW/cm2) exposure (n = 3) were determined. Evaporation and polymerisation extent versus time and final changes were calculated using acetone (1360 cm−1) and methacrylate (1320 cm−1) peaks. OS, OU, and GB filler contents were 0, 9.6, and 5.3%. FTIR suggested OS and OU were Bis-GMA based, GB was urethane dimethacrylate (UDMA) based, and that each had a different diluent and acidic monomers and possible UDMA/acetone interactions. Furthermore, initial acetone percentages were all 40–50%. After 5 min drying, they were 0% for OS and OU but 10% for GB. Whilst OS had no water, that in OU declined from 18 to 10% and in GB from 25 to 20% upon drying. Evaporation extents were 50% of final levels at 23, 25, and 113 s for OS, OU, and GB, respectively. Polymerisation extents were all 50 and 80% of final levels before 10 and at 20 s of light exposure, respectively. Final monomer polymerisation levels were 68, 69, and 88% for OS, OU, and GB, respectively. An appreciation of initial and final adhesive chemistry is important for understanding the properties. The rates of evaporation and polymerisation provide indications of relative required drying and light cure times. UDMA/acetone interactions might explain the considerably greater drying time of GB.

Ordered isoporous membranes from ionic diblock copolymers via SNIPS: Optimizing effective factors with a structural survey

The membrane formation directly through the self-assembly and nonsolvent induced phase separation (SNIPS) method without the aid of foreign additives has been more challenging in the case of ionic block copolymers, like polystyrene-block-poly (acrylic acid) (PS-b-PAA), in comparison with non-ionic amphiphilic systems. Herein, the influence of governing factors on the structure tuning, including physicochemical characteristics of polymer, solvent and nonsolvent, casting parameters and process conditions to prepare additive-free and ordered isoporous membranes was studied. Due to the high degree of ionization and hydrophilicity of PAA blocks, micellization in the form of “reverse micelles” was aimed to induce more stable micelles assembly. The well-ordered micelles assembly was generated by the suitable selection of solvent (1,4-dioxane), strongly segregated characteristic of PS-b-PAA (high χN) and proper adjustment of casting parameters including polymer concentration and solvent evaporation rate and time. The uniformity and regularity of the micelles assembly during phase inversion step was preserved owing to the high freezing point of solvent. Highly permeable asymmetric isoporous membranes prepared over a wide range of evaporation times (40–120 s) using relatively low polymer concentrations (15 wt%) with adjustable and monodispersed pore-size in the range of sub-10 up to 22 nm. FESEM and AFM images in addition to DLS measurements and solution SAXS analysis were applied to demonstrate the hexagonal close-packed (HCP) structure of micelles assembly and partially hexagonal arrangement of pores at the membrane selective-layer. It was also demonstrated that corona (PS) of adjacent micelles on the membrane surface fused together to form a continuous membrane matrix, while surface-pores were the nanoscale voids, formed between the densely packed spherical reverse micelles practically immobilized by immersion in low-temperature water bath. Such additive-free, asymmetric, iso- and nano-porous membranes have attractive potential practical applications in biomedical and pharmaceutical industries for size-based separations, in addition to their conventional applications in water purification.

Freeze-printing of pectin/alginate scaffolds with high resolution, overhang structures and interconnected porous network

We report herein the fabrication of a pectin-based scaffold (6 wt% pectin, 3 wt% alginate) with high resolution (small-diameter rods), small pores, and interconnected porosity using a low temperature 3D printing process known as freeze-printing. The ability to successfully print natural polymers has been a long-standing challenge in the field of additive manufacturing of polymeric tissue scaffolds. This is due to the slow evaporation rate of the aqueous solvent, which leads to unstable structures. This problem has been addressed by utilizing the fast solidification rate of the freeze-printing process. Scaffolds with a hgresolution (rod-diameter of 83 ± 14 µm), small pores (<250 µm), overhang structures, and an interconnected porous network (pore height of 319 µm in the z-direction) were obtained. The scaffolds were also found to support the viability of chondrocytes and their synthesis of type II collagen. This report investigates the processing-structure relationship and fundamental science of structurally stable scaffold structures produced by additive manufacturing of natural polymers. • A pectin-rich scaffold was fabricated with high resolution and 3D-interporosity. • The scaffold has a small rod-diameter at 83 ± 14 µm and small pores (<250 µm). • Rapid solidification by freeze-printing prevented broadening and collapse of the printed rods. • The dimension of the pores in the z-diection is adjustable.

A Bioinspired Stretchable Sensory-Neuromorphic System.

Conventional stretchable electronics that adopt a wavy design, a neutral mechanical plane, and conformal contact between abiotic and biotic interfaces have exhibited diverse skin-interfaced applications. Despite such remarkable progress, the evolution of intelligent skin prosthetics is challenged by the absence of the monolithic integration of neuromorphic constituents into individual sensing and actuating components. Herein, a bioinspired stretchable sensory-neuromorphic system, comprising an artificial mechanoreceptor, artificial synapse, and epidermal photonic actuator is demonstrated; these three biomimetic functionalities correspond to a stretchable capacitive pressure sensor, a resistive random-access memory, and a quantum dot light-emitting diode, respectively. This system features a rigid-island structure interconnected with a sinter-free printable conductor, which is optimized by controlling the evaporation rate of solvent (≈160% stretchability and ≈18550 S cm-1 conductivity). Devised design improves both areal density and structural reliability while avoiding the thermal degradation of heat-sensitive stretchable electronic components. Moreover, even in the skin deformation range, the system accurately recognizes various patterned stimuli via an artificial neural network with training/inferencing functions. Therefore, the new bioinspired system is expected to be an important step toward implementing intelligent wearable electronics.

Effect of the solvent evaporation rate of silver ink on the electrohydrodynamic-printing formability of textile-based printing electronics

The enabling electrohydrodynamic (EHD) printing technology in a one-step forming, continuous, and controllable manner has gained wide attention in the field of flexible printed electronics. The evaporation characteristic of ink solvent during the EHD printing greatly affects the shape of the jet as well as the penetration and diffusion of inks on fabrics, which is crucial to the formation of high-quality printed electronics. However, few works have deeply investigated the control of ink solvent evaporation to adjust the formability of EHD printing electronics on rough and porous textiles. Here, conductive inks with different solvent evaporation rates are formulated. The effect of solvent evaporation on the motion of inks is evaluated by the contact angle over time. Furthermore, the morphology and electrical properties under different deformation of EHD-printed conductive lines are observed and measured. The results show that the morphology of conductive lines printed on fabric could be accurately controlled by the ratios of the solvent in inks, and the solvent evaporation rate has a significant inverse-parabolic effect on electrical resistance and its stability under deformation. Moreover, the serviceability of the optimal ink is demonstrated by the performance of an EHD-printed antenna for ultra-high frequency radio frequency identification tags, and its maximum reading range is 9.1 m under typical application examples. These findings will provide a guide for ink formulation and process control of EHD printing in flexible textile-based electronics.

On the Formation Mechanism of Nonsolvent-Induced Porous Polylactide Electrospun Fibers

Polylactide (PLA) fibers were electrospun from the solutions of PLA dissolved in the mixtures of its good and poor solvents, and the formation mechanism of the poor solvent-induced porous structure on the fibers was investigated. From a systematic study using the pairs of a variety of good/poor solvents for electrospinning, the conditions, specifically the solvent properties, for producing uniform fibers with controllable pores that appear not only on the surface but also throughout the fibers were proposed. The water miscibility of the good/poor solvents is crucial, which is because the ambient moisture that condenses during electrospinning plays an important role in the formation of the pores. Furthermore, the evaporation rate of the good/poor solvents is another key factor that affects the pore size and pore distribution on fibers because the solvent evaporation rate regulates the moisture condensation and the phase-separated scale that are closely related to fiber morphology. The principles generalized in this work can be applied to other low-polar polymers for controlling the porosity of fibers. In addition, this work demonstrates that the porous PLA fibers can be electrospun from low-toxic solvents and that with a large surface area and storage space provided by the pores, the PLA porous fibers are highly capable of adsorbing oils, with a capacity double that of the smooth counterpart.

Hierarchical Microphase Behaviors of Chiral Block Copolymers under Kinetic and Thermodynamic Control

Hierarchical Microphase Behaviors of Chiral Block Copolymers under Kinetic and Thermodynamic Control

Surface Analyses of PVDF/NMP/[EMIM][TFSI] Solid Polymer Electrolyte.

Thermal treatment conditions of solid polymer polymer electrolyte (SPE) were studied with respect to their impact on the surface morphology, phase composition and chemical composition of an imidazolium ionic-liquid-based SPE, namely PVDF/NMP/[EMIM][TFSI] electrolyte. These investigations were done using scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry as well as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A thoroughly mixed blend of polymer matrix, ionic liquid and solvent was deposited on a ceramic substrate and was kept at a certain temperature for a specific time in order to achieve varying crystallinity. The morphology of all the electrolytes consists of spherulites whose average diameter increases with solvent evaporation rate. Raman mapping shows that these spherulites have a semicrystalline structure and the area between them is an amorphous region. Analysis of FTIR spectra as well as Raman spectroscopy showed that the β-phase becomes dominant over other phases, while DSC technique indicated decrease of crystallinity as the solvent evaporation rate increases. XPS and ToF-SIMS indicated that the chemical composition of the surface of the SPE samples with the highest solvent evaporation rate approaches the composition of the ionic liquid.

Coffee‐Stain‐Free Perovskite Film for Efficient Printed Light‐Emitting Diode

AbstractInkjet printing is a powerful technology for realizing high‐density pixelated perovskite light‐emitting diodes (PeLEDs). However, the coffee‐stain effect in the inkjet printing process often leads to uneven thickness and poor crystallization of printed perovskite features, which deteriorates the performance of PeLEDs. Here, a strategy is developed to suppress the coffee‐stain effect via enhancing Marangoni flow strength. An interfacial poly(vinylpyrrolidone) (PVP) layer is incorporated to tune the surface tension of the underlying hole transport layer (HTL) and enhance the perovskite crystallization. The substrate temperature is also carefully controlled to tune the printing solvent evaporation rate rationally. By optimizing the thickness of the PVP layer and the temperature of the printing stage, the coffee‐stain effect is dramatically restrained. In addition, the interfacial insulating PVP layers play a positive role in suppressing leakage current level of PeLEDs by avoiding any direct electrical contact between HTL and electron transporting layer. Finally, an inkjet‐printed PeLED with a brightness of 3640 cd m–2 and external quantum efficiency of 9.0% is achieved. This work highlights the availability of inkjet‐printing technology for fabricating patterned PeLEDs in information display applications.

Experimental Measurement of Molecular Diffusion and Evaporation Rate of Battery Organic Electrolytes in Ambient Air

In this paper, we measured the molecular diffusivity and evaporation rate of organic solvents—1,2-dimethoxyethane (DME), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC)—in ambient air, which are commonly used in light metal batteries, such as Li-ion, Li-air, and Na-O2 batteries. The measurement was conducted through the evolution of the evaporation rate of a liquid solvent in a glass tube, which was designed based on a one-dimensional (1-D) mass transfer model. The experiment successfully measured the diffusion coefficients of DME (0.0925 cm2 s−1), DMC (0.2116 cm2 s−1), and DEC (0.0569 cm2 s−1) in dry air, but failed for that of PC. The PC testing showed a liquid loss smaller than the measurement uncertainty due to its slow evaporation rate under the experimental condition. In the ambient air with the relative humidity (RH) of 50 ± 5%, higher water-soluble solvents showed more decrease in diffusivity calculation compared to that under the dry condition, which is likely due to uncertainty arising from water dissolving to the testing liquid. In addition, we also investigated the time constant for experimental measurement. For the organic liquids, the effective running time can be up to 10 days under room temperature.

Assessment of Vehicle Volatility and Deposition Layer Thickness in Skin Penetration Models.

Systemic disposition of dermally applied chemicals is often formulation-dependent. Rapid evaporation of the vehicle can result in crystallization of active compounds, limiting their degree of skin penetration. In addition, the choice of vehicle can affect the permeant’s degree of penetration into the stratum corneum. The aim of this study is to build a predictive, mechanistic, dermal absorption model that accounts for vehicle-specific effects on the kinetics of permeant transport into skin. An existing skin penetration model is extended to explicitly include the effect of vehicle volatility over time. Using in vitro measurements of skin penetration by chemicals applied in both a saline and an ethanol solvent, the model is optimized to learn two vehicle-specific quantities: the solvent evaporation rate and the extent of permeant deposition into the upper stratum corneum immediately following application. The dermal disposition estimates of the trained model are subsequently compared against those of the original model using further in vitro measurements. The trained model showed a 1.5-fold improvement and a 19-fold improvement in overall goodness of fit among compounds tested in saline and ethanol solvents, respectively. The proposed model structure can thus form a basis for in vitro to in vivo extrapolations of dermal disposition for skin formulations containing volatile components.

Template-Free Construction of Tin Oxide Porous Hollow Microspheres for Room-Temperature Gas Sensors.

Porous hollow microsphere (PHM) materials represent ideal building blocks for realizing diverse functional applications such as catalysis, energy storage, drug delivery, and chemical sensing. This has stimulated intense efforts to construct metal oxide PHMs for achieving highly sensitive and low-power-consumption semiconductor gas sensors. Conventional methods for constructing PHMs rely on delicate reprogramming of templates and may suffer from the structural collapse issue during the removal of templates. Here, we propose a template-free method for the construction of tin oxide (SnO2) PHMs via the competition between the solvent evaporation rate and the phase separation dynamics of colloidal SnO2 quantum wires. The SnO2 PHMs (typically 3 ± 0.5 μm diameter and approximately 200 nm shell thickness) exhibit desirable structural stability with desirable processing compatibility with various substrates. This enables the realization of NO2 gas sensors having a superior response and recovery process at room temperature. The superior NO2-sensing characteristic is attributed to the effective gas adsorption competition on solid surfaces benefiting from efficient diffusion channels, enhancing the interaction of metal oxide solids with gas molecules in terms of the receptor function, transducer function, and utility factor. In addition, the one-step deposition of SnO2 PHMs directly onto device substrates simplifies the fabrication conditions for semiconductor gas sensors. The desirable structural stability of PHMs combined with the functional diversity of metal oxides may open new opportunities for the design of functional materials and devices.

Crystallization of nanoparticles induced by precipitation of trace polymeric additives

Orthogonal to guided growth of nanoparticle (NP) crystals using DNA or supramolecules, a trace amount of polymeric impurities (<0.1 wt.%) leads to reproducible, rapid growth of 3D NP crystals in solution and on patterned substrates with high yield. When polymers preferentially precipitate on the NP surfaces, small NP clusters form and serve as nuclei for NP crystal growth in dilute solutions. This precipitation-induced NP crystallization process is applicable for a range of polymers, and the resultant 3-D NP crystals are tunable by varying polymeric additives loading, solvent evaporation rate, and NP size. The present study elucidates how to balance cohesive energy density and NP diffusivity to simultaneously favor nuclei formation energetically and kinetic growth in dilute solutions to rapidly crystalize NPs over multiple length scales. Furthermore, the amount of impurities needed to grow NP crystals (<0.1%) reminds us the importance of fine details to interpret experimental observations in nanoscience.

Morphological Stability of Organic Photovoltaics: Coarse‐grained Molecular Dynamics Simulation Studies

We have performed coarse‐grained molecular dynamics simulations of organic photovoltaic (OPV) 5wcells consisting of poly(3‐hexyl‐thiophene) (P3HT), phenyl‐C61‐butyric acid methyl ester (PC61BM), and phenyl‐C71‐butyricacid methyl ester (PC71BM) to investigate the effects of the solvent evaporation rate and the number of components in the morphological stability of OPV. Two different solvent evaporation processes were employed in this study. In the instantaneous solvent removal process, unstable pores are formed because of the slow translational relaxation of the electron receptors. In case of the gradual solvent removal process, the stable film formation is observed without any pore. In addition, the ternary OPV system shows better stability than binary systems by slowing down the phase separation.

A new empirical diffusion model for solvents in sprayed seals based on evaporation measurements

ABSTRACT Prediction of solvent diffusion and evaporation rate in the initial days after construction of a sprayed seal is of special concern for pavement performance assessment. It is still a major challenge as solvent evaporation is a very complicated process. In this study, laboratory tests were conducted on bitumen-solvent binder films, under different experimental conditions and varying solvent properties. A solution of Fick’s diffusion equation was then used to calculate solvent diffusion coefficient (D) values for the initial 7 days. While a strong correlation was found between D and solvent viscosity as well as D and solvent distillation range, no relationship was found between D and solvent aniline point nor aromatic content. These findings were utilised in developing a multiple linear regression (MLR) diffusion model for the initial 7 days of evaporation. The evaluation of the model indicated close agreement between the predictions and experimental values (R 2 = 0.95). The model enables road agencies to predict solvent diffusion and residual solvent for the early life of a sprayed seal without needing to conduct extensive experiments thereby saving time and labour cost. Accurate prediction of residual solvent via the developed model will further ensure long-term performance of sprayed seals.

Molecular dynamics simulations of solvent evaporation-induced repolymerization of covalent adaptable networks

Covalent adaptable networks (CANs) can be decomposed in suitable solvents via bond exchange reactions. Repolymerization can occur by heating the decomposed solution and evaporating the solvent. This solvent-assisted decomposition and repolymerization approach can be used to recycle CANs. In this study, the solvent evaporation from decomposed CAN solutions along with the repolymerization of decomposed chain segments are investigated using molecular dynamics simulations. The evolution of density profiles and chain segment lengths are presented to characterize the solvent evaporation and network repolymerization. The effects of solvent molecule size and evaporation rate on the evaporation and repolymerization processes are analyzed. Our results show that a polymer-rich layer at the solution surface quickly forms when evaporating into a vacuum. The polymer-rich layer significantly inhibits the evaporation of solvent molecules with larger size. Molecules have sufficient time to diffuse when evaporating at a slow rate, thus a more homogenous density distribution can be achieved.

Crystallinity-dependent device characteristics of polycrystalline 2D n = 4 Ruddlesden–Popper perovskite photodetectors

Ruddlesden–Popper (RP) perovskites have attracted a lot of attention as the active layer for optoelectronic devices due to their excellent photophysical properties and environmental stability. Especially, local structural properties of RP perovskites have shown to play important roles in determining the performance of optoelectronic devices. Here, we report the photodetector performance variation depending on the crystallinity of n = 4 two-dimensional (2D) RP perovskite polycrystalline films. Through controlling the solvent evaporation rate, 2D RP perovskite films could be tuned between highly- and randomly-orientated phases. We investigated how different factors related to the film crystallinity are reflected in the variation of photodetector performances by considering grain boundary and low energy edge state effects in n = 4 RP perovskites. Better understanding the interplay between these factors that govern the photophysical properties of the devices would be beneficial for designing high-performance RP perovskite-based optoelectronic devices.

Microfluidic fabrication of polymer blend particles containing poly(4-butyltriphenylamine)-block-poly(methyl methacrylate): effect of block copolymer and rate of solvent evaporation on morphology

Here, we reported particles with approximately 80-μm diameter with phase-separated morphology of ternary polymer blends containing poly(4-butyltriphenylamine) (PBTPA), poly(methyl methacrylate) (PMMA), and PBTPA-b-PMMA fabricated via a microfluidic emulsification technique with a Y-shaped microreactor followed by a solvent evaporation. Addition of block copolymer changed the macroscopic structure from core-shell to Janus and more complicated sea-island type with the increase of the block copolymer content. The Janus structure with a PMMA hemisphere containing small PBTPA domain was observed at 10 wt% of the block copolymer. Meanwhile, the rapid evaporation changed the morphology macroscopically from the Janus to the undeveloped one where PMMA-rich phase mainly located at center sandwiched with outside PBTPA phases, suggesting that morphologies are governed by the kinetical factors together with the conventionally accepted thermodynamic ones. After the solvent annealing with toluene, distinct and enlarged PMMA phase appeared radiately, of which size gradiently decreased from the surface to the center (200–500 nm) in each particle.

Dynamical Density Functional Theory for the Drying and Stratification of Binary Colloidal Dispersions.

We develop a dynamical density functional theory based model for the drying of colloidal films on planar surfaces. We consider mixtures of two different sizes of hard-sphere colloids. Depending on the solvent evaporation rate and the initial concentrations of the two species, we observe varying degrees of stratification in the final dried films. Our model predicts the various structures described in the literature previously from experiments and computer simulations, in particular the small-on-top stratified films. Our model also includes the influence of adsorption of particles to the interfaces.