Solvent Evaporation Time Research Articles

Crystallization of Poly(l-lactic acid) on Water Surfaces via Controlled Solvent Evaporation and Langmuir-Blodgett Films.

Solvent evaporation is one of the most fundamental processes in soft matter. Structures formed via solvent evaporation are often complex yet tunable via the competition between solute diffusion and solvent evaporation time scales. This work concerns the polymer evaporative crystallization on the water surface (ECWS). The dynamic and two-dimensional (2D) nature of the water surface offers a unique way to control the crystallization pathway of polymeric materials. Using poly(l-lactic acid) (PLLA) as the model polymer, we demonstrate that both one-dimensional (1D) crystalline filaments and two-dimensional (2D) lamellae are formed via ECWS, in stark contrast to the 2D Langmuir-Blodgett monolayer systems as well as polymer solution crystallization. Results show that this filament-lamella biphasic structure is tunable via chemical structures such as molecular weight and processing conditions such as temperature and evaporation rate.

Capacity degradation of lithium-ion cell: The role of free carbon black content in the slurry and drying induced cracks in LiFePO4 electrode

Conductive additives, such as carbon black (CB), are incorporated into LiFePO4 (LFP) electrodes to address their low electronic conductivity. Within the electrode, a portion of CB remains as free carbon while the remaining amount attaches itself to the LFP particles. We have attempted to quantify the free carbon content in an LFP/CB/binder electrode composition via rheology studies. A low carbon content leads to an increased CB-binder domain formation thereby reducing electronic conduction. An increase in the carbon content is found to induce cracks and form islands within the electrode at the time of solvent evaporation and first cycling. Here we demonstrate the impact of free carbon content on the changes in the percentage of electronically well-connected and ill-connected active materials and its effect on the capacity in the nominal voltage zone during cycling studies. The electrode with 2.06 vol% CB exhibited a higher nominal zone capacity compared to electrodes with higher and lower CB content throughout 200 cycles of charge and discharge at 1C. Finally, the influence of premixing time, which affects the percentage of free CB, on the cyclic stability for a specific volume percentage of CB is investigated.

Insight into polydopamine coating on microfiltration membrane with controlled surface pore size for enhanced membrane rejection

Membrane modification with polydopamine (PDA) is a common practice to enhance membrane selectivity and improve membrane compatibility with nanoparticles or thin films. Depending on the membrane surface properties, dopamine can deposit or penetrate into microporous membranes, leading to alteration in the membrane's physicochemical properties and consequently its performance. In this study, microfiltration (MF) polyethersulfone membranes with varying surface pore sizes were fabricated by manipulating the precasting time (solvent evaporation time of 3s, 15s, 30s and 60s) prior to non-solvent induced phase separation (NIPS) process. Notably, the coating of PDA slightly reduced the membrane's surface pore size and membrane's porosity. M60 membrane which possessed the smallest mean surface pores (∼300 nm), exhibited PDA clusters predominantly formed on top of the membrane surface. With an increase in surface pore size, dopamine can penetrate the porous structure of the MF membrane, leading to the polymerization of dopamine into PDA aggregates on both the membrane surface and inner pores. The M30 membrane had the largest surface pore size (∼500 nm), showing the formation of large PDA globules in the finger-like pores. The membrane (M30P) experienced significant narrowing of the inner pores, resulting in reduced water permeability. Overall, all PDA-coated membranes exhibited improved sucrose rejection (85–95%) compared to the uncoated ones (64–83%). These finding provides insight into the polymerization mechanism of dopamine on porous membranes prior to the incorporation of nanomaterials or thin film coating.

Preparation of cellulose tri-acetate membranes for high-alcohol beverages via genetic algorithms and high throughput experimentation

In fermented beverages, volatile esters are trace compounds with a significant effect on the flavour profile. Some of the most important esters in beer are ethyl acetate (solvent-like aroma) and isoamyl acetate (banana aroma). These esters have a defined threshold which, when exceeded, will be experienced as unpleasant upon tasting. Therefore, the industry needs to selectively remove and fractionate esters by means of adsorption and tune the level of esters in the different process streams.Nanofiltration (NF) and Reverse Osmosis (RO) membranes are known to have a high potential towards removal of low molecular weight components from liquid streams. However, membrane preparation depends on several parameters with complex interactions to obtain the targeted membrane performance. Multi-parameter optimization strategies are thus very useful to reduce material consumption, minimize time and labour during the development of a ‘bottom-up’ preparation method. High throughput (HT) filtration techniques in combination with genetic algorithms (GAs) are known to be very powerful to direct such membrane preparation.This optimization strategy is used to obtain cellulose tri-acetate (CTA) membranes for filtration of high-alcoholic beverages towards ethyl acetate and isoamyl acetate depletion. Before the implementation of the proposed strategy, a successful optimization of the HT operating conditions was setup together with a selection of benchmark membranes by screening the performance of various commercially available nanofiltration (NF) and reverse osmosis (RO) membranes.Next, the non-compositional (solvent impregnation, membrane thickness, solvent evaporation time, annealing time and temperature) and compositional parameters (polymer concentration, solvents and additives selection) used during non-solvent induced phase separation (NIPS) preparation of CTA membranes were determined. Finally, CTA membranes were optimized using GAs.

Role of Draw Rate and Molecular Weight when Electrospun Nanofibers are Post‐Drawn with Residual Solvent

AbstractThe postdrawing process is poorly understood for polymer nanofibers due to the difficulty of manipulating nanofiber structures. Here, an angled track system facilitates postdrawing of individual nanofibers with control of parameters including molecular weight, draw rate, draw ratio, and solvent evaporation time. In this study, the effects of molecular weight, draw rate, and relative residual solvent content on final nanofiber properties are investigated. Molecular weight is first investigated to clarify any influence polymer chain length can have on drawing in facilitating or hindering chain extensibility. Polyacrylonitrile nanofibers with 50 and 150 kDa molecular weights behave similarly with postdrawing resulting in reduced diameters and enhanced mechanics. Since solvent quantity during drawing is a time sensitive component it is meaningful to assess the impact of draw rate on the chemical and structural makeup of postdrawn fibers. Chemical bond vibrations and chain orientation are sensitive to draw rate when polycaprolactone nanofibers are dried for 3 minutes prior to postdrawing, but this dependency to draw rate is not observed when fibers are postdrawn immediately upon collection. These findings demonstrate that the amount of retained solvent at collection is relevant to this postprocessing approach, and highlights the dynamics of solvent evaporation during postdrawing.

Construction of porous poly (aryl sulfide sulfone) film with low dielectric constant and excellent mechanical property

AbstractThe low dielectric constant and excellent mechanical property polymer film plays important roles in the high‐speed integrated circuits. In this work, porous poly (aryl sulfide sulfone) (PASS) films with different pore regularities and distributions were systematically fabricated via a combination process with solvent evaporation, wet induced phase separation, and hot pressing. It is found that the macroporous structure of PASS films changed from irregular shape with large pore size distribution to regular shape with small pore size distribution and the sponge‐like pore structure disappeared then formed a dense layer by controlling the time of solvent evaporation and hot pressing, to realize the effective control of the pore structure. The optimal PASS porous film D3 which was heated for 25 min and then hot pressed for 4 min has a low dielectric constant (2.44) and dielectric loss (0.010), high tensile strength (62.14 MPa) and breakdown strength (139.32 kV/mm), and low water absorption (0.54%). The comprehensive excellent properties are beneficial to the application of PASS films in microelectronic devices.

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.

Substrate-Independent Control of Polymorphs in Tetraphenylporphyrin Thin Films by Varying the Solvent Evaporation Time Using a Simple Spin-Coating Technique

Porphyrin derivatives are promising materials for various thin-film-based devices such as solar cells, field-effect transistors, and gas sensors. Since the molecular aggregation structure in a thin film significantly influences the device performance, controlling the aggregation structure is of crucial importance. In this study, we show that three different crystalline polymorphs of free-base tetraphenylporphyrin (H2TPP) can be made to form in spin-coated thin films depending on the evaporation time of the solvent. The results show that the aggregation structure in the as-spun films is controlled by the solvent evaporation time, and the initial film structure determines the polymorphs obtained after thermal annealing.

Effect of Solvent Evaporation Time of Polysulfone Incorporated Copper Oxide Nanoparticles Incorporated Polysulfone Ultrafiltration Membrane on Protein Removal

Polysulfone (PSf) membranes are becoming more popular in wastewater treatment recently, mostly due to its stability in chemical, thermal and mechanical properties. PSf membranes are hydrophobic, causing difficulty of water permeation. Incorporating metal oxide nanoparticles improving the membrane hydrophilicity, thus increasing membrane permeation and rejection. In this study, copper oxide nanoparticle (CuO NPs) incorporated PSf membranes were fabricated under different evaporation times of 3s, 6s, 8s, and 9s to investigate on membrane morphology and performance. The membrane morphologies were characterized by using scanning electron microscope (SEM) while the membrane performance was determined through pure water flux (PWF) and bovine serum albumin (BSA) rejection. When characterized by SEM, all membranes showed an asymmetric structure with thin and dense at the top while the bottom layer was thick and porous. It was discovered that as the evaporation time increased, the formation of the finger-like structure became narrower while dense layer became thicker. When tested with PWF, membranes with higher evaporation times showed less permeability, decreasing from 139.74 Lm-2h-1 to 89.89 Lm-2h-1. In terms of BSA rejection, increased in evaporation time caused the rejection rate to increase from 87.79% to 92.15%. This study proved that evaporation time is one of important parameters that influences the membrane performance significantly.

Porous polyether sulfone for direct methanol fuel cell applications: Structural analysis

Porous poly ether sulfone (PES) membranes were prepared using two different solvents which were N-methyl-2-pyrrolidone and dimethylacetamide (DMAc) via dry/wet non-solvent phase inversion (NIPS) techniques. PES with the compositions of 18 wt% is prepared for each dope solution. During the membrane casting process, 0 to 5 minutes delay prior to immersion in coagulant bath is set in order to allow solvent evaporation to take place. Water is used as the non-solvent for solvent exchange process. The prepared membranes are characterised based on their morphological aspect using scanning electron microscopy towards the effect of solvent evaporation time and solution viscosity. The changes in proton conductivity, methanol permeability, water uptake and hydrophilicity/hydrophobicity behaviours are also studied. Conclusively, the 18 wt% PES membranes prepared with DMAc as solvent at 3 minutes solvent evaporation time exhibited desirable pore size for proton conduction (0.04 × 10−3 Scm−1) and methanol resistant effect that consequently contribute to considerably low methanol permeability rate at 0.06 × 10−7 cm2 s−1 which could elevate the direct methanol fuel cell performance.

Effect of alternative solvent evaporation techniques on mechanical properties of primer–adhesive mixtures.

This study evaluated the influence of the mode and time of solvent evaporation on the tensile strength (TS), flexural strength (FS) and elastic modulus (EM) of two adhesive systems: Scotchbond Multipurpose (SBMP) and Clearfil SE (CSEB). For this purpose, rectangular samples (2x1x7 mm) were prepared with 10 μL of primer and the solvents were evaporated with air spray at (23±1) ºC, (40±1) ºC and negative control (without spray). For each temperature, the times of 5, 20, 30, and 60 seconds were investigated. The statistical results showed that evaporation at 40±1ºC resulted in better EM for the two adhesives tested and all the evaporation times evaluated. However, there were no significant differences between the times and modes of evaporation for TS. The results of this study indicate that evaporation at a temperature of (40±1) °C could improve the elastic modulus of both adhesives tested, regardless of the evaporating time.

Correlation between molecular structures and reaction conditions (temperature–pressure–time) in the preparation of secondary, tertiary, and quaternary ammonium-functionalized polyhedral oligomeric silsesquioxanes

Polyhedral oligomeric silsesquioxanes (POSSs) were prepared by the hydrolytic condensation reaction of organotrialkoxysilanes containing secondary and tertiary amino moieties, as well as quaternary ammonium groups. The employed methodology involved using aqueous trifluoromethanesulfonic acid (HOTf) as the catalyst and solvent at various temperatures and pressures in a Kugelrohr apparatus, which controlled the solvent evaporation time. At lower setting temperature (60 °C) or at shorter solvent evaporation times (≤2 h), the main product was a cage octamer (T8-POSS). Moreover, even at higher temperatures (≥100 °C), the T8 compound was the primary product observed for short evaporation time (≤1.5 h). However, when the solvent evaporation times increased (≥4 h, controlled by pressure) at higher temperatures (≥100 °C), the proportion of a cage decamer (T10-POSS) in the POSS mixtures was larger. Hence, T10-POSS was formed more readily than the corresponding T8 compound when the solvent was evaporated at higher temperatures and over the longer periods of time.

Flexible Bottom-Gated Organic Field-Effect Transistors Utilizing Stamped Polymer Layers from the Surface of Water.

The facile sequential deposition of functional organic thin films by solution processes is critical for the development of a variety of high-performance organic devices without restriction in terms of materials and processes. Herein, we propose a simple fabrication process that entails stacking multiple layers of functional polymers to fabricate organic field-effect transistors (OFETs). The process involves stamping organic semiconducting layers formed on the surface of water onto a commonly used polymeric dielectric layer. Our scheme makes it possible to independently optimize organic semiconductor films by controlling the solvent evaporation time during the process of film formation on the surface of water. This approach eliminates the need to be concerned about any interference with adjacent layers. Utilizing this process, the fabrication of high-performance bottom-gated OFETs is demonstrated on a glass and a flexible substrate. The OFETs consist of a vertically stacked diketopyrrolopyrrole-based polymer semiconducting layer on the poly(methyl methacrylate) film with a maximum hole mobility of 0.85 cm2/V s.

Synthesis of Calcium Fluoride Ultrafine Particles for the Preparation of Integral Asymmetric Cellulose Acetate/Calcium Fluoride Membranes

The present work reports on the synthesis of cellulose acetate (CA) asymmetric membranes with the incorporation of inorganic fluorides, CaF2 particles. These fillers of polymeric composites can, according to the literature, promote the ordering of the polymer matrix, which can lead to interesting permeation properties. In order to achieve that, fluorite (CaF2 ) fine particles were prepared by a double jet injection method using CaCl2 and NaF solutions as precursors and polyvinylpyrrolidone as a stabilizing agent. The fluorite particles were incorporated in the casting solutions of cellulose acetate/acetone/formamide. Dynamic light scattering measurements showed that formamide acting as the poor solvent in the membrane casting solutions can lead to some agglomeration of the fluorite particles and evident changes in structure and permeation properties. The CA/CaF2 composite membranes were casted by the phase inversion method at different solvent evaporation times. The permeation experiments indicated that the active layer of the membranes prepared with shorter solvent evaporation times is composed of an organic-inorganic network with bigger pores, which allows the permeation of molecules approximately two times the size of those retained by the CA membranes. Further increase in the solvent evaporation time has the opposite effect, as particle agglomerates may be formed.

Mathematical Modeling for the Design and Scale-Up of a Large Industrial Aerosol-Assisted Chemical Vapor Deposition Process under Uncertainty.

Aerosol-assisted chemical vapor deposition (AACVD) can be used to produce coatings and thin films such as transparent conducting oxide (TCO) films, which are used in self-cleaning surfaces, solar cells, and other electronic and optoelectronic applications. A process based on AACVD consists of a number of steps: aerosol generation, aerosol transport, aerosol delivery, and chemical deposition. Predicting the behavior of such a process at an industrial scale is challenging due to a number of factors: the aerosol generation creates droplets of different sizes, losses are incurred in the transport, the delivery must evaporate the solvent to release the precursors, and the reactions on the surface of the deposition target may be complex. This paper describes a full process model, including the prediction of the size distribution of the generated aerosol, the number and size of droplets delivered, the carrier gas temperature profile at the reaction site, the solvent evaporation time, and the rate of film formation. The key modeling challenges addressed include incorporating the impact of uncertainties in parameters such as heat and mass transfer coefficients and reaction rate constants. Preliminary simulations demonstrate a proof of concept for the use of simulation for gaining insights into the feasibility of a process scale-up for an industrial-scale AACVD.

Experimental and statistical investigation on fabrication and performance evaluation of structurally tailored PAN nanofiltration membranes for produced water treatment

The present study aims at investigating the effects of multiple fabrication and design parameters on the performance of nanofiltration (NF) membranes. By employing the Plackett-Burman design method, obtained results demonstrate that citric acid (0–1.5 wt.%), TiO2 (0–1 wt.%), and solvent evaporation time (1–3 min) are the top dominant factors affecting the pure water flux (PWF) of NF membranes. Also, the effects of the dominant factors and their corresponding interactions are statistically assessed through RSM technique by employing a quadratic model. Based on the ANOVA results the proposed models for the PWF and CaSO4 rejection responses are statistically significant. The calculated optimum values for citric acid, TiO2, and solvent evaporation time are 0.87 wt.%, 0.98 wt.%, and 1.34 min respectively. It is shown that by increasing the concentration of TiO2 both PWF and rejection of membrane enhanced from 108.8–131.5 (lit.m−2.h-1) and from 73.5–83 % respectively. Furthermore, an increment in citric acid concentration leads to the promotion of the surface hydrophilicity and salt rejection of membranes. From the morphological point of view, increasing the TiO2 concentration leads to formation of membranes with more porous sublayers while longer solvent evaporation times results in the formation of membranes with smaller macrovoids.

Poly(ether-block-amide) copolymer membrane for CO2/N2 separation: the influence of the casting solution concentration on its morphology, thermal properties and gas separation performance.

The present work is focused on the study of the effect that the casting solution concentration has on the morphology and gas separation performance of poly(ether-block-amide) copolymer membranes (Pebax® MH 1657). With this aim, three different concentrations of Pebax® MH 1657 in the casting solution (1, 3 and 5 wt%) were used to prepare dense membranes with a thickness of 40 µm. The morphology and thermal stability of all membranes were characterized by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, rotational viscometry and thermogravimetric analyses. An increase in crystallinity was notable when the amount of solvent in the Pebax® MH 1657 solution was higher, mainly related to the polymer chains arrangement and the solvent evaporation time. Such characteristic seemed to play a key role in the thermal degradation of the membranes, confirming that the most crystalline materials tend to be thermally more stable than those with lower crystallinity. To study the influence of their morphology and operating temperature on the CO2 separation, gas separation tests were conducted with the gas mixture CO2/N2. Results indicated that a compromise must be found between the amount of solvent used to prepare the membranes and the crystallinity, in order to reach the best gas separation performance. In this study, the best performance was achieved with the membrane prepared from a 3 wt% casting solution, reaching at 35°C and under a feed pressure of 3 bar, a CO2 permeability of 110 Barrer and a CO2/N2 selectivity of 36.

Circular economy in membrane technology: Using end-of-life reverse osmosis modules for preparation of recycled anion exchange membranes and validation in electrodialysis

In the current study, the indirect recycling of discarded reverse osmosis modules as i) membrane support for the preparation of anion exchange membranes and ii) polypropylene components for the assembly of an electrodialysis stack have been investigated for the first time. In such a way, 51% of the discarded module could be recycled into an electrodialysis system composed of 54% of recycled components. Recycled anion exchange membranes have been prepared by casting and phase inversion methods using discarded reverse osmosis membranes, preconditioned as support. The influence of casting thickness and solvent evaporation time in membrane properties has been studied. Besides, a complete membrane characterization has been carried out (SEM, water content, ion exchange capacity, permselectivity, electrical resistance, diffusion coefficients and mechanical properties) to select the optimal membrane preparation conditions, obtaining recycled anion exchange membranes with a high permselectivity (87%, similar to the commercial membranes). Finally, the technical viability of the recycled membranes has been tested by brackish water desalination experiments in the assembled electrodialysis stack, achieving 84.5% of salt removal. This study could open an alternative within the recycling of discarded reverse osmosis membranes, avoiding their disposal in landfills and moving membrane technology into a circular economy.

Effect of Solvent Evaporation Time and Casting Thickness on the Separation Performance of Cellulose Acetate Butyrate Blend Membrane

Global warming and climate change due to greenhouse gases (GHGs) emission, mostly carbon dioxide (CO2), have induced global efforts to minimize the concentration of atmospheric CO2. To reduce the effects of this problem, membrane technology is selected for the separation of CO2 due to the energy efficiency and economic advantages exhibited. In this study, the chosen polymeric material, cellulose acetate butyrate (CAB) is optimized using a wet phase inversion method with various molecular weight and different casting conditions due to its outstanding film-forming specifications and capabilities of fabricating a defect-free layer of neat membrane. The membrane was synthesized by blending three different molecular weights (Mn) of 12,000, 30,000 and 70,000 at different casting thickness, 150 µm to 300 µm and solvent evaporation time of 3.5 to 5 min. The results of these predominant parameters were then utilized to determine a high performance CAB membrane suitable for an enhanced CO2/Nitrogen (N2) separation. Eventually, a high separation performance CAB membrane was successfully synthesized with a CO2/N2 selectivity of 1.5819 ± 0.0775 when the solvent evaporation time and casting thickness was optimized at 4.5 min and 300 µm, respectively. Through this study, an improved understanding between membrane casting conditions and membrane performance has been achieved, for future development and progress.

Fabrication of PES/PVP Water Filtration Membranes Using Cyrene®, a Safer Bio-Based Polar Aprotic Solvent

A more sustainable dialysis and water filtration membrane has been developed, by using the new, safer, bio-based solvent Cyrene® in place of N-methyl pyrrolidinone (NMP). The effects of solvent choice, solvent evaporation time, the temperature of casting gel, and coagulation bath together with the additive concentration on porosity and pore size distribution were studied. The results, combined with infrared spectra, SEM images, porosity results, water contact angle (WCA), and water permeation, confirm that Cyrene® is better media to produce polyethersulfone (PES) membranes. New methods, Mercury Intrusion Porosimetry (MIP) and NMR-based pore structure model, were applied to estimate the porosity and pore size distribution of the new membranes produced for the first time with Cyrene® and PVP as additive. Hansen Solubility Parameters in Practice (HSPiP) was used to predict polymer-solvent interactions. The use of Cyrene® resulted in reduced polyvinylpyrrolidone (PVP) loading than required when using NMP and gave materials with larger pores and overall porosity. Two different conditions of casting gel were applied in this study: a hot (70°C) and cold gel (17°C) were cast to obtain membranes with different morphologies and water filtration behaviours.