Aqueous Alcohol Solutions Research Articles

Design and Fabrication of a Robust Chitosan/Polyvinyl Alcohol-Based Humidity Sensor energized by a Piezoelectric Generator

Due to their rapid growth in industrial and environmental applications, there is a need to develop self-powered humidity sensor systems with improved sensitivity, a wide detection range, and an eco-friendly nature. In this study, an aqueous solution of chitosan (CS) and polyvinyl alcohol (PVA) was blended to yield a composite film material with enhanced humidity detection properties. Meanwhile, a polyvinylidene difluoride (PVDF)-loaded chitosan composite film was developed and employed as a piezoelectric generator. Moreover, the developed composite materials for both devices (the piezoelectric generator and the humidity sensor) were optimized based on output performance. The piezoelectric generator generates a maximum of 16.2 V when a force of 10 N is applied and works as a power source for the humidity-sensing film. The sensing film swells in response to changes in relative humidity, which affects film resistance. This change in resistance causes a change in voltage through the piezoelectric generator and allows the precise measurement of relative humidity (RH). The fabricated sensor showed a linear response (R2 = 0.981) with a reasonable sensitivity (0.23 V/% RH) in an environment with an RH range of 21–89%. In addition, the device requires no external power, and therefore, it has numerous sensing applications in various fields.

Dissolution of 5-azacytidine in aqueous solution of alcohols at various temperatures: Preferential solvation and thermodynamic analysis

In this work, the dissolution process of 5-azacytidine in mixtures of (methanol + water), (ethanol + water), (n-propanol + water) and (isopropanol + water) at several temperatures was studied and correlated by Jouyban-Acree model and CNIBS/R-K model. In pure solvent, the maximum solubility is observed in water (1.862 × 10-3) followed by isopropanol (1.025 × 10-4), ethanol (5.804 × 10-5), methanol (4.280 × 10-5) and n-propanol (3.478 × 10-5) at 318.15 K. In the mixed solvent, with the increasing water molecules around the solute molecules, the polarity of the solvent system increases, which is conducive to the dissolution of solute molecules. According to the preferential solvation results in water-rich mixtures, it is possible that 5-azacytidine is acting as a Lewis acid due to the more basic alcoholic solvent molecules respect to water. –OH and –NH2 in 5-azacytidine provide hydrogen protons to form hydrogen bonds with oxygen atoms on alcohol molecules. While in the mixtures with compositions of 0.30 < x1 < 1 for methanol, 0.20 < x1 < 1 for ethanol, 0.15 < x1 < 1 for n-propanol and isopropanol, 5-azacytidine molecule is preferential solvation by water and acting as a Lewis base in front to alcohols. The calculation of thermodynamic properties for the whole composition range of aqueous binary mixtures indicates the dissolution process is endothermic and entropy-increasing. Moreover, the enthalpy is the main contributor to Gibbs energy of the solution process in each binary mixtures. The experimental solubility data and thermodynamic parameters of 5-azacytidine achieved in present work could be very useful in drug development method, purification and crystallization.

Peculiar points of aqueous solutions of mono-hydrogen alcohols

The work is devoted to the detailed study of the peculiar points in aqueous solutions of mono-hydrogen alcohols. The main attention is focused on water-methanol and water–ethanol solutions for which there are numerous experimental data. It is taken into account that H-bond interaction between alcohol and water molecules stimulates the formation of hydration complexes or elementary clusters, stable for temperatures: T<42°C. A solution at the peculiar point has a cell-like structure, where every cell consists of one alcohol molecule surrounded by water molecules forming mono-molecular layer. The volume and dissolution heat per cluster are determined. It is shown that the peculiar point arises at the concentration leading to the full filling of a solution by elementary clusters. The instability of elementary clusters near the peculiar point is considered. The possible existence of peculiar point of another type is discussed.

Adsorptive separation of dye by filled polymeric FIPN hydrogel

ABSTRACT Acrylic acid (AA) and Acrylamide (AM) are copolymerised to produce copolymer of Poly-acrylic acid-co-acrylamide (PAA) in the aqueous solution of Polyvinyl alcohol (PVA). Both the polymers PVA and PAA were cross-linked in situ by glutaraldehyde and N, N O-methylene bis acrylamide (MBA) respectively using 2 mass% of polymer basis for both of them. Thus, three different full interpenetrating network (FIPN) hydrogels were synthesised varying the mass ratio of PVA to PAA. The hydrogel of PVA: PAA = 1:0.50 composition designated as PAA50 found competitive for separating Malachite green from its 50 ppm aqueous solution by adsorption compared to the other two. PAA50 was further modified by incorporating 2, 5, 8 and 10 mass% nano size sodium monomontellite filler and produced four filled FIPN hydrogels designated as PAA52, PAA55, PAA58 and PAA510, respectively. These four nano-filled FIPN hydrogels along with unfilled PAA50 and pure nano size sodium monomontellite were used for adsorption in same dye solution of 5, 10, 25, 50, 75 and 100 ppm concentrations and different pH of 4, 7, 9, 10 & 11. Highest 98.039% dye removal was done by PAA58 from 75 ppm feed at 9 pH. 93.7% recovery was observed at 3 pH in desorption study.

The dissolution behavior and thermodynamic properties analysis of pentoxyverine citrate in aqueous solutions of alcohols

The objective of this work is to study the dissolution behavior and thermodynamic properties of pentoxyverine citrate in aqueous solutions of alcohols. The results of solubility data at temperature range from 278.15 K to 318.15 K were obtained by the isothermal equilibrium method under atmospheric condition. In pure solvents, the largest solubility data in mole fraction is found in water at 318.15 K (2.756 × 10−2), followed by ethanol (1.156 × 10−2), n-propanol (8.129 × 10−3), isobutanol (5.233 × 10−3), isopropanol (4.340 × 10−3) and 1-butanol (3.435 × 10−3). The order of solubility from large to small is consistent with the order of solvent polarity. The solubility profile in mixtures of (ethanol + water), (n-propanol + water) and (isopropanol + water) increases firstly and then decreases with the increasing mass fraction of alcohols at all studied temperatures, and it reaches a maximum at w = 0.60 (the mass fraction of ethanol) in mixtures of (ethanol + water) at all investigated temperatures, for two other binary mixtures, the mass fraction of n-propanol and isopropanol is 0.40. The analysis of extended Hildebrand solubility approach indicate the solvent–solvent interactions and specific interactions are unfavorable for the dissolution process. The values of relative average deviation (RAD) for crystalline pentoverine citrate demonstrated well correlation of solubility values with Apelblat equation and Jouyban-Acree model. The positive values of ΔHsolo and ΔSsolo for dissolution behavior indicate the dissolution process was not only endothermic but also entropic-favouring. Moreover, the enthalpy is the main contributing force to the Gibbs free energy during the dissolution of pentoverine citrate.

Effect of Hydrogen Bonding on Dynamic Rheological Behavior of PVA Aqueous Solution.

The rheological behavior of polyvinyl alcohol (PVA) aqueous solution is crucial to optimizing the processing technology and performance of PVA products. In this paper, the dynamic rheological behavior of PVA aqueous solution was investigated in detail. PVA solution with a concentration of 10 wt% showed unnormal rheological behaviors, that is, the liquid-like behavior in the high frequency (ω) region and the solid-like behavior in the low ω region. A storage modulus (G′) plateau appears in the relatively low ω region as a gel with a network structure. Different from conventional hydrogel, this plateau has a low modulus, and the corresponding size of the relaxation unit is estimated to be 554 nm, being higher than the size of a whole PVA chain. It is believed that the network mesh is formed by the intermolecular hydrogen bonding interactions among PVA chains. The relaxation time of these meshes is longer than the reptation time of a PVA chain. Based on the relaxation spectrum and calculation analysis, it is found that the destruction of intermolecular hydrogen bonds, such as by heating up, adding sodium dodecyl sulfate, and shear operation, will make the relaxation unit (mesh) larger and lead to the left shift of the intersection of G′ and loss modulus (G″). In a PVA solution with a high concentration, multiple meshes of various sizes could be formed and thus generate multiple relaxation peaks. The large-sized meshes mainly contribute to the left shift of the intersection of G′ and G″, and the small-sized meshes contribute to the high plateau modulus. The results in this paper offer a new angle to analyze polymer solutions with strong intermolecular interaction.

Etching and optical properties of 1–2 MeV alpha particles irradiated CR-39 radiation detectors

A comparison of track etch parameters at low energy alpha particles is presented, using the Lantrak and the Baryotrak CR-39 nuclear track detectors. Experimental data from literature, obtained through exposing CR-39 detectors at low energy alpha particles from a 241Am source and, subsequently, etching them in NaOH, KOH, and NaOH+ethyl alcohol aqueous solutions at 70°C and 80°C, have been numerically analyzed here. Radial etch rates of alpha particle etch pits have been determined, compared, and critically discussed for both CR-39 types. Ratios of alpha etch pit diameters and etch pit densities have also been examined as a function of etching time, showing no notable differences in the comparison between these two detectors. This study has been extended from the structural point of view by performing new Ultraviolet–visible (UV–Vis) and Raman spectroscopy measurements on non-irradiated, α-irradiated and α-irradiated/etched Lantrak and Baryotrak detectors. The direct band-gap energies have been determined and no significant differences have been observed in detectors subjected to different conditions. The Raman spectra show that the CH2 functional group has been decreased when comparing the non-irradiated/α-irradiated and α-irradiated/etched detectors, suggesting a degradation of the detectors due to alpha particle irradiation and also due to the different chemical etching treatments applied. The uncertainties have been determined and reported along with the results.

Regulation of morphology and electrochemical properties of Ni-Co LDHs electrode materials by lower saturated monohydric alcohols coordination

The alcohol solvent can effectively regulate the electrochemical property of Ni-Co LDH. In this study, the aqueous solutions of lower monohydric alcohols were used to synthesize Ni-Co LDH using the solvothermal method, and the effects of alcohol type and content on the electrochemical performance of Ni-Co LDH were investigated. The ab initio calculation and characterization analysis were performed to elucidate the mechanism of how coordination of alcohol molecules regulates the nucleation and growth of materials at the micro-level. The electrochemical property of the battery-type Ni-Co LDH is improved by optimizing the molar ratio of Ni to Co. The causes of the specific capacity decay of Ni-Co LDHs are also explored by electron microscopy and spectroscopy. Finally, a button supercapacitor with high energy density has been assembled, in which activated carbon (AC) is the negative material, and Ni-Co LDH is the positive material. This study provides some insights into controllable preparation of Ni-Co LDHs as alternative materials for SCs.

Bimetallic MMoS4 (M = Ni, Co, Cu) cocatalysts architected CdS nanoflowers for synergistically boosting visible-light-driven photocatalytic H2 evolution from water and benzyl alcohol

Exploring efficient photocatalysts to facilitate water splitting into green hydrogen (H2) energy is of great significance nowadays. In this work, we successfully synthesized CdS nanoflowers coated by zero-dimensional MMoS4 (M = Ni, Co, Cu) cocatalysts using a mild two-pot solvothermal method. Notably, 2.5%-NiMoS4/CdS catalyst exhibits optimal photocatalytic H2 evolution from benzyl alcohol aqueous solution under visible-light irradiation, and its photocatalytic H2 activity (7269.5 μmol·h−1·g−1) is 10.1 times higher than that of pure CdS (716.6 μmol·h−1·g−1). Simultaneously, benzyl alcohol can be synergistically converted into benzaldehyde after dehydrogenation. Such excellent photocatalytic performance mainly benefits from the existence of an internal electric field (IEF), which is demonstrated by experimental analysis and density functional theory calculations. And the IEF greatly accelerates the separation of electron-hole pairs during the photocatalytic H2 evolution process.

Ecology of preimaginal phases of mosquitoes in the north of Yakutia

The experimental part of the work was carried out in the Momsky district of the Republic of Sakha (Yakutia) in 2008. Office processing of the collected material was carried out at the Yakut Scientific Research Institute of Agriculture, the All-Russian Research Institute of Veterinary Entomology and Arachnology. The larvae were taken with a net from the mill gas and their number was counted. To determine the density of larvae, a recalculation per 1 m2 of the water surface was performed. Then the larvae and pupae were placed in vessels with water and delivered to the laboratory, where they were preserved with 70% aqueous alcohol solution in 10 ml vials with rubber stoppers, the vials were supplied with labels. Samples were taken once a week, from the third decade of May to the third decade of July. A total of 14120 mosquito larvae were collected. district is located at 66°27ў18ўў north latitude and 143°13ў11ўў east longitude. In temporary reservoirs, the density of mosquito larvae in the second decade of June is up to 876 ind./m2. At the beginning of the third decade of June, the density of larvae reaches up to 1432 ind./m2. At the end of June, a decrease in the density of mosquito larvae to 233 ind./m2 was noted with a simultaneous increase in the number of pupae. The species composition of adults emerging from the cage was determined as Aedes punctor Kirby and A. hexodontus Dyar. The percentage of emergence from pupae is 95%. Mosquitoes have been flying since June.

Effect of Impregnation with a Low-Concentration Furfuryl Alcohol Aqueous Solution on Hygroscopic Properties of Chinese Fir and Poplar Wood

Furfurylation with a low concentration of furfuryl alcohol (FA) promotes the improvement of the properties and the effectiveness of FA on cell–wall action without darkening the furfurylated wood to the point that it affects its applications. In this paper, the effects of furfurylation on the hygroscopicity and water uptake dimensional stability of poplar (Populus sp.) and Chinese fir (Cunninghamia lanceolata) were analyzed. Meanwhile, the distribution of FA resin, the relationship between wood and water, the change in pore size distribution, and the weight percentage gain and cell wall bulking coefficient of wood were also investigated. The results were as follows: (1) A low concentration of FA could better enter the cell walls of the Chinese fir than the poplar, as FA resin was almost cured in the secondary walls, cell corners, and compound middle lamellae when a 10% concentration of FA was applied to the Chinese fir and poplar. When the FA concentration was increased to 30%, there were no significant increases in the amount of FA entering the cell walls and the amounts of FA cured in the cell lumen of the poplar were greater than those of the Chinese fir. Meanwhile, the modification of cell walls was more suitable in poplar than in Chinese fir. (2) The pointed ends of the pit chambers and the pit apertures (800–1000 nm) in the poplar and the small pores of the pit membranes and the pit apertures (1–6 μm) in the Chinese fir were partially deposited by the FA resin, which formed new pores in the size ranges of 80–600 nm and 15–100 nm, respectively. The porosity of the poplar was greater than that of the Chinese fir, and the bulk density of the poplar was less than that of the Chinese fir before and after modification. (3) Furfurylation with a low concentration of FA was able to better reduce the equilibrium moisture content, improve the anti-swelling efficiency, and enhance the dimensional stability of the poplar wood compared to the Chinese fir. Furfurylation effectively reduced water uptake due to the hydrophobic property of the FA resin. The water uptake of the Chinese fir increased by 17%–19% in second cyclic water soaking when treated with FA with various concentrations, which indicated the loss and leaching of FA resin during the test. Low-field NMR was used to demonstrate that the furfurylation not only reduced the amount of water but also affected the combination state of bound and free water with wood. Thus, furfurylation at a low concentration is a feasible method by which to extend applications of furfurylated wood.

Kinetics of Stability of Foams from Aqueous Solutions of Polyvinyl Alcohol with Different Molecular Weight

Kinetics of Stability of Foams from Aqueous Solutions of Polyvinyl Alcohol with Different Molecular Weight

Acoustically induced birefringence in polymer aqueous solutions: The case of polyvinyl alcohol

Transient and stationary ultrasonically induced birefringence traces of various relatively dilute poly-vinyl alcohol aqueous solutions were measured over a range 500–1400 kHz of ultrasonic frequencies and 0.02–0.13 W/cm2 of acoustic field amplitudes. The intrinsic value of the stationary birefringence for all polymer solutions investigated in this study was found to be proportional to the solution mass concentration, the square root of the ultrasonic intensity and the frequency of the ultrasound in agreement with theoretical predictions. Systematic analysis of the transient birefringence signals caused by the applied ultrasonic field has been performed in order to evaluate the orientational relaxation times from the viewpoint of dynamics of polymer chain orientation and anisotropy changes in polarizability. The results are discussed in the context of recent experimental studies and theoretical predictions of the ultrasonically induced birefringence in terms of transport phenomena.

Mutable bubble surface mobility in water – propanol mixtures and its impact on bubble motion and deformation

Various anomalies are typical for aqueous solutions of simple alcohols, with viscosity maxima and changing bubble surface mobility being significant for multiphase systems. Three regions of the hydrodynamic behaviour of spherical and ellipsoidal bubbles are described, depending on the propanol concentration. At low concentration (xP ≤ 0.005), alcohol behaves as a surfactant and the increase in concentration increases the drag coefficient and decreases bubble deformation. At intermediate concentration, the increase of concentration leads to more deformed bubbles with increasing rise velocity, because of the advantage of formation of bulk clusters. At high concentration (xP ≥ 0.07), bubbles behave as fully mobile with a low drag coefficient. Because of the fast desorption of molecules from the bubble surface, neither a concentration gradient nor a surface tension gradient arises, and thus the conditions for bubble surface mobility are fulfilled. The transition in the hydrodynamic behaviour is evident for all bubble sizes.

РЕОЛОГИЯ ВОДНОГО РАСТВОРА НИЗКОМОЛЕКУЛЯРНОГО ПОЛИВИНИЛОВОГО СПИРТА

The rheology of aqueous solutions of polyvinyl alcohol (PVA) was studied by the method viscometry. The values of the verification coefficients were estimated depending on both the concentration of PVA, and on the average molecular weight of the PVA itself. It is shown that in water a solution of low molecular weight PVA (70-140 kDa) with a concentration of up to 0.035% dominant is the interaction of polymer chains with water (the first belief coefficient), and above 0.035% PVA, the interaction of polymer chains between itself (the second confidence factor).

Luminescent hybrid materials based on organic phosphors and fluorides in the PbF2-LaF3 system

Powder hybrid materials based on 8-hydroxyquinolate lithium organic phosphor and - LaF3 inorganic fluoride matrix PbF2 have been synthesized. Hybrid materials were obtained by co-precipitation from aqueous-alcoholic solutions with ammonium fluoride under various conditions - different concentrations of precursor solutions, Pb/La ratio, and the siquensy of reagents’ mixing. All obtained hybrid materials showed effective broadband luminescence in the region of 390-500 nm. The photoluminescence intensity during reverse deposition was found to be higher than during direct deposition for different concentrations of reagents.

Conducting Polymer Hydrogel Driven By Sodium Chloride as High Performance Flexible Supercapacitor Electrode

With the rapid development of the wearable devices and flexible supercapacitors (FSCs), urgent demand for electrodes with high specific capacitance and excellent flexibility have been put forward. Herein, a self-standing conducting polymer hydrogel electrode has been successfully synthesized by in situ polymerization of aniline (ANI) in aqueous solution of polyvinyl alcohol (PVA), phytic acid (PA) and sodium chloride (NaCl). The prepared PANI/PVA/NaCl (PPN) hydrogel electrode shows high specific capacitance (1544 mF cm−2 at current density of 1 mA cm−2), good flexibility (elongation at fracture of 110%), satisfactory electrochemical stability (92% capacitance retention after 500 repeated bending cycles) and excellent cycling stability (78.2% capacitance retention after 10000 cycles) due to the uniform 3D interconnected structure driven by NaCl pseudo template. In order to further explore the potential application prospects of the synthesized hydrogel in flexible devices, a series of all-hydrogel-state FSCs are assembled based on the prepared PPN hydrogel electrodes and typical PVA/H2SO4 electrolyte. The assembled FSCs exhibit high energy density of 51.1 μWh cm−2 at power density of 250 μW cm−2 and long-life stability of 81.10% capacitance retention after 10000 charge/discharge cycles. This work provides a new synthesis strategy for the high performance energy storage electrodes and devices.

Fabrication of moldable chitosan gels via thermally induced phase separation in aqueous alcohol solutions

Wide application of chitosan in modern technologies is limited by the lack of reliable and low-cost techniques to prepare size-tuned constructs with a complex surface morphology, improved optical and mechanical properties. We report a new simple method for preparation of transparent thermoreversible chitosan alcogels from chitosan/H2O/ethanol ternary systems. This method, termed “low temperature thermally induced phase separation under non-freezing conditions” (LT-TIPS-NF), fine tunes gelation by adjusting only temperature (from 5 to −25 °C) and varying the initial content of chitosan (from 0.5 to 2.0 wt%) and ethanol (from 28.5 to 47.5 vol%). Transparent non-swelling final constructs of complex shape are prepared by fixing the pre-formed alcogels with a base solution. The size of the gel constructs is limited only by the dimensions of the mold and the cooling chamber. The LT-TIPS-NF is applicable both in injection molding and 3D printing techniques. The in vitro and in vivo experiments show the absence of prominent cytotoxicity and well-defined cell adhesion on the obtained hydrogels. Thus, this facile and scalable technique provides the multifunctional chitosan gel preparation with easily controlled properties exploiting inexpensive, renewable, and environmentally friendly source polysaccharide. These materials have prospects for a variety of uses, especially for biomedical applications.

In Situ Detection of Chemical Compositions at Nanodroplet Surfaces and In-Nanodroplet Phases.

Small-volume nanodroplets play an increasingly common role in chemistry and biology. Such nanodroplets are believed to have unique chemical and physical properties at the interface between a droplet and its surrounding medium, however, they are underexamined. In this study, we present the novel technique of vibrational sum frequency scattering (VSFS) spectroscopy as an interface-specific, high-performance method for the in situ investigation of nanodroplets with sub-micron radii; as well as the droplet bulk through simultaneous hyper-Raman scattering (HRS) spectroscopy. We use laboratory-generated nanodroplets from aqueous alcohol solutions to demonstrate this technique's ability to separate the vibrational phenomena which take place at droplet surfaces from the underlying bulk phase. In addition, we systemically examine interfacial spectra of nanodroplets containing methanol, ethanol, 1-propanol, and 1-butanol through VSFS. Furthermore, we demonstrate interfacial differences between such nanodroplets and their analogous planar surfaces. The sensitivity of this technique to probe droplet surfaces with few-particle density at standard conditions validates VSFS as an analytical technique for the in situ investigation of small nanodroplets, providing breakthrough information about these species of ever-increasing relevance.

Covalent modification of zein with polyphenols: A feasible strategy to improve antioxidant activity and solubility.

Covalent modification of protein with polyphenols is an attractive research topic, since it is an effective way to improve the properties and broaden the applications of protein. However, the majority of prolamin-polyphenol reactions were carried out in alcohol aqueous solution, and this study aimed to investigate the covalent interaction of zein and polyphenols in water. Chlorogenic acid (CGA), gallic acid (GA), and caffeic acid (CA) were used as polyphenol models. The grafting ratio revealed that zein interacted more strongly with CGA and CA than with GA, which was probably due to the larger molecular weight of CGA and the hydroxycinnamic acid structure of CA. Afterward, the differences in structural and functional properties between control zein and zein-polyphenol complexes were compared. Covalent interaction with polyphenols induced great changes in the morphology and secondary structure of zein. Compared with control zein and non-covalent complexes, covalent zein-polyphenol complexes exhibited better solubility, antioxidant activity, and thermal stability. PRACTICAL APPLICATION: Covalent modification of zein with polyphenols in water is a simple and efficient method, which can ameliorate the antioxidant activity as well as the hydrophilicity of zein and improve its application value. The findings of this research carry important implications for using zein-polyphenol complexes as novel food additives, or to design more efficient delivery systems.