The role of solute conformation,solvent–solute and solute–solute interactions in crystal nucleation

The induction time for nucleation can differ based on the solutions used to conduct a crystallization, which can in turn impact the efficiency and economics of a crystallization process, the crystal size distribution, the morphology and ultimately functionality of the final product. Establishing a link between the nucleation pathway/solution structure and nucleation induction time is essential to achieve improved comprehension of the process of crystal nucleation from solution. In this study, the role of solute conformation, solvent–solute interaction, and solute–solute interaction in nucleation was examined using tolbutamide as a model compound in toluene and toluene–alcohol solutions. Through a combination of induction time experiments, attenuated total reflection Fourier transformed infrared spectroscopy, nuclear magnetic resonance spectroscopy, molecular dynamics simulations, and quantum chemical calculations, it was found that not only solvent–solute interactions but also solute–solute interactions and structural similarities between molecular self-assemblies in the solution and synthons in the crystal structure, can significantly influence the nucleation induction time.     

Polymer–lipid interactions: Biomimetic self-assembly behaviour and surface properties of poly(styrene-alt-maleic acid) with diacylphosphatidylcholines

Various lubricating body fluids at tissue interfaces are composed mainly of combinations of phospholipids and amphipathic apoproteins. The challenge in producing synthetic replacements for them is not replacing the phospholipid, which is readily available in synthetic form, but replacing the apoprotein component, more specifically, its unique biophysical properties rather than its chemistry. The potential of amphiphilic reactive hypercoiling behaviour of poly(styrene-alt-maleic acid) (PSMA) was studied in combination with two diacylphosphatidylcholines (PC) of different chain lengths in aqueous solution. The surface properties of the mixtures were characterized by conventional Langmuir–Wilhelmy balance (surface pressure under compression) and the du Noüy tensiometer (surface tension of the non-compressed mixtures). Surface tension values and ³¹P NMR demonstrated that self-assembly of polymer–phospholipid mixtures were pH and concentration-dependent. Finally, the particle size and zeta potential measurements of this self-assembly showed that it can form negatively charged nanosized structures that might find use as drug or lipids release systems on interfaces such as the tear film or lung interfacial layers. The structural reorganization was sensitive to the alkyl chain length of the PC.     

Synthesis, characterization, and sorption properties of water-insoluble poly(2-acrylamido-2-methyl-1-propane sulfonic acid)–montmorillonite composite

The sorption properties of composites based on 2-acrylamido-2-methyl-1-propane sulfonic acid and montmorillonite are presented. Gel-type composites were obtained via in situ polymerization. Resin particles presented exfoliated morphologies, as suggested by X-ray diffraction. The addition of montmorillonite resulted in enhanced mechanical properties, as evaluated by Vickers microhardness tests. The swelling performances of the resins exhibited a fast initial water uptake, reaching the maximum absorption capacity after less of 1 h of contact. A batch procedure was used to evaluate the sorption characteristics of the composites, and the effects of pH, montmorillonite content, and time were studied. The composites showed high adsorption capacities at pH values of 3.0 and 5.0, and the addition of montmorillonite did not result in a significant enhancement of their adsorption capacity. The equilibrium adsorption performance can be described by the Langmuir isotherm, while kinetic experiments revealed an excellent agreement with the pseudo-second-order model.     

Influence of solvent,Lewis acid–base complex,and nanoparticles on the morphology and gas separation properties of polysulfone membranes

A series of polysulfone (PSF) membranes were prepared using different solvents: dimethylformamide (DMF), tetrahydrofuran, dimethylacetamide, and n-methyl-2-pyrrolidone (NMP). The PSF membrane prepared by NMP showed the highest gas permeability. The influence of propionic acid as a Lewis acid on gas separation properties of the PSF was explored. The PSF membrane prepared by the casting solution containing 25 wt% PSF, 35 wt% propionic acid, and 40 wt% NMP showed a superior gas separation performance. The gas permeation measurements indicated that incorporating 30 wt% γ-alumina nanoparticles into the PSF matrix resulted in about the respective 43% and 41% increase in CO₂ and O₂ permeability together with a rise in CO₂/CH₄ and O₂/N₂ selectivities (13% and 7%, respectively). Furthermore, by rearranged modified Maxwell model, the role and nature of the interfacial layer in the PSF-based mixed matrix membranes were mathematically analyzed considering a reduced permeability factor.     

Effects of interactions among polyaniline, dodecylbenzylsulfonic acid and silica on the morphology and properties of their sol–gel hybrids

In this work, the effects of interactions among polyaniline (PAn), dodecylbenzylsulfonic acid (DBSA) and silica on the morphology and properties of their sol–gel hybrids are investigated. DBSA acts as dopant for PAn and an efficient catalyst for the formation of SiO₂ network. Also, DBSA promotes the dissolution of PAn in organic solvent for preparing uniform hybrids. The interaction between DBSA and PAn components raises conductivities of the DBSA-doped PAn/SiO₂ (d-PAn/SiO₂) hybrids. Moreover, the hydrogen bonding interaction between d-PAn and SiO₂ precursor (silicic acid) leads to a less degree of three-dimensional network structure of the SiO₂ component in a hybrid with higher d-PAn content. In addition, because of the interactions among DBSA, PAn, and SiO₂, the conductive d-PAn-rich phase distributes uniformly in the hybrids. Besides, the d-PAn/SiO₂ hybrid with higher SiO₂ content exhibits lower conductivity, higher thermal resistance and more significant blue-shift of its polaron band.     

Effect of modified rubber powder on the morphology and thermal and mechanical properties of blown poly(lactic acid)–hydroxyl epoxidized natural rubber films for flexible film packaging

In this study, we prepared and used modified natural rubber powder to increase the toughness of poly(lactic acid) (PLA) films. We blended PLA and hydroxyl epoxidized natural rubber (HENR) via a melt-mixing process with twin-screw extruder and a blowing machine. We investigated the influence of the HENR content in the blend films on the microstructure, thermal, mechanical, and optical properties. The morphology of the blend showed a coarse surface and elongated fibrils of HENR in the PLA matrix. After blowing, the dispersion of small particles of HENR in the substrate was seen. The size of the remaining HENR particles was smaller than that of the starting powder. The compatibility of HENR and the remaining rubber particles may have synergistically contributed to improvements in the elongation at break, impact strength, and ultraviolet–visible transition protection of the PLA films. The elongation at break drastically increased from 3 to 228% after PLA was blended with 20 wt % HENR. On the other hand, all of the blends exhibited lower glass-transition temperatures and cold crystallization temperatures than the pure PLA films. We concluded that the blend was partially compatible and may have increased the flexibility of the PLA films. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47503.     

Investigation of microstructure and mechanical properties of Cu/Ti–B–SiCp hybrid composites

In this study, Cu/Ti–B-SiC_p hybrid composite materials were produced by powder metallurgy method using three different sintering temperatures (950, 1000, 1050 °C). The optimum sintering temperature of Cu main matrix composites reinforced with Ti–B-SiC_p reinforcement materials at 2-4-6-8 wt.% were determined and their microstructure and mechanical properties were investigated. As a result of microstructure studies, it was determined that reinforcement elements have a homogeneous interface in the main matrix. The hardness of the produced composites was determined by the Brinell hardness method. The highest hardness value (77.74 HB) was determined in the sample with 6 wt% reinforcement ratio. In the tensile and three point bending tests, maximum strength values (112.96 MPa, 37.76 MPa) were found in samples with a reinforcement ratio of 4 wt%. It was determined that increasing reinforcement ratios and sintering temperature made a positive contribution to the hybrid composite materials produced.     

Preparation and dielectric properties of dense and amorphous alumina film by sol–gel technology

Dense and crack-free aluminum oxide films were fabricated by sol–gel spin-coating technology. Aluminum nitrate (Al(NO₃)₃.9H₂O) was used as the precursor material. X-ray diffraction shows that the fabricated films are amorphous. X-ray photoelectron spectroscopy confirms that the thin films are alumina (Al₂O₃). Field-emission scanning electron microscopy images of the films reveal that the films are compact with a dense cross section. Dielectric measurements were carried out on samples with a metal–insulator–metal structure. The electrical characteristics of the films were affected by the thermal sintering temperature of the films. The leakage current density of the films decreases with the increase in the sintering temperature and increases with the increase in the measuring temperature. The leakage current shows a linear dependence on the voltage in the low-electric field-regime. The current density ascends to higher values due to the effect of space charges in the high-electric-field regime. The ionization energy of the top-electrode metals (Au, Pt or Ti–Au) has a strong effect on the leakage current.     

Investigation of structure and conductivity properties of polyaniline synthesized by solid–solid reaction

Conductive polyaniline has been prepared by solid–solid reaction using ammonium peroxydisulfate as an oxidant. The obtained polymer was examined by X-ray diffraction, UV visible, FTIR spectroscopy, thermogravimetric analysis and impedance spectroscopy. The effect of oxidant/monomer molar ratio (R) on the structure and electrical properties of polymer has been examined. The analyses of X-ray diffraction patterns demonstrated that polyaniline prepared by this method is more crystalline than that obtained by conventional solution method. The FTIR spectroscopy showed that the emeraldine salt has been formed. The electrical properties were measured at different temperatures in the range of 296–523 K. The ac conduction shows a regime of constant dc conductivity at low frequencies and a crossover to a frequency-dependent regime of the type A ω^S at high frequencies.     

Development of mefenamic acid–loaded polymeric microparticles using solvent evaporation and spray-drying technique

Ethyl cellulose (EC) and Eudragit RL-100 (ERL-100) were used for the preparation of sustained released microparticles of mefenamic acid (MFN) by using oil-in-oil (o/o) solvent evaporation as well as spray drying. A Plackett-Burman design was employed using Design-Expert software. The resultant microparticles were characterized for their size, surface morphology, encapsulation efficiency, and drug release. Imaging of microparticles was performed by field emission scanning electron microscopy. The drug and polymer interaction was investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray powder diffractometry (XRPD). The microparticles showed encapsulation efficiency in the range of 29.44 to 89.20% by solvent evaporation and 83.73 to 96.69% by spray drying. The surface of the microparticles was smooth, round, and regular, without any erosion and cracking. The size of the microparticles was found to be in the range of 6.55 to 41.1 µm. FTIR analysis confirmed no interaction of MFN with the polymers. XRPD showed the dispersion of the drug within the microparticle formulation. These results helped in finding the optimum formulation variables for encapsulation efficiency (EE) of microparticles.     

Urushiol/polyurethane–urea dispersions and their film properties

A series of aqueous polyurethane–urea (PUU) dispersions having urushiol were synthesized by in situ step polymerization of isophorone diisocyanate (IPDI), poly(ethylene glycol) (PEG, M_n = 1000 g/mol), urushiol, dimethylol propionic acid (DMPA), and ethylene diamine (EDA). Urushiol was extracted with acetone from the purified lacquer of Toxicodendron vernicifluum and the different concentrations (0, 11.8, 17.6, and 22.2 wt.% based on the total solids) of urushiol were introduced during the PU prepolymer synthesis. Thermal stability, mechanical strength, antimicrobial, and anticorrosive properties of the urushiol/PUU films were investigated in terms of urushiol concentration.     

Comparison of film properties for crosslinked core–shell latexes

Thermosetting acrylic latexes were synthesized using butyl acrylate (BA), methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA) via seeded two-stage process. A 2-level factorial experimental design was employed to investigate the effect of hydroxyl (core phase), carboxylate (shell phase) groups, and type of surfactant (Triton X200, Tergitol XJ) on the mechanical properties of thermosetting latexes. Eight latexes with varying concentration of HEMA, MAA and two types of surfactants were synthesized and crosslinked with three crosslinkers. Latex functionality for crosslinking was located in the core only, the shell only, and both the core–shell with varying concentrations. Melamine-formaldehyde (hexamethoxymethyl melamine) resin was employed to crosslink hydroxyl functionalities in the core. Carboxylic acid groups in the shell were crosslinked with zinc ammonium carbonate. HDI isocyanurate (Desmodur N3300A) were used to crosslink with hydroxyl or carboxyl functional groups in core and shell. The mechanical properties of coatings were evaluated in terms of tensile properties, cross-hatch adhesion, pencil hardness, and impact resistance. Design of experiment (DOE) was utilized to investigate the effect of variables on mechanical properties of crosslinked thermoset films.     

Adhesion-to-fibers and film properties of etherified–oxidized cassava starch/polyvinyl alcohol blends

In our previous work, it was demonstrated that etherified–oxidized cassava starch (EOCS) showed greater adhesion and film properties than oxidized cassava starch (OCS). Therefore, the purpose of this paper is to reveal if blending EOCS with polyvinyl alcohol (PVA) could further enhance the adhesion of OCS to cotton and polylactic acid (PLA) fibers and toughen OCS film. The EOCS samples were synthesized through etherification of OCS with 3-chloro-2-hydroxypropyl sulfonic acid sodium in an aqueous medium, and were characterized by Fourier transform infrared spectroscopic technique. The apparent viscosity of cooked EOCS/PVA paste was measured, and the adhesion was evaluated by measuring the bonding forces of the blends to cotton and PLA fibers. Film properties were analyzed in terms of tensile strength, breaking elongation, bending endurance, scanning electron microscopy and X-ray diffraction. It was found that blending EOCS with PVA was able to further enhance the adhesion of OCS to both fibers and toughen OCS film. The enhancement in the adhesion and the film toughness was correlated with blending ratio of EOCS to PVA. With the decrease in the ratio, the breaking elongation and bending endurance of the blend films and bonding forces significantly increased. By increasing the degree of substitution (DS) of EOCS, the bonding forces of EOCS/PVA blends to both fibers gradually increased. In the adhesion, the positive influence performed by the ratio is more than that performed by the DS. The EOCS/PVA with a ratio of 50:50 and a DS of 0.031 could be adopted to further improve the adhesion and film toughness of OCS.

     

Application of molecular dynamics computer simulations to evaluate polymer–solvent interactions

In this article, systematic calculation of the radius of gyration (R _g) of a block copolymer immersed in various solvents is presented. Using atomistically detailed, molecular dynamics computer simulations, we carry out the calculation of R _g at different polymerization degrees, for each solvent. Our results show that, given a solvent and a polymerization degree, R _g can display different values. This aspect is found to be a consequence of the spatial conformation of the constitutive blocks that make up the polymer molecule. Finally, we find that there exists a correlation between R _g and the solubility parameter and that the trend in R _g predicted by our calculations agrees with previous experimental results.     

Investigation on ferromagnetic and ferroelectric properties of (La,K)-doped BiFeO3–BaTiO3 solid solution

Multiferroic materials of BiFeO₃–BaTiO₃ solid solution have been fabricated in order to improve ferromagnetic and ferroelectric properties. The effects of La (1 mol%) and K (varied from 0.5–5 mol%) doped 0.75BiFeO₃–0.25BaTiO₃ on phase formation, ferromagnetic and ferroelectric properties have been investigated and discussed. The rhombohedral perovskite phase of specimens was characterized by XRD technique. Fracture morphology reveals the grain growth characteristics with increasing K content. (La, K)-doped 0.75BiFeO₃–0.25BaTiO₃ with La=1 mol% and K=3 mol% exhibits the highest remnant polarization and remnant magnetization.     

Effect of phosphorus–nitrogen compound on flame retardancy and mechanical properties of polylactic acid

A phosphorus-nitrogen flame retardant (PN) was synthesized by using cytosine and diphenylphosphinic chloride. The flame retardancy and thermal stability of polylactic acid (PLA)/PN composites were investigated by the UL-94 vertical burning test, limited oxygen index (LOI), cone calorimeter test, and thermogravimetric analysis. The PN performs efficiently on improving the flame retardancy of PLA. The PLA composite achieves the UL-94 V-0 rating and its LOI increases to 30.4 vol% by adding 0.5 wt% PN. The flame retardant mechanism analysis showed that PN catalyzes the degradation of PLA to improve the flame retardancy by melting-away mode. Meanwhile PN reduces the release of flammable gasses during thermal degradation of PLA by promoting the transesterification of PLA, which is helpful for extinguishing flame. Moreover, triglycidyl isocyanurate (TGIC) was used as a micro-crosslinking agent to reduce the loss of mechanical properties of PLA/PN composites caused by degradation. Adding 0.1 wt% TGIC and 1.0 wt% PN into PLA, the tensile strength and elongation at break of PLA/PN are increased to the same level as that of PLA. Therefore, PLA with excellent comprehensive performance can be obtained.     

Preparation and properties of soapless poly(styrene–butyl acrylate–acrylic acid)/SiO2 composite emulsion

Soapless emulsion polymerization of styrene-butyl acrylate-acrylic acid was carried out using single or combined polymerizable emulsifiers, such as hydroxypropyl methacrylate sodium sulfate (HPMAS), sodium vinyl sulfate, and vinyl alkylphenol polyether sulfates (NRS-10), in the presence of colloidal nano-SiO₂ solution in order to obtain films with high degree of hardness and water-resistance. Monomer conversion, formation of coagulum, viscosity, particle size, size distribution, and surface tension of the emulsions, as well as the film properties, were determined and compared with those of an emulsion prepared with the conventional emulsifier sodium dodecyl sulfate and polyoxyethylene octylphenol ether. Emulsions prepared from a mixture of two polymerizable emulsifiers NRS-10 and HPMAS (1:1, weight ratio) have presented high monomer conversion, low coagulum, and small particle sizes. When the emulsifier level increased within a certain level, the monomer conversion increased but particles size decreased. Increased amounts of reactive emulsifiers led to low monomer conversion, large amount of coagulum and small particle sizes. With the increase of nano-SiO₂ the particle sizes and the viscosity of the emulsion also increased. The introduction of reactive emulsifiers improved the water-resistance of the resulting films, and the addition of nano-SiO₂ increased the hardness of the coatings. Under optimal conditions, the coatings made from emulsions produced from a combination of reactive emulsifiers such as NRS-10 and HPMAS (1:1, weight ratio) at 2?% level (based on monomer weight) exhibited remarkable hardness, adhesion force and water-resistance.     

Preparation of highly flexible chitin nanofiber-graft-poly(γ-l-glutamic acid) network film

In the previous study, we successfully prepared a chitin nanofiber film by regeneration from a chitin ion gel with an ionic liquid using methanol. In this study, we performed surface-initiated graft polymerization of γ-benzyl l-glutamate N-carboxyanhydride (BLG-NCA) from amino groups on a partially deacetylated chitin nanofiber (PDA-CNF) film. First, the chitin nanofiber film was immersed in 40 % NaOH aq. at 80 °C for 7 h for partial deacetylation. Then, the PDA-CNF film was immersed in a solution of BLG-NCA in ethyl acetate at 0 °C for 24 h for graft polymerization from amino groups on nanofibers to give a chitin nanofiber-graft-poly(γ-benzyl l-glutamate) (CNF-g-PBLG) film. The analytical results of the film indicated that graft polymerization of BLG-NCA occur on surface of nanofibers. Furthermore, the film was treated with 1.0 mol/L NaOH aq. to convert PBLG on nanofibers into poly(γ-l-glutamic acid sodium salt) (PLGA). Then, condensation of the resulting carboxylates with amino groups at the terminal ends of PLGAs or the remaining amino groups on nanofibers was performed using the condensing agent to produce a CNF-g-PLGA network film. The resulting film showed the good mechanical properties with high flexibility, which has potentials as promising materials for practical applications.     

Electrochemical study of isopoly- and heteropoly-oxometallates film modified microelectrodes —vi. preparation and redox properties of 12-molybdophosphoric acid and 12-molybdosilicic acid modified carbon fiber microelectrodes

The redox behaviours of 12-molybdophosphoric acid (12-MPA) and 12-molybdosilicic acid (12-MSA) in aqueous acid media are characterized at the carbon fiber (CF) microelectrode. The preparation of CF microelectrode modified with 12-MPA or 12-MSA monolayer and the oxidation-reduction properties of the modified electrode in aqueous acid media or 50% (v/v) water-organic media containing some inorganic acids are studied by cyclic voltammetry. 12-MPA or 12-MSA monolayer modified CF microelectrode with high stability and redox reversibility in aqueous acidic media can be prepared by simple dip coating. The cyclic voltammograms of 12-MPA and 12-MSA and their modified CF microelectrodes in aqueous acid solution exhibit three two-electron reversible waves with the same half-wave potentials, which defines that the species adsorbed on the CF electrode surface are 12-MPA and 12-MSA themselves. The acidity of electrolyte solution, the organic solvents in the electrolyte solution, and the scanning potential range strongly influence on the redox behaviours and stability of 12-MPA or 12-MSA monolayer modified electrodes. On the other hand, the catalytic effects of the 12-MPA and 12-MSA and chlorate anions in aqueous acidic solution on the electrode reaction processes of 12-MPA or 12-MSA are described.     

Ternary Ti–Si–C alloy film formation on GaN and contact properties

Ternary Ti–Si–C alloy films were deposited on GaN substrates (n-type and p-type) by the radio- frequency magnetron sputtering method. The electrical properties of contact films with various chemical compositions were investigated. The microstructures were examined by X-ray diffractometry and transmission electron microscopy. The electrical properties of the contact films were improved after annealing at 873?K for 60?s. Ohmic contact characteristics were obtained for n-type GaN. The TiN phase plays an important role in obtaining the ohmic contact. The effect of deposition and annealing on the electrical properties between Ti–Si–C film and GaN are discussed based on the experimental results.