Upper critical solution temperature—type cononsolvency of poly(N,N-dimethylacrylamide) in water—organic solvent mixtures

The behaviour of linear poly(N,N-dimethylacrylamide) (PDMAM) chains was studied by turbidimetry and viscometry in mixtures of water with the polar organic solvents methanol, dioxane and acetone. The swelling-deswelling behaviour of PDMAM gels in the same solvent mixtures was also investigated. Contrary to the behaviour in water-methanol mixtures, in water-dioxane and water-acetone mixtures a significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, was observed for high organic solvent fractions. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon decreasing temperature. This upper critical solution temperature (UCST) phase separation behaviour in mixed solvents was studied by turbidimetry and compared to the well-known lower critical solution temperature (LCST) behaviour of poly(N-isopropylacrylamide) (PNIPAM) in similar solvents mixtures.     

Cloud point curves for poly(vinyl methyl ether) and monodisperse polystyrene mixtures

The compatibility behaviour of poly(vinyl methyl ether) (PVME) and monodisperse polystyrene (PS) is studied for solution cast films. The molecular weight of monodisperse PS ranges from 2100 to 2 000 000 whereas the PVME used is polydisperse and has weight-average molecular weight of 51 500. When cast from toluene solution, the mixtures undergo phase separation at elevated temperatures. The cloud point curves move to markedly lower temperatures with increasing molecular weight which is similar to the lower critical solution temperature (LCST) behaviour for polymer solutions. They move to lower temperatures until the molecular weight of PS reaches about 51 500.The effect of molecular weight distribution on the cloud point of equal amounts of PS and PVME mixtures simulated by mixing two monodisperse polystyrenes of different molecular weight for PS part is accurately predicted by using weight-average molecular weight for PS in this range. However, if the molecular weight of PS exceeds about 110 000 the molecular weight dependence of cloud point temperature is reversed and the prediction for polydisperse polymer by using weight-average molecular weight fails. This phenomenon is discussed from several viewpoints including the possibility of the effect of chain entanglement.Mixtures of PVME and PS of M_w = 20 400 were also cast from an ‘incompatible’ solvent, trichloroethylene. Compatibility is found to be dependent on composition and even phase-separated samples show at least one cloud point, indicating at least partial mixing of the two polymers. Finally, it is demonstrated that crosslinking of compatible films can be achieved by electron irradiation to form true interpenetrating networks. The cloud point temperatures are increased drastically after crosslinking.     

Investigation of gas properties, design, and operational parameters on hydrodynamic characteristics, mass transfer, and biomass production from natural gas in an external airlift loop bioreactor

An external airlift loop bioreactor (EALB) was used for production of biomass from natural gas. The effect of riser to downcomer cross sectional area ratio (A_r/A_d), volume of gas-liquid separator, superficial gas velocity (U_sgr), and physical properties of gases and their mixtures [υ_g (μ/ρ) and D_g] were investigated on mixing time, gas hold-up, and volumetric gas liquid mass transfer coefficients (k_La). It was found that A_r/A_d has remarkable effects on gas hold-up and k_La due to its influence on mixing time. Kinematic viscosity (υ_g) showed its significant role on mixing time, gas hold-up and k_La when different gases used (mixing time changes directly whereas gas hold-up and k_La change indirectly). Moreover, it was found that diffusion coefficient of gas in water (D_g) has remarkable effect on k_La. The volumetric mass transfer coefficients for methane and its mixtures with oxygen (three different mixtures) were determined at different geometrical and operational factors. In average, the rate of oxygen utilization is approximately 1.8 times higher than that of methane. A gas mixture of 25 vol% methane and 75 vol% oxygen was the best gas mixture for biomass production in the EALB. The correlations developed for predicting the mixing time, gas hold-up, and k_La in terms of U_sgr, A_r/A_d, volume of gas-liquid separator, and gas phase properties have been found to be encouraging.     

Molecular thermodynamic analysis for phase transitions of linear and cross-linked poly(N-isopropylacrylamide) in water/2-propanol mixtures

Ternary liquid–liquid phase transitions of linear poly(N-isopropylacrylamide) (PNIPA) and the swelling behavior of cross-linked PNIPA gels in water/2-propanol mixtures were investigated using thermo-optical analysis (TOA) and a photon correlation spectroscopy (PCS) technique, respectively. Closed immiscibility gaps in ternary phase diagrams were obtained below 35 °C although all binary mixtures involved in this system were completely miscible. At a fixed concentration of PNIPA (1.0 wt%), a decrease in the lower critical solution temperature (LCST) occurred first, and with an increasing 2-propanol fraction of the solvent mixture, the upper critical solution temperature (UCST) subsequently developed. Corresponding to the linear PNIPA solution behavior, swollen PNIPA gels in pure water first shrank and then reswelled with increasing 2-propanol content in a typical reentrant transition. For theoretical treatment of the mixtures, a multi-component lattice theory of mixing and Flory–Rehner chain model for elasticity were employed for molecular thermodynamic analysis. A secondary lattice concept of specific interactions was used to model binary water/PNIPA solutions, and a temperature dependence of the intermolecular interactions for 2-propanol/PNIPA was used to describe island type ternary phase diagrams. The swelling transitions of cross-linked PNIPA gels were calculated using model parameters obtained from the ternary phase diagrams of linear PNIPA or from experimental conditions. The predicted results were in good agreement with experimental data without the need for further adjustable parameters.     

A thermodynamic interpretation of the compatibility of chlorinated polyethylene with poly(methylmethacrylate)

The compatibility of chlorinated polyethylene with poly(methylmethacrylate) and the oligomer analogue chlorinated octadecane with oligomeric PMMA are interpreted using the equation of state theory. It is found that the interaction energy parameter X₁₂ and the interaction entropy parameter Q₁₂, obtained from the heat of mixing and the phase boundary of oligomeric mixtures, can be used to generate the phase boundary of the polymer mixture. The spinodals of different molecular weights so generated have less molecular weight dependence than might be expected, in agreement with experimental results. A negative Q₁₂ indicates that some ordering may exist in the mixture due to specific interactions.     

A theoretical and experimental heat of mixing study for polymer‐polymer mixtures

Heat of mixing is introduced as a guide for phase stability predictions of polymer mixtures, and an appropriate equation is presented for it. The form of this equation is a combined function of temperature and mixture composition. The capability of the presented equation has been treated qualitatively and it has been shown that all types of exothermic, endothermic, and s‐shaped or sigmoidal heat of mixing curves can be produced. Utilizing the low molecular weight analogue calorimetry method, heat of mixing was measured at two temperatures, 27°C and 37°C for three polymer mixtures—poly(styrene)/poly(vinylchloride) (PS/PVC), poly(styrene)/ poly(methylmethacrylate) (PS/PMMA), and poly(styrene)/poly(vinylacetate) (PS/ PVAc) at an entire composition range. It has been shown that excellent agreement between the results of the calculations and the experimental heat of mixing data was achieved. Using the results of analogue calorimetric measurements for phase stability studies of polymer mixtures, it was found that often, acceptable predictions can be made by this method, but they are not always completely true.     

Solid-state structure of melt blended incompatible polymeric mixtures involving poly(vinyl chloride)

Poly(vinyl chlorides) having different melt viscosities were melt blended with several different incompatible polymers using a two-roll mill and a Brabender Plasticorder. The properties of the mixtures can be easily reproduced from batch to batch only if the viscosity of the components does not change during the mixing process. Within this limitation, the order of addition of the components during the mixture preparation does not have a significant influence on the mixture properties. The shear storage modulus of the incompatible mixtures in the temperature range between the Tg's of the components varies with the difference in component viscosities at the temperature of mixing. The moduli of these mixtures are compared to moduli calculated using Kerner's equations. Based on this comparison it is concluded that in any incompatible mixture the component having the lower melt viscosity at the temperature of processing tends to form a continuous phase in the mixture. The greater is the viscosity difference, the greater is this tendency. The viscosity of one component relative to the other can be changed by changing the molecular weight of the components and/or the temperature of mixing.     

Investigation of alternating-flow mixing in microchannels

A number of different approaches to mixing liquids in microscale systems can be found in the literature. In the case of miscible liquids it is desirable to produce mixtures with residual non-uniformity in composition that is below some specified level. Yet very little quantitative information is available concerning the conditions required to produce a given level of mixture uniformity. A theoretical approach to this problem is described. Computational fluid dynamics and simple scaling are used to develop a quantitative understanding of the alternating flow method of mixing using pressure driven flow. In this approach, external flow control is used to produce alternating injection into a single microchannel of two or more solutions to be mixed. The resulting streamwise slugs of solution then mix by the stretching of the slugs into thin striations resulting from shear strain. The most challenging condition for mixing is where the Reynolds number is approaching zero and inertia effects are negligible, a common situation in microchannel flows, particularly where relatively high-viscosity liquids, for example ionic liquids, are involved. The scaling theory demonstrates that an initial time period of rapid mixing of fluid outside the core of the flow, scaling as Pe^-2/3, is followed by a far slower process of mixing in the core region, scaling as Pe^-1/2. An approximate correlation for the deviation from the perfectly mixed state as a function of time is found. This correlation applies over the range of Peclet number, slug length and solution mixture ratio that are of interest. The mixture uniformity produced is shown to be limited by the initial uniformity of each solution over the channel section resulting from the injection process.     

Determination of standard pH values for potassium hydrogen phthalate reference buffer solutions in 10, 20, 50, 64 and 84.2 wt per cent methanol/water mixed solvents at temperatures from 283.15 to 313.15 K

Standard pH⁰ values for 0.05 mol kg^?1 potassium phthalate reference buffer solutions in 10, 20, 50, 64 and 84.2 wt % methanol/water solvent mixtures have been obtained from cells without transport, in the temperature range 283.15–313.15 K. The consistency of results has been analysed by a new method of multilinear regression of the quantity p(a_Hγ_Cl) as a function of both temperature and solution composition. The pH° values found can be reproduced within ± 0.01 by the equation pH⁰ = 4.00 + 4.38x ? 5.02x² + 4.23x³ + 0.13z ? 0.91xz, where x = mole fraction of methanol in the solvent mixture, z = (T ? θ)/θ and θ = 298.15 K. Subsidiary values of the first ionization constant of o-phthalic acid in the above solvent mixtures have also been obtained by the buffered cell method.     

Tuned phase behavior of weakly interacting polystyrene-block-poly(n-pentyl methacrylate) by selective solvent

We investigated, via small angle X-ray scattering, depolarized light scattering, rheometry, and transmission electron microscopy, the phase behavior of the mixture of a symmetric polystyrene-block-poly(n-pentyl methacrylate) copolymer (PS-b-PnPMA) showing the closed-loop phase behavior and excellent baroplasticity, and dodecanol, a PnPMA-selective solvent. We found that the addition of a selective solvent is simple, but very effective to obtain various microdomains including hexagonally packed cylinders and gyroids. Also, with increasing temperature, the mixtures showed multiple ordered-to-ordered transitions (OOTs) in addition to upper ordered-to-disordered transition (UODT). The first observation of gyroid microdomains in PS-b-PnPMA is very important, although they have been widely reported in many block copolymers, for instance, PS-block-polyisoprene copolymer (PS-b-PI) and PS-block-poly(d,l-lactide) copolymer (PS-b-PLA). Since the gyroid microdomains of PS-b-PnPMA show excellent baroplasticity, external pressure instead of temperature could easily change the microdomains.     

How does poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) trigger phase separation in aqueous alcohol?

Short chain alcohols, such as methanol and ethanol, are fairly well miscible in water over full mixing ratios. Moreover, when poly(N-isopropylacrylamide) is added in the same mixtures, the solution phase separates at low alcohol concentrations. From the fundamental understanding of phase separation within the mean-field picture, we can expect interaction parameter χ between water and alcohol to be significantly larger than unity. On the contrary, however, χ remains invariant and close to zero over full mixing ratios of aqueous alcohol mixtures. Here, we show how the preferential binding of poly(N-isopropylacrylamide) with alcohols facilitates local phase separation without altering bulk solution χ.     

Spectroscopic study of the decomposition process of tetramethylsilane in the N2–H2 and N2–Ar low pressure plasma

The optical emission spectroscopy has been used to study the decomposition process of tetramethylsilane in a low pressure plasma. The Si(CH₃)₄–N₂–H₂ and Si(CH₃)₄–N₂–Ar reactive mixtures, which are used for the deposition of SiCN layers, have been studied here. High energy active species were identified in the plasma phase and the electron excitation, vibrational and rotational temperatures as well as electron number density were determined for various compositions of the reactive mixtures. The electron excitation temperature (Si I, Ar I, H) was found to be higher than the vibrational temperatures (CN, N₂, N₂⁺) and considerably higher than the N₂⁺ rotational temperature, as the results of nonequilibrium state of plasma generated. It was observed that introduction of tetramethylsilane as well as growth of hydrogen percentage led to lowering of the electron density and the rotational temperature. Optical actinometry was applied to study the Si(CH₃)₄–N₂–H₂ reactive mixture.     

Effect of mixture ratio on water uptake and corrosion performance of silicone-epoxy hybrid coatings coated 2024 Al-alloy

A silicone-epoxy hybrid coating cured with amino silane was developed to provide corrosion protection on 2024 Al-alloy using air spraying. Water uptake characteristics of the silicone-epoxy hybrid coatings were investigated by electrochemical impedance spectroscopy in a 5 wt% NaCl solution. The effect of mixture ratio of silicone-epoxy and amino-silane on the water uptake (solubility, diffusion coefficient and permeation) was studied by using a single frequency (10 kHz) capacitance method. The glass transition temperature (T_g) was also investigated through differential scanning calorimeter (DSC) before and after immersion in the NaCl solution. Consequently, the excess of silicone-epoxy resin or amino silane improved the solubility of water in the coatings. A low water permeation coefficient was obtained with the mixing ratio 8/2 of silicone-epoxy and amino-silane, in which the T_g value was found to be larger than other three mixing ratios before immersion. After immersion for 750 h, the impedance modulus of EFA 2 coating (mixing ratio 8/2) in the low frequency was still close to 10⁸ Ω cm² that accounts for the good protective performance.     

Coleaching behavior of lead of incineration ash waste mixtures

In this paper, the authors reported the coleaching behavior of lead of incineration ash waste mixtures, i.e., fabric filter residues [called fly ash (FA)] and semidry scrubber residues [called reaction product (RP)]. The leaching potential of lead metal of those mixtures was estimated by toxicity characteristic leaching procedure (TCLP) with acidic extractant. And it was found to be under the controls of dissolution rate and interparticulate interactions. The author has developed a linear regression equation to fit the coleaching behavior well, the equation is basing on the chemical compositions of (RP/FA) mixtures. The impact of this study is that the leaching toxicity of mixture could be reduced to be nonhazardous, just only to adjust the mixing ratio of these two ash wastes. And the authors are able to use these ash wastes for wider recycling applications without any intermediate stabilization treatment.     

Compatibility of polyacrylates and polymethacrylates with poly(vinyl chloride): 1. Compatibility and temperature variation

Mixtures of a series of polymethacrylates and polyacrylates with PVC were prepared by solvent casting from methyl ethyl ketone. Some mixtures were also prepared by mechanical mixing and in situ polymerization (polymerization of vinyl chloride monomer in the presence of the other polymer). The mixtures were assessed for compatibility by dynamic mechanical measurements and optical clarity. It was found that all polymethacrylates from poly(methyl methacrylate) to poly(n-hexyl methacrylate) were compatible with PVC as were poly(n-propyl acrylate) and poly(n-butyl acrylate). Higher chain polyacrylates are incompatible. Poly(methyl acrylate) and poly(ethyl acrylate) appear incompatible with PVC when mixtures are prepared by solvent casting, but compatible when prepared by in situ polymerization, and mechanical mixtures show some sign of compatibility. It seems possible that in this case the solvent interferes with the compatibility. Mixtures of PVC with poly(n-hexyl methacrylate), poly(n-butyl acrylate) and poly(n-propyl acrylate) phase separate when heated in the region between 100°C and 160°C indicating the existence of a lower critical solution temperature.     

Thermoreversible and salt-sensitive turbidity of methylcellulose in aqueous solution

The turbidity of methylcellulose (MC) aqueous solutions without or with salt was investigated by optical transmittance. The optical transmittance was found to decrease with heating, while it recovered upon cooling. This phenomenon reflected the micro-phase transition from an unassociated state to a hydrophobically associated state in the solution when the system underwent the sol-gel transition. The derivative of absorbance (dA/dT) was used to determine the clouding point during gelation and the melting point during degelation. A salt-out salt (NaCl), a salt-in salt (NaI) and a salt mixture (NaCl+NaI) were, respectively, added into a MC solution to further investigate effects of salts on the gelation behavior. The critical transition temperatures obtained from rheological and micro thermal measurements were found to be consistent with the clouding points obtained by turbidity measurements. In the MC solutions with the salt mixtures, the critical temperatures followed a linear rule of mixing, indicating that the effects of salts on the sol-gel transition of MC are completely independent.     

Effect of crystallization rate on the formation of the polymorphs of solution cast poly(vinylidene fluoride)

A systematic study was carried out to investigate the effect of solvent type and temperature on the formation of the α and β phases from solution cast PVDF. Three solvents with different boiling points were used: N,N, dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and hexamethylphosphoramide (HMPA). Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) revealed that the type of phase formed depends on the crystallization rate of PVDF, which in turn is determined by the evaporation rate of the solvent. Low rates result predominantly in the trans-planar β phase, high rates predominantly in the trans-gauche α phase and intermediate rates in a mixture of these two phases, regardless of solvent and temperature used. Since evaporation rate of the solvent is intimately related to temperature, PVDF films can be obtained predominantly in either one of these phases, or a mixture of these, by an adequate choice of the evaporation temperature range for a given solvent. The possible solubility curves of the two polymorphs α and β of PVDF were sketched. The formation of different types of spherulites, associated with the two different PVDF polymorphs, could be verified by surface micrographs of the cast films.     

Gas hydrate formation from hydrogen/carbon dioxide and nitrogen/carbon dioxide gas mixtures

Gas hydrates from CO₂/N₂ and CO₂/H₂ gas mixtures were formed in a semi-batch stirred vessel at constant pressure and temperature of 273.7 K. These mixtures are of interest to CO₂ separation and recovery from flue gas and fuel gas, respectively. During hydrate formation the gas uptake was determined and the composition changes in the gas phase were obtained by gas chromatography. The rate of hydrate growth from CO₂/H₂ mixtures was found to be the fastest. In both mixtures CO₂ was found to be preferentially incorporated into the hydrate phase. The observed fractionation effect is desirable and provides the basis for CO₂ capture from flue gas or fuel gas mixtures. The separation from fuel gas is also a source of H₂. The impact of tetrahydrofuran (THF) on hydrate formation from the CO₂/N₂ mixture was also observed. THF is known to substantially reduce the equilibrium formation conditions enabling hydrate formation at much lower pressures. THF was found to reduce the induction time and the rate of hydrate growth.     

Low-temperature phase behavior of vegetable oil/co-solvent blends as alternative diesel fuel

Vegetable oils (triacylglycerols) have many characteristics that make them attractive candidates as renewable alternative fuels for compression-ignition (diesel) engines. Unfortunately, vegetable oils are too viscous to be compatible with modern direct-injection diesel fuel systems and engines. Co-solvent blending is a simple and flexible technology that reduces viscosity by mixing the oil with low molecular weight alcohol. A co-solvent (A), consisting, of surfactant plus an amphiphilic compound, is added to solubilize otherwise nearly immiscible oil-alcohol mixtures into a single-layer (isotropic) solution. This work examines low-temperature phase behavior of two soybean oil (SBO)/methanol mixtures solubilized by A=unsaturated long-chain (C₁₈) fatty alcohol/medium-chain alkanol (n-butanol and 2-octanol), one SBO/methanol mixture solubilized by A=triethylammonium linoleate/2-octanol, and one SBO/95 wt% ethanol (E95) mixture solubilized by n-butanol. The E95-blend was further blended in 1∶1 (vol/vol) mixtures with No. 2 diesel fuel. Two types of anisotropic phase behavior were observed; formation of a cloudy layer of solid crystals suspended in bulk solution (Type 1) and formation of two immiscible liquid layers (Type II). The type of phase separation in a given solution was influenced by phase separation temperature (T _ϕ) relative to the crystallization characteristics of compounds in the SBO and fatty alcohol or amine constituents present in solution. Solutions with relatively low T _ϕ values experienced crystallization of small solid particles favoring Type 1 separations. Conversely, solutions with T _ϕ sufficient to avert crystallization of high melting point compounds favored Type II separations where T _ϕ=critical solution temperature (T _critical). Increasing the A/oil (SBO or No. 2 diesel/SBO mixture) mass ratio decreased T _ϕ while increasing the mass fraction of alcohol (methanol or E95) increased T _ϕ. This work shows that vegetable oil/A-based blends can be formulated with cold flow properties superior with respect to cloud point and comparable with respect to kinematic viscosity (v) of methyl soyate (biodiesel), either neat or blended with petroleum middle distillates. Retired     

Cyanamide and Dicyandiamide Separation

Abstract

Solvent extraction of cyanamide and dicyandiamide (1-cyano-guanidine) from aqueous ammoniacal solution with Aliquat 336 dissolved in Shellsol T has been studied. Extraction isotherms with different ionic forms of the anion-exchanger are reported for the separation of the compounds of interest as well as for mixtures of the solutes. The optimum organic phase consists of a mixture of 10% (v/v) 2-ethylhexanol and 30% Aliquat in Shellsol T. With this phase the influence of temperature, extractant concentration, and the effect of changing ammonia concentration in the feed solution on the degree of extraction as well as the selectivity between the components have been investigated. In addition, experiments with different reextractants have been examined for the recovery of cyanamide and dicyandiamide. The evaluation of a physical chemical model for the extraction mechanism is done with the support of a computer program.