Phase Separation Conditions Research Articles

Salt-induced phase separation can effectively remove the acetonitrile from the protein sample after the preparative RP-HPLC

Acetonitrile (ACN)–water system is one of the most commonly used mobile phases in practical reverse-phase high-performance liquid chromatography (RP-HPLC). However, a higher concentration of ACN (normally greater than 60% (v/v)) is required to elute the target protein from the RP-HPLC column in which, further steps to remove the ACN from the protein samples are demanded. It has been demonstrated that the phase separation occurring under the sub-zero temperature could easily remove the majority of ACN from the effluent of RP-HPLC. Recently, we found that the comparable phase separation could be achieved by adding a small amount of proper salts, such as K 2HPO 4 and KH 2PO 4, and the phase separation could take place effectively at 4 °C where the protein-purification processes were usually carried out. In addition, the pH value of the solution could be maintained properly by using potassium phosphate buffer (pH 7.0). With an optimized condition for this salt-induced phase separation, we demonstrated that greater than 60% of ACN could be easily removed; on the other hand, more than 90% of water-soluble protein could be successfully recovered within five hours.

A Fourth-Order Stationarity and Ergodicity Conditions for Harmonic Processes

This paper considers the problem of estimating the fourth-order cumulant sequence of a harmonic process. Both stationarity and ergodicity conditions for this kind of signal are derived through the imposition of restrictions to the frequencies and amplitudes that define the signals. Statistical properties for the mean value and the variance of the sample mean estimator are deduced as well. These conditions are applied to cubic-phase coupling detection, stressing the study of nonergodic signals and possible strategies to study them. Numerical examples to illustrate these conditions for cubic phase coupling detection and separation of mixed signals using independent component analysis (ICA) methods are also showed in this paper.

HCToolkit/EOS interface: an open source, multi-platform phase equilibria framework for exploring phase behaviour of complex mixtures

Abstract We present a computational framework that can be used to estimate phase equilibria, equation of state properties and composition-dependent viscosity, aimed at the geochemical community for modelling reservoir processes, and at the chemical community to quickly estimate continuum properties of known mixtures. The framework presented is an extensible, component-based set of modules that can be used in calculating phase properties (volumes and densities, compositions and conditions of phase separation, Henry’s Law constants and viscosities) at a wide range of pressures, temperatures and starting compositions. There are two pieces to the model: the HCToolkit (a set of Perl modules that act as computational engines) and the EOSInterface (an ActiveX wrapper for the HCToolkit) which allow the models in the HCToolkit to be usable in Microsoft Office programs. An application hosted in Microsoft Excel is included within the distribution. The EOS models are adaptable for mixtures of arbitrary complexity, with number and types of components only limited by hardware. Model runs with mixtures of over 100 components have been tested, and are perfectly feasible. Implemented within the software are four equations of state; additional equations of state can easily be added. Also implemented are G E models and mixture viscosities. Finally, the EOS models provide liquid-vapour flash calculations, liquid-liquid flash (designed for petroleum-aqueous solutions) and the generation of phase diagrams.

Microporosity of Porous Glasses: New Investigation Techniques

Two new methods are developed for investigating the microporosity of porous materials. The first method, namely, diffusion diagnostics, is based on a computer simulation of the kinetics of gas desorption from a porous material into high vacuum. In this method, the kinetics of gas desorption is measured using mass spectrometry. Another method is based on the analysis of the equilibrium isotherms of gas desorption at low pressures. The microporous and mesoporous substructures of the porous glasses prepared by leaching of two-phase alkali borosilicate glasses in a 3 M HCl solution at 100°C are investigated using both the new methods and the classical adsorption methods. A correlation between the porous structure of glasses and their synthesis and phase separation conditions is revealed. It is demonstrated that porous glasses have a through mesoporous substructure with mean pore diameters ranging from 4 to 15 nm and a polymodal microporous substructure with pore sizes ranging from 0.35 to 2 nm. This microporous substructure is formed by ultramicropores of molecular sizes and also medium- and large-sized micropores. It is found that porous glasses contain bottle-shaped pores with sizes corresponding to the micropore range. An increase in the temperature of heat treatment of glasses from 550 to 700°C and an increase in the boron oxide content in the silica phase lead to an increase in the volume of micropores in porous glasses.

Polymer Blends and Interpenetrating Polymer Networks at the Interface with Solids

AbstractFor Abstract see ChemInform Abstract in Full Text.

Specific Features of the Diffusion Gas Saturation of Some Alloys under the Conditions of Internal Phase Separation

We make an attempt to give an adequate mathematical description of the kinetics of gas saturation of metallic materials by taking into account the surface and bulk phenomena. For this purpose, we pose and solve the initial-boundary-value problems of diffusion of admixtures and alloying elements taking into account their chemical interaction. The process of gas saturation runs in the presence of a given time dependence of the surface concentration of admixtures and in the absence of mass exchange of alloying elements. We deduce equations for the concentrations of admixtures and alloying elements after subsequent isothermal annealing. The influence of various factors, such as the surface phenomena on the medium–metal interface and the intensity of bulk chemical reactions, on the results of chemical and thermal processing of alloys is estimated. The accumulated analytic results are compared with the experimental data obtained for vanadium and vanadium alloys held in vacuum and helium media at T = 1023°K and 1123°K for 120–2500 h.

Current-induced metastable resistive states with memory in low-doped manganites

The influence of dc current flow on the resistivity and phase transitions in low-doped ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_{3}$ single crystals has been investigated. At low temperatures, where the resistivity strongly increases with decreasing temperature, dc current depresses resistivity in a way consistent with the domination of tunneling-conduction mechanisms. Current flow exceeding some threshold currents results in resistivity switching and metastability. Bipolar current sweep exceeding threshold currents in both positive and negative direction creates low-resistivity states in the sample. The low-resistivity state converts into a very-low- and stable-resistivity state under a stronger bipolar current sweep. Current-induced low-resistivity states are characterized by long-term memory persisting even after storing the sample for a few days at room temperature. The memory can be erased by ac current flow at high temperatures. The results are interpreted in terms of a spin-polarized tunnel conduction mechanism, which modifies phase-separation conditions along the percolation path.

Phase behavior of polymer containing colloidal dispersions: The integral equation theory

We present an integral equation theory based on the polymer reference interaction site model (PRISM) formalism to describe a phase behavior of polymer containing colloidal dispersion. We focus on the thermodynamic stability of dispersed component, i.e., on the conditions of percolation and phase separation in this subsystem. Different phase diagrams for the colloid subsystem are constructed in the variables: volume fraction of the colloid component–temperature. We analyze the behavior of the spinodal line and the percolation threshold. It was shown that the spinodal lines do not exhibit a critical point. The additivity of a polymer induced and a direct attraction between the colloidal particles is examined.

Phase Separation and Collective Excitations of Two-Component Bose-Einstein Condensates in Traps

The phase separation and collective excitations of two-component Bose-Einstein condensates in traps are studied. Using the variational method, we show that the separated state is favorable in the case where the interspecies interaction is strongly repulsive and the number of atoms is large enough. This phase separation condition is explained in terms of the softening of a dipole mode collective excitation. Other low-lying excitation modes and their softenings which lead to the instability of the mixed state are also studied by use of the sum-rule approach.

Analysis of Phase Separation in Compressible Polymer Blends and Block Copolymers

For the analysis of phase-separation behavior of compressible polymer blends and block copolymer melts, an equation-of-state (EOS) model is combined with the compressible random-phase approximation (RPA) formalism. The EOS model to be employed is obtained from extending an off-lattice model, recently given for interpreting compression response of pure polymers to pressure by Cho and Sanchez (CS), to polymer blends. The free energy for the CS model consists of an ideal free energy of Gaussian chains and a nonideal free energy that represents the excluded volume effects and the attractive interactions in given blend systems. This nonideal free energy yields the RPA interaction fields, with which monomer−monomer correlation functions for polymer blends or block copolymers are calculated to determine the condition of phase separation. It is shown that the theory can predict not only macrophase separation in some polymer blends but also microphase separation in the corresponding block copolymer melts. Especial...

Stability of Two-Component Bose-Einstein Condensates in Traps

Static and dynamic stabilities of two-component Bose-Einstein condensates trapped in harmonic potentials are studied. Using the variational method, we obtain the static stability condition and the phase separation condition. They are expressed as functions of the particle numbers and the s-wave scattering lengths. We find that the interaction between the different species of atoms (simply, interspecies interaction) has significant effects on the stability of each condensate. The instability of the ground state is explained in terms of the lowering (softening) of the collective excitation energies. We investigate the low-lying excitations and the possibility of their softening by use of the Gaussian ansatz and the sum-rule approach.

Comment on “Robustness of a Local Fermi Liquid against Ferromagnetism and Phase Separation”

In this paper we comment on the "Local Fermi Liquid Theory", proposed by Engelbrecht and Bedell [1]. We emphasize several important properties of the limit of infinite dimensions, in particular the k-dependence of the irreducible vertex function, the anisotropy of the Fermi surface and the necessary conditions for phase separation. It appears that these issues have not been fully appreciated in Ref. [1].

Phase separation in magnetic colloids

The influence of a temperature, a magnetic field strength and an excess electrolyte on the phase separation conditions in magnetic colloids has been studied theoretically, taking into account the ferroparticle polydispersity.

Spontaneous spatial symmetry breaking in two-component Bose-Einstein condensates

We discuss the general features of spontaneous spatial symmetry breaking in trapped two-component alkali-metal--atom Bose-Einstein condensates, and give qualitative guidelines for when it will occur. We further show that the Hartree-Fock equations admit symmetry-broken solutions for as few as two trapped atoms, discussing the particular system of one ${}^{85}\mathrm{Rb}$ atom and one ${}^{87}\mathrm{Rb}$ atom. It is also shown that the critical value of the interspecies scattering length for a mixture of Na and Rb in an isotropic trap depends strongly on the number of atoms in a manner not described by the standard Thomas-Fermi phase separation condition.

Solubility of Blowing Agents HCFC 142b, HFC 134a, HFC 125 and Isopropanol in Polystyrene

The vapor-liquid equilibria of HCFC 142b, HFC 134a, HFC 125 and isopropanol in polystyrene were determined in a closed high pressure vessel at temperatures up to 220°C. Complete solubility maps are presented for each blowing agent, including conditions for phase separation in the polystyrene phase. In order of decreasing solubility, the blowing agents rank isopropanol > HCFC 142b > HFC 134a > HFC 125. In the cases of isopropanol and HFC 134a, some solubility results obtained by the vapor pressure method and those using a high-pressure electrobalance are compared.

Effect of gas liquid separator and liquid height on the global hydrodynamic parameters of an external loop airlift contactor

Abstract This study is devoted to the measurement of global hydrodynamic characteristics (gas hold-up and liquid circulating velocity) of an external loop airlift contactor filled with tap water, with different conditions for phase separation and for liquid height. It is shown that these two operating parameters have a great influence on the behaviour of the airlift reactor. These parameters generally are not specified for the use of the relations proposed in the literature, despite their importance. However, this study reveals that two openings in the top junction between the riser and the downcomer are able to generate doubling of the liquid circulation velocity and a decrease in the gas hold-up of about 30% for high gas throughputs. Furthermore, under these conditions, the liquid circulation velocity is multiplied by a factor of 2.7 with little change in the liquid height before aeration, and the gas hold-up is decreased about 27%.

Morphology and electro-optic properties of polymer-dispersed liquid-crystal films

An attractive way of making polymer-dispersed liquid-crystal (PDLC) films is through photopolymerization-induced phase separation. The electro-optic properties of these films are determined in large part by the size, shape, and packing of the embedded liquid-crystal drops. We explore the relationships between the conditions of phase separation, morphology, and electro-optic properties. A strikingly strong dependence of electro-optic properties on the fraction of liquid crystal in the film is demonstrated and explained by consideration of the phase separation process. Also, confocal microscopy is shown to be a useful, noninvasive means of obtaining three-dimensional information on PDLC morphology. Not only does it provide very clear images of liquid crystalline drops in the film, but unexpected features were revealed. The drops exhibit a morphology much like a polyhedral foam in the films studied. Polymeric filaments inside the drops were observed as well as a drift in the average size of the drops with proximity to the film substrates. All of these features have important consequences for the electro-optic performance of PDLC films.

Reversible thermothickening of aqueous solutions of polycations from natural origin

This paper concerns our first set of experimental data on alkyl chitosans in acidic medium allowing to compare the roles of the degree of alkylation and that of the length of the alkyl chains on their physicochemical properties in aqueous solution. The balance between electrostatic repulsion (related to the fraction of -NH3+) and the hydrophobic attraction is discussed on the CC12 sample, a chitosan modified with a C12 aliphatic chain. A phase diagram is established separating the conditions for gel-like structure formation and phase separation. The roles of the net charge and that of the temperature on the formation of hydrophobic aggregates are examined.

Phenomenological Effects of Solvent-Casting Conditions on Pore Characteristics of Regenerated Cellulose Membranes

An attempt was made (1) to prepare porous regenerated cellulose membranes by casting cellulose cuprammonium solutions and then immersing them into aqueous acetone solutions as coagulant, and (2) to investigate membrane characteristics such as radius of secondary particles S2 on the surfaces of the membranes, mean pore diameter measured by the water-flow-rate method 2rf, membrane porosity by apparent density method Pr(d3), and membrane thickness of dry membrane Ld, and (3) to clarify phenomenological effects of solvent-casting conditions on pore characteristics of the membrane formed and to explain the effect in terms of the particle growth theory proposed previously by Kamide-Iijima et al. (KI). Surfaces of membranes prepared by immersing cast solutions in coagulation solution having weight fraction of acetone wAcetone below 0.30 consisted of the secondary particles of polymer-rich phase (referred to as “polymer particle”). As the ammonia concentration in the system was higher, polymer particles of polymer-rich phase grow faster; ammonia was one of the most important factors dominating the size of polymer particles, composing the membranes. Ld was in proportion to the cellulose weight fraction wCell of cast solutions; on the contrary, Pr(d3) and 2rf were inversely proportional to wCell. These experimental findings suggest strongly that density of dried polymer particles increases in proportion to wCell in the solutions. Pore shape in a whole body of a membrane changed drastically from noncircular pores to circular pores when wAcetone in coagulation solutions exceeded 0.30, indicating that wAcetone dominates phase separation conditions such as phase volume ratio R(≡V(1)/V(2); V(1) and V(2) are volumes of polymer-lean and -rich phases, respectively), compositions of phase separation points. Changes in Pr(d3), 2rf and tensile strength TS of the membranes, prepared by using coagulation solutions having different wAcetone, coincide fairly well with that of pore shape. Membranes constructed by larger cellulose particles have larger pores, and this tendency agreed well with results obtained by KI’s lattice theory on pore size distribution proposed before.

Copolyesters of poly(ethylene terephthalate), hydroquinone diacetate, and terephthalic acid: A simple rate model for catalyzed synthesis in melt

Transesterification reactions between poly(ethylene terephthalate) (PET), hydroquinone diacetate (HQDA), and terephthalic acid (TA), were conducted via the melt polymerization route with the objective of analyzing the copolyesterification kinetics of a phase separated system. At first homopolymerization of HQDA and TA were conducted at 50 mol % composition of each monomer. Then the polymerization kinetics of four compositions [PET 30/70 (HQDA + TA), PET 40/60 (HQDA + TA), PET 50/50 (HQDA + TA), PET 60/40 (HQDA + TA) with 30 : 35 : 35, 40 : 30 : 30, 50 : 25 : 25, and 60 : 20 : 20 mol % PET, HQDA, and TA] were investigated. The following assumptions were made to make kinetic analysis tractable. HQDA and TA combine to form acetic acid and higher oligomers. The oligomer subsequently adds on to the PET chain to give a copolymer of PET/HQDA/TA, the product of interest. The reaction between PET, HQDA, and TA proceeds in a heter-ogeneous two-phase system consisting of PET-rich and PET-poor regions. The reaction sequence is HQDA and TA react to form a dimer and subsequently the dimer is added onto the PET chain. This reaction sequence is assumed to be valid for the PET-rich and PET-poor phases. Both these reactions were assumed to be second order with respect to the reactants. Reactions wherein the dimer reacts with HQDA or TA to form acetic acid exist, but the probabilities of these processes are small with respect to the main reaction postulated above, thus maintaining the overall mass balance. Moles of acetic acid found experimentally were computed using a standard procedure. The rate constant k under the conditions of phase separation was determined. The rate constant in the presence of PET was higher than that observed in the HQDA and TA reaction. An Arrhenius plot revealed that the catalyst plays a marginal role. Microscopic analysis revealed that the HQDA and TA polymer were nonmelting while copolyesters PET 30/70 (HQDA + TA) to PET 60/40 (HQDA + TA) melted and were liquid crystalline. © 1996 John Wiley & Sons, Inc.