Phase Separation Of Particles Research Articles

In Situ Observation of Liquid-Liquid Phase Separation of Glass under Microgravity

We succeeded in the in situ observation of liquid-liquid phase separation of glass under microgravity at the Japan Microgravity Center (JAMIC), which provides a 10 s microgravity duration. The microgravity level is 10-5 g (g≡gravitational field at Earth's surface). We constructed an apparatus for the observation of phase separation suitable for the experimental facility. The melt of 3BaO•97B2O3 (mol%) was held as a film on a Pt wire loop. The sample was initially heated above the immiscibility temperature and held at that temperature. After the homogenization stage, the melt was cooled. Liquid-liquid phase separation of the melt was observed directly with a video camera. It was found that the nucleation and growth of phase-separated particle under microgravity are slower than in the case of 1-g, and the delay time of phase separation between the case of microgravity and 1-g depends on the flow rate of the melt under microgravity. These observations could be interpreted in terms of Marangoni convection and a change of diffusion.

Latex Particle Morphology, Fundamental Aspects: A Review

The control of particle morphology is an essential part of producing high quality latex products for applications in coatings, adhesives, impact modifiers, and medical diagnostics, among others. A great variety of formulation and process variables are available to manipulate the particle structure and many different morphologies have been created. Techniques to characterize these morphologies are varied, but electron microscopy of both whole and sectioned particles is the most common one used. Atomic force microscopy is gaining in utility and often two or more characterization methods are simultaneously used to gain clarity of interpretation. A great deal of basic understanding of the factors controlling the morphology has been achieved by applying equilibrium thermodynamics to phase separated particles in aqueous media. Interfacial tensions at the polymer‐water interface and at the polymer–polymer interface, along with crosslinking density are found to be the dominant factors controlling the equilibrium morphology. In turn there is a significant number of formulation variables which determine the interfacial tensions and the crosslinking density. Successful models have been developed and applied to a number of different polymer systems. Much less progress has been made in understanding the development of non‐equilibrium morphologies where the possible number of particle structures is essentially infinite. Here, characterization techniques become somewhat less precise in identifying exact structure and further work is needed to advance this capability. In the dynamic reaction environment of the latex process the morphology develops within very viscous phases and is a result of competitive reaction and diffusion processes. Some progress has been made to quantitatively describe these phenomena, but more work is needed. This is even more evident when extension to carboxylic and hybrid (e.g. polyurethane/acrylic) latices is desired.

Interface and bulk properties in films of phase separated dispersion particles

Structured latex particles are of high interest as tailor made dispersion binders to meet contradictory requirements in different fields of applications. Aqueous dispersions, e.g. used as binders in solvent-free, low pigmented paint formulations, have to cope with the challenge to guarantee an excellent film forming ability at room temperature as well as a low tack. In this work, the synthesis and characterizations of hemisphere-like particles with different chemical constitutions are described. The single particles were placed onto various types of substrates. The particle–surface interface was then investigated by atomic force microscopy (AFM). Characteristic differences were found as a function of the polarity of both, polymer and substrate. Including these findings, AFM was used to determine the impact of the interface structure on the bulk properties of the final dispersion films. The results are compared to computer simulations of the packing of the particulate materials. A correlation of microscopic interface structure to macroscopic application properties of the corresponding dispersion films is presented. The results are compared to sets of blends with identical chemical composition and equivalent volume fraction and the corresponding statistical copolymers.

Recent developments and ASAXS measurements at the ultra small angle X-ray scattering instrument of HASYLAB

The wiggler beamline BW4 at the synchrotron radiation facility HASYLAB (DESY) is mainly designed for Ultra Small Angle X-ray Scattering (USAXS) and usually operated with detector–sample distances up to 13 m and at photon energies between 4 and 16 keV. With a new optical design the largest observable correlation distances have now been increased up to 9×10 3 Å. A grazing incidence set-up [P. Müller-Buschbaum et al., Europhys. Lett. 42 (5) (1998) 517], vapor chamber, furnace, tensile testing machine and other instruments make the USAXS beamline attractive for a variety of scattering experiments [A. Endres et al., Rev. Sci. Instrum. 11 (1997) 68; A. Karl et al., J. Macromolecular Sci.-Phys. B 38 (5&6) (1999) 901; S. Minko et al., J. Macromolecular Sci., Phys. B 38 (5&6) (1999) 913]. A fully evacuated beampath allows high quality measurements with very low background signal. A photodiode mounted in the primary beam stop registers the primary beam flux simultaneously to the data acquisition and thus provides a precise method for measuring absolute scattering intensities. Anomalous small angle X-ray scattering (ASAXS) experiments at the K absorption edge of titanium were recently performed to investigate phase separated fluorine titania silicate glass. From these measurements we expect some new results concerning the distribution of titanium atoms within the diffusion zone outside the phase separated particles.

Life as a set of matter transformation cycles: ecological attributes of life.

An approach to searching for extraterrestrial life on the base of "autotroph" concept of the origin of life is presented in the paper. According to this concept the origin of life took place in three stages. The first stage was developed inside the global geochemical cycle in which the turnover of different chemical transformations was implemented by solar radiation and/or heat energy of bowels of the Earth. At the second stage, after the autocatalytic systems have emerged these systems evolved as a result of "natural selection" by autocatalysis parameters up to emergence of special inheritance systems that drastically improved the autocatalysis parameters. The best in terms of autocatalysis parameters were the autocatalysis systems based on phase-separated particles where complex structures can form not only on the basis of covalent interactions. Such autocatalysis systems can emerge only in liquid in a certain range of temperatures and pressures. At this stage the geochemical cycle complicated involving new substances. At the third stage the evolution involved improvement of inheritance systems resulting in formation of the modern type of genetic apparatus. This concept formed the basis to consider approaches to experimental modeling of major aspects of the origin of life and to outlining some general features of life that can extend the sensitive horizon of searching for extraterrestrial life.

Stabilization of lipid/DNA complexes during the freezing step of the lyophilization process: the particle isolation hypothesis

The instability of nonviral vectors in aqueous suspensions has stimulated an interest in developing lyophilized formulations for use in gene therapy. Previous work has demonstrated a strong correlation between the maintenance of particle size and retention of transfection rates. Our earlier work has shown that aggregation of nonviral vectors typically occurs during the freezing step of the lyophilization process, and that high concentrations of sugars are capable of maintaining particle size. This study extends these observations, and demonstrates that glass formation is not the mechanism by which sugars protect lipid/DNA complexes during freezing. We also show that polymers (e.g., hydroxyethyl starch) are not capable of preventing aggregation despite their ability to form glasses at relatively high subzero temperatures. Instead, our data suggest that it is the separation of individual particles within the unfrozen fraction that prevents aggregation during freezing, i.e., the particle isolation hypothesis. Furthermore, we suggest that the relatively low surface tension of mono- and disaccharides, as compared to starch, allows phase-separated particles to remain dispersed within the unfrozen excipient solution, which preserves particle size and transfection rates during freezing.

Analytical solution to the equation for pair correlation function of particles formed in the course of phase separation in a glass

The problem of determining the pair correlation function of phase-separated particles from the experimental data obtained for the plane section of a sample has already been consul and in the literature. The integral equation relating the pair correlation function of monodisperse spherical particulers and the pair correlation function of their traces on the secant plane was obtained, and the method of numerical solution of this equation was elaborated with the aim of determining the pair correlation function of places. The present paper describes the analytical solution to this equation.

Small-angle X-ray scattering and Rayleigh scattering studies of the microstructure of some optical glasses

Several optical glass samples were studied by small-angle X-ray Scattering (SAXS) in order to verify the presence of inhomogeneity in the range (1–100 nm). The results were compared with Rayleigh scattering measurements in order to verify a possible correlation between microstructure and scattering losses. For most glasses investigated, the presence of phase separation was excluded and the Rayleigh scattering intensities were attributed to refractive index fluctuations. For glasses ZKN7 and SK11 evidence of phase separation, with size of about 8 nm and less than 2 nm respectively, was obtained using SAXS. The particle size was insensitive to annealing treatments in the case of SK11 and showed a continuous growth with annealing time at 610°C in the case of ZKN7. For these two glasses the overall Rayleigh scattering intensity includes a contribution due to the presence of phase separated particles.

Effect of elastomer modification on the adhesive characteristics of maleimide-functional phenolic resins

The effect of addition of elastomeric modifiers on the adhesive properties like lap shear strength and T-peel strength of an addition curable, maleimide functional novolac phenolic resin (PMF), self-cured and cocured with a novolac epoxy resin, was studied using aluminium adherends. The modifiers used were (1) two grades of carboxyl terminated butadiene acrylonitrile copolymer (CTBN) of different molecular weights, (2) a low molecular weight, epoxidized hydroxyl-terminated polybutadiene, and (3) a high molecular weight acrylate terpolymer containing pendant epoxy functionality. The adhesive properties, when examined as a function of the varying concentrations of the additives, ranging from 10 to 30 parts per hundred parts (phr) of the resin, were found to depend on the nature of the matrix being modified as well as on the nature and concentration of the elastomer. The adhesive properties at ambient temperature of the self-cured, highly brittle PMF resin were dramatically improved by the inclusion of all the elastomers, the increase being substantial in the case of high molecular weight CTBN. For the more rigid, less ductile, epoxy-cured PMF system, the adhesive properties were marginally improved by the high molecular weight CTBN, whereas the other elastomers were practically ineffective. For both self-cured and epoxy-cured PMF systems, the inclusion of these elastomers generally decreased the high-temperature adhesive properties, implying impairment of thermal characteristics, evidenced also from their dynamic mechanical spectra. The presence of phase-separated elastomer particles in the modified systems has been evidenced from scanning electron micrographs. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2321–2332, 1999

EELS Study of Phase Separation in Glasses

The phase separation in glasses plays a great role in the glass science and technology. By controlling the chemical composition and the degree of phase separation, it is possible to produce various kinds of materials of predicted microstructure. To determine the kinds of separated phases, the chemical composition and the fraction or sizes of each separated phase are the main problem in thermodynamics and kinetics study of phase separation in glasses. The sizes of phase separated particles are usually in the range of several nm to several hundred nm, which can be determined by a rather simple method instead of the small angle x-ray scattering with trivial calibration. It has been showed that electron energy loss spectroscopy (EELS) not only can be used to determined the constituents of at. No. 2-92 but also is more sensitive than EDS.Two phase separated glasses of initial composition 8Na2O27B2O3 65SiO2 and 60ZrF431BaF25LaF34AlF3 were used to prepare specimens by ion bombardment.

Anionic dispersion polymerization of 1,4-divinylbenzene

Highly cross-linked 1,4-divinylbenzene (1,4-DVB) microgels with a shell of poly(4-tert-b~- tylstyrene) (PtBS) chains were prepared by anionic dispersion polymerization in n-heptane at 50 C. Liv- ing PtBS chains with various lengths were used as the initiator of the DVB polymerization and also as steric stabilizers for the phase-separated particles. The effect of the polymerization parameters such as the length of PtBS chains and the DVB concentration on the properties of the microgels was studied using static and dynamic light-scattering techniques and viscosimetry. As the DVB concentration in the reac- tion medium increases, both the molecular weight of the microgels and their intrinsic viscosities increased, at first slowly and then abruptly at about 30-35 mol % DVB, corresponding to the transition from the microgel to the macrogel region. It was also found that the length of PtBS chains at the nuclei surface controls the intrinsic viscosities of the microgels. The calculations indicate that the solvated PtBS chains are close-packed on the surface of the nuclei. A mechanism for microgel formation and growth in the anionic dispersion polymerization is presented which consists of three stages: (1) DVB polymerization in a homogeneous solution up to the critical micelle concentration of PtBS-poly(4-vinylstyrene) block copol- ymers formed, (2) fast polymerization and cross-linking reactions within the microgel nuclei, and (3) poly- merization at the nuclei surface leading to interparticular reactions.

Coarsening Process of Nucleation-Growth Type Phase-Separated Particles in Binary Germanate Glasses

The coarsening process of nucleation-growth type phase-separated particles in a metastable immiscible region of binary GeO2 systems was investigated in detail, and is discussed in terms of the mechanism of connection and coalescence for fluid mixtures. Furthermore, the factors which affect the coarsening process were investigated.At the later stage of the growth of particles, their mean radius \barr changed in proportion to the αth power of time t (\barr(t)∝tα), and the value of growth rate α varied in the range of 0.34∼0.68 depending on the number of connected and coalesced particles n. It was found that nucleation-growth type phase-separated particles grow coarser intermittently by the mechanism of connection and coalescence, and that this coarsening process can not be explained by the usual theory of the 1/3rd power rule.The factors which affect this coarsening process of particles are volume fraction Vf of particles and interfacial tension γA/B between the particles and the dispersed phase. Additionally, it is found that the mean number n of connected and coalesced particles concerning all the measured compositions can be arranged on one line by the cohesive coefficient Vf·γA/B defined in this study.

Phase separation and crystallization in fluorozirconate glasses

Optical waveguide fluoride glasses face a number of difficult problems despite their potential for ultralow loss. One of the most serious is scattering loss from defects such as inclusions, phase separation particles and crystallites. By means of a Leitz optical microscope, X-ray diffraction, transmission electron microscope (TEM) and differential thermal analysis (DTA), we have investigated the phase separation and crystallization phenomena in ZrF 4BaF 2LaF 3AlF 3 fluoride glasses. Phase-separated particles, which formed via the nucleation and growth mechanism, were observed in the glass. The crystallites in the glass are confirmed to be beta-BaF 2·ZrF 4 and alpha-BaF 2·2ZrF 4. The activation energies of crystallization of these phases were determined by DTA.

Study of phase separation in Na 2OB 2O 3SiO 2 glasses by tem and optical diffraction

As an extension of the small angle X-ray scattering and electron microscopy techniques for investigating phase separation in glasses, a method has been developed which involves taking electron microscopy phase separation morphology micrographs and then using an optical diffractometer (OD) to perform a Fourier transformation so as to obtain the small angle scattering intensity. By using this method, phase separation in Na 2OB 2O 3SiO 2 glasses was investigated. The results obtained are as follows: (1) The size of the interconnecting phase-separated particles measured by this method seemed to be proportional to the cube root of the heat treatment time. (2) The sequence of phase separation in the three liquid regions of the Na 2OB 2O 3SiO 2 system is as follows: first, the glasses separate into a silica-rich phase and a sodium-borate-rich phase , and then the sodium-borate-rich phase separates into two other phases, on being borate-rich and the other sodium-rich.

Elastomer Modification of Structural Adhesives

Abstract An attempt has been made to review the highlights of the chemistry and physical properties of the rubber modification of structural thermosetting polymers that are used as adhesives. The elastomers are added in order to improve the characteristics of these structural thermosets such that they would be more useful as structural adhesives. The addition of an elastomer acts to increase the resistance of the structural thermoset to crack propogation. The resistance to crack propogation is obtained either by plasticization to increase the ductility of the thermoset or by generation of a two-phase system where the structural polymer forms a matrix in which the phase-separated elastomeric particles are imbedded. In the case of flexibilization by plasticization, the increase in peel strength (fracture toughness) is accompanied by a decrease in shear strength (modulus) at high temperatures. In the case of the two phase system, the matrix properties are unaffected for the most part, and increases in peel strength are not accompanied by significant decreases in high-temperature shear strength. In the case of flexibilization, the increase in fracture toughness is accomplished by increasing the ductility of the resin while in the case of the two-phase system, the rubber particles act as stress concentrators to cause conditions of exceeding the yield stress of the matrix near the particles. Exceeding the yield stress increases the amount of plastic deformation of the matrix. We have briefly reviewed the chemistry and physical properties of phenolic, epoxy, acrylic, and polyimide structural adhesives and their modification with vinyl, nitrile, acrylic, siloxane, and other types of elastomers.

The assembly and properties of protobiological structures: The beginnings of cellular peptide synthesis

New data indicate that lysine-rich proteinoids have the ability to catalyze the synthesis of peptide bonds from a variety of amino acids and ATP. This capacity is evident in aqueous solution, in suspension of phase-separated complexes of lysine-rich proteinoid with acidic proteinoids, and in suspension of phase-separated particles composed of lysine-rich proteinoids with polynucleotides. Since the proteinoid complexes can contain other catalytic activities, including ability to catalyze internucleotide bond formation, we infer that the first protocells on Earth already had a number of biological types of activity.

Elongation and spheroidization of phase-separated particles in glass

When certain phase-separated glasses are elongated by redrawing near their softening point, the spherical second-phase particles are found to elongate as well. The elongation process is discussed, and the conditions under which high particle elongations are possible are estimated. Annealing the glass tends to spheroidize cylindrical-shaped particles by an ‘ovulation’ process. The spacing of the resulting spheroidal particles is compared with theoretical predictions.

Studies on Phase Separation in Glaze Containing Zinc Oxide by Infra-red Reflection Method

Phase separation in glaze containing zinc oxide was studied by infra-red reflection method. The difference in the infra-red reflection spectra in the neighbourhood of 1180 cm-1 was found between the slowly cooled glaze and quenched glaze in which the growth of phase separated particles was suppressed. The slowly cooled sample was opaque, but no crystal was found by the X-ray diffraction method and the electron-micrography. Many spherical droplets about 0.1μ in diameter were found by electron-microscopic observation.Phase separation was prevented by the increase of Al3+ ion and/or the substitution of CaO, SrO, or BaO for ZnO in the glaze composition.In the case of non phase separable glaze containing such components, no difference in the shape of infra-red reflection spectra in the neighbourhood of 1180cm-1 was found between the slowly cooled and quenched samples. The difference in the shape of infra-red reflection spectra of those samples was considered to be based on phase separation into silica rich glass droplets and modifier rich glass matrix.