Showing papers on "Phase (matter) published in 1977"
TL;DR: In this paper, a scaling description of the chain configurations and interactions is used, and it is shown that the presence of a uniform surface attraction changes the phase diagram drastically, and the transition between the two phases is first order.
Abstract: The adsorption of chain molecules at an interface is investigated assuming that the molecule has both a polar head type of attraction localized on the chain and a uniform interaction of the chain monomers with the surface. A scaling description of the chain configurations and interactions is used. It is shown that the presence of a uniform surface attraction changes the phase diagram drastically. Both a low density two-dimensional regime and a high density phase with the chains confined in narrow cylinders can occur. The transition between the two phases is first order. Power laws for the surface density, layer thickness and surface pressure are derived. The qualitative similarity with the behaviour observed for short chain lipids and surfactants is also noted and it is suggested that a uniform surface interaction may also play an important role there.
1,360 citations
TL;DR: In this article, the authors present a computer program in Algol 60 by means of which enthalpy effects can be calculated for binary alloys in which at least one transition metal is involved.
Abstract: We present a computer program in Algol 60 by means of which enthalpy effects can be calculated for binary alloys in which at least one transition metal is involved. Predictions can be made by means of this program for seven fixed ordered compositions in the solid phase and for the two limiting heats of solution and the heat of mixing at the equlatomic composition in the liquid phase. For solid alloys the predictions are representative for equilibrium compounds. As an example, we Include the output for combinations of iron and cobalt with all other metals. In addition, we include a complete table of heats of solution in liquid alloy systems. A discussion is given of both the accuracy of the predictions and the differences between predictions and the experimentally observed quantities that vary systematically with the position of the elements in the periodic table.
1,151 citations
TL;DR: In this paper, a thermodynamic study of the liquid-solid phase transformations in porous materials provides the relationships between the size of the pores in which solidification takes place and the temperature of the triple point of the divided liquid, on the one hand, and between this temperature and the apparent solidification energy on the other hand.
703 citations
TL;DR: In this article, the retention of ionized analytes on a nonpolar bonded stationary phase is enhanced by the presence of a "hydrophobic" counterlon (hetaeron) in the mobile phase.
Abstract: In Ion-pair reversed-phase chromatography, the retention of ionized analytes on a nonpolar bonded stationary phase is enhanced by the presence of a "hydrophobic" counterlon (hetaeron) in the mobile phase. Either ion-pair formation in the mobile phase with relatively strong retention of the complex or the conversion of the stationary phase into an ion-exchanger may explain the phenomenon. Analysis of the pertinent equilibria shows that the observed hyperbolic or parabolic dependence of the capacity factors on the hetaeron concentration cannot shed light on the mechanism. The experimental data obtained for the retention of catecholamlnes by using C4-C10 alkyl sulfates and other similar hetaerons in a wide concentration range, however, could be mechanistically interpreted from the chain length dependence of the parameters for the relationship between the capacity factors and hetaeron concentration. Although the results clearly demonstrate that in the system investigated, ion-pair formation governs retention, ion-exchange mechanism can be operative under certain conditions. Changes in retention upon addition of salt to the eluent are treated both theoretically and experimentally. The effect of organic solvents on the behavior of the chromatographlc system is discussed in view of the proposed theory.
390 citations
TL;DR: In this paper, the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria.
Abstract: It is shown that the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria. Such sintered body containing the metastable phase undergoes stress-induced phase transformation by the absorption of thermal or mechanical stress and exhibits strengths in excess of 690 MPa (100ksi).
387 citations
TL;DR: In this paper, the electroclinic effect of chiral molecules was studied in the second order, smectic-$A$---smectic/$C$ phase transition.
Abstract: When a smetic-$A$ phase is composed of chiral molecules, it exhibits an electroclinic effect, i.e., a direct coupling of molecular tilt to applied field. The pretransitional behavior of the electroclinic effect in the $A$ phase is used to study the critical behavior near the second order, smectic-$A$---smectic-$C$ phase transition. This behavior is measured by monitoring the change in birefringence of a sample as the electroclinic effect causes a tilt of the molecules. A large pretransitional effect is measured, and constants describing the critical behavior are determined.
342 citations
327 citations
TL;DR: In this article, the tensile properties of various alloys of the FeMn-Cr-C system were studied and the effect of temperature on both twinning and f.c.p.
323 citations
TL;DR: In this article, the authors examined the statistical interdependence of the faster rotational reorientation of the individual spinbearing molecules and the (slower) director or order-parameter fluctuations.
Abstract: The theory of spin relaxation for liquid crystals is examined with the objective of properly analyzing the statistical interdependence of the faster rotational reorientation of the individual spin‐bearing molecules and the (slower) director or order‐parameter fluctuations. The analysis is presented in terms of a composite Markov process including both types of motions. It is shown that one recovers a sum of spectral‐density terms which, in lowest order in fluctuations, correspond to (1) reorientation of the molecule relative to the equilibrium potential of mean torque, (2) effects of director fluctuations, and (3) a negative cross‐term between these two processes which bears a simple relation to (2). Detailed results are given for the particular models of director fluctuations in the nematic phase, quasicritical order fluctuations on either side of the isotropic–nematic phase transition, and slow fluctuations in the local structure. Effects of localized cooperative modes of molecular reorientation are als...
320 citations
TL;DR: In this paper, the volume fraction of dispersed phase necessary to form an infinitely long network as a function of the particle size ratio is considered, where neither a monolayer nor a double layer of dispersed particles around the primary phase is a necessary condition for continuity.
Abstract: A model is developed which considers the volume fraction of dispersed phase necessary to form an infinitely long network as a function of the particle size ratio. Recognizing that neither a monolayer nor a double layer of dispersed particles around the primary phase is a necessary condition for continuity, the surface fraction of primary phase covered by the dispersed phase and the ratio of dispersed phase particles which are occluded from, versus contiguous to, the primary phase are estimated either empirically or by reference to probability theory. The theoretical results are compared with earlier experimental work on electrical properties of compacted mixtures of polymer and metal powders.
251 citations
TL;DR: In this article, the authors studied the surface of Re γ-Al 2 O 3 -supported reforming catalysts and showed the existence of two aggregation states of Re on the surface: a dispersed two-dimensional phase and three-dimensional crystallites.
TL;DR: In this paper, a correlation valid for a free liquid trickling, modified in order to take into account the effect of the pressure drop, is proposed and used to correlate liquid holdup in the presence of a concurrent gas flow.
TL;DR: In this paper, five commercially available reversed phases are examined, and the effects of chain length, carbon content and extent of derivatization on wettability, retention and selectivity are investigated.
TL;DR: In this article, a mixture of two identical Lennard-Jones liquids in which the interactions between the components are characterized by a range parameter σ12 obeying the Lorentz rule, but an energy parameter e12= (1−α) (e11e22)1/2 violating the Berthelot rule is presented.
Abstract: Recently developed nonphysical sampling methods—umbrella sampling—have been used to obtain the free energy and other properties of a binary liquid mixture exhibiting phase separation with an upper critical solution point. The system is a mixture of two identical Lennard‐Jones liquids in which the interactions between the components are characterized by a range parameter σ12 obeying the Lorentz rule, but an energy parameter e12= (1−α) (e11e22)1/2 violating the Berthelot rule. The sampling methods enable one to cover wide ranges of temperature and composition with few Monte Carlo experiments, successfully sampling the metastable regions and obtaining the coexistence curve. The case α=0.25 is studied in detail, and compared with some theoretical predictions. An estimate is made of the minimum value of α required for phase separation at low pressures.
TL;DR: The retention behaviour of amino acids in phase systems consisting of a hydrophobic solid support as the stationary phase and water-organic solvent mixtures containing a small amount of an anionic detergent as the mobile phase was investigated and shows a greater selectivity than conventional ion-exchange systems towards amino acids.
TL;DR: Advantages include easy sample preparation, involving only addition of internal standard and centrifugation before injection, long column life, and the suitability of the internal standard, which is adjusted to a peak height equivalent to 20 mg of theophylline per liter for easy computation of results.
Abstract: We describe a micro-scale method for determining serum theophylline. The chromatography system includes a muBondapack C18 column and acetonitrile, 70 ml/liter of sodium acetate buffer (10 mmol/liter, ph 4.0) as the mobile phase. Test serum or plasma, 30 mul, is mixed with an equal quantity of a solution containing the internal standard, beta-hydroxyethyltheophylline in acetonitrile/sodium acetate buffer (20 mmol/liter, pH 4.0), 7/43 by vol. After the precipitate is removed by centrifugation, the mixture is chromatographed and the amount of theophylline calculated from the ratio between peak heights for theophylline and the internal standard. Advantages include easy sample preparation, involving only addition of internal standard and centrifugation before injection, long column life, and the suitability of the internal standard, which is adjusted to a peak height equivalent to 20 mg of theophylline per liter for easy computation of results.
TL;DR: In this article, a tentative model of the bilayer smectic phase held in place via the attractive interaction of the alkyl or alkoxy chains accounts for most of the experimental results.
Abstract: We find that certain cyano Schiff bases and cyanobiphenyls with alkyl or alkoxy end groups exhibiting a bilayer smectic-$A$ phase also exhibit a reentrant nematic phase at high pressure. A tentative model of the bilayer smectic phase held in place via the attractive interaction of the alkyl or alkoxy chains accounts for most of our experimental results.
TL;DR: KITAIGORODSKY, A. I., HOTSYANOVA, T. L. as discussed by the authors, RIETVELD, H. M. and STRUCHKOV, YU.
Abstract: KHOTSYANOVA, T. L., KITAIGORODSKY, A. I. & STRUCHKOV, Yu. T. (1953). Zh. Fiz. Khim. SSSR, 27, 1330-1343. KxpPs, M. (1973). MSc Dissertation, Univ. o f Surrey. KITAIGORODSKY, A. I. (1961). Organic Chemical Crystallography, pp. 165-168, 252-253, London: Heywood. KITAIGORODSKY, A. I., KHOTSYANOVA, T. L. & STRUCHKOV, YU. T. (1953). Zh. Fiz. Khim. SSSR, 27, 1490-1502. RIETVELD, H. M. (1969a). Reactor Centrum Nederland, Res. Rep. RCN-104. RIE'rVELD, H. M. (1969b). J. Appl. Cryst. 2, 65-71. STRAND, T. G. (1967). Acta Chem. Scand. 21, 2111-2118. THACKERAY, D. P. C., SHmLE',', R., ORALRATMANEE, C., KIPPS, M. & STACE, B. C. (1974). J. Mol. Struct. 20, 293-299. WILSON, E. B. (1952). An Introduction to Scientific Research, p. 237. New York: McGraw-Hill.
TL;DR: Theoretical expressions have been developed to relate the optical and thermal properties of such samples to the amplitude and phase of the signals observed in optoacoustic spectrometry when using dispersive and non-dispersive techniques as discussed by the authors.
Abstract: Optoacoustic spectrometry can be employed to obtain data concerning the spectral absorption characteristics and thermal diffusivity of small solid samples. Theoretical expressions have been developed to relate the optical and thermal properties of such samples to the amplitude and phase of the signals observed in optoacoustic spectrometry when using dispersive and non-dispersive techniques. The validity of these expressions has been examined by using transparent and opaque materials with widely differing thermal diffusivities.
01 Jan 1977
TL;DR: In this article, the authors show that reactions between substances located in an organic phase and in an aqueous phase are frequently slow and ineffective, and they propose a solution to this problem.
Abstract: Reactions between substances located partly in an organic phase and partly in an aqueous phase are frequently slow and ineffective.
TL;DR: In this article, the formation of membranes from two systems has been studied and the mechanism for formation of the sponge-like structure proves to be a liquid-liquid phase separation with nucleation and growth of the diluted phase.
Abstract: The formation of membranes from two systems has been studied. In the system polyurethane-dimethylformamide-water, the mechanism for the formation of the sponge-like structure proves to be a liquid-liquid phase separation with nucleation and growth of the diluted phase. This mechanism has been confirmed for the system modified polystyrene-polyisoprene-polystyrene/o-dichlorobenzene/(methanol-water). Crystallization and gelation is discussed. The membranes prepared showed hyperfiltration activity. The mechanism proposed here is believed to be valid for other systems, too.
TL;DR: In this paper, phase relationships in the La1−xSrxCrO3 (0.25 ≤ x ≤ 0) system have been investigated and the orthorhombic and rhombohedral structure of La0.75Sr 0.25 CrO3 were refined by profile fitting of neutron powder diffraction data.
TL;DR: In this article, a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion was proposed to explain the dielectric anomalies of LiNbO3 and LiTaO3.
Abstract: Vitreous LiNbO3 and LiTaO3 have been prepared by roller quenching these compositions from the melt. The transparent glasses exhibit pronounced dielectric anomalies with peaks of e≳105 close to the crystallization temperature which are not characteristic of the crystalline phase. Pyroelectricity is induced after cooling the glass in an electric field. The data are discussed in terms of a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion.
TL;DR: Water deuteron NMR spectra studied for the system dipalmitoyllecithin (DPL)-heavy water (D2O) at different compositions and temperatures show evidence that the "pretransition" observed by differential scanning calorimetry is caused by a crossing of a three-phase line.
Abstract: Water deuteron NMR spectra have been studied for the system dipalmitoyllecithin (DPL)-heavy water (D2O) at different compositions and temperatures. From an analysis of the spectra in terms of quadrupole splittings, a phase diagram has been constructed for the temperature range 25-60 degrees C and the composition range 4-15 mol of D2O/mol of DPL. Evidence is given that the "pretransition" observed by differential scanning calorimetry is caused by a crossing of a three-phase line. Strong support for a specific hydration of about 11 water molecules per lecithin molecule in the phase between the pretransition and main transition is also found.
TL;DR: In this paper, two techniques are described which permit complete separation of phase in two-dimensional resolved spectroscopy of rare nuclei, without phase adjustment by phase adjustment is possible.
TL;DR: In this paper, the electronic structure of the ordered Zintl phase of LiAl has been studied in a molecular-cluster model within the framework of the Hartree-Fock-Slater theory.
Abstract: The electronic structure of the ordered Zintl ($B32$) phase of LiAl has been studied in a molecular-cluster model within the framework of the Hartree-Fock-Slater theory. ${\mathrm{Li}}_{5}$${\mathrm{Al}}_{4}$ and ${\mathrm{Al}}_{5}$${\mathrm{Li}}_{4}$ clusters were embedded in a potential field representative of the alloy environment; energy levels and wave functions were obtained by self-consistent iteration. Density-of-states and charge-density results are used to interpret NMR and electrical-conductivity studies. The case of a single Li vacancy was also treated, and discussed in the light of positronannihilation data.