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Showing papers on "Crystallization published in 1968"


Journal ArticleDOI
TL;DR: In this paper, the glass transition phenomenon was found near 135°K with the sudden change of the heat capacity amounting to 35 J/(mol°K) and the drastic crystallization with the exothermic effect which amounts to 1.64 kJ/mol was then followed at this temperature.
Abstract: By making use of the vapor-condensation type calorimeter, the heat capacity measurements of amorphous, cubic and hexagonal ices were made between 20°K and 250°K. The glass transition phenomenon was found near 135°K with the sudden change of the heat capacity amounting to 35 J/(mol°K). The drastic crystallization with the exothermic effect which amounts to 1.64 kJ/mol was then followed at this temperature. The transformation of the cubic crystal to the hexagonal one was confirmed to occur in the temperature region from 160 to 210°K and to proceed in two steps with the activation energies of 21.3 and 44.7 kJ/mol, respectively. The amount of the exothermic effect accompanying this transformation was found to be about 160 J/mol.

401 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the width of the metastable zone of concentrations under varying conditions and found that the nucleation rate at the beginning of nucleation will be identical with the supersaturation rate for a limited period of time.

299 citations


Journal ArticleDOI
TL;DR: Procedures for the crystallization of human and horse haemoglobins are described and animal models show good consistency in both the liquid and the solid phase.

262 citations



Journal ArticleDOI
01 Jan 1968-Polymer
TL;DR: The cross-hatched pattern persists during the growth of polypropylene α-spherulites, and explains their low birefringence as mentioned in this paper, which is different from the radiating lamellar structure of polyethylene and several other polymers.

204 citations


Journal ArticleDOI
TL;DR: In this article, a modified triclinic unit cell for isotactic polypropylene has been proposed for the γ phase and a conclusion that the transformation is martensitic in nature.
Abstract: Samples of very low molecular‐weight fractions of isotactic polypropylene have been crystallized by means of a solvent‐evaporation technique as well as by melt recrystallization. The crystalline entities obtained by these methods have been examined in terms of their internal structure and associated morphology. The particular polymorphic form observed for these fractions is dependent on both the length of the molecule and the particular crystallization conditions employed. The morphological characteristics of the samples have been found to be qualitatively similar to those previously reported for unfractionated polypropylene and high‐molecular‐weight fractions, in spite of the fact that the molecular lengths of the samples investigated are sufficiently short to prevent chain folding. Selected‐area electron‐diffraction patterns have been obtained from the γ form and from mixed α and γ form of the isotactic polymer. The diffraction data have resulted in a modification of the previously proposed triclinic unit cell for the γ phase, and a conclusion that the γ→α transformation in isotactic polypropylene is martensitic in nature. The mechanism of this solid‐solid transformation involves relative motion between the (040) planes which are found to be invariant in the two crystal phases.

154 citations


Journal ArticleDOI
TL;DR: The use of microdiffusion cells for crystallization of small volumes of protein solutions by equilibrium dialysis against a precipitant and for chemical treatment of one or a few single crystals in their mother liquor is explored.

151 citations


Journal ArticleDOI
01 Oct 1968
TL;DR: In this paper, the structural changes during the melting process of polyethylene, polypropylene and polybutene-1 were studied making use of direct measurements, including diameter, birefringence and surface temperature.
Abstract: The structural changes during melt spinning process of polyethylene, polypropylene and polybutene-1 were studied making use of direct measurements. A model spinning apparatus was devised for this purpose. Measurements of diameter, birefringence and surface temperature were carried out. Wide and small angle x-ray photographs were taken at the successive points below the spinneret, moreover, the change in crystallinity of polyethylene was measured along the spinning way. In the case of polyethylene, thec-axis of woundup filament tilts against the fiber axis and the crystalline reflections observed in the intial stage of the crystallization are already nearly the same as those of the woundup filament in their features. There is a sudden change in birefringence in the region of crystallization. Crystallization takes place very fast and crystallinity reaches a saturated value in a fraction of a second. The rate of crystallization in melt spinning process is much higher than that of the unoriented state at the same crystallization temperature. The crystallization temperature decreases as take-up velocity increases. As for polypropylene, the structure of the filament consists ofc-axis anda*-axis oriented crystallites, and the process of structural formation is discussed. The transition from tetragonal to hexagonal form of polybutene-1 crystal is very rapid in oriented state.

137 citations


Journal ArticleDOI
TL;DR: The first level of native granule morphology is 100 to 150 A fibrils, involving extended polymeric chains as mentioned in this paper, which represent a unique morphology which develops because of the simultaneous synthesis and crystallization which occurs during some stage of formation.

123 citations


Journal ArticleDOI
Julius Ciric1
01 Oct 1968
TL;DR: In this article, the effects of aqueous sodium aluminosilicate gels to zeolite were studied by means of sorption, and the effect of changing caustic concentration could be interpreted in terms of mass transfer of some dissolved species from the bulk of the gel medium to the surface of the crystal.
Abstract: Conversion of aqueous sodium aluminosilicate gels to zeolite. A was measured by means of sorption. Effects of SiO 2 Al 2 O 2 in the starting gel, caustic concentration, and stirring rate were studied. At excess silica, the gels were found to be unsuitable for kinetics studies because they tended to produce an amorphous by-product and addition to zeolite A. At excess alumina, the effect of changing caustic concentration could be interpreted in terms of mass transfer of some dissolved species from the bulk of the gel medium to the surface of the crystal. From the consideration of the effect of stoichiometry on growth rate, the diffusing species apears to contain two negative distribution of crystals showed a predominance of small particles. All observations are consistent with a diffusion mechanism of crystal growth.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the spherulite growth rate in mixtures of isotactic polystyrene and benzophenone has been measured over a concentration range extending from pure polymer to a mixture containing about 30%.
Abstract: As an extension of earlier work on the crystallization kinetics of isotactic polystyrene, the spherulite growth rate in mixtures of isotactic polystyrene and benzophenone has been measured over a concentration range extending from pure polymer to a mixture containing about 30% benzophenone. The glass transition temperature has been measured over the entire range from pure polymer to pure benzophenone. For the mixtures the dependence of the growth rate on temperature is similar to that of the undiluted polymer. The addition of benzophenone causes a shift of the crystallization range to lower temperatures. For mixtures containing up to about 20% benzophenone, the maximum in the growth rate increases with increasing content of benzophenone. On addition of more benzophenone, the maximum rate is depressed. Taking into account the glass transition temperature of the mixtures, the influence of benzophenone on the melting point of isotactic polystyrene, and the volume fraction of polymer, we can describe the influence of benzophenone on the growth rate in a semiquantitative way.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the f.c.p. phase is stable at radius ratio values less than 3.24, the d.h.c., and the h.c, and the Sm structure (δ) between 3.60 and 3.68.

Journal ArticleDOI
TL;DR: In this article, the preparation of so-called antimonic acid under various experimental conditions has been investigated in order to establish its usefulness as a chemically stable cation-exchange material.
Abstract: The preparation of so-called antimonic acid under various experimental conditions has been investigated in order to establish its usefulness as a chemically-stable cation-exchange material. In this experiment, the antimonic acid was mainly obtained by the hydrolysis of antimony pentachloride, and was rarely obtained from metallic antimony or potassium pyroantimonate. The hydrolyzed precipitate was amorphous at first, but it was gradually transformed into crystalline powder by keeping it in the mother liquor for a long time. The crystallization of the amorphous precipitate was facilitated by raising the temperature within a range of 0–80°C, and by increasing the concentration of strong mineral acid on aging, regardless of the kinds of starting antimony substances. The water-content of the air-dried samples is decreased by increasing the period of aging; the composition of the sample approximates Sb2O5·4H2O. The crystal of the antimonic acid is cubic and belong to the space group Oh7(Fd3m), with a lattice c...

Journal ArticleDOI
TL;DR: The method involves extraction in the cold of a protein precipitate with decreasing concentrations of ammonium sulfate followed by warming of the extract to room temperature and allows the inclusion of reagents necessary to limit inactivation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the melting behavior of polyvinylidene fluoride under a range of conditions and showed that the melting temperature of phase II and phase III has a single constant value within experimental error.
Abstract: The crystallization and melting of poly(vinylidene fluoride) as a function of hydrostatic pressure was investigated. Poly(vinylidene fluoride) can be crystallized in at least two crystalline modifications at pressures of 1 atm (phase I and phase II). The crystallization of poly(vinylidene fluoride) under hydrostatic pressure over a range of conditions yields a new crystalline phase, designated phase III. The new phase melts at 185°C, approximately 25C° higher than phase I or phase II. A noticeable similarity in the melting behavior of phase II and phase III as a function of pressure was observed. Over a range of pressures (up to 3000 atm) the rate of change of the melting temperature with pressure for phases II and III has a single constant value within experimental error. The specific volume of melting (ΔVm) and the entropy of melting (ΔSm) of the two phases varied with pressure in a similar manner. The higher values of ΔVm and ΔSm observed for phase III apparently reflect the difference in dens...

Journal ArticleDOI
TL;DR: In this paper, an adiabatic Nernst-type calorimeter with a cell for condensing a sample vapor as an amorphous state was constructed, and the heat capacities of the glassy, supercooled liquid, and crystalline states of methanol were measured from 20°K to 120°K.
Abstract: An adiabatic Nernst-Type calorimeter with a cell for condensing a sample vapor as an amorphous state was constructed. By making use of this calorimeter, the heat capacities of the glassy, supercooled liquid, and crystalline states of methanol were measured from 20°K to 120°K. It was found that the state of methanol deposited on the chilled substrate at about 95°K from its vapor state shows a glass transition phenomenon at about 103°K accompanied with the sudden increase of heat capacity, ΔCP, amounting to 26 J/(mol°K). The drastic crystallization with the exothermic effect coming to 1.54 kJ/mol was observed near 105°K. The residual entropy for the glassy methanol was found to be 7.07 J/(mol°K). Based on these results it seems very plausible to propose that any non-crystalline solid deposited on the chilled substrate from the vapor state will show the glass transition phenomenon.

Journal ArticleDOI
TL;DR: Of particular interest in living systems are liquid crystals, which are formed by cholesteric esters and many protein materials, and the two-dimensional crystals (smectic structure), which are form by fatty acid derivatives.
Abstract: Most lipids do not pass, on heating, directly from a crystalline structure to an isotropic structure. They are often characterized by a number of intermediate phases, ranging from the plastic crystal, where the center of gravity of the molecule may rotate about one or more axes while the three-dimensional order of the crystal remains, to nematic liquid crystals, which have birefrigent properties of crystals and yet are characterized by completely random ordering of the molecular centers. The smectic and cholesteric liquid crystalline structures are most commonly encountered in lipids. The structural characteristics of these systems are discussed. Of particular interest in living systems are liquid crystals, which are formed by cholesteric esters and many protein materials, and the two-dimensional crystals (smectic structure), which are formed by fatty acid derivatives. The mechanisms of energy transfer and the mechanical alignment in these liquid crystalline systems are unique and require different considerations from those found adaptable to liquids or solids. The properties of liquid crystals which might best be associated with living systems will be discussed, including surface properties and diffusivity.

Journal ArticleDOI
TL;DR: In this article, a special-purpose analog computer has been assembled and used online to process the thermal and mechanical data obtained in high speed tensile testing, and rough first-order room temperature crystallization kinetics curves were obtained having time constants of 50-60 msec in the range of 400-540% extension.
Abstract: Stress-induced crystallization in a rapidly stretched natural rubber gum vulcanizate has been studied using thermal techniques to follow the development of crystallinity. A special-purpose analog computer has been assembled and used online to process the thermal and mechanical data obtained in high speed tensile testing. Roughly first-order room temperature crystallization kinetics curves were obtained having time constants of 50–60 msec in the range of 400–540% extension. While the rate of this rapid, presumably primary crystallization appears rather insensitive to elongation in this limited range, the extent of crystallization at 400 msec increases smoothly from zero at 340% elongation to around 18% at 540% elongation. It is shown that our high-speed tensile tester can stretch this vulcanizate fast enough that most of the crystallization takes place after extension has been completed. Stress—strain curves obtained at this high rate are compared with those obtained at lower rates where crystalli...

Journal ArticleDOI
TL;DR: In this article, the kinetics of crystallization of Li2Si2O5 from glasses in the Li2O-SiO2 system were studied using quantitative X-ray diffraction.
Abstract: The kinetics of crystallization of Li2Si2O5 from glasses in the Li2O-SiO2 system were studied using quantitative X-ray diffraction. Analysis of the data using the Johnson-Mehl-Avrami equation showed that crystallization occurred through the nucleation and growth of rods. The spherulitic nature of the crystals was substantiated by petrographic examinations of the partially crystalline glass. Analysis of the temperature dependence of the crystallization rate using a modification of the Johnson-Mehl-Avrami equation showed that the activation energy for nucleation was a function of composition and thermal treatment.



Journal ArticleDOI
TL;DR: In this article, it was suggested that the initial fast periods correspond to nucleation on the surface of the added seed crystals is supported by the results of experiments made in the presence of strongly adsorbed anions.


Journal ArticleDOI
TL;DR: In this paper, the spherulitic growth rate of isotactic polystyrene has been measured in a wide range of temperature by means of a polarizing microscope provided with a hot stage.
Abstract: The spherulitic growth rate of isotactic polystyrene has been measured in a wide range of temperature by means of a polarizing microscope provided with a hot stage. It was possible to fit the experimental data to theory by choosing a value of 75 for the constant C2 of the WLF equation. The growth rate parameters were compared with those of polyethylene and polychlorotrifluoroethylene. The slowness of crystallization of isotactic polystyrene is mainly a consequence of the lower mobility of the molecules caused by the bulky phenyl groups.

Journal ArticleDOI
TL;DR: In this article, it was shown that the orthorhombic unit cell dimensions of polyethylene are not unique, but depend on the physical history of a sample, and that the changes correlate with the reciprocal of crystal thickness.
Abstract: It is shown that the orthorhombic unit cell dimensions of a given polyethylene are not unique, but depend on the physical history of a sample. For polymer crystallized from a ¾% p‐xylene solution, the values of a and b measured at 23°C by powder camera technique vary up to 0.8% for crystallization temperatures of 50°, 70°, and 90°C, annealing temperatures from 50° to 127°C, and deformation. The as‐crystallized values of a and b as well as the effects of annealing and deformation are smaller the thicker the crystals. For ``undeformed'' crystals the changes correlate with the reciprocal of crystal thickness but for deformed crystals the changes occur before the thickness increases (even below the crystallization temperature). The dimensions undergo the greatest change within the first 2 min of annealing and change very little with time thereafter. The only exception observed is a slow decrease of b with time of annealing at 100°C. Crystals grown from other solvents exhibit very nearly identical effects, and...

Journal ArticleDOI
TL;DR: In this article, a model of two-dimensional polymer crystallization by chain folding is treated by equilibrium statistical mechanics, and the Laplace transform of the partition function with respect to the length of the polymer chain is obtained in exact analytical form.
Abstract: A model of two‐dimensional polymer crystallization by chain folding is treated by equilibrium statistical mechanics. The Laplace transform of the partition function with respect to the length of the polymer chain is obtained in exact analytical form. The model leads to thermodynamically well‐defined chain‐folded crystals. Under certain circumstances in the limit of an infinitely long polymer chain, the model shows a second‐order phase transition from an “extended‐chain” crystal to the chain‐folded crystal.

Journal ArticleDOI
TL;DR: Simultaneous as well as successive polymerization and crystallization is possible as discussed by the authors, while crystallization after polymerization usually produces folded chain lamellar crystals, crystallzation during polymerization frequently produces fibrillar extended chain crystals.
Abstract: Simultaneous as well as successive polymerization and crystallization is possible. While crystallization after polymerization usually produces folded chain lamellar crystals, crystallzation during polymerization frequently produces fibrillar extended chain crystals.

Journal ArticleDOI
TL;DR: In this paper, the effects of certain variables on α-lactose crystallization were examined, and it was found that the rate of crystallization was not directly proportional to seed crystal surface area, probably because of false graining or because mutarotation has a limiting effect on rate as surface area is increased.

Journal ArticleDOI
TL;DR: The growth of the crystals, the absorption spectra, extinction coefficient, and the isoionic and isoelectric points are described and the presence of Mg++ has been found essential for full enzyme activity; in the absence of this ion, the activity decreased by 40%.
Abstract: The paramount role of acetylcholinesterase (ACh-esterase) in the control of electrical activity of excitable membranes of nerve and muscle cells appears well established.1-' In view of its vital function in nerve impulse conduction, the enzyme has been intensively studied since it was first extracted, in 1938, from electric tissue.4 In the early 1940's a several-hundredfold purification of this enzyme was achieved;5 however, the amounts of pure protein available, while adequate for kinetic studies, for the analysis of the molecular groups in the active site and other related studies, did not permit an investigation of the protein structure and its properties. The advances of macromolecular chemistry in the last decade, especially the possibility of exploring tridimensional structures, made apparent the desirability of obtaining the enzyme in sufficiently large amounts for carrying out such studies. A large-scale purification was started about four years ago, and a successful and readily reproducible procedure was described in a preceding paper :6 60-70 mg pure protein were obtained from 10 kg of electric tissue. Evidence for the purity of the enzyme and an amino acid analysis were also reported. In a footnote added in proof, a crystallization of the enzyme was announced. In the present paper the growth of the crystals, the absorption spectra, extinction coefficient, and the isoionic and isoelectric points are described. Materials and Methods.-ACh-esterase, with a specific activity of approximately 750 mmoles ACh hydrolyzed per milligram of protein per hour, has been used throughout the experiments described here. The reaction mixture in which the specific activity was tested contained 0.02 M MgCl2, 0.01% recrystallized bovine albumin, and 2.7 X 10-I M1 acetylcholine. The presence of Mg++ has been found essential for full enzyme activity; in the absence of this ion, the activity decreased by 40%. The effect of Mg++ has been previously discussed.7 8 A more detailed evaluation of the effects of monoand divalent cations on the activity will be described elsewhere. A radiometer automatic titrator was used for determining the enzyme activity. The protein concentrations were measured by the optical absorption at 280 my and by micro-Kjeldal methods. The UV-absorption spectra were recorded with a Cary 14 spectrophotometer. Results.-Crystallization: When a concentrated solution of pure enzyme protein (0.5-1%) is kept in 35 per cent ammonium sulfate solution at 40C, crystals are formed within about two to four days.6 These crystals have a length of about 10 u. Growth of the crystals has been obtained in the following way: saturated ammonium sulfate is slowly added to a solution of 0.5-1 per cent pure enzyme in 0.06 M potassium phosphate buffer, pH 6.85, until a slight turbidity occurs. This represents approximately 35 per cent saturation. The solution is then clarified by centrifugation and slowly concentrated over a period of two to three months by evaporating water through a thin capillary tube. Using this method, crystals of 150 1A length and 120 u width have been isolated. The

Journal ArticleDOI
TL;DR: In this paper, a comparison of the morphology of fibrillar polyethylene crystals prepared by shear-induced crystallization and heterogeneous Ziegler-Natta catalysis under similar solvent and temperature conditions was made.
Abstract: A comparison has been made of the morphology of fibrillar polyethylene crystals prepared by shear-induced crystallization and heterogeneous Ziegler-Natta catalysis under similar solvent and temperature conditions. Both specimens had a shish-kebab superstructure consisting of lamellar overgrowths on a filamentary backbone. For polyethylenes stirrer-crystallized at small supercoolings, the overgrown lamallae were removed by nitric acid oxidation followed by selective dissolution, leaving naked filamentary ribbons. Thermal analysis of these specimens suggested a dual molecular conformation of both folded and extended chains. The fact that these fibrils did not deform easily under uniaxial stress conforms with a core of extended chains. Thermal and oxidative behavior of polyethylenes prepared at lower crystallization temperatures suggested a greater content of chain folds in the central thread as the degree of supercooling increased. The Ziegler-Natta fibrils were degraded into lamellar fragments on ...