Cubic Phase Structure Research Articles

Nuclear magnetic resonance studies of motion and structure of cubic liquid crystalline phases

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNuclear magnetic resonance studies of motion and structure of cubic liquid crystalline phasesPer-Olof Eriksson, Ali Khan, and Goeran LindblomCite this: J. Phys. Chem. 1982, 86, 3, 387–393Publication Date (Print):February 1, 1982Publication History Published online1 May 2002Published inissue 1 February 1982https://doi.org/10.1021/j100392a021RIGHTS & PERMISSIONSArticle Views86Altmetric-Citations63LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Structure of the body-centered cubic phase of lipid systems does not consist of indefinitely long straight rods

The observed intensities of the reflections from the body-centered cubic phase of lipid systems are shown to be incompatible with a recently reported model consisting of straight, indefinitely long rods.

Structure of the body-centered cubic phase of lipid systems

A new model is proposed for the structure of the body-centered cubic phase of lipid systems. Infinite rods of polar groups (and water) are arranged with axes parallel to the four cubic [unk]1 1 1[unk] directions. The hydrocarbon chains fill the space between the rods to form a continuous matrix. With this unified topology, the model explains satisfactorily the x-ray diffraction patterns of strontium soaps, lecithin, galactolipids, potassium soaps, and hexadecyltrimethylammonium bromide and explains the transition between cubic/H(II) phases. The paradoxical thermal effects on the lipid cubic phase, in particular the decrease of unit cell dimensions with increasing temperature, can be explained with the proposed model by mechanisms similar to those used for the monodimensional and bidimensional (mesomorphic) phases.

Investigation of Cobalt (II)-Tungsten (VI)-Oxide Reduction in Hydrogen: Part I

CoWO4 reduction in dry hydrogen, at temperatures lower than 550°C brings about an intermediate unstable phase of cubic structure, (a = 10.846A) and composition Co4W2.5O; the tungsten which is not retained in this phase appears in the form ofβ- W (A-15 structure,a = 5.039A). Another phase (noted ϕ@#@) which does not give any X-ray diffraction pattern forms by further reduction of Co4W2.5O. The whole set of these transformations is characterized by a kinetic global law described by a Johnson-Mehl equationξ = 1- exp(-kt)3/2 and an activation energy, 24 kcal/Mole, determined byβ-W continuous growth. The rate of C03W crystallization fromϕ becomes substantial, only from around 700°C, temperature at whichβ-W is also converted into α-W. The final alloy Co7W6 is formed from about 800°C on, through reaction of Co3W and α-W. In wet hydrogen, WO2 forms instead ofβ- W and Co4W2.5O—which may be stabilized under certain conditions-is directly reduced into Co3W after WO2 reduction into α-W.

The electronic structure of cubic laves phases: ZrZn 2

A simplified model for the calculation of the electronic structure of Laves phase materials is developed that focuses on the effects of d bonds between tetrahedrally coordinated sites. This model is show to be in good agreement with all of the existing data on ZrZn 2. Indirect evidence for the validity of the model in other systems is sketched.

A novel cubic phase—A cage-like network of rods with enclosed spherical micelles

Among the numerous lipid-water phases a few crystallize in the cubic system and offer interesting crystallographic problems. One of these (space group Ia3d) consists of rods of finite length, joined three by three and forming two three-dimensional networks, mutually interwoven and unconnected. We describe the structure of another widespread cubic phase, space group Pm3n. The structure consists of a three-dimensional networks of rods of finite length, all crystallographically equivalent, which meet three of three at one end and four by four at the other and form the bars of a system of cages, each of which encloses a spherical micelle (chlathrate-type structure). The “liquid” hydrocarbons occupy the interior of the rods and spheres, the water fills the interstices. The hydrocarbon-water interface is covered by the polar groups of the lipid molecules.

The anisotropy of thermal expansion as a cause of deformation in metals and alloys

Plastic deformation produced by repeated heating and cooling of certain non-cubic metals has been studied over a temperature range from ─ 190 to 250° C. The extent of the deformation which results from the anisotropy of thermal expansion of individual crystals becomes greater as the temperature range is increased. In the case of cadmium, plastic deformation was detected even after 20 cycles over the temperature range 30 to 75° C; in cyclic treatment to higher temperatures the deformation was associated with extensive grain-boundary migration. Cyclic treatment of tin, cadmium and zinc between room temperature and that of liquid air resulted in complex slipping and twinning, but grain-boundary migration was practically absent. Cooling from the liquid state which represents half a thermal cycle sets up stresses in metals possessing anisotropy of thermal expansion, and leads to plastic deformation. This is shown by the detection of slip lines and grain -boundary accentuation in certain cast noncubic metals. In cadmium, subsequent annealing results in marked grain growth. In order to investigate the interaction between the crystals of the two phases of a duplex alloy during cyclic thermal treatment, experiments were carried out with a series of tin-rich tin-antimony alloys. The majority of the alloys consisted of the tin-rich matrix in which particles of a hard second phase of cubic crystal structure were embedded. It was found that the deformation in the region of the boundaries between crystals of the two phases was considerably smaller than that in the region of the crystal boundaries of the anisotropic matrix. Similar results were obtained with tin-base bearing alloys.