Structure des savons alcalins

Summary In the first part of this work we describe the results of a systematic X-ray diffraction study of the structure of cesium soaps at high temperatures. Three types of structure have been identified. The first is lamellar with both polar groups and paraffin chains in the crystalline state. The second is also lamellar, but with both polar groups and paraffin chains in the liquid state. The third corresponds to the localization of polar groups in the crystalline state within discs surrounded by paraffin chains in a partially disorganized configuration. In the second part of this work we discuss the mechanism of the stepwise melting of alkali-metal soaps, the polymorphism exhibited by polar groups when crystallized and the amphipathic character of soaps. We present some empirical rules which seem to govern the occurrence of different types of structure as a function of the nature of the cation and the length of the paraffin chains.

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Zusammenfassung Es werden Ergebnisse der Untersuchung der Strukturen von C?siumseifen bei hohen Temperaturen mit R?ntgenstrahldiffraktion beschrieben. Drei Strukturtypen wurden gefunden. Die erste, in welcher die polaren Gruppen und die Paraffinketten kristallisiert sind, ist lamellar. Die zweite ist ebenfalls lamellar; aber die polaren Gruppen und Paraffinketten sind geschmolzen. Die dritte Struktur entspricht diskusf?rmigen Strukturelementen; die polaren Gruppen befinden sich im kristallinen Zustand in Scheiben, die von zum Teil ungeordneten Paraffinketten umgeben sind. Im zweiten Teil dieser Arbeit diskutieren wir den Mechanismus des stufenweisen Schmelzens von Alkaliseifen, die Polymorphie der kristallisierten polaren Gruppen und den amphipathischen Charakter der Seifen. Wir schlagen einige empirische Regeln vor, welche die verschiedenen Strukturtypen in Hinsicht auf die Natur des Kations und auf die L?nge der Paraffinketten zu bestimmen scheinen.

     

Structure des savons alcalins

Summary This is a systematic x-ray diffraction study of the structure of alkali-metal di-soaps as a function of temperature. Two types of structure have been identified. The first is lamellar with both polar groups and paraffin chains in the crystalline state. The second is also lamellar, but with polar groups and paraffin chains in the liquid state. These structures have been discussed and compared to those of usual alkali-metal and alkaline-earth soaps.

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Zusammenfassung Aus r?ntgenographischen Daten wurde die Struktur der Lithium-, Natrium-, Kalium-, Rubidium- und C?siumsalze von Alkylendicarbons?uren („Doppelseifen“) abgeleitet. Es wurden zwei lamellare Strukturtypen gefunden. In einer davon entspricht die Anordnung der polaren Gruppen und der Paraffinketten dem kristallisierten Zustand, in der anderen dem geschmolzenen Zustand. Die beobachteten Strukturen wurden mit denen der einfachen Seifen (Monos?uren) mit einwertigen und zweiwertigen Metallen verglichen.

     

Structure des savons alcalins

Summary This is a systematic X-ray diffraction study of the structure of the mesomorphic phases occurring with potassium soaps ranging from C₈ to C₂₂.Four types of structure have been identified. The first is lamellar with both polar groups and paraffin chains in the crystalline state. The second is also lamellar, but with both polar groups and paraffin chains in the liquid state. The third corresponds to the localization of indefinitely long ribbons on a two-dimensional oblique lattice; polar groups are crystalline and paraffin chains desorganized. The fourth corresponds to the localization of discs on a three-dimensionnalB-faces centered orthorhombic lattice; polar groups are crystalline and paraffin chains disorganized.The structural parameters and the polymorphism of the polar groups have been discussed.

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Zusammenfassung Wir beschreiben hier eine systematische Röntgenstrahlendiffraktionsforschung der Struktur der mesomorphen Phasen von Kalium Seifen von C₈ bis C₂₂.Vier Strukturtypen wurden gefunden. Die erste Struktur ist lamellar; beides, die polaren Gruppen und die Paraffinketten sind kristallisiert. Die zweite Struktur ist auch lamellar; aber in diesem Falle sind beides, die polaren Gruppen und Paraffinketten geschmolzen. Die dritte Struktur entspricht einer Lokalisation von Seifenbändern in einem zweidimensionalen monoklinen Gitter; die polaren Gruppen sind kristallisiert und die Paraffinketten geschmolzen. Die vierte Struktur entspricht einer Lokalisation von Seifenscheiben in einemB-flächenzentrierten orthorhombischen Raumgitter; die Polargruppen sind kristallisiert und die Paraffinketten geschmolzen.Wir haben aus den experimentellen Resultaten einige Schlußfolgerungen gezogen.

     

Etude cristallographique de membranes obtenues a partir d'alcools polyvinyliques alcoyles

Low and wide angle X-ray diffraction was used to study the structure of paraffin grafted polyvinylalcohol membranes as a function of water content. The structure was found to be lamellar resulting in the pile-up of crystalline paraffin double layers, covered with polymer chains. Such an organization would be impossible if grafting of paraffin chains upon polyvinylalcohol were random. The membranes must be considered as two phase systems, consisting of amorphous and crystalline regions.     

Etude par diffraction des rayons X des structures rencontrees dans les solutions aqueuses concentrees d'un polyelectrolyte amphipathique

Low and wide-angle X-ray diffraction was used to study the structure of aqueous gels of a maleic anhydride-hexadecylvinylether alternating copolymer, as a function of water content, degree of neutralization and temperature. Two types of structure have been found: a lamellar structure observed at low degrees of neutralization and a cylindrical structure observed at high degrees of neutralization. In both cases, the structural parameters have been analysed.     

pH- and Ionic-Strength-Induced Structural Changes in Poly(acrylic acid)-Lipid-Based Self-Assembled Materials

Summary: The effect of a polyanion introduced as a lipid conjugate (poly(acrylic acid)- dimyristoyl-sn-glycero-3-phosphoethanolamine, PAA-DMPE) on the structure of a self-assembled, biomembrane mimetic has been evaluated using synchrotron small-angle X-ray scattering (SAXS). At high grafting density (8–11 mol.%), the PAA chains were found to produce significant changes in structure in response to changes in pH and electrolyte composition. At low pH and in the absence of salt (NaCl), the neutral PAA chains adopt a coil conformational state that leads to the formation of a swollen lamellar structure. Upon the addition of salt at low to intermediate pH values, two lamellar phases, a collapsed and an expanded structure, coexist. Finally, when the polymer is fully ionized (at high pH), the extended conformation of the polymer generates a cubic phase. The results of this study contribute to an understanding of how polyelectrolytes may ultimately be harnessed for the preparation of self-assembling materials responsive to external stimuli.     

Thermotropic phase behaviour of long-chain alkylmaltosides

The thermotropic phase behaviour and phase structure of crystalline and non-crystalline n-tetradecyl-beta-D-maltoside (C14G2) and n-hexadecyl-beta-D-maltoside (C16G2) have been investigated by means of differential scanning calorimetry and X-ray techniques. Upon lyophilisation, both compounds form a solid, lamellar phase comprising disordered head groups and hexagonally packed alkyl chains that are suggested to be tilted and interdigitated. This ordered lamellar phase melts into a metastable lamellar liquid crystal, which re-crystallises to a high-temperature crystalline polymorph comprising interdigitated, non-tilted alkyl chains. Remarkably, the high-temperature polymorph of C14G2 has the same melting point as that of C16G2, namely 105 degrees C for both surfactants. A low-temperature polymorph of anhydrous C14G2 crystallises from water at room temperature, whereas the hemihydrate of C14G2 crystallises at 6 degrees C from water, or from chloroform containing trace water. X-ray data suggest both these crystalline modifications to comprise interdigitated and tilted alkyl chains.     

Crystallization of short aliphatic chains. II. Example of even fold surface with adjacent fold reentry and of a transition to chain extension

As a continuation of the preceding study on the folding behavior of short polymer chains, an iodine-terminated paraffin having 156 Å peak molecular length and a sharp molecular weight distribution was prepared. The paraffin could be crystallized in lamellae of two different thicknesses: (A) thickness close to half the chain length (the most readily obtained); (B) thickness intermediate between half chain length and fully extended chain. Case A corresponds to each chain folding once with equal stems and with ends at the surface. Degradation behavior revealed that the folds must be of closely equal length giving rise to an even fold surface. In case B the situation is more involved: here the chain ends must turn into the lattice. Adjacent reentry is a necessity throughout. In both cases the lamellar thickness could be increased by annealing up to complete chain extension.     

The structures of Langmuir-Blodgett films of fatty acids and their salts

Recent advances in several experimental techniques have enabled detailed structural information to be obtained for floating (Langmuir) monolayers and Langmuir-Blodgett films. These techniques are described briefly and their application to the study of films of fatty acids and their salts is discussed. Floating monolayers on aqueous subphases have been shown to possess a complex polymorphism with phases whose structures may be compared to those of smectic mesophases. However, only those phases that exist at high surface pressures are normally used in Langmuir-Blodgett (LB) deposition. In single LB monolayers of fatty acids and fatty acid salts the acyl chains are in the all-trans conformation with their long axes normal to the substrate. The in-plane molecular packing is hexagonal with long-range bond orientational order and short-range positional order: known as the hexatic-B structure. This structure is found irrespective of the phase of the parent floating monolayer. The structures of multilayer LB films are similar to the structures of their bulk crystals, consisting of stacked bilayer lamellae. Each lamella is formed from two monolayers of fatty acid molecules or ions arranged head to head and held together by hydrogen bonding between pairs of acids or ionic bonding through the divalent cations. With acids the acyl chains are tilted with respect to the substrate normal and have a monoclinic structure, whereas the salts with divalent cations may have the chains normal to the substrate or tilted. The in-plane structures are usually centred rectangular with the chains in the trans conformation and packed in a herringbone pattern. Multilayer films of the acids show only a single-step order-disorder transition at the melting point. This temperature tends to rise as the number of layers increases. Complex changes occur when multilayer films of the salts are heated. Disorder of the chains begins at low temperatures but the arrangement of the head groups does not alter until the melting temperature is reached. Slow heating to a temperature just below the melting temperature gives, with some salts, a radical change in phase. The lamellar structure disappears and a new phase consisting of cylindrical rods lying parallel to the substrate surface and stacked in a hexagonal pattern is formed. In each rod the cations are aligned along the central axis surrounded by the disordered acyl chains.     

Evidence of formation of ammonium perfluorononanoate/2H2O multilamellar vesicles: morphological analysis by rheology and rheo-2H NMR experiments

Rheology and rheo-(2)H NMR measurements are presented for 30 wt % ammonium perfluorononanoate (APFN)/(2)H(2)O mixture in the temperature range 20-70 °C. A first-order lamellar-to-nematic transition occurs at 42 °C, and a first-order nematic-to-isotropic transition occurs at 49 °C. Different rheological behaviors of the lamellar phase were observed with increasing the temperature. The lamellar structure at low temperature (Lα(-)) has a clear gel-like viscoelasticity, while at high temperature the lamellar structure (Lα(+)) has a liquid-like response. In this study we have observed for the first time, along with the lamellar phase of a surfactant containing fluorinated fatty acid, the formation of multilamellar vesicles (MLVs) ("onions") induced by shear. With the aid of nonlinear rheology and rheo-NMR techniques, onion formation was found to occur in both temperature regimes of the lamellar phase, but at different strain units. It is suggested that the lamellar phase consists of smectic structures in both Lα(-) and Lα(+), but with different percentages of defect density.     

A thermodynamic and N.M.R. study of the ribbon lyotropic mesophases. An investigation of the potassium palmitate/potassium laurate/water system

Lyotropic ternary mixtures of K-palmitate/K-laurate/water with different compositions have been investigated by ²H N.M.R., differential scanning calorimetry and thermo-volumetric analysis. The transitions between rectangular ribbon-like aggregates and lamellar structures have been characterized and explained on the basis of a theoretical model. Our results suggest that for ternary systems containing a small amount of short chain lipids the ribbon structure is more stable at low temperature. Moreover, the rectangular shape is favoured both by the segregation of the short chain lipids at the curved edges of the ribbon and by a tighter packing of the hydrocarbon chains in the same region.     

Thermotropic organization of hydrogen-bond-bridged bolaform amphiphiles

A series of quaternary ammonium amphiphiles (A-n) bearing carboxylic acid groups were designed and synthesized. The branched bolaform structures can be constructed by dimerizations of carboxylic acid groups through intermolecular hydrogen bonding, as demonstrated by the Fourier transform infrared (FT-IR) spectra and the temperature-dependent FT-IR spectra. The thermotropic organizations of branched bolaform ammonium dimer complexes were characterized by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. We investigated the influence of the spacer between the cationic group and the benzene ring on the thermotropic organization. A-6 with short lateral alkyl chains formed a simple layered structure at room temperature and exhibited smectic A mesophase above 145 °C, whereas A-8 with intermediate lateral chain length organized into smectic A phase over a wide temperature range. A further increase of the length (n = 10, 12) of the lateral chains resulted in the formation of lamellar structure with in-plane layered periodicity, which is rare in the organization of ionic compounds. A packing model of the quasi-2D lamellar was proposed on the basis of the experimental data of X-ray diffraction results. Notably, the quasi-2D lamellar structure could evolve into a simple layer with the increase of temperature. The present results showed a direct relationship in which the branched architecture can be applied to tune the self-assembly behavior of ionic amphiphiles and is allowed to construct new layered superstructure.     

On the deformation mechanisms of oriented PET and PP films under load

Uniaxially orienred semicrystalline poly(ethylene terephthalate) (PET) and poly(propylene) (PP) films were loaded parallel to draw direction at various temperatures. Changes in the submicroscopical structure of the films under load were examined by small and wide-angle x-ray scattering (SAXS; WAXS) and birefringence measurements. WAXS measurements reveal a decrease of the initial high orientation of the chains in the crystallites during deformation. Simultaneously, an increase of the birefringence was detected, indicating an orientation of chains in the amorphous regions. The alteration of the long period reflections in the SAXS patterns give strong evidence that lamellar stacks with different orientation angles according to load direction are present. Depending on the orientation of stacks, the contribution of lamellar separation to sample deformation alters, giving rise to different amounts of density changes in the stacks. Absolute intensity measurements of SAXS using a Kratky apparatus reveal that lamellar separation occurs preferentially below or in the range of the glass-transition temperature at small strain. With increasing strain and temperatures above the glass-transition slip deformation mechanisms become more important. The formation of microvoids was observed at strain near to elongation at break below or in the range of glass-transition temperature.     

Criss‐cross amphiphilic polymers and analogous model systems

A new class of amphiphilic polymers carrying two pendant docosyl (C22) chains, located at periodic intervals that are separated by PEG chains of varying lengths, was synthesized via a simple melt‐transesterification polymerization, using dimethyl, 2,5‐didocosyloxyterephthalate as one of the monomers. DSC, variable temperature FT‐IR, and WAXS studies demonstrated that immiscibility between the pendant docosyl units and the backbone PEG segments drives their self‐segregation; this results in the crystallization of the pendant docosyl segments and the generation of a lamellar morphology with the alkyl segments and the PEG chains occupying alternate layers. Based on the study of model criss‐cross amphiphiles that resemble the polymer repeat unit, it is postulated that the chains reconfigure such that both the docosyl chains fold to one side of the terephthalate unit while the PEG segments form a loop on the other side; these chains then organize in a bilayer to form the lamellar structure. The simplicity of the synthesis and the rather unique properties of these polymers suggests that such a design could be translated to develop other interesting functional materials that could exploit the immiscibility‐driven microphase separation for the generation of sub‐10 nm domains; these could have potential applications, such as in membranes, solid polymer electrolyte formulations, and so forth. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1554–1563     

SAXS experiments on gel-spun polyethylene fibers

The properties of gel-spun polyethylene fibers hot-drawn to the maximum draw ratio depend on the spinning conditions. Different spinning conditions result in two types of structure in the paraffin oil containing fibers: an isotropic lamellar structure or a shish-kebab structure. Meridional SAXS experiments can identify the structure present. After extraction, these structures are still present but can be detected only in a more indirect way by SAXS experiments because of an excessive contribution of void scattering. During hot-drawing both structures are transformed into a more fibrillar structure. The shish-kebab structures can be drawn only to relatively low hot-draw ratios with an incomplete transformation of the lamellar overgrowth into the fibrils, as demonstrated by the presence of a meridional SAXS maximum/shoulder. This leads to relatively weak fibers. Lamellar structures can be drawn to high draw ratios by chain unfolding. A nearly complete transformation of the lamellae into fibrils is obtained and the fibers have excellent properties. The information about the morphology obtained by SAXS, DSC, WAXS, and SEM can be used to establish a relation between morphology and properties.     

油酸/三乙醇胺/液体石蜡水体系层状润滑性能

采用^2HNMRT和IR,表征了油酸／三乙醇胺／液体石蜡／水体系层状液晶的结构,并以该体系为润滑剂,测定了其在铝合金表面的磨痕宽度和摩擦系数,同时与液体石蜡和商用润滑剂12－羟基硬脂酸锂进行了比较。结果表明,OLA／TEA／LP／H2O体系丑状液晶具有较好的极压性能,对于铝合金材料是一种较好的润滑剂。     

STRUCTURAL PHASE TRANSITION OF ALIPHATIC NYLONS VIEWED FROM THE WAXD/SAXS AND VIBRATIONAL SPECTRAL MEASUREMENTS AND MOLECULAR DYNAMICS CALCULATION

The crystalline phase transition of aliphatic nylon 10/10 has been investigated on the basis of the simultaneous measurement of wide-angle and small-angle X-ray scatterings, the infrared spectral measurement and the molecular dynamics calculation. An interpretation of infrared spectra taken for a series of nylon samples and the corresponding model compounds was successfully made, allowing us to assign the infrared bands of the planar-zigzag methylene segments reasonably. As a result the methylene segmental parts of molecular chains were found to experience an order-to-disorder transition in the Brill transition region, where the intermolecular hydrogen bonds are kept alive although the bond strength becomes weaker at higher temperature. The small-angle X-ray scattering data revealed a slight change in lamellar stacking mode in the transition region. The crystal structure has been found to change more remarkably in the temperature region immediately below the melting point, where the conformationally disordered chains experienced drastic rotational and translational motions without any constraints by hydrogen bonds, and the lamellar thickness increased largely along the chain axis. These experimental results were reasonably reproduced by the molecular dynamics calculation performed at the various temperatures.     

Structural properties of nonionic surfactant/glycerol/paraffin lyotropic liquid crystals

Lamellar lyotropic liquid-crystalline systems are thermodynamically stable, optically isotropic and are formed spontaneously. New possibilities for the development of controlled drug delivery systems are inherent in these systems in consequence of their stability and special, skin-friendly structure. The aim was to formulate and study two-component or multicomponent compositions with a relatively low Brij 96V content, liquid paraffin, glycerol and water for therapeutic purposes. The liquid crystals were examined by polarizing light microscopy and transmission electron microscopic observation of replicas produced by the freeze–fracture technique to demonstrate the presence of lamellar liquid-crystalline domains. The existence of a regular structure was determined by X-ray diffraction.     

Predicting the location of weld line in microinjection‐molded polyethylene via molecular orientation distribution

The microstructure and molecular orientation distribution over both the length and the thickness of microinjection‐molded linear low‐density polyethylene with a weld line were characterized as a function of processing parameters using small‐angle X‐ray scattering and wide‐angle X‐ray diffraction techniques. The weld line was introduced via recombination of two separated melt streams with an angle of 180° to each other in injection molding. The lamellar structure was found to be related to the mold temperature strongly but the injection velocity and the melt temperature slightly. Furthermore, the distributions of molecular orientation at different molding conditions and different positions in the cross section of molded samples were derived from Hermans equation. The degree of orientation of polymeric chains and the thickness of oriented layers decrease considerably with an increase of both mold temperature and melt temperature, which could be explained by the stress relaxation of sheared chains and the reduced melt viscosity, respectively. The level of molecular orientation was found to be lowest in the weld line when varying injection velocity, mold temperature, and melt temperature, thus providing an effective means to identify the position of weld line induced by flow obstacles during injection‐molding process. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1705–1715     

Deformation in lamellar and crystalline structures: in situ simultaneous small‐angle X‐ray scattering and wide‐angle X‐ray diffraction measurements on polyethylene terephthalate fibers

Changes in the lamellar and crystalline structures were followed as a function of applied stress to understand the influence of the interactions between the crystalline and amorphous domains on the fiber properties. We observed a reversible transformation from a structure giving a four‐point small‐angle pattern to a structure giving a two‐point pattern; these structures corresponded to the lamellae with oblique and normal lamellar surfaces, respectively. The characteristics of these two structures such as the stack diameter, stack height, and tilt angle were different and were determined by the processing conditions and did not change when the fiber was elastically deformed. The structure giving a two‐point pattern was probably the load‐carrying lamellar entity in these fibers. The diameter of the lamellar stacks, tilt angle of the lamellae, and the strain in the lamellar spacing appeared to have the most influence on properties such as tenacity and dimensional stability. The long‐spacing strain, which is about the same as the fiber strain, determined the modulus at low elongation as well as ultimate elongation. These indicate that the lamellar stacks have at least as much influence as the interfibrillar chains on fiber properties. Structural features that determine the performance in semicrystalline polymers were investigated by analyzing four generations of polyethylene terephthalate fibers. Some of the fiber properties correlate with changes in the crystalline domains such as the crystalline orientation, size, and unit cell dimensions. Fibers in which the crystalline strain was large because of their strong linkages to the amorphous chains, and better load transfer, had the highest modulus and lowest ultimate elongation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1538–1553, 2003