Lamellar Regions Research Articles

Composites based on poly(ethylene terephthalate) fibers with polyaniline. II. The effect of the growth of the polyaniline molecules during the polymerization in the morphology of the PET substrate

PET fibers of different drawn ratios were used as substrates to produce composites with PANi. The influence of the growth of the polyaniline molecules in the structure of the fibers previously pretreated in the presence of aniline at different conditions were studied by different characterization techniques (differential scanning calorimetry, X-ray scattering, dynamic and mechanical thermal analysis, sonic modu- lus, and scanning electron microscopy). The polymerization of the aniline inside the fiber substrates modified the structure of the fibers. In the case of the drawn fiber substrates the growth of the PANi molecules occurred mainly in the interfibrillar regions, which promoted reorganization of the preexisting crystals such as defect elimination (mainly in the interface of these regions with the lamellar regions) and at same time reorientation of their amorphous and crystalline regions. Also, due to this reorientation process the crystals became not only bigger and more perfect, but also they became more homogeneous. In the case of the undrawn fiber substrates, due to the lack of previous orientation, the growth of the PANi molecules would be occurring in the amorphous interlamellar regions only. Finally, the use of fibers with different drawn ratios as substrates for the composites was essential to reach such conclusions. © 2000

Crystal Growth Habits of DNA Fractions. 2. Low-Voltage SEM and TEM Examination of Lamellar Structure and Growth Fronts

In a previous publication we reported the first documentation of the crystal growth habits in a polydisperse, heterogeneous DNA fraction of reasonable molecular weights under quiescent and isothermal conditions. In the relative humidity (RH) range where the A-DNA helix conformation is adopted, these morphologies could best be described as sheaves and spherulites. Here, we extend those light microscopic observations to the nanoscale, with the following conclusions: (1) the growth habit of A-DNA is lamellar with chain (helix) folding, exhibiting the formation of sheaves consisting of individual lamellae similar to those formed by synthetic semicrystalline polymers; (2) the lamellar crystals are thinner than the mean molecular length of the DNA fraction; (3) the lamellae exhibit topological differences in their lateral and basal aspects; (4) the lamellar tips are round and thinner than in the lamellar region behind the tips, which appear more faceted and of a different organizational structure; (5) these tw...

Microstructure of reaction zone at the Ti–AlN interface

The phase composition of the reaction zone between Ti matrix and AlN particles was investigated employing electron probe X-ray microanalysis (EPMA) and electron backscatter diffraction techniques (EBSD) in scanning electron microscopy (SEM). The TiN (cubic, NaCl type), Ti 3AlN (cubic, perovskite type) and Ti-rich Ti 3Al (hexagonal, Ni 3Sn type) phases were identified in the reaction zone after anneals at 900, 1000 and 1100°C. The binary nitride TiN and the ternary nitride Ti 3AlN exhibit a complex interpenetrating morphology. A two-phase, Ti 3AlN/Ti 3Al, lamellar region was observed between the Ti 3AlN and Ti 3Al layers after annealing at 1000 and 1100°C.

Hydrotrope Action of Vitamin C (VC) and Its Application in a Sunscreen

The solubility regions of the sunscreen 2-ethyIhexyl p-methoxycinnamate (E557) in the CTAB/ n-CsHnOH/ H2 O system with and without the hydrotrope agent vitamin C (VC) are determined. E357 was only sohibilized in the bicontinuous microemulsion (BI), the W/ O microemulsion area and the lamellar liquid crystal region (LLC). The addition of VC in the system greatly enlarged the solubility amount of E557in the bicontinuous region, but reduced h in the lamellar liquid crystal area. Small angle X-ray diffraction measurement was used to determine the location of E557 in the lamellar liquid crystal showing the suncreen molecule penetrating between the hydrocarbon chains in the liquid crystal structure.The UV absorption spectra of E557 in various media was measured, surprisingly showing a dependence on the colloidal structure.

Swelling Behavior of Lamellar Phases with Calcium Dodecyl Sulfate, Heptanol or Octanol, and Water

The swelling behavior of calcium dodecyl sulfate (CDS)/water with heptanol and octanol was investigated at 25 °C. Both systems form a condensed lamellar phase at a high content of surfactant and cosurfactant and a highly swollen lamellar phase at a low surfactant content. There is no single-phase channel between both lamellar regions. A dilute L3 phase exists in the heptanol system as well as in the octanol system. This L3 phase is water-like transparent and shows no streaming birefringence. On dilution of samples with an appropriate composition of water, iridescent phases can be obtained which display bright blue to green colors. In contrast to CDS with pentanol or hexanol, the lamellar region is broken into a dilute phase and a condensed phase because of decreasing undulation forces of systems containing longer chain alcohols.

Coexistence of lamellae and vesicles in multi-stacked fluid membranes with polymer lipids

A continuum model for multi-stacked fluid membranes with polymer lipids is proposed, and a Monte Carlo calculation is carried out to observe defect structures in multi-lamellar membranes. We find three different phases: (1) undulating lamellae; (2) vesicles; and (3) coexisting undulating lamellae and vesicles. The phase diagram is determined by the calculation, and the coexistence states are characterized by the proportion of vesicle area. There are two qualitatively different coexistence states. In one, the vesicle regions and lamellar regions are rather clearly separated, and in the other the vesicle regions are entangled with lamellae in a complex way.

Formation of early-light-inducible-protein complexes and status of xanthophyll levels under high light and cold stress in barley ( Hordeum vulgare L.)

In our previous work we found considerable accumulation of early light-inducible proteins (ELIPs) in barley during adaptation to combined high light and cold stress, an accumulation which occurred preferen tially in the apical part of the leaves (M.-H. Montane et al., 1997, Planta 202: 293-302). Here we studied, under the same conditions, the effect of adaptation on the composition of thylakoid membrane proteins and pigments, particularly xanthophylls and chlorophyll, and their distribution within the barley leaf. It was observed that high light fluxes appeared to favour the trimerization of the light-harvesting complex of photo system II (LHC II) whereas cold appeared to favour the monomers of LHC II. High light, cold or the combina tion of both factors had only a small effect on the protein composition of the thylakoid membranes except for the proteins of LHC II which were found to decrease under high light to a greater extent at 25 °C than at 5 °C. The total xanthophyll-cycle carotenoid content increased linearly with cellular development, the highest amount being observed in the apical part of the leaf. Cold and high light acted synergistically to induce less than a doubling in the amount of total xanthophylls, while chlorophylls a and b remained nearly constant. The fraction consisting of antheraxanthin plus zeaxan thin was up to 4- to 5-fold higher at 5 °C than at 25 °C. As determined previously (Montane et al. 1997), the same conditions caused a 15-fold increase in the accu mulation of ELIPs. Consequently, neither the distribu tion of total xanthophylls nor that of antheraxanthin plus zeaxanthin along the leaf followed the same pattern as ELIP. Thus, the accumulation of xanthophylls cannot be stoichiometrically correlated with that of ELIPs. Using electrophoresis in the presence of decylmaltoside, we could demonstrate for the first time that ELIPs of 13.5 kDa are contained in high-molecular-mass com plexes of >100 kDa, which are located in the unstacked stroma lamellar region of the thylakoid membranes.

The Physicochemical Behavior of Phytosterol Ethoxylates

In this work the physicochemical behavior of a series of phytosterol ethoxylates in water is presented. The influence of the length of the polyoxyethylene chain is studied. The surfactant solutions have been examined by means of birefringent microscopy, surface tension, self-diffusion1H NMR, dynamic and static light scattering, and rheology. The surfactants with a hydrophilic chain of 10 oxyethylene units or more gave a micellar region. The CMC values were generally very low and a reverse relationship between the CMC value and the polyoxyethylene chain length was obtained. The time required to reach equilibrium surface tension was very long, more than 150 min. For the hydrophobic surfactants large lamellar regions appeared while for the more hydrophilic surfactants cubic and hexagonal structures were present which remained stable up to temperatures of 100°C. In the micellar region prolate aggregates were formed which showed “ghostlike” behavior, consisting of cross-linked micelles with very fast relaxation times.

Shear-Induced Formation of Multilamellar Vesicles (“Onions”) in Block Copolymers

The use of shear to control the microstructure in the lyotropic lamellar region of a ternary isothermal poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic P123)/water/butanol system was investigated by means of small angle neutron and light scattering (SANS, SALS), birefringence, and rheology. A transition from parallel to perpendicular alignment of lamellae, with a corresponding decrease in the viscosity, was found with increasing shear rate at high block copolymer concentrations. At low polymer content, however, the samples were shear thickening, and a shear-induced formation of multilamellar vesicles (“onions”) was observed for the first time in block copolymer systems.

Crystalline structure and morphology of microphases in compatible mixtures of poly(tetrahydrofuran-methyl methacrylate) diblock copolymer and polytetrahydrofuran

The crystalline structure and morphology of compatible mixtures of poly(tetrahydrofuran-methyl methacrylate) diblock copolymers (PTHF-b-PMMA) with a polytetrahydrofuran homopolymer (PTHF) were studied with synchrotron X-rays. Wide-angle diffraction was used to study the crystalline structures in a confined lamellar region with a PTHF thickness ranging from 12.2 to 19.5 nm, and in a PTHF matrix with an interface distance between the PMMA cylinders ranging from 17 to 22 nm. As the above thickness values are around the long period (ca. 17 nm) of PTHF homopolymer under the crystallization condition used, the crystalline structure has been found to be very sensitive to the average thickness of the PTHF phase. The changes in the diffraction patterns with changing PTHF homopolymer content suggested a chain folding model in confined PTHF lamellae with the PTHF fiber axes being perpendicular to the thick PTHF lamella. In the case of hexagonally packed cylindrical PMMA microdomains with an interface distance ranging from 12 to 16 nm, the effects of PMMA cylinders on the crystallization morphology of PTHF in the PTHF matrix, and the effects of the PTHF crystallization on the hexagonally packed structure of PMMA cylinders were also studied. It is shown that only when the interdistance of two neighboring PMMA cylinders is comparable with the long period of the pure PTHF homopolymer, ordered PTHF stacks can be formed in the PTHF matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 779–792, 1999

Phase Behavior and Microstructure of Water/Trisiloxane E6 and E10 Polyoxyethylene Surfactant/Silicone Oil Systems

The binary and ternary phase behavior of the trisiloxane E6 and E10 polyoxyethylene surfactants with water and three low molecular weight silicone oils has been determined. The silicone oils were the tetra- and pentacyclosiloxanes, D4 and D5, and the short linear tetrasiloxane oil, MD2M. Microstructures were investigated using small-angle X-ray scattering, polarized light microscopy, and cryogenic transmission electron microscopy. Our results illustrate the differences and similarities between the trisiloxane surfactants and conventional hydrocarbon surfactants. Both water/surfactant binary systems form the isotropic spongelike phase, L3, in a narrow temperature band above the lamellar phase region. The L3 phase is found at significantly higher temperatures for the E10 homolog. In the water/M(D‘E6)M system, no two-phase region was detected between the region labeled L3 and the isotropic surfactant-rich region, L2. The different birefringent appearance as one progresses between the L3, the L2, and the lame...

Kinetics of high temperature deformation of lamellar Ti48Al–2Nb–2Cr

Based on microstructural observations, the deformation resistance of lamellar Ti48Al–2Nb–2Cr in the temperature range between 1000 and 1200 K is expressed by treating the material as a composite of regions with lamellar and globular structure deforming independently of each other. For stresses below 1000 MPa the dislocation velocity is lower in the lamellar regions compared to the globular ones due to a larger athermal hardening component caused by interfaces (lamella boundaries in the lamellar structure and (sub)grain boundaries in the globular structure). Combining deformation kinetics and structural evolution allows the modelling of the maximum deformation resistance and the subsequent softening resulting from the increase in globular volume fraction. The model is applied to predict the creep life.

Shear induced structures in lamellar phases of amphiphilic block copolymers

The influence of shear on the mesoscopic structure in the lamellar region of ternary poly(ethylene oxide)–b-poly(propylene oxide)–b-poly(ethylene oxide) block copolymers PEO20–b-PPO70–b-PEO20 and PEO100–b-PPO70–b-PEO100 (Pluronic P123 and F127)/water/butanol systems was investigated by different techniques namely: small angle neutron and light scattering (SANS, SALS), as well as birefringence. A transition from parallel to perpendicular alignment of lamellae, with a corresponding decrease in the viscosity, was found with increasing shear rate at high block copolymer concentrations. However, a shear-induced formation of multilamellar vesicles (“onions’') was observed when the polymer concentration was reduced.

Mechanism of Host-Layer Restacking in HgxTiS2

High-resolution transmission electron microscopy has been used to observe the host-layer restacking processin situduring HgxTiS2(1.24≥x≥0.00) deintercalation to better understand the role of elastic strain in reaction dynamics and phase formation for this low-valent system (Hgδ+,δ⪡1). Hg forms novel incommensurate one-dimensional guest chains that occupy channels between the host layers. These channels undergo trigonal prismatic (TP)-to-distorted trigonal antiprismatic (DTAP) coordination restacking during deintercalation. Initially, a small metastable TP-coordinated, empty-gallery region forms. This region usually undergoes rapid restacking to octahedral coordination (1T-TiS2), which induces an intragallery TP-to-DTAP HgxTiS2phase transition to minimize elastic host-layer strain. Occasionally, TP empty-gallery regions become too large to allow coherent gallery restacking, resulting in host-layer fault/crack formation. TP and DTAP intercalate lamella can readily form coherent lamellar intergrowths, resulting in lamellar mixed-phase regions forming during deintercalation.

Formation kinetics and stability of surfactant vesicles

AbstractA three‐component phase diagram of a system containing water, dimethyl isosorbide and Laureth 4 (Brij® 30), a commercial surfactant, was determined, and the kinetics of vesicle formation from dilution with water of the hydrotrope solution was studied using a stop‐flow process in conjunction with light‐scattering determinations. The phase diagram consisted of a large microemulsion phase and a lamellar liquid crystalline region. Results from the stop‐flow/light‐scattering determinations were tentatively interpreted using the Aniansson‐Kahlweit‐Zana theory of micellar relaxation for a system close to equilibrium. The interpretation indicated the vesicles to be formed by monomolecular buildup for surfactant concentrations less than 5%, while for vesicles formed at greater concentrations an agglomeration of vesicle fractions appeared more reasonable.

Surfactant–Polymer Interactions: Phase Diagram and Fusion of Vesicle in the Didodecyldimethylammonium Bromide–Poly(ethylene oxide)–Water System

The phase behavior of the mixed didodecyldimethylammonium bromide (DDAB)–poly(ethylene oxide) (PEO)–water system is investigated by optical microscopy and NMR methods at 298 K. DDAB forms two different lamellar liquid crystalline phases in water, and, at high water contents, prior to the formation of the first lamellar phase, a vesicular region is also detected. The solubilization of the nonadsorbing, water soluble polymer PEO in the phases formed by DDAB is limited for the lamellar phase regions, and up to 20 wt% of polymer can be solubilized in the binary vesicular phase. A segregative type of phase separation is observed between surfactant and polymer. The triangular phase diagram is dominated by multiphase heterogeneous regions. Rich microstructural transformations are found to occur upon addition of PEO into the vesicle region. Microstructural transformations are followed by a combination of methods including direct imaging of microstructure by cryogenic transmission electron microscopy (cryo-TEM) and water self-diffusion measurements by the pulse gradient field NMR method. At a concentration of 2 wt% of DDAB cryo-TEM detects multiwall, polydisperse vesicles in equilibrium with single-wall vesicles. Upon addition of PEO to the solution of 2 wt% DDAB the vesicles show a tendency to fuse at and above 8 wt% of PEO. In correspondence, an increase in viscosity and a decrease in water self-diffusion coefficient are registered. With further addition of polymer more vesicles aggregate to form a cluster-like structure. This behavior can be described in the framework of the theory of colloid–polymer interactions such as an attractive osmotic force between vesicles due to polymer depletion near the vesicles.

γ α 2 B2 Lamellar Domains in Rolled TiAl

The structure of γ + α 2 + B2 lamellar domains have been examined in rolled TiAl containing B2-phase stabilised by Cr and Mo. Directly after rolling and rapid cooling the lamellar regions consist only of non-equilibrium γ and α 2. Annealing at 1000°C initiates both a α 2→B2 solid state decomposition and γ-lamellae coarsening. The resulting γ + α 2 + B2 lamellar domains consist of composite α 2 + B2 laths lying between γ-lamellae. The B2 grains precipitate with the orientation relationship (0002) α2//{110} B2 and <11–20> α2//<111> B2, having semi-coherent interfaces with both the parent α 2 and the adjacent γ-grains. A given α 2 lamella may decompose to one or more of the six possible orientations of B2 phase resulting from this transformation. © 1998 Acta Metallurgica Inc.

Comparison of the pitch induced from lamellar and nematic regions in some lyotropic liquid crystal systems

Lamellar phases (Lalpha) composed of decylammonium chloride(DACl), NH4Cl and H2O were doped with cholesteryl-2-ethoxyethoxyethyl carbonate (CEEC) and with (L-MA) or its racemic mixture (DL-MA). Lalpha phases of the novel intrinsic optically active L-serine hydrochloride decylester (L-SDE) and its racemic mixture (DL-SDE) were also prepared. From the chiral Lalpha phases, cholesteric phases (ChD) were induced with increased temperature and it was found that the pitch length shortened as the temperature was raised. This phenomenon is new for micellar cholesterics. The non-chiral Lalpha phases gave pseudo-isotropic and nematic regions with increased temperature. On the basis of these results and those in the literature, a new interpretation of the distorted micelle shape and the formation of the fingerprint texture is presented. The pitches induced from Lalpha regions were always larger than those obtained from nematic regions. From these results it is inferred that the interactions between the micelles in the cholesteric state at room temperature are of 'ideal' type. In addition, the temperature dependence of the pitch in micellar cholesterics is discussed.

Phase behaviour of the dioctadecyldimethylammonium bromide-water system

The phase behaviour of the twin-tailed surfactant dioctadecyldimethylammonium bromide with water was studied by DSC, FT-IR, X-ray and polarizing microscope. The phase diagram of DODAB-water system is very similar to that of DODAC-water. The dihydrate is in equilibrium with isotropic solution below 55°C. Above this temperature there is a lamellar liquid crystalline region, in equilibrium with isotropic liquid and solid crystals of DODAB·2H2O, up to 69°C. From 69 to 86°C, the lamellar mesophase is in equilibrium with ‘waxy’ anhydrous DODAB. From 86 to 116°C and very high DODAB content, there is a very narrow region of existence of inverse hexagonal mesophase, in equilibrium via a narrow biphase region with lamellar mesophase. AtT > 116°C an isotropic liquid appears. There seems to exist two different lamellar mesophases, one of them between 10 and 40 wt.% DODAB and the other between 60 and about 97 wt.% DODAB, with a biphase zone between them.

Disintegration of the Lecithin Lamellar Phase by Cationic Surfactants

The phase behavior of egg lecithin mixed with two cationic surfactants, hexadecyl- and dodecyltrimethylammonium chloride (C16TAC and C12TAC, respectively), in brine (100 mM NaCl) has been studied. Combining results from NMR spectroscopy, small-angle X-ray diffraction, and cryo-transmission electron microscopy, the phase sequence in less solvent rich regions of the phase diagram is linked to the aggregate structures appearing in dilute samples. The focus is set on the lamellar phases and their relationship to neighboring phases of positive curvature. NMR line shape studies on 2H-labeled surfactants are employed to reveal changes in bilayer structure. The results demonstrate large differences in the way that the two surfactants disintegrate the lamellar structure in the two closely related systems. Lecithin in mixture with the surfactant of the longer hydrocarbon tail (C16TAC) forms lamellar phase regions where the bilayers display curvature defects. A corresponding defect formation is not observed in the l...