Lamellar Regions Research Articles

Plane Stress Fracture Toughness of Partially Miscible, High-Density Polyethylene/Poly (Ethylene-CO-1-Octene) Blends

: Blends of high-density polyethylene (PE) with poly(ethylene-co-1-octene) (EOC) were found to be partially miscible in the melt-state. Rapid crystallization of the sheared melts led to the formation of a physically interpenetrating, solid-state morphology comprising PE lamellar crystals and EOC-rich regions. Samples were extruded through a coat-hanger die at 170°C to produce thin sheet specimens for fracture toughness testing under plane stress conditions. While crystallinity and crystal size of the PE, determined through differential scanning calorimetry, were not significantly affected by the presence of the copolymer, X-ray diffraction experiments showed that there was a preferred crystal orientation that was the result of crystallization of the oriented PE melt. Moreover, a bimodal crystal orientation was observed in the pure PE compounds. The level of bimodality was reduced with increasing concentration of copolymer in the blends. For the sheet extrusion material, plane-stress fracture toughness tests revealed that the presence of the branched copolymer in the blends did not affect the work of fracture when crack propagation took place in the transverse direction of the extruded sheet, in comparison with the pure PE. The branched copolymer increased the overall work of fracture for crack propagation in the machine direction due to an increase in the nonessential work of fracture, but had no significant effect upon the essential work of fracture.

Ultrastructural Aspects of Long-term Cat Placental Explant Culture

Changes in tissue architecture and ultrastructure in the cat placenta during long-term explant culture have been examined over an 11-day period. Pieces of cat placenta, dissected from the lamellar region, were cultured in CMRL-1066 medium and tissue was fixed for electron microscopy at 2, 5, 7, and 11 days' culture, as well as before culture was initiated (day 0). Four samples were examined at each time point. After two days, the trophoblast basal lamina and attached cytotrophoblast cells had begun to separate from the syncytium and the cytotrophoblasts were spreading over the surface of the exposed fetal stromal compartment, and by five days were showing signs of growth. At seven days' culture, cytotrophoblast multilayering was common, and vascular and stromal components were also well preserved with collagen biosynthesis evident. By 11 days, the centre of the culture was compacted and degenerate with loss of tissue architecture, but on the outside polyp-like growths could be seen, with a well-developed covering of trophoblast containing fat and secretory droplets, lining a connective tissue matrix and stromal components. The cat placenta, therefore, like the human, has the capacity for regrowth in explant culture, including both trophoblast and stromal components.

Deformation of the lamellar structure in semi-crystalline polymers studied by computer simulations

Abstract Yield in a semi-crystalline polymer involves the disruption of the crystalline phase in an irreversible deformation process. In a semi-crystalline polymer, the crystalline lamellar regions are bridged together by inter-lamellar amorphous layers, which act as a loading transfer medium. The deformation of both phases is, therefore, to some extent inter-related. In this work we adopted a continuous mechanic approach (neglecting atomic/molecular interactions) of the lamellar deformation of semi-crystalline polymers in the sense that we simulated the mechanical response of a lamellar structure (two lamellae interconnected by amorphous regions) in a finite element analysis. The use of computer simulations allows studying independently the effect of each relevant morphological parameter on the mechanical response. Several simulations were performed considering isolated variations of the following morphological parameters: i) mechanical behaviour of the amorphous material; ii) thickness of the crystalline regions; iii) length of the amorphous regions; iv) number of amorphous regions connected with a crystalline lamella; v) relative angle between the crystalline and the amorphous regions; vi) mode of loading (tension and compression). The thickness of the crystalline lamellae is evidenced as the most significant factor affecting the tensile response of the lamellar structure, followed by the mechanical behaviour of the amorphous phase. The connection angle between amorphous and crystalline regions and the number of amorphous regions bridging adjacent crystalline lamellae play only a minor role. The length of the amorphous regions has a negligible influence. As expected, the lamellar structure shows also distinct behaviours under distinct loading modes, tensile loading showing the highest stresses.

Spatio-temporal growth of broken spiral and concentric ringed spherulites in blends of poly(vinylidene fluoride) and ethylene-vinylacetate copolymers

Melting and crystallization behavior in mixtures of poly(vinylidene fluoride) (PVDF) and several ethylene-vinyl acetate copolymers (EVAc) with various ethylene contents have been investigated by means of differential scanning calorimetry, atomic force microscope, and optical microscopy. PVDF/EVAc-80 exhibits the melting point depression of PVDF crystals, suggestive of a miscible character of the pair. Crystallization behavior and morphology development in blends of PVDF/EVAc-80 have been investigated with an emphasis on the spherulitic growth demonstrating the spiral and concentric ringed (or target) patterns. Of particular interest is the break-up of the spiral or concentric ringed patterns at very shallow supercoolings, which may be attributed to instabilities driven by the exclusion of amorphous PVDF and EVAc chains into the emerging inter- and intra-spiral (or target) lamellar regions.

Phase diagram of α‐sulfonate methyl esters derived from palm stearin/alcohol/water systems

AbstractPhase diagrams of α‐sulfonate methyl ester derived from palm stearin (α‐SMEPS)/alcohol/water systems were mapped at 30±0.1°C. Two main regions—an isotropic and a lamellar liquid crystalline—were the focal points in this system. An increase in alcohol chain length decreased the isotropic region and increased the lamellar liquid crystal region. In the isotropic region, self‐assembly of α‐SMEPS at different alcohol chain lengths was determined by using conductivity and viscosity measurements. The phase boundaries of micelle to bicontinuous structure and bicontinuous structure to inverse micelle transitions in the isotropic regions are proposed from these analytical methods. The increase in alcohol chain length shifted the micelle ⇆ bicontinuous structure to the water‐rich corner, and the bicontinuous structure ⇆ inverse micelle transition moved toward the alcohol‐rich corner.

Mechanistic analysis of acute, Ni-induced respiratory toxicity in the rainbow trout ( Oncorhynchus mykiss): an exclusively branchial phenomenon

In moderately hard Lake Ontario water (∼140 mg L −1 as CaCO 3) waterborne Ni (9.7–10.7 mg Ni L −1) is acutely toxic to adult rainbow trout ( Oncorhynchus mykiss) exclusively via branchial mechanisms. Ventilation in resting trout (evaluated using a ventilatory masking technique) was adversely affected, as ventilation rate ( V R), ventilation volume ( V G), opercular stroke volume ( V SV) and resting oxygen consumption ( M ̇ O 2 ) were all increased, and oxygen extraction efficiency ( U%) decreased over 48 h of Ni exposure. Extensive gill Ni accumulation (41-fold over control levels) during 82 h of waterborne Ni exposure resulted in marked ultrastructural damage to the respiratory epithelium of the gill, including swelling of the secondary lamellae evidenced by changes to both the lamellar region (increased secondary lamellar tissue volume ( V SL/ V LR)), and to the secondary lamellae themselves (increased volume of tissue lying outside the pillar system ( V OPS/ V SL)). Additionally, decreased lamellar height and increased lamellar width indicated a reduction in lamellar surface area available for gas diffusion. The relative diffusing capacity of experimental fish was only 59% of that of control fish. Infusion of Ni into the blood, achieving a similar time course and magnitude of plasma [Ni] elevation to that during waterborne exposure, failed to elicit any signs of respiratory toxicity typically diagnostic of acute, high level waterborne Ni exposure. Infusion of Ni into the blood for 96 h resulted in only minor accumulation of Ni in the gill, suggesting that acute Ni-induced respiratory toxicity is related to accumulation of high levels of Ni in the gill from the water. Additionally, infusion of Ni into the bloodstream led to significant extrabranchial Ni accumulation only in the kidney. White muscle, heart, liver, stomach, and intestine did not significantly accumulate Ni following infusion into the bloodstream and trapped plasma analysis revealed that, with the exception of the kidney, a substantial portion of Ni accumulated in tissues following infusion could be accounted for by extracellular (blood-bound) Ni.

Mitochondrial structure in steroid-producing cells: three-dimensional reconstruction of human Leydig cell mitochondria by electron microscopic tomography.

Mitochondria of human Leydig cells were reconstructed in three dimension utilizing the technique of electron microscopic tomography to obtain a better understanding of the topology of the internal membrane system and the relationship of these cristae to the inner boundary membrane (IBM). Cristae structure, in many respects, is consistent with previous tomographic studies from typical mitochondria, i.e., mitochondria from nonsteroid-producing cells. Cristae are diverse in form, with well-defined lamellar cristae interconnected to pleomorphic and tubular regions. Occasional fenestrations are present in the lamellar regions. Also consistent with other mitochondria studied by tomography, the openings of the cristae to the IBM (referred to as crista junctions) are roughly circular or elliptical and approximately 20-25 nm in diameter. Morphological contact sites between the outer mitochondrial membrane and IBM are also present. Cristae membranes in these steroid-producing mitochondria are often found in close proximity to the IBM. Unique to steroid-producing mitochondria is a form of the cristae in which multiple lamellae are in very close apposition, previously defined as the lamellar association. Tomographic reconstructions of the lamellar association reveal that these well-organized membranes also open to the IBM via crista junctions. These regions of closely apposed lamellar cristae are also interconnected and display small tubular extensions from the lamellae. The current study is the first electron microscopic tomography study of mitochondria from steroid-producing cells. The results show the cristae interconnect to form an extensive internal membrane system, which is perhaps better termed the cristae compartment. This internal membrane system is notable due to the high surface area with few small openings to the IBM. Such a morphology is more analogous to the thylakoid membrane system of chloroplasts than the long-standing view of mitochondrial cristae. The significance of the lamellar association form of the cristae is unknown.

Epidermal cell proliferation in the equine hoof wall

Current theories explaining how the hoof wall 'grows' and moves past the stationary distal phalanx are speculative and based on incomplete evidence. Movement in the lamellar region could occur by cell proliferation or an enzyme-based remodelling process. Since laminitis pathogenesis appears to involve increased transcription and activation of enzymes normally involved in tissue remodelling, it is important to know precisely which process dominates the lamellar region of the hoof.. To investigate epidermal cell proliferation in the equine hoof wall and calculate a proliferative index (PI) for the coronet, lamellae and toe. An analogue of thymidine, 5-bromo-2'-deoxyuridine (BRdU), was infused i.v. into 5 ponies. After tissue harvesting, BRdU (and therefore basal cell proliferation) was detected immunohistochemically using mouse anti-BRdU. PIs were calculated for the coronet and 10 levels of the dorsal hoof wall lamellae. The highest PIs (mean +/- s.e.) were in the coronet; 12.04% +/- 1.59 and proximal lamellae (7.13% +/- 1.92) and are therefore growth zones of the proximal hoof wall. PIs of more distal lamellae were 0.11% +/- 0.04 to 0.97% +/- 0.29; significantly lower (P = 0.05) than the lamellar growth zone. A 20-fold PI decrease between proximal and more distal lamellae suggests that the majority of the normal lamellae are nonproliferative and their main function is to suspend the distal phalanx within the hoof capsule. Remodelling within the hoof wall epidermal lamellae, which must occur as the hoof wall moves past the stationary distal phalanx, is a process not requiring epidermal cell proliferation. A hoof lamellar epidermis that remodels using the same MMPs involved in laminitis pathogenesis implies that laminitis is a normal process out of control. Understanding MMP control and how the normal lamellar epidermis achieves this will help in the development of better laminitis preventative and treatment strategies.

Effect of Long-Term Aging and Creep Exposure on the Microstructure of TiAl-Based Alloy for Industrial Applications

ABSTRACTThe effect of long-term aging and creep exposure on the microstructure of a cast TiAl-based alloy with nominal chemical composition Ti-46Al-2W-0.5Si (at.%) was studied. The aging experiments were performed at temperatures between 973 and 1073 K for various times ranging from 10 to 14000 h in air. Constant load tensile creep tests were performed at applied stresses ranging from 150 to 400 MPa and at temperatures between 973 and 1123 K up to 25677 h. During aging and creep testing the α2(Ti3Al)-phase in the lamellar and feathery regions transforms to the γ(TiAl)-phase and fine needle-like B2 precipitates. Microstructural instabilities lead to a softening of the alloy. The effect of this softening on long-term creep resistance is negligible at temperatures of 973 and 1023 K.

Effect of Inorganic Salts on the Phase Behavior of an Aqueous Mixture of Heptaethylene Glycol Dodecyl Ether

The effect of LiCl, NaCl, and CsCl on the phase behavior of an aqueous mixture of heptaethylene glycol dodecyl ether (C12E7) was investigated by means of differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and Fourier transform infrared (FT-IR) spectroscopy. Phase diagrams for the mixtures containing the inorganic salts with a concentration of 1.0 M were constructed on the basis of the DSC experiments. The addition of the salts induced an expansion of the lamellar (Lα) phase region toward higher temperatures and a shrinkage of the normal hexagonal (H1) and the bicontinuous cubic (V1) phase regions toward lower temperatures. The effectiveness of the salt species followed the sequence of CsCl < NaCl < LiCl for the expansion of the Lα phase region and of LiCl < CsCl ≤ NaCl for the shrinkage of the H1 and V1 phase regions. The influence of different salts on the phase behavior of the mixture is qualitatively interpreted in terms of the hydration of ions. The SAXS and FT-IR results revealed the salt effect on the molecular assemblies in the Lα phase and H1 phase and on the conformational changes of the surfactant molecules in the two mesophases, respectively.

Liquid crystals and microemulsions formed by mixtures of a non-ionic surfactant with palm oil and its derivatives

The phase behaviour of palm olein (PO) and its derivative oils (palm oil methyl esters and medium chain triglycerides) with Imbentin coco 6.9EO, an ethoxylated C 12–14 alcohol, in water has been investigated to identify compositions where microemulsions occur. The techniques used were the optical microscope phase penetration scan and small angle X-ray diffraction (SAXS). Mixed surfactant/oil samples were prepared at wt. ratios of 0.1:1, 0.25:1, 0.5:1 and 1:1 for the phase penetration scan. For SAXS analysis, the initial concentration of surfactant in water ( W) was fixed at 38% (w/w), which forms a hexagonal mesophase ( H 1). Palm oil methyl esters (POME) and medium chain triglycerides (MCT) were added to this at 0.04:1 (or 0.05:1 for MCT), 0.1:1, 0.2:1 (or 0.25:1 for MCT), 0.5:1 and 1:1 ratios of oil to surfactant. Schematic phase diagrams were constructed to document the changes of phase structures using both bulk samples and phase penetration scans techniques. The extent of microemulsion formation (or solubilisation) decreases in the sequence POME>MCT>PO, and increases substantially with temperature, particularly for POME and MCT. All of the oils destabilise the hexagonal phase; for POME and MCT there is an increase in the surfactant cloud point temperature by ca. 10 °C or more, but the temperature for the onset of the lamellar ( L α ) phase dispersion region ( W+ L α ) is hardly affected. There was a pronounced tendency for the lamellar phase formed in the presence of high oil concentrations and low water levels to have a reduced melting point. With the highest MCT levels a bicontinuous cubic phase (probably V 2) is present at 25 °C, although this phase is not present in the binary surfactant/water system. The X-ray diffraction results show that the average area per head group ( a o) at the micelle surface is decreased by the addition of the oils, consistent with the observation of a V 2 phase. Possible molecular mechanisms for this observation are discussed.

Structure and Conformation of Bipolar Tetraether Lipid Membranes Derived from Thermoacidophilic Archaeon Sulfolobus acidocaldarius as Revealed by Small-Angle X-ray Scattering and High-Pressure FT-IR Spectroscopy

The phase behavior, conformation, and structure of bipolar tetraether liposomes composed of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius have been studied by small-angle X-ray scattering (SAXS) and high-pressure Fourier transform infrared spectroscopy (FT-IR) at pD 2.15. The SAXS data on PLFE multilamellar vesicles in 85 wt % D 2 O showed two orders of lamellar Bragg reflections over the temperature range 5-75 °C. The lamellar repeat distances d indicate three lamellar regions: 5-50 °C (d, ∼49-50 A), 50-60 °C (∼50-54 A), and 60-74 °C (∼54-56 A). The 4-A increase in d-spacing from 50 to 60 °C is probably due to an increase in hydration at the PLFE polar headgroups and/or a stretch of the polar headgroups toward the bulk aqueous phase. At 74-75 °C, a lamellar-to-cubic phase transition occurs. The reciprocal spacings of the cubic phases correspond to the coexistence of the inverse bicontinuous cubic phases Q I I D and Q I I P with lattice constants of 105 and 82 A, respectively. At atmospheric pressure, the vibrational frequency of the CH 2 symmetric stretching mode showed transitions at ∼46-48, 61, and 74 °C, in agreement with the SAXS data. The overall 2 cm - 1 increase in wavenumber between 61 and 74 °C indicates a transition from a rigid, gellike lipid conformation to a chain conformation with considerable disorder, as expected from cubic phases which appear above ∼74 °C. The pressure dependence (up to 15 kbar) of the symmetric CH 2 stretching vibrational wavenumber at various temperatures has also been examined. A variety of new gellike phases are observed at elevated pressures, showing again a rich polymorphism in PLFE liposomes. The most prominent pressure-induced transition involves a ∼2 cm - 1 increase in wavenumber, which appears at 8.0 kbar at 60 °C, 8.4 kbar at 43 °C, and 10.8 kbar at 20 °C, giving an unusual negative dT/dp value. The possible source of this anomaly has been discussed in terms of the temperature attenuation of the hydrogen bond network in the polar headgroup region.

Effect of lacunocanalicular architecture on hydraulic conductance in bone tissue: implications for bone health and evolution.

Bone tissue health depends largely on efficient fluid and solute transport between the blood supply and cells that are the living component of the tissue. We hypothesized that the lacunocanalicular hydraulic network, which is defined by the pericellular fluid space that is common to all bone tissue, is optimized to transport fluid and solutes between the blood supply and bone cells. An analytical study was carried out to evaluate the effect of osteonal architecture, including the osteon diameter, number of annular lamellar regions, and number and length of canalicular channels, on fluid transport between the blood supply and bone cells. On the basis of this analysis, we conclude that osteon size is limited to the distance over which fluid and solutes can be transported efficiently between the blood supply and cells. This analytic model suggests that hydraulic conductivity is highest in lamellar regions closest to the Haversian canal (HC) and decreases with increasing distance from the blood supply, reaching a plateau after the fifth lamella (169 micro m radius). Furthermore, an increase in the diameter of the HC, or a decrease in the length of canaliculi, reduces the hydraulic conductivity within the lacunocanalicular network. Applying the principle of minimal expenditure of energy to this analysis, the path distance comprising five or six lamellar regions represents an effective limit for fluid and solute transport between the blood supply and cells; beyond this threshold, hydraulic resistance in the network increases and additional energy expenditure is necessary for further transportation. This suggests that transport is optimized to meet metabolic demands concomitant with a minimal expenditure of energy. This fundamental new insight into bone structure and physiology may provide a new basis of understanding for tissue engineering, bone physiology in health and disease, and evolutionary biology.

Phase behavior and structural properties for the triton X‐100/n‐CnH2n+1COOH/H2O system

AbstractIn the Triton X‐100/n‐CnH2n+1COOH/H2O system, n‐CnH2n+1COOH can be used as a cosurfactant. As its chain length increases, the regions of the microemulsions showing oil‐in‐water (O/W), water‐in‐oil (W/O), and bicontinuous structures decrease and at the same time, the region of the lamellar liquid crystal increases. In the O/W region, the distribution coefficient K of n‐CnH2n+1COOH between Triton X‐100 micellar phase and water phase increases with the chain length of saturated unbranched monocarboxylic acid. The relationship between the standard solubilization Gibbs free energy of saturated unbranched monocarboxylic acid and the number of methylene groups in the saturated unbranched monocarboxylic acid is given by the equation: ΔGm0=−2.364−2.818 n(CH2) kJ·mol−1 in the Triton X‐100 micellar system. In the lamellar liquid crystal region, small‐angle X‐ray diffraction shows that the thickness of the bilayer d0 is independent of the weight ratio of n‐CnH2n+1COOH to Triton X‐100, but the volume of the solvent penetrating from the solvent layer to the amphiphilic bilayer increases with the weight ratio of n‐CnH2n+1COOH to Triton X‐100. Furthermore, the d0 value increases with the chain length of saturated unbranched monocarboxylic acid, which will contribute to the formation and stabilization of the lamellar liquid crystal.

STRUCTURE AND PHASE BEHAVIOUR OF SYNTHETIC GLYCOLIPIDS

We have used X-ray diffraction and differential scanning calorimetry (DSC) to study the structure and lyotropic phase behaviour of two synthetic dialkyl glycolipids having β-D-glucose and β-D-galactose headgroups and two saturated tetradecyl (C14) chains. The diastereomeric compounds, 1,2-di-O-tetradecyl-3-O-(β-D-glucopyranosyl)-sn-glycerol (di-14:0–β-D-GlcDAG) and 1,2-di-O-tetradecyl-3-O-(β-D-galactopyranosyl)-sn-glycerol (di-14:0-β-D-GalDAG) show striking differences in their phase behaviour, particularly in the ordered lamellar phase region. Both compounds adopt the fluid lamellar Lα phase upon cooling from the HII phase, but below the chain-melting transition,di-14:0-β-D-GlcDAG forms a metastable Lβ gel phase, whereas di-14:0–β-D-GalDAG forms only crystalline lamellar phases, on the timescale of our measurements. We have determined the limiting hydrations of the various phases, and compare the findings from these glycolipids with those from our previous studies of the phospholipid didodecyl phosphatidylethanolamine (di-12:0-PE).

Electron Tomography of Frozen-Hydrated Isolated Triad Junctions

Cryoelectron microscopy and tomography have been applied for the first time to isolated, frozen-hydrated skeletal muscle triad junctions (triads) and terminal cisternae (TC) vesicles derived from sarcoplasmic reticulum. Isolated triads were selected on the basis of their appearance as two spherical TC vesicles attached to opposite sides of a flattened vesicle derived from a transverse tubule (TT). Foot structures (ryanodine receptors) were resolved within the gap between the TC vesicles and TT vesicles, and some residual ordering of the receptors into arrays was apparent. Organized dense layers, apparently containing the calcium-binding protein calsequestrin, were found in the lumen of TC vesicles underlying the foot structures. The lamellar regions did not directly contact the sarcoplasmic reticulum membrane, thereby creating an ≈5-nm-thick zone that potentially constitutes a subcompartment for achieving locally elevated [Ca 2+ ] in the immediate vicinity of the Ca 2+-conducting ryanodine receptors. The lumen of the TT vesicles contained globular mass densities of unknown origin, some of which form cross-bridges that may be responsible for the flattened appearance of the transverse tubules when viewed in cross-section. The spatial relationships among the TT membrane, ryanodine receptors, and calsequestrin-containing assemblage are revealed under conditions that do not use dehydration, heavy-metal staining, or chemical fixation, thus exemplifying the potential of cryoelectron microscopy and tomography to reveal structural detail of complex subcellular structures.

Self-Assembly of Mixed Ionic and Zwitterionic Amphiphiles: Associative and Dissociative Interactions between Lamellar Phases

The phase behavior and phase structure of the mixed lecithin/DDAB system in water are studied by SAXS, H-2 NMR, cryo-TEM, and optical polarization microscopy methods. Macroscopically, the triangular phase diagram is dominated by one lamellar liquid crystalline region. SAXS data in combination with 2H NMR detect the presence of two different lamellar phases. The collapsed lamellar phase originated from the water-poor part of the DDAB/water system interacts in associative nature with the binary lamellar phase of the lecithin while the swollen lamellar phase, in the water-rich part of the DDAB/water system, interacts in dissociative nature with the lecithin lamellar phase. The swollen lamellar phase can solubilize less than 12 wt % lipid prior to the phase separation, whereas the collapsed lamellar phase swells considerably with water. The two lamellar phases coexist in equilibrium. Both the collapsed and swollen lamellar phases exhibit an ideal swelling behavior with water. The thickness values of the bilayer are very similar in both lamellar regions and the values decrease on the addition of DDAB. The values of the average area per polar headgroup are slightly higher for the mixed systems than for the binary amphiphile/water systems. There is also a bicontinuous type Ialpha3d (Q(230)) cubic liquid crystalline phase that occupies a small area in the water-poor part of the phase diagram.

Synthesis of Nanosized Silver Platelets in Octylamine-Water Bilayer Systems

The synthesis of nanosized powders with targeted properties and their assembly is of considerable importance to the microelectronics industry because of the pervasive drive to miniaturize components. In the current work, synthesis of nanosized silver (Ag) metal platelets was studied. The platelets were synthesized in the lamellar bilayer phase region (neat phase D) of the octylamine−water binary system. Amylamine was used as cosurfactant to increase the phase stability of the lamellar region. The influences of the synthesis conditions and the concentrations of the system components on morphology and size of the platelets were examined. Low-angle X-ray diffraction studies revealed that the water/surfactant molar ratio (R) has a strong influence on the thickness of bilayers (d1 + d2) and consequently particles grown in them. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) studies have shown the effect of R on platelet thickness (t) and face size (a). Thickness and face area of platelets is controlled by regulating the bilayer dimensions by changing R. Platelets with face sizes ranging from 12 to 83 nm and thicknesses from 0.3 to 5 nm have been synthesized at room temperature.

In Situ Polymerization of N,N-Dimethylacrylamide in Aerosol OT−Water: Modified Lamellar Structure and Multiphase Separation

N,N-Dimethylacrylamide is polymerized in the lyotropic surfactant system containing Aerosol-OT (AOT) and water. The polymerization is thermally initiated with AIBN, which allows a homogeneous initiation in this very viscous mixture. The starting mixture contains a lamellar liquid crystalline phase and an isotropic phase in equilibrium. After the polymerization, new phases develop which appear to have a lamellar structure, even if originated from the initial isotropic phase. More phases appear after the polymerization, and they are lamellar, since the phase behavior shifts toward the lamellar region when the monomer is consumed. Once the polymer is formed in situ, it segregates from the lamellae and forms an isotropic microphase which does not macroscopically separate. The appearance of this polymer-rich phase modifies the structure of the lamellar mesophase by partially deswelling it. This gives a shorter lamellar spacing. The law that expresses how the AOT-H2O spacing is contracted by the polymer is deduced from the equilibrium between the two (lamellar and isotropic) microphases. All the macroscopic final phases contain polymer, although in different proportions. The molecular weight of the polymer is the same in all phases. The presence of AOT in the medium has no influence on the resulting tacticity, which is the same as that for a polymer obtained in pure water. (Less)

Influence of Shear on Solvated Amphiphilic Block Copolymers with Lamellar Morphology

The effect of shear on lyotropic lamellar phases consisting of amphiphilic block copolymers was studied by in situ small-angle neutron scattering (SANS) and rheo-optics. Two different ternary systems containing a commercially available Pluronic type poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block copolymer, P123 (EO20PO70EO20) or F127 (EO100PO70EO100), as well as water and butanol were investigated over a wide range of concentrations. Orientation diagrams were constructed for both ternary systems; both exhibited a parallel-to-perpendicular transition of planar lamellae and a shear-induced formation of multilamellar vesicles (also termed liposomes, onions, or spherulites). For both systems, the vesicle formation occurred at low polymer content close to the phase boundary of the lamellar region and was accompanied by shear thickening. In addition, the kinetics and temperature dependence of the parallel-to-perpendicular transition were studied.