Lamellar Interface Research Articles

The role of the cosurfactant in the CTAB/water/n-pentanol/n-hexane system: Pentanol effect on the phase equilibria and mesophase structure

We report on the effect of 1-pentanol loading on the phase behaviour of mixtures of CTAB/water/n-hexane at fixed mole ratios 1∶80∶47. The cosurfactant induces changes in the interfacial film curvature. By increasing the pentanol/CTAB mole ratio, the system evolves from oil-in-water to water-in-oil structures. For very large 1-pentanol loading some water is expelled from the reverse micelles resulting in a L2plus water equilibrium (emulsification failure). In the range of compositions investigated most of the phase equilibria reveals the coexistence of liquid crystals and hexane/pentanol solutions. In these cases, we estimate the interface composition by assuming a constant 1-pentanol concentration in all the oil domains, and by tacking into account the alcohol solubility in water. In the case of single-phase sample the interfacial composition was determined by means of turbidimetric titration. The adsorption of cosurfactant at the interface of direct micelles, planar lamellae, bicontinuous microemulsions, and spherical reverse micelles follows the same adsorption isotherm (independently from the curvature of the interface). Moreover, the results obtained unambiguously show that the interface composition dictates the spontaneous curvature of interfacial film. Actually positive, null, and negative curvatures correspond to different compositions of the interfacial film. Once the influence of cosurfactant on the spontaneous curvature of the interface is understood, the appearance of the emulsification failure upon pentanol loading can be rationalised within the framework of the flexible surface model.

Tissue-specific dysregulation of cortisol metabolism in equine laminitis.

The role of glucocorticoids (GCs) in the pathogenesis of laminitis is incompletely understood. Local tissue activity of GC is regulated by the steroid converting enzyme, 11beta-hydroxysteroid dehydrogenase-1 (11beta-HSD-1). Changes in integumentary (skin and hoof lamellar) 11beta-HSD activity occurring during laminitis could affect the extent to which GCs are involved in its development. That changes in integumentary 11beta-HSD-1 activity associated with the laminitic condition would lead to elevated local tissue levels of GCs, which could subsequently contribute, through paracrine and autocrine mechanisms, to the further development of laminitis; and that similar changes in 11beta-HSD-1 activity would be evident in both skin and hoof lamellar tissue. Activity of 11beta-HSD-1 was determined in skin and hoof lamellar tissue specimens obtained from normal and laminitic horses using a radiometric assay. Skin samples were obtained from 10 normal horses and from 10 horses before and after induction of acute laminitis following administration of starch via nasogastric tube. Hoof lamellar samples were obtained from 10 normal horses, 10 horses following induction of acute laminitis and 4 chronically-foundered horses. Bidirectional 11beta-HSD-1 activity was measured in both skin and lamellar tissues. 11-ketoreductase activity exceeded 11beta-dehydrogenase activity in both skin and lamellar tissues. Cutaneous activity was higher than lamellar 11beta-HSD-1 activity in all groups. Both ketoreductase and dehydrogenase activity increased in skin and lamellae following experimental induction of acute laminitis, but the increase in ketoreductase activity was substantially greater than that for dehydrogenase in the lamellae. Induction of acute laminitis was attended by increases of 227 and 220% in cutaneous dehydrogenase and ketoreductase activity, respectively, and 173 and 398% in lamellar dehydrogenase and ketoreductase activity, respectively (P<0.05). The 11-ketoreductase moiety of 11beta-HSD-1 plays a role in equine skin and hoof lamellae regarding the regulation of local glucocorticoid activity. Increased 11-ketoreductase activity will lead to increased local tissue GC activity by virtue of conversion of cortisone to cortisol. The laminitic condition is attended by integumentary biochemical changes that enhance the local concentration of cortisol, especially in the hoof lamellar interface. Through multiple and diverse actions, increased local GC activity contributes to the pathogenesis and morbidity associated with laminitis. Pharmacological manipulation of 11beta-HSD-1 deserves further investigation regarding the prevention and treatment of laminitis.

An analysis of growth direction of β phase precipitates in a TiAlW alloy

β phase precipitates at the lamellar interface after aging heat treatment in a TiAlW alloy. The orientation relationship (OR) between the β and γ phase is 〈 1 ̄ 0 1〉 γ//〈1 1 1〉 β, (1 1 1) γ//( 1 ̄ 1 0) β. Six different β phase variants can be observed along the [1 1 1] γ zone axis. The OR between β and γ phase and the growth directions of β precipitates are predicted from the invariant line strain model.

Gene transfer into rabbit keratocytes using AAV and lipid-mediated plasmid DNA vectors with a lamellar flap for stromal access

Development of gene transfer methods that can precisely deliver therapeutic genes to the localized or targeted tissue(s) would be highly beneficial in developing new gene therapy approaches and may also extend animal models for studying in vivo gene function and regulation at molecular levels in the selected tissues. We investigated lipid- and AAV-mediated gene transfer in rabbit cornea using a lamellar flap-technique. The goals of this study were to (1) analyze methods for in situ gene transfer into keratocytes, (2) identify efficient and suitable vectors for gene transfer into keratocytes, and (3) characterize times of first detectable expression, localization and duration of transgene expression in keratocytes with different vectors. A lamellar flap was produced in the rabbit cornea with a microkeratome. Recombinant adeno-associated viral vector (rAAV) expressing either β-galactosidase (rAAV-β-gal) or chloramphenicol acetyltransferase (rAAV–CAT) reporter genes, or plasmid-cationic lipid complexes expressing CAT (pMP6-CAT) or β-galactosidase (pTR-β-gal) were applied beneath the lamellar flap for two minutes. The flap was repositioned and eyelids sutured overnight. Corneas were removed at 4 hr, 12 hr, 36 hr, 3 days, 7 days, or 10 days after application and either fixed in 2% formaldehyde, cryosectioned and stained for β-galactosidase activity or homogenized and measured for CAT levels by ELISA. Corneas infected with rAAV-β-gal vector showed positive β-gal staining in the center and periphery of the flap interface in whole corneas and corneal beds at 3, 7, and 10 days, but not at earlier time points. Corneas treated with pTR-β-gal plasmid vector showed positive β-gal expression at the interface at 4, 12 and 36 hr, but not at 3 or 7 days. The posterior surface of the lamellar interface where the vector was applied showed more expression than the overlying anterior surface with both plasmid and viral vectors. The level of gene expression was less with plasmid vector than viral vector monitored using β-gal staining. CAT-ELISA confirmed expression of the CAT reporter gene with either the plasmid or rAAV vector. These results demonstrate that foreign genes can be introduced into keratocytes with plasmid or viral vectors using a lamellar flap to gain access to the stroma. The expression profile of the reporter genes depended on the vector. Transfection of keratocytes with plasmid vectors produced rapid expression of the reporter genes, but for a short duration. Reporter gene expression following transduction by rAAV vector was delayed several days, but was at higher levels and for a longer duration. This is the first report to demonstrate selective gene transfer into keratocytes and would be highly useful in studying function and regulation of genes in vivo and may eventually furnish a tool for the treatment of corneal dystrophies.

Confocal Microscopy in Late-Onset Diffuse Lamellar Keratitis After Laser In Situ Keratomileusis

This article reports a case of diffuse lamellar keratitis, without exposure of the flap interface, that developed in a patient who underwent intraepithelial photorefractive keratectomy 1 year after bilateral LASIK. Confocal microscopy was performed in both eyes at the onset of the diffuse lamellar keratitis and after its resolution. In the eye with diffuse lamellar keratitis, abundant round structures (inflammatory cells) were present at the interface; these structures disappeared after the keratitis resolved and were not present in the contralateral eye at any time. These confocal microscopic findings further support the hypothesis that diffuse lamellar keratitis is a nonspecific inflammatory response in corneas with a lamellar interface.

Modeling of eutectic structure formation by a modified cellular automaton model

In this paper, a modified cellular automaton (MCA) model was extended to the multi-phase solidification system for the eutectic structure simulation. The present model incorporates the effects of constitutional undercooling and curvature undercooling on the interface local undercooling and takes into account the solute redistribution during eutectic solidification. Different growth algorithms were employed for the growth of non-faceted and faceted crystals. This model was applied to simulate the eutectic structure formation in a transparent organic eutectic alloy, and eutectic and hypoeutectic Al-Si alloys. The effects of interface undercooling and growth velocity on the eutectic morphology, such as the lamellar spacing and interface shape, were investigated. It can be concluded that the present MCA model can successfully predict the eutectic growth morphology in both regular non-faceted / non-faceted and irregular non-faceted / faceted eutectic alloy systems.

Deformation mechanisms in TiAl intermetallics—experiments and modeling

The mechanical properties of intermetallic γ-TiAl based materials depend strongly on the microstructure, which in turn is influenced by the alloy chemistry and the applied heat treatment. First, a computational study of the room temperature deformation behavior of γ-TiAl based two-phase alloys exhibiting a globular near-γ microstructure is presented. The micromechanical model is based on the unit-cell technique using the finite element method. In the applied crystal plasticity concept crystallographic slip and deformation twinning are taken into account as the dominant deformation mechanisms. The conclusions drawn from the simulations are discussed and compared to experimental results obtained from acoustic emission measurements and transmission electron microscopy investigations. Furthermore, the creep behavior of a designed fully lamellar (DFL) γ-TiAl microstructure is investigated. Differently spaced DFL microstructures were adjusted in order to investigate their influence on creep. The interface spacing was varied in the range of 1.2–0.14 μm by altering the cooling rates from 1 to 200 K/min, and short term creep tests were carried out in air under various temperature/load conditions. A first approach in modeling the steady state creep deformation of the fully lamellar material in question is presented. A power law description for diffusion controlled dislocation creep is proposed, and a structure factor is introduced which depends on the lamellar orientation with respect to the loading axis as well as on the mean lamellar interface spacing.

Modeling of microstructure evolution in regular eutectic growth

The growth morphology of regular eutectics has been studied using a model eutectic alloy and a transparent ${\mathrm{CBr}}_{4}\ensuremath{-}{\mathrm{C}}_{2}{\mathrm{Cl}}_{6}$ eutectic alloy. A modified cellular automaton (MCA) model is developed to model the evolution of regular eutectic microstructures. Different from the classical cellular automata in which only the temperature field is involved, the present model also includes the solute redistribution and the curvature effect during eutectic solidification. The finite-volume method, which is coupled with the cellular automaton model, is used to calculate the solute field in the calculation domain. The growth velocities of both eutectic phases are evaluated according to the local undercooling, consisting of thermal, solutal, and curvature undercoolings. The cooperative and competitive growth mechanisms of two eutectic phases are embedded in the present MCA model. The effects of diffusion and growth velocity on eutectic growth morphology, such as lamellar spacing and interface shape, were systematically investigated. The simulation results reveal a wide range of realistic eutectic growth features, such as eutectic oscillatory growth, selection of eutectic lamellar spacing accomplished by lamellar branching or lamellar termination, as well as interaction between the solute redistribution and the adjustment of volume fractions.

Investigation of α 2/γ phase transformation mechanism under the interaction of dislocation with lamellar interface in primary creep of lamellar TiAl alloys

Under creep condition, the microstructural behavior of lamellar TiAl alloy is different from that of general materials. At as-received state, the amount of initial dislocations is very high and intrinsic dislocations, b → =〈110〉, are existed in lamellar interface with irregular interface morphology. In early primary stage, the amount of dislocation density in γ matrix is rapidly decreased. These dislocations are gliding on lamellar interface during primary creep. When they reach interface ledge, atomistic deformation caused by gliding dislocations can change the stacking sequence and the composition of α 2-ledge. As a result of this process, α 2 is transformed to γ phase. During this phase transformation process, a new unstable phase, Ti 2Al, is observed. This new phase is intermediate and disordered phase between α 2 and γ ordered phases. The atomistic model for α 2→Ti 2Al→γ phase transformation process is newly proposed.

Effect of stress axis orientation on the creep deformation behavior of Ti–48Al polysynthetically twinned (PST) crystals

The creep deformation behavior of PST crystals Ti–48Al was investigated at 1150 K under 100–400 MPa. Two hard orientations with the lamellar plates parallel or perpendicular to the compression axis and a soft orientation with the lamellar plates oriented 35° to compression axis were compared to investigate the effect of the orientation of lamellar interface on the creep behavior. The soft PST orientation exhibited the highest creep rates and larger primary creep strain than those of the hard PST orientations. The stress exponents were evaluated as 7.0 in the hard PST orientations for the stress dependence of the minimum creep rates. In the soft PST orientations, the stress exponent increased with decreasing stress from 4 at high stress regime to 8 at low stress regime. The primary creep strain increased with decreasing stress. The rotation of lamellar played an important role to accommodate the creep deformation in the soft PST orientation. The acceleration of creep rate after the minimum strain rates were attributed to the microstructural softening at strain concentrated regions. Those are kinking and dynamic recrystallization along the shear band in the hard PST orientations and recrystallization along the region at which angle of lamellar boundaries abruptly change in soft PST orientation.

Steroid-induced glaucoma after laser in situ keratomileusis associated with interface fluid

PurposeTo report the ocular manifestations and clinical course of eyes developing interface fluid after laser in situ keratomileusis (LASIK) surgery from a steroid-induced rise in intraocular pressure. DesignRetrospective, noncomparative interventional case series. Participants/interventionWe examined six eyes of four patients who had diffuse lamellar keratitis develop after uneventful myopic LASIK surgery and were treated with topical corticosteroids. Principal outcome measureSlit-lamp findings, intraocular pressure measurements, and visual field loss. ResultsAll eyes had a pocket of fluid develop in the lamellar interface between the flap and the stromal bed associated with a corticosteroid-induced rise in intraocular pressure. However, because of the interface fluid, intraocular pressure was normal or low by central corneal Goldmann applanation tonometry in all eyes. The elevated intraocular pressure was diagnosed by peripheral measurement in several cases after months of elevated pressure. All six eyes had visual field defects develop. Three eyes of two patients had severe glaucomatous optic neuropathy and decreased visual acuity develop as a result of undiagnosed steroid-induced elevated intraocular pressure. ConclusionsA steroid-induced rise in intraocular pressure after LASIK can cause transudation of aqueous fluid across the endothelium that collects in the flap interface. The interface fluid leads to inaccurately low central applanation tonometry measurements that obscure the diagnosis of steroid-induced glaucoma. Serious visual loss may result.

Effects of alloying elements on creep of TiAl alloys with a fine lamellar structure

Creep experiments were conducted on five powder-metallurgy TiAl alloys with fine grains (65–80 μm), fine lamellar spacings (0.1–0.16 μm), and different compositions [Ti–47Al (+Cr, Nb, Ta, W, Si)] at temperatures of 760°C and 815°C and stresses from 35 to 723 MPa. Results show that at a given lamellar spacing, replacing 1% Nb (atomic percent) with 1% Ta and replacing 0.2% Ta with 0.2% W induced little effect, but addition of 0.3% Si decreased the creep resistance by a factor of 3–4 under otherwise identical conditions. Field emission TEM was used to characterize the changes of microstructure and alloy element distribution before and after creep. It was found that thinning and dissolution of α 2 lamellae and continuous coarsening of γ lamellae were the main creep processes and the microalloying elements tended to segregate at lamellar interfaces, especially at ledges during creep. The effects of different alloying elements are interpreted in terms of the interaction of alloy segregants with misfit and/or misorientation dislocations at the lamellar interface. That is, the interaction retards the climb of interfacial dislocations and thus the creep process in the case of large segregants (Nb, Ta, W), but facilitates the climb and creep in the case of small segregants (Si).

Effects of α2 lamellae on deformation and fracture in fully lamellar TiAl based alloys

The deformation and fracture behaviours in fully lamellar TiAl alloys were investigated by unixial compression and an in situ TEM technique. The results indicated that the deformation and fracture behaviours in fully lamellar TiAl alloys were closely related to the relative orientation of the lamellae to the loading axis. When the lamellae were parallel to the loading axis, the slip in the α2 phase occurred along its prism plane, and microcracks nucleated preferentially along its prism plane. When the lamellae were perpendicular to the loading axis, slip became difficult, slip in the α2 phase occurred along its pyramidal plane, microcracks nucleated and propagated preferentially along its lamellar interface.

Effective Lattice Behavior of Fluorescence Energy Transfer at Lamellar Macromolecular Interfaces

Fluorescence energy transfer between donors and acceptors confined to macromolecular interfaces is considered. In particular, we discuss two theoretical models for the ensemble-average fluorescence intensity decay of the donor when both fluorophores are incorporated into a planar (e.g., lamellar) interface. The first model is based on a continuous distribution of donor and acceptor molecules on a two-dimensional surface, whereas the other assumes a discrete distribution of fluorophores along the nodes of a two-dimensional square lattice. Results for the discrete model show that the fluorescence intensity kinetics of a donor depends strongly on the geometry of the molecular distribution (i.e., the lattice constant) and the photophysics of fluorophores (i.e., critical radius of the energy transfer). Furthermore, a “discrete molecular distribution” might manifest itself in the experimental data as an increase in the apparent dimensionality of the energy transfer with increasing acceptor concentration. Altogether, the experimental and theoretical underpinnings indicate the enormous potential of using fluorescence energy-transfer kinetics for revealing structural features of molecular ensembles (i.e., geometry, shape) based on a single experimental measurement. However, further understanding the effects of restricted geometries on the fluorescence energy transfer is required to take full advantage of this information. Basic theoretical considerations to that end are provided.

Talc as nucleating agent of polypropylene: morphology induced by lamellar particles addition and interface mineral-matrix modelization

The efficiency of talc used as nucleating agent (0.5% by weight) in polypropylene (PP) was determined taking into account the particle size d50, particle morphology and BET specific surface areas. These findings were compared to a mineral with similar properties, pyrophyllite. Talc samples with the finest particle sizes induce a significant increase in the starting crystallization temperature of PP and irrespective of the particle size d50, pyrophyllite was found to be less efficient than talc. X-Ray results show that PP oriented crystallization due to talc or pyrophyllite addition, corresponds to an epitaxial growth whereby the mineral c*-axis is merged with the PP b*-axis. Microscopic observations revealed that in the presence of talc, nuclei density of PP increased strongly. In addition, a large number of nuclei was observed to appear everywhere on the talc surface. A PP-talc interface model is proposed by matching the (001) talc plane and the (010) PP plane. In this model, 3% of PP cell accommodation on talc is necessary with a 15° angle between PP chains elongation and the crystallographic directions of talc. Hexagonal rings on talc surface are believed to represent hydrogen bonds with PP methyl groupings. This fine structure relation between talc and PP is discussed, and is used to characterize the differences observed between the efficiency of talc and that of pyrophyllite.

A new experimental technique to investigate the α2/γ interface of lamellar TiAl alloy three dimensionally

The abundant two-dimensional defects, lamellar interface, have an important role in the deformation behavior of lamellar TiAl alloys. Transmission electron microscopy (TEM) has been used to investigating the lamellar interface. However, a very limited area only could be observed by using TEM. The observation of interface morphology and dislocations inner α2 phase of lamellar TiAl is very difficult by using TEM. The purpose of this study is to propose a new experimental method to observe the lamellar interface perpendicularly and investigate the crystallographic morphology of the α2 lamellar interface. The γ phase of the lamellar TiAl alloy was selectively dissolved and the α2 phase was separated from the TiAl lamellar alloy without significant damage. These separated α2 plates were observed with atomic force microscopy (AFM), scanning electron microscopy and TEM for the investigation of dislocations and interface of the α2 phase in the lamellar TiAl alloy.

Relationship between tensile and primary creep properties of near γ-TiAl intermetallics

This paper presents the tensile and primary creep behaviour of fully lamellar microstructures for three near γ-TiAl compositions: binary TiAl, ternary TiAl+W and TiAl+NbMnWMoSi. Reducing the lamellar interface spacing or aging to precipitate β along interfaces increases the 760 °C tensile strength. Primary creep at stresses from 140 to 276 MPa and 760 °C is characterized in terms of the instantaneous strain occurring during creep loading and a subsequent primary transient. The presence of interface β precipitates reduces the instantaneous strain and increases the time to 0.5% creep strain. Reducing lamellar interface spacing does not influence the instantaneous strain, but decreases the strain rate during the primary transient. Correlating the creep response with deformation structures after primary creep suggests that the instantaneous strain depends on the mobility of interface dislocations and the primary transient depends on dislocation mobility in both the lamellar interfaces and γ lamellae.

Making Sense of Refractive Surgery in 2001: Why, When, for Whom, and by Whom?

Making Sense of Refractive Surgery in 2001: Why, When, for Whom, and by Whom?

Ultrastructure of the lamellar corneal wound after laser in situ keratomileusis in human eye

A 30-year-old patient with keratoconus, a stable refraction, and normal central corneal thickness had laser in situ keratomileusis (LASIK). Six months later, she had uneventful penetrating keratoplasty for keratectasia. The lamellar LASIK interface could not be clearly identified by light microscopy. The corneal wound site did not stain for methyl metalloproteinase 1 or 2. Both the corneal flap undersurface and the stromal bed were devoid of interconnections and cells. Throughout the lamellar incision, including the laser-ablated zone, the surface was smooth on scanning electron microscopy. The collagen fibrils on both sides of the incision remained well aligned with one another, indicating good flap apposition. Under higher magnification transmission electron microscopy, some collagen fragments were found in the interface, especially adjacent to the hinge. The diameter of the collagen fibrils along the lamellar wound were identical to those farther from the incision. The absence of bridging collagen fibrils and cells between the flap undersurface and the stromal bed confirms the clinically known lack of wound repair at the interface and explains the easy separation of the flap from the stromal bed months after LASIK and the possible formation of an interface fluid pocket.

Energy Transfer in the Restricted Geometry of Lamellar Block Copolymer Interfaces

We carried out simulations of energy transfer kinetics for lamellar block copolymer systems in which donor and acceptor dyes were attached to the block junctions. We considered blocks of homopolymers that were sufficiently immiscible and of sufficiently high molecular weight to employ the Helfand-Tagami distribution of block junctions. The morphology of such block copolymers has been frequently discussed in terms of an apparent dimension parameter, which is recovered from the analysis of fluorescence decay curves, using the Klafter-Blumen (KB) formalism. Here, we investigate how such apparent dimensions are influenced by the interface thickness between the two blocks (which is dependent on the Flory-Huggins parameter of the system). We also probe the dependence of this apparent dimension on the concentration of the dyes in labeled samples. This kind of dependence has been experimentally observed but never explained, perhaps because of the approximations inherent in using the KB model to analyze fluorescent decay curves for block copolymer systems. We have found that apparent dimensions approach three for reasonably broad interfaces, but decrease to near two for very narrow interfaces, in accordance with asymptotic formulas that we propose for strongly segregated, lamellar block copolymer melts. Global analysis of the decay curves, as well as weighted linear regression of the parameters obtained from individual analyses of the decays, suggest linear relationships between the apparent dimensions from KB analyses and acceptor concentrations. We discuss the dependence