Continuous Shell Research Articles

Spreading Dynamics of Biomimetic Actin Cortices

Reconstituted systems mimicking cells are interesting tools for understanding the details of cell behavior. Here, we use an experimental system that mimics cellular actin cortices, namely liposomes developing an actin shell close to their inner membrane, and we study their dynamics of spreading. We show that depending on the morphology of the actin shell inside the liposome, spreading dynamics is either reminiscent of a bare liposome (in the case of a sparse actin shell) or of a cell (in the case of a continuous actin shell). We use a mechanical model that qualitatively accounts for the shape of the experimental curves. From the data on spreading dynamics, we extract characteristic times that are consistent with mechanical estimates. The mechanical characterization of such stripped-down experimental systems paves the way for a more complex design closer to a cell. We report here the first step in building an artificial cell and studying its mechanics.

Buckling of Carbon Nanotubes: a Molecular Static Approach

AbstractAxially loaded cylindrical continuous shells collapse either globally like a rod (Euler buckling), or locally (local shell wall buckling), depending on the ratio of the length of the shell over the diameter [1]. There are many published investigations, which show that this behaviour is also true for Carbon Nanotubes CNTs [2]. In this work a systematic analysis of the problem is given in the framework of molecular statics. This approach has the advantage of taking care of the discrete structure of CNTs. The covalent bonds of the hexagonal carbon network are modelled as nonlinear springs, and the compressive load is applied quasistatically, excluding follower forces. The software package LAMMPS [3] offers the AIREBO potential [4] and is suitable for describing CNTs. To identify the stability boundary in the parameter plane, LAMMPS is extended to compute the definiteness of the Hessian. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Significant enhancement of the sensing characteristics ofIn2O3 nanowires by functionalization with Pt nanoparticles

We report a significant enhancement in the gas sensing properties ofIn2O3 nanowires by functionalizing their surfaces with Pt nanoparticles. For Pt-functionalization,In2O3–Pt core–shell nanowires are synthesized by the sputtering deposition of Pt layers on bareIn2O3 nanowires. Next, continuous Pt shell layers are transformedinto Pt nanoparticles of cubic phase by heat treatment. In anO2 gas sensing test, thePt-functionalized In2O3 nanowires reveal exceptionally higher sensitivity and faster response than bareIn2O3 nanowires.

Growth, condition, and survival of the Pacific oyster Crassostrea gigas cultivated within and outside a subtropical lagoon

Mass die-offs of Pacific oysters have become a widespread concern in northwestern Mexico. Cultivation of the species occurs in shallow inland waters (lagoons, estuaries, and reservoirs) at high stocking densities and under elevated seasonal temperatures; all conditions that are potential causes for high die-offs. Cultivation outside inland waters may be an alternative to reduce the impact of possible stressors. This study compares growth, condition, and survival of oysters ( Crassostrea gigas) cultivated at different densities within a subtropical lagoon and on the gulf side of Laguna La Cruz in the State of Sonora. Three densities were tested at each site using cultivation trays. Temperature, salinity, oxygen, pH, seston content, and chlorophyll a content were measured at sampling stations inside and outside the lagoon. Results showed that cumulated mortality was significantly lower for oysters cultivated outside the lagoon. Peak mortality occurred in November–December 2006 and March–May 2007, which coincided with mass die-offs in the region and with abrupt changes in temperature. High variations in temperature were related to water masses from the open ocean. Lagoon oysters were influenced by slightly higher mean daily temperatures and showed continuous shell growth and were significantly larger than oysters on the gulf side. However, lagoon oysters showed similar dry weights as gulf side oysters, indicating retarded somatic growth, probably from a relatively low food supply. Gulfside oysters had a higher condition index than oysters in the lagoon throughout the period of study. Results showed that oysters were sensitive to overstocking, since growth at high densities was less than at low densities at both sites. This suggested an advantage for cultivation at intermediate and low densities. Although C. gigas responded in a similar way to overstocking at both sites, they responded differently in relation to culture site. Diminished somatic growth, condition, and survival suggest that oysters in the lagoon experienced more stress than oysters at the gulfside site, probably from differences in water quality. Cultivation of these oysters outside of protected waters is an alternative that producers may try to obtain a better product and reduce mortality.

Gold/mesoporous silica-fiber core-shell hybrid nanostructure: a potential electron transfer mediator in a bio-electrochemical system

Mesostructured silica fibers synthesized by electrospinning silica sol were used as templates for the assembly of gold nanoparticles and the formation of continuous gold shells along the fiber axis. Dense and uniform spherical gold nanoparticles were formed by in situ reduction of hydrochloroauric acid absorbed on self-assembled polyelectrolyte film of silica fiber surface. The gold-seeded silica fibers were further coated by continuous gold shells via solution-phase reduction of an appropriate metal ion in PVP solution. The thickness and morphology of gold shell could be tailored by the molar ratio of repeating units of PVP to gold ions (R) and growth time. Experimental results showed that low R tended to form a thick gold layer with sharp tips, whereas high R favored obtaining thin and uniform Au shell. The SiO2@Au fiber hybrid nanostructures are further used as substrates for fabrication of a glucose biosensor, which exhibited excellent bio-electrochemical activity with high sensitivity and rapid response. These hybrid nanostructures are, therefore, regard as molecule wires for potential application in highly sensitive chemical or biological sensors.

Synthesis and characterization of mesoporous silica core-shell particles

Core-shell particles were formed by deposition of primary silica particles synthesized from sodium silicate solution on functionalized silica core particles (having size of ~0.5 ?m) prepared by hydrolysis and condensation of tetraethylortosilicate. The obtained mesoporous shell has thickness of about 60 nm and consists of primary silica particles with average size of ~21 nm. Scanning electron microscopy and zeta potential measurements showed that continuous silica shell exists around functionalized core particles which was additionally proved by FTIR and TEM results.

Metal Coated Polymer Particles for Electronic Packaging

Anisotropic conductive adhesives (ACA) are widely used as interconnect materials in the manufacturing of LCD screens. To be integrated in a broader range of interconnect applications several technical and economic issues still need to be addressed. One significant challenge is to encapsulate polymer particles with well controlled modal diameter and size distribution into continuous, compact, and uniform conductive metallic shells. This presentation describes a method to deposit layers of nickel with different thickness (30 – 120 nm) onto monosized polymer particles ranging in size from 1 to 10 micrometers. The novelty of the approach consists in a pre-treatment of the epoxy functionalized polymer particles with linear polymeric amines. We show that by increasing amine chain length the distribution of the palladium catalyst, and consequently the adhesion and distribution of nickel metal deposited, can be improved dramatically. The effect of several plating parameters is discussed and illustrated.

Synthesis and surface enhanced optical properties of multibranched spindle particles and core–shell structures

A facile approach has been developed for the synthesis of monodisperse spindle-shaped α-Fe 2O 3 and multibranched spindle FeO(OH) as well as their core–shell structures. The formation of unique multibranched spindle FeO(OH) particles depended on the smooth liberation of hydroxide ions by urea which inhibited the nucleation and growth rate of crystals. The amount of different metal ions and oleic acid exhibited significant effect on the shape of the particles, in which the formation of multibranched ends was induced. Their core–shell structures were fabricated by attaching the small Au nanoseeds onto the core surfaces followed with the catalyzed reduction to form continuous Au shell. The FeO(OH) and FeO(OH)@Au core–shell crystals were characterized using transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). The surface-enhanced Raman scattering (SERS) activities from different core–shell substrates were investigated. The results revealed that the intensity of SERS signal was dependent on the shell thickness. The multibranched core–shell particles exhibited optimum SERS activity and could serve as candidate substrate for both theoretical and practical applications in SERS.

Fabrication of Silica Shell Photonic Crystals through Flexible Core Templates.

We attached very small silica particles onto flexible monodisperse poly (N-isopropylacrylamide, PNIPAm) core particles synthesized by dispersion polymerization. These silica particles were attached to the partially swollen PNIPAm particles by the hydrolysis and condensation of tetraethoxysilane at 24 °C. The resulting silica particle-functionalized PNIPAm core particles show reversible swelling and shrinking as the temperature is cycled. These particles form close-packed-array photonic crystals as the solvent evaporates; the cores shrink to form a silica shell around the pure PNIPAm dry core particles as they close pack. The PNIPAm cores were removed by calcination, leaving a PC composed of essentially pure continuous silica shells. These silica shell photonic crystals Bragg diffract UV light at ~310 nm. The close packed particle interstices are continuous and are easily filled by water. In contrast, the silica shells are impervious to water because the process of making them results in a continuous shell of silica without holes.

A novel route for the synthesis of composite dielectric core/silver shell particles

We demonstrated the possibility of preparing continuous silver shells on particles of polystyrene latex by enlarging adsorbed seeding metal nanoparticles in solution containing ascorbic acid and silver nitrate. It is shown that a strong batochromic shift of the maximum of surface plasmon resonance is observed for such composite structures.

Mixed platinum–gold electrocatalysts for borohydride oxidation prepared by the galvanic replacement of nickel deposits

Mixed platinum/gold coatings were prepared by partial galvanic replacement of nickel layers that had been electrodeposited onto glassy carbon electrode substrates. The process (termed “transmetalation”) involves the spontaneous replacement of surface Ni atoms by Pt and Au upon immersion of the former metal into equimolar mixed chloroplatinic and chlorolaurate acid solutions. The multimetallic deposits on glassy carbon substrates, PtAu(Ni)/GC, were characterised by SEM/EDS, XRD, AES and electrochemical techniques. Smooth films with a bulk composition enriched in Au and minimum quantities of Ni left were obtained. Pt and Au were found to be alloyed and both Pt and Au to co-exist with Ni down to the core of the layers. The PtAu(Ni) deposits displayed typical Pt and Au surface electrochemistry indicating the formation of a continuous noble metal shell; the estimated electroactive surface areas point again to an excess of Au on the surface. The activity of the PtAu(Ni)/GC electrodes towards the oxidation of borohydride was studied by voltammetry at a rotating disc electrode, RDE, and compared to that of bulk Pt and Au. As expected, the Pt–Au alloy catalyst showed behaviour intermediate to that of its pure components. However, in the limiting current potential range the alloy tended more to bulk Au behaviour (number of electrons was closer to eight) while at low overpotentials it resembled the catalytic activity of pure Pt.

Dynamic Multicompartment-Core Micelles in Aqueous Media

We investigate micellar aggregates of amphiphilic block terpolymers, polybutadiene-block-poly(2-vinyl pyridine)-block-poly(methacrylic acid) (PB800P2VP190PMAA550) and their quaternized analogues polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB800P2VPq190PMAA550) in aqueous solution using light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM). At high pH, PB800P2VP190PMAA550 forms core--shell--corona micelles with a hydrodynamic radius Rh approximately 100 nm and a continuous shell of P2VP. However, at pH 4 partial intramicellar interpolyelectrolyte complex (im-IPEC) formation between P2VP and PMAA results in a patchy, collapsed shell. This is far more pronounced for the quaternized analogue, PB800P2VPq190PMAA550, which forms aggregates of similar size, also exhibiting a noncontinuous, patchy shell. Here, these im-IPECs of the positively charged P2VPq and the partially negatively charged PMAA are present over the whole investigated pH range (4-10). We further demonstrate that size and charge of the corona can be tuned through the block terpolymer composition, in particular, the ratio between P2VPq and PMAA. These micelles are dynamic and able to react to changes in pH or salinity in terms of corona diameter and aggregation number.

Magnetic−Plasmonic Core−Shell Nanoparticles

Nanoparticles composed of magnetic cores with continuous Au shell layers simultaneously possess both magnetic and plasmonic properties. Faceted and tetracubic nanocrystals consisting of wustite with magnetite-rich corners and edges retain magnetic properties when coated with a Au shell layer, with the composite nanostructures showing ferrimagnetic behavior. The plasmonic properties are profoundly influenced by the high dielectric constant of the mixed iron oxide nanocrystalline core. A comprehensive theoretical analysis that examines the geometric plasmon tunability over a range of core permittivities enables us to identify the dielectric properties of the mixed oxide magnetic core directly from the plasmonic behavior of the core-shell nanoparticle.

ZnO sputter coating on SnO 2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO 2–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO 2–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO 2–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO 2 nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.

Influence of surrounding plates on 3D subduction dynamics

Our 3D modelling study shows that the presence of lithospheric plates around a subducting plate has a significant influence on subduction dynamics, in particular on trench retreat rate, slab dip, and lateral shortening of the subducting plate. Neighbouring plates prevent unrealistic plate behaviour with no need for complex rheologies. Because, at the Earth's surface, plates form a continuous shell, they should not be neglected.

Synthesis of hollow ferrite nanospheres for biomedical applications

Hollow ferrite spheres of 220–340 nm diameter were synthesized at 60 °C as multi-functionalized magnetic carriers which are potentially applicable both as drug delivery systems (DDS) and hyperthermia treatment. We found that SH and OH groups on the silica template spheres enabled the fabrication of continuous ferrite shells of 20–30 nm in thickness. Transmission electron microscopy and energy-dispersive spectroscopy revealed that the templates were dissolved by a NaOH solution, yielding hollow particles exhibiting saturation magnetization of 78 emu/g. The results suggested that the ferrite shells are porous and the pores work as pathway for releasing drugs from the hollow particle inside.

Interactions Between Lipid Bilayer And Protein Skeleton In Erythrocyte Deformations

We study mechanics of a red blood cell in large deformations by using a multi-scale modeling approach, in which the interactions between the lipid bilayer and the protein skeleton are considered as two parts: vertical contact and lateral sliding. The sliding is caused by the mobility of the transmembrane proteins (e.g. band 3 and glycophorin C). Our model consists of a complete-cell model which depicts the cell membrane as two continuous shells, and a molecular-detailed model of a junctional complex (JC) that provides the constitutive properties of the inner layer (the skeleton).

Crystallization Kinetics and Influencing Factors in the Syntheses of MFI/MFI Core-Shell Zeolites

MFI/MFI core-shell zeolites with a low silica to alumina ratio core and a continuous shell of high silica to alumina ratio were successfully synthesized by a novel two-step procedure. This was done by a secondary growth of the ZSM-5 shell onto the modified ZSM-5 crystals and the pre-treatment step played an important role during the synthesis. Critical factors for the growth of the ZSM-5 shell including synthesis temperatures, periods, and core dosages were summarized. Results from cumene and 1,3,5-triisopropylbenzene (1,3,5-TIPB) cracking reactions showed that the core-shell zeolite and the core crystal had comparable activities for the cumene cracking reaction. Compared to the core crystal, the cracking activity of 1,3,5-TIPB of the core-shell zeolite was reduced by 68%, which coincided with the extent of aluminum reduction on the external surface. These results suggested that the acidity of the core crystals was largely preserved in the MFI/MFI core-shell structure. Crystallization kinetics curves were determined at different synthesis temperatures. The apparent energy of crystallization activation was found to be 26.5 kJ·mol-1 and the activation energy of nucleation was 51.5 kJ·mol-1.

Microcapsules filled with reactive solutions for self-healing materials

Microcapsules containing a solvent and reactive epoxy resin are a critical component for the development of cost-effective, low toxicity, and low flammability self-healing materials. We report a robust in situ encapsulation method for protection of a variety of oil soluble solvents and reactive epoxy resins surrounded by a thin, polymeric, urea–formaldehyde (UF) shell. Resin–solvent capsules are produced in high yield with diameters ranging from 10 to 300μm by controlling agitation rates. These capsules have a continuous inner shell wall and a rough exterior wall that promotes bonding to a polymer matrix. Capsules as small as 300nm in diameter are achieved through sonication and stabilization procedures. The presence of both the epoxy resin and solvent core components is confirmed by differential scanning calorimetry (DSC) measurements, and the relative amount of epoxy and solvent in the liquid core is determined by thermogravimetric analysis (TGA). The capsules are shown to satisfy the requirements for use in self-healing materials including processing survivability, thermal stability, and efficient in situ rupture for delivery of healing agent.

Geometrically exact shells in a flexible multibody framework

AbstractThe present work deals with the extension of contemporary finite element methods for nonlinear structural dynamics to the realm of flexible multibody dynamics. In particular, we aim at the incorporation of geometrically exact shell formulations into a multibody framework. Geometrically exact shell formulations are capable of dealing with finite deformation problems. In particular we focus on (i) a finite element discretization in space which inherits the frame–indifference of the nonlinear strain measures from the underlying continuous shell formulation, and (ii) a discretization in time which leads to an energy and momentum conserving scheme or an energy decaying variant thereof. In nonlinear structural dynamics energy–momentum schemes have proven to be well–suited for the stable numerical integration of large deformation problems.We show that semi–discrete formulations emanating from the finite element discretization of geometrically exact shell theories can be regarded as discrete mechanical systems subject to holonomic constraints. Accordingly, the corresponding equations of motion can be written as differential–algebraic equations (DAEs) with index three. In particular, this viewpoint fits perfectly well into the framework of a rotationless description of rigid bodies [1] and geometrically exact beams [2]. Thus the DAEs provide a uniform framework for flexible multibody systems. Moreover, the DAEs turn out to be beneficial to the design of energy–momentum schemes [3–5]. Indeed our shell formulation can be shown to be equivalent to the previous work by Simo & Tarnow [6]. The newly established DAE framework facilitates the use of geometrically exact shells in flexible multibody dynamics. Representative numerical examples will demonstrate the capability of the proposed methodology. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)