Planar Assembly Research Articles

“Raft” Formation by Two‐Dimensional Self‐Assembly of Block Copolymer Rod Micelles in Aqueous Solution

AbstractBlock copolymers can form a broad range of self‐assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free‐standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core‐crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)‐block‐polycaprolactone in water, co‐assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one‐dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.

Modular pixelated detector system with the spectroscopic capability and fast parallel read-out

A modular pixelated detector system was developed for imaging applications, where spectroscopic analysis of detected particles is advantageous e.g. for energy sensitive X-ray radiography, fluorescent and high resolution neutron imaging etc. The presented system consists of an arbitrary number of independent versatile modules. Each module is equipped with pixelated edgeless detector with spectroscopic ability and has its own fast read-out electronics. Design of the modules allows assembly of various planar and stacked detector configurations, to enlarge active area or/and to improve detection efficiency, while each detector is read-out separately. Consequently read-out speed is almost the same as that for a single module (up to 850 fps). The system performance and application examples are presented.

Electron-Hole Transfer in G-Quadruplexes with Different Tetrad Stacking Geometries: A Combined QM and MD Study

G-quadruplex nucleic acids represent a unique avenue for the building of electrically conductive wires. These four-stranded structures are formed through the stacking of multiple planar guanine assemblies termed G-tetrads. The diverse folding patterns of G-quadruplexes allow for several geometries to be adopted by stacked guanine bases within the core and at the dimeric interface of these structures. It is currently not clear how different G-tetrad stacking arrangements affect electron hole mobility through a G-quadruplex wire. Using a combined quantum mechanics and molecular dynamics approach, we demonstrate that the electron-hole transfer rates within the G-tetrad stacks vary greatly for different stacking geometries. We identify a distinguished structure that allows for strong electronic coupling and thus enhanced molecular electric conductance. We also demonstrate the importance of sampling a large number of geometries when considering the bulk properties of such systems. Hole hopping within single G-tetrads is slower by at least two orders of magnitude than between stacked guanines; therefore, hole jumping within individual tetrads should not affect the hole mobility in G-quadruplexes. The results of this study suggest engineering G-tetrads with continuous 5/6-ring stacking from an assembly of single guanosine analogs or through modification of the backbone in G-rich DNA sequences.

Rhombus-Shaped Tetranuclear [Ln4] Complexes [Ln = Dy(III) and Ho(III)]: Synthesis, Structure, and SMM Behavior

The reaction of a new hexadentate Schiff base hydrazide ligand (LH3) with rare earth(III) chloride salts in the presence of triethylamine as the base afforded two planar tetranuclear neutral complexes: [{(LH)2Dy4}(μ2-O)4](H2O)8·2CH3OH·8H2O (1) and [{(LH)2Ho4}(μ2-O)4](H2O)8·6CH3OH·4H2O (2). These neutral complexes possess a structure in which all of the lanthanide ions and the donor atoms of the ligand remain in a perfect plane. Each doubly deprotonated ligand holds two Ln(III) ions in its two distinct chelating coordination pockets to form [LH(Ln)2](4+) units. Two such units are connected by four [μ2-O](2-) ligands to form a planar tetranuclear assembly with an Ln(III)4 core that possesses a rhombus-shaped structure. Detailed static and dynamic magnetic analysis of 1 and 2 revealed single-molecule magnet (SMM) behavior for complex 1. A peculiar feature of the χM" versus temperature curve is that two peaks that are frequency-dependent are revealed, indicating the occurrence of two relaxation processes that lead to two energy barriers (16.8 and 54.2 K) and time constants (τ0 = 1.4 × 10(-6) s, τ0 = 7.2 × 10(-7) s). This was related to the presence of two distinct geometrical sites for Dy(III) in complex 1.

Water assisted anion chains and anion dependent fluorescence emission in salts of N,N′-bis(3-imidazol-1-ylpropyl)naphthalenediimide

In this article we demonstrate the role of anion–π interactions of different anions with protonated N,N′-bis(3-imidazol-1-ylpropyl)naphthalenediimide (L). The compound L shows fluorescence quenching with hydrochloric acid and hydrobromic acid, whereas it shows fluorescence enhancement with perchloric, sulphuric, phosphoric and nitric acid. A similar trend in fluorescence emission of the corresponding salt in the solid state is also observed. The fluorescence quenching is attributed to the anion–π interactions of the chloride and bromide with H2L, whereas the oxy-anion-containing acids cause fluorescence enhancement by protonation of L. The structures of the salts of N,N′-bis(3-imidazol-1-ylpropyl)naphthalenediimide (L), namely [H2LCl2]·2H2O (1), [H2LBr2]·2H2O (2), [H2L(ClO4)2] (3), [H2L(HSO4)2]·H2O (4), [H2L(MeSO4)2] (5), [H2L(HPO4)]·H2O (6) [H2L(NO3)2] (7), [H2L(SiF6)]·1.5H2O (8) are studied. Chloride and bromide ions form a hydrogen bonded halide–water chain; whereas the hydrogen phosphate salt forms a one dimensional water bridged polymeric chain. Planar nitrate anions appear as pairs and form planar assemblies with imidazolium ions and such assemblies are sandwiched between naphthalenediimide rings; whereas bisulphate and methylsulphate salts guide formation of helical supramolecular arrangements of H2L2+ ions. The perchlorate anions facilitate formation of a zigzag 2-D network structure and the SiF62− anions guide formation of a spiral chain-like structure to hold the SiF62− anions.

Synthesis of an embedded metal nanoparticle planar assembly by low-energy ion irradiation of a thin discontinuous metal film sandwiched in silica

Synthesis of a planar assembly of metal nanoparticles embedded in silica by low-energy ion irradiation is presented here. Argon ions of 350 keV were used to irradiate SiO2/Au/SiO2 and SiO2/Ag/SiO2 tri-layered films, with oxide thicknesses of 40 nm and metal layer thickness of 2 nm, to synthesize well isolated nanoparticles without the need of annealing. The nanoparticles have an average diameter of about 6 nm as revealed by transmission electron microscopy. Simulations by three-dimensional kinetic lattice Monte Carlo were performed to understand the ion-induced nanoparticle array formation from the initially percolated as-deposited metal layer embedded in the silica matrix.

Prestress stability of pin-jointed assemblies using ant colony systems

Prestress stability of pin-jointed assemblies using ant colony systems

Fungal Melanins Differ in Planar Stacking Distances

Melanins are notoriously difficult to study because they are amorphous, insoluble and often associated with other biological materials. Consequently, there is a dearth of structural techniques to study this enigmatic pigment. Current models of melanin structure envision the stacking of planar structures. X ray diffraction has historically been used to deduce stacking parameters. In this study we used X ray diffraction to analyze melanins derived from Cryptococcus neoformans, Aspergillus niger, Wangiella dermatitides and Coprinus comatus. Analysis of melanin in melanized C. neoformans encapsulated cells was precluded by the fortuitous finding that the capsular polysaccharide had a diffraction spectrum that was similar to that of isolated melanin. The capsular polysaccharide spectrum was dominated by a broad non-Bragg feature consistent with origin from a repeating structural motif that may arise from inter-molecular interactions and/or possibly gel organization. Hence, we isolated melanin from each fungal species and compared diffraction parameters. The results show that the inferred stacking distances of fungal melanins differ from that reported for synthetic melanin and neuromelanin, occupying intermediate position between these other melanins. These results suggest that all melanins have a fundamental diffracting unit composed of planar graphitic assemblies that can differ in stacking distance. The stacking peak appears to be a distinguishing universal feature of melanins that may be of use in characterizing these enigmatic pigments.

Mechanical Properties of Topologically Interlocked Structures with Elements Produced by Freeze Gelation of Ceramic Slurries

AbstractIn the present paper, the force‐fit connection of discrete ceramic components by means of geometrically interlocking surfaces is studied. These surfaces possess a concavo‐convex topology permitting assembly of structures in which each individual element is kinematically locked by its neighbors. Such structures have a tuneable bending stiffness, allow for large deformations and are tolerant to missing or destroyed elements. These properties of topologically interlocked structures make them particularly attractive in construction with brittle materials. The elements used were produced by freeze gelation of ceramic slurries, leading to near net shape with the coefficient of shrinkage below 3%. It is shown that planar assemblies of interlocked ceramic elements can withstand flexural deflections up to a ten‐fold of those a solid plate from the same material can sustain. The response of these structures to concentrated load can be divided into an elastic and a quasi‐plastic, i.e., irreversible, part. After the point of maximum load, the interlocked structures investigated were still able to withstand further deformation, whereas solid plates showed brittle failure.

In Vitro Coralling of a Transmembrane Protein in a Double Cushioned Lipid Bilayer Assembly

In Vitro Coralling of a Transmembrane Protein in a Double Cushioned Lipid Bilayer Assembly

Magnetostatic fields in planar assemblies of magnetic nanoparticles

Magnetostatic fields are studied in the model of a planar assembly of magnetic particles forming a periodic lattice infinite in the $xy$ plane and finite along the $z$ axis. Two types of lattices are considered: simple cubic and body-centered cubic. Exact analytical expressions of the magnetostatic fields for the magnetization perpendicular and parallel to the $xy$ plane, ${H}_{\ensuremath{\perp}}(x,y,z)$ and ${H}_{\ensuremath{\parallel}}(x,y,z)$, are obtained in the form of Fourier series both inside the particles, and in the surrounding matrix. Exact formulas for mean magnetostatic fields inside the particles, ${\overline{H}}_{\ensuremath{\perp}}$ and ${\overline{H}}_{\ensuremath{\parallel}}$, are obtained by averaging over the particle volume. A numerical analysis of these formulas shows linear dependences of ${\overline{H}}_{\ensuremath{\perp}}$ and ${\overline{H}}_{\ensuremath{\parallel}}$ on the volume filling factor $c$. A comparison of these exact solutions with the results of earlier works where such dependences were obtained using different approximate approaches, confirms the correctness of some of them. The correctness of methods allowing the estimation of the filling factor $c$ from both magnetic resonance and magnetometric data is also confirmed.

Direct-write assembly of microperiodic planar and spanning ITO microelectrodes

Printed Sn-doped In(2)O(3) (ITO) microelectrodes are fabricated by direct-write assembly of sol-gel inks with varying concentration. This maskless, non-lithographic approach provides a facile route to patterning transparent conductive features in planar arrays and spanning architectures.

Surface plasmon resonance of gold nanoparticles assemblies at liquid | liquid interfaces

Surface plasmon resonance (SPR) was observed when a planar close-packed assembly of gold nanoparticles (Au NPs) is adsorbed at the water|1,2-dichloroethane interface. Aqueous gold nanoparticles, 13 or 16 nm in diameter, are deposited at the interface by adding methanol to form a close-packed film with a visible gold mirror reflectance. By total internal reflection of a light beam on the interface, the angular dependence of the interfacial reflectivity was measured in a pseudo-Kretschmann configuration and compared to Fresnel simulations for a homogeneous gold film. The experimental angles for minimum reflectivity were found to match the simulated values. Then, the fluorescence of dye molecules co-adsorbed within 13 and 16 nm gold nanoparticles assemblies at the liquid|liquid interface was measured. The fluorescence intensity under SPR is revealed to be much greater than under total internal reflection conditions, yielding an enhancement factor of approximately 30 and 50 for 13 and 16 nm Au NPs assemblies, respectively. Also, the fluorescence lifetime was found to decrease under SPR conditions.

Mechanical Gradient Cues for Guided Cell Motility and Control of Cell Behavior on Uniform Substrates

AbstractA novel method for the fabrication and the use of simple uniform poly(dimethylsiloxane) PDMS substrates for controlling cell motility by a mechanical gradient is reported. The substrate is fabricated in PDMS using soft lithography and consists of a soft membrane suspended on top of a patterned PDMS substrate. The difference in the gradient stiffness is related to the underlying pattern. It is shown experimentally that these uniform substrates can modulate the response of cell motility, thus enabling patterning on the surfaces with precise cell motility. Because of the uniformity of the substrate, cells can spread equally and a directional movement to stiffer regions is clearly observed. Varying the geometry underlying the membrane, cell patterning and movement can be quantitatively characterized. This procedure is capable of controlling cell motility with high fidelity over large substrate areas. The most significant advance embodied in this method is that it offers the use of mechanical features to control cell adhesion and not topographical or chemical variations, which has not been reported so far. This modulation of the response of cell motility will be useful for the design and fabrication of advanced planar and 3D biological assemblies suitable for applications in the field of biotechnology and for tissue‐engineering purposes.

Guided Cell Migration on Microtextured Substrates with Variable Local Density and Anisotropy

AbstractThis work reports the design of and experimentation with a topographically patterned cell culture substrate of variable local density and anisotropy as a facile and efficient platform to guide the organization and migration of cells in spatially desirable patterns. Using UV‐assisted capillary force lithography, an optically transparent microstructured layer of a UV curable poly(urethane acrylate) resin is fabricated and employed as a cell‐culture substrate after coating with fibronectin. With variable local pattern density and anisotropy present in a single cell‐culture substrate, the differential polarization of cell morphology and movement in a single experiment is quantitatively characterized. It is found that cell shape and velocity are exquisitely sensitive to variation in the local anisotropy of the two‐dimensional rectangular lattice arrays, with cell elongation and speed decreasing on symmetric lattice patterns. It is also found that cells could integrate orthogonal spatial cues when determining the direction of cell orientation and movement. Furthermore, cells preferentially migrate toward the topographically denser areas from sparser ones. Consistent with these results, it is demonstrated that systematic variation of local densities of rectangular lattice arrays enable a planar assembly of cells into a specified location. It is envisioned that lithographically defined substrates of variable local density and anisotropy not only provide a new route to tailoring the cell‐material interface but could serve as a template for advanced tissue engineering.

Uranyl–organic bilayer assemblies with flexible aromatic di-, tri- and tetracarboxylic acids

The reaction of uranyl nitrate hexahydrate with three flexible aromatic polycarboxylic acids under hydrothermal conditions has been found to give 2-D assemblies in all three cases. The complex formed with phenylsuccinic acid (H2L1), [UO2(L1)(H2O)] (1), comprises a planar grid-like assembly with all the phenyl substituents directed outwards on the same side. These layers are organized in a face-to-face fashion by inter-layer π-stacking interactions. 1,3,5-Benzenetriacetic acid (H3L2) gives the compound [UO2(H2O)5][UO2(L2)]2·5H2O (2), in which a novel bilayer arrangement results from both the uranyl ions and the ligand behaving as trigonal nodes. Interdigitation of the anionic bilayers leaves spaces occupied by the [UO2(H2O)5]2+ counter ions. Complex 2 is a novel example of a molecular bilayer involving other building blocks than the usual T-shaped nodes and linear spacers. Finally, [(UO2)3(HL3)2(H2O)]·3H2O (3) was obtained with benzophenone-3,3′,4,4′-tetracarboxylic acid (H4L3) generated in situ from the corresponding dianhydride. The high overall denticity of the ligand (bound to as much as six cations) and the twisting of the two aromatic rings around the central bonds result in the formation of a pillared bilayer of the “double floor” type, with channels containing water molecules.

Redox-controlled multistability of double-decker cerium tetra-(15-crown-5)-phthalocyaninate ultrathin films

The optical and electrochemical properties of novel double-decker cerium bis-tetra-15-crown-5-phthalocyaninate [ Ce ( R 4 Pc 2−)2]0 (R4Pc2− = [4,5,4',5',4",5",4'",5'"-tetrakis-(1,4,7,10,13-pentaoxapentadecamethylene)-phthalocyaninate-anion]) Langmuir-Blodgett and cast films were investigated. The particular feature of cerium ion in complex with tetra-15-crown-5-phthalocyanine is the stability of oxidation state +4 unlike other lanthanide metal centers. Cyclic voltammetry curves exhibited three stable redox states in the Langmuir-Blodgett and cast films. Redox processes in Langmuir-Blodgett films are reversible and reproducible at multiple scan procedures. The mechanisms of redox transformations in Langmuir-Blodgett films are suggested. We demonstrated that the well-defined structure of Langmuir-Blodgett film is essential for fast electron transfer within the planar system, in which the charge is delocalized along the conjugated assembly of uniformly ordered stacks of discotic crown-phthalocyaninate. Fast charge relaxation was observed in highly ordered Langmuir-Blodgett film whereas the electrochemically written redox states remained unchanged in unordered cast film. The combination of electrochemistry with surface plasmon resonance spectroscopy allowed us to demonstrate that stepwise change of potential in the range 200-850 mV induced the respective optical response, which can be observed as the change in resonance angle value. High-speed response and reversibility of the switching process between stable states may be utilized as the basis for switchable optoelectronic devices. Electrochemical multistability of cerium crown-phthalocyaninate provided a basis for developing a simple strategy to fabricate nanoelectromechanical systems with high efficiency and fast response. Our approach relies on the modulation of the distance between decks in a complex stack via redox-controlled change of metal center size that results in change of linear dimensions of the stacks. The reported results are valuable, not only because of their potential applications, for instance, in OFET and MEMS fabrication, but also from a fundamental point of view since they illustrate the interplay between the orientation of stacks bearing discotic aromatic molecules and charge transfer within such a planar assembly.

A Planar Assembly Technique for PEMFCs without Bolt

not Available.

Case Studies in Planar Part Feeding and Assembly Based on Design of Limit Sets

Vibration is commonly used in industrial parts feeding and alignment processes, and to provide energy to encourage mobility among self-assembling parts. We are studying a simple model of agitation where planar parts are repetitively thrown by a simple one-degree-of-freedom throwing surface, caught and allowed to settle. Throwing actions result in nonlinear discrete-time maps in the parts' configuration space, exhibiting behaviors such as unique fixed points and uncertainty-reducing forward limit sets with large basins of attraction. We show how to shape these maps by choosing the arm geometry, throwing velocity and mass parameters of the parts. In some cases, we can design a single map that is guaranteed to uniquely position and orient a part. In other cases, we can design multiple maps corresponding to different throw velocities such that the composition of the maps can be used to drive multiple parts to a desired assembly. Switching between the throw actions is triggered by simple sensors that recognize when the system has achieved a configuration in the basin of attraction of a subsequent map.

Impact of Materials and Design on Solid Oxide Fuel Cell Stack Operation

Planar SOFC stack technology based on a unique concept (SOFConnex™) uses structured gas distribution layers between unprofiled metal sheet interconnects and thin Ni-YSZ anode supported electrolyte cells. The layers are flexible both in material and design and allow to implement new configurations relatively simply; manifolding can be internal, external, or combined. Together with thin stack components, independent of the supplier, the SOFConnex™ stacking approach allows compact planar assembly with low cost potential and adequate power density. Different cell and flow designs have been realized. With a basic flow configuration, short stacks (50cm2 cell active area) were assembled and tested, power density at 800°C reaching 0.5W∕cm2 at 0.7V average cell voltage (1.5kWe∕L, 0.36Ωcm2 area specific resistance), for 65% fuel utilization and 35% lower heating value electrical efficiency. Short stacks were thermally cycled and operated with both hydrogen and syngas. Degradation was essentially Ohmic (confirmed from impedance spectroscopy on stacks) and at first mainly due to the cathode-electrolyte interfacial reaction, performance loss was subsequently strongly reduced after cathode replacement. Using multiple voltage probes with additional interconnects allowed to separately monitor current collection losses during polarization. With an improved design in terms of sealing, postcombustion control and flow field, stacks up to 1kWe have been operated.