Lateral Order Research Articles

Surface‐Confined Self‐Assembled Janus Tectons: A Versatile Platform towards the Noncovalent Functionalization of Graphene

AbstractA general strategy for simultaneously generating surface‐based supramolecular architectures on flat sp2‐hybridized carbon supports and independently exposing on demand off‐plane functionality with controlled lateral order is highly desirable for the noncovalent functionalization of graphene. Here, we address this issue by providing a versatile molecular platform based on a library of new 3D Janus tectons that form surface‐confined supramolecular adlayers in which it is possible to simultaneously steer the 2D self‐assembly on flat C(sp2)‐based substrates and tailor the external interface above the substrate by exposure to a wide variety of small terminal chemical groups and functional moieties. This approach is validated throughout by scanning tunneling microscopy (STM) at the liquid–solid interface and molecular mechanics modeling studies. The successful self‐assembly on graphene, together with the possibility to transfer the graphene monolayer onto various substrates, should considerably extend the application of our functionalization strategy.

Surface-confined self-assembled Janus tectons: a versatile platform towards the noncovalent functionalization of graphene.

A general strategy for simultaneously generating surface-based supramolecular architectures on flat sp(2) -hybridized carbon supports and independently exposing on demand off-plane functionality with controlled lateral order is highly desirable for the noncovalent functionalization of graphene. Here, we address this issue by providing a versatile molecular platform based on a library of new 3D Janus tectons that form surface-confined supramolecular adlayers in which it is possible to simultaneously steer the 2D self-assembly on flat C(sp(2))-based substrates and tailor the external interface above the substrate by exposure to a wide variety of small terminal chemical groups and functional moieties. This approach is validated throughout by scanning tunneling microscopy (STM) at the liquid-solid interface and molecular mechanics modeling studies. The successful self-assembly on graphene, together with the possibility to transfer the graphene monolayer onto various substrates, should considerably extend the application of our functionalization strategy.

Evolution of lateral ordering in symmetric block copolymer thin films upon rapid thermal processing

This work reports experimental findings about the evolution of lateral ordering of lamellar microdomains in symmetric PS-b-PMMA thin films on featureless substrates. Phase separation and microdomain evolution are explored in a rather wide range of temperatures (190–340 °C) using a rapid thermal processing (RTP) system. The maximum processing temperature that enables the ordering of block copolymers without introducing any significant degradation of macromolecules is identified. The reported results clearly indicate that the range of accessible temperatures in the processing of these self-assembling materials is mainly limited by the thermal instability of the grafted random copolymer layer, which starts to degrade at T > 300 °C, inducing detachment of the block copolymer thin film. For T ⩽ 290 °C, clear dependence of correlation length (ξ) values on temperature is observed. The highest level of lateral order achievable in the current system in a quasi-equilibrium condition was obtained at the upper processing temperature limit after an annealing time as short as 60 s.

Columnar molecular aggregation in the aqueous solutions of disodium cromoglycate.

Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with π-π stacking at a separation of 3.4 Å between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from ∼35 to 42 Å in the orientationally ordered nematic (N) phase and from 27 to 32 Å in the columnar or middle (M) phase having long range lateral positional order. The assemblies' length depends on concentration and consists of ∼23 molecules in the N phase, becoming three to ten times larger in the M phase. The scission energy is concentration dependent in the N phase with values ∼7.19 ± 0.14 k_{B}T (15 wt %), 2.73 ± 0.4 k_{B}T (20 wt %), and 3.05 ± 0.2 k_{B}T (25 wt %). Solutions of all concentrations undergo a spinodal decomposition at temperatures above ∼40 °C, resulting in DSCG-rich regions with the M phase and water-rich regions in the N and isotropic phases.

Electric-field modulation of liquid crystal structures in contact with structured surfactant monolayers.

We present experiments in which we use an electric field to switch between different configurations in the cellular patterns induced in a confined nematic liquid crystal by the contact with a surfactant monolayer that features lateral order and surface defects. By using different combinations of far-field alignment and mesogen dielectric anisotropy, we unravel the nature and stability of point defects and disclinations resulting from the hybrid boundary conditions.

Enhancing Ordering Dynamics in Solvent-Annealed Block Copolymer Films by Lithographic Hard Mask Supports

We studied solvent-driven ordering dynamics of block copolymer films supported by a densely cross-linked polymer network designed as organic hard mask (HM) for lithographic fabrications. The ordering of microphase separated domains at low degrees of swelling corresponding to intermediate/strong segregation regimes was found to proceed significantly faster in films on a HM layer as compared to similar block copolymer films on silicon wafers. The ten-fold enhancement of the chain mobility was evident in the dynamics of morphological phase transitions and of related process of terrace-formation on a macroscale, as well as in the degree of long-range lateral order of nanostructures. The effect is independent of the chemical structure and on the volume composition (cylinder-/ lamella-forming) of the block copolymers. In-situ ellipsometric measurements of the swelling behavior revealed a cumulative increase in 1-3 vol. % in solvent up-take by HM-block copolymer bilayer films, so that we suggest other than dilution effect reasons for the observed significant enhancement of the chain mobility in concentrated block copolymer solutions. Another beneficial effect of the HM-support is the suppression of the film dewetting which holds true even for low molecular weight homopolymer polystyrene films at high degrees of swelling. Apart from immediate technological impact in block copolymer-assisted nanolithography, our findings convey novel insight into effects of molecular architecture on polymer-solvent interactions.

Self-alignment of zinc oxide nanorods into a 3D-smectic phase

We focus on thin films from ZnO nanorod dispersions in order to generate a high lateral order and a dense space filling structure applicable e. g. in printed optoelectronic devices. Highly stable dispersions with a solid content of up to 60wt.% in ethanol were prepared using trioxadecanoic acid as stabilizer. With the dispersions we prepared thin films on substrates with a 3D-smectic phase in lateral dimension of cm2 and thicknesses from below 100nm up to 1μm. We show how the concentration of the initial solid content is influencing the formation of domains in our films and discuss the self-assembly process into ordered structures.

Homopolymers as nanocarriers for the loading of block copolymer micelles with metal salts: a facile way to large-scale ordered arrays of transition-metal nanoparticles

A new and facile approach is presented for generating quasi-regular patterns of transition metal-based nanoparticles on flat substrates exploiting polystyrene-block-poly2vinyl pyridine (PS-b-P2VP) micelles as intermediate templates. Direct loading of such micellar nanoreactors by polar transition metal salts in solution usually results in nanoparticle ensembles exhibiting only short range order accompanied by broad distributions of particle size and inter-particle distance. Here, we demonstrate that the use of P2VP homopolymers of appropriate length as molecular carriers to transport precursor salts into the micellar cores can significantly increase the degree of lateral order within the final nanoparticle arrays combined with a decrease in spreading in particle size. Thus, a significantly extended range of materials is now available which can be exploited to study fundamental properties at the transition from clusters to solids by means of well-organized, well-separated, size-selected metal and metal oxide nanostructures.

Transient Effect of Calcium Influx on PIP2 Clusters and Cholesterol-Stabilized Nano-Domains in the Inner Plasma Membrane Leaflet of Intact Cells

When calcium ion channels open, local calcium levels are estimated to reach up to 500uM, which may be sufficient to affect negatively charged lipids, such as phosphatidylinositol 4,5-bisphosphate (PIP2), in the inner leaflet of the plasma membrane (PM). The PM is a complex lipid protein mixture in which at least two mechanisms create lateral order: interactions between the acyl-chains of the lipids, stabilized by Cholesterol, lead to transient submicroscopic nano-domains, and lipid head-group interactions of charged lipids with divalent ions may cluster lipids.

Analysis of the physical properties of developing cotton fibres

Cotton fibres develop over four stages: initiation, elongation, secondary-wall thickening, and maturation. They develop a significant crystalline structure during the secondary wall thickening stage of development. Cotton fibres were harvested from 17days to 60days after flowering (dpa). Transmission Electron Microscopy (TEM), Interferometry, Attenuated Total Reflectance Fourier–transform Infrared (ATR–FTIR) spectroscopy, immunofluorescence labelling, and fluorescence spectroscopy were used to characterise the cotton fibres in different stages. It was found that, secondary wall thickening and micronaire remain fairly constant from 17 to 24dpa, after that time significant change occurs until maturity. Maturity ratio increases as the fibres develop. Birefringence increases rapidly from 17dpa to 26dpa, then levels off up to 60dpa. It is evident by comparing the lateral order index (LOI) and results from the binding of a crystalline-cellulose binding probe (CBM3a) that there is a significant increase in the degree of cellulose crystallinity from 17dpa to 26dpa. Hydrogen Bond Intensity (HBI) increased to 24dpa and decreased from 24 to 40dpa indicating significant changes in inter-molecular hydrogen bonds. From 40 to 60dpa an increase of HBI was observed. It is concluded that during the maturation stage of cotton fibre development, water loss from lumen allows the cellulose chains to come closer together and to form intermolecular hydrogen-bonds. TEM, Interferometry, ATR–FTIR spectroscopy, and immunofluorescence labelling combined with fluorescence spectroscopy, were demonstrated to be useful techniques in quantifying physical changes in cotton fibres during development, offering advantages over traditional analytical techniques.

Orientation Control of Block Copolymer Thin Films Placed on Ordered Nanoparticle Monolayers

We investigate orientation and lateral ordering of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) diblock copolymer (diBCP) thin films placed on ordered nanoparticle (NP) monolayers. The densely packed NP monolayers were prepared on silicon substrates with the Langmuir–Blodgett (LB) deposition technique. The perpendicular domain orientation of BCP thin films is obtained on the ordered NP monolayers due to the nanoscale regular roughness which exerts the elastic deformation on the BCP nanodomains and suppresses the substrate-induced parallel orientation. The effect of BCP film thickness as well as the NP size on the orientation of BCP nanodomains was systematically investigated. We also demonstrate the defect-tolerant ordering of the perpendicular orientation of BCP thin films on the NP-vacant sites.

Multicomponent Nanopatterns by Directed Block Copolymer Self-Assembly

Complex nanopatterns integrating diverse nanocomponents are crucial requirements for advanced photonics and electronics. Currently, such multicomponent nanopatterns are principally created by colloidal nanoparticle assembly, where large-area processing of highly ordered nanostructures raises significant challenge. We present multicomponent nanopatterns enabled by block copolymer (BCP) self-assembly, which offers device oriented sub-10-nm scale nanopatterns with arbitrary large-area scalability. In this approach, BCP nanopatterns direct the nanoscale lateral ordering of the overlaid second level BCP nanopatterns to create the superimposed multicomponent nanopatterns incorporating nanowires and nanodots. This approach introduces diverse chemical composition of metallic elements including Au, Pt, Fe, Pd, and Co into sub-10-nm scale nanopatterns. As immediate applications of multicomponent nanopatterns, we demonstrate multilevel charge-trap memory device with Pt-Au binary nanodot pattern and synergistic plasmonic properties of Au nanowire-Pt nanodot pattern.

Liposomes as Vehicles for Lutein: Preparation, Stability, Liposomal Membrane Dynamics, and Structure

Lutein was loaded into liposomes, and their stability against environmental stress was investigated. Subsequently, these findings were correlated with the interactions between lutein and lipid bilayer. Results showed that the liposomes with loaded lutein at concentrations of 1 and 2% remained stable during preparation, heating, storage, and surfactant dissolution. However, with further increase in the loading concentration to 5 and 10%, the stabilization role of lutein on membrane was not pronounced or even opposite. Membrane fluidity demonstrated that at 1 and 2%, lutein displayed less fluidizing properties both in the headgroup region and in the hydrophobic core of the liposome, whereas this effect was not significant at 5 and 10%. Raman spectra demonstrated that lutein incorporation greatly affected the lateral packing order between acyl chains and longitudinal packing order of lipid acyl chains. These results may guide the potential application of liposomes as carriers for lutein in nutraceuticals and functional foods.

EFFECT OF PHOSPHORUS APPLICATION ON HIERARCHICAL LATERAL ROOT MORPHOLOGY AND PHOSPHORUS ACQUISITION IN SOYBEAN

Root growth systems are hierarchical and sensitive to nutrient availability in soil. Lateral roots are an important component of plant root morphology. Phosphorus (P) availability regulates root branching in plants such as Arabidopsis thaliana, barley (Hordeum vulgare), and rice (Oryza sativa L.). However, little information is available for soybean (Glycine max L.). A pot experiment was conducted to determine the morphological characteristics of lateral roots of different orders and P acquirement of soybean seedlings under three levels of applied P of 0, 50 and 100 mg P kg−1 soil. Root length, an important parameter of root characteristics, differed in four orders. Lateral roots in the second and third order contributed 39.4 and 34.2% of total root length, respectively. Moreover, since most of lateral roots were fine roots (roots having a diameter 0.5 mm), fine roots had a frequency distribution of 58.5 to 61.4% in the second and third orders. Phosphorus application significantly increased dry weight, total length and number of lateral roots in the four orders with the ranking of fourth > third > second > first (P ≤ 0.05), but did not affect the average length of a lateral root. Phosphorus application reduced the frequency distribution of fine lateral roots in the first and second orders, while increased in the third and fourth orders (P ≤ 0.05). Compared with the medium P application (50 mg P kg−1 soil), the high P application (100 mg P kg−1 soil) inhibited lateral root growth with decreases in root dry weight, root length and root number at all orders. Phosphorus concentration and content increased with the increase in P application. The correlation between characteristics of lateral root and P status in the plants varied among root orders. The length of lateral roots from first to third order had a positive correlation with P concentration in root and shoot, and had a good relationship with P content. Lateral root numbers at the second, third and fourth orders were significantly correlated with P content while no correlation was found with the average length of a lateral root. It is proposed that the main effect of P application appears to be on the lateral root initiation rather than on lateral root elongation, and P favors the lateral root formation of the higher orders. The total length and number of lateral root at the second and third orders play a more important role in P content than those at other lateral root orders.

ORDERING IN DENSE FIBER BUNDLES, THE PHYLLOTACTIC SOLUTION AND ITS APPLICATION TO COLLAGEN FIBRILS

The shape of the cross section of a dense fiber bundle is related to the symmetry of its molecular packing. However, this statement might be belied by type I collagen fibrils which have a rounded section of high symmetry while structural studies suggest that their molecules are assembled with a long range lateral order of lower symmetry. We examine how phyllotaxis, which is a nonconventional crystallographic solution to packing efficiency in situations of high radial symmetry, can establish a link between those two apparently conflicting points. The lateral order imposed by the algorithm of phyllotaxis, which implies an enlargement of the notion of long range lateral order beyond that used for classical crystals, provides a basis for a new analysis of the experimental data.

Solvent‐Assisted Directed Self‐Assembly of Spherical Microdomain Block Copolymers to High Areal Density Arrays

The fabrication process for 5 Tb/in(2) bit patterns using solvent-assisted directed self-assembly is investigated. The N-methyl-2-pyrrolidone solvent vapor-annealing method was used to achieve good long-range lateral ordering of low-molecular-weight polystyrene-block-polydimethylsiloxane with a lattice spacing of 11 nm on flat Si substrates, PS modified substrates and lithographically patterned substrates, respectively.

A new dasycladalean alga from the Lower Cretaceous of the Eastern Carpathians (Romania): Andreiella rajkae nov. gen., nov. sp.

Lower Cretaceous limestones from Bicaz Gorges (Eastern Carpathians, Romania), developed in Urgonian facies, frequently contain dasycladalean algae. In limestone samples collected from the eastern sector of the Bicaz Gorges, we have identified a large dasycladalean alga that we assign here to a new species and genus: Andreiella rajkae nov. gen. nov. sp. The general morphological features and the calcification pattern distinguish this new alga from previously known dasycladaleans with two orders of laterals.

Effect of lignocellulosic composition and structure on the bioethanol production from different poplar lines

Branches from three transgenic poplar lines and their wild type line 107 were used to study the effect of lignocellulosic composition and structure on the production of glucose and ethanol. Experimental results showed that the transgenic line 18-1 had the high cellulose content and amorphous fibril structure. After poplar meals were pretreated with 10% NaOH and a mixture of hydrogen peroxide and acetic acid, their lateral order index decreased significantly. The highest glucose yield in enzymatic hydrolysis and ethanol yield from the substrate of 18-1 was much higher than that from feedstock of 107 by 192.7% and 108.7%, respectively. Scanning electron microscopy images confirmed that lignocellulose from the 18-1 could be destroyed by chemicals more easily than those from other lines. These results demonstrated that changing lignocellulose structure could be more effective on improving the digestibility and enzymatic hydrolysis of poplar biomass than increasing the cellulose content in biomass.

Solid State NMR Strategy for Characterizing Native Membrane Protein Structures

Unlike water soluble proteins, the structures of helical transmembrane proteins depend on a very complex environment. These proteins sit in the midst of dramatic electrical and chemical gradients and are often subject to variations in the lateral pressure profile, order parameters, dielectric constant, and other properties. Solid state NMR is a collection of tools that can characterize high resolution membrane protein structure in this environment. Indeed, prior work has shown that this complex environment significantly influences transmembrane protein structure. Therefore, it is important to characterize such structures under conditions that closely resemble its native environment. Researchers have used two approaches to gain protein structural restraints via solid state NMR spectroscopy. The more traditional approach uses magic angle sample spinning to generate isotropic chemical shifts, much like solution NMR. As with solution NMR, researchers can analyze the backbone chemical shifts to obtain torsional restraints. They can also examine nuclear spin interactions between nearby atoms to obtain distances between atomic sites. Unfortunately, for membrane proteins in lipid preparations, the spectral resolution is not adequate to obtain complete resonance assignments. Researchers have developed another approach for gaining structural restraints from membrane proteins: the use of uniformly oriented lipid bilayers, which provides a method for obtaining high resolution orientational restraints. When the bilayers are aligned with respect to the magnetic field of the NMR spectrometer, researchers can obtain orientational restraints in which atomic sites in the protein are restrained relative to the alignment axis. However, this approach does not allow researchers to determine the relative packing between helices. By combining the two approaches, we can take advantage of the information acquired from each technique to minimize the challenges and maximize the quality of the structural results. By combining the distance, torsional, and orientational restraints, we can characterize high resolution membrane protein structure in native-like lipid bilayer environments.

Molecular Self-Assembly at Metal-Electrolyte Interfaces

The self-assembly of molecular layers has become an important strategy in modern design of functional materials. However, in particular, large organic molecules may no longer be sufficiently volatile to be deposited by vapor deposition. In this case, deposition from solution may be a promising route; in ionic form, these molecules may even be soluble in water. In this contribution, we present and discuss results on the electrochemical deposition of viologen- and porphyrin molecules as well as their co-adsorption on chloride modified Cu(100) and Cu(111) single crystal electrode surfaces from aqueous acidic solutions. Using in situ techniques like cyclic voltametry and high resolution scanning tunneling microscopy, as well as ex-situ photoelectron spectroscopy data the highly ordered self-assembled organic layers are characterized with respect to their electrochemical behavior, lateral order and inner conformation as well as phase transitions thereof as a function of their redox-state and the symmetry of the substrate. As a result, detailed structure models are derived and are discussed in terms of the prevailing interactions.