Lamellar Stacks Research Articles

Ectothiorhodospira lacustris sp. nov., a New Purple Sulfur Bacterium from Low-Mineralized Soda Lakes That Contains a Unique Pathway for Nitric Oxide Reduction

Several strains of a Gram-negative, anaerobic photoautotrophic, motile, rod-shaped bacterium, designated as B14B, A-7R, and A-7Y were isolated from biofilms of low-mineralized soda lakes in central Mongolia and Russia (southeast Siberia). They had lamellar stacks as photosynthetic structures and bacteriochlorophyll a as the major photosynthetic pigment. The strains were found to grow at 25–35 °C, pH 7.5–10.2 (optimum, pH 9.0), and with 0–8% (w/v) NaCl (optimum, 0%). In the presence of sulfide and bicarbonate, acetate, butyrate, yeast extract, lactate, malate, pyruvate, succinate, and fumarate promoted growth. The DNA G + C content was 62.9–63.0 mol%. While the 16S rRNA gene sequences confirmed that the new strains belonged to the genus Ectothiorhodospira of the Ectothiorhodospiraceae, comparison of the genome nucleotide sequences of strains B14B, A-7R, and A-7Y revealed that the new isolates were remote from all described Ectothiorhodospira species both in dDDH (19.7–38.8%) and in ANI (75.0–89.4%). The new strains are also genetically differentiated by the presence of a nitric oxide reduction pathway that is lacking from all other Ectiothiorhodospiraceae. We propose to assign the isolates to the new species, Ectothiorhodospira lacustris sp. nov., with the type strain B14BT (=DSM 116064T = KCTC 25542T = UQM 41491T).

Chiral Polymer Dots Show Unexpected Versatility of Highly Ordered Self-Assembly into Chiroptical Liquid Crystals, Ultra-Thin Films, and Long-Ribbons.

Compared to the organic counterparts, chiral self-assembly of nanomaterials shows persistency to kinetic factors such as solvent environments, and consequently, dynamic modulation of self-assembly and functions remains major challenge. Here, it is shown that alkylated, chiral polymer dots (c-PDs) give highly ordered self-assemblies with amplified chirality adaptive to solvent environments, and one-to-many hierarchical aggregation can be realized. The c-PDs tended to self-assemble into nanohelices with cubic packing in the solid state, which, thanks to the thermo-responsiveness, transformed into thermic liquid crystals upon heating. Cotton effects and circularly polarized luminescence evidenced the chirality transfer from central chirality to supramolecular chirality. At the air-water interface, the c-PDs are self-assembled into monolayers, which further stack into multiple layers with chirality transfer and highly ordered packing. In addition, undergoing a good/poor solvent exchange, the c-PDs afforded ultra-long microribbons up to a length scale of millimeters, which are constituted by the bilayer lamellar stacking. The versatile chiral self-assembly modalities with long-range ordered packing arrays of carbonized c-PDs via solvent strategy are realized. This feature is comparable to the organic species, although the c-PDs have no atomic precise structures. This work would surely expand the applications of quantum dot ordered self-assembly with adaptiveness to kinetic factors.

Blended Conjugated Host and Unconjugated Dopant Polymers Towards N‐type All‐Polymer Conductors and High‐ZT Thermoelectrics

AbstractN‐Type thermoelectrics typically consist of small molecule dopant+polymer host. Only a few polymer dopant+polymer host systems have been reported, and these have lower thermoelectric parameters. N‐type polymers with high crystallinity and order are generally used for high‐conductivity ( ) organic conductors. Few n‐type polymers with only short‐range lamellar stacking for high‐conductivity materials have been reported. Here, we describe an n‐type short‐range lamellar‐stacked all‐polymer thermoelectric system with highest of 78 S−1, power factor (PF) of 163 μW m−1 K−2, and maximum Figure of merit (ZT) of 0.53 at room temperature with a dopant/host ratio of 75 wt%. The minor effect of polymer dopant on the molecular arrangement of conjugated polymer PDPIN at high ratios, high doping capability, high Seebeck coefficient (S) absolute values relative to , and atypical decreased thermal conductivity ( ) with increased doping ratio contribute to the promising performance.

Blended Conjugated Host and Unconjugated Dopant Polymers Towards N-type All-Polymer Conductors and High-ZT Thermoelectrics.

N-Type thermoelectrics typically consist of small molecule dopant+polymer host. Only a few polymer dopant+polymer host systems have been reported, and these have lower thermoelectric parameters. N-type polymers with high crystallinity and order are generally used for high-conductivity ( ) organic conductors. Few n-type polymers with only short-range lamellar stacking for high-conductivity materials have been reported. Here, we describe an n-type short-range lamellar-stacked all-polymer thermoelectric system with highest of 78 S-1 , power factor (PF) of 163 μW m-1 K-2 , and maximum Figure of merit (ZT) of 0.53 at room temperature with a dopant/host ratio of 75 wt%. The minor effect of polymer dopant on the molecular arrangement of conjugated polymer PDPIN at high ratios, high doping capability, high Seebeck coefficient (S) absolute values relative to , and atypical decreased thermal conductivity ( ) with increased doping ratio contribute to the promising performance.

Keto-enamine-based covalent organic framework with controllable anthraquinone moieties for superior H2O2 photosynthesis from O2 and water

Photocatalytic H2O2 production is a promising strategy for decentralized applications, but to realize efficient H2O2 production in the ambient conditions and absence of organic sacrifice remains challengeable. Herein, anthraquinone functionalized covalent organic frameworks (TpAQ-COFs) were fabricated by β-ketoenamines links of 2,6-diaminoanthraquinone (AQ) and 2, 4, 6-triformylphloroglucinol (Tp), and the structures and compositions were tuned by controlling the condensation time. The increase of time favors the assembly of TpAQ-COFs into more ordered lamellar stacking structure, and induces the increase of enol-imine form. The critical role of anthraquinone moieties as the active sites for oxygen reduction was proved, that is, facilitating charge separation and enhancing the activity and selectivity of H2O2 production. Upon visible light irradiation, the TpAQ-COF synthesized after 12 h reaction has the highest content of anthraquinone moieties and the best performance for H2O2 production (420 μmol h−1 g−1) in the absence of organic sacrificial agents. These findings bring insights to incorporate anthraquinone chemistry into photocatalysts at molecular levels for efficient H2O2 production.

Plastic contribution via DRX induced by kink and twin in a hot compressed Mg-Gd-Zn-Mn alloy with 14H LPSO

The plastic deformation behavior in Mg alloy with long period stacking ordered phases (LPSO) has not fully understood yet. To understand the interaction between twins, kink and dynamic recrystallization in a Mg alloy with long period stacking ordered phases, the plastic forming behavior under compression at elevated temperatures of the Mg-4Gd-1Zn-0.5Mn alloys containing lamellar long period stacking order phases were investigated. The lamellar long period stacking ordered phases hindered the occurrence of grain boundary migration, thus delaying dynamic recrystallization. The dominated deformation mechanisms of the compressed alloy were slip and discontinuous dynamic recrystallization accompanied by the occurrence of kink bands at low deformation rates. The twinning was the domination deformation mechanisms of the alloy at high deformation rates, a few recrystallized grains distributed along the boundaries of the twins and it was an obvious twin-induced dynamic recrystallization mechanism. The dissolving of long period stacking ordered phases reduced the grain boundary migration resistance of dynamic recrystallization and thus promoted the nucleation of the recrystallized grains at 500 °C. The broken small-sized lamellar long period stacking ordered phases became effective heterogeneous nucleation sites and thus promoted DRX. The parallel and beak-like kink bands are clearly observed in the microstructures of the deformed alloys. The severe kink behavior improves the plastic formability of the alloy.

Multi-ion competition mechanism within MXene interlayer and Li ion intercalated electrode function

2D layered MXene material offers atomic level intervals that can expand the function of ion intercalated electrode. Challenges remain in modulating the interlayer environment and overcome the problem of lamellar stacking. Herein, to accurate control the interlayer structure of MXene and understand these ions confined by MXene, Li+, Na+ and K+ are pre-inserted into the inner space, which is the spaced voids of two adjacent Ti3C2Tx MXene layers with Al3+ ions, and the relationship between the interlayer spacing and the multi-ion interaction mechanism is explored. Furthermore, the electrochemical behavior and performance induced by multi-ion intercalated MXene electrodes are evaluated. The results show that the capacity of MXene electrodes with Na+ pre-intercalation obtained a capacity of 250.80 mAh g−1, and the capacity is maintained after 200 cycles is 179.67 mAh g−1, which attenuation is 28.36%. In addition, the pre-intercalated Na+ ions can maintain a more stable structure and benefit to electrochemical cycling performance than these pre-intercalated Li+ ions occupying the transport channels of the electrolyte ion. It provides data support for in-depth understanding of the mechanism and derivation of ion pre-intercalated MXene.

Liquid Phase Exfoliation of Chemically Prelithiated Bilayered Vanadium Oxide in Aqueous Media for Li-Ion Batteries

Bilayered vanadium oxides are attractive for energy storage due to their high initial specific capacities, which could be stabilized by integrating the bilayers with conductive nanoflakes often produced in a form of aqueous dispersions. Therefore, exfoliation of the bilayered vanadium oxides in water with high yield is desirable. This work introduces the first aqueous exfoliation of chemically prelithiated bilayered vanadium oxide (i.e., δ-LixV2O5·nH2O or LVO) followed by vacuum filtration to produce a free-standing film, exhibiting a lamellar stacking of the bilayered vanadium oxide nanoflakes as evidenced by scanning electron microscopy. Due to the hydrated nature of bilayered vanadium oxides, the relationship between interlayer water content and the vacuum drying temperature (105 °C vs 200 °C) was studied using X-ray diffraction, thermogravimetric analysis, and Raman spectroscopy. It was found that vacuum drying the LVO nanoflakes at 200 °C enabled more efficient removal of crystallographic water than drying at 105 °C, and did not induce a phase transformation. Scanning transmission electron microscopy confirmed the layered structure of the samples, which was more well-ordered in the 200 °C case and had no clear boundaries between flakes at the atomic scale. Furthermore, electrochemical testing in nonaqueous Li-ion cells revealed that vacuum drying at 200 °C led to improvements in ion storage capacity and electrochemical stability. Improvements in electrochemical charge storage properties of the electrodes obtained via LVO exfoliation and free-standing film assembly in water dried at 200 °C reveal that conventional battery electrode drying protocols need to be revised as new electrochemically active materials are synthesized, such as hydrated layered oxides with expanded interlayer regions. The remaining capacity fading can be attributed to the structural LVO degradation, dissolution of vanadium oxide in electrolyte, and parasitic effects of the remaining interlayer water molecules. Our results establish an environmentally friendly and safe approach to obtain two-dimensional (2D) bilayered vanadium oxide nanoflakes and create a pathway to constructing novel 2D heterostructures for improved performance in energy storage applications.

Thermal Conduction and Phonon Transport in Folded Polyethylene Chains

Using theory and simulations, we have investigated the phonons and their role in thermal energy transport in semicrystalline polyethylenes. Considering alternating stacks of lamellae and amorphous regions, and labeling one polyethylene chain interwoven among two amorphous regions and one lamella, we have explored the underlying mechanism of thermal conductivity of polyethylene in its semicrystalline state. We report that hairpin-like folds at the crystalline–amorphous interface significantly scatter phonons, allowing only less than half of the phonons to transmit through polyethylene backbone. Monitoring the phonon propagation and scattering at the interfaces, we have computed thermal conductivity of semicrystalline polyethylene. We have derived a design principle to control thermal conductivity of semicrystalline polyethylene in terms of lamellar thickness and the number of folds per chain at the crystalline–amorphous interface.

Lamellar diffraction from lipid bilayers on MIRA, a triple axis spectrometer at the MLZ

Diffraction used in conjunction with molecular deuteration provides a model independent means to examine detailed structural and compositional information of model and real biological membranes in the lamellar phase. The technique provides specific information of localization of molecules and smaller units with respect to the unit cell. Deuteration is used to provide specific labelling and to provide phasing for the crystallographic reconstruction. Typical data sets consist of a series of lamellar diffraction peaks, usually collected under conditions of 3 contrasts of the water gas phase. Accurately integrated the diffraction peaks can be used for a Fourier reconstruction of the composition of the lamellar unit cell in real space. Each diffraction peak which can be integrated for 3 contrasts contributes to an additional Fourier term in the reconstruction and optimization of the number of peaks enhances the spatial resolution of the crystallographic reconstruction. Here we report on the use of the flexibly configurable cold triple-axis spectrometer, MIRA, at the Heinz Maier-Leibnitz Zentrum (Garching, Germany) for investigations of different lamellar systems using this approach. The data sets are acquired from lamellar stacks in an sample environment with humidity and temperature control with exceptionally low background. We discuss further enhancements of the instrument and sample environment which will provide information on the composition and equilibration of the sample.

An investigation into the modification of microwave-assisted oxidation in the macromolecular structure of coal via XRD and Raman spectroscopy

The macromolecular structure of coal governs the generation and expansion of micro/mesopores, contributing significantly to the storage and transport of coalbed methane (CBM). To reveal the modification mechanism of microwave-assisted oxidation at molecular scale, this paper presents a comprehensive analysis of the evolutionary characteristics of macromolecular structure of coal using X-ray diffraction and Raman spectroscopy tests. Results show that microwave irradiation triggers the conversion of ordered graphitic crystalline carbon to amorphous carbon, as well as the condensation and heterogeneous spatial arrangement of aromatic clusters. The oxidation of NaClO or Na2S2O8 destroys the initial aromatic structure and reduces the aromaticity of coal, whereas Fenton's reagent oxidation causes the cyclocondensation of macromolecular structure and contributes to the graphitization and crystallization of coal. Microwave-assisted oxidation not only facilitates the directional growth of aromatic rings and the cross-linking of aliphatic chains, but also induces the rotation, displacement, stacking and gradual parallel alignment of aromatic lamellae, thus improving the integrity of three-dimensional lattice of graphite structure and the orderliness of macromolecular structure. As the average size of microcrystalline structural units increases and align directionally to form molecularly oriented domains, the pore size and volume subsequently increases, thereby enhancing the gas transport capacity of coal and the extraction of CBM. This study provides theoretical guidance for the optimisation of microwave-assisted oxidant modification and the paramount consideration of CBM development strategy.

Effect of lamellar LPSO phase on mechanical properties and damping capacity in cast magnesium alloys

The effect of the lamellar long period stacking order (LPSO) phase on both mechanical properties and damping capacity of magnesium alloys is still vague. After heat treatment at 540 °C for 4 h and 450 °C for 10 h, the Mg-10Gd-2Y–1Zn-0.5Zr-0.2Nd (wt%) alloy with the lamellar LPSO phase is prepared to study the influence of lamellar LPSO phase on damping capacity and mechanical properties. Combined transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with electron back-scattering patterns (EBSD) system, it is surprisingly found that the growth direction of the lamellar LPSO phase on basal plane is nearly parallel to the slip direction of basal dislocations, which is benefit from dislocations movement on basal plane. The dislocations move on basal plane easily, lead to a relative high damping capacity. The alloy with LPSO phases shows higher ultimate tensile strength (UTS) and elongation (EL), increased from 234 MPa to 2.6% to 254 MPa and 4.6%, respectively. The lamellar LPSO phase has an attribution to UTS and EL due to its kink deformation mechanism. Therefore, the lamellar LPSO phase can be used as a functional phase to enhance the damping capacity and mechanical properties at the same time, and providing new ideas about preparing high-strength and high-damping magnesium alloy.

Two-step post-treatment to deliver high performance thermoelectric device with vertical temperature gradient

The power factor of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film can be significantly improved by optimizing the oxidation level of the film in oxidation and reduction processes. However, precise control over the oxidation and reduction effects in PEDOT:PSS remains a challenge, which greatly sacrifices both S and σ. Here, we propose a two-step post-treatment using a mixture of ethylene glycol (EG) and Arginine (Arg) and sulfuric acid (H2SO4) in sequence to engineer high-performance PEDOT:PSS thermoelectric films. The high-polarity EG dopant removes the excess non-ionized PSS and induces benzenoid-to-quinoid conformational change in the PEDOT:PSS films. In particular, basic amino acid Arg tunes the oxidation level of PEDOT:PSS and prevents the films from over-oxidation during H2SO4 post-treatment, leading to increased S. The following H2SO4 post-treatment further induces highly orientated lamellar stacking microstructures to increase σ, yielding a maximum power factor of 170.6 μW m−1 K−2 at 460 K. Moreover, a novel trigonal-shape thermoelectric device is designed and assembled by the as-prepared PEDOT:PSS films in order to harvest heat via a vertical temperature gradient. An output power density of 33 μW cm−2 is generated at a temperature difference of 40 K, showing the potential application for low-grade wearable electronic devices.

Freestanding wide layer spacing MoS2@WS2@CC ternary structure with fast diffusion path for a highly activity zinc-ion batteries

Water system zinc ion batteries (ZIBs) displays the attractive advantages and it has been considered as the main energy storage device to replace lithium ion batteries (LIBs). Unfortunately, the existing cathode materials are far from achieving the excellent performance required by increasing energy consumption. In recent years, the popular MoS2 materials still suffer from the inherent defects of poor electrical conductivity, unstable structure, and large volume expansion and lamellar stacking during charging and discharging, resulting in weak periodic stability and severely hindering its commercial applications. In view of the special requirements of cathode materials for ZIBs, this work innovatively proposes the construction of new-type ternary composite nanomaterials, comprehensively improve the practicability of MoS2 materials. The experimental results confirm that the prepared MoS2@WS2@CC composite material has high specific capacity and excellent rate performance, due to the synergistic effect of conductive carbon fiber substrate and large layer spacing WS2 which can improve the volume expansion and diffusion rate fundamentally. Therefore, we can predict that the MoS2@WS2@CC composite is expected to accelerate the commercial application of ZIBs, and provide ideas for the design of other energy storage materials.

Synergistic Contribution of Oligo(ethylene glycol) and Fluorine Substitution of Conjugated Polymer Photocatalysts toward Solar Driven Sacrificial Hydrogen Evolution.

To separately explore the importance of hydrophilicity and backbone planarity of polymer photocatalyst, a series of benzothiadiazole-based donor-acceptor alternating copolymers incorporating alkoxy, linear oligo(ethylene glycol) (OEG) side chain, and backbone fluorine substituents is presented. The OEG side chains in the polymer backbone increase the surface energy of the polymer nanoparticles, thereby improving the interaction with water and facilitating electron transfer to water. Moreover, the OEG-attached copolymers exhibit enhanced intermolecular packing compared to polymers with alkoxy side chains, which is possibly attributed to the self-assembly properties of the side chains. Fluorine substituents on the polymer backbone produce highly ordered lamellar stacks with distinct π-π stacking features; subsequently, the long-lived polarons toward hydrogen evolution are observed by transient absorption spectroscopy. In addition, a new nanoparticle synthesis strategy using a methanol/water mixed solvent is first adopted, thereby avoiding the screening effect of surfactants between the nanoparticles and water. Finally, hydrogen evolution rate of 26000 µmolg-1 h-1 is obtained for the copolymer incorporated with both OEG side chains and fluorine substituents under visible-light irradiation (λ> 420nm). This study demonstrates how the glycol side chain strategy can be further optimized for polymer photocatalysts by controlling the backbone planarity.

Stack of cellular lamellae forms a silvered cortex to conceal the opaque organ in a transparent gastropod in epipelagic habitat.

Gelatinous zooplankton in epipelagic environments often have highly transparent bodies to avoid detection by their visual predators and prey; however, the digestive systems are often exceptionally opaque even in these organisms. In a holoplanktonic gastropod, Pterotrachea coronata, the visceral nucleus is an opaque organ located at the posterior end of its alimentary system, but this organ has a mirrored surface to conceal its internal opaque tissue. Our ultrastructural observation proved that the cortex of the visceral nucleus comprised a stack of thin cellular lamellae forming a Bragg reflector, and the thickness of lamellae (0.16 µm in average) and the spaces between the lamellae (0.1 µm in average) tended to become thinner toward inner lamellae. Based on the measured values, we built virtual models of the multilamellar layer comprising 50 lamellae and spaces, and the light reflection on the models was calculated using rigorous coupled wave analysis to evaluate their properties as reflectors. Our simulation supported the idea that the layer is a reflective tissue, and the thickness of the lamella/space must be chirped to reflect sunlight as white/silver light, mostly independent of the angle of incidence. In P. coronata, the cortex of the visceral nucleus comprised multicellular lamellae that form a chirped Bragg reflector. It is distinct in structure from the intracellular Bragg structures of common iridophores. This novel Bragg reflector demonstrates the diversity and convergent evolution of reflective tissue using reflectin-like proteins in Mollusca.

Solvent‐Induced Polymorphism in Non‐Fullerene‐Based Organic Solar Cells

Organic photovoltaics have achieved breakthroughs in power conversion efficiency due to the superior aggregation and packing nature of non‐fullerene acceptors (NFAs). Solution processing and various treatments would tend to form distinct packing motifs for state‐of‐the‐art NFAs. Herein, the solvent‐induced polymorphism for 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophne) (ITIC) prepared by chloroform (CF) and chlorobenzene (CB) is revealed. The packing motif of ITIC exhibits dense π–π stacking from CF induction, which presents red‐shifted absorption and reversible high‐temperature crystallization and melting. Meanwhile, strong lamellar stacking and π–π stacking can be formed in the CB solution with unstable low‐temperature crystallization and melting. Combining in situ absorption spectra and interaction calculation, the stronger preaggregation of ITIC in the CF solution was found to be the main reason for forming a different packing motif from in the CB solution. The packing and thermodynamic features are retained in the PBDB‐T:ITIC blends, though good miscibility weakens characteristic features. Benefiting from the polymorph structure, CB‐processed devices denote more favorable performance but less thermal stability. This research indicates the significant effect of solvent induction for manipulating and optimizing the morphology of organic solar cell devices.

Freezing of Rotation of P3HT Crystallites by PCBM Molecules during Thermal Relaxation of the Blend Thin Films

AbstractPoly(3‐hexylthiophene), or P3HT, is a semicrystalline polymer with charge conduction anisotropy with respect to its different axes, which calls for gaining better control of texture for targeted device applications. A blend system of P3HT and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) is studied for understanding the role of PCBM in texture control of P3HT crystallites. 2D grazing incidence diffraction (2D‐GIXD) combined with high resolution grazing incidence X‐ray diffraction (1D‐GIXD) is performed on thin films of pristine P3HT and blend (P3HT/PCBM) thin films prepared by spin coating. Thermal annealing at 110 °C is used for relaxing the films. The lamellar P3HT crystallites preferably orient along the surface plane with lamellar stacking in a vertical direction and have a distribution of orientation with a limiting angle of 44°. In the pristine P3HT system, the rotations of crystallites are confirmed by the retreat of the limiting angle. The observed intensity cross‐over for precursor and annealed samples is again the signature of the rotations of crystallites. For the blend system, the intensity cross‐over is absent and there is no sign of retreat of the limiting angle, which explicitly confirms the blocking of rotation lamellar crystallites. This study provides, for the first time, the clear evidence with unambiguous analysis of blocking of rotation of crystallites due to presence of PCBM, which is explained with an analogy of the “ball‐and‐stick” mechanism. Atomic force microscopy (AFM) studies of surface morphology correlates with the above findings.

Two-Stage Evolution of Gamma-Phase Spherulites of Poly (Vinylidene Fluoride) Induced by Alkylammonium Salt.

We investigated the evolution of the γ-phase spherulites of poly(vinylidene fluoride) (PVDF) added to 1 wt% of tetrabutylammonium hydrogen sulfate during the isothermal crystallization at 165 °C through polarized optical microscopy and light scattering measurements. Optically isotropic domains grew, and then optical anisotropy started to increase in the domain to yield spherulite. Double peaks were seen in the time variation of the Vv light scattering intensity caused by the density fluctuation and optical anisotropy, and the Hv light scattering intensity caused by the optical anisotropy started to increase during the second increase in the Vv light scattering intensity. These results suggest the two-stage evolution of the γ-phase spherulites, i.e., the disordered domain grows in the first stage and ordering in the spherulite increases due to the increase in the fraction of the lamellar stacks in the spherulite without a change in the spherulite size in the second stage. Owing to the characteristic crystallization behavior, the birefringence in the γ-phase spherulites of the PVDF/TBAHS was much smaller than that in the α-phase spherulites of the neat PVDF.

A combined TEM and SAXS study of the growth and self-assembly of ultrathin Pt nanowires

Ultrathin Pt nanowires possess high activity for various electrocatalytic applications. However, little work has focused on understanding their growth mechanisms. Herein, we utilize a combination of time-dependent, ex situ transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS) techniques to observe the growth process in addition to associated surfactant-based interactions. TEM images indicate that initially nanoparticles are formed within 30 s; these small ‘seed’ particles quickly elongate to form ultrathin nanowires after 2 min. These motifs remain relatively unchanged in size and shape up to 480 min of reaction. Complementary SAXS data suggests that the initial nanoparticles, which are coated by a surfactant bilayer, arrange into a bcc superlattice. With increasing reaction time, the bcc lattice disappears as the nanoparticles grow into nanowires, which then self-assemble into a columnar hexagonal structure in which the individual nanowires are covered by a CTAB monolayer. The hexagonal structure eventually degrades, thereby leading to the formation of lamellar stacking phases comprised of surfactant bilayers. To the best of our knowledge, this is the first time that SAXS has been used to monitor the growth and self-assembly of Pt nanowires. These insights can be used to better understand and rationally control the formation of anisotropic motifs of other metallic nanostructures.