Stacking Of Chains Research Articles

High Conductivity in PEDOT:PSS Thin‐Films by Secondary Doping with Superacid Vapor: Mechanisms and Application to Thermoelectrics

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a conductive polymer, have attracted attention as promising materials for future electronic applications, owing to its tunable doping level for high electrical conductivity (σ) through simple post‐treatments. A novel post‐treatment method for conventionally doped PEDOT:PSS thin‐films (immersed in methanol) is presented to further enhance σ via doping with the superacid, trifluoromethanesulfonic acid (TFSA). The origin of the improved σ in PEDOT:PSS thin‐films treated with this dual approach is investigated. The study reveals that the superacid vapor treatment uniquely enhances the lamellar stacking of PEDOT chains and induces vertical phase separation between PEDOT and PSS, leading to improved carrier mobility by a factor of three. This behavior differs from conventional post‐treatments, making the combined methanol immersion and TFSA vapor treatment an effective strategy for achieving a high σ of ≈2053 S cm−1, making these films ideal candidates for various polymer‐based electronics. Furthermore, the findings demonstrate that the thermoelectric power factor of PEDOT:PSS subjected to secondary doping with superacid vapor exhibits a threefold enhancement (104.2 µW m−1 K−2) compared to samples treated solely with methanol (29.7 µW m−1 K−2). This post‐treatment method and the resulting insights will advance the understanding of doping mechanisms and charge transport in conductive polymers.

Syntheses and Crystal Structures of Two Metal–Organic Frameworks Formed from Cd2+ Ions Bridged by Long, Flexible 1,7-bis(4-Pyridyl)heptane Ligands with Different Counter-Ions

The ethanol–water layered syntheses and crystal structures of the coordination polymers [Cd(C17H22N2)2(H2O)2]·2(ClO4)·C17H22N2·C2H5OH 2 and [Cd(C17H22N2)2(NO3)2] 3 are reported, where C17H22N2 is a flexible spacer, 1,7-bis(4-pyridyl)heptane. In compound 2, trans-CdO2N4 octahedral nodes are linked by pairs of bridging ligands to result in [001] looped polymeric chains. The chains stack in the [100] direction to form (010) pseudo layers. Sandwiched between them are secondary sheets of free ligands, perchlorate ions and ethanol solvent molecules. Hydrogen bonds between these species help to consolidate the structure. Compound 3 contains trans-CdO2N4 octahedral nodes as parts of regular 44 nets, which propagate in the (103) plane. Three independent nets are interpenetrated.

Size scalability of Monte Carlo simulations applied to oxidized polypyrrole systems

Oxidized polypyrrole (PPy) is a conducting polymer with diverse applications such as supercapacitors, sensors, batteries, actuators, neural prosthetics, among others. PPy is most commonly synthesized for the specific application yielding low molecular weight oligomers that form amorphous polymer matrices. Hence, molecular simulation analyses are challenging. This work generalizes the recently proposed coarse grained force field (CGFF) for halogen oxidized PPy in the condensed phases and introduces a novel implementation of the Monte Carlo (MC) simulation based on the CGFF that enables simulations of polymer systems with more than 100000 particles. The MC implementation utilizes a combination of CPU and GPUs and exploits a numerical approximation based on polynomial piecewise interpolation for the calculation of the CGFF pairwise additive terms. The MC simulations evidence that the oxidized PPy thermodynamic and structural properties are consistent as the system size is scaled up. Predicted properties include density, enthalpy, potential energy, heat capacity, coefficient of thermal expansion, caloric curve, glass transition temperature range, compressibility, bulk modulus, radial distribution functions, and polymer chain characteristics. The oxidized PPy samples display oligomer chain stacking that persists with temperatures up to the glass transition. Simulated properties are consistent with experimental observations when available and predict trends in all other cases.

Synthesis and characterization of polyimides with rigid folded fragments

The macromolecular chain of conventional polyimide (PI) is a predominant linear extension, which is anticipated to uphold robust interchain interactions essential for preserving overall mechanical and thermal performance. This study is dedicated to the design and synthesis for the novel PIs containing folded chains, with a particular emphasis on modifying the chain conformational behavior with respect to the structure of the aggregation state and the corresponding gas separation properties. First, two unidirectional diamine monomers, dibenzo [c, g] phenanthrene-9,12-diamine (NPDA) and anthracene-1,8-diamine (ADA), were meticulously synthesized through a sequence of chemical reactions, including Witting olefination and photocyclization. These monomers possess distinctive spatial characteristics: NPDA adopts a helical conformation, while ADA maintains a planar structure. Subsequently, the corresponding folded chain-containing PIs, denoted as NPI and API, were successfully achieved by copolymerizing one of the unidirectional monomers with the 6FDA-TPDA system. API and NPI generally exhibit a propensity for enhanced molecular chain stacking, while retaining their good solubility and processability. Drawing from both experimental data and simulation results, it was ascertained that the inclusion of these two monomers produces a rearrangement of pore sizes with a decrease in large-size micropores and an increase in the percentage of ultra-micropores. Moreover, the PI membranes with the folded fragments have a much better CO2 plasticization resistance.

Carbon nanotube intermediate layer intercalation and its influence on surface charge of thin film composite membrane

The surface charge of a separation membrane is a critical factor affecting its performance in ion separation and fouling resistance. Thin-film composite (TFC) polyamide (PA) membrane, commonly used in water treatment, often suffer from excessive surface negative charges, which significantly limits their application and fouling resistance. To address this issue, this work introduces a carbon nanotubes (CNT) intermediate layer to adjust the surface charge of TFC PA membranes, aiming to achieve a PA layer with neutral properties. Novel grazing-incidence wide-angle x-ray scattering (GIWAXS) measurements were employed to elucidate the effect of CNT on the molecular chain stacking of PA. The CNT intermediate layer was found to influence the PA cross-linking, which is related to surface negative charge, by controlling the storage and release of the m-phenylenediamine monomer during interfacial polymerization. The neutral CNT-TFC membrane demonstrated improved NH4+ retention and increased resistance to fouling by protein, surfactant, and E. coli. However, other surface properties, such as roughness and hydrophilicity, could counteract the antifouling benefits of a neutral surface. This work provides insights into additional advantages of CNT intermediate layer intercalation in TFC PA membranes, such as enhanced cross-linking and surface charge control.

A novel strategy inspired by Luban lock towards endowing polyzwitterionic electrolyte hydrogel with UCST behaviors

The electrostatic interaction in polyzwitterionic electrolyte hydrogels is the prerequisite for materials to exhibit temperature-sensitive behaviors. Few reports mention the potential temperature-sensitive properties of these hydrogels, although amounts of polyzwitterionic electrolyte hydrogels with bright prospects in advanced fields have been reported. PMAD (copolymer of AM, AA and DMC) is a typical polyzwitterionic electrolyte, which is taken as an example to elucidate the essential conditions for the UCST behaviors of polyzwitterionic electrolyte hydrogels. The temperature-sensitive properties of PMAD hydrogels depends on the tight stacking of zwitterionic polymer chains, while the introduction of chemical crosslinker could limit the movement of PMAD chains and increase the difficulty of forming effective electrostatic interactions between zwitterionic segments resulting in the disappearance of UCST behaviors. Accordingly, the strategy inspired by the Chinese Luban lock for compressing the distance of PMAD chains by utilizing the “mortise-tenon” structure could recovery the UCST behaviors of PMAD and are expected to endow more polyzwitterionic electrolyte hydrogels with temperature-responsive properties.

Tartaric acid anion intercalated layered double hydroxides constructed a CO2-favorable transport channel in PIM-1 mixed matrix membranes for CO2/N2 separation

As a unique polymer of intrinsic microporosity, PIM-1 has great potential in mixed matrix membranes (MMMs) for gas separation with ultra-high permeability. However, the separation performance, e.g. CO2/N2 separation, is still limited by its poor selectivity. In this work, PIM-1-based MMMs containing tartaric acid anion intercalated layered double hydroxides (TA-LDH) nanofillers are successfully prepared. The uniformly dispersed TA-LDH in the PIM-1 matrix contributes to optimizing the stacking of polymer chains for accessible pores, which is conducive to CO2 diffusion. In addition, the assistant experiment and theoretical calculation point out that the -COO-, –OH between the TA-LDH layers had an affinity for CO2, creating a two-dimensional fast transport channel between the enlarged interlayer space. Compared with the pristine PIM-1 membrane, the CO2 permeability and CO2/N2 selectivity of 0.7 % TA-LDH/PIM-1 membrane is increased by 43.19 % and 105.48 %. The excellent gas separation performance with CO2 permeability of 8343.18 Barrer and CO2/N2 selectivity of 39.02 exceeds the 2019 Robson upper limit. This paves a new way to improve the gas separation performance of PIM-1-based MMMs and suggests high perspectives for real applications.

A Perspective on tellurium-based optoelectronics

Tellurium (Te) has been rediscovered as an appealing p-type van der Waals semiconductor for constructing various advanced devices. Its unique crystal structure of stacking of one-dimensional molecular chains endows it with many intriguing properties including high hole mobilities at room temperature, thickness-dependent bandgap covering short-wave infrared and mid-wave infrared region, thermoelectric properties, and considerable air stability. These attractive features encourage it to be exploited in designing a wide variety of optoelectronics, especially infrared photodetectors. In this Perspective, we highlight the important recent progress of optoelectronics enabled by Te nanostructures, which constitutes the scope of photoconductive, photovoltaic, photothermoelectric photodetectors, large-scale photodetector array, and optoelectronic memory devices. Prior to that, we give a brief overview of basic optoelectronic-related properties of Te to provide readers with the knowledge foundation and imaginative space for subsequent device design. Finally, we provide our personal insight on the challenges and future directions of this field, with the intention to inspire more revolutionary developments in Te-based optoelectronics.

Tuning poly(isatin biphenyl) anion exchange membranes by copolymerization and branching

The cardo structure and long side chain of poly(isatin biphenyl) are conducive to the motion and aggregation of cations over mainchain type membranes, therefore it is used as the pristine membrane. It is well known that random copolymerization and branching can effectively modify the configuration and properties of polymers. Herein, we use random copolymerization and branching to improve the behaviors of poly(isatin biphenyl) anion exchange membranes (AEMs). High-curvature random copolymers (QPIDBP-n) and high free volume branched polymers (b-QPIBP-x) are synthesized via polycondensation. The random copolymerization results in the formation of a twisted chain structure, while the introduction of branching agent leads to the formation of orderly stacking of chains. Both of these approaches have been demonstrated to boost the microphase-separated morphology of the pristine polymer. A series of QPIDBP-n and b-QPIBP-x are tested and an optimal ratio is explored. QPIDBP-40 and b-QPIBP-5 exhibit high overall performance. Among the as-prepared membranes, b-QPIBP-5 exhibits the highest conductivity (80 °C, 160.7 mS cm−1) with a swelling ratio of 20.7 %. The residual conductivity of b-QPIBP-5 is 93.1 % after the 1200 h alkali stability test. The cell assembled by b-QPIBP-5 achieves a peak power density of 680 mW cm−2. Moreover, the b-QPIBP-5 based cell holds 88.6 % voltage after the in-situ stability test for 50 h.

Aerogel honeycombs with orientation-induced microstructures for high-temperature lightweight composite sandwich structures

Lightweight honeycomb structures are widely used in applications that require high strength-to-weight ratios and low densities, including aircraft, automobiles, and various engine components. However, due to the immaturity of microstructure conditioning techniques and the fact that highly porous structures usually fracture during stretching, it is challenging to obtain both high-strength and lightweight porous structures. Herein, a newly developed multilayer interconnected polyimide aerogel-based paper honeycomb is successfully prepared based on the ice crystal reverse template method and multi-level structure regulation via chemical and physical interactions. The synergistic effect of the hot extrusion-stress strategy and the heat imidization process provides the submicron layer of the paper honeycomb wall with more orderly molecular chain stacking, excellent orientation, and an enhanced folding degree between layers. The prepared polyimide aerogel paper honeycombs have low density (approx. 8–9 kg/m3), good shear strength of 1.07 MPa (W direction) and 0.86 MPa (L direction), excellent specific compressive strength (0.38 MPa), and excellent thermal stability. These integrally molded polyimide paper honeycombs, as sandwich resin-based composite structures, provide a new versatile platform for aerospace and marine applications.

Phosphoric acid pre-swelling strategy constructing acid-doped fluoropoly(aryl pyridinium) membranes to enable high-performance vanadium flow batteries

Vanadium flow batteries (VFBs) have promising applications for grid-scale energy storage. Unfortunately, the widespread integration of VFBs into large-scale energy storage applications is hindered by the lack of low-cost ion-conducting membranes (ICMs) with high ion selectivity and excellent stability. Herein, we propose an intrinsically stabilized ether-free fluoropoly(aryl pyridine) (PFNP) and provide a high-performance acid-doped membrane via a phosphoric acid pre-swelling strategy for the battery. Effective acid-doping enables the formation of discrete hydrophilic nano-channels within the PFNP matrix, and the extensive internal hydrogen-bonding network synergistically facilitates charge carrier transport. Simultaneously, the close stacking of PFNP chains and the Donnan effect of protonated piperidinium groups within the membrane effectively prevent vanadium ions permeation. Consequently, this innovative strategy allows the acid-doped membrane to achieve nearly perfect ion selectivity (3.64 × 105 S min cm−3), outperforming the Nafion 212 membrane (3.01 × 104 S min cm−3). Moreover, the fluorinated ether-free structure and non-weak-bondpyridine structure impart excellent mechanical and chemical stability to the acid-doped membrane, ensuring long-term membrane operation. As expected, the VFBs assembled with the acid-doped membrane achieve high energy efficiency (83.1 %) at high current density (200 mA cm−2), offer an ultra-low capacity decay rate of 0.08 % per cycle and retain outstanding stability after 1500 cycles at 120 mA cm−2. This study provides a potential material system for commercial VFB membranes by achieving high performance at low cost.

Tailoring the microstructure of zwitterionic nanofiltration membranes via post-treatment for antibiotic desalination

Zwitterionic nanofiltration membranes, with high rejection to organic molecules while low rejection to monovalent salts, are promising for antibiotic desalination. However, due to the heterogeneous issue of interfacial polymerization, the residual amine groups result in polymer chain aggregation via hydrogen bonds, blocking the mass transfer of water and monovalent salts. Herein, EtOH-assisted Michael-addition/Schiff-base reaction strategy was proposed to solve the issue. NaOH was initially utilized to provisionally interrupt the hydrogen bonds between polymer chains. Meanwhile, with the assistance of EtOH, gallic acid diffused into the membrane and reacted with the amine groups on the polymer chains to form covalent bonds, which thoroughly destroyed the stacking of polymer chains. As a consequence, water permeance and antibiotic desalination efficiency of the membrane are improved. For example, the pure water permeance reaches 8.9 L m−2 h−1 bar−1, 1.7-fold enhancement compared with the pristine membrane. The membrane is applied for antibiotic desalination, offering long-term running stability, antifouling ability, as well as high efficiency in concentrated antibiotics.

Modulation of Phase Separation Morphology by Configuration Engineering in Bulk Heterojunction Organic Solar Cells

For bulk‐heterojunction organic solar cells (OSCs), molecular structure design to control molecular stacking is crucial to obtain ideally phase‐separated morphology and high device performance. Herein, the investigation focuses on two polythiophene‐quinoxaline (PTQ) derivatives (PTQ8 and PTQ10) blended with Y6, utilizing coarse‐grained molecular dynamics simulations based on the Lennard–Jones static potential (LJSP) method. The study reveals that the diminished photovoltaic efficiencies of PTQ8:Y6 blends, compared to PTQ10:Y6 blends, are not solely attributed to reduced driving forces. The introduction of fluorine‐substituted sites in the thiophene group of PTQ polymer is identified as a significant factor. This alteration causes PTQ polymers in PTQ8:Y6 blends to coil, compromising the crystalline structure. PTQ8's bifluorine group induces a repulsive effect on the quinoxaline group, leading to a coiled‐chain structure that hinders chain stacking. Conversely, PTQ10 exhibits a straighter chain conformation. Additionally, PTQ8's high solubility in chloroform prevents effective aggregation, further impeding suitable morphology formation. Coarse‐grained simulations employing LJSP prove effective in precisely exploring the morphology of OSCs, offering crucial insights for materials in this field.

Theoretical and Experimental Study of Different Side Chains on 3,4-Ethylenedioxythiophene and Diketopyrrolopyrrole-Derived Polymers: Towards Organic Transistors.

In this research, two polymers of P1 and P2 based on monomers consisting of thiophene, 3,4-Ethylenedioxythiophene (EDOT) and diketopyrrolopyrrole (DPP) are designed and obtained via Stille coupling polycondensation. The material shows excellent coplanarity and structural regularity due to the fine planarity of DPP itself and the weak non-covalent bonding interactions existing between the three units. Two different lengths of non-conjugated side chains are introduced and this has an effect on the intermolecular chain stacking, causing the film absorption to display different characteristic properties. On the other hand, the difference in the side chains does not have a significant effect on the thermal stability and the energy levels of the frontier orbitals of the materials, which is related to the fact that the materials both feature extremely high conjugation lengths and specific molecular compositions. Microscopic investigations targeting the side chains provide a contribution to the further design of organic semiconductor materials that meet device requirements. Tests based on organic transistors show a slight difference in conductivity between the two polymers, with P2 having better hole mobility than P1. This study highlights the importance of the impact of side chains on device performance, especially in the field of organic electronics.

Terahertz spectroscopy of interchain hydrogen bond changes of poly (L-lactic acid)/poly (D-lactic acid) blends during solution crystallization

The blending of poly (L-lactic acid) (PLLA) and poly (D-lactic acid) (PDLA) achieves an effective transformation of properties based on the formation of interchain hydrogen bonds. Therefore, it is important to study the stereo-complex (SC) system. We studied the solution crystallization of PLLA/PDLA blends based on the sensitivity of terahertz (THz) spectroscopy to hydrogen bonds. The results revealed an abnormal red-shift in the characteristic peak frequency of the blends with the increase of PLLA, which is attributed to the difference in chain stacking of the main components in the blends. Moreover, we believe that the peak height of the SC at 1.43 THz is an accurate index reflecting the interchain hydrogen bonds in the case of blending ratio changes. When the blend ratio is determined, we found that the blue shift of this peak frequency corresponded to the weakening of interchain hydrogen bonds. The results show that THz spectroscopy can effectively observe the solution crystallization behavior of blends, and its different characteristic indexes contain the information of interaction and aggregation structure.

Fast and accurate method for short-circuit current calculation in distribution network with IIDGs

The fault behavior of Inverter Interfaced Distributed Generators (IIDGs) diverges from that of synchronous generators. When a substantial number of IIDGs are integrated into the distribution network, the conventional short-circuit current calculation technique, grounded in a mechanical framework, struggles to simultaneously satisfy the demands for both rapid computation and precision. This study introduces an alternative approach reliant on data analysis, enabling swift and precise computation of short-circuit currents across the IIDG-infused distribution grid. The investigation delves into the efficacy of multi-output regression techniques and the selection of the foundational learning algorithm. Specifically, two strategies are advanced: Multi-Target Regressor Stacking and Regressor Chains, both utilizing the Light Gradient Boosting Machine as the base learner. The influence of varying sample sizes on the multi-output computational model's performance is assessed. To ascertain the real-world viability of the multi-output regression methodology, two distinct fault characteristics pertaining to data-driven short-circuit current calculation are scrutinized using existing distribution network measurement conditions. The study reveals that, given a known distribution network structure, the proposed method can compute network-wide short-circuit currents across diverse IIDG penetration levels and fault scenarios through a singular model, maintaining a balance between computation precision and speed. If the distribution network's structure undergoes minor modifications, the model demonstrates reasonable adaptability, yet a retraining of the short-circuit current calculation model is recommended to ensure sustained accuracy in the face of significant network changes.

Crystal structure of 2-methyl-1H-imidazol-3-ium 3,5-di-carb-oxy-benzoate.

The structure of the title salt, C4H7N2 +·C9H5O6 - (1), is reported. The compound is built from a protonated 2-methyl-imidazole and a singly deprotonated trimesic acid. Detailed analysis of bond distances and angles for both ions reveals subtle differences compared with their neutral mol-ecule counterpart. Analysis of the crystal packing in compound 1 reveals the formation of undulating chains by the ions through hydrogen bonding. The chains stack along the b axis through π-π inter-actions and inter-connect with other chains in an out-of-phase arrangement along the ac plane through further hydrogen-bonding inter-actions.

Spiral-Structured Dielectric Polymers Exhibiting Ultrahigh Energy Density and Charge-Discharge Efficiency at High Temperatures.

The growing need for high-power and compact-size energy storage in modern electronic and electrical systems demands polymer film capacitors with excellent temperature capability. However, conventional polymer dielectrics feature dramatic deterioration in capacitive performance under concurrent high temperature and electric field because the high thermal stability traditionally relies on the conjugated, planar molecular segments in the polymer chains. Herein, inspired by the stable double helix structures of deoxyribonucleic acid, spiral-structured dielectric polymers that exhibit simultaneous high thermal stability and great capacitive performance are demonstrated. Both the experimental results and computational simulations confirm that the spiral groups serve to weaken the electrostatic molecular interaction, induce proper molecular chain stacking structure, and regulate the charge transfer process by breaking the conjugated planes and introducing deep trap sites. The resultant polymer exhibits the maximum discharged energy densities of 7.29 and 6.13 Jcm-3 with the charge-discharge efficiency above 90% at 150 and 200°C, respectively, more than ten times those of the original dielectric at the same conditions. Here a completely new dimension is offered for the molecular design of polymers, giving rise to well-balanced thermal and dielectric properties, and ultimately the desired capacitive energy storage performance at high temperatures.

Structure and properties of comb-like non-silicone release agent: Effect of alcoholysis degree and polymerization degree of precursor polymers

Non-silicone release agents with surface-protecting functions are highly desirable in various industrial applications such as electronics and packaging. In this study, a series of comb-like polyvinyl n-octadecyl carbamate (PVODC) with different structures were synthesized using polyvinyl alcohol (PVA) grafted with octadecyl isocyanate (ODI). The effects of the alcoholysis degree (DA), polymerization degree (DP), and substitution degrees (DS) of alkyl side chains of PVA precursor on the structure-property correlation of PVODCs were explored by using various techniques. Results indicated that at a low DS of ∼40 mol%, decreasing the DA of PVA led to lower melting points and thermal stability but enhanced the release performance of PVODCs. However, the crystal form and chain stacking behavior of PVODCs appear unaffected by the DA. The effect of DA was less significant at a high DS of ∼68 mol%. Within the DP range studied, the DP of PVA had little effect on the structure and properties of PVODCs. Only when the DP of PVA surpassed 1700, the thermal stability was enhanced due to stronger molecular interactions, but at a cost of deteriorated solubility and film-forming performance.

A structure-property study for the effect of methyl substituents on the gas separation of spirodifluoranthene-based polymers of intrinsic microporosity

A simple methyl substitution on the structural building blocks of a PIM can alter its chain stacking behavior. Hence, we have introduced differing amounts of methyls on bulky and rigid spirodifluoranthene (EN) configured as two fluorenyl groups perpendicular to anthracene to obtain a series of spirodifluoranthene-based PIMs with increased intrinsic microporous, as demonstrated by nitrogen adsorption and enhanced gas permeability. The methyl substitution increased the free volume of polymer membranes, but the free volume does not increase in proportion to the number of methyl groups, and the increment is relatively slight at high methyl substitution amounts. Also, the effect of methyl substitution was closely associated with the molar contents of EN structures in PIMs. The series of polymers exhibited excellent CO2/N2, CO2/CH4, and O2/N2 gas separation performances, ranking among state-of-the-art polymeric materials for gas separation. Particularly, PIM-OMEN-40 exhibited the highest CO2 permeability, up to 12,431 barrer, which corresponds to 2.94 times higher than that of PIM-1 and along with comparable gas selectivity. Even after more than 100 days of aging, the series of PIMs still showed higher gas permeability and selectivity than fresh PIM-1, demonstrating great potential in separation areas for CO2 capture and storage, natural gas and biogas upgrading of prime importance to energy and the environment.