Designing a Hybrid Perovskite with Enlarged Birefringence and Bandgap for Modulation of Light Polarization.

Birefringent crystals have important applications in optoelectronics areas due to their ability to modulate and polarize light. Despite increasing discovery of the birefringence potential of new crystals, it remains a great challenge to optimize both birefringence and bandgap simultaneously. Herein, a 1D chain-like hybrid perovskite birefringent crystal designed by 3D-to-1D dimensional tailoring, (GAM)2 PbI7 ·H2 O (GAM = C5 N10 H10 ), is presented, showing enlarged birefringence of 0.49@550 nm and enlarged optical bandgap (2.48 eV). Consequently, the birefringent quality factor of (GAM)2 PbI7 ·H2 O is up to 2.8 times that of the template MAPbI3 . In particular, the birefringence is much larger than those of commercial birefringent crystals and surpasses that of the vast majority of hybrid perovskite known to date. Theoretical calculations reveal that the strongly anisotropic arrangement of (GAM)2.5+ π-conjugated cations and ordered PbI6 octahedra contributes to the large birefringence and wide bandgap of (GAM)2 PbI7 ·H2 O. It is believed that this work will provide a new pathway toward the rational design and synthesis of hybrid perovskite birefringent crystals for compact wide-bandgap polarization dependent devices.

A High-Performance Nonlinear Optical Crystal with a Building Block Containing Expanded π-Delocalization.

Common nonlinear optical (NLO) crystals consist of traditional functional building blocks with inherent optical limitation. Herein, inspired by traditional (B3 O6 )3- inorganic building block, we theoretically identified a new type of organic functional building blocks and then successfully synthesized the first cyamelurate NLO crystal, Ba(H2 C6 N7 O3 )2 ⋅ 8 H2 O. To our surprise, the constituent (H2 C6 N7 O3 )- building block is not in structurally optimal arrangement, but Ba(H2 C6 N7 O3 )2 ⋅ 8 H2 O exhibits excellent optical properties including wide band gap of 4.10 eV, very large birefringence of 0.24@550 nm, and exceptionally strong second-harmonic generation (SHG) response of about 12×KH2 PO4 . Both the SHG response and birefringence are much larger than those of commercial NLO crystal ß-BaB2 O4 with optimally aligned (B3 O6 )3- building block. Theoretical calculations suggest that the expanded π-conjugation delocalization within (H2 C6 N7 O3 )- vs (B3 O6 )3- should be responsible to the enhanced performance. This work implies that there is still much room to develop new NLO crystals with excellent functional building blocks that may be longly neglected.

A Hydrogen Bonded Supramolecular Framework Birefringent Crystal.

Birefringent crystals could modulate the polarization of light and are widely used as polarizers, waveplates, optical isolators, etc. To date, commercial birefringent crystals have been exclusively limited to purely inorganic compounds such as α-BaB2 O4 with birefringence of about 0.12. Herein, we report a new hydrogen bonded supramolecular framework, namely, Cd(H2 C6 N7 O3 )2 ⋅8 H2 O, which exhibits exceptionally large birefringence up to about 0.60. To the best of our knowledge, the birefringence of Cd(H2 C6 N7 O3 )2 ⋅8 H2 O is significantly larger than those of all commercial birefringent crystals and is the largest among hydrogen bonded supramolecular framework crystals. First-principles calculations and structural analyses reveal that the exceptional birefringence is mainly ascribed to strong covalent interactions within (H2 C6 N7 O3 )- organic ligands and the perfect coplanarity between them. Given the rich structural diversity and tunability, hydrogen bonded supramolecular frameworks would offer unprecedented opportunities beyond the traditional purely inorganic oxides for birefringent crystals.

Enhancing Gas Solubility in Nanopores: A Combined Study Using Classical Density Functional Theory and Machine Learning.

Geometrical confinement has a large impact on gas solubilities in nanoscale pores. This phenomenon is closely associated with heterogeneous catalysis, shale gas extraction, phase separation, etc. Whereas several experimental and theoretical studies have been conducted that provide meaningful insights into the over-solubility and under-solubility of different gases in confined solvents, the microscopic mechanism for regulating the gas solubility remains unclear. Here, we report a hybrid theoretical study for unraveling the regulation mechanism by combining classical density functional theory (CDFT) with machine learning (ML). Specifically, CDFT is employed to predict the solubility of argon in various solvents confined in nanopores of different types and pore widths, and these case studies then supply a valid training set to ML for further investigation. Finally, the dominant parameters that affect the gas solubility are identified, and a criterion is obtained to determine whether a confined gas-solvent system is enhance-beneficial or reduce-beneficial. Our findings provide theoretical guidance for predicting and regulating gas solubilities in nanopores. In addition, the hybrid method proposed in this work sets up a feasible platform for investigating complex interfacial systems with multiple controlling parameters.

Molecular Dynamics Simulation Insight into Interfacial Stability and Fluidity Properties of Microemulsions.

Although the interfacial properties of microemulsions have been extensively studied in both experimental and simulation research studies, the molecular mechanisms of stability and fluidity about microemulsion are still poorly understood. Herein, we report a molecular dynamics simulation study to elaborate the motion of an emulsion droplet involving dichain surfactant Aerosol OT (AOT) and its dynamics evolution at the oil-water interface. By varying the concentrations of AOT, we show that the interfacial thickness and emulsification rate display a piecewise change as the interfacial coverage increases and the W/O emulsion is more stable than the O/W one while O/W emulsion presents better fluidity. In addition, the dispersed system combined with water/AOT/n-heptane tends to form a W/O microemulsion instead of an O/W microemulsion due to the structural collapse of the latter. This work provides a molecular understanding of microemulsion interfacial stability and fluidity.

Membrane Wrapping Pathway of Injectable Hydrogels: From Vertical Capillary Adhesion to Lateral Compressed Wrapping.

Membrane wrapping pathway of injectable hydrogels (IHs) plays a vital role in the nanocarrier effectiveness and biomedical safety. Although considerable progress in understanding this complicated process has been made, the mechanism behind this process has remained elusive. Herein, with the help of large-scale dissipative particle dynamics simulations, we explore the molecular mechanism of membrane wrapping by systematically examining the IH architectures and hydrogel-lipid binding strengths. To the best of our knowledge, this is the first report on the membrane wrapping pathway on which IHs transform from vertical capillary adhesion to lateral compressed wrapping. This transformation results from the elastocapillary deformation of networked gels and nanoscale confinement of the bilayer membrane, and it takes long time for the IHs to be fully wrapped owing to the high energy barriers and wrapping-induced shape deformation. Collapsed morphologies and small compressed angles are identified in the IH capsules with a thick shell or strong binding strength to lipids. In addition, the IHs binding intensively to the membrane exhibit special nanoscale mixing and favorable deformability during the wrapping process. Our study provides a detailed mechanistic understanding of the influence of architecture and binding strength on the IH membrane wrapping efficiency. This work may serve as rational guidance for the design and fabrication of IH-based drug carriers and tissue engineering.

Amphiphilic nanosheet self-assembly at the water/oil interface: computer simulations.

In this paper, dissipative particle dynamics simulations are performed to study the interfacial and emulsion stabilizing properties of various systems of amphiphilic nanosheets (ANs) self-assembled at the oil/water (O/W) interface. The ANs have a dimensional symmetry structure that encompasses a triangular-plate at the center and two soft comb-like shells constructed with hydrophilic and hydrophobic polymers. As the simulation results show, the AN molecules are highly oriented in interfacial films with their triangular nanosheets parallel to the O/W interface, while their hydrophobic and hydrophilic segments attempt to immerse into the oil phase and aqueous phase, respectively. These results reveal that the rotation of ANs at oil/water interfaces is greatly restricted, meanwhile, their nanosheet (or planar) configuration facilitates their favorable orientation thereby, thus making the emulsion more stable. At higher concentrations, a wrapped-like or micelle morphology is observed. The O/W emulsions stabilized by ANs were also simulated, and it is interesting to find AN 'patches' at the O/W interface which resembles the leather patches on a football. By introducing the "amphiphilic nanosheet balance" concept, the hydrophilic-lipophilic balance (HLB) values of ANs were calculated. Due to their properties of two-dimensional symmetry, the HLB values of ANs tend to approximately 1 which reveals a stronger stability for emulsions.

Mesoscopic Simulations of Adsorption and Association of PEO-PPO-PEO Triblock Copolymers on a Hydrophobic Surface: From Mushroom Hemisphere to Rectangle Brush.

The dissipative particle dynamics (DPD) method is used to investigate the adsorption behavior of PEO-PPO-PEO triblock copolymers at the liquid/solid interface. The effect of molecular architecture on the self-assembled monolayer adsorption of PEO-PPO-PEO triblock copolymers on hydrophobic surfaces is elucidated by the adsorption process, film properties, and adsorption morphologies. The adsorption thicknesses on hydrophobic surfaces and the diffusion coefficient as well as the aggregation number of Pluronic copolymers in aqueous solution observed in our simulations agree well with previous experimental and numerical observations. The radial distribution function revealed that the ability of self-assembly on hydrophobic surfaces is P123 > P84 > L64 > P105 > F127, which increased with the EO ratio of the Pluronic copolymers. Moreover, the shape parameter and the degree of anisotropy increase with increasing molecular weight and mole ratio of PO of the Pluronic copolymers. Depending on the conformation of different Pluronic copolymers, the morphology transition of three regimes on hydrophobic surfaces is present: mushroom or hemisphere, progressively semiellipsoid, and rectangle brush regimes induced by decreasing molecular weight and mole ratio of EO of Pluronic copolymers.

A highly birefringent metal-free crystal assembled by cooperative non-covalent interactions.

Birefringent crystals can manipulate the phase and polarization of light, so they are widely used as essential components in various optical devices. Common strategies to construct birefringent crystals are introducing metal cations that are either able to realize favorable coordination with functional anionic units or are susceptible to polarizability anisotropy. Herein, we report a metal-free crystal, NH4(H2C6N7O3)·2H2O, synthesized using the facile solution method. In the crystal structure of NH4(H2C6N7O3)·2H2O, (H2C6N7O3)- functional units are assembled in an optimal manner by cooperative non-covalent interactions, i.e., hydrogen bonding and π-π interactions. As a result, this metal-free crystal possesses exceptional birefringence up to 0.54@550 nm, which is larger than those of most metal-containing birefringent crystals. In addition, the interference color of this crystal does not change obviously from 243 K to 313 K, indicating that the birefringence is robust at different temperatures. This work will inspire useful insights into the role of non-covalent interactions in designing outstanding birefringent crystals for efficient polarized optical devices.

Combining rigid and deformable groups to construct a robust birefringent crystal for compact polarization components.

There is a pressing demand for the development of novel birefringent crystals tailored for compact optical components, especially for crystals exhibiting large birefringence across a range of temperatures. This has commonly been achieved by introducing various deformable groups with high polarizability anisotropy. In this study, we combined both rigid and deformable groups to synthesise a new birefringent crystal, Al2Te2MoO10, which demonstrates an exceptional birefringence value of 0.29@550 nm at room temperature. Not only is this higher birefringence than that of commercial crystals, but Al2Te2MoO10 exhibits excellent birefringence stability over a wide temperature range, from 123 to 503 K. In addition, the first-principles theory calculations and structural analyses suggest that although the rigid AlO6 groups do not make much contribution to the prominent birefringence, they nonetheless played a role in maintaining the structural anisotropy at elevated temperatures. Based on these findings, this paper proposes a novel structural design strategy to complement conventional approaches for developing optimal birefringent crystals under various environmental conditions.

A Second-Order Nonlinear Optical Material Consisting of Two π-Conjugated Groups.

This work reports a new second-order nonlinear optical (NLO) material [C(NH2 )3 ]3 C3 N3 S3 (GU3 TMT), consisting of π-conjugated planar (C3 N3 S3 )3- and triangular [C(NH2 )3 ]+ groups. Interestingly, GU3 TMT exhibits a large NLO response (2.0×KH2 PO4 ) and moderate birefringence 0.067 at wavelength 550 nm, even though (C3 N3 S3 )3- and [C(NH2 )3 ]+ do not exhibit the most favorable arrangement in the structure of GU3 TMT. First-principles calculations suggest that NLO properties mainly originate from the highly π-conjugated (C3 N3 S3 )3- rings, and the π-conjugated [C(NH2 )3 ]+ triangles contribute much less to the overall NLO response. This work will inspire new thoughts with in-depth on the role of π-conjugated groups in NLO crystals.

Engulfing Behavior of Nanoparticles into Thermoresponsive Microgels: A Mesoscopic Simulation Study.

The engulfing of nanoparticles into microgels provides a versatile platform to design nano- and microstructured materials with various shape anisotropies and multifunctional properties. Manipulating the spontaneous engulfment process remains elusive. Herein, we report a mesoscopic simulation study on the engulfing behavior of nanoparticles into thermoresponsive microgels. The effects of the multiple parameters, including binding strength, temperature, and nanoparticle size, are examined systematically. Our simulation results disclose three engulfing states at different temperatures, namely full-engulfing, half-engulfing, and surface contact. The engulfing depth is determined by the complementary balance of interfacial elastocapillarity. Specifically, the van der Waals interaction of hybrid microgel-nanoparticle offers the capillary force while the internally networked structure of microgel reinforces the elasticity repulsion. Our study, validated by relevant experimental results, provides a mechanistic understanding of the interfacial elastocapillarity for nanoparticle-microgels.

Mechanochemical Cellular Membrane Internalization of Nanohydrogels: A Large-Scale Mesoscopic Simulation.

By combining large-scale dissipative particle dynamics and steered molecular dynamics simulations, we investigate the mechanochemical cellular internalization pathways of homogeneous and heterogeneous nanohydrogels and demonstrate that membrane internalization is determined by the crosslink density and encapsulation ability of nanohydrogels. The homogeneous nanohydrogels with a high crosslink density and low encapsulation ability behave as soft nanoparticles partially wrapped by the membrane, while those with a low crosslink density and high encapsulation ability permeate into the membrane. Regardless of the crosslink density, the homogeneous nanohydrogels undergo typical dual morphological deformations. The local lipid nanodomains are identified at the contacting region between the membrane and nanohydrogels because of different diffusion behaviors between lipid and receptor molecules during the internalization process. The yolk@shell heterogeneous nanohydrogels present a different mechanochemical cellular internalization pathway. The yolk with strong affinity is directly in contact with the membrane, resulting in partial membrane wrapping, and the contacting area is much reduced when compared to homogenous nanohydrogels, leading to a smaller lipid nanodomain and thus avoiding related cellular toxicity. Our findings provide a critical mechanism understanding of the biological pathways of nanohydrogels and may guide the molecular design of the hydrogel-based materials for controlled release drug delivery, tissue engineering, and cell culture.

Towards High Performance Li-S Batteries via Sulfonate-Rich COF-Modified Separator.

Lithium-sulfur (Li-S) batteries are held great promise for next-generation high-energy-density devices; however, polysulfide shuttle and Li-dendrite growth severely hinders their commercial production. Herein, a sulfonate-rich COF (SCOF-2) is designed, synthesized, and used to modify the separator of Li-S batteries, providing a solution for the above challenges. It is found that the SCOF-2 features stronger electronegativity and larger interlayer spacing than that of none/monosulfonate COFs, which can facilitate the Li+ migration and alleviate the formation of Li-dendrites. Density functional theory (DFT) calculations and in situ Raman analysis demonstrate that the SCOF-2 possesses a narrow bandgap and strong interaction on sulfur species, thereby suppressing self-discharge behavior. As a result, the modified batteries deliver an ultralow attenuation rate of 0.047% per cycle over 800 cycles at 1 C, and excellent anti-self-discharge performance by a low-capacity attenuation of 6.0% over one week. Additionally, even with the high-sulfur-loading cathode (3.2-8.2 mgs cm-2 ) and lean electrolyte (5 µL mgs -1 ), the batteries still exhibit ≈80% capacity retention over 100 cycles, showing great potential for practical application.