A practical guide to pulsed laser deposition

Nanoscale thin films are widely implemented across a plethora of technological and scientific areas, and form the basis for many advancements that have driven human progress, owing to the high degree of functional tunability based on the chemical composition. Pulsed laser deposition is one of the multiple physical vapour deposition routes to fabricate thin films, employing laser energy to eject material from a target in the form of a plasma. A substrate, commonly a single-crystal oxide, is placed in the path of the plume and acts as a template for the arriving species from the target to coalesce and self-assemble into a thin film. This technique is tremendously useful to produce crystalline films, due to the wide range of atmospheric conditions and the extent of possible chemical complexity of the target. However, this flexibility results in a high degree of complexity, oftentimes requiring rigorous optimisation of the growth parameters to achieve high quality crystalline films with desired composition. In this tutorial review, we aim to reduce the complexity and the barrier to entry for the controlled growth of complex oxides by pulsed laser deposition. We present an overview of the fundamental and practical aspects of pulsed laser deposition, discuss the consequences of tailoring the growth parameters on the thin film properties, and describe in situ monitoring techniques that are useful in gaining a deeper understanding of the properties of the resultant films. Particular emphasis is placed on the general relationships between the growth parameters and the consequent structural, chemical and functional properties of the thin films. In the final section, we discuss the open questions within the field and possible directions to further expand the utility of pulsed laser deposition.

Side-Chain Engineering in Hydrophilic n-Type π-Conjugated Polymers for Enhanced Reactivity

Minor changes to side chains in conjugated polymers (CPs) can have pronounced effects on polymer properties by altering backbone planarity, solubility, and interaction with ions. Here, we report the photocontrolled synthesis of hydrophilic CPs from Grignard monomers and find that switching from alkyl to oligo(ethylene glycol) (OEG) side chains changes their photoreactivity. Specifically, installing hydrophilic side chains on the same monomer core yields higher molecular weight polymers and allows polymerization to proceed with lower-energy red light. Additionally, we discover a side chain decomposition pathway for N-OEG monomers, which are prevalent in CP research. Decomposition can be overcome by adding an extra methylene unit in the side chains without compromising polymer molecular weight or hydrophilicity. Importantly, this polymerization does not require transition metal catalysts and is a promising approach to the preparation of n-type conjugated block copolymers.

Chemo-mechanical-microstructural coupling in the tarsus exoskeleton of the scorpion Scorpio palmatus

The multiscale structure of biomaterials enables their exceptional mechanical robustness, yet the impact of each constituent at their relevant length scale remains elusive. We used SAXD analysis to expose the intact chitin-fiber architecture within the exoskeleton on a scorpion's claw, revealing varying orientations, including Bouligand and unidirectional regions different from other arthropod species. We uncovered the contribution of individual components' constituent behavior to its mechanical properties from the micro- to the nanoscale. At the microscale, in-situ micromechanical experiments were used to determine site-specific stiffness, strength, and failure of the biocomposite due to fiber orientation, while metal-crosslinking of proteins is characterized via fluorescence maps. At the constituent level, combined with FEA simulations, we uncovered the behavior of fiber-matrix deformation with fiber diameter <53.7 nm and protein modulus in the range 1.4-11 MPa. The unveiled microstructure-mechanics relationship sheds light on the evolved structural functionalities and constituents' interactions within the scorpion cuticle. STATEMENT OF SIGNIFICANCE: The pincer exoskeleton is a fundamental part of the scorpion's body due to its multifunctionality. Precise structural and compositional analysis within the hierarchy is paramount to understand the fundamentals of the mechanical properties of the composite exoskeleton. Here, we expose the intact chitin-fiber architecture of the pincer exoskeleton using nondestructive analysis. In-situ mechanical characterization was performed at nanometer levels within the exoskeleton hierarchy, which complemented with simulations, uncovered the elastic modulus of the protein matrix. Our findings confirm the presence and distribution of metal ions and their role as reinforcements in the protein matrix via ligand coordinate bonds. In future work, these findings can be of great potential to inspire the design of composite materials.

Digital light processing-based multi-material bioprinting: Processes, applications, and perspectives

In the past decade, three-dimensional (3D) printing technology based on digital light processing (DLP) has developed rapidly and shown application prospects in several fields such as pneumatic robotics, flexible electronics, and tissue engineering. In particular, DLP-based multi-material printing has been capable of constructing heterogeneous 3D structures with characteristic gradients. DLP 3D printing technology has a wide range of applications in the field of bioprinting due to its high precision and mild printing conditions, including functionalized artificial tissues, medical models, and bioreactors. This paper focuses on the development of DLP-based multi-material 3D printing technology and its applications in the field of bioprinting, followed by giving an outlook on future efforts on overcoming the challenges and obstacles of this promising technique.

A circle/sphere populating method to generate 2D/3D stochastic microstructures

A circle/sphere populating method is proposed to generate 2D/3D stochastic microstructures. The proposed method uses circles/spheres as the basic elements and generates microstructure features through the populating process of the circles/spheres. In the populating process, the cores are first generated randomly and circles/spheres start to populate around the cores or the previous generation's circles/spheres. The populating process is controlled by the input parameters including the volume fraction, core number, circle/sphere size distribution, circle/sphere populating distance distribution, circle/sphere populating number, and populating direction constraint angle. The proposed method was compared with the QSGS method and random circle/sphere method in 2-dimensional (2D) and 3-dimensional (3D) cases. The proposed method shows advantages in generating microstructures with clear feature geometries and boundaries. Furthermore, parametric studies are conducted in 2D and 3D to investigate the effect of input parameters on the generated microstructures. With the consideration of circle/sphere spatial distributions, the proposed method can achieve different degrees of feature clustering and agglomerating. A wide range of microstructure morphologies can be achieved by adjusting the input parameters. A more accurate description of the features in the microstructures can be achieved without the involvement of the annealing-based optimization process. As a case study, the proposed method was used to generate sandstone microstructures with different grain size distributions and spatial distributions, and the permeability of generated sandstone was analyzed. Furthermore, the proposed method was applied to generate the microstructure model with a target radial distribution function to demonstrate its computational efficiency by comparing it with the random sphere method and simulated annealing based method.

Zwitterionic surface modification of polyethylene via atmospheric plasma-induced polymerization of (vinylbenzyl-)sulfobetaine and evaluation of antifouling properties

Zwitterionic polymer brushes were grafted from bulk polyethylene (PE) by air plasma activation of the PE surface followed by radical polymerization of the zwitterionic styrene derivative (vinylbenzyl)sulfobetaine (VBSB). Successful formation of dense poly-(VBSB)-brush layers was confirmed by goniometry, IR spectroscopy, XPS and ToF-SIMS analysis. The resulting zwitterionic layers are about 50-100 nm thick and cause extremely low contact angles of 10° (water) on the material. Correspondingly we determined a high density of > 1.0 × 10¹⁶ solvent accessible zwitterions/cm² (corresponding to 2,0 *10^-8 mol/cm²) by a UV-based ion-exchange assay with crystal violet. The elemental composition as determined by XPS and characteristic absorption bands in the IR spectra confirmed the presence of zwitterionic sulfobetaine polymer brushes. The antifouling properties of the resulting materials were evaluated in a bacterial adhesion test against gram-positive bacteria (S. aureus). We observed significantly reduced cellular adhesion of the zwitterionic material compared to pristine PE. These microbiological tests were complemented by tests in natural seawater. During a test period of 21 days, confocal microscopy revealed excellent antifouling properties and confirmed the operating antifouling mechanism. The procedure reported herein allows the efficient surface modification of bulk PE with zwitterionic sulfobetaine polymer brushes via a scalable approach. The resulting modified PE retains important properties of the bulk material and has excellent and durable antifouling properties.

Recent advances in biomimetic hemostatic materials

Although the past decade has witnessed unprecedented medical advances, achieving rapid and effective hemostasis remains challenging. Uncontrolled bleeding and wound infections continue to plague healthcare providers, increasing the risk of death. Various types of hemostatic materials are nowadays used during clinical practice but have many limitations, including poor biocompatibility, toxicity and biodegradability. Recently, there has been a burgeoning interest in organisms that stick to objects or produce sticky substances. Indeed, applying biological adhesion properties to hemostatic materials remains an interesting approach. This paper reviews the biological behavior, bionics, and mechanisms related to hemostasis. Furthermore, this paper covers the benefits, challenges and prospects of biomimetic hemostatic materials.

Mechanical Structures of Sidewalk Plants: Anatomical Evaluation

The mechanical structure of plant tissues has recently attracted a lot of attention. The present study aims to evaluate the importance of collenchymatous and sclerenchymatous tissues in supporting plant species in their harsh environments like road and street plant habitats. Dicots and monocots are classified into different models according to the types of supporting mechanisms. Mass cell percentage and soil analysis are used in this investigation. The tissues are distributed with different percentage masses and arrangements to overcome various severe conditions. Statistical analyses enhance the role of these tissues and clarify their significant values. The gear support mechanism is claimed to be the perfect mechanical method used.

Next-generation biomaterials for dental pulp tissue immunomodulation

OBJECTIVES

The current standard for treating irreversibly damaged dental pulp is root canal therapy, which involves complete removal and debridement of the pulp space and filling with an inert biomaterial. A regenerative approach to treating diseased dental pulp may allow for complete healing of the native tooth structure and enhance the long-term outcome of once-necrotic teeth. The aim of this paper is, therefore, to highlight the current state of dental pulp tissue engineering and immunomodulatory biomaterials properties, identifying exciting opportunities for their synergy in developing next-generation biomaterials-driven technologies.

METHODS

An overview of the inflammatory process focusing on immune responses of the dental pulp, followed by periapical and periodontal tissue inflammation are elaborated. Then, the most recent advances in treating infection-induced inflammatory oral diseases, focusing on biocompatible materials with immunomodulatory properties are discussed. Of note, we highlight some of the most used modifications in biomaterials' surface, or content/drug incorporation focused on immunomodulation based on an extensive literature search over the last decade.

RESULTS

We provide the readers with a critical summary of recent advances in immunomodulation related to pulpal, periapical, and periodontal diseases while bringing light to tissue engineering strategies focusing on healing and regenerating multiple tissue types.

SIGNIFICANCE

Significant advances have been made in developing biomaterials that take advantage of the host's immune system to guide a specific regenerative outcome. Biomaterials that efficiently and predictably modulate cells in the dental pulp complex hold significant clinical promise for improving standards of care compared to endodontic root canal therapy.

A silicone-based slippery polymer coating with humidity–dependent nanoscale topography

HYPOTHESIS

Slippery Omniphobic Covalently Attached Liquids (SOCAL) have been proposed for making omnirepellent thin films of self-assembled dimethylsiloxane polymer brushes grafted from silica surfaces. Smooth and flat at very small scale, these fluid surfaces could exhibit a more complex multiscale structure though showing very weak contact angle hysteresis (less than 5°).

EXPERIMENT

In this work, coatings were deposited on glass surfaces from an acidic dimethoxydimethylsilane solution under carefully controlled relative humidity. Ellipsometry mapping was used to analyze the surface structuration with nanometric thickness sensitivity. The sliding properties were determined using a drop shape analyzer with a tilting device, and chemical analyses of the coatings were performed using on-surface techniques (XPS, ATR-FTIR spectroscopy).

FINDINGS

Coated materials possessed an unexpected surface structure with multiscale semispherical-like features, which surprisingly, did not increase the contact angle hysteresis. A careful study of some parameters of the coating process and the related evolution of the surface properties allowed us to propose a new model of the chemical organization of the polymer to support this remarkable liquid-like behavior. These structures are made of end-grafted strongly adsorbed Guiselin brushes with humidity-dependent thickness: the higher the humidity, the thinner and the more slippery the coating.

An atomically smooth container: Can the native oxide promote supercooling of liquid gallium?

Metals tend to supercool-that is, they freeze at temperatures below their melting points. In general, supercooling is less favorable when liquids are in contact with nucleation sites such as rough surfaces. Interestingly, bulk gallium (Ga) can significantly supercool, even when it is in contact with heterogeneous surfaces that could provide nucleation sites. We hypothesized that the native oxide on Ga provides an atomically smooth interface that prevents Ga from directly contacting surfaces, and thereby promotes supercooling. Although many metals form surface oxides, Ga is a convenient metal for studying supercooling because its melting point of 29.8°C is near room temperature. Using differential scanning calorimetry (DSC), we show that freezing of Ga with the oxide occurs at a lower temperature (-15.6 ± 3.5°C) than without the oxide (6.9 ± 2.0°C when the oxide is removed by HCl). We also demonstrate that the oxide enhances supercooling via macroscopic observations of freezing. These findings explain why Ga supercools and have implications for emerging applications of Ga that rely on it staying in the liquid state.

Spreading dynamics of microdroplets on nanostructured surfaces

HYPOTHESIS

Droplet spreading governs various daily phenomena and industrial processes. Insights about microdroplet spreading are limited due to experimental difficulties arising from microdroplet manipulation and substrate wettability control. For droplet sizes approaching the capillary length scale, the gravitational force plays an important role in spreading. In contrast, capillary and viscous forces dominate as the droplet size reduces to smaller length scales. We hypothesize that the dynamic spreading behavior of microdroplets whose radius is far lower than the capillary length differs substantially from established and well understood dynamics.

EXPERIMENTS

To systematically investigate the spreading dynamics of microdroplets, we develop contact-initiated wetting techniques combined with structuring-independent wettability control to achieve microdroplet (<500 μm) spreading on arbitrary surfaces while eliminating parasitic pinning effects (pining force ∼ 0) and initial impact momentum effects (Weber number ∼ 0).

FINDINGS

Our experiments reveal that the capillary-driven initial spreading of microdroplets is shorter, with significantly reduced oscillation dampening, when compared to millimeter-scale droplets. Furthermore, spreading along with capillary wave propagation results in coupling between the spreading velocity and dynamic contact angle at the contact line. These findings, along with our proposed microdroplet manipulation platform, may find application in microscale heat transfer, advanced manufacturing, and aerosol transmission studies.

A Large-Diameter Vascular Graft Replacing Animal-Derived Sealants With an Elastomeric Polymer

INTRODUCTION

To assess the safety and efficacy of an experimental large-diameter vascular graft externally sealed with an elastomeric polymer when used as an interposition graft in the descending aorta of sheep.

METHODS

The experimental vascular grafts as well as control gelatin sealed interposition grafts were inserted into the descending aorta of juvenile sheep. The grafts were assessed by time to hemostasis and blood loss during surgery and hematology and biochemistry panels at distinct time points. Magnetic resonance imaging (MRI) was performed at 3 and at 6 mo after surgery, after which the animals were euthanized and necropsies were carried out including macroscopic and microscopic examination of the grafts, anastomoses, and distal organs.

RESULTS

All animals survived the study period. There was no perceivable difference in the surgical handling of the grafts. The median intraoperative blood loss was 27.5 mL (range 10.0-125.0 mL) in the experimental group and 50.0 mL (range 10.0-75.0 mL) in the control group. The median time to hemostasis was 5.0 min (range 2.0-16.0 min) minutes in the experimental group versus 6.0 min (range 4.0-6.0 min) in the control group. MRI showed normal flow and graft patency in both groups. Healing and perianastomotic endothelialization was similar in both groups.

CONCLUSIONS

The experimental graft has a similar safety and performance profile and largely comparable necropsy results, in comparison to a commonly used prosthetic vascular graft, with the experimental grafts eliciting a nonadherent external fibrous capsule as the major difference compared to the control grafts that were incorporated into the periadventitia. Survival, hemostatic sealing, and hematologic and radiologic results were comparable between the study groups.

Flexible organic field-effect transistors-based biosensors: progress and perspectives

Organic field-effect transistors (OFETs) have been proposed beyond three decades while becoming a research hotspot again in recent years because of the fast development of flexible electronics. Many novel flexible OFETs-based devices have been reported in these years. Among these devices, flexible OFETs-based sensors made great strides because of the extraordinary sensing capability of FET. Most of these flexible OFETs-based sensors were designed for biological applications due to the advantages of flexibility, reduced complexity, and lightweight. This paper reviews the materials, fabrications, and applications of flexible OFETs-based biosensors. Besides, the challenges and opportunities of the flexible OFETs-based biosensors are also discussed.

Prosthetic vascular grafts engineered to combat calcification: Progress and future directions

Calcification in prosthetic vascular conduits is a major challenge in cardiac and vascular surgery that compromises the long-term performance of these devices. Significant research efforts have been made to understand the etiology of calcification in the cardiovascular system and to combat calcification in various cardiovascular devices. Novel biomaterial design and tissue engineering strategies have shown promise in preventing or delaying calcification in prosthetic vascular grafts. In this review, we highlight recent advancements in the development of acellular prosthetic vascular grafts with preclinical success in attenuating calcification through advanced biomaterial design. We also discuss the mechanisms of action involved in the designs that will contribute to the further understanding of cardiovascular calcification. Lastly, recent insights into the etiology of vascular calcification will guide the design of future prosthetic vascular grafts with greater potential for translational success.

First-principle investigations of structural, electronic, thermal, and mechanical properties of AlP1-xBix alloys

CONTEXT

In this work, a comprehensive study concerning the physical properties of ternary alloys system (AlP_1-xBi_x) at different concentrations is presented. The obtained results from our first-principle calculations are compared with previously reported studies in the literature and discussed in detail. Our computed results are found in a nice agreement where available with earlier reported results. Electronic band structures at the above-mentioned concentrations are also determined. Likewise, the impact of the varying temperature and pressure on Debye temperature, heat capacity, and entropy is analyzed as well. Furthermore, elastic constants and related elastic moduli results are also computed. Our results show that alloys are stable and found to be in brittle nature. This is the first quantitative study related to ternary alloys (AlP_1-xBi_x) at mentioned concentrations. We soon expect the experimental confirmation of our predictions.

METHOD

The calculations are performed, at concentrations x=0.0, 0.25, 0.5, 0.75, and 1.0 by using the "full potential (FP) linearized (L) augmented plane wave plus local orbital (APW+lo) method framed within density functional theory (DFT)" as recognized in the "WIEN2k computational code". The "quasi-harmonic Debye model" approach is employed to determine the thermal properties of the title alloys.

Composite-veneering of polyether-ether-ketone (PEEK): evaluating the effects of different surface modification methods on surface roughness, wettability, and bond strength

This study aimed to evaluate the effects of different surface modification methods on the surface roughness, contact angle, and bond strength of composite-veneer materials of polyether-ether-ketone (PEEK). Fifty-five specimens (n = 11) with a size of 7 × 7 × 2 mm were cut out from PEEK discs. The specimens were divided into five groups with different surface treatments: no treatment (NO) (control group), sulfuric acid (SA), plasma (P), femtosecond laser (FS), and Nd-YAG laser (NY). After the surface treatments, the specimens were checked for roughness, contact angle, and bond strength of the composite-veneer material. Data were analyzed with the Welch test for roughness, contact angle, and bond strength parameters. Individual Pearson correlation tests were executed for all surface treatment groups to determine any significant correlations among roughness, contact angle, and bond strength parameters (P < .001). Roughness, contact angle, and bond strength values were affected by surface modification methods (P < .001). In comparison to the control group, NY and FS treatments increased the surface roughness and bond strength; they also provided bond strength values comparable to the SA group. When the relationship between the variables was examined, no correlation was seen between roughness, contact angle, and bond strength values for the NY, SA, and control groups (P > .05); however, significant correlations were determined between the contact angle and surface roughness values for the P and FS groups (P < .05). Femtosecond and Nd-YAG laser treatments are viable surface modification alternatives to the sulfuric acid treatment for the PEEK material.

The effective interfacial tensions between pure liquids and rough solids: a coarse-grained simulation study

The effective solid-liquid interfacial tension (SL-IFT) between pure liquids and rough solid surfaces is studied through coarse-grained simulations. Using the dissipative particle dynamics method, we design solid-liquid interfaces, confining a pure liquid between two explicit solid surfaces with different roughness degrees. The roughness of the solid phase is characterized by Wenzel's roughness factor and the effective SL-IFT is reported as a function of it also. Two solid-liquid systems, different from each other by their solid-liquid repulsion strength, are studied to measure the effects caused by the surface roughness on the calculation of . It is found that the roughness changes the structure of the liquid, which is observed in the first layer of liquid near the solid. These changes are responsible for the effective SL-IFT increase, as surface roughness increases. Although there is a predominance of surface roughness in the calculation of it is found that the effective SL-IFT is directly proportional to the magnitude of the solid-liquid repulsion strength. The insights provided by these simulations suggest that the increase of Wenzel's roughness factor increases the number of effective solid-liquid interactions between particles, yielding significant changes in the local values of the normal and tangential components of the pressure tensor.

Optimizing chemistry at the surface of prodrug-loaded cellulose nanofibrils with MAS-DNP

Studying the surface chemistry of functionalized cellulose nanofibrils at atomic scale is an ongoing challenge, mainly because FT-IR, NMR, XPS and RAMAN spectroscopy are limited in sensitivity or resolution. Herein, we show that dynamic nuclear polarization (DNP) enhanced ¹³C and ¹⁵N solid-state NMR is a uniquely suited technique to optimize the drug loading on nanocellulose using aqueous heterogenous chemistry. We compare the efficiency of two conventional coupling agents (DMTMM vs EDC/NHS) to bind a complex prodrug of ciprofloxacin designed for controlled drug release. Besides quantifying the drug grafting, we also evidence the challenge to control the concurrent prodrug adsorption and to optimize washing procedures. We notably highlight the presence of an unexpected prodrug cleavage mechanism triggered by carboxylates at the surface of the cellulose nanofibrils.

Multifunctional Underwater Adhesive Film Enabled by a Single-Component Poly(ionic liquid)

Tremendous efforts have been devoted to exploiting synthetic wet adhesives for real-life applications. However, developing low-cost, robust, and multifunctional wet adhesive materials remains a considerable challenge. Herein, a wet adhesive composed of a single-component poly(ionic liquid) (PIL) that enables fast and robust underwater adhesion is reported. The PIL adhesive film possesses excellent stretchability and flexibility, enabling its anchoring on target substrates regardless of deformation and water scouring. Surface force measurements show the PIL can achieve a maximum adhesion of 56.7 mN·m^-1 on diverse substrates (both hydrophilic and hydrophobic substrates) in aqueous media, within ∼30 s after being applied. The adhesion mechanisms of the PIL were revealed via the force measurements, and its robust wet adhesive capacity was ascribed to the synergy of different non-covalent interactions, such as of hydrogen bonding, cation-π, electrostatic, and van der Waals interactions. Surprisingly, this PIL adhesive film exhibited impressive underwater sound absorption capacity. The absorption coefficient of a 0.7 mm-thick PIL film to 4-30 kHz sound waves could be as high as 0.80-0.92. This work reports a multifunctional PIL wet adhesive that has promising applications in many areas and provides deep insights into interfacial interaction mechanisms underlying the wet adhesion capability of PILs.

Sequence-Enhanced Self-Healing in “Lock-and-Key” Copolymers

Van der Waals-driven self-healing in copolymers with "lock-and-key" architecture has emerged as a concept to endow engineering-type polymers with the capacity to recover from structural damage. Complicating the realization of "lock-and-key"-enabled self-healing is the tendency of copolymers to form nonuniform sequence distributions during polymerization reactions. This limits favorable site interactions and renders the evaluation of van der Waals-driven healing difficult. Here, methods for the synthesis of lock-and-key copolymers with prescribed sequence were used to overcome this limitation and enable the deliberate synthesis of "lock-and-key" architectures most conducive to self-healing. The effect of molecular sequence on the material's recovery behavior was evaluated for the particular case of three poly(n-butyl acrylate/methyl methacrylate) [P(BA/MMA)] copolymers with similar molecular weights, dispersity, and overall composition but with different sequences: alternating (alt), statistical (stat), and gradient (grad). They were synthesized using atom transfer radical polymerization (ATRP). Copolymers with alt and stat sequence displayed a 10-fold increase of recovery rate compared to the grad copolymer variant despite a similar overall glass transition temperature. Investigation with small-angle neutron scattering (SANS) revealed that rapid property recovery is contingent on a uniform microstructure of copolymers in the solid state, thus avoiding the pinning of chains in glassy MMA-rich cluster regions. The results delineate strategies for the deliberate design and synthesis of engineering polymers that combine structural and thermal stability with the ability to recover from structural damage.

Strategic Tuning of Photophysical Response in the Polyhedral Framework of the Garnet Structure toward White Light-Emitting Devices with Enhanced Color Rendering

Designing a single-phase phosphor with high quantum efficiency and full spectrum emission is inevitable for today's scientific world. Herein, an optimal strategy for realizing white emission in a single component matrix is envisaged based on the structure-property-design-device policy. Cationic substitution corresponding to polyhedral expansion and contraction in A₂A'B₂V₃O₁₂ confirms the existence of strong and intricate linkage in the garnet structure. The dodecahedral expansion causes compression of VO₄ tetrahedra and a blue shift. The direct correlation of V-O bond distance with red shift validates the distortion of the VO₄ tetrahedra. The interdependence of photophysical properties via cationic substitution and subsequent correlation of the V-O bond distance with emission bands enabled the tailoring of phosphor-CaSrNaMg₂V₃O₁₂ with a high quantum efficiency of 52% and excellent thermal stability of 0.39 eV. Bright warm white light-emitting diode (WLED) devices are fabricated based on Eu³⁺ and Sm³⁺-activators. A high quantum efficiency-74% is obtained for the designed Eu³⁺ phosphor. CIE coordinates near the achromatic point (0.329, 0.366), low CCT-5623 K, and high color rendering index (CRI)-87 are obtained for the single-phase WLED device. This work puts forth a new direction for designing and engineering promising WLEDs with enhanced color rendering based on single-phase phosphors with full spectrum emission.

MPpredictor: An Artificial Intelligence-Driven Web Tool for Composition-Based Material Property Prediction

The applications of artificial intelligence, machine learning, and deep learning techniques in the field of materials science are becoming increasingly common due to their promising abilities to extract and utilize data-driven information from available data and accelerate materials discovery and design for future applications. In an attempt to assist with this process, we deploy predictive models for multiple material properties, given the composition of the material. The deep learning models described here are built using a cross-property deep transfer learning technique, which leverages source models trained on large data sets to build target models on small data sets with different properties. We deploy these models in an online software tool that takes a number of material compositions as input, performs preprocessing to generate composition-based attributes for each material, and feeds them into the predictive models to obtain up to 41 different material property values. The material property predictor is available online at http://ai.eecs.northwestern.edu/MPpredictor.

Radial-tangential mode of single-wall carbon nanotubes manifested by Landau regulation: reinterpretation of low- and intermediate-frequency Raman signals

The low-frequency Raman signals of single-wall carbon nanotubes (SWNTs), appearing in the range of 100-300 cm^-1, have been interpreted as radial-breathing mode (RBM) comprising pure radial Eigenvectors. Here, we report that most of the low-frequency and intermediate-frequency signals of SWNTs are radial-tangential modes (RTMs) coexisting radial and tangential Eigenvectors, while only the first peak at the low-frequency side is the RBM. Density functional theory simulation for SWNTs of ~ 2 nm in diameter shows that dozens of RTMs exhibit following the RBM (~ 150 cm^-1) up to G-mode (~ 1592 cm^-1) in order with Landau regulation. We specify the RBM and the RTM on Raman spectra obtained from SWNTs, where both appear as prominent peaks between 149 and 170 cm^-1 and ripple-like peaks between 166 and 1440 cm^-1, respectively. We report that the RTMs have been regarded as RBM (~ 300 cm^-1) and ambiguously named as intermediate-frequency mode (300-1300 cm^-1) without assignment. The RTMs gradually interlink the RBM and the G-mode resulting in the symmetric Raman spectra in intensity. We reveal high-resolution transmission microscope evidence for a helical structure of SWNTs, informing the typical diameter of commercial SWNTs to be 1.4-2 nm.

Research Progress of Intelligent Polymer Plugging Materials

Intelligent polymers have become the focus of attention worldwide. Intelligent polymer materials through organic synthesis methods are used to make inanimate organic materials become “feeling” and “sentient”. Intelligent polymer materials have been applied in actual engineering production, and they are becoming a new research topic for scientists in various fields and countries, especially in the areas of drilling and plugging. The development of intelligent polymer materials can provide new solutions and technical means for drilling and plugging. Unlike traditional plugging materials, intelligent polymer plugging materials can cope with environmental changes. They have the characteristics of a strong target, good plugging effect, and no damage to the reservoir. However, there are currently no reviews on intelligent polymer plugging materials in the drilling field, so this paper fills that gap by reviewing the research progress of intelligent polymer plugging materials. In addition, this paper describes the mechanism and application status of intelligent polymer shape-memory polymers, intelligent polymer gels, intelligent polymer membranes, and intelligent polymer bionic materials in drilling and plugging. It is also pointed out that some intelligent polymer plugging materials still have problems, such as insufficient toughness and a poor resistance to salt and high temperature. At the same time, some suggestions for future research directions are also presented for reference.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

One-dimensional organic metal halide nanoribbons with dual emission

Organic metal halide hybrids with low-dimensional structures at the molecular level have received great attention recently for their exceptional structural tunability and unique photophysical properties. Here we report for the first time the synthesis and characterization of a one-dimensional (1D) organic metal halide hybrid, which contains metal halide nanoribbons with a width of three octahedral units. It is found that this material with a chemical formula C₈H₂₈N₅Pb₃Cl₁₁ shows a dual emission with a photoluminescence quantum efficiency (PLQE) of around 25%. Photophysical studies and density functional theory (DFT) calculations suggest the coexisting of delocalized free excitons and localized self-trapped excitons in metal halide nanoribbons leading to the dual emission.

Frontal Polymerizations: From Chemical Perspectives to Macroscopic Properties and Applications

The synthesis and processing of most thermoplastics and thermoset polymeric materials rely on energy-inefficient and environmentally burdensome manufacturing methods. Frontal polymerization is an attractive, scalable alternative due to its exploitation of polymerization heat that is generally wasted and unutilized. The only external energy needed for frontal polymerization is an initial thermal (or photo) stimulus that locally ignites the reaction. The subsequent reaction exothermicity provides local heating; the transport of this thermal energy to neighboring monomers in either a liquid or gel-like state results in a self-perpetuating reaction zone that provides fully cured thermosets and thermoplastics. Propagation of this polymerization front continues through the unreacted monomer media until either all reactants are consumed or sufficient heat loss stalls further reaction. Several different polymerization mechanisms support frontal processes, including free-radical, cat- or anionic, amine-cure epoxides, and ring-opening metathesis polymerization. The choice of monomer, initiator/catalyst, and additives dictates how fast the polymer front traverses the reactant medium, as well as the maximum temperature achievable. Numerous applications of frontally generated materials exist, ranging from porous substrate reinforcement to fabrication of patterned composites. In this review, we examine in detail the physical and chemical phenomena that govern frontal polymerization, as well as outline the existing applications.

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

Hydrogels-A Promising Materials for 3D Printing Technology

Hydrogels are a promising material for a variety of applications after appropriate functional and structural design, which alters the physicochemical properties and cell signaling pathways of the hydrogels. Over the past few decades, considerable scientific research has made breakthroughs in a variety of applications such as pharmaceuticals, biotechnology, agriculture, biosensors, bioseparation, defense, and cosmetics. In the present review, different classifications of hydrogels and their limitations have been discussed. In addition, techniques involved in improving the physical, mechanical, and biological properties of hydrogels by admixing various organic and inorganic materials are explored. Future 3D printing technology will substantially advance the ability to pattern molecules, cells, and organs. With significant potential for producing living tissue structures or organs, hydrogels can successfully print mammalian cells and retain their functionalities. Furthermore, recent advances in functional hydrogels such as photo- and pH-responsive hydrogels and drug-delivery hydrogels are discussed in detail for biomedical applications.

Unraveling different influences of the fraction of the tetragonal phase in oxide films on the corrosion resistance of Zr alloys from the phase transition mechanism

The mechanism of Sn and Nb influence on the fraction of tetragonal ZrO₂ in oxide films on Zr alloys and their influence mechanism on corrosion resistance of Zr alloys, despite decades of research, are ambiguous due to the lack of kinetic knowledge of phase evolution of ZrO₂ with doping. Using stochastic surface walking and density functional theory calculations, we investigate the influence of Nb and Sn on the stability of tetragonal (t) and monoclinic (m) ZrO₂, and t-m phase transition in oxide films. We found that though Nb and Sn result in similar apparent variation trends in the t-phase fraction in oxide films, their influences on t-m phase transition differ significantly, which is the underlying origin of different influences of the t-phase fraction in oxide films on the corrosion resistance of Zr alloys with Sn and Nb alloying. These results clarify an important aspect of the relationship between the microstructure and corrosion resistance of Zr alloys.

Study of pnictides for photovoltaic applications

For the transition into a sustainable mode of energy usage, it is important to develop photovoltaic materials that exhibit better solar-to-electricity conversion efficiencies, a direct optimal band gap, and are made of non-toxic, earth abundant elements compared to the state-of-the-art silicon photovoltaics. Here, we explore the non-redox-active pnictide chemical space, including binary A₃B₂, ternary AA'₂B₂, and quaternary AA'A''B₂ compounds (A, A', A'' = Ca, Sr, or Zn; B = N or P), as candidate beyond-Si photovoltaics using density functional theory calculations. Specifically, we evaluate the ground state configurations, band gaps, and 0 K thermodynamic stability for all 20 pnictide compositions considered, besides computing the formation energy of cation vacancies, anion vacancies, and cation anti-sites in a subset of candidate compounds. Importantly, we identify SrZn₂N₂, SrZn₂P₂, and CaZn₂P₂ to be promising candidates, exhibiting optimal (1.1-1.5 eV) hybrid-functional-calculated band gaps, stability at 0 K, and high resistance to point defects (formation energies >1 eV), while other possible candidates include ZnCa₂N₂ and ZnSr₂N₂, which may be susceptible to N-vacancy formation. We hope that our study will contribute to the practical development of pnictide semiconductors as beyond-silicon light absorbers.

A Short Review on Nanostructured Carbon Containing Biopolymer Derived Composites for Tissue Engineering Applications

The development of new scaffolds and materials for tissue engineering is a wide and open realm of material science. Among solutions, the use of biopolymers represents a particularly interesting area of study due to their great chemical complexity that enables creation of specific molecular architectures. However, biopolymers do not exhibit the properties required for direct application in tissue repair-such as mechanical and electrical properties-but they do show very attractive chemical functionalities which are difficult to produce through in vitro synthesis. The combination of biopolymers with nanostructured carbon fillers could represent a robust solution to enhance composite properties, producing composites with new and unique features, particularly relating to electronic conduction. In this paper, we provide a review of the field of carbonaceous nanostructure-containing biopolymer composites, limiting our investigation to tissue-engineering applications, and providing a complete overview of the recent and most outstanding achievements.

The efficiency of tumble finishing as a final post-treatment for fatigue enhancement of notched laser powder bed fusion AlSi10Mg

A hybrid post-treatment combining tumble finishing as a final step after shot peening and heat treatment was developed to alleviate the adverse effects of internal and surface defects on the fatigue performance of laser powder bed fusion AlSi10Mg samples. The effects of each post-treatment were investigated individually and synergistically on microstructure, surface morphology and roughness, hardness, residual stresses, porosity, and rotating bending fatigue behavior of V-notched AlSi10Mg samples. The results reveal that tumble finishing can highly reduce surface roughness by 28 and 32% compared to the as-built and heat-treated states while inducing extra surface layer hardening and compressive residual stresses. The hybrid post-treatment of heat treatment + shot peening + tumble finishing significantly increased the fatigue life of the samples by over 500 times higher compared to the as-built series.

Free energy of critical droplets-from the binodal to the spinodal

Arguably, the main challenge of nucleation theory is to accurately evaluate the work of formation of a critical embryo in the new phase, which governs the nucleation rate. In Classical Nucleation Theory (CNT), this work of formation is estimated using the capillarity approximation, which relies on the value of the planar surface tension. This approximation has been blamed for the large discrepancies between predictions from CNT and experiments. In this work, we present a study of the free energy of formation of critical clusters of the Lennard-Jones fluid truncated and shifted at 2.5σ using Monte Carlo simulations, density gradient theory, and density functional theory. We find that density gradient theory and density functional theory accurately reproduce molecular simulation results for critical droplet sizes and their free energies. The capillarity approximation grossly overestimates the free energy of small droplets. The incorporation of curvature corrections up to the second order with the Helfrich expansion greatly remedies this and performs very well for most of the experimentally accessible regions. However, it is imprecise for the smallest droplets and largest metastabilities since it does not account for a vanishing nucleation barrier at the spinodal. To remedy this, we propose a scaling function that uses all relevant ingredients without adding fitting parameters. The scaling function reproduces accurately the free energy of the formation of critical droplets for the entire metastability range and all temperatures examined and deviates from density gradient theory by less than one k_BT.

PyQMC: An all-Python real-space quantum Monte Carlo module in PySCF

We describe a new open-source Python-based package for high accuracy correlated electron calculations using quantum Monte Carlo (QMC) in real space: PyQMC. PyQMC implements modern versions of QMC algorithms in an accessible format, enabling algorithmic development and easy implementation of complex workflows. Tight integration with the PySCF environment allows for a simple comparison between QMC calculations and other many-body wave function techniques, as well as access to high accuracy trial wave functions.

Polymorphism and polymorph-dependent luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2

Building on studies of monoclinic Li₃SiNO₂, a polymorph, β-Li₃SiNO₂, with a previously unknown structure type was synthesized. The β-phase crystallizes in the orthorhombic space group Pbca (no. 61) with lattice parameters of a = 18.736(2), b = 11.1267(5), c = 5.0897(3) Å, and a cell volume of V = 1057.2(1) ų. Using high-temperature solid-state reactions in sealed tantalum tubes, it was possible to obtain high purity samples (<5 wt% of side phase LiSi₂N₃ according to Rietveld analysis) containing exclusively one or the other polymorph, depending solely on the cooling rate. In contrast to the monoclinic phase, orthorhombic β-Li₃SiNO₂ additionally contains a third layer and shows a layer-sequence of the type ABCB. Doped with the activator ion Eu²⁺, the new polymorph exhibits an intense yellow emission (λ_max = 586 nm, fwhm = 89 nm, 0.33 eV, 2650 cm^-1) under irradiation with UV to blue light. Hence, the structural difference between the two polymorphs goes along with a significant blue-shift of 16 nm. The results from single-crystal diffraction and single-grain luminescence measurements were confirmed by Rietveld analysis of bulk samples and powder luminescence data.

Effect of Raw Material Particle Size on the Synthesis of La2Zr2O7 by the Molten Salt Method

In this study, a process based on the molten salt method was proposed to prepare La₂Zr₂O₇ for improving the kinetic conditions of synthesis. Considering that the particle size of raw materials is an important factor that may have an effect on the kinetic process of synthesis, ZrO₂ and La₂O₃ with different particle sizes are used as raw materials, and the synthesis experiment is carried out at 900-1300 °C through the combination of raw materials with different particle sizes. The results show that the particle size of ZrO₂ plays an important role in the synthesis of La₂Zr₂O₇. The "dissolution precipitation" mechanism of the synthesis process in the NaCl-KCl molten salt was confirmed by SEM image observation. Furthermore, the influence of the dissolution rate of each raw material on the synthesis reaction was studied by introducing the Noyes-Whitney equation and testing the specific surface area and solubility of each raw material, and it was confirmed that the particle size of ZrO₂ was the limiting condition of the synthesis reaction, and use of ZrO₂(Z50) with a nominal particle size of 50 nm could significantly improve the kinetic condition of the reaction, thus reducing the synthesis temperature, which can help realize the energy-saving and -efficient synthesis of pyrochlore La₂Zr₂O₇.

Role of aluminium hydrides in localised corrosion of aluminium revealed by operando Raman spectroscopy

Filiform corrosion (FFC) is characteristic of metals such as aluminium and magnesium, usually takes place on coated metals, and spreads from coating defects in the form of filaments with a width on the order of 100 μm. In this work, in situ and operando Raman spectroscopy and optical microscopy were used to characterize the composition and distribution of corrosion products inside growing filaments. The filament head contains water (OH stretching modes, 3000-3600 cm^-1), and corrosion products based on aluminium oxide with both tetrahedrally (840 cm^-1) and octahedrally (600 cm^-1) coordinated Al³⁺, and with some hydroxyl group content (3075, 1420, 1164 cm^-1). Remarkable is the prominent presence of structural motifs as in γ-AlH₃ (1045, 1495 cm^-1). The tail contains predominantly aluminium oxide with octahedrally coordinated Al³⁺ and in addition carbonate (1100 cm^-1) and aluminium chloride (347 cm^-1). Video recordings of the active filigree show hydrogen evolution inside the active head and a very fast precipitation of corrosion products. Re-dissolution, transport and re-formation of the corrosion products is also observed, accompanying start-stop-cycles of the propagation of FFC; this mechanism leads to wavy surface morphologies by lifting of certain coating areas after the passage of the corrosion front as evidenced by 3D optical profilometer analysis. When exposed to the acidic head conditions for a sufficient time, the initiation of other forms of localised corrosion, such as pitting, is possible, which in turn facilitates further propagation of the filament. The in situ detection of hydride which transforms into the typical aluminium corrosion products in due course points to a prominent role of hydride as intermediate in the aqueous corrosion of aluminium.

Influence of Backbone Regioregularity on the Optoelectronic and Mechanical Response of Conjugated Polyelectrolyte-Based Hydrogels

The ability to form robust, optoelectronically responsive, and mechanically tunable hydrogels using facile processing is desirable for sensing, biomedical, and light-harvesting applications. We demonstrate that such a hydrogel can be formed using aqueous complexation between one conjugated and one nonconjugated polyelectrolyte. We show that the rheological properties of the hydrogel can be tuned using the regioregularity of the conjugated polyelectrolyte (CPE) backbone, leading to significantly different mesoscale gel morphologies. We also find that the exciton dynamics in the long-time limit reflect differences in the underlying electronic connectivity of the hydrogels as a function CPE regioregularity. The influence of excess small ions on the hydrogel structure and the exciton dynamics similarly depends on the regioregularity in a significant way. Finally, electrical impedance measurements lead us to infer that these hydrogels can act as mixed ionic/electronic conductors. We believe that such gels possess an attractive combination of physical-chemical properties that can be leveraged in multiple applications.