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Today: 21 January 2021, Thursday.

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#1

 

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Description Amphiphilic thermoresponsive copolymer bottlebrushes based on methoxy oligo(ethylene glycol)7 methacrylate and alkoxy(C12–C14) oligo(ethylene glycol)6 methacrylate have been successfully synthesized via RAFT and conventional free-radical polymerization in toluene. The thermoresponsive behavior of the copolymers in dilute aqueous solutions was studied by turbidimetry and laser light scattering. In water, the copolymer brushes form flower-like micelles with a hydrophobic core consisting of a polymer backbone and alkyl(C12–C14) groups and poly(ethylene glycol) linear chains and loops forming a hydrophilic shell. The size and aggregation number of the micelles and the cloud point of solutions were found to depend on the copolymer composition and chain length, as well as on the synthesis method. The conditions needed for the formation of uni- and multimolecular micelles were determined. Fluorescence techniques were used to determine the CMC of the copolymers and the drug loading capacity of the micelles using pyrene as a model hydrophobic drug. Amphiphilic thermoresponsive copolymer bottlebrushes based on methoxy oligo(ethylene glycol) methacrylate (MOEGM) and alkoxy(C12-C14) oligo(ethylene glycol) methacrylate (DOEGM) have been synthesized via RAFT and conventional free-radical polymerization in toluene. In water, these copolymer brushes form flower-like micelles with a hydrophobic core consisting of a polymer backbone and alkyl(C12–C14) groups and poly(ethylene glycol) linear chains and loops forming a hydrophilic shell. The size and aggregation number of the micelles depend on the copolymer composition and chain length, as well as on the synthesis method.

#Materials
Field # Materials
Updated 20 January 2021

#2

 

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Description Cleavage of siloxane bonds (Si-O) in organosiloxanes (OSs) is one of the most fundamentally and practically important challenges in the modern chemistry of silicones. However, no benign approaches have been found to cleave these bonds under mild conditions. In this paper, siloxane bond cleavage in polydimethylsiloxane (PDMS) was studied using a mixture of the “green” reagent dimethyl carbonate (DMC) and an environmentally benign reagent, tris(pentafluorophenyl)borane (B(C6F5)3). The obtained results indicate that the Si-O bonds are cleaved by reaction with DMC to form lower-weight polymer fragments with alkoxy end groups, while the addition of B(C6F5)3 to the depolymerizing mixture significantly increases the degree of PDMS depolymerization at room temperature or with increasing temperature. Quantum chemical calculations show that the DMC molecules form stable complexes with B(C6F5)3 by preferable formation of C=O····B bonds, which increases the solvation effects and kinetic energy upon collision with PDMS. This result provides an appropriate electronic structure and orientation for the complexes for more effective interaction with Si-O-Si via a concert mechanism. This proposed benign approach can be used for the production of new OS polymers, silicone recycling and functionalization of metal or metalloid oxides. We report a novel approach of siloxane bond splitting in organosiloxane using mixture of tris(pentafluorophenyl)borane and dimethyl carbonate. In the first part of this note, depolymerization of polydimethylsiloxane by dimethyl carbonate and with the addition of tris(pentafluorophenyl)borane is studied. Reactions are studied at different concentrations of above-mentioned reagents and temperature while the second part of this note represents theoretical calculation results which explain the mechanism of the depolymerization reaction.

#Materials
Field # Materials
Updated 20 January 2021

#3

 

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Description Flat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However, materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission spectroscopy, we show the emergent flat band in a VSe2 / Bi2Se3 heterostructure. Our photoemission study demonstrates that the flat band covers the entire Brillouin zone and exhibits 2D nature with a complex circular dichroism. In addition, the Dirac cone of Bi2Se3 is not reshaped by the flat band even though they overlap in proximity of the Dirac point. These features make this flat band distinguishable from the ones previously found. Thereby, the observation of a flat band in the VSe2 / Bi2Se3 heterostructure opens a promising pathway to realize strongly correlated quantum effects in topological materials. Dispersionless flat bands are often required to observe unusual quantum states of matter. Here, angle-resolved photoemission spectroscopy (ARPES) reveals a flat band electronic structure in a VSe2/Bi2Se3 heterostructure, and exhibits complex circular dichroism.

#Materials
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Updated 20 January 2021

#4

 

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Description Photomediated-reversible-deactivation radical polymerisation (photo-RDRP) has a limited scope of available photocatalysts (PCs) due to multiple stringent requirements for PC properties, limiting options for performing efficient polymerisations under long wavelengths. Here we report an oxygen-mediated reductive quenching pathway (O-RQP) for photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerisation. The highly efficient polymerisations that are performed in the presence of ambient air enable an expanded scope of available PCs covering a much-broadened absorption spectrum, where the oxygen tolerance of PET-RAFT allows high-quality polymerisation by preventing the existence of O2 in large amounts and efficient O-RQP is permitted due to its requirement for only catalytic amounts of O2. Initially, four different porphyrin dyes are investigated for their ability to catalyse PET-RAFT polymerisation via an oxidative quenching pathway (OQP), reductive quenching pathway (RQP) and O-RQP. Thermodynamic studies with the aid of (time-dependent) density functional theory calculations in combination with experimental studies, enable the identification of the thermodynamic constraints within the OQP, RQP and O-RQP frameworks. This knowledge enables the identification of four phthalocyanine photocatalysts, that were previously thought to be inert for PET-RAFT, to be successfully used for photopolymerisations via O-RQP. Well-controlled polymerisations displaying excellent livingness are performed at wavelengths in the red to near-infrared regions. The existence of this third pathway O-RQP provides an attractive pathway to further expand the scope of photocatalysts compatible with the PET-RAFT process and facile access to photopolymerisations under long wavelengths. Photomediated-reversible-deactivation radical polymerisation has a limited scope of available photocatalysts due to multiple stringent requirements of properties. Here the authors show, an oxygen-mediated reductive quenching pathway for photoinduced electron transfer reversible addition-fragmentation chain transfer polymerisation.

#Materials
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Updated 20 January 2021

#5

 

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Description Researchers from South Korea have invented a new method to transform liquid gallium into a more usable paste- or putty-like form.

#Materials
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Updated 20 January 2021

#6

 

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Description TBD

#Materials
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Updated 20 January 2021

#7

 

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Description Solid-phase synthesis represents the methodological showcase for technological advances such as split-and-pool combinatorial chemistry and the automated synthesis of peptides, nucleic acids and polysaccharides. These strategies involve iterative coupling cycles that do not generate functional diversity besides that incorporated by the amino acids, nucleosides and monosaccharide building blocks. In sharp contrast, multicomponent reactions (MCRs) are traditionally used to generate both skeletal and appendage diversity in short, batchwise procedures. On-resin MCRs have traditionally been employed for the construction of heterocycle and peptidomimetic libraries, but that scenario has changed recently, and today the focus is more on the solid-phase derivatization of peptides and oligonucleotides. This review presents relevant experimental details and addresses the synthetic scope of such on-resin multicomponent protocols employed to accomplish specific biopolymer covalent modifications that are practically inviable by traditional solution-phase methodologies. Recommendations are provided to facilitate the implementation of solid-supported protocols and avoid possible pitfalls associated with the selection of the polymeric resin, the solvent and the order and amount of the reagents employed. We describe procedures comprising the multicomponent lipidation, biotinylation and labeling of both termini and the side chains, as well as the use of MCRs in the traceless on-resin synthesis of ligated and cyclic peptides. Solid-phase protocols for the assembly of α-helical and parallel β-sheet peptides as well as hybrid peptide–peptoid and peptide–peptide nucleic acid architectures are described. Finally, the solid-supported multicomponent derivatization of DNA oligonucleotides is illustrated as part of the DNA-encoded library technology relying on MCR-derived heterocyclic compounds. This review illustrates the power of on-resin multicomponent reaction protocols to create complexity and diversity in biomolecular skeletons such as peptides and oligonucleotides, including strategies to assemble, label and conjugate them.

#Materials
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Updated 20 January 2021

#8

 

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Description TBD

#Materials
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Updated 20 January 2021

#9

 

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Description TBD

#Materials
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Updated 20 January 2021

#10

 

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Description Hybrid materials constructed from the assembly of inorganic building blocks and organic linkers have shown unique properties and applications. Superstructures of semiconductor magic-sized nanoclusters linked by diamines now join this class of materials.

#Materials
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Updated 19 January 2021

#11

 

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Description We have studied optical properties of single-layer and multi-fold nanoporous gold leaf (NPGL) metamaterials and observed highly unusual transmission spectra composed of two well-resolved peaks. We explain this phenomenon in terms of a surface plasmon absorption band positioned on the top of a broader transmission band, the latter being characteristic of both homogeneous “solid” and inhomogeneous “diluted” Au films. The transmission spectra of NPGL metamaterials were shown to be controlled by external dielectric environments, e.g. water and applied voltage in an electrochemical cell. This paves the road to numerous functionalities of the studied tunable and active metamaterials, including control of spontaneous emission, energy transfer and many others.

#Materials
Field # Materials
Updated 19 January 2021

#12

 

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Description An article in Nature Photonics reports a one-dopant alloying strategy for the synthesis of monodisperse perovskite nanoparticles for high-efficiency light-emitting diodes.

#Materials
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Updated 19 January 2021

#13

 

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Description TBD

#Materials
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Updated 18 January 2021

#14

 

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Description In the present work, we constructed nanoscale graphene oxide (NGO) as a drug nanocarrier to improve the process of tumor-targeted drug releases, promote cellular uptake and accumulation of chemotherapy drugs in tumor tissues, and reduce the toxic effects of chemotherapy drugs on normal cells. Hence, great stability was obtained in the biological solution. Moreover, we designed an effective nanoparticle system for the doxorubicin (DOX) delivery targeting the oral squamous cell carcinoma (OSCC) by mediating the HN-1 (TSPLNIHNGQKL) through hydrogen and π–π bonds. DOX@NGO-PEG-HN-1 showed significantly higher cellular uptakes and cytotoxicity in OSCC cells (CAL-27 and SCC-25), compared to free DOX. Moreover, HN-1 showed considerable tumor-targeting and competition inhibition phenomenon. As we expected, the nanocarrier showed pH-responsive drug release. In total, our study represented a good technique to construct OSCC-targeted delivery of nanoparticles and improve the anticancer medicines’ efficiency.

#Materials
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Updated 18 January 2021

#15

 

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Description A multifunctional device produces a much-improved thermoelectric-driven transverse voltage by exploiting a thermoelectric current to drive an anomalous Hall effect in a ferromagnet.

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Updated 18 January 2021

#16

 

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Description Two-dimensional (2D) crystals are promising materials for developing future nano-enabled technologies1–6. The cleavage of weak, interlayer van der Waals bonds in layered bulk crystals enables the production of high-quality 2D, atomically thin monolayers7–10. Nonetheless, as earth-abundant compounds, metal oxides are rarely accessible as pure and fully stoichiometric monolayers owing to their ion-stabilized ‘lamellar’ bulk structure11–14. Here, we report the discovery of a layered planar hexagonal phase of oxides from elements across the transition metals, post-transition metals, lanthanides and metalloids, derived from strictly controlled oxidation at the metal–gas interface. The highly crystalline monolayers, without the support of ionic dopants or vacancies, can easily be mechanically exfoliated by stamping them onto substrates. Monolayer and few-layered hexagonal TiO2 are characterized as examples, showing p-type semiconducting properties with hole mobilities of up to 950 cm2 V−1 s−1 at room temperature. The strategy can be readily extended to a variety of elements, possibly expanding the exploration of metal oxides in the 2D quantum regime. A wide range of highly crystalline, two-dimensional layered metal oxides can be formed by controlled oxidation of the metals at the metal–gas interface.

#Materials
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Updated 18 January 2021

#17

 

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Description Using polymerase chain reaction (PCR)-mediated recombination, single ribonucleic acid (RNA) chains containing bifunctional RNA sequences involving substrate binding and phosphorescent signaling were prepared. For substrate binding and phosphorescent labeling, thrombin- or lysozyme-binding and ruthenium complex-binding RNA aptamer sequences were used. It was demonstrated that the structural properties of the conjugated RNAs showed similar characteristics to the original aptamers using circular dichroism (CD) spectrometry. Furthermore, electrophoretic mobility shift assays of the proteins and phosphorescence measurements of the ruthenium complexes suggested that the binding abilities of the conjugated RNAs maintained the original aptamer functions. Finally, it was established that the conjugated RNA sequences were suitable as phosphorescent RNA probes for protein cognates. Therefore, this “one stroke drawing” strategy is proposed as a promising biological method for the generation of phosphorescent RNA probes that do not culminate in a loss of function of the original aptamers. Using polymerase chain reaction (PCR)-mediated recombination, we prepared single ribonucleic acid (RNA) chains containing bifunctional RNA sequences involving substrate binding and phosphorescent signaling. The prepared RNAs largely maintained the functionalities of the original aptamers even after bifunctionalization. We demonstrated that the bifunctionalized RNAs can be used as phosphorescent detection probes for the target protein. Therefore, we suggested that the PCR-mediated “one stroke drawing” is a promising strategy for the preparation of RNA detection probes.

#Materials
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Updated 18 January 2021

#18

 

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Description Contact-mode high-speed atomic force microscopy (HS-AFM) has been utilised to measure in situ stress corrosion cracking (SCC) with nanometre resolution on AISI Type 304 stainless steel in an aggressive salt solution. SCC is an important failure mode in many metal systems but has a complicated mechanism that makes failure difficult to predict. Prior to the in situ experiments, the contributions of microstructure, environment and stress to SCC were independently studied using HS-AFM. During SCC measurements, uplift of grain boundaries before cracking was observed, indicating a subsurface contribution to the cracking mechanism. Focussed ion beam milling revealed a network of intergranular cracks below the surface lined with a thin oxide, indicating that the SCC process is dominated by local stress at oxide-weakened boundaries. Subsequent analysis by atom probe tomography of a crack tip showed a layered oxide composition at the surface of the crack walls. Oxide formation is posited to be mechanistically linked to grain boundary uplift. This study shows how in situ HS-AFM observations in combination with complementary techniques can give important insights into the mechanisms of SCC.

#Materials
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Updated 18 January 2021

#19

 

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Description Organocatalytic atom transfer radical polymerization (O-ATRP) is recently emerging as an appealing method for the synthesis of metal-free polymer materials with well-defined microstructures and architectures. However, the development of highly effective catalysts that can be employed at a practical low loading are still a challenging task. Herein, we introduce a catalyst design logic based on heteroatom-doping of polycyclic arenes, which leads to the discovery of oxygen-doped anthanthrene (ODA) as highly effective organic photoredox catalysts for O-ATRP. In comparison with known organocatalysts, ODAs feature strong visible-light absorption together with high molar extinction coefficient (ε455nm up to 23,950 M–1 cm–1), which allow for the establishment of a controlled polymerization under sunlight at low ppm levels of catalyst loading. Organocatalytic atom transfer radical polymerization (O-ATRP) is attractive due to its metal-free nature but catalysts are rarely applied at a low loading. Here the authors introduce a catalyst design logic based on heteroatom-doping of polycyclic arenes, which led to the discovery of oxygen-doped anthanthrene as an organic photoredox catalysts for O-ATRP.

#Materials
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Updated 18 January 2021

#20

 

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Description TBD

#Materials
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Updated 15 January 2021

#21

 

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Description Nanoscale variations in the structure and composition of an object are an enticing basis for verifying its identity, due to the physical complexity of attempting to reproduce such a system. The biggest practical challenge for nanoscale authentication lies in producing a system that can be assessed with a facile measurement. Here, a system is presented in which InP/ZnS quantum dots (QDs) are randomly distributed on a surface of an aluminium-coated substrate with gold nanoparticles (Au NPs). Variations in the local arrangement of the QDs and NPs is shown to lead to interactions between them, which can suppress or enhance fluorescence from the QDs. This position-dependent interaction can be mapped, allowing intensity, emission dynamics, and/or wavelength variations to be used to uniquely identify a specific sample at the nanoscale with a far-field optical measurement. This demonstration could pave the way to producing robust anti-counterfeiting devices.

#Materials
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Updated 15 January 2021

#22

 

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Description Over the past decade, the materials science community has fostered the development of materials databases from high-performance computation. While these databases have achieved great success, there are still several challenges to be addressed for the community to realize the full potential of the materials-by-design era.

#Materials
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Updated 14 January 2021

#23

 

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Description In the long history of development and elimination, the creatures have derived a variety of exquisite structures and unique properties, typically natural nacre, marine mussel and Glycera to adapt to the environment and resist the predation of the enemy. Hence, inspired by the combination of special structures and properties of multiple creatures, a novel type of graphene-based micro/nano architecture was proposed, and the related bioinspired nanocomposites were fabricated, Polydopamine coated Graphene oxide/Nanocellulose/Polydopamine (P-GCP). Apart from replicating the layered structure of natural nacre, P-GCP also introduced copper ions and polydopamine to simulate the hardening mechanism of the Glycera’s jaw and the composition of adhesive proteins in mussels to further improve the tensile strength and conductivity of nanocomposites, respectively. The test results showed that the tensile strength of P-GCP reached 712.9 MPa, which was 5.3 times that of natural nacre. The conductivity of artificial nacre was as high as 207.6 S/cm, which was equivalent to that of reduced graphene oxide (rGO). Furthermore, the material exhibited outstanding electrical conductivity when it connected as wires in a circuit, demonstrating the practical application prospects in aerospace, supercapacitors, biomaterials, artificial bones and tissue engineering.

#Materials
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Updated 14 January 2021

#24

 

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Description Advancements in energy technologies, healthcare, semiconductors and food production all have one thing in common: they rely on developing new materials—new combinations of atoms—that have specific properties enabling ...

#Materials
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Updated 14 January 2021

#25

 

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Description Utilizing methods such as scanning electron microscopy observation and mercury intrusion porosimetry, this paper investigates the basic microstructure and pore structure properties of polymer-cement composite joint sealants for pavements, and analyzes the effects and rules of various material types, ratio parameters and processing conditions. Further, the fractal characteristics and variation rules of pore size distribution are investigated for the joint sealants by introducing the fractal theory. The results show that changes in material type, ratio parameter and processing condition produce insignificant effects on the basic microstructure properties and configuration of joint sealants, with effects reflected primarily in the change of sealant pore structure. Measures like increasing the powder-liquid ratio and cement ratio, blending with sulphoaluminate cement or mica powder, adding latex powder or coupling agent, cold drawing and hot pressing, as well as ultraviolet irradiation treatment are all capable of reducing the total pore volume of joint sealants and refining their pore structure. In contrast, opposite effects are yielded when low-grade cement is used, styrene-acrylic emulsion is blended, or plasticizer is added. Additionally, after blending with talc powder or adding carbon fiber additive, the total pore volume of joint sealants remains basically unchanged or reduced, despite the coarsened pore structure. The total pore volume of joint sealants increases after wet–dry cycling treatment, while no obvious change in the pore size distribution is observed. Pore size distribution of the studied joint sealants presents distinct fractal characteristics, and the corresponding fractal dimension of pore surface area ranges between 2.6 and 2.8.

#Materials
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Updated 14 January 2021

#26

 

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Description In this paper, two optimization algorithms (randomly initialized hill climbing and genetic algorithms) are considered to design broadband polarization converters based on coded metasurfaces. A pixeled graphene patch with an elliptic structure is proposed for the initial solution. Each pixel can be 1 and 0 which represents the presence and absence of the graphene. The initial guess tends to the optimum configuration after several optimization processes. Four broadband polarization converters are designed utilizing the optimization algorithms. By changing the chemical potential of graphene, the operation frequency of the polarization converters can be adjusted. Furthermore, the effects of relaxation time of graphene and incident angle on the polarization conversion bandwidth of the four designed structures are investigated.

#Materials
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Updated 14 January 2021

#27

 

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Description Quench hardening aims at the microstructural transformation of steels in order to improve hardness and mechanical strength. The aim phase is, in most cases, the martensite. It is necessary to heat the material until it obtains its austenitization and quenching by immersion in a fluid. Currently, it is common to use watery polymeric solutions in this procedure. These fluids, which are the mixture of polymers in water, vary their thermal exchange capacity depending on the concentrations applied. The increase in concentration minimizes the removal of heat from the part, reducing the formation capacity of martensite, and developing a lower hardness and strong steel. In this work, microstructural characteristics and properties of AISI 1045 steel quenched in solutions based on polyvinylpyrrolidone (PVP) in 10, 15, 20, and 25% concentration were evaluated. The microstructural characterization quantified the percentage of the phases in each concentration, demonstrating a reduction of martensite as the concentrations were high. The investigation of the samples by x-ray diffraction confirmed the absence of austenite retained in the material. Furthermore, a microhardness scale between the core and the surface was constructed, in which a reduction gradient of the indices of this property towards the core of the sample was evidenced.

#Materials
Field # Materials
Updated 14 January 2021