Powder Method Research Articles

A New Processing Method for Laser Sintering Polymer Powders at Low Bed Temperatures

Most current laser sintering (LS) machines for polymer powders operate with a maximum bed temperature of 200 °C, limiting the use of higher melting polymers like polyethylene terephthalate (PET), which melts at ~250 °C. Using bed temperatures of ≤200 °C leads to severe part-distortion due to curl and warpage during the sintering process. The paper presents a processing method for LS at low bed temperatures, using an in situ printed anchor film to conquer curl and warpage. With the use of the anchor film, PET parts were successfully printed without machine stoppage at bed temperatures as low as 150 °C, which is about 80 °C lower than the bed temperature for a regular process for PET without the anchor film. The anchor film acts as a frictional restraint, effectively preventing the curling and warping during printing that typically result from crystallization-induced shrinkage at low bed temperatures. Whereas previous studies have employed 13 mm thick anchoring sheets bolted to the machine to prevent curl and warpage at low bed temperatures, our method uses a flexible in situ printed ~70 μm thick film to which the built part naturally adheres. The in situ printed film is easily detachable from the part after the build. The standard LS material, polyamide 12 (PA12), was also printed with lowered bed temperaturewhere the benefit would be reduced thermal degradation of the powder and decreased energy consumption during the sintering process.

Ferrocene Appended Linear Chromophores for Aggregation‐Induced Emission (AIE) and Nonlinear Optics (NLO): Combined Experimental and Theoretical Studies

AbstractNew nonlinear optical (NLO)‐active chromophores, featuring phenyl and methoxy phenyl substitutions at the D‐π‐A motif [(Fc‐C(C6H4‐R) = CH‐CH = C(CN)‐C6H4‐Br)] [R = H (1), OCH3 (2)] are synthesized and structurally analyzed. Chromophore 2 crystallized in a triclinic system (P‐1), consistent with DFT‐optimized structures. Non‐covalent interactions in the crystal packing suppress antiparallel alignment, enhancing SHG efficiencies. Molecular electrostatic potential (MEP) maps reveal structure‐property relationship and electronic communication between donor–acceptor moieties. Both chromophores exhibit suppressed emission in solution due to twisted intramolecular charge transfer (TICT) facilitated by the cyano vinylene group. However, Upon aggregation‐induced emission in a THF/H2O mixture, fluorescence significantly increases, attributed to restricted intramolecular rotation (RIR). Second Harmonic Generation (SHG) efficiencies, measured using the Kurtz–Perry powder technique with potassium dihydrogen phosphate (KDP) as a reference, show chromophore 2 is 1.1 times higher efficiency than chromophore 1. Density functional theory (DFT) derived hyperpolarizability values follow this trend, with chromophore 2 (β0 = 40.39 × 10−30 esu in B3LYP functional) surpassing chromophore 1. DFT and time‐dependent density functional theory (TD‐DFT) calculations employing B3LYP, CAM‐B3LYP, and LC‐BLYP functionals determined second‐order nonlinear optical parameters, B3LYP and CAM‐B3LYP produced values with minimal differences and a close correlation with the experimental results.

3D characterisation of metal powders for additive manufacturing using Nano-CT and deep learning

ABSTRACT The geometrical properties of metal powders, the main raw material in additive manufacturing processes, can have a significant impact on the quality of the parts produced. Therefore, it is essential to characterise these powders effectively. Nano-computed tomography (Nano-CT) technology, with its high-resolution 3D measurement capability, is ideally suited to measure the geometrical characteristics of tiny powders. However, the current CT testing methods for metal powders has two main drawbacks. Firstly, it does not take into account the effect of particle adhesion. Second, it cannot achieve high-precision measurements of the internal pores of powders. To address these limitations, we propose a novel testing method for metal powders that utilises Nano-CT technology. The method first obtains highly dispersed powder samples through a specially sample preparation technique. Then, an improved U-shape networks with multi-level supervision are proposed to achieve high-precision segmentation of the internal pores of the powder. Ultimately, this paper achieves high-precision 3D characterisation of metal powders.

A Facile Method to Incorporate Di-Dopant Elements (F and Sb) into Crystalline Mesoporous Tin Dioxide Nano Powder at Ambient Temperature and Pressure.

A simple two step synthetic method for di-doped crystalline mesoporous tin dioxide powder containing antimony and fluoride at ambient pressure and temperature has been developed. This approach produced materials with high surface areas and improved electrical and optoelectrical conductance. The two dopant elements; antimony and fluoride were introduced to tin dioxide by two approaches. Both approaches produced mesoporous tin dioxide with antimony and fluoride that are integrated in the framework. The structures of these materials are analyzed by powder X-ray diffraction, N2 sorption analysis, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The conductance of the materials improved by factor of 13-34 compared to undoped mesoporous tin dioxide. The effect of the di-doped elements on structure, conductance and optoelectronic properties of these materials are discussed in this paper.

The crystal structure of R3Fe0.1Ga1.6S7 chalcogenides (R – La, Ce, Pr and Tb)

The paper reports the study of the crystal structure of chalcogenides of the composition R3Fe0.1Ga1.6S7 (R = La, Ce, Pr and Tb) as promising materials predicted to possess interesting nonlinear optical and electrical properties. Samples of stoichiometric composition were synthesized by co-melting the elements in quartz containers evacuated to a residual pressure of 10–2 Pa at the maximum synthesis temperature of 1100 °C. The crystal structure of the chalcogenides La3Fe0.1Ga1.6S7 {a = 10.1884(6) Å, c = 6.0515(4) Å}, Ce3Fe0.1Ga1.6S7 {a = 10.0864(4) Å, c = 6.0440(3) Å}, Pr3Fe0.1Ga1.6S7 {a = 9.9853(3) Å, c = 6.0648(2) Å} and Tb3Fe0.1Ga1.6S7 {a = 9.6692(7) Å, c = 6.0799(5) Å} was studied by X-ray powder method. It was determined that the structure of the synthesized phases belongs to the hexagonal symmetry (La3CuSiS7 structure type; space group P63). The structure of the complex chalcogenides (A), (B), (C) and (D) is based on the R3Ga1.67S7 sulfides (R = La, Ce, Pr, and Tb) by substituting gallium atoms in the 2a sites with atoms of statistical mixture M1{0.57(2) Ga + 0.10(2) Fe}, M2{0.56(1) Ga + 0.10(2) Fe}, M3 {0.61(8) Ga + 0.09(1) Fe} and M4 {0.57(2) Ga + 0.10(2) Fe}, respectively. Rare earth atoms are localized in the 6c sites and center sulfur atoms to form trigonal prisms with an additional atom [R 3S13S21S3]. Atoms of statistical mixtures M1, M2, M3, M4 are localized in the 2a sites forming [M 6S2] octahedra. Ga atoms in the 2b sites are surrounded by four sulfur atoms [Ga 3S11S3].

Laser powder bed fusion of SiC particle-reinforced pre-alloyed TiB2/AlSi10Mg composite with high-strength and high-stiffness

Recently, laser powder bed fusion (LPBF) of particle-reinforced aluminum matrix composites (PAMCs) with high-strength and high-stiffness have attracted extensive attention in aviation and aerospace. However, performance improvement of single or dual PAMCs using traditional mechanical mixing method is still limited. Therefore, this study innovatively employed pre-alloyed ∼6.5 wt% TiB2/AlSi10Mg composite as the matrix and mechanically mixed SiC particles with different contents (5 vol% and 10 vol%) to fabricate dual PAMCs with high particles content through LPBF. The results indicated that the 5 vol% SiC+TiB2/AlSi10Mg composite revealed relatively weak agglomeration effect of SiC particle and highest relative density (∼99.1 %), thus exhibiting optimal processability. Using this composition material as the research object, it was found that the microstructure maintains the basic features of pre-alloyed TiB2/AlSi10Mg composite except for the slight grain coarsening. However, SiC particles react with α-Al matrix and Al3Ti. Then Al4C3 and TiC enhancement phase were formed, and micron-sized Si particles precipitated within the Al cells surrounded by the eutectic Al-Si. More importantly, due to novel preparation method of dual PAMCs powder, simultaneous enhancement in ultimate tensile strength (∼554.0 MPa), yield strength (∼376.0 MPa), and elastic modulus (∼97.4 GPa) was achieved. Total particle content (∼14.0 wt%) and tensile property were higher than those of reported other PAMCs processed by LPBF. Finally, expect for the fracture characteristics inherent to the pre-alloyed TiB2/AlSi10Mg composite, new fracture mechanism for the tearing of SiC particles was exhibited. This work provides new insights into the preparation of high-strength and high-stiffness PAMCs processed by LPBF.

Growth, characterization and cognition of 2-cyanopyridinium perchlorate single crystals for nonlinear optical applications.

The fascinating electronic applications attracted researchers to explore the field of nonlinear optical (NLO) materials. The slow evaporation of solvent technique (SEST) was employed to grow the 2-cyanopyridinium perchlorate (2-CPPC) NLO single crystals. The cell parameters of the grown 2-CPPC crystal are confirmed by the single crystal X-ray diffraction (SCXRD) study. The powder X-ray diffraction studies confirm the crystallinity of 2-CPPC crystals, and the peaks were indexed. The computation for the geometry optimization, HOMO-LUMO energy gap, global reactivity parameters, natural bond orbital (NBO) analysis, polarizability, and hyperpolarizability of the 2-CPPC molecule was done using B3LYP (6-311G basis set) functional of DFT method. The experimental FTIR and UV-Vis results of the 2-CPPC compound were compared with the simulated results. The second harmonic generation (SHG) study for the 2-CPPC crystal was employed using Kurtz-Perry powder technique. Single beam Z-scan technique using He-Ne laser is used to study the third-order NLO properties.

Synthesis of α-LiAlO<sub>2</sub> powders of controlled particle size composition for a matrix electrolyte based on carbonate melts

Three methods of synthesis α-LiAlO2 powders for the preparation of a matrix electrolyte for a molten carbonate fuel cell have been considered. The submicron fraction with a specific surface area of 79 m2/g was obtained from an aqueous solution by spray pyrolysis and the large rod-shaped fractions with particles up to 19 μm in length were obtained by synthesis in halide melt and in aqueous solution. Tape casted ceramic matrices were tested in the single fuel cell with 53Li2CO3–47Na2CO3 melt as an electrolyte. The matrices have demonstrated good gas tightness; nitrogen inleakage in anode space did not exceed 0.6 % during 1100 h lifetime test, which included 15 thermal cycles with cooling the cell below melting point of the electrolyte.

Unraveling the Ultrasonic-Assisted Synthesis of Green-Emitting CsPbBr3@Cs4PbBr6: Reaction Process, Luminescence Property, and Display Application.

The pursuit of stable and highly emissive perovskite materials has garnered increasing attention in optoelectronic applications. Green-emitting CsPbBr3@Cs4PbBr6, as a green-emissive material in the solid-state form, has great potential as a color conversion material for full-color displays. However, it is a challenge to achieve mass preparation under ambient conditions. Meanwhile, the formation mechanism is ambiguous. This study reports a ligand-free and rapid mass synthesis of nanomicrosized CsPbBr3@Cs4PbBr6 solid via an ultrasonic-assisted method. The synthesized CsPbBr3@Cs4PbBr6 solids exhibit uniform morphology, high stability, and solid-state quantum efficiency of approximately 55%. Moreover, the transformation mechanism from Pb-Br complexes in the synthesis process is fully investigated by monitoring the phase and spectral evolution. By employing it as a green emitter, the obtained white light-emitting diode (LED) device shows high performance with a correlation color temperature of 7635 K and a wide color gamut of 123% NTSC. This study offers a low-cost and simple operation mass production method for solid-state perovskite powders with excellent chemical stability. Additionally, it provides new insights into the formation mechanism of highly efficient perovskite materials and promotes their practical applications.

Effect of Al2O3 coating on the properties of Si3N4 ceramics prepared by vat photopolymerization

The preparation of Si3N4 ceramics by vat photopolymerization (VPP) has motivated increasing research interest. However, it is challenging to prepare Si3N4 ceramics by VPP due to the high UV-light absorbance and refractive index of powder. In this paper, a method for Al2O3-coated Si3N4 powder was proposed. Combined with the boehmite-coated and high-temperature treatment, Al2O3 was successfully coated on the surface of Si3N4 powder. The effect of Al2O3 content on the properties of Si3N4 powders, slurry and the sintered Si3N4 samples were investigated. The Al2O3 coating layer not only improves the curing forming ability of Si3N4 slurries, but also can directly act as one of the sintering aids of Si3N4 ceramics. The bulk density of the samples decreases from 3.04 ± 0.02 g/cm3 to 2.97 ± 0.01 g/cm3 with the increase of coating content, while the porosity increases from 5.38 ± 0.89 % to 7.54 ± 0.63 %. The sample of 5 wt % Al2O3 coating content has the maximum flexural strength of 474.28 ± 16.38 MPa and the highest relative density of 94.62 ± 0.89 %. This work can not only obtain a great modification effect, but also promote the dense sintering of Si3N4 ceramics during subsequent stages, which provides a constructive method for modifying Si3N4 powders to achieve photopolymerization.

The effect of oxidation on tribology behavior of nickel-graphite coated stainless steel SS420

The main solution to the challenge of maintaining maximum sealing in the compressor section of each gas turbine is the use of abradable coatings. These coatings have a double duty, including (a) maintaining the lagging and (b) protecting the tips of the rotor blades. Choosing the type of abradable coating primarily depends on the service temperature of the coating. Nickel-graphite (Ni-G) coating is a good choice for use up to 480 °C and, or steel/sub-alloy rotor blades. In this research, the Ni-G coating was applied by the flame spraying method of Ni-G powder with a thickness of about 250 μm on an SS420 stainless steel substrate. The effect of the composition of the bonding layer was also investigated using two compositions, Ni-5Al and NiCrAlY. Obtaining the knowledge of applying Ni-G coating by flame spraying, identifying the structural and compositional characteristics of the coating (through optical and electron metallography), and the effect that oxidation can have on the tribological behavior of the coating were among the goals of this project. The best conditions for spraying the Ni-G coating were achieved an oxygen gas pressure of 6 bar, oxygen flow rate of 18 L min−1, acetylene pressure of 1.5 bar, acetylene flow rate of 24 L min−1, and the distance between the gun head and the sample surface was 22 cm. The results showed that placing the coating in oxidizing conditions increases its coefficient of friction. The increase in the coefficient of friction was attributed to the formation of oxide shells on the surface of the coating after 500 h of exposure to oxidation conditions. Corresponding to the higher coefficient of friction, the oxidized coating showed a decrease in wear resistance as a result of oxidation. This result can show the decrease in abradable of this coating with increasing service time.

Properties and characteristics of steam-exploded donkey bone powder and corresponding whole wheat cookies

Steam explosion was found to be the most effective preparation method for donkey bone powder, compared with non-treatment, autoclave and steam processing. And the effect of steam-exploded donkey bone powder (SEDBP) on the quality characteristics of whole wheat cookies was evaluated. Compared with untreated powder, particle size of SEDBP was reduced by 55.60 %, while oil- and water-holding capacity, water solubility and ABTS radical-scavenging rate significantly increased by 13.94 %, 26.86 %, 298.26 % and 91.47 %, respectively. Steam explosion enhanced protein digestibility from 32.17 % to 71.43 %, increased the Ca2+ release rate from 37.47 % to 47.82 %, and increased the release of 11 amino acids during digestion. SEDBP reduced the solvent retention capacity of flour blends and improved the color, hardness and spread ratio of whole wheat cookies. Cookies with 30 % SEDBP addition had better flavor, texture and scored the highest on overall acceptability. The results will help expand animal bone applications and develop nutrition-fortified foods.

Rapid identification method of milk powder from different animals based on Raman spectroscopy

This study developed an efficient method for identifying and quantitatively analyzing animal-origin milk powders using Raman spectroscopy combined with chemometrics. By employing the MultiClassClassifier model, the method achieved high accuracy in distinguishing various types of animal-origin milk powders, with sensitivity and specificity both exceeding 80% and an overall accuracy of 93%. Furthermore, the quantitative models based on Partial Least Squares Regression and Support Vector Machine Regression exhibited excellent linear correlations, with both Root Mean Square Error and Mean Relative Error below 0.2. These models successfully quantified adulteration in camel, mare, and donkey milk powders in comparison to goat and cow milk powders. The study's approach not only holds significant promise for detecting adulteration in specialty milk powders but also demonstrates wide applicability in analyzing other powdered adulterants.

DACTYLOGRAPHY: The Scientific Study of Fingerprint

Fingerprint analysis has become important because of its reliability and scientific explanation in the courts. Fingerprint has three principles classification, uniqueness and identification. Now there are digital biometric scanner has the ability to access by fingerprint within a minute. This Automated Fingerprint Identification System has made easier to accessible. But the reliability would be little less than other ways to identify fingerprints. Because due to the malfunction of the scanner database can be manipulated or hacked by anyone to access the security. There are various types of fingerprints which needed to know for analyzing it. These types are 1. Patent Fingerprint(visible) 2. Latent Fingerprint(invisible) 3. Plastic/3d; to developing fingerprints there are different methods for different types of fingerprint. Fingerprint experts tend to develop fingerprint in crime scene for solving the crime. Whereas fingerprint become most important physical evidence in matter of solving crime. For developing to analyzing fingerprint expertise would be necessary for establishment. But there are various challenges for forensic experts which are distort prints, smudge prints, contaminated crime scene, database error, partial prints, etc. for the recording of the fingerprint on the wall also be challenging for experts which only can be recorded by photography. Henry classification system would be time consuming to evaluate the recorded fingerprints. Then there is chemical method to develop fingerprint due to the secretion of sweat, oil and other body fluids which make an invisible print. The outermost skin layers have various pores through where body fluid tend to secrets which is responsible for making fingerprints. To make it visible various chemical need to apply so that the secreted body fluid will react with chemical and its visibility will appear. There are some pattern types which tend to administer the individuality such as Arch, Loop and Whorl. Every pattern in itself is unique which can’t be match with any other person. Another way is ridge characteristics which is also valuable way to identify fingerprint. Because of its unique characteristics which tend to differ for every person and not only one characteristics but also 14 ridge characteristics are possible to identify through fingerprint. Porescopy and Edgescopy these are other ways to identify fingerprints but it is not practicable in India right now. There are basic two ways to develop latent fingerprints powder method and chemical methods. Through powder method, various powder and brushes will be need to develop fingerprints but it need to be know the surface where fingerprints are found. In chemical method there would be various chemical compound which needed to apply for the development of the latent fingerprints

Effect of multi-donor and extended π-conjugation in ferrocene appended indanedione chromophores for aggregation induced emission enhancement (AIEE) and nonlinear optics†

A new (D-D’π-A) type ferrocene and methoxyphenyl (D-D′) conjugated indanedione (A) based linear and π-extended multi-donor-π-acceptor chromophores 1–4 were synthesized and characterized. The chromophores 2–4 were further investigated by single-crystal analysis through X-ray diffraction, revealing centrosymmetric space groups with non-covalent interactions (inter, intramolecular hydrogen bonding, and C–H…π interactions) and these molecular packing interactions favor SHG efficiencies. Electrochemical studies show the one-electron charge transfer (Fe2+⇌Fe3+) and observed greater redox potential of chromophore 4 than the parent ferrocene due to the substitution effect. The solvatochromic studies in emission spectra resulted in redshift (56–109 nm) for the chromophores 1–4 by increasing the solvent polarities, which indicates higher excited state stabilization relative to the ground state, results effective intramolecular charge transfer process within the chromophores. The occurrence of ferrocene moieties lowers the fluorescence intensities of the chromophores 1–4, which was overcome through aggregation induced emission enhancement (AIEE) studies at 60 % (THF/H2O). The AIEE state also shows 23 times higher quantum yield than the THF solution for chromophore 4. In addition, a thin film using polymethyl methacrylate as a binder shows a significant blue shift with higher emission intensity than those obtained in the solution due to the intermolecular interactions and enhancement of viscosity. The SHG efficiency studied using the Kurtz and Perry powder technique results in a higher value for chromophore 4 (2 times higher than the reference KDP) attribute to the multi donors, acceptor, and extended π conjugation reducing the anti-parallel alignment in the solid state. The computational calculations were done to validate the experimental results using B3LYP/6-31+G** level of theory.

Method for profile reconstruction of the workpiece surface during groove micromilling

A leading trend in modern industry is hybrid manufacturing methods. The intention is to integrate additive and subtractive methods into a single machine. In such a process, it is difficult to evaluate the quality of the manufactured component between successive processes. A solution that would make it possible to determine the quality of a component produced by incremental technologies on the basis of forces recorded in a machining process is not yet available. In the present study, an attempt was made to reconstruct the surface of the machined workpiece solely on the basis of recorded forces during the groove micromilling process. A workpiece with a known surface geometry in the form of a sinuous wave was machined. The geometry of the workpiece corresponded to a structure typical of the selective laser sintering method for metallic powders. A process conducted with two different axial cutting depths was considered. The reconstructed surface profiles were evaluated by comparative analysis with the real machined surface.

Novel synthesis of Ti3C2 MXene/ZnO/CdSe for sonoelectron and photoelectron triggered synergetic sonophotocatalytic degradation with various antibiotics

A straightforward and precise method was employed to generate Ti3C2 MXene/ZnO/CdSe photocatalysts by a simple synthesis process involving calcination at a temperature of 400 °C. Optical, structural, morphology, microstructure, and compositional properties of these catalysts were characterized. Results demonstrated that the presence of ZnO and CdSe doping sustained their existence inside the Ti3C2 MXene structure. Effects of catalyst powder, pollutant powder, and different degrading methods such as sonophotocatalytic, sonocatalytic, and photocatalytic methods on various antibiotic pollutants were then compared. The degradation efficiencies of sonophotocatalytic method were found to be highly efficient, resulting of 99.99, 99.98, and 99.90 % for ciprofloxacin, amoxicillin, and ofloxacin, respectively. Analysis of scavenger effect also illustrated the deterioration of ciprofloxacin and amoxicillin, suggesting that superoxide radicals (O2−) had a substantial role in the sonophotocatalytic degradation process. Based on data obtained for ofloxacin, it was clear that the existence of holes (h+ quencher) affected the deterioration of ofloxacin in the system. Ti3C2 MXene/ZnO/CdSe had a performance in electrochemical sensing. Limits of detection (LODs) for ciprofloxacin, amoxicillin, and ofloxacin were 39.29, 4.49, and 13.04 ppm, respectively. Limits of quantification (LOQs) for ciprofloxacin, amoxicillin, and ofloxacin were 119, 13.61, and 39.52 ppm, respectively. Efficient degradation of pollutants using visible light can be achieved by employing straightforwardly manufactured Ti3C2 MXene/ZnO/CdSe photocatalysts, making them a practical and promising option.

Design and numerical analysis of perforated plate lattice structures

The plate lattice structure, a novel mechanical metamaterial, surpasses traditional truss lattice structures in stiffness and strength. However, its closed-walled topology poses challenges for manufacturing using powder or liquid-based additive manufacturing methods. This study addresses this issue by focusing on designing manufacturable plate lattice structures with various perforations. Through numerical simulations, we conducted a parametric study to investigate how different perforations influence the stiffness, isotropy, strength, and buckling resistance of the plate lattice structures. The results demonstrate that perforated plate lattice structures maintain higher stiffness compared to the traditional stretching-dominated octet truss lattice. The degree of stiffness deterioration is dependent on the geometry of the perforations. While plate lattice structures exhibit high stiffness at an extremely low relative density of 0.009, their strength is limited by premature elastic buckling. In contrast, at this relative density, the octet truss lattice demonstrates much greater strength. Interestingly, the introduction of perforations improves the plate lattices’ buckling resistance as compared to the unperforated design. With an increase in relative density, the plate lattices’ yielding mechanism shifts from elastic buckling-dominated to material plasticity-dominated. Moreover, when compared to other lattice structures in literature, it becomes evident that perforated plate lattice structures exhibit superior stiffness and strength, underscoring their considerable potential. The perforated lattices designed in this study contribute to the advancement of infill structures applicable in additive manufacturing and expanding the current state of the art in this field.

Spectral, optical, thermal, dielectric, micro hardness analysis and computational calculations of a novel crystal, 2-amino-3-methylpyridinium 2, 4-dinitrobenzoate

By adapting slow evaporation technique novel single crystals of 2-Amino-3- Methylpyridinium 2, 4-Dinitrobenzoate (AMPD) were synthesized. The grown crystal was subjected to Single crystal X‒Ray Diffraction technique to explicate the crystal structure. The spectral analyses were carried out to identify the vibrational modes of various functional groups. To explore the optical transparency of the synthesized crystal UV‒Visible study has been performed and its cut-off wavelength was found to be 209 nm. By Kurtz‒Perry powder technique, the assessment of second harmonic generation efficiency of the crystal has been calculated. Using TG/DTA analysis, the thermal behavior of the crystal was studied. The mechanical strength of the crystal was examined by Vicker′s micro hardness test and the work hardening coefficient was 3.59, affirming that the grown crystal belongs to soft material category. Optimized structural geometry, vibrational wavenumbers, frontier molecular orbitals energy, chemical reactivity indices and density of states were also computed using DFT method. Nonlinear optical property of the molecule was explored by the first‒order hyperpolarizability calculation. These experimental and theoretical studies reveal that the molecules can be suitable to use in optoelectronic devices.

Second harmonic generation and reverse saturable absorption in electrospun picric Acid-PMMA nanofibers

Picric acid (PA) – polymethyl methacrylate (PMMA) nanofibers were synthesised using electrospinning technique by optimising all the required parameters. The nonlinear optical behaviour of the synthesised nanofibers was investigated along with their preliminary characterisations like morphological, structural, thermal, mechanical, dielectric and linear optical studies. The nanofibers with average diameter around ∼800 nm, were found to crystallise in Pca21 space group under the orthorhombic crystal system. The incorporation of Picric acid nanocrystals inside the PMMA nanofibers enhanced their tensile strength. Second harmonic generation imaging of picric acid embedded PMMA nanofibers was done by nonlinear microscopy and the emission was confirmed by power dependence as well as Kurtz – Perry powder technique. Nonlinear absorption studies by Z – scan technique were conducted with a Q – switched Nd: YAG laser and the nanofibers exhibited reverse saturable absorption nature at all the input intensities (0.616 × 1012 W/m2, 1.23 × 1012 W/m2 and 2.46 × 1012 W/m2) and the value of the nonlinear absorption coefficient increased corresponding to an increase in input intensity (0.98 × 10−10 m/W, 1.39 × 10−10 m/W and 1.61 × 10−10 m/W) owing to a sequential two photon absorption. Using the transmittance data optical limiting properties of the nanofibers were also analysed and the limiting threshold values (1.92 × 1012 W/m2, 1.80 × 1012 W/m2 and 1.54 × 1012 W/m2) at respective intensities were extracted. The low optical limiting threshold obtained in the present case confirms that picric acid – PMMA nanofibers can be an assured contender as optical limiters in laser safety devices.