Evaluation of the Mooney Viscosity of Natural Rubber by Near‐Infrared Spectroscopy

Abstract

The direct near‐infrared spectroscopic reflectance measurements of prevulcanized natural rubber (brown crepe) was employed for determination of its Mooney viscosity. NIR reflectance spectra were obtained for a total of 100 samples whose Mooney viscosity (VM in the range 68–95 units) have been determined by the standard reference procedure using a commercial computerized Mooney viscometer. These samples were employed as the raw material or were treated to achieve better homogenization. A Fourier transform near infrared (FT‐NIR) spectrophotometer was employed, and the reflectance spectra were obtained with resolution of 4 cm^?1 in the range 4000–10,000 cm^?1 as an average of 75 scans. The samples were split in a calibration set containing 70 samples and in an external validation set consisting of the remaining 30 samples. The calibration and validation spectra sets were treated to correct for baseline shift, further transformed by first derivative and finally modeled by partial least squares (PLS) employing four latent variables. The model was evaluated with the external sample test set, and a RMSEP of 3.6 and 3.9 units of Mooney viscosity were obtained for homogenized and nonhomogenized samples, respectively. The NIR method is capable of determining the Mooney viscosity in few minutes in the non‐pretreated sample with an error that is satisfactory for quality control of natural rubber destined for automobile tire manufacturing.     

Vibrational Spectroscopic Studies on the Dicyclopropylaminecadmium(II)Tetracyanometallate(II) Benzene Clathrates

ABSTRACT

New Hofmann–T_d-type clathrates of the forms Cd(CPA)₂M(CN)₄.C₆H₆ (CPA = cyclopropylamine; M?Cd or Hg) prepared in powder form and characterized by FT-IR, FT-Raman, far-IR spectra, X-ray diffraction, and elemental analyses are reported. Vibrational assignments are proposed for the bands of the host lattice and guest molecule. It is shown that the spectra are consistent with a proposed crystal structure for the compounds derived from X-ray diffraction measurements. The C, H, and N analyses were carried out for all the compounds. All the vibrational modes of coordinated CPA are characterized. The spectral features suggest that these compounds are similar in structure to the Hofmann–T_d-type clathrates.     

Improved calibration transfer between near-Infrared (NIR) spectrometers using canonical correlation analysis

The application of mobile near-infrared (NIR) spectrometers in field measurements is growing. Calibration transfer techniques offer simple solutions for enabling models constructed on benchtop instruments for use on mobile spectrometers. Since different types of spectrometers with different components, scanning ranges and resolutions cause great differences in the spectral response, calibration transfer is difficult to apply. In this paper, we focus on calibration transfer among benchtop, portable and handheld spectrometers by a method of calibration transfer based on canonical correlation analysis (CTCCA). Its capability was illustrated by the example of a group of NIR spectra dataset for predicting reducing sugars, total sugar, and nicotine contents in tobacco leaves. The experimental results showed that the transferability of CTCCA was superior to other conventional calibration transfer methods, including piecewise direct standardization, spectral space transformation, calibration transfer based on independent component analysis, and calibration transfer based on the weight matrix. Moreover, the best transfer results were obtained in the three cases by canonical correlation analysis method executing transfer while the spectra were not interpolated, which shows that this approach has the advantage of easy implementation for calibration transfer. Therefore, CTCCA without interpolation calculation offers a new and simple solution for transferring the spectra acquired by mobile spectrometers to the optimized spectral models built on benchtop devices to improve the accuracy of the results. Additionally, the results show that the benchtop spectrometer is more suitable as the master instrument for calibration transfer with more accurate prediction than using a portable device as the master.     

Visible and NIR luminescence of nanocrystalline β-Ga2O3:Er prepared by solution combustion synthesis

In this paper we report on facile solution combustion synthesis of erbium doped β-Ga₂O₃ with urea as fuel. The product was characterized using powder X-ray diffraction and transmission electron microscopy (TEM). X-ray diffraction and TEM showed that the material is nanostructured. Luminescence properties of β-Ga₂O₃:Er are studied with excitation in near infrared (Nd:YAG laser at 1064 nm) and visible (argon laser at 514.5 nm). A strong NIR emission of Er³⁺ in the window of minimal optical loss in silica based optical fibers, due to the ⁴I_13/2→⁴I_15/2 transition at 1.55 μm has been observed. Codoping with Yb³⁺ significantly increases the intensity of that important emission.     

Fluorescent Phthalocyanine-Encapsulated Bovine Serum Albumin Nanoparticles: Their Deployment as Therapeutic Agents in the NIR Region

In recent times, researchers have aimed for new strategies to combat cancer by the implementation of nanotechnologies in biomedical applications. This work focuses on developing protein-based nanoparticles loaded with a newly synthesized NIR emitting and absorbing phthalocyanine dye, with photodynamic and photothermal properties. More precisely, we synthesized highly reproducible bovine serum albumin-based nanoparticles (75% particle yield) through a two-step protocol and successfully encapsulated the NIR active photosensitizer agent, achieving a good loading efficiency of 91%. Making use of molecular docking simulations, we confirm that the NIR photosensitizer is well protected within the nanoparticles, docked in site I of the albumin molecule. Encouraging results were obtained for our nanoparticles towards biomedical use, thanks to their negatively charged surface (−13.6 ± 0.5 mV) and hydrodynamic diameter (25.06 ± 0.62 nm), favorable for benefitting from the enhanced permeability and retention effect; moreover, the MTT viability assay upholds the good biocompatibility of our NIR active nanoparticles. Finally, upon irradiation with an NIR 785 nm laser, the dual phototherapeutic effect of our NIR fluorescent nanoparticles was highlighted by their excellent light-to-heat conversion performance (photothermal conversion efficiency 20%) and good photothermal and size stability, supporting their further implementation as fluorescent therapeutic agents in biomedical applications.     

Conformational Changes and Redox Properties of Bimetallic Single Helicates of Hexapyrrole-α,ω-dicarbaldehydes

The hexapyrrole-α,ω-dicarbaldehydes 1 a and 1 b were metallated with Cu^II, Ni^II, and Pd^II to give bimetallic complexes where a pair of 3 N+O four-coordinate metal planes are helically distorted and the central 2,2′-bipyrrole subunit adopts a cis or trans conformation. X-ray crystallographic analysis of the bisCu complex revealed a closed form with a cis-2,2′-bipyrrole subunit and an open form with a trans-2,2′-bipyrrole subunit. The bisPd complexes took a closed form both in the solid state and in solution. They are regarded as single helicates of two turns and the energy barrier for the interchange between an M helix and a P helix was remarkably influenced by the bulky 3,3′-substituent of the central 2,2′-bipyrrole subunit. Although the bisNi complexes adopt a closed form in the solid state, they exist as a homohelical open C₂-symmetric form or a heterohelical open C_i-symmetric form in solution. A theoretical study suggested that the closed form of 1 a Pd was stabilized by the Pd–Pd interaction. Compound 1 a Pd was reversibly oxidized by one electron at 0.14 V versus ferrocene/ferrocenium (Fc/Fc⁺) and this oxidized species showed Vis/NIR absorption bands at λ=767 and 1408 nm.     

Modular synthesis of photodegradable polymers with different sensitive wavelengths as UV/NIR responsive nanocarriers

We report the modular and facile synthesis of three novel polymers able to photodegrade by UV and visible light via the Passerini multicomponent polymerizations of 1,6‐hexanedioic acid and 1,6‐diisocyanohexane with 5‐methoxy‐2‐nitrobenzaldehyde ( M2 ), 4,5‐dimethoxy‐2‐nitrobenzaldehyde ( M3 ) or 7‐(N,N‐diethylamino)‐4‐formylcoumarin ( M4 ) respectively. This synthetic strategy takes the advantage of the in situ formation of a photolabile chromophore via the Passerini reaction of an aromatic aldehyde with an acid and an isocyanide, thus it is a versatile approach to regulating the photochemical property of the photolabile chromophores by just changing the aldehyde structure. Importantly, two polymers ( P3 and P4 ) even exhibit NIR degradability due to the two‐photon absorption, and their nanoparticles formulated by the single emulsion method have been used as the NIR‐responsive nanocarriers for hydrophobic dyes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 334–341     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

Photocontrolled Multidirectional Differentiation of Mesenchymal Stem Cells on an Upconversion Substrate

The effective guidance of mesenchymal stem cell (MSC) differentiation on a substrate by near‐infrared (NIR) light is particularly attractive for tissue engineering and regenerative medicine. However, most of current substrates cannot control multidirectional differentiation of MSCs like natural tissues. Herein, a photocontrolled upconversion‐based substrate was designed and constructed for guiding multidirectional differentiation of MSCs. The substrate enables MSCs to maintain their stem‐cell characteristics due to the anti‐adhesive effect of 4‐(hydroxymethyl)‐3‐nitrobenzoic acid modified poly(ethylene glycol) (P1) attached on the upconversion substrate. Upon NIR irradiation, the P1 is released from the substrate by photocleavage. The detachment of P1 can change cell–matrix interactions dynamically. Moreover, MSCs cultured on the upconversion substrate can be specifically induced to differentiate to adipocytes or osteoblasts by adjusting the NIR laser. Our work provides a new way of using NIR‐based upconversion substrate to modulate the multidirectional differentiation of MSCs.     

Thiophene‐Fused‐Heteroaromatic Diones as Promising NIR Reflectors for Radiative Cooling

Developing appropriate NIR‐reflective materials to combat near–infrared (NIR) heat radiation (700–2500 nm) from sunlight, avoiding energy accumulation and reduce energy consumption, is important and highly desirable. In this research, four thiophene‐fused‐heteroaromatic diones were used as basic reflectors to investigate the relationship between their intrinsic molecular structures and NIR‐reflective properties. The reflectance intensity can be readily tuned by adjusting the length of the appended aliphatic side chains, as well as the strength of the electron‐donating groups. A methoxy‐substituted thiophene‐fused‐heteroaromatic dione showed the best performance in reflecting NIR, and it was used as a coating for a model glass house. The comparison of the internal temperature difference relative to a control house was measured and the maximum temperature was 12 °C lower than that in the control house.