Thermal degradation kinetics of thermoresponsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers prepared via RAFT polymerization

Reversible addition-fragmentation chain transfer polymerization at 70 °C in N,N-dimethylformamide was used to prepare poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers in various compositions to afford well-defined polymers with pre-determined molecular weight, narrow molecular weight distribution, and precise chain end structure. The copolymer compositions were determined by ¹H NMR spectroscopy. The reactivity ratios of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were calculated as r _NIPAM = 0.838 and r _DMA = 1.105, respectively, by the extended Kelen–Tüdös method at high conversions. The lower critical solution temperature of PNIPAM can be altered by changing the DMA content in the copolymer chain. Differential scanning calorimetry and thermogravimetric analysis at different heating rates were carried out on these copolymers to understand the nature of thermal degradation and to determine its kinetics. Different kinetic models were applied to estimate various parameters like the activation energy, the order, and the frequency factor. These studies are important to understand the solid state polymer degradation of N-alkyl substituted polymers, which show great potential in the preparation of miscible polymer blends due to their ability to interact through hydrogen bonding.     

Synthesis, structure, negative thermal expansion, and photocatalytic property of Mo doped ZrV2O7

A new series of compounds identified in the phase diagram of ZrO(2)-V(2)O(5)-MoO(3) have been synthesized via the solution combustion method. Single crystals of one of the compounds in the series, ZrV(1.50)Mo(0.50)O(7.25), were grown by the melt-cool technique from the starting materials with double the MoO(3) quantity. The room temperature average crystal structure of the grown crystals was solved using the single crystal X-ray diffraction technique. The crystals belong to the cubic crystal system, space group Pa3 (No. 205) with a = 8.8969 (4) ?, V = 704.24 (6) ?(3), and Z = 4. The final R(1) value of 0.0213 was achieved for 288 independent reflections during the structure refinement. The Zr(4+) occupies the special position (4a) whereas V(5+) and Mo(6+) occupy two unique (8c) Wyckoff positions. Two fully occupied O atoms, (24d) and (4b), one partially occupied O atom (8c) have been identified for this molybdovanadate, which is a unique feature for these crystals. The structure is related to both ZrV(2)O(7) and cubic ZrMo(2)O(8). The temperature dependent single crystal studies show negative thermal expansion above 370 K. The compounds have been characterized by powder X-ray diffraction, solid-state UV-vis diffuse reflectance spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activity of these compounds has been investigated for the degradation of various dyes, and these compounds show specificity toward the degradation of non-azoic dyes.     

Theoretical framework for quantitatively estimating ultrasound beam intensities using infrared thermography

In the characterization of high-intensity focused ultrasound (HIFU) systems, it is desirable to know the intensity field within a tissue phantom. Infrared (IR) thermography is a potentially useful method for inferring this intensity field from the heating pattern within the phantom. However, IR measurements require an air layer between the phantom and the camera, making inferences about the thermal field in the absence of the air complicated. For example, convection currents can arise in the air layer and distort the measurements relative to the phantom-only situation. Quantitative predictions of intensity fields based upon IR temperature data are also complicated by axial and radial diffusion of heat. In this paper, mathematical expressions are derived for use with IR temperature data acquired at times long enough that noise is a relatively small fraction of the temperature trace, but small enough that convection currents have not yet developed. The relations were applied to simulated IR data sets derived from computed pressure and temperature fields. The simulation was performed in a finite-element geometry involving a HIFU transducer sonicating upward in a phantom toward an air interface, with an IR camera mounted atop an air layer, looking down at the heated interface. It was found that, when compared to the intensity field determined directly from acoustic propagation simulations, intensity profiles could be obtained from the simulated IR temperature data with an accuracy of better than 10%, at pre-focal, focal, and post-focal locations.     

A facile IL–DMSO assisted synthesis of 5-, 6-, and 7-membered benzo-annelated cyclic guanidines

A new and facile IL–DMSO assisted method has been developed for the synthesis of biologically important cyclic guanidines like 2-aminobenzimidazole, 2-imino-4-quinazolinone, and 2-imino-5-benzotriazepinones at ambient temperatures. The desired products could be obtained by microwave irradiation³² also, but at elevated temperatures. A plausible mechanism for catalysis has been proposed.     

Photooxidative and pyrolytic degradation of methyl methacrylate-alkyl acrylate copolymers

Different compositions of poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA) copolymers were synthesized and characterized. The photocatalytic oxidative degradation of all these copolymers were studied in presence of two different catalysts namely Degussa P-25 and combustion synthesized titania using azobis-iso-butyronitrile and benzoyl peroxide as oxidizers. Gel permeation chromatography (GPC) was used to determine the molecular weight distribution of the samples as a function of time. The GPC chromatogram indicated that the photocatalytic oxidative degradation of all these copolymers proceeds by both random and chain end scission. Continuous distribution kinetics was used to develop a model for photocatalytic oxidative degradation considering both random and specific end scission. The degradation rate coefficients were determined by fitting the experimental data with the model. The degradation rate coefficients of the copolymers decreased with increase in the percentage of alkyl acrylate in the copolymer. This indicates that the photocatalytic oxidative stability of the copolymers increased with increasing percentage of alkyl acrylate. From the degradation rate coefficients, it was observed that the photocatalytic oxidative stability follows the order PMMABA > PMMAEA > PMMAMA. The thermal degradation of the copolymers was studied by using thermogravimetric analysis (TGA). The normalized weight loss and differential fractional weight loss profiles indicated that the thermal stability of the copolymer increases with an increase in the percentage of alkyl acrylate and the thermal stability of poly(methyl methacrylate-co-alkyl acrylate)s follows the order PMMAMA > PMMAEA > PMMABA. The observed contrast in the order of photostability and thermal stability of the copolymers was attributed to different mechanisms involved for the scission of polymer chain and formation of different products in both the processes.     

Design,Synthesis, and Biological and In Silico Study of Fluorine‐Containing Quinoline Hybrid Thiosemicarbazide Analogues

A novel series of fluorine‐containing quinoline hybrid thiosemicarbazide analogues ( 8a–8l ) were synthesized and tested for their biological activities. The antibacterial results demonstrated that compounds 8d and 8l [minimal inhibitory concentration (MIC) 62.5 μg/mL] were shown to have higher biological activity than ampicillin against Escherichia coli. Compound 8b (MIC 25 μg/mL) was shown to have the highest activity than was ampicillin against Staphylococcus aureus. The antifungal results demonstrated that compound 8j (MIC 100 μg/mL) has shown good activity. Most of the targeted compounds have shown potent antimalarial activity. Compounds 8d (0.19 μg/mL), 8g (0.30 μg/mL), 8h (0.36 μg/mL), 8k (0.10 μg/mL), 8l (0.28 μg/mL), 8k (0.10 μg/mL), and 8l (0.28 μg/mL) have notable activity than does the reference drug quinine. Compounds 8d (0.27 μg/mL), 8g (0.30 μg/mL), and 8k (0.17 μg/mL) have shown excellent activity against chloroquine‐resistant strain. The MTT assay performed on peripheral blood lymphocyte cultures showed a high percentage of lymphocyte viability [ 8d (99.64), 8g (99.46), 8h (98.83), and 8k (99.51)] at a maximum dose (10 μg/mL), depicting no cytotoxicity of these compounds on human lymphocytes in vitro. A molecular docking study was performed on Pf‐DHFR‐TS inhibitor. A molecular dynamics study has shown compound 8g to have better affinity with protein. ADME‐Tox and pharmacophore study of synthesized compounds suggested prediction of active site.     

Effect of slip on porous-walled squeeze films in the presence of a transverse magnetic field

The present investigation is devoted to study the effect of viscous resistance, arising due to sparse distribution of particles in porous media, on the load capacity and thickness time response of porous-walled squeeze films in the presence of a uniform magnetic field. The results of the analysis obtained by using Beavers and Joseph [1] slip-boundary condition show that the viscous resistance increases the load capacity and thickness time response of squeeze films when compared with the results of Chandrasekhara [2] obtained in the absence of viscous resistance. Hence, for efficient performance of a porous walled squeeze film a suitable porous media in which the material is loosely packed may be used.Nomenclature p pressure in the squeeze film - h thickness of the squeeze film at time t - h ₀ thickness of the film at t=0 - u streamwise velocity component in the squeeze film - v transverse velocity component in the squeeze film - P pressure in the porous material - H thickness of the porous material - U streamwise velocity component in the porous material - V transverse velocity component in the porous material - B B ₀+b - B ₀ impressed uniform magnetic field - b induced magnetic field - E electric field vector (E _x , E _y , E _z ) - m ₀ constant defined in (6), (B ₀ ² / _{m f m})^1/2 - v _h value of v at y=h - h/h ₀, the non-dimensional variable - _n eigen values - _f viscosity - _m magnetic permeability - density - _m magnetic diffusivity, 1/ _{m e} - dimensionless parameter, - _e electrical conductivity - q velocity vector (u, v) - L load capacity - I _n integral defined in (37) - M Hartmann number defined in (7), (m ₀ ² h ²)^1/2 - l length of the strips in x-direction - K permeability of the porous material - J current density vector (J _x , J _y , J _z ) - t time - G _n series coefficient appearing in equation (27)     

Crystal Structure Dependent Dissolution of Non-Cubic Au Crystallites in Aqua Regia

Properties of metal crystallites are governed by their morphologies and inherent crystal structures. In this work, bipyramidal Au microcrystallites hosting non-cubic lattices, body-centered orthorhombic and tetragonal (together termed as bc(o,t)), are investigated for their stability in aqua regia. Specifically, microcrystallites comprising 92 % of bc(o,t) have been subjected to aqua regia of different concentrations and the changes in morphology and lattice phases have been monitored using scanning electron microscopy and X-ray diffraction techniques. The dissolution process was found to be crystal structure dependent and begin at the bipyramidal tips enriched with fcc lattice while retaining the bc(o,t) rich body. Interestingly, with increasing the reaction times, the remaining core was found to be highly reluctant to dissolution and instead, transformed to tetragonal lattices which with increasing treatment, exhibited lattice parameters closer to that of fcc. The study reveals the presence of a bc(o,t)-fcc core-shell structure with the tips enriched with fcc.     

Ultrasonic degradation of poly (styrene-co-alkyl methacrylate) copolymers

The ultrasonic degradation of poly (styrene-co-methyl methacrylate) (SMMA), poly (styrene-co-ethyl methacrylate) (SEMA) and poly (styrene-co-butyl methacrylate) (SBMA) copolymers of different compositions was studied. The copolymers were synthesized and NMR spectroscopy was used to determine the composition, and the glass transition temperatures were determined by DSC. The reactivity ratios were determined by the Kelen–Tudos method and it indicated that the copolymers were random. The effect of solvent, temperature and copolymer composition on the ultrasonic degradation rate of these copolymers was investigated. A model based on continuous distribution kinetics was employed to study the degradation kinetics. The degradation rate coefficients of the copolymers decreased with an increase in the styrene content in the copolymer. At any particular copolymer composition the rate of degradation follows the order: SBMA > SEMA > SMMA. Thermogravimetric analysis (TGA) of the copolymers was carried in order to assess their thermal stability. The same order of degradation was observed for the thermal degradation of the copolymers as that observed for ultrasonic degradation.