Sorption and desorption properties of random copolymer hydrogels of N‐isopropylacrylamide and N‐ethylacrylamide: Effect of monomer composition

Random copolymer hydrogels of N‐isopropylacrylamide and N‐ethylacrylamide (NEAM) were prepared using different monomer compositions in 1:1 methanol–water mixtures. The samples were characterized by cononsolvency study in methanol‐water mixtures at various temperatures, swelling properties measurements, scanning electron microscopy. With changing ratio of the monomers in the reaction mixture, the thermal, morphological and swelling properties, varied significantly. The change in the properties with monomer composition variation are interpreted based on the different thermoresponsive characteristics and interactions of gels of N‐isopropylacrylamide and NEAM (homo‐ and copolymer gels) in water and different methanol‐water mixtures, their variable compositions in the synthesis mixtures, and their morphologies. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45176.     

Cocoa Butter Substitute (CBS) Produced from Palm Mid-fraction/Palm Kernel Oil/Palm Stearin for Confectionery Fillings

This study investigated the physicochemical properties of ternary mixtures of palm mid-fraction (PMF):refined bleached deodorized palm kernel oil (RBDPKO):refined bleached deodorized palm stearin (RBDPS) for cocoa butter substitute (CBS). Fatty acid constituents, triacylglycerol constituents, solid fat contents (SFCs), melting behavior, polymorphism and crystal morphology were determined using gas chromatography (GC), high-performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), pulsed nuclear magnetic resonance (p-NMR), X-ray diffraction (XRD) and polarized light microscopy (PLM), respectively. Eight blends of various ratios of ternary mixtures were investigated based on the previously studied binary fat mixtures. The composition of palmitic (P) and oleic (O), POP, and crystal morphology (size and shape) of the PMF/RBDPKO/RBDPS [14.9/59.6/25.5 (%w/w)] mixture were comparable to cocoa butter (CB), while its melting profile (18.5 and 37 °C), SFC at 20 °C and polymorphism were different from CB. The iso-solid diagrams of the mixture displayed a monotectic effect at 20–25 °C. Therefore, the 14.9/59.6/25.5 PMF/RBDPKO/RBDPS mixture could be used as a CBS in confectionery fillings because of the crystal morphology and monotectic behaviors comparable to those of CB.     

Kinetics of Solvent Extraction of Iron(III) from Sulfate Medium by Purified Cyanex 272 using a Lewis Cell

Abstract

The kinetics of the forward and backward extraction of the title process have been investigated using a Lewis cell operated at 3 Hz and flux or (F) – method of data treatment. The dependences of (F) in the forward extraction on [Fe³⁺], [H₂A₂]_(o), pH, and [HSO₄ ^?] are 1, 0.5, 1, and ?1, respectively. The value of the forward extraction rate constant (k _f ) has been estimated to be 10^?7.37 kmol^3/2 m^?7/2 s^?1. The analysis of the experimentally found flux equation gives the following simple equation: F _f =10^0.13 [FeHSO₄ ²⁺] [A^?], on considering the monomeric model of BTMPPA and the stability constants of Fe(III)‐HSO₄ ^? complexes. This indicates the following elementary reaction occurring in the aqueous film of the interface as rate determining: [FeHSO₄]²⁺+A^?→[FeHSO₄.A]⁺. The very high activation energy of 91 kJ mol^?1 supports this chemical reaction step as rate-determining. The negative value of the entropy change of activation (?94 J mol^?1 K^?1) indicates that the slow chemical reaction step occurs via the S_N2 mechanism.

The backward extraction rate can be expressed by the equation: F _b =10^?5.13 [[FeHSO₄A₂]]_(o) [H⁺] [H₂A₂]_(o) ^?0.5. An analysis of this equation leads to the following chemical reaction step as rate-determining: [FeHSO₄A₂]_(int)→[FeHSO₄A]+A_(i) ^?. However, the activation energy of 24 kJ mol^?1 suggests that the backward extraction process is intermediate controlled with greater contribution of the diffusion of one or the other species as a slow process. The equilibrium constant obtained from the rate study matches well with that obtained from the equilibrium study.     

Unbalanced and Partial Group Sequential Methods for Normal Responses in Clinical Trials

Abstract

Group sequential methods for a two-treatment clinical trial with normal responses are discussed. First we consider the case where the sample sizes for two treatments are possibly unequal between the treatments due to an unequal randomization. Then we discuss group sequential design in the context of a historical control study, that is, under the partial sequential sampling scheme, in which the samples on one treatment, say control, are available at the outset, and the samples on the other treatment, say experimental, are obtained in the group sequential way. We discuss the cases of known and unknown variance for both unbalanced and partial group sequential setups. All of the procedures are discussed with numerical studies.     

SO2 SCRUBBING IN A TAPERED BUBBLE COLUMN SCRUBBER

SO₂ emissions from various sources are found to occur in various concentrations and quantities. Abatement of SO₂ emission, therefore, assumes significant importance over the decades. Wet scrubbers offer great advantage over other devices for gas cleaning. That is the reason that compliance with SO₂ standards will in many cases result in the installation of scrubbing devices. This article presents results of a study on the scrubbing of SO₂ (initial concentration ranging between 400 and 1780 ppm) in a tapered bubble column scrubber using water and dilute sodium alkali. Preliminary studies reveal that the tapered bubble column is capable of generating higher fractional gas holdup than a standard bubble column under similar situations. Moreover, the tapered bubble column has generated bubbles with less power consumption than the existing columns under comparable hydrodynamical conditions. Experimental results indicate that almost 100% SO₂ removal (i.e., zero penetration) can be achieved in the scrubber developed in alkali scrubbing at an optimum Q_L/Q_G ratio of 3.0 m³/1000 ACM. The selection of any gas-cleaning device is based on the performance of the system. In view of this, empirical and semi-empirical correlations are put forward for the prediction of the performance of the scrubber in terms of different pertinent variables of the system for water as well as alkali scrubbing. Experimental results fit extremely well with the correlations. The removal efficiency achievable in the present tapered bubble column scrubber has been found to be higher than that of a single-stage standard bubble column with some modification. The present tapered bubble column is, therefore, hydrodynamically, energetically, and efficiency-wise much better than a standard bubble column.     

Sintering Rates for Pristine and Doped Titanium Dioxide Determined Using a Tandem Differential Mobility Analyzer System

Sintering rates of pristine and V-doped TiO ₂ were obtained using a tandem DMA system. A range of experiments were conducted to first map out the variation of mobility size of a monodisperse (by mobility) agglomerate with time at three fixed temperatures. Using relationships of the surface area to the mobility size, the sintering equation was solved to determine the activation energy and pre-exponential factor. The value of the activation energy was 236 (± 46) kJ/mol for pristine TiO ₂ and 363 (± 1) kJ/mol for V-doped TiO ₂ . The corresponding pre-exponential factors were 7.22 × 10 ¹⁹ and 2.22 × 10 ¹² s/m ⁴ K, respectively. These values were then used to predict changes in mobility diameter at different temperatures, and good agreement was obtained with measurements. Possible reasons for faster sintering rates of V-TiO ₂ relative to pristine TiO ₂ were conjectured.     

Size Distribution and Morphology of Liposome Aerosols Generated By Two Methodologies

Pulmonary delivery of sustained release formulations needs drug encapsulation in a suitable matrix, as well as the generation of aerosols with high lung penetration and suitable release characteristics. Nanometer sized liposomes offer the potential for biocompatibility, controlled release and easy internalization in the lung. For uniform dose delivery and drug release kinetics, it is of interest to understand generation techniques to obtain aerosols containing nearly monodispered nanometer sized dry particles. Two aerosolization techniques, air-jet atomization and electrohydrodynamic atomization (EHDA) were studied to identify conditions under which the inclusion of one-liposome-per-drop could be achieved. In air-jet atomization, low lipid concentrations resulted in a unimodal aerosol with a median mobility diameter of 94 (± 3.5) nm, while higher concentrations led to larger median diameters, implying possible inclusion of multiple liposomes per drop. In EHDA, tuning drop sizes in the range of 130 to 200 nm, as well as the use of high lipid concentrations, resulted in a bimodal aerosol distribution, with peaks at 35 and 100 nm mobility diameters. TEM images of the liposome aerosol from EDHA showed fused liposomes, resulting in cylindrical structures with different physical diameters. It was hypothesized that deformation of liposomes to cylindrical structures in the micro-capillary liquid tip of the electrospray, and interactions along the axial or cross sectional surfaces led to dry particles with different mobility sizes.     

Synthesis of alkyne‐terminated xanthate RAFT agents and their uses for the controlled radical polymerization of N‐vinylpyrrolidone and the synthesis of its block copolymer using click chemistry

Two new alkyne‐terminated xanthate reversible addition‐fragmentation chain‐transfer (RAFT) agents: (S)‐2‐(Propynyl propionate)‐(O‐ethyl xanthate) (X₃) and (S)‐2‐(Propynyl isobutyrate)‐(O‐ethyl xanthate) (X₄) were synthesized and characterized and used for the controlled radical polymerization of N‐vinylpyrrolidone (NVP). X₃ showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X₃ showed the pseudo‐first order kinetics up to 67% monomer conversion. Molecular weight (M_n) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain‐end analysis of the resulting polymer by ¹H‐NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo‐chain extension experiment and the hetero‐chain extension experiment involving synthesis of poly(NVP)‐b‐polystyrene amphiphilic diblock copolymer. Formed alkyne‐terminated poly(NVP) also allowed easy conjugation to azide‐terminated polystyrene by click chemistry to prepare well‐defined poly(NVP)‐b‐polystyrene block copolymers. Resulting polymers were characterized by GPC, ¹H‐NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Removal of chromium (VI) from dilute aqueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride

Different structured activated carbons were prepared from Terminalia arjuna nuts, an agricultural waste, by chemical activation with zinc chloride for the adsorption of Cr(VI) from dilute aqueous solutions. The most important parameter in chemical activation was found to be the chemical ratio (activating agent/precursor, g/g). Carbonization temperature and time are the other two important variables, which had significant effect on the pore structure of carbon. A high surface area of was obtained at a chemical ratio of 300%, carbonization time and temperature of 1 h and 500 °C, respectively. The activated carbon developed shows substantial capability to adsorb Cr(VI) from dilute aqueous solutions. The parameters studied include pH, adsorbent dosage, contact time, and initial concentrations. The kinetic data were best fitted to the Lagergren pseudo-first-order model. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models. The maximum removal of chromium was obtained at pH 1.0 (about 99% for adsorbent dose of 2 g/l and 10 mg/l initial concentration).     

A Novel RFET Sensor for Label-Free Biomolecule Detection

Silicon - In the current scenario, COVID-19 has created a havoc negative impact on the lives of the people, which have triggered the research interest on the design and development of sensitive,...