G. Roshan Deen

New stimuli-responsive copolymers of N-acryloyl-N′-alkyl piperazine and methyl methacrylate and their hydrogels

Water-soluble copolymers of N-acryloyl-N′-alkylpiperazine (alkyl: methyl, ethyl) with methyl methacrylate were synthesized and the lower critical solution temperatures (LCSTs) of the copolymers which depend on the compositions and pH of the aqueous solutions are described. The effects of cationic surfactants and simple inorganic salts on the LCSTs are also reported. The influences of pH and temperature on the swelling of the ionizable and thermosensitive hydrogels are studied.

Preparation and Luminescence Properties of Neodymium(III) Oxide Nanocrystals Dispersed in Sol-gel Titania/ (γ-glycidoxypropyl)Trimethoxysilane Composite Thin Films

Neodymium(III) oxide nanocrystals prepared by an inverse microemulsion technique have been dispersed in sol-gel titania/(γ-glycidoxypropyl)trimethoxysilane composite thin films at low temperature. Transmission electron microscopy and x-ray diffraction were used to characterize the phosphor nanoparticles and show that the neodymium(III) oxide nanoparticles have a nanocrystal structure and the size of the nanoparticles is in the range from 5 to 60 nm. An intense up-conversion emission in violet (399 nm) color from neodymium(III) oxide nanocrystals upon excitation with a yellow light (577 nm) has been observed. Two ultraviolet emissions at 347 and 372 nm and a blue emission at 466 nm have also been observed, and those are assigned to electronic transitions appropriately. A relatively strong room-temperature photoluminescence emission at 1064 nm corresponding to the 4 F 3 / 2 → 4 I 1 1 / 1 2 transition of neodymium ion has been measured as a function of the heat treatment temperature. In addition to this emission, two other emissions at 890 and 1336 nm have also been observed. Especially, a clear shoulder peak at 1145 nm, which could probably be resulting from the host matrix, was observed in all measured samples, and this shoulder peak reached a maximum intensity after a heat treatment at 300 °C.

Copolymers of N-acryloyl-N′-methylpiperazine and methyl methacrylate: Synthesis and its application for Hg(II) detection by anodic stripping voltammetry

Abstract Copolymers of N -acryloyl- N ′-methylpiperazine and methyl methylacrylate were synthesized and characterized. The monomer ratio in the copolymer was analyzed by FTIR spectroscopy. The copolymer was found to form a complex with Hg(II) ions. A chemically modified electrode (CME) fabricated by attaching a copolymer film to a glassy carbon electrode for the detection of Hg(II) ions is described. The polymer swelled in aqueous solution, allowing easy access of Hg(II) ion for binding. Anodic stripping voltammetry was employed for the detection of Hg(II) ions. The effects of pH of the measurement and deposition solutions, deposition time and the Hg(II) concentration were studied. The limit of detection was estimated to be 0.23 μg/ml.

Fluorescence characteristics from microemulsion technique derived erbium (III) oxide nanocrystals

Abstract This paper reports the preparation and fluorescence characteristics of erbium (III) oxide nanocrystals. The erbium oxide phosphors were synthesized through a microemulsion technique. Transmission electron microscopy and X-ray diffraction were used to characterize the phosphor nanoparticles and reveals a nanocrystal structure and the size in the range from 5 to 30 nm in diameter. A room-temperature photoluminescence was observed at 1.54 μm with a full width at half-maximum (FWHM) of 22 nm due to intra-atomic transitions ( 4 I 13/2 → 4 I 15/2 ) levels in the erbium (III) ions. It was also observed that the shape and the FWHM of the photoluminescence signals from the composite film prepared by embedding the nanocrystals into titania/organically modified silane composite matrix are quite similar to those from the nanocrystal, but its peak position shifted from 1.540 μm to 1.531 μm.

Preparation and characterization of erbium oxalate and erbium oxide nanoparticles by microemulsion technique

Abstract This paper reports the preparation and characterization of erbium oxalate and erbium oxide nanoparticles. The erbium oxalate and erbium oxide phosphor materials were synthesized through the microemulsion technique. Transmission electron microscopy (TEM) was used to characterize the phosphor materials and reveal a nanocrystal structure for the studied phosphors. A strong green up-conversion emission at 543 nm ( 4 S 3/2 → 4 I 15/2 ) and another weak emission at 528 nm ( 2 H 11/2 → 4 I 15/2 ) have been measured for the studied phosphors upon excitation at 993 nm ( 4 I 11/2 → 4 I 15/2 ). The up-conversion emission mechanism has been explained by means of an energy level diagram. The lifetimes of these emissions have been measured. The green up-conversion emission equally strong in both the phosphors and for these phosphors, color coordinates ( X , Y ) have been obtained in order to assess their color emitting efficiency.

Up-conversion emission in violet from neodymium oxalate and neodymium oxide phosphors obtained by microemulsion technique

This paper presents an up-conversion emission in violet (404 nm) color from neodymium oxide and neodymium oxalate nanoparticles upon excitation with a yellow light (580 nm). Powder phosphors of neodymium oxide and neodymium oxalate nanoparticles were synthesized by the microemulsion technique. In addition to this violet emission, two UV emissions at 342 and 370 nm, and a weak blue emission at 450 nm have been observed and these are assigned to electronic transitions appropriately. The lifetimes of the violet color emission transition at 404 nm have been obtained; the mechanism of the up-conversion emission has heen explained. The oxide-based phosphor has shown strong up-conversion emission compared to the oxalate-based phosphor. The transmission electron microscopy (TEM) measurement shows that the oxide phosphor is in nanocrystal structure.

Copolymers of N-acryloyl-N′-methyl piperazine and methyl methacrylate: Synthesis and determination of monomer reactivity ratios

Abstract Copolymers of N -acryloyl- N′ -methylpiperazine (AcrNMP) and methyl methacrylate (MMA) were synthesized in 1,4-dioxane using benzoyl peroxide as initiator at 70 ± 1 °C. The copolymers were analyzed by FTIR spectroscopy. The monomer reactivity ratios were determined by the methods of Fineman-Ross (F-R) and Kelen-Tudos (K-T), yielding the results r 1 (AcrNMP) = 0.552 and r 2 (MMA) = 1.074 by the F-R method and r 1 = 0.466 and r 2 = 0.980 by the K-T method. The latter r values in turn yielded Q = 0.56 and e = −0.49 for AcrNMP.

Characterization and degradation of elastomeric four-armed star copolymers based on caprolactone and L-lactide.

Although biodegradable polymers have found extensive applications in medical areas, there are limited reports that show elastomeric behavior. In this work, a biodegradable, elastomeric polymer is demonstrated from a four-armed star copolymer. With a fixed middle core composition, comprising caprolactone (CL) and L-lactide (LA), an elastomer is obtained by increasing the polylactide (PLA) end block lengths to obtain sufficient end block crystallinity. This increase suppressed the middle cores crystallinity yet ensured cocrystallization of the PLA ends of individual star copolymer chains to form a three-dimensional network via physical crosslinking. Cyclic and creep test of the star copolymers showed that at least 75% of recovery was achieved. Degradation study of the copolymer showed that degradation first occurred in the caprolactone-co-lactide (CLLA) core, followed by degradation in the PLA ends. Chain scission in the middle core resulted in immediate formation of CL crystals within the core and increased crystallinity over time, in both CLLA core and PLA ends.

Network Structure and Congo Red Dye Removal Characteristics of New Temperature-Responsive Hydrogels

New temperature-responsive hydrogels containing various composition of N-acryloyl morpholine (AM) and N-isopropyl acrylamide (NIPAM) were prepared by free-radical solution polymerization using poly(ethyleneglycol) diacrylate (PEGDA) as the chemical crosslinker. The gels were responsive to changes in external temperature, and exhibited the volume phase transition phenomenon. The gels swelled extensively in water at 23°C, with water-uptake of more than 90% at swelling equilibrium. The influence of molecular heterogeneity of the gels in terms of co-monomer and crosslinker composition on the swelling capacity and equilibrium water uptake was evaluated. The dye adsorption capacity of the gels at room temperature was studied using Congo red as a model dye. The gels displayed significant adsorption capacity of the dye, and the adsorption capacity was found to be dependent on the hydrophilic character of the gel. The characteristic adsorption parameters were determined using the Langmuir isotherm model. The value of equilibrium binding constant was below 1 which indicated favorable adsorption of dye by the hydrogels. The dye release behavior was studied below and above the volume phase transition temperature of the gels. The dye release from the gels was about 95% at temperatures above the volume phase transition temperature of the gels. These gels can be used as reversible sorbents in the efficient removal of Congo red from waste water.

Influence of a New Stiff Crosslinker on the Swelling of Poly(N-isopropyl Acrylamide-co-Sodium Acrylate) Hydrogels and Silver Nanocomposite

Hydrogels composed of N-isopropyl acrylamide and sodium acrylate were prepared using a new stiff crosslinker 1,4-diacryloyl piperazine by a room-temperature free-radical solution polymerization. The gels swelled extensively in water and the swelling increased with increase in sodium acrylate content. Compared to similar gels with N,N’-methylene bisacrylamide as crosslinker the swelling ratio was lower by 25%. Silver nanoparticles were prepared in the hydrogel matrix by in-situ chemical reduction of silver nitrate with sodium borohydride. The new crosslinker being hydrophobic with less structural flexibility controlled the diffusion of silver and borohydride ions into the gel matrix. Silver nanoparticles were formed only on the periphery of the gel as diffusion into the central matrix was hindered by the nonflexible crosslinker. The gels were responsive to temperature changes and the difference in equilibrium water content from 23 to 55°C was 4.5-fold due to strong hydrophobic interactions. The temperature dependence of equilibrium water content was studied by applying the Gibbs-Helmholtz equation and the diffusion process was found to be exothermic. The diffusion of water into the gel matrix followed a non-Fickian behavior due to polymer relaxation. The diffusion coefficient and the penetration velocity decreased with increasing crosslinker content and also with the incorporation of silver nanoparticles in the gel.