Fast responsive poly(N-sopropylacrylamide) hydrogels prepared by γ-ray irradiation

γ-ray irradiation of N-isopropylacrylamide (NIPAAm) monomer. solution resulted in the formation of the opaque poly (N-isopropylacrylamide) (PNIPAAm) gel having a microporous structure. The thermo-responsive properties of the microporous gel were the same as that of a homogeneous gel prepared by conventional methods. The gel swelled below and shrunk above the lower critical solution temperature (LCST) (33 °C). The rapid and reversible volume change was observed by changing temperature.     

The effect of 60Co (γ-ray) irradiation on the electrical characteristics of Au/SnO2/n-Si (MIS) structures

The effect of ⁶⁰Co (γ-ray) irradiation on the electrical properties of Au/SnO₂/n-Si (MIS) structures has been investigated using the capacitance–voltage (C–V) and conductance–voltage (G/ω−V) measurements in the frequency range 1 kHz to 1 MHz at room temperature. The MIS structures were exposed to γ-rays at a dose rate of 2.12 kGy/h in water and the range of total dose was 0–500 kGy. It was found that the C–V and G/ω−V curves were strongly influenced with both frequency and the presence of the dominant radiation-induced defects, and the series resistance was increased with increasing dose. Also, the radiation-induced threshold voltage shift (ΔV_T) strongly depended on radiation dose and frequency, and the density of interface states N_ss by Hill–Coleman method decreases with increasing radiation dose.     

Synthesis of carbon nanotube—nanodiamond hierarchical nanostructures and their polyurea nanocomposites

Hierarchical carbon nanostructures (HCNs) comprising functionalized nanodiamond particles (ND) covalently bonded to carbon nanotubes (CNTs) through urea or ethylene diamine linkers were synthesized using wet chemistry technique. Atomic force microscopy, transmission electron spectroscopy, and scanning electron spectroscopy reveal the pearl-necklace-like morphology of new HCNs with up to 50% of the CNT surface decorated by ND particles. Nanocomposites fabricated using polyuria/polyurethane hybrid polymer matrix and 0.2 wt.% of HCNs as a reinforcing filler show a 64% increase in tensile and elongation strength at break relatively to neat polymer.     

Synthesis and characterization of silver—poly(methylmethacrylate) nanocomposites

The optical properties of silver nanoparticles embedded in poly(methylmethacrylate) (PMMA) was investigated as well as the influence of silver nanoparticles on the thermal properties of polymer matrix. The average size and particle size distribution of silver nanoparticles was determined using transmission electron microscopy. The obtained transparent nanocomposite films were optically characterized using UV-Vis and FTIR spectroscopy. Thermal stability of polymer matrix was improved upon incorporation of small amount of silver nanoparticles. Also, silver nanoparticles have pronounced effect on thermo-oxidative stability of PMMA matrix. The glass transition temperatures of nanocomposites are lower compared to the pure polymer.     

The role of 60Co γ-ray irradiation on the interface states and series resistance in MIS structures

The effect of γ-ray exposure on the metal–insulator–semiconductor (MIS) structures has been investigated using the electrical characteristics at room temperature. The MIS structures are irradiated with ⁶⁰Co γ-ray source. The energy distribution of interface states was determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height and ideality factor. The value of series resistance decreases with increasing dose. Experimental results confirmed that γ-ray irradiation have a significant effect on electrical characteristics of MIS structures.     

The co-continuous morphology of biocompatible ethylene-vinyl acetate copolymers/poly(��-caprolactone) blend: effect of viscosity ratio and vinyl acetate content

The phase behavior and its linear viscoelastic responses of a biocompatible blend based on ethylene-vinyl acetate copolymers and poly(??-caprolactone) (EVA/PCL) were studied in this work in terms of blending ratios and annealing. The effects of viscosity ratios and vinyl acetate contents of the EVA on the co-continuous morphology were addressed. The results show that EVA/PCL is a typical immiscible blend due to the high interfacial tension between the two polymers. Thus, the blend shows a wide percolation range with a narrow fully co-continuous region. Although the phase inversion point can be well predicted by the viscous Utracki model, the dynamic viscoelastic responses of the blend cannot be well described by the emulsion model. The elasticity ratio was proposed to play an important role together with the viscosity ratio on the phase inversions. During dynamic annealing, the phase size of both the sea?Cisland and the co-continuous structures increases evidently, but the principle of time?Ctemperature superposition is only valid for the co-continuous blend while fails with that with the sea?Cisland phase structure. Beside, the phase size of the co-continuous structure is dependent strongly on the viscosity ratio between EVA and PCL. With reduced viscosity ratio, the phase size increases remarkably. However, vinyl acetate (VA) contents of the EVA have little influences on the interfacial properties and phase size of the co-continuous blends in the experimental content ranges (28?C12?wt.%).     

Abiotic degradation of poly(dl-lactide), poly(ɛ-caprolactone) and their blends

An effective hydrolytic degradation of PDLLA, PCL and their blends in a phosphate-buffered solution of pH 4.0 at 37 °C for 18 weeks was achieved, observing a considerably faster degradation of PDLLA as compared to PCL due to the hydrophobic and semicrystalline nature of PCL matrix, able to partially prevent water diffusion into the bulk specimen.DSC and FTIR results indicated that PCL phase, in compositions rich in PCL, was very stable against hydrolysis, but the presence of PDLLA in the PDLLA/PCL blends seemed to catalyze the hydrolytic degradation of the PCL phase, probably associated to easier diffusion of water into the PCL domains by the presence of PDLLA amorphous regions. This last trend was proportional to the content of PDLLA in the blends, excepting for the composition 64%PDLLA/36%PCL. It was confirmed that PCL molecules partially delayed hydrolysis of PDLLA molecules, according to FTIR analysis, and the water diffusion prevention level was proportional to the content of PCL in the blends, except for the system 64%PDLLA/36%PCL, which presented a lower extent of degradation than neat PDLLA but higher than the blend 80%PDLLA/20%PCL. This indicated that PCL molecules did not significantly impede hydrolysis of PDLLA molecules in this blend, possibly due to the achievement of a particular structure of the PDLLA/PCL interphase in this blend. In general, hydrolysis of PDLLA/PCL blends was found to be a complex phenomenon depending not only on the content of both polymer phases, but also on the polymer phase crystallinity and morphology.     

Non-enzymatic sensing of uric acid using a carbon nanotube ionic-liquid paste electrode modified with poly(β-cyclodextrin)

We describe a nonenzymatic electrochemical sensor for uric acid. It is based on a carbon nanotube ionic-liquid paste electrode modified with poly(β-cyclodextrin) that was prepared in-situ by electropolymerization. The functionalized multi-walled carbon nanotubes and the surface morphology of the modified electrodes were characterized by transmission electronic microscopy and scanning electron microscopy. The electrochemical response of uric acid was studied by cyclic voltammetry and linear sweep voltammetry. The effects of scan rate, pH value, electropolymerization cycles and accumulation time were also studied. Under optimized experimental conditions and at a working voltage of 500 mV vs. Ag/AgCl (3 M KCl), response to uric acid is linear in the 0.6 to 400 μΜ and in the 0.4 to 1 mΜ concentration ranges, and the detection limit is 0.3 μΜ (at an S/N of 3). The electrode was successfully applied to the detection of uric acid in (spiked) human urine samples.

SEM images of (a) carbon ionic liquid electrode (CILE) (b) MWNT-CILE (c) β-CD/CILE (d) β-CD/ MWNT-CILE. The surfaces of carbon ionic liquid electrode (CILE) (a) and MWNT-CILE (b) were homogenous and no separated carbon layers can be observed; After β- cyclodextrin (CD) was modified on CILE and MWNT-CILE, the surfaces of β-CD modified electrodes (c and d) exhibited loose and porous morphologies.

     

The effect of crystallization behavior on high conductivity,enhanced mechanism and thermal stability of poly(ε-caprolactone)/multi-walled carbon nanotube composites

Poly(ε-caprolactone) (PCL) composites filled by multi-walled carbon nanotubes (MWCNTs) which was non-covalently modified by the combined surfactants of poly(sodium 4-styrenesulfonate) and cetyltrimethyl-ammonium bromide (PSS-CTAB) were fabricated via simple solution precipitation method. PCL/MWCNTs composites provided with the low procolation threshold (0.4?wt%) and high electrical conductivity due to good dispersion of MWCNTs. And the excellent mechanical properties and enhanced thermal stability were also obtained with the addition of modified MWCNTs. In addition, all PCL composites showed significantly enhanced crystallization with increasing the MWCNTs contents, which demonstrated that the MWCNT-induced crystallization of PCL could effectively regulate the properties of composites. In a word, introducing non-covalent functionalized MWCNTs in the polymer system was a promising way for developing excellent conductive composites.     

Purification, cloning and expression of an Aspergillus niger lipase for degradation of poly(lactic acid) and poly(ε-caprolactone)

A lipase from Aspergillus niger MTCC 2594 was purified 53.8-fold to homogeneity by hydrophobic interaction chromatography using octyl sepharose and the enzyme showed two protein bands with apparent molecular mass of 35 and 37 kDa respectively. The lipase exhibited maximum activity at pH 7.0 and 37 °C and was stable between pH 4.0 and 10.0 and temperatures up to 50 °C. The values of K_m and V_max were 3.83 mM and 32.21 μmol/min/mg respectively, using olive oil as substrate. Lipase encoding gene, lipA, coded for 297 amino acid residues with conserved pentapeptide sequence, G-H-S-L-G, was cloned and expressed in Pichia pastoris. Although lipA showed high homology with the known Aspergillus lipases, it exhibited differences in putative lid domain. Both native and recombinant lipases have potential for degradation of poly(lactic acid) and poly(ε-caprolactone), and the present study will serve as a baseline of initial studies for its exploitation in polymer degradation.     

Living/controlled free radical copolymerization of chlorotrifluoroethene and butyl vinyl ether under 60Co γ-ray irradiation in the presence of S-benzyl O-ethyl dithiocarbonate

Living/controlled free radical copolymerization of chlorotrifluoroethene and butyl vinyl ether has been successfully achieved at room temperature under (60)Co γ-ray irradiation in the presence of S-benzyl O-ethyl dithiocarbonate. The alternating and block copolymers have been obtained with well-defined molecular weights and narrow molecular weight distributions.     

Extraction of U(VI), Th(IV) and some fission products from nitric acid by n,n-disubstituted amides and effect of γ-ray irradiation on the extraction

In this work, ten disubstituted amides have been synthesized and the extracting ability for U and Th fission products (mainly Zr, Nb and Ru) and the tendency of third phase formation have been studied. From the preliminary studies, two disubstituted amides, N-octylcaprolactam (OCLA) and N-(2-ethyl) hexylcaprolactam (EHCLA) were chosen for further studies. All studies were compared with those obtained by using TBP under exactly the same conditions. The dependence of aqueous nitric acid concentration, extractant concentration, temperature, -ray irradiation on extraction of Th, U and some fission products were studied. Back extraction of Th and U from organic phases and third phase formation were also studied. The studies of the reaction mechanism indicate that Th and U are extracted as disolvates, whereas HNO₃ is extracted as monosolvate. Extraction distribution of Th and U decrease with increase of temperature, indicating the extraction reaction to be exothermic. Preliminary studies show that OCLA and EHCLA have better -irradiation stabilities compared with TBP.     

Synergetic effect of poly(vinyl butyral) and calcium carbonate on thermal stability of poly(vinyl chloride) nanocomposites investigated by TG–FTIR–MS

In order to improve poly(vinyl chloride) (PVC) thermal stability, poly(vinyl butyral) (PVB) matrix and calcium carbonate nanoparticles were incorporated in plasticized PVC. Thermal properties of these composites were investigated by thermogravimetry analysis coupled with mass spectrometry and Fourier transform infrared spectroscopy (FTIR). This approach highlighted the efficiency of both PVB and CaCO₃ as HCl scavengers by postponing both the onset degradation temperature and the HCl release. Moreover, a synergetic effect was evidenced regarding the HCl release. Finally, kinetic parameters of the PVC first degradation stage, determined using the Flynn–Wall–Ozawa’s method, revealed a significant increase of the activation energy by incorporation of CaCO₃ in the presence or not of PVB.     

Hydrogen production in γ-ray and helium-ion radiolysis of polyethylene,polypropylene, poly(methyl-methacrylate), and polystyrene

The production of molecular hydrogen in the radiolysis of high-density polyethylene, isotactic polypropylene (PP), poly(methyl-methacrylate) (PMMA), and polystyrene (PS) by γ rays and 5–20-MeV helium ions was investigated. Molecular hydrogen is the dominant gaseous product from these polymers, and the yields with γ rays are 3.3, 2.6, 0.24, and 0.033 molecules per 100 eV of energy absorbed for polyethylene, PP, PMMA, and PS, respectively. The decrease in observed hydrogen is due to increased branching and the chemical nature of the groups on the side chains. There is an increase in hydrogen production with increasing linear energy transfer (LET) from γ rays to helium ions, but the relative increase depends on the polymer type. With incident 5-MeV helium ions, the respective yields of molecular hydrogen are 4.6, 3.2, 0.62, and 0.15 molecules per 100 eV. The increase in molecular hydrogen with increasing LET may be due to changes in the kinetics of hydrogen precursors in the particle tracks. The differences in the relative increases in molecular hydrogen with increasing LET for each of the polymers suggests that self-scavenging reactions may be important for low LET particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1656–1661, 2000     

Thermal degradation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ϵ-caprolactone) or poly(ethylene glycol)

Thermodegradative investigations of two classes of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and either poly(ethylene glycol) (PEG) or poly(ϵ-caprolactone) diol-terminated (PCDT) segments were performed. In particular, the influence of the type and length of the segments as well as of the molar ratio between the D,L-lactic acid (LA) and glycolic acid (GA) residues was investigated at 180°C in air by viscometry, FT-IR analysis and isothermal thermogravimetry. The thermal oxidative degradation of these materials is largely affected by the LA/GA ratio, a higher LA content generally imparting higher stability. The FT-IR analysis suggests that, depending on the composition of the PLGA segments, degradative processes are triggered which can lead to a preferential degradation of the blocks.     

Mechanical properties,surface morphology and failure mode of γ-ray irradiated blends of polypropylene and ethylene-vinyl acetate rubber

The effect of ⁶⁰Co γ-radiation on the mechanical properties, surface morphology and failure characteristics of blends of polypropylene [PP] and ethylene-vinyl acetate rubber [EVA] has been studied with specific reference to the effect of blend ratio, dynamic crosslinking of the rubber phase and absorbed radiation doses. Samples were subjected to radiation in the dose range of 1 to 100 Mrad in air at room temperature at the rate of 0·321 Mrad/h. Both chain scission and crosslinking occur simultaneously in the blend samples. PP and blends containing higher proportions of PP (≥50%) undergo predominant chain scission at lower doses (≤50 Mrad), which causes a drastic drop in tensile strength, followed by a levelling out at higher doses of 100 Mrad. EVA undergoes crosslinking at lower doses resulting in an increase in tensile strength in the dose range 1 to 10 Mrad followed by a decrease in the range 10–25 Mrad. Further increase in radiation dose has little effect on tensile strength. The effect of radiation on stress-strain behaviour, elongation at break, energy at rupture and hardness was also studied. The morphology of the irradiated surfaces after an absorbed dose of 100 Mrad has been examined by scanning electron microscopy (SEM). In order to understand the effect of γ-radiation on the failure mechanism, tensile failure surfaces of both unirradiated and irradiated samples have also been examined by SEM.     

Swelling–shrinking behaviors of poly(N-isopropylacrylamide) and poly(N-n-propylacrylamide) gels prepared by chemical and radiation crosslinking methods

The swelling and shrinking kinetics of thermosensitive gels based on N-isopropylacrylamide (NiPAAm) and N-n-propylacrylamide (NnPAAm) were studied. Four gels cylindrical in shape were prepared by two different methods: γ-ray irradiation to aqueous solutions of poly(NiPAAm) (PNiPAAm) or poly(NnPAAm) (PNnPAAm) and redox polymerization of NiPAAm or NnPAAm monomer using N,N′-methylenebisacrylamide as a crosslinker. There were a few differences in the swelling kinetics among these gels. However, a marked difference was observed in the shrinking processes, the rate of which was faster in the order of radiation-crosslinked PNiPAAm gel > radiation-crosslinked PNnPAAm gel > chemically crosslinked PNnPAAm gel > chemically crosslinked PNiPAAm gel. This difference was discussed in terms of the microscopic structure of the gels, which was studied by light scattering techniques. It was found that the static inhomogeneities frozen in the chemically and radiation-crosslinked gels play a key role in their shrinking kinetics.     

Morphology and thermal degradation studies of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology and thermal stability of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend nanocomposites with small amounts of TiO₂ nanoparticles were investigated. The nanoparticles were mostly located in the PLA phase, with good dispersion of individual particles, although significant aggregation was also visible. The thermal stability and degradation behaviour of the different samples were studied using thermogravimetric analysis (TGA) and TGA-Fourier-transform infrared (FTIR) spectroscopy. Neat PCL showed better thermal stability than PLA, but the degradation kinetics revealed that PLA had a higher activation energy of degradation than PCL, indicating its degradation rate more strongly depends on temperature, probably because of a more complex degradation mechanism based on chain scission and re-formation. Blending of PLA and PCL reduced the thermal stabilities of both polymers, but the presence of TiO₂ nanoparticles improved their thermal stability. The nanoparticles also influenced the volatilization of the degradation products from the blend, acted as degradation catalyst and/or retarded the escape of volatile degradation products.