Bin Fei

Hydrogel of biodegradable cellulose derivatives. I. Radiation-induced crosslinking of CMC

Radiation crosslinking of carboxymethylcellulose (CMC) with a degree of substitution (DS) from 0.7 to 2.2 was the subject of the current investigation. CMC was irradiated in solid-state and aqueous solutions at various irradiation doses. The DS and the concentration of the aqueous solution had a remarkable affect on the crosslinking of CMC. Irradiation of CMC, even with a high DS, 2.2 in solid state, and a low DS, 0.7 in 10% aqueous solution, resulted in degradation. However, it was found that irradiation of CMC with a relatively high DS, 1.32, led to crosslinking in a 5% aqueous solution, and 20% CMC gave the highest gel fraction. CMC with a DS of 2.2 induced higher crosslinking than that with a DS of 1.32 at lower doses with the same concentration. Hence, it was apparent that a high DS and a high concentration in an aqueous solution were favorable for high crosslinking of CMC. It is assumed that; high radiation crosslinking of CMC was induced by the increased mobility of its molecules in water and by the formation of CMC radicals from the abstraction of H atoms from macromolecules in the intermediate products of water radiolysis. A preliminary biodegradation study confirmed that crosslinked CMC hydrogel can be digested by a cellulase enzyme

Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate)

In order to improve its thermal stability, poly(propylene carbonate)(PPC) was end-capped by different active agents. Thermogravimetric data show that the degradation temperature of uncapped PPC was lower than that of end-capped PPC. The kinetic parameters of thermal degradation of uncapped and end-capped PPC were calculated according to Changs method. The results show that different mechanisms operate during the whole degradation temperature range for uncapped PPC. In the first stage, chain unzipping dominates the degradation. With increasing temperature, competing multi-step reactions occur. In the last stage, random chain scission plays an important role in degradation. For end-capped PPC, random chain scission dominates the whole degradation process.

Dual-modal fluorescent/magnetic bioprobes based on small sized upconversion nanoparticles of amine-functionalized BaGdF5:Yb/Er

A new type of BaGdF(5):Yb/Er nanoprobe for dual-modal fluorescent and magnetic resonance imaging (MRI) is demonstrated. Water soluble and amine-functionalized BaGdF(5):Yb/Er nanoparticles (NPs) with average size of about 10 nm were synthesized by a facile one-pot hydrothermal method. The in vitro up-converted emission of BaGdF(5):Yb/Er NPs is observed in HeLa cells with near-infrared excitation at 980 nm and served as a fluorescent label. In addition, the cytotoxicity assay in HeLa cells shows low cell toxicity of the amine-functionalized BaGdF(5):Yb/Er NPs. Moreover, these BaGdF(5) NPs exhibit excellent intrinsic paramagnetic properties and enhanced T(1)-weighted MRI images with increased concentrations of BaGdF(5) NPs. Therefore, these results suggest that the amine-functionalized BaGdF(5) NPs with an optimized size and low cell toxicity are promising dual-modal bioprobes for optical bioimaging and MRI.

Room temperature synthesis of rutile nanorods and their applications on cloth

In order to achieve better photocatalytic performance, rutile nanorods dispersed in anatase and brookite phases were synthesized from titanium isopropoxide (TIP) in a concentrated HNO3 solution at room temperature (23 °C). X-ray diffraction results indicated that the percentage of rutile increased with increasing peptization time. Scanning electron microscopy and and high-resolution transmission electron microscopy measurements revealed that the nanosized titania particles mainly consisted of granular anatase and brookite, and rod-like rutile. It was interesting that the stability of the colloid increased with increasing nanoparticle concentration, and the tricrystalline titania showed a photocatalytic activity higher than that of pure anatase. These nanocrystals were applied onto cotton fabrics, and achieved a promising bactericidal photocatalytic activity and excellent protection against UV radiation.

In vitro cell imaging using multifunctional small sized KGdF4:Yb3+,Er3+ upconverting nanoparticles synthesized by a one-pot solvothermal process.

Multifunctional KGdF4:18%Yb(3+),2%Er(3+) nanoparticles with upconversion fluorescence and paramagnetism are synthesized. The average sizes of the nanoparticles capped with branched polyethyleneimine (PEI) and 6-aminocaproic acid (6AA) are ~14 and ~13 nm, respectively. Our KGdF4 host does not exhibit any phase change with the decrease of particle size, which can prevent the detrimental significant decrease in upconversion luminescence caused by this effect observed in the well-known NaYF4 host. The branched PEI and 6AA capping ligands endow our nanoparticles with water-dispersibility and biocompatibility, which can favor internalization of our nanoparticles into the cytoplasm of HeLa cells and relatively high cell viability. The strong upconversion luminescence detected at the cytoplasm of HeLa cells incubated with the branched PEI-capped nanoparticles is probably attributed to the reported high efficiency of cellular uptake. The magnetic mass susceptibility of our nanoparticle is 8.62 × 10(-5) emu g(-1) Oe(-1). This is the highest value ever reported in trivalent rare-earth ion-doped KGdF4 nanoparticles of small size (≤14 nm), and is very close to that of nanoparticles used as T1 contrast agents in magnetic resonance imaging. These suggest the potential of our KGdF4:Yb(3+),Er(3+) nanoparticles as small-sized multifunctional bioprobes.

Nonisothermal crystallization and melting behavior of poly(3-hydroxybutyrate) and maleated poly(3-hydroxybutyrate)

Nonisothermal crystallization and melting behavior of poly(3-hydroxybutyrate) (PHB) and maleated PHB were investigated by differential scanning calorimetry using various cooling rates. The results show that the crystallization behavior of maleated PHB from the melt greatly depends on cooling rates and its degree of grafting. With the increase in cooling rate, the crystallization process for PHB and maleated PHB begins at lower temperature. For maleated PHB, the introduction of maleic anhydride group hinders its crystallization, causing crystallization and nucleation rates to decrease, and crystallite size distribution becomes wider. The Avrami analysis, modified by Jeziorny, was used to describe the nonisothermal crystallization of PHB and maleated PHB. Double melting peaks for maleated PHB were observed, which was caused by recrystallization during the heating process.

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n = 3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U-* = 1500 cal mol(-1), T-infinity = 30 K and T-g = 278 K, the nucleation parameter K-g was determined, which was found to be 3.14+/-0.07 x 10(5) (K-2), lower than that for pure PHB. The surface-free energy sigma = 2.55 x 10(-2) J m(-2) and sigma(e) = 2.70+/-0.06 x 10-2 J m(-2) were estimated and the work of chain-folding (q = 12.5+/-0.2 kJ mol(-1)) was derived from sigma(e), and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.

Quantitative FTIR study of PHBV/bisphenol A blends

Abstract FTIR spectroscopy was used to verify the presence of intermolecular hydrogen bond (inter-H-bond) between poly(3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV) and bisphenol A (BPA). By monitoring the spectral changes during PHBV crystallization and blends dissociation, the absorptivity ratio of CO bonds in crystalline and amorphous regions in PHBV and that of H-bonded and free CO in PHBV/BPA blends were experimentally determined as 1.40 and 1.68, respectively. Using curve-fitting program, the CO absorptions in spectra of blends were ascribed to three types of bonds: amorphous, crystalline and H-bonded CO. The crystallinity of PHBV and the fraction of H-bonded CO were calculated. These results indicated that the H-bond clearly suppressed the PHBV crystallization. Furthermore, the fraction of BPA molecules that simultaneously formed two hydrogen bonds (H-bonds) with CO was estimated. It revealed that there existed a H-bond network in PHBV/BPA blends. This network was compared with the covalent network by estimating the number of atoms between every two adjacent crosslink points in chain. Up to the high density of H-bond discussed in this paper, there was always a certain part in PHBV that crystallized due to the dynamic character of hydrogen bonds; however, the hydrogen bonds significantly reduced the crystallization rate of PHBV.

Super-tough and thermo-healable hydrogel – promising for shape-memory absorbent fiber

Recoverable hydrogels with high stretch and toughness have been synthesized by a one-step radical polymerization. They consist of covalently crosslinked polyacrylamide (PAAm) and ionically crosslinked carrageenan. Such double network (DN) hydrogels can be stretched beyond 20 times their initial length, and their fracture energy reached a high value of ∼9500 J m-2. By comparing hydrogel tensile properties at different temperatures, the contribution of ionic network to the toughness was quantitatively determined in percentage for the first time. The stretched hydrogels were completely healed by short treatment at a mild temperature. Through drying at stretch, they were also transformed into stiff absorbent fibers that still preserved their shape memory of wet state.

Modification of Conductive Polymer for Polymeric Anodes of Flexible Organic Light-Emitting Diodes

A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), was modified with dimethyl sulfoxide (DMSO) in solution state, together with sub-sequential thermal treatment of its spin-coated film. The electrical conductivity increased by more than three orders of magnitude improvement was achieved. The mechanism for the conductivity improvement was studied at nanoscale by particle size analysis, field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). Smaller particle size was observed, resulting in larger contact area and better electrical conductive connections. Connection of conductive PEDOT increased on the surface of the PEDOT:PSS particles, which promoted high conductivity. Flexible anodes based on the modified PEDOT:PSS were fabricated. Flexible organic light-emitting diodes (FOLED) based the polymeric anodes have a comparable performance to those on indium–tin–oxide (ITO) anodes.