Institute of Chemistry
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Stereocomplex crystallite network in poly(D,L-lactide): formation, structure and the effect on shape memory behaviors and enzymatic hydrolysis of poly(D,L-lactide)
No full textStereocomplex crystallization is a very interesting crystal modification formed between enantiomeric polymers, such as poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA). Herein, biodegradable poly(D,L-lactide) (PDLLA) and stereocomplex-poly(L- and D-lactide) (sc-PLA) blends were prepared by solution blending at various sc-PLA loadings ranging from 2.5 to 10 wt%. Wide-angle X-ray diffraction and differential scanning calorimetry results verified that complete stereocomplex crystallites without any evidence of the formation of homocrystallites in the PDLLA could be achieved. By a rheological approach, a transition from the liquid-like to solid-like viscoelastic behaviour was observed for the stereocomplex crystallites reserved PDLLA melt, and a frequency-independent loss tangent at low frequencies appeared at a sc-PLA concentration of 5 wt%, revealing the formation of stereocomplex crystallite network structure. By a delicately designed dissolution experiment, the structure of the formed network structure was explored. The results indicated that the network structure were not formed by stereocomplex crystallites connected directly with each other or by bridging molecules, but by the interparticle PDLLA chains which were significantly restrained by the crosslinking effect of sc-PLA. Accordingly, the mechanical properties of PDLLA were greatly enhanced after blending with sc-PLA. Moreover, the most intriguing result was that the shape memory behaviors of PDLLA had been improved obviously in the blends than in neat PDLLA, especially when a percolation network structure had formed, which may be of great use and importance for the wider practical application of PDLLA. Finally, it was found that the enzymatic hydrolytic degradation rates had been retarded in the blends than in neat PDLLA. The erosion mechanism of neat PDLLA and the blends was further discussed
Sonochemistry-synthesized CuO nanoparticles as an anode interfacial material for efficient and stable polymer solar cells
No full textSolution-processible copper oxide (CuO) nanoparticles have been synthesized via sonochemistry. Colloidal crystalline CuO nanoparticles with diameters of 3-12 nm were obtained from the CuCl2 metal salt at low temperature under ultrasound irradiation. The solution-processible CuO nanoparticles are applied as an anode buffer layer in a PCDTBT:PC71BM bulk heterojunction solar cell to substitute the commonly used hygroscopic PEDOT:PSS. It is found that UV-ozone treatment increases the work function of the CuO buffer layer from -4.7 to -5.4 eV, facilitating the interfacial contact and hole extraction. The UVO-treated CuO-based solar cells show enhanced fill factor and photocurrent, resulting in an increased photovoltaic performance from 6.00% to 6.44% in comparison to the PEDOT:PSS-based solar cells. Moreover, the solar cells with a CuO buffer layer show better ambient stability than those with a PEDOT:PSS buffer layer. The facile preparation of solution-processed CuO and effectiveness in polymer solar cells render it a promising anode interfacial material for solution-processed flexible polymer solar cells
Flammability properties and electromagnetic interference shielding of PVC/graphene composites containing Fe3O4 nanoparticles
No full textThe effects of combined graphene/Fe3O4 nanoparticles on the flame retardancy and smoke suppression of PVC were studied. The dispersion state of graphene in the PVC matrix was improved with the help of Fe3O4 nanoparticles. As a result, the peak values of heat release rate and smoke production rate measured by cone calorimetry were obviously decreased in the PVC/graphene/Fe3O4 composites. According to the results from TGA tests and structural characterization of residual char, the improved flame retardancy was partially attributed to the formation of a network-like structure due to the good dispersion state of graphene in the PVC matrix, and partially to the carbonization of degradation products of PVC catalyzed by Fe3O4 nanoparticles. In addition, ternary PVC composites showed higher mechanical properties than pure PVC. More importantly, the resulting material possessed both electrical and magnetic properties. As a result, the ternary composites showed favorable electromagnetic shielding efficiency in the X-band frequency region (8-12 GHz), due to the formation of conducting interconnected graphene-based networks in the insulating PVC matrix and the magnetic properties
Impact of particle surface chemistry on the structure and rheological properties of graphene-based particle/polydimethylsiloxane composites
No full textThe structure and rheological properties of graphene-based particle (GP-x)/polydimethylsiloxane (PDMS) composites are investigated as the surface oxygen content of graphene-based particle is varied, i.e., from 6.6% (GP-1) to 15.3% (GP-2), 25.5% (GP-3) and 43.1% (GP-4). Interestingly, the dispersion state of graphene-based particles in PDMS does not change monotonically with increasing surface oxygen content. The size of layered stacks and aggregates first decreases from GP-1 to GP-3 and then increases from GP-3 to GP-4 with increasing surface oxygen content. The larger size of layered stacks and aggregates in GP-1 and GP-4 suspensions results from strong inter-particle p-p and hydrogen bonding interactions. Under weak shear, GP-1 and GP-4 form larger aggregates in PDMS, which align along the vorticity direction, inducing negative normal stress differences (Delta N) in the composites. However, GP-2 and GP-3 do not further aggregate under weak shear and the Delta N is almost zero. It is further inferred that the strong inter-particle attractive interaction leads to the vorticity alignment of aggregates under weak shear
Confined polymerization: catalyzed synthesis of high T-m, nanofibrous polyethylene within porous polymer microspheres
No full textCrystalline nanofibers of linear polyethylene were formed through ethylene confined polymerization with porous polymer microsphere-supported titanocene. Polyethylene nanofibers (<70 nm) aggregated to form intertwined thicker fibers (300 nm to 22 mu m). The obtained PE has high M-w and T-m. Interestingly, the high Tm (142.4 degrees C) was maintained in the second stage of heating
Label-free aptamer biosensor for thrombin detection based on functionalized graphene nanocomposites
No full textA label-free and amplified electrochemical impedimetric aptasensor based on functionalized graphene nanocomposites (rGO-AuNPs) was developed for the detection of thrombin, which played a vital role in thrombosis and hemostasis. The thiolated aptamer and dithiothreitol (TBA15-DTT) were firstly immobilized on the gold electrode to capture the thrombin Molecules, and then aptamer functionalized graphene nanocomposites (rGO-TBA29) were used to fabricate a sandwich sensing platform for amplifying the impedimetric signals. As numerous negative charges of TBA29 on the electrode repelled to the [Fe(CN)(6)](4-/3-) anions, resulting in an obvious amplified charge-transfer resistance (R-ct) signal. The R-ct increase was linearly proportional to the thrombin concentration from 0.3 to 50 nM and a detection limit of 0.01 nM thrombin was achieved. In addition, graphene could also be labeled with other probes via electrostatic or pi-pi stacking interactions to produce signals, therefore different detection methods expanding wide application could be used in this model. (C) 2015 Published by Elsevier B.V
The use of cisplatin-loaded mucoadhesive nanofibers for local chemotherapy of cervical cancers in mice
No full textPolymer-based local drug delivery system may be suitable for the treatment of cervix cancer. A pilot study was carried out to examine the efficacy of cisplatin-loaded poly(ethylene oxide)/polylactide composite electrospun nanofibers as a local chemotherapy system against cervical cancer in mice via vaginal implantation. The nanofibers were proven to have good mucoadhesive property by in vitro mucoadhesion test and in vivo vaginal retention evaluation. An orthotopic cervical/vaginal cancer model was established by injecting murine cervical cancer U14 cells into the vaginal submucosa nearby the cervix. By inserting the nanofibers mat into the vagina of mice, the cisplatin released from the fiber-mat showed a much more accumulation in the vagina/cervix region than in the peripheral organs such as kidneys, liver, or blood, in contrary to the case of intravenous (i.v) injection. The in vivo trials showed that a better balance between anti-tumor efficacy and systemic safety was achieved in nanofibers group than that in i.v injection group at the equal drug dose. Therefore, electrospun nanofibers present a promising approach to the local drug delivery via vagina against cervical cancer. (C) 2015 Elsevier B.V. All rights reserved
A facile approach to prepare porous cup-stacked carbon nanotube with high performance in adsorption of methylene blue
No full textNovel porous cup-stacked carbon nanotube (P-CSCNT) with special stacked morphology consisting of many truncated conical graphene layers was synthesized by KOH activating CSCNT from polypropylene. The morphology, microstructure, textural property, phase structure, surface element composition and thermal stability of P-CSCNT were investigated by field-emission scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, N-2 sorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and thermal gravimetric analysis. A part of oblique graphitic layers were etched by KOH, and many holes with a diameter of several to a doze of nanometers connecting inner tube with outside were formed, which endowed P-CSCNT with high specific surface area (558.7 m(2)/g), large pore volume (1.993 cm(3)/g) and abundant surface functional groups. Subsequently, P-CSCNT was used for adsorption of methylene blue (MB) from wastewater. Langmuir model closely fitted the adsorption results, and the maximum adsorption capacity of P-CSCNT was as high as 319.1 mg/g. This was ascribed to multiple adsorption mechanisms including pore filling, hydrogen bonding, pi-pi and electrostatic interactions. Pseudo second-order kinetic model was more valid to describe the adsorption behavior. Besides, P-CSCNT showed good recyclablity and reusability. These results demonstrated that PCSCNT had potential application in wastewater treatment. (C) 2015 Elsevier Inc. All rights reserved
Synthesis and Characterization of Soft-Hard Stereoblock Polybutadiene with Fe(2-EHA)3/Al(i-Bu)3/DEP Catalyst System
No full textStereoblock polybutadiene (PBD) composed of amorphous equibinary cis-1,4/1,2 PBD (e-PBD, soft) and crystalline syndiotactic 1,2-PBD (s-1,2-PBD, hard) segments is synthesized through one-pot sequential polymerization with iron(III)2-ethylhexanoate/triisobutylaluminum/diethyl phosphate [Fe(2-EHA)(3)/Al(i-Bu)(3)/DEP] catalyst system. The first-stage polymerization of 1,3-butadiene (BD) is carried out at a low [Al]/[Fe] ratio to give amorphous e-PBD block, and sequentially, the in situ addition of excessive Al(i-Bu)(3) and BD to the living polymerization system give rise to a second crystalline s-1,2-PBD block. The length of each block is controllable by adjusting cocatalyst and monomer feed ratio. The syndiotactic pentad content is in the range of 63.8-76.6% and increases with the length of s-1,2-PBD block. The copolymer exhibits glass transition temperature (T-g) around -40 degrees C and melting point (T-m) around 168 degrees C originating from e-PBD and s-1,2-PBD blocks, respectively. The incompatibility between s-1,2-PBD and e-PBD blocks as well as the crystallization of s-1,2-PBD block induce the microphase separation in stereoblock PBD. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1182-118
Rare-earth metal alkyl complexes bearing an alkoxy N-heterocyclic carbene ligand: synthesis, characterization, catalysis for isoprene polymerization
No full textTreatment of imidazolium iodide [R-NHC-CH2CH(Bu-n)OH] I (1a (R = methyl), 1b (R = isopropyl)) and benzimidazole iodide [R-NHC(C6H4)-CH2CH(Bu-n)OH] I (2a (R = methyl), 2b (R = isopropyl)), respectively, with ((trimethylsilyl)methyl)lithium (LiCH2SiMe3) followed by rare-earth metal tris(alkyl)s (Ln(CH2SiMe3)(3)(THF)(2)) (Ln = Sc, Y, Lu) afforded the alkoxy-modified N-heterocyclic carbene ligated rare-earth metal bis(alkyl) complexes {[R-NHC-CH2CH(Bu-n)OLn(CH2SiMe3)(2)](2) (3a (R = methyl, Ln = Sc), 3b (R = methyl, Ln = Lu), 4a (R = isopropyl, Ln = Y), 4b (R = isopropyl, Ln = Lu)) and [(CH3)(2)CH-NHC(C6H4)-CH2CH(Bu-n)OY(CH2SiMe3)(2)](2) (5)} via double-deprotonation reactions. All complexes were characterized by NMR spectroscopy, elemental analysis and X-ray crystallography. They are dimers in which two rare-earth metal ions are bridged by two mu(2)-O atoms. Under the activation of an organoborate, complex 3a showed cis-1,4 enriched regioselectivity for isoprene polymerization (84.3%)