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1.
Langmuir ; 40(10): 5360-5368, 2024 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-38427799

RESUMO

Emulsions, formed by dispersing a liquid into another immiscible one by virtue of emulsifiers, have been widely applied in commercial applications like foods, pharmaceuticals, cosmetics, and personal care, which always confront environmental and/or toxic questions due to emulsifiers' high dosage. Recently, a study on Pickering emulsions points out a solution to stable emulsions based on the costabilizing effect of colloidal particles, which focused on surface-active particles cooperating with oppositely charged ionic surfactants. Costabilized emulsions adopting a charge-similar ionic surfactant and particles were less studied. In this article, a hexane-in-water emulsion was prepared in use of a cationic surfactant cetyltrimethylammonium bromide (CTAB) with positively charged magnesium hydroxide (MH) nanosheets at low concentrations (10-5 M and 10-2 wt %, respectively). The emulsion is stable due to the synergy by CTAB and MH nanosheets, which functions in virtue of the electric repulsion by similarly charged particles, the mechanical shielding by MH nanosheets, and restrained water drainage in lamellae between droplets due to the gelation of MH nanosheets. Moreover, the emulsion is doubly switchable within emulsification/demulsification via convenient pH or ion manipulation, a mechanism based on the breakdown and rebuilding of the costabilizing synergy. Such dual-responsive emulsions show high potential for the delicate control of drug delivery, release, and biphasic biocatalysis applications.

2.
Langmuir ; 37(14): 4082-4090, 2021 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-33784455

RESUMO

Surfactants are often used as a cooperation stabilizer with solid particles for increasing the efficiency of Pickering emulsion. Accordingly, the effects of interaction between surfactants and solid particles on stabilizing Pickering emulsions have been attracting great attention. In this study, magnesium hydroxide (MH) nanosheets adsorbed with different amounts of sodium dodecyl sulfate (SDS) surfactants were designed and used to stabilize paraffin-water emulsions. Using SDS-adsorbed MH nanosheets as a stabilizer, the phenomenon of double phase inversion was found for Pickering emulsion. Pickering emulsion was inverted initially from O/W to W/O at about 0.022 mmol/g of the adsorption amount of SDS on the MH nanosheets, and subsequently back to O/W at about 2.312 mmol/g. The first phase inversion was because of the increased hydrophobicity of modified MH nanosheets, where SDS molecules were monolayer-adsorbed on the MH nanosheets surface. The second phase inversion occurred due to the bilayer adsorption of SDS on MH nanosheets, which converted the modified MH nanosheets hydrophilic again. These results are of great importance to understanding the double phase inversion of Pickering emulsions with the addition of surfactants and finding prospective applications in fields such as reversible drilling fluids and oil extraction.

3.
Langmuir ; 36(2): 591-599, 2020 01 21.
Artigo em Inglês | MEDLINE | ID: mdl-31909630

RESUMO

Crystallization modification has been applied in many fields, such as materials science, petroleum engineering, and chemical engineering. The modification of organic-inorganic hybrids via paraffin hydrocarbon crystallization has been significantly important for the exploration of undersea oil and gas resources. In this work, a metal oxide organic-inorganic hybrid pour point depressant (MOIH-PPD) is provided along with an analysis of the microscopic structure of the paraffin hydrocarbon crystal employing small-angle X-ray scattering and X-ray diffraction. The MOIH-PPD modified crystal grain exhibited a decrease in the long period and in the radius of gyration of the crystal grain and an increase in the thickness of the interface layer compared with those of the unmodified paraffin crystal. In addition, the synergistic effect of heterogeneous nucleation and the magnetic response of MOIH-PPD on the paraffin hydrocarbon system was also investigated, revealing that the synergism modification yields stress superior to that of MOIH-PPD or magnetic field alone, which provides insight into the possibility of the modification of paraffin hydrocarbon crystallization.

4.
Nanotechnology ; 29(12): 125602, 2018 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-29311422

RESUMO

Rutile TiO2 are widely used for applications of coatings, cosmetics, photoelectric devices and so on. However, effective control of well-defined morphology, size and composition of rutile TiO2 nanoparticles from agglomeration has always been a challenge. A new synthesis strategy was proposed to prepare rutile TiO2 with controllable morphology varied from flower-like structures to single-separated nanorods. The ß-FeOOH nanoparticles were generated by the hydrolysis of FeCl3 solution and could prevent the aggregation of TiO2 nanocrystals at early stages of the reaction; thus, could control the morphology of rutile nanoparticles. The morphology of rutile TiO2 nanoparticles could be controllably regulated from flower-like structures to individually separated nanorods. Meanwhile, the preformed ß-FeOOH also played a role of dopant. Fe ions were substitutionally doped into the bulk lattice of TiO2 nanocrystals and reduced the bandgap, which extended the solar radiation absorption range of rutile TiO2. The prepared TiO2 may be suitable for novel UV-blue light shielding agents and many other applications in photoelectric devices, photocatalysis, and so on due to its small size, unprecedented discrete rod-like structure and unique UV-vis light permeability.

5.
J Exp Bot ; 64(4): 871-84, 2013 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-23268839

RESUMO

Calcium-dependent protein kinases (CDPKs) have been shown to be involved in abscisic acid (ABA)-mediated physiological processes, including seed germination, post-germination growth, stomatal movement, and plant stress tolerance. However, it is not clear whether CDPKs are involved in ABA-induced antioxidant defence. In the present study, the role of the maize CDPK ZmCPK11 in ABA-induced antioxidant defence and the relationship between ZmCPK11 and ZmMPK5, a maize ABA-activated mitogen-activated protein kinase (MAPK), in ABA signalling were investigated. Treatments with ABA and H(2)O(2) induced the expression of ZmCPK11 and increased the activity of ZmCPK11, while H(2)O(2) was required for the ABA-induced increases in the expression and the activity of ZmCPK11. The transient gene expression analysis and the transient RNA interference (RNAi) test in protoplasts showed that ZmCPK11 is involved in ABA-induced up-regulation of the expression and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), and in the production of H(2)O(2). Further, ZmCPK11 was shown to be required for the up-regulation of the expression and the activity of ZmMPK5 in ABA signalling, but ZmMPK5 had very little effect on the ABA-induced up-regulation of the expression and the activity of ZmCPK11. Moreover, the transient gene expression analysis in combination with the transient RNAi test in protoplasts showed that ZmCPK11 acts upstream of ZmMPK5 to regulate the activities of antioxidant enzymes. These results indicate that ZmCPK11 is involved in ABA-induced antioxidant defence and functions upstream of ZmMPK5 in ABA signalling in maize.


Assuntos
Ácido Abscísico/farmacologia , Antioxidantes/metabolismo , Proteínas Quinases Ativadas por Mitógeno/genética , Proteínas de Plantas/metabolismo , Transdução de Sinais , Zea mays/efeitos dos fármacos , Ascorbato Peroxidases/genética , Ascorbato Peroxidases/metabolismo , Ativação Enzimática , Ensaios Enzimáticos , Regulação Enzimológica da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Peróxido de Hidrogênio/metabolismo , Peróxido de Hidrogênio/farmacologia , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Folhas de Planta/classificação , Folhas de Planta/enzimologia , Folhas de Planta/genética , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Protoplastos/citologia , Protoplastos/metabolismo , Interferência de RNA , RNA de Plantas/genética , RNA de Plantas/metabolismo , Superóxido Dismutase/genética , Superóxido Dismutase/metabolismo , Zea mays/enzimologia , Zea mays/metabolismo
6.
Injury ; 54(2): 778-783, 2023 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-36481053

RESUMO

PURPOSE: The study aimed to introduce anterior superior iliac spine distraction to treat severe and recalcitrant diabetic foot ulcers. For comparison, we also included another group of diabetic foot ulcers treated with proximal tibial cortex transverse distraction. METHODS: From February 1998 to February 2020, 87 patients (87 feet) with severe and recalcitrant diabetic foot ulcers were treated. The mean age of patients at surgery was 64 years (range, 47 to 87 years). The severity of the narrowed artery was assessed using the ankle-brachial index test. For comparison, another group of 91 patients (91 diabetic foot ulcers) treated with proximal tibial cortex transverse distraction was included. RESULTS: The mean preoperative ankle-brachial indexes of the two groups were 0.41±0.07 and 0.39±0.05 (OR 0.65 [95% CI -0.77 to 1.58]; P=0.62), respectively. The mean preoperative limb pain was 3.42±2.84 cm and 3.52±3.11 cm (OR 1.54 [95% CI -077 to 1.35]; P=0.083), respectively. At the 2-year follow-up visit, ulcers healed in 72 (83%) and 74 (81%) patients, respectively (P=0.188). The mean postoperative limb pain was 0.52±0.23 cm and 0.49±0.41 cm (OR 2.32 [95% CI -0.27 to 1.66]; P=0.078), respectively. Pin-site infection occurred in 2 patients and 8 patients (P=0.09), respectively. Ulcer recurrence occurred in 13 (15%) patients and 15 (16%) patients (P=0.205), respectively. CONCLUSIONS: Anterior superior iliac spine transverse distraction may be an effective alternative treatment for severe and recalcitrant diabetic foot ulcers. It may be associated with fewer distraction-site complications than proximal tibial cortex transverse distraction. LEVEL OF EVIDENCE: Therapeutic study, Level IIa.


Assuntos
Diabetes Mellitus , Pé Diabético , Humanos , Pessoa de Meia-Idade , Idoso , Idoso de 80 Anos ou mais , Pé Diabético/cirurgia , Cicatrização , , Tíbia/cirurgia , Resultado do Tratamento , Dor
7.
ACS Appl Mater Interfaces ; 15(40): 47531-47540, 2023 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-37787377

RESUMO

Polypropylene (PP) has been widely used in health care and food packaging fields, however, it lacks antibacterial properties. Herein, we prepared the polymeric antibacterial agents (MPP-NDAM) by an in situ amidation reaction between 2,4-diamino-6-dialkylamino-1,3,5-triazine (NDAM) and maleic anhydride grafted polypropylene (MPP) using the melt grafting method. The effects of reaction time and monomer content on the grafting degree of N-halamine were investigated, and a grafting degree of 4.86 wt % was achieved under the optimal reaction conditions. PP/MPP-NDAM composites were further obtained by a melt blending process between PP and MPP-NDAM. With the adoption of surface segregation technology, the content of N-halamine structure on the surface of PP/MPP-NDAM composites was significantly increased. The antibacterial tests showed that the PP/MPP-NDAM composite could achieve 99.9% bactericidal activity against 1.0 × 107 CFU/mL of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) within 10 and 5 min of contact, respectively. The antibacterial effect became more pronounced with the prolongation of chlorinated time, and it could achieve 99.9% bactericidal activity against E. coli within merely 1 min of contact.


Assuntos
Escherichia coli , Polipropilenos , Polipropilenos/química , Staphylococcus aureus , Antibacterianos/farmacologia , Antibacterianos/química
8.
Appl Bionics Biomech ; 2022: 9368920, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35251304

RESUMO

Effective triage tools are indispensable for doctors to make a prompt decision for the treatment of multiple trauma patients in emergency departments (EDs). The Modified Early Warning Score (MEWS), National Early Warning Score (NEWS), standardized early warning score (SEWS), Modified Rapid Emergency Medicine Score (mREMS), and Revised Trauma Score (RTS) are five common triage tools proposed for trauma management. However, few studies have compared these tools in a multiple trauma cohort and investigated the influence of nighttime admission on the performance of these tools. This retrospective study was aimed at evaluating and comparing the performance of MEWS, NEWS, SEWS, mREMS, and RTS for identifying the mortality risk and trauma severity of patients with multiple trauma admitted to the ED during the daytime and nighttime. Retrospective data were collected from the medical records of patients with multiple trauma admitted in the daytime or nighttime to calculate scores for each triage tool. Logistic regression analysis was conducted on each triage tool for identifying in-hospital mortality and severe trauma (injury severity score > 15) in the daytime and nighttime. The performance of the tools was evaluated and compared by calculating area under the receiver operating characteristic curve (AUROC) of the retrospective logistic model of each tool. We collected data for 1,818 admissions, including 1,070 daytime and 748 nighttime admissions. A comparison of performance for identifying in-hospital mortality between daytime and nighttime yielded the following results (AUROC): MEWS (0.95 vs. 0.93, p = 0.384), NEWS (0.95 vs. 0.94, p = 0.708), SEWS (0.95 vs. 0.94, p = 0.683), mREMS (0.94 vs. 0.92, p = 0.286), and RTS (0.93 vs. 0.93, p = 0.87). Similarly, a comparison of performance for identifying trauma severity between daytime and nighttime yielded the following results (AUROC): MEWS (0.78 vs. 0.78, p = 0.95), NEWS (0.8 vs. 0.8, p = 0.885), SEWS (0.78 vs. 0.78, p = 0.818), mREMS (0.75 vs. 0.69, p = 0.019), and RTS (0.75 vs. 0.74, p = 0.619). All five scores are excellent triage tools (AUROC ≥ 0.9) for identifying in-hospital mortality for both daytime and nighttime admissions. However, they have only moderate effectiveness (AUROC < 0.9) at identifying severe trauma. The NEWS is the best triage tool for identifying severe trauma for both daytime and nighttime admissions. The MEWS, NEWS, SEWS, and RTS exhibited no significant differences in performance for identifying in-hospital mortality or severe trauma during the daytime or nighttime. However, the mREMS was better at identifying severe trauma during the daytime.

9.
Ying Yong Sheng Tai Xue Bao ; 31(3): 769-777, 2020 Mar.
Artigo em Chinês | MEDLINE | ID: mdl-32537971

RESUMO

We examined the effects of five shading treatments (0, 20%, 40%, 60% and 80% shading) on chlorophyll content, photosynthetic characteristics, and chlorophyll fluorescence chara-cteristics of four Corydalis species (C. incisa, C. decumbens, C. edulis and C. pallida) in a pot experiment. The results showed that the contents of chlorophyll a, chlorophyll b and chlorophyll (a+b) increased with the increment of shading, with that of C. incisa reaching the maximum under 80% shading treatment and that of C. decumbens, C. edulis and C. pallida reaching a maximum under 60% shading treatment. In contrast, chlorophyll a/b, light saturation point, light compensation point and dark respiration rate decreased with increasing shading. Among the four Corydalis species, C. incisa reached up to the maximum chlorophyll fluorescence parameters under 80% shading treatment, and C. decumbens, C. edulis and C. pallida reached the maximum at 60% shading treatment. The shade tolerance of four species was as follows: C. incisa > C. decumbens > C. edulis > C. pallida. C. incisa under 80% shading treatment and C. decumbens, C. edulis, C. pallida at 60% shading treatment had the highest light energy utilization and photosynthetic capacity, which would facilitate their growth.


Assuntos
Corydalis , Clorofila , Clorofila A , Fluorescência , Luz , Fotossíntese , Folhas de Planta
10.
J Nanosci Nanotechnol ; 8(4): 1775-81, 2008 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-18572577

RESUMO

In this paper, intercalated and partially exfoliated melamine-formaldehyde (MF)/montmorillonite (MMT) nanocomposites have been synthesized successfully via in-situ polymerization based on pristine montmorillonite, acidified montmorillonite and organic modified montmorillonite respectively. The obtained nanocomposites were characterized by XRD, TEM, TGA, and Raman spectroscopy. Free formaldehyde content of those composites was also determined by acetyl acetone technique. It was found that acidified montmorillonite and organic modified montmorillonite could catalyze the polycondensation reaction of methylolmelamines. The thermal stability and chemical resistance of those two nanocomposites were also improved dramatically compared to pure melamine-formaldehyde resin.


Assuntos
Bentonita/química , Cristalização/métodos , Formaldeído/química , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Nanotecnologia/métodos , Triazinas/química , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
11.
Sci China C Life Sci ; 51(9): 842-53, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18726532

RESUMO

Sacred lotus (Nelumbo nucifera Gaertn. 'Tielian') seed is long-lived and extremely tolerant of high temperature. Water content of lotus and maize seeds was 0.103 and 0.129 g H2O [g DW](-1), respectively. Water content, germination percentage and fresh weight of seedlings produced by surviving seeds gradually decreased with increasing treatment time at 100 degrees C. Germination percentage of maize (Zea mays L. 'Huangbaogu') seeds was zero after they were treated at 100 degrees C for 15 min and that of lotus seeds was 13.5% following the treatment at 100 degrees C for 24 h. The time in which 50% of lotus and maize seeds were killed by 100 degrees C was about 14.5 h and 6 min, respectively. With increasing treatment time at 100 degrees C, relative electrolyte leakage of lotus axes increased significantly, and total chlorophyll content of lotus axes markedly decreased. When treatment time at 100 degrees C was less than 12 h, subcellular structure of lotus hypocotyls remained fully intact. When treatment time at 100 degrees C was more than 12 h, plasmolysis gradually occurred, endoplasmic reticulum became unclear, nuclei and nucleoli broke down, most of mitochondria swelled, lipid granules accumulated at the cell periphery, and organelles and plasmolemma collapsed. Malondialdehyde (MDA) content of lotus axes and cotyledons decreased during 0 -12 h of the treatment at 100 degrees C and then increased. By contrast, the MDA content of maize embryos and endosperms increased during 5-10 min of the treatment at 100 degrees C and then decreased slightly. For lotus seeds: (1) activities of superoxide dismutase (SOD) and glutathione reductase (GR) of axes and cotyledons and of catalase (CAT) of axes increased during the early phase of treatment at 100 degrees C and then decreased; and (2) activities of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) of axes and cotyledons and of CAT of cotyledons gradually decreased with increasing treatment time at 100 degrees C. For maize seeds: (1) activities of SOD and DHAR of embryos and endosperms and of GR of embryos increased during the early phase of the treatment at 100 degrees C and then decreased; and (2) activities of APX and CAT of embryos and endosperms and of GR of endosperms rapidly decreased with increasing treatment time at 100 degrees C. With decrease in seed germination, activities of SOD, APX, CAT, GR and DHAR of axes and cotyledons of lotus seeds decreased slowly, and those of embryos and endosperms of maize seeds decreased rapidly.


Assuntos
Antioxidantes/metabolismo , Temperatura Alta , Nelumbo , Sementes/enzimologia , Ascorbato Peroxidases , Catalase/metabolismo , Clorofila/química , Ácido Desidroascórbico/metabolismo , Germinação , Glutationa Redutase/metabolismo , Hipocótilo/citologia , Hipocótilo/metabolismo , Nelumbo/citologia , Nelumbo/fisiologia , Peroxidases/metabolismo , Sementes/química , Superóxido Dismutase/metabolismo , Água/química , Zea mays/anatomia & histologia
12.
Chemosphere ; 197: 526-534, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29407814

RESUMO

As a new member of carbon dots (CDs), Polymer dots (PDs) prepared by hydrothermal treatment of polymers, usually consist of the carbon core and the connected partially degraded polymer chains. This type of CDs might possess aqueous solubility, non-toxicity, excellent stability against photo-bleaching and high visible light activity. In this research, PDs were prepared by a moderate hydrothermal treatment of polyvinyl alcohol, and PDs grafted TiO2 (PDs-TiO2) nanohybrids with TiOC bonds were prepared by a facile in-situ hydrothermal treatment of PDs and Ti (SO4)2. Under visible light irradiation, the PDs-TiO2 demonstrate excellent photocatalytic activity for methyl orange degradation, and the photocatalytic rate constant of PDs-TiO2 is 3.6 and 9.5 times higher than that of pure TiO2 and commercial P25, respectively. In addition, the PDs-TiO2 exhibit good recycle stability under UV-Vis light irradiation. The interfacial TiOC bonds and the π-conjugated structures in PDs-TiO2 can act as the pathways to quickly transfer the excited electrons between PDs and TiO2, therefore contribute to the excellent photocatalytic activity.


Assuntos
Processos Fotoquímicos , Polímeros/química , Titânio/química , Compostos Azo , Carbono , Catálise , Luz , Modelos Químicos , Raios Ultravioleta , Água/química
13.
J Clin Neurosci ; 22(3): 570-4, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25487174

RESUMO

Findings from multiple studies on microRNA (miRNA) expression profiling in schizophrenia patients have produced conflicting results. In order to investigate miRNA as specific biomarkers in the peripheral plasma and peripheral blood mononuclear cells (PBMC) of schizophrenia patients, expression levels of the nine most frequently reported schizophrenia-associated miRNA (miR-30e, miR-34a, miR-181b, miR-195, miR-346, miR-432, miR-7, miR-132 and miR-212) were examined in the peripheral plasma and PBMC in 25 schizophrenia patients and 13 healthy controls using quantitative real-time reverse transcription polymerase chain reaction. We observed significantly increased expressions of miR-132, miR-195, miR-30e and miR-7 in plasma samples (p<0.05 to p<0.001), and miR-212, miR-34a and miR-30e in PBMC samples (p<0.05 to p<0.01). Receiver operating characteristic curve analysis revealed that the area under the curve (AUC) of miR-30e in plasma was 0.767 (95% confidence interval [CI] 0.608-0.926) with sensitivity and specificity of 90.90% and 60.00% respectively, and the AUC of miR-30e in PBMC was 0.756 (95% CI 0.584-0.929) with sensitivity and specificity of 81.80% and 68.00%, respectively. Logistic regression analysis demonstrated that miR-30e in plasma was more sensitive to differentiate schizophrenia patients from normal controls than miR-30e in PBMC. Our findings indicate that miRNA expression is more significant in plasma than in PBMC, and suggest that miR-30e in plasma may be a more sensitive biomarker for schizophrenia diagnosis, although its aberrant expression can be detected in both plasma and PBMC.


Assuntos
Leucócitos Mononucleares/metabolismo , MicroRNAs/sangue , Esquizofrenia/diagnóstico , Adolescente , Adulto , Biomarcadores/sangue , Feminino , Humanos , Masculino , MicroRNAs/genética , Pessoa de Meia-Idade , Reação em Cadeia da Polimerase em Tempo Real , Esquizofrenia/sangue , Sensibilidade e Especificidade , Adulto Jovem
14.
ACS Appl Mater Interfaces ; 6(4): 2370-6, 2014 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-24422430

RESUMO

Abundant and renewable solar light is an ideal resource for the industrial application of TiO2 photocatalysis in environmental purification. Over the past decades, the pursuit for visible-light photocatalysts with low cost, simple process, and high efficiency remains a challenging task. Here, we report a novel organic-inorganic nanohybrid photocatalyst (conjugation-grafted-TiO2) by chemically grafting conjugated structures onto the surfaces of TiO2 nanoparticles through controlled thermal degradation of the coacervated polymer layer. The interfacial C-O-Ti bonds between TiO2 and conjugated structures can act as the pathway to quickly transfer the excited electrons from conjugated structures to TiO2, therefore contribute to high visible-light photocatalytic efficiency. Our findings provide an economic route to prepare the conjugation-grafted-TiO2 nanohybrid, and develop a routine to improve the photocatalytic efficiency of organic-inorganic hybrid materials through the interfacial interaction.

15.
ACS Appl Mater Interfaces ; 6(15): 12252-60, 2014 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-24969179

RESUMO

Acrylonitrile-butadiene-styrene resin (ABS)/graphene nanocomposites were prepared through a facile coagulation method. Because the chemical reduction of graphene oxide was in situ conducted in the presence of ABS at the dispersion stage, the aggregation of the graphene nanosheets was avoided. It was shown by transmission electron microscopy that the graphene nanosheets were selectively located and homogeneously dispersed in the styrene-acrylonitrile (SAN) phase. The electrical conductivity and linear viscoelastic behavior of the nanocomposites were systematically studied. With increasing filler content, graphene networks were established in the SAN phase. Consequently, the nanocomposites underwent a transition from electrical insulator to conductor at a percolation threshold of 0.13 vol %, which is smaller than that of other ABS composites. Such a low percolation threshold results from extreme geometry, selective localization, and homogeneous dispersion of the graphene nanosheets in SAN phase. Similarly, the rheological response of the nanocomposites also showed a transition to solid-like behavior. Due to the thermal reduction of graphene nanosheets and structure improvement of graphene networks, enhanced electrical conductivity of the nanocomposites was obtained after annealing.

16.
J Appl Polym Sci ; 123(2): 1085-1093, 2012 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-24696526

RESUMO

A new flame retardant polycarbonate/magnesium oxide (PC/MgO) nanocomposite, with high flame retardancy was developed by melt compounding. The effect of MgO to the flame retardancy, thermal property, and thermal degradation kinetics were investigated. Limited oxygen index (LOI) test revealed that a little amount of MgO (2 wt %) led to significant enhancement (LOI = 36.8) in flame retardancy. Thermogravimetric analysis results demonstrated that the onset temperature of degradation and temperature of maximum degradation rate decreased in both air and N2 atmosphere. Apparent activation energy was estimated via Flynn-Wall-Ozawa method. Three steps in the thermal degradation kinetics were observed after incorporation of MgO into the matrix and the additive raised activation energies of the composite in the full range except the initial stage. It was interpreted that the flame retardancy of PC was influenced by MgO through the following two aspects: on the one hand, MgO catalyzed the thermal-oxidative degradation and accelerated a thermal protection/mass loss barrier at burning surface; on the other hand, the filler decreased activation energies in the initial step and improved thermal stability in the final period.

17.
Colloid Polym Sci ; 290(14): 1371-1380, 2012 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-24729654

RESUMO

After the surface silylation with 3-methacryloxypropyltrimethoxysilane, silica nanoparticles were further modified by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The immobilization of DOPO on silica nanoparticles was confirmed by Fourier transform infrared spectroscopy, UV-visible spectroscopy, magic angle spinning nuclear magnetic resonance, and thermogravimetric analysis. By incorporating the DOPO-immobilized silica nanoparticles (5 wt%) into polypropylene matrix, the thermal oxidative stability exhibited an improvement of 62 °C for the half weight loss temperature, while that was only 26 °C increment with incorporation of virgin silica nanoparticles (5 wt%). Apparent activation energies of the polymer nanocomposites were estimated via Flynn-Wall-Ozawa method. It was found that the incorporation of DOPO-immobilized silica nanoparticles improved activation energies of the degradation reaction. Based on the results, it was speculated that DOPO-immobilized silica nanoparticles could inhibit the degradation of polypropylene and catalyze the formation of carbonaceous char on the surface. Thus, thermal stability was significantly improved.

18.
J Hazard Mater ; 227-228: 185-94, 2012 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-22658211

RESUMO

Nano titanium dioxide (TiO(2)) photocatalyst is generally immobilized onto the matrix through the physical absorption, hydrogen bonding or chemical bonding, which is utilized for the application of wastewater treatment. In this research, TiO(2) nanoparticles were immobilized in polyvinyl alcohol (PVA) matrix via solution-casting combined with heat-treatment method. Structure characterization indicated that Ti-O-C chemical bond formed via dehydration reaction between TiO(2) and PVA during the heat treatment process, and TiO(2) nanoparticles had been chemically immobilized in PVA matrix. Photodegradation results of methyl orange (MO) showed that the film with 10 wt% TiO(2) and treated at 140°C for 2h exhibited a remarkable ultraviolet (UV) photocatalytic activity, approximately close to the TiO(2) slurry system. This was mainly attributed to the fixation effect by Ti-O-C chemical bonds, which was indirectly confirmed by the slight loss of TiO(2) photocatalysts even after 25-cycle use. In addition, the good swelling ability of PVA matrix provided the MO molecules with more opportunities to fully contact with TiO(2), thus benefited the photocatalysis. This route to chemically immobilize TiO(2) nanoparticles is simple and cheap to prepare polymer/TiO(2) hybrid materials with high photocatalytic activity for multi-cycle use, which is of significance to the practical application of TiO(2) catalysts.


Assuntos
Nanopartículas Metálicas/química , Álcool de Polivinil/química , Titânio/química , Raios Ultravioleta , Poluentes Químicos da Água/química , Poluentes Químicos da Água/efeitos da radiação , Compostos Azo/química , Compostos Azo/efeitos da radiação , Catálise , Temperatura Alta , Fotólise
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