Mao Peng

Multi-scale carbon fiber reinforced polymer (CFRP) composites with continuous carbon fiber as the primary reinforcement and nanoscale fillers as the secondary reinforcement have attracted great research interests in the last decade. Herein we report a new organically modified montmorillonite (MMT) for epoxy nanocomposites and multi-scale CFRP composites with superior mechanical properties. The organically modified MMT is prepared by ion-exchanging natural MMT with the hydrochlorate of triglycidyl para-aminophenol (TGPAP), a tertiary amine-type epoxy oligomer used as a CFRP matrix for the aerospace industry. The TGPAP-modified MMTs disperse uniformly in the matrix as thin stacks of intercalated nanoplatelets and exfoliated single-layer nanoplatelets, and are reactive with the epoxy matrices, thus remarkably enhance the mechanical properties of the nanocomposites and multi-scale CFRP composites. In contrast to reference CFRP composites, the incorporation TGPAP-modified MMTs greatly retards the propagation of inter-layer delamination, and fiber breakage becomes the major damage mode in the three-point bending tests. In particular, 4 wt% of TGPAP-modified MMTs increases the interlaminar shear strength of the multi-scale CFRP composites by 52%, and the flexural strength by 52.3%, which is superior to those of MMT-containing CFRP composites ever reported.

Green Preparation of Epoxy/Graphene Oxide Nanocomposites Using a Glycidylamine Epoxy Resin as the Surface Modifier and Phase Transfer Agent of Graphene Oxide

Co-reporter:Xinlei Tang, Yang Zhou, and Mao Peng

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 3) pp:1854

Publication Date(Web):December 31, 2015

DOI:10.1021/acsami.5b09830

In studies of epoxy/graphene oxide (GO) nanocomposites, organic solvents are commonly used to disperse GO, and vigorous mechanical processes and complicated modification of GO are usually required, increasing the cost and hindering the development and application of epoxy nanocomposites. Here, we report a green, facile, and efficient method of preparing epoxy/GO nanocomposites. When triglycidyl para-aminophenol (TGPAP), a commercially available glycidyl amine epoxy resin with one tertiary amine group per molecule, is used as both the surface modifier and phase transfer agent of GO, GO can be directly and rapidly transferred from water to diglycidyl ether of bisphenol A and other types of epoxy resins by manual stirring under ambient conditions, whereas GO cannot be transferred to these epoxy resins in the absence of TGPAP. The interaction between TGPAP and GO and the effect of the TGPAP content on the dispersion of GO in the epoxy matrix were investigated systematically. Superior dispersion and exfoliation of GO nanosheets and remarkably improved mechanical properties, including tensile and flexural properties, toughness, storage modulus, and microhardness, of the epoxy/GO nanocomposites with a suitable amount of TGPAP were demonstrated. This method is organic-solvent-free and technically feasible for large-scale preparation of high-performance nanocomposites; it opens up new opportunities for exploiting the unique properties of graphene or even other nanofillers for a wide range of applications.Keywords: epoxy; graphene oxide; nanocomposites; organic-solvent-free; phase transfer; surface modifier; triglycidyl para-aminophenol

Fast phase transfer of graphene oxide from water to triglycidyl para-aminophenol for epoxy composites with superior nanosheet dispersion

Co-reporter:Mao Peng, Xinlei Tang, Yang Zhou

Polymer 2016 Volume 93() pp:1-8

Publication Date(Web):14 June 2016

DOI:10.1016/j.polymer.2016.03.016

•Graphene oxide (GO) can form complexes with triglycidyl para-aminophenol (TGPAP).•Complexing leads to rapid phase transfer of GO from water to TGPAP, an epoxy oligomer.•The strength of the epoxy/reduced GO (rGO) composites are remarkably enhanced.•rGO greatly improves the mechanical properties of multiscale reinforced composites.Currently the incorporation of graphene within polymer matrices requires complicated, energy-intensive, and time-consuming sample preparation steps. We report that the self-assembly of graphene oxide (GO) with triglycidyl para-aminophenol (TGPAP), a liquid tertiary amine-type epoxy oligomer, results in the direct and fast phase transfer of GO from water to TGPAP via simple manual stirring under ambient conditions for a very short time. The formation of TGPAP/GO complexes by the partial charge transfer from the carboxylic acid groups of GO to the tertiary amine group of TGPAP was found to be responsible for the fast phase transfer. After the in-situ thermal reduction and curing process, few-layer nanosheets of the reduced GO (rGO) disperse very uniformly in the final epoxy/rGO composites. The mechanical properties of the epoxy/rGO composites and the multiscale reinforced composites with continuous microscale carbon fiber and rGO as the primary and secondary reinforcements, respectively, are remarkably enhanced.

Oscillatory shear-induced alignment of ketjen black conductive particles in polylactic acid and its effect on the electrical anisotropy

Co-reporter:Liangyao Su;Pengfei Wang;Zhongbin Xu;Dong Chen

Journal of Polymer Science Part B: Polymer Physics 2016 Volume 54( Issue 3) pp:369-373

Publication Date(Web):

DOI:10.1002/polb.23950

ABSTRACT

This study aligned Ketjen black (KB) particles along one preferred direction in a polylactic acid (PLA) matrix using an oscillatory shear flow and investigated the effect of aligned KB on the electrical anisotropy. Under the oscillatory shear, the KB particles are aligned along the flow direction in the PLA matrix, resulting in an oriented conductive network. When the concentration of KB is in the range of 0.88–1.56 vol %, the electrical volume resistivity along the flow direction (ρ_∥) decreases to ∼3 × 10⁴ Ω m and that perpendicular to the flow direction (ρ_⊥) remains at ∼1 × 10¹⁰ Ω m, showing an extremely large electrical anisotropy, and the ρ_⊥/ρ_∥ value is 3–4 orders of magnitude higher than that of previously reported carbon-nanotube-based electrical anisotropic composites. This strong anisotropy is attributed to the preferential alignment of KB particles with lower percolation threshold for conductive path along the flow direction. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 369–373

Crystallization behavior and water vapor permeability of poly(lactic acid) nanocomposite under oscillatory shear

Co-reporter:Zhongbin Xu;Liangyao Su;Shichao Jiang;Wei Gu;Pengfei Wang

Journal of Applied Polymer Science 2015 Volume 132( Issue 30) pp:

Publication Date(Web):

DOI:10.1002/app.42321

ABSTRACT

The crystallization behavior and water vapor permeability of a poly(lactic acid) (PLA) nanocomposite containing 5 wt % organic montmorillonite (OMMT) under oscillatory shear were investigated. Under the oscillatory shear, OMMT platelets exhibited a better intercalated structure and oriented along the flow direction, some of the OMMT platelets are exfoliated and dispersed in the form of single or few-layer platelets. These well-dispersed OMMT platelets acted as more effective nucleating and accelerating agent for the crystallization of PLA, as a result, the cold crystallization enthalpy was significantly decreased, the cold crystallization temperature was much closer to the melting temperature and the crystallinity is dramatically increased, which are observed for the first time. Moreover, the water vapor permeability is decreased by 36% due to the barrier effect of the well-dispersed OMMT and the increased crystallinity of PLA, which increase the tortuous path that water molecules required to permeate. The mechanical properties are also enhanced owing to the well-dispersed OMMT and increased crystallinity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42321.

Effect of oscillatory shear on the mechanical properties and crystalline morphology of linear low density polyethylene

Co-reporter:Zhong-bin Xu;Liang-yao Su;Peng-fei Wang

Chinese Journal of Polymer Science 2015 Volume 33( Issue 8) pp:1114-1124

Publication Date(Web):2015 August

DOI:10.1007/s10118-015-1663-6

In this study, effects of oscillatory shear with different frequencies (0–2.5 Hz) and amplitudes (0–20 mm) on the mechanical properties and crystalline morphology of linear low density polyethylene (LLDPE) were investigated. It was found that the mechanical properties of LLDPE are improved because of the more perfect crystalline structure when LLDPE crystallizes under low-frequency and small-amplitude (0.2 Hz/4 mm) oscillatory shear. The mechanical properties can be further improved by increasing either the frequency or the amplitude of oscillatory shear. The Young’s modulus and tensile strength of LLDPE are improved by 27% and 20%, respectively, when the frequency is increased to 2.5 Hz and the amplitude is maintained at 4 mm; while the Young’s modulus and tensile strength are improved by 49% and 47%, respectively, when the amplitude is increased to 20 mm and the frequency is remained as 0.2 Hz. The crystallinity and microstructure of LLDPE under different oscillatory shear conditions were investigated by using differential scanning calorimetry, wide angle X-ray diffraction and scanning electron microscopy to shed light on the mechanism for the improvement of mechanical properties.

Toughening of epoxy resin with functionalized core-sheath structured PAN/SBS electrospun fibers

Co-reporter:Tanghua Guo;Zhi Zhou;Honglei Guo;Guohua Xiao;Xinglei Tang

Journal of Applied Polymer Science 2014 Volume 131( Issue 23) pp:

Publication Date(Web):

DOI:10.1002/app.41119

ABSTRACT

Core-sheath structured electrospun fibers with styrene-butadiene-styrene (SBS) block copolymer as a rubbery core and polyacrylonitrile (PAN) as a hard sheath were prepared by coaxial electrospinning, and used to improve the toughness of epoxy resin. The surface of the fibers was aminated by reacting PAN with diethylenetriamine to improve the interfacial interaction between the fibers and epoxy. Scanning and transmission electron microscopies confirm the core-sheath structure of the PAN/SBS fibers. The Charpy impact energy is increased by the addition of electrospun fibers. When the content of aminated core-sheath fibers is 4 wt %, the Charpy impact energy is increased by 150%. Dynamic mechanical analysis shows that the glass transition temperature of epoxy is not decreased by the addition of core-sheath fibers. The high impact resistance is attributed to the rubbery core of the fibers that can absorb and dissipate impact energy, and the chemical bonding between the fibers and epoxy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41119.

Flame-retardant coating by alternate assembly of poly(vinylphosphonic acid) and polyethylenimine for ramie fabrics

Co-reporter:Li-li Wang;Tao Zhang;Hong-qiang Yan 彭懋

Chinese Journal of Polymer Science 2014 Volume 32( Issue 3) pp:305-314

Publication Date(Web):2014 March

DOI:10.1007/s10118-014-1408-y

A novel intumescent flame retardant coating, consisting of poly(vinylphosphonic acid) (PVPA) as the acid source and branched polyethylenimine (BPEI) as the blowing agent, was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie. The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie. Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 °C, while the control (uncoated) fabric left less than 1.4 wt% residue. Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time, and the residues well preserved the original weave structure and fiber morphology, whereas, the uncoated fabric left only ashes. Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%, relative to those of the uncoated fabric.

Hydrogen-Bonding Assembly of Rigid-Rod Poly(p-sulfophenylene terephthalamide) and Flexible-Chain Poly(vinyl alcohol) for Transparent, Strong, and Tough Molecular Composites

Co-reporter:Mao Peng, Guohua Xiao, Xinglei Tang, and Yang Zhou

Macromolecules 2014 Volume 47(Issue 23) pp:8411-8419

Publication Date(Web):November 17, 2014

DOI:10.1021/ma501590x

Molecular composites comprising poly(p-sulfophenylene terephthalamide) (sPPTA), a sulfonated polyaramid rigid-rod polyelectrolyte, and flexible-chain poly(vinyl alcohol) (PVA) were prepared by a green and easy-to-scale-up water casting method. Influence of sPPTA on the microstructure and properties of the molecular composites was systematically investigated. Fourier transform infrared spectroscopy confirms the existence of hydrogen bonding between sPPTA and PVA. Wide-angle X-ray diffraction patterns do not show the characteristic of neat sPPTA crystalline aggregates in the composites even when the sPPTA content is as high as 33 wt %, suggesting that the strong interaction between sPPTA and PVA prevents the self-aggregation of sPPTA and leads to the formation of PVA/sPPTA complexes inside the composites. Transmission electron microscopy shows that sPPTA has good compatibility with PVA, and nanoscale fibril-like supramolecular assemblies dispersing uniformly in the composites become observable with the increase of sPPTA content. Moreover, the PVA/sPPTA complexes have a strong effect on the melt point, crystallinity, mechanical properties, and thermal stability of PVA. The PVA/sPPTA composites exhibit both high strength and high ductility. When the content of sPPTA is 5 wt %, the PVA/sPPTA composite exhibits the best mechanical properties, with a tensile strength of 169 ± 13 MPa, which is 54% higher than that of neat PVA (110 ± 10 MPa). Surprisingly, the reinforcement factor is even superior to that of multiwalled carbon nanotubes, vapor grown carbon fibers, and nanodiamonds previously reported for the reinforcement of PVA nanocomposites. Moreover, the PVA/sPPTA molecular composites have a relatively low modulus but a much larger elongation at break than prefabricated nanocomposites, showing good ductility. The strong and tough PVA/sPPTA molecular composites can be potentially used as high performance membranes or fibers in the future.

Preparation of reduced graphene oxide by infrared irradiation induced photothermal reduction

Co-reporter:Honglei Guo, Mao Peng, Zhongming Zhu and Lina Sun

Nanoscale 2013 vol. 5(Issue 19) pp:9040-9048

Publication Date(Web):25 Jul 2013

DOI:10.1039/C3NR02805D

We present a green and scalable route toward the formation of reduced graphene oxide (r-GO) by photothermal reduction induced by infrared (IR) irradiation, utilizing a bathroom IR lamp as the source of IR light. Thermogravimetric analysis, Raman, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirm the reduction of r-GO by IR light. Ultraviolet-visible-infrared spectra indicate that adsorption of IR light by original GO films is less than that of UV and visible light; but when GO is exposed to IR light, its adsorption of IR light increases very rapidly with time. The influence of the power density of the IR light on the structure and properties of r-GO was investigated. At high IR power density, the reduction reaction was so fierce that r-GO became highly porous due to the rapid degassing and exfoliation of GO sheets. The r-GO powder revealed good performance as the anode material for lithium ion batteries. At relatively low IR power density, the reduction process was found to be mild but relatively slow. Crack-free and uniform conductive r-GO thin films with a volume conductivity of 1670 S m−1 were then prepared by two-step IR irradiation, i.e. first at low IR power density and then at high IR power density. Moreover, the r-GO films were also observed to exhibit obvious and reversible IR light-sensing behavior.

High-intensity ultrasonication modification of vapor grown carbon fibers with poly(vinyl alcohol) for the preparation of high strength composites by simple water casting

Co-reporter:Lina Sun, Honglei Guo, Zhongming Zhu, Tanghua Guo and Mao Peng

RSC Advances 2013 vol. 3(Issue 27) pp:10983-10993

Publication Date(Web):26 Apr 2013

DOI:10.1039/C3RA00116D

High-intensity ultrasonication was demonstrated to be facile and efficient for the preparation of water-dispersible poly(vinyl alcohol) functionalized vapor-grown carbon fibres (f-VGCFs). In contrast to multiwalled carbon nanotubes, VGCFs are mechanically strong and not observably shortened or damaged by ultrasonication. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy show that the surface of f-VGCFs is decorated with a thin layer of PVA, imparting good dispersibility and suspending stability in water. High-strength PVA–f-VGCF composite films were then successfully obtained by the green and low-cost water casting method, which is totally free of organic solvents. The tensile strength and Young's modulus of the composite films filled with 5 wt% f-VGCFs are remarkably increased to 177.5 ± 9.8 MPa and 4.6 ± 0.4 GPa, respectively, which are about 45.0% and 53.3% higher than those of neat PVA. After being stretched by 5 times their length, the tensile strength and Young's modulus are increased to 681.0 ± 4.3 MPa and 12.1 ± 0.6 GPa, which are 58.8% and 49.4% higher than those of neat PVA stretched by 5 times their length, respectively. The uniform dispersion of f-VGCFs and the effective load transfer between the fillers and the matrix are responsible for the greatly improved mechanical properties.

Synthesis of novel poly(aminophosphonate ester)s flame retardants and their applications in EVA copolymer

Co-reporter:Yan Liu;Yan Zhang;Zhenhu Cao;Zhengping Fang

Polymers for Advanced Technologies 2013 Volume 24( Issue 2) pp:197-203

Publication Date(Web):

DOI:10.1002/pat.3070

Novel oligomeric intumescent flame retardants, poly(amino phosphonate ester)s (PAPEs), containing both phosphorous and nitrogen, were synthesized by reacting diethyl phosphite with two different polyschiff bases obtained from the reaction of diamines with dialdehyde. The target PAPEs (designated as PAPE-d and PAPE-e, respectively) were characterized by ¹H NMR, ³¹P NMR, Fourier Transform infrared spectroscopy, elemental analysis, gel permeation chromatography and thermogravimetric analysis (TGA) techniques. Thermal stability and flammability of ethylene-vinyl acetate copolymer (EVA)/PAPE blends with various PAPE content were investigated by TGA, limited oxygen index (LOI), vertical burning test (UL-94) and microscale combustion colorimeter (MCC). The results indicate that PAPEs effectively improve the flame retardancy of EVA. The EVA/30%PAPE-e blend has a LOI value of 28, and its peak heat release rate (PHRR) value in MCC measurement is reduced by 36%. At the same time, the EVA/PAPE blends also have high yield of residual char, indicating that PAPEs are effective charring agents. Scanning electron microscopy observations of the residues of the EVA/PAPE blends show the existence of compact char layer on the surface of the residues, which is responsible for the improvement of the flame retardancy of EVA. Copyright © 2012 John Wiley & Sons, Ltd.

Combination of double-modified clay and polypropylene-graft-maleic anhydride for the simultaneously improved thermal and mechanical properties of polypropylene

Co-reporter:Yuanyuan Xu;Zhenghong Guo;Zhengping Fang;Lie Shen

Journal of Applied Polymer Science 2013 Volume 128( Issue 1) pp:283-291

Publication Date(Web):

DOI:10.1002/app.38178

Abstract

Double-modified montmorillonite (MMT) was first prepared by covalent modification of MMT with 3-aminopropyltriethoxysilane and then intercalation modification by tributyl tetradecyl phosphonium ions. The obtained double-modified MMT was melt compounded with polypropylene (PP) to obtain nanocomposites. The dispersion of the double-modified MMT in PP was found to be greatly improved by the addition of PP-graft-maleic anhydride (PP-g-MA) as a “compatibilizer,” whose anhydride groups can react with the amino groups on the surface of the double-modified MMT platelets and thus improve the dispersion of MMT in PP. Fourier transform infrared, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, scanning electron microscopy, and tensile test were used to characterize the structure of the double-modified MMT, morphology, and the thermal and mechanical properties of the nanocomposites. The results show that PP-g-MA promotes the formation of exfoliated/intercalated morphology and obviously increases the thermal properties, tensile strength, and Young's modulus of the PP/double-modified MMT nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A novel zinc chelate complex containing both phosphorus and nitrogen for improving the flame retardancy of low density polyethylene

Co-reporter:Zhenhu Cao, Yan Zhang, Pingan Song, Yuanzheng Cai, Qi Guo, Zhengping Fang, Mao Peng

Journal of Analytical and Applied Pyrolysis 2011 Volume 92(Issue 2) pp:339-346

Publication Date(Web):November 2011

DOI:10.1016/j.jaap.2011.07.007

A novel metal chelate complex containing phosphorus, nitrogen and zinc (II) ion was synthesized and used as the flame retardant of low density polyethylene (LDPE). The zinc chelate complex was synthesized by reacting zinc acetate with the ligand of tetraethyl (1,2-phenylenebis(azanediyl)) bis (2-hydroxylphenylmethylene) diphosphonate (TEPAPM). The chemical structure of the target Zn-TEPAPM was confirmed by FTIR, 1H NMR, 13C NMR and 31P NMR spectra. The flame retardancy and thermal behavior of LDPE containing various amount of Zn-TEPAPM were investigated by limiting oxygen index test, thermogravimetric (TG) analysis and cone calorimetry. The results show that Zn-TEPAPM can greatly increase the thermal stability, the char formation and smoke suppression ability of LDPE. The TG curves show that even when the filler content of Zn-TEPAPM is as low as 1 wt% in LDPE, the onset degradation temperature of LDPE is increased from 429 °C to 442 °C, and the maximum degradation temperature is increased from 469 °C to 488 °C. Also, a reduction of 32% for the peak heat release rate (PHRR) is obtained in the cone test. Moreover, Zn-TEPAPM is demonstrated to be a very effective synergist of ammonium polyphosphate (APP). When 1 wt% of Zn-TEPAPM was introduced into the LDPE/APP (mass ratio 80/19) blend, the PHRR value is reduced by 32%, compared with that of LDPE/APP blend without Zn-TEPAPM, and the char layer becomes more compact and intact.

Preparation of isotactic polypropylene-grafted multiwalled carbon nanotubes (iPP-g-MWNTs) by macroradical addition in solution and the properties of iPP-g-MWNTs/iPP composites

Co-reporter:Jun Zheng;Zhongming Zhu;Ji Qi;Zhi Zhou;Peng Li

Journal of Materials Science 2011 Volume 46( Issue 3) pp:648-658

Publication Date(Web):2011 February

DOI:10.1007/s10853-010-4787-7

Isotactic polypropylene (iPP) was successfully grafted onto multiwalled carbon nanotubes (MWNTs) by direct macroradical addition by sonication in hot xylene with BPO as an initiator. A quantitative determination of the grafting ratio was first realized after the iPP-g-MWNTs were extensively purified by repeated hot vacuum filtration and redispersion in xylene at 130 °C. It was found that both iPP macromolecular radicals and small-molecular benzoic acid free radicals were grafted onto MWNTs. iPP-g-MWNTs dispersed more uniformly in iPP than pristine MWNTs. The iPP-g-MWNTs/iPP composites have much higher elongations at break than the iPP composites filled with pristine MWNTs, and the Young’s modulus and yield strength were also improved to some extent. iPP-g-MWNTs also have a stronger nucleation effect on the crystallization of iPP than pristine MWNTs.

Surface-initiated graft polymerization on multiwalled carbon nanotubes pretreated by corona discharge at atmospheric pressure

Co-reporter:Lihua Xu, Zhengping Fang, Ping'an Song and Mao Peng

Nanoscale 2010 vol. 2(Issue 3) pp:389-393

Publication Date(Web):24 Nov 2009

DOI:10.1039/B9NR00222G

Surface-initiated graft polymerization on multi-walled carbon nanotubes pretreated with a corona discharge at atmospheric pressure was explored. The mechanism of the corona-discharge-induced graft polymerization is discussed. The results indicate that MWCNTs were encapsulated by poly(glycidyl methacrylate) (PGMA), demonstrating the formation of PGMA-grafted MWCNTs (PGMA-g-MWCNTs), with a grafting ratio of about 22 wt%. The solubility of PGMA-g-MWCNTs in ethanol was dramatically improved compared to pristine MWCNTs, which could contribute to fabricating high-performance polymer/MWCNTs nanocomposites in the future. Compared with most plasma processes, which operate at low pressures, corona discharge has the merit of working at atmospheric pressure.

Effects of corona discharge on the surface structure, morphology and properties of multi-walled carbon nanotubes

Co-reporter:Lihua Xu, Zhengping Fang, Ping’an Song, Mao Peng

Applied Surface Science 2010 Volume 256(Issue 21) pp:6447-6453

Publication Date(Web):15 August 2010

DOI:10.1016/j.apsusc.2010.04.033

Abstract

Multi-walled carbon nanotubes (MWCNTs) were modified by corona discharge and then heat treated in the air. The influences of corona discharge parameters such as treatment time and processing power were investigated. The results of energy dispersive X-ray analysis (EDX) and thermogravimetric analysis (TGA) indicated the introduction of oxygen-containing functional groups onto the surface of the MWCNTs after heat treatment. The water contact angle tests showed that the hydrophobicity of the MWCNTs was decreased to some extent. The static water contact angle was reduced from 146° to 122° when the time of the corona discharge treatment reached 3 min at the processing power of 200 W. The enhanced thermomechanical and mechanical properties of epoxy nanocomposites filled with the corona discharge treated MWCNTs were observed. The modified MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between the treated MWCNTs and epoxy.

Ionization-induced ultrarapid response behavior of fibrous and porous electrospun hydrogels containing carboxyl groups

Co-reporter:Huijun Wang;Jun Zheng

Journal of Applied Polymer Science 2010 Volume 115( Issue 4) pp:2485-2492

Publication Date(Web):

DOI:10.1002/app.31041

Abstract

Fibrous porous membranes composed of poly(N-isopropylacrylamide-co-acrylic acid) and poly(N-isopropylacrylamide-co-hydroxyethyl methacrylate) were prepared by electrospinning. The membranes behaved like hydrogels in water after being crosslinked at elevated temperatures. Investigations of the swelling and deswelling behavior indicated that the response rates significantly increased after the carboxyl and/or anhydride groups in the hydrogel membranes were ionized or neutralized with NaOH. It took them less than 60 s to reach equilibrium swelling and about 90 s to reach equilibrium deswelling. The response rates were much higher than those of the parent un-ionized membranes; this indicated that ionization played an important role in the ultrarapid response behavior. The response rate was also higher than that of most hydrogel materials previously reported and was even comparable to superporous hydrogels with high moisture contents. The mechanism of the ultrarapid response behavior of the ionized membranes was qualitatively analyzed. We believe that the fine fiber diameter, high porosity, and improved wettability with water contributed to the ultrarapid response behavior. This study presents a new and facile method for improving the response rate of hydrogel materials made by electrospinning. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of surface modification of montmorillonite on the properties of rigid polyurethane foam composites

Co-reporter:Zhong-bin Xu;Wei-wei Kong;Ming-xing Zhou

Chinese Journal of Polymer Science 2010 Volume 28( Issue 4) pp:615-624

Publication Date(Web):2010 July

DOI:10.1007/s10118-010-9111-0

This study investigated the influence of various organically modified montmorillonites (organoclays) on the structure and properties of rigid polyurethane foam (RPUF) nanocomposites. The organoclays were modified with cetyltrimethyl ammonium bromide (CTAB), methyl tallow bis(2-hydroxyethyl) quaternary ammonium chloride (MT2ETOH) and tris(hydroxymethyl)aminomethane (THMA) and denoted as CMMT, Cloisite 30B and OMMT, respectively. MT2ETOH and THMA contain hydroxyl groups, while THMA does not have long aliphatic tail in its molecule. X-ray diffraction and transmission electron microscopy show that OMMT and Cloisite 30B can be partially exfoliated in the RPUF nanocomposites because their intercalating agents MT2ETOH and THMA can react with isocyanate. However, CMMT modified with nonreactive CTAB is mainly intercalated in the RPUF matrices. At a relatively low filler content, the RPUF/CMMT composite foam has a higher specific compressive strength (the ratio of compressive strength against the apparent density of the foams), while at relatively high filler contents, RPUF/Cloisite 30B and RPUF/OMMT composites have higher specific compressive strengths, higher modulus and more uniform pore size than the RPUF/CMMT composite.

A Simple Polymerizable Polysoap Greatly Enhances the Grafting Efficiency of the “Grafting-to” Functionalization of Multiwalled Carbon Nanotubes

Co-reporter:Mao Peng, Zhangjie Liao, Zhongming Zhu, and Honglei Guo

Macromolecules 2010 Volume 43(Issue 23) pp:9635-9644

Publication Date(Web):November 18, 2010

DOI:10.1021/ma101953h

A simple polymerizable polysoap was synthesized for the functionalization of multiwalled carbon nanotubes (MWNTs) by “grafting to” method, which greatly enhances the grafting efficiency (i.e., the ratio between the quantity of grafted polymer and the total polymerized monomer). Self-assembly of MWNTs with the polysoaps in a 1,4-dioxane/water mixture results in the formation of micellized MWNTs; then, by a single step of polymerization of the polysoaps or copolymerization of the polysoaps with methyl methacrylate (MMA), the polymer layer of the micellized MWNTs is permanently cross-linked and covalently bonded to the nanotube surface. For the poly(polysoap-co-MMA) modified MWNTs, the grafting efficiency can be as high as 65.7%. The functionalized MWNTs are robust, readily redispersible in water and some organic solvents, and increase the dynamic mechanical properties of epoxy resin more effectively than oxidized or noncovalently modified MWNTs.

Nonaligned Carbon Nanotubes Partially Embedded in Polymer Matrixes: A Novel Route to Superhydrophobic Conductive Surfaces

Co-reporter:Mao Peng, Zhangjie Liao, Ji Qi and Zhi Zhou

Langmuir 2010 Volume 26(Issue 16) pp:13572-13578

Publication Date(Web):July 14, 2010

DOI:10.1021/la101827c

A new method for transforming common polymers into superhydrophobic conductive surfaces, with both a high static water contact angle (∼160°) and a low sliding angle (2.0°−4.5°), and a low sheet resistance on the order of 101−103 Ω/sq is presented. A layer of multiwalled carbon nanotubes (MWNTs) is first distributed on the surface of a polymer substrate, then by a single step of pressing, the MWNTs are partially embedded inside the substrate surface and form a superhydrophobic coating with a “carpet-” or “hair”-like morphology. The infiltration of polymer melts into the porous MWNT layer follows Darcy’s law, and the pressing time greatly influence the morphology and superhydrophobicity. Moreover, the coating can be electrically heated by 20−70 °C with a voltage as low as 4−8 V at an electric energy density below 1.6 J/cm2 and therefore can be used for deicing applications. Hydroxylation and fluoroalkylsilane treatment can greatly improve the stability of the superhydrophobicity of MWNTs. This method is convenient and applicable to a variety of thermoplastic polymers and nonpolymer substrates coated by silicone rubber.

Carbon Nanotubes Noncovalently Functionalized by an Organic−Inorganic Hybrid: New Building Blocks for Constructing Superhydrophobic Conductive Coatings

Co-reporter:Mao Peng, Ji Qi, Zhi Zhou, Zhangjie Liao, Zhongming Zhu and Honglei Guo

Langmuir 2010 Volume 26(Issue 16) pp:13062-13064

Publication Date(Web):July 14, 2010

DOI:10.1021/la102350t

A facile method for constructing superhydrophobic, conductive, and transparent/translucent coatings is presented. Pristine multiwalled carbon nanotubes (MWNTs) are first noncovalently (wrapped) modified by an organic−inorganic hybrid of an amphiphilic copolymer of styrene and maleic anhydride and silica with the existence of γ-aminopropyltriethoxysilane (a silane coupling agent). The modified MWNTs were mixed with tetraethyl orthosilicate in ethanol, air sprayed, coated with a fluoroalkylsilane, and then heat treated to obtain the superhydrophobic, conductive, and transparent/translucent coatings. Scanning electron microscopy shows that the coatings have a micrometer- and nanometer-scale hierarchical structure similar to that of lotus leaves; therefore, they show both high water contact angles (>160°) and low sliding angles (<2°). The coatings also exhibit good transmittance and greatly improved conductivities. This method is convenient, inexpensive, and easy to scale up. Moreover, it does not require any chemical modification of the MWNTs or use any harsh chemicals.

Fumed silica/polymer hybrid nanoparticles prepared by redox-initiated graft polymerization in emulsions

Co-reporter:Mao Peng;Zhangjie Liao;Zhongming Zhu;Honglei Guo

Journal of Materials Science 2009 Volume 44( Issue 23) pp:6286-6293

Publication Date(Web):2009 December

DOI:10.1007/s10853-009-3865-1

Hybrid particles comprising aggregated fumed silica nanoparticles as the core and hydrophobic polymers existing around the nanoparticles were prepared by ‘grafting from’ polymerization in emulsions. The emulsion polymerization employed cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant, respectively, to stabilize the emulsion polymerization. The polymerization was initiated by the redox reaction between ceric ion Ce(IV) and the amine groups on the surfaces of aminated fumed silica nanoparticles that were modified by 3-aminopropyltriethoxysilane. Infrared spectroscopy and thermogravimetric analysis demonstrated that both poly(methyl methacrylate) (PMMA) and polystyrene (PS) were successfully grafted onto the fumed silica surface. The type of surfactant greatly affected the grafting ratio, monomer-to-polymer conversion, and morphology of the product. When CTAB was used as the surfactant, both the grafting ratio and monomer-to-polymer conversion were lower than when SDS was used, but transmission electron microscopy and light scattering analysis indicated that most of the resultant particles were sub-100 nm hybrid nanoparticles with a non-spherical shape and particles sizes of 75–90 and 57–85 nm for PMMA and PS-grafted fumed silica, respectively. Whereas, when SDS was used as the surfactant, the particles agglomerated to form large irregular clusters or even networks, possibly due to the electrostatic attractions between SDS and Ce(IV) and/or the aminated fumed silica nanoparticles in aqueous solution.

Encapsulation of silica nanoparticles by redox-initiated graft polymerization from the surface of silica nanoparticles

Co-reporter:Huijun Wang, Mao Peng, Jun Zheng, Peng Li

Journal of Colloid and Interface Science 2008 Volume 326(Issue 1) pp:151-157

Publication Date(Web):1 October 2008

DOI:10.1016/j.jcis.2008.07.031

This study describes a facile and versatile method for preparing polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce4+) as an oxidant and an organic reductant immobilized on the surface of silica nanoparticles. The silica nanoparticles were firstly modified by 3-aminopropyltriethoxysilane, then reacted with poly(ethylene glycol) acrylate through the Michael addition reaction, so that hydroxyl-terminated poly(ethylene glycol) (PEG) were covalently attached onto the nanoparticle surface and worked as the reductant. Poly(methyl methacrylate) (PMMA), a common hydrophobic polymer, and poly(N-isopropylacrylamide) (PNIPAAm), a thermosensitive polymer, were successfully grafted onto the surface of silica nanoparticles by ‘grafting from’ polymerization initiated by the redox reaction of Ce4+ with PEG on the silica surface in acid aqueous solutions. The polymer-encapsulated silica nanoparticles (referred to as silica@PMMA and silica@PNIPAAm, respectively) were characterized by infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. On the contrary, graft polymerization did not occur on bare silica nanoparticles. In addition, during polymerization, sediments were observed for PMMA and for PNIPAAm at a polymerization temperature above its low critical solution temperature (LCST). But the silica@PNIPAAm particles obtained at a polymerization temperature below the LCST can suspend stably in water throughout the polymerization process.Polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce4+) as a oxidant and an organic reductant immobilized on the surface of silica nanoparticles.

Mesoporous silica fibers prepared by electroblowing of a poly(methyl methacrylate)/tetraethoxysilane mixture in N,N-dimethylformamide

Co-reporter:Mao Peng, Qiujian Sun, Qianli Ma, Peng Li

Microporous and Mesoporous Materials 2008 Volume 115(Issue 3) pp:562-567

Publication Date(Web):1 November 2008

DOI:10.1016/j.micromeso.2008.02.035

Electroblowing and sol–gel reaction were combined to prepare mesoporous silica fibers. Poly(methyl methacrylate) (PMMA), a simple commercial polymer with weak hydrogen bonding to silica, was demonstrated to be valuable in improving the electrospinnability and as a porogenic agent. Compared with that in electrospinning, the jet stream in electroblowing was more stable and the resultant fibers were more uniform. The electroblown fibers were characterized by infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption and desorption isotherms. The phase separation behavior and mechanism for the formation of the amorphous mesoporous structure were discussed. Although there was no covalent bonding between PMMA and silica, macrophase separation was completely prevented in the electroblown fibers and the pore size in the calcined silica fibers ranged from 10 to 20 nm. However, the previously reported electrospun silica fibers, in which surfactants or polymers with strong hydrogen or covalent bonding to silanol groups were used as structure directing agents, had average pore sizes below 10 nm. The present study offers a facile method for the preparation of highly mesoporous silica fibers with large mesopores.

Encapsulation of microgels with polystyrene (PS): A novel method for the preparation of hollow PS particles

Co-reporter:Mao Peng, Huijun Wang, Ying Chen

Materials Letters 2008 Volume 62(10–11) pp:1535-1538

Publication Date(Web):15 April 2008

DOI:10.1016/j.matlet.2007.09.017

Novel core-shell particles with polystyrene (PS) as the shells and thermosensitive poly(N-isopropylacrylamide) (PNIPAM) microgels (i.e. submicrometer-sized hydrogel particles) as the cores were prepared by a seeded emulsion polymerization of styrene using a PNIPAM microgel suspension as the seed latex. It was found that upon the dehydration of microgels inside the core-shell particles, hollow PS particles were obtained. The morphology and size of the hollow particles were observed by transmission electron microscopy and light scattering. It was also found that the shell thickness of the hollow particles increases apparently with the increase of the amount of PS. The merit of this method is that the microgel templates need not to be removed by calcination or etching to obtain hollow particles.

Effect of an organoclay on the reaction-induced phase-separation kinetics and morphology of a poly(ether imide)/epoxy mixture

Co-reporter:Mao Peng;Ying Chen;Qiang Zheng;Dasong Li;Dasong Li;Ying Chen;Qiang Zheng

Journal of Applied Polymer Science 2007 Volume 104(Issue 2) pp:1205-1214

Publication Date(Web):26 JAN 2007

DOI:10.1002/app.25759

Organically modified layered silicates with a hydroxyl-substituted quaternary ammonium surfactant as the modifier were incorporated into a mixture of poly (ether imide) and epoxy with 4,4′-diaminodiphenyl sulfone as the hardener. The influence of the organically modified layered silicates on the reaction-induced phase-separation kinetics and morphology of the poly(ether imide)/epoxy mixture was investigated with time-resolved small-angle light scattering, phase-contrast microscopy, and scanning electron microscopy. The phase-separation kinetics were analyzed by means of the temporal evolution of scattering vector q_m and scattering intensity I_m at the scattering peak. The organically modified layered silicates obviously facilitated an earlier onset of phase separation but reduce the phase-separation rate and greatly retarded the domain-coarsening process in the late stage of spinodal decomposition. The temporal evolution of both q_m and I_m followed the power law q_m ∼ (t − t_os)^−α and I_m ∼(t − t_os)^−β, where t is the reaction time, t_os is the onset time of phase separation, and α and β are growth exponents. For the samples filled with organically modified layered silicates, α crossed over from 0 to about 1/3, following Binder–Stauffer cluster dynamics, and an interconnected phase structure was observed for cure temperatures ranging from 120 to 230°C. For the unfilled samples, the interconnected phase structure was observed only at cure temperatures below 140°C. At temperatures above 150°C, α crossed over from 0 to 1/3 < α ≤ 1 under the interfacial tension effect, following Siggia's theory, and the domain-coarsening rate was very fast; this resulted in macroscopic epoxy-rich domains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1205–1214, 2007

Electrostatic-Assembly of Carbon Nanotubes (CNTs) and Polymer Particles in Water: a Facile Approach to Improve the Dispersion of CNTs in Thermoplastics

Co-reporter:Mao Peng;Dasong Li;Ying Chen;Qiang Zheng

Macromolecular Rapid Communications 2006 Volume 27(Issue 11) pp:859-864

Publication Date(Web):18 MAY 2006

DOI:10.1002/marc.200500884

Summary: A facile and organic-solvent-free method for preparing thermoprocessable multiwalled carbon nanotube (MWCNT)-filled thermoplastics is presented. MWCNTs are oxidized, neutralized, and then assembled with cationic soap-free poly(methyl methacrylate) (PMMA) particles directly in water. The spontaneous electrostatic coupling between the negatively charged MWCNTs and positively charged PMMA particles, and the viscoelastic and thermomechanical behavior of the nanocomposites, are investigated. The electrostatic coupling interactions improve the dispersion of nanotubes and facilitate the formation of filler networks in the polymer matrix.

Porous poly(vinylidene fluoride) membrane with highly hydrophobic surface

Co-reporter:Mao Peng;Hongbing Li;Lijuan Wu;Qiang Zheng;Ying Chen;Wenfang Gu

Journal of Applied Polymer Science 2005 Volume 98(Issue 3) pp:1358-1363

Publication Date(Web):12 AUG 2005

DOI:10.1002/app.22303

The preparation of very hydrophobic poly(vinylidene fluoride) (PVDF) membranes was explored by using two methods. The first one was the modified phase inversion method using a water/N,N-dimethylacetamide (DMAc) mixture instead of pure water as a soft precipitation bath. The second method was a precipitation-bath free method, that is, the PVDF/DMAc casting solution underwent gelation in the open air instead of being immersed into a precipitation bath. The morphology of the surface and cross section of the membranes was investigated by using scanning electron microscopy (SEM). It was found that the membranes exhibited certain micro- and nanoscale hierarchical roughness on the surface, which brought about an enhanced hydrophobicity of the membrane. The contact angle (CA) of the samples obtained by the second method was as high as 150° with water. The conventional phase inversion method preparing PVDF porous membrane using pure water as precipitation bath usually results in an asymmetric membrane with a dense skin layer having a CA close to that of a smooth PVDF surface. The modified approach avoided the formation of a skin-layer and resulted in a porous and highly hydrophobic surface of PVDF. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1358–1363, 2005

Phase Separation of Hydrophilic Monomer/Surfactant Aqueous Solution Studied by a Combined Light Scattering and Interference Approach

Co-reporter:Mao Peng;Xiaoxue Yuan

Macromolecular Chemistry and Physics 2004 Volume 205(Issue 2) pp:256-265

Publication Date(Web):21 JAN 2004

DOI:10.1002/macp.200300090

Summary: Polymerization-induced phase separation behavior of 2-acryllamido-2-methyl-1-propanesulfonic acid (AMPS)/sodium dodecylsulfonate (SDS) aqueous solution was investigated by using a combined small angle light scattering (SALS) and laser light interference (LI) system. Compared with the conventional SALS technique that has been widely used in studying the phase separation kinetics and mechanism of multicomponent polymer blends or solution, the present combined SALS and LI system can additionally provide valuable information on polymerization kinetics prior to the onset of phase separation. It was found that the 1 mol · L⁻¹ AMPS aqueous solution in the presence of 0.2 mol · L⁻¹ SDS underwent apparent phase separation when polymerization conversion approached 82%. The phase separation rate is so rapid that it takes only 90 s for scattering intensity to reach the maximum. The early stage phase separation follows the spinodal decomposition (SD) mechanism that can be described by the classic linear theory sponsored by Cahn and Hilliard. At late stage of phase separation, however, an observable shift of characteristic vector q_m to larger values take place, which may result from the secondary phase separation in the monomer-rich phase that leads to a deceased average domain size in sample solution. On the other hand, the integral scattering intensity decreased apparently at late stage of phase separation due to the decreased refractive index difference between the monomer-rich and polymer-rich phases as a result of the continued polymerization in the monomer-rich phase.