Poly(propylene) (PP) nanocomposites filled with shorter‐ and longer‐aspect‐ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin‐screw extruder and an injection moulding machine. It is shown that with only 1 vol.‐% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long‐term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1 000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications.
This letter focuses on the first result of the preparation and the swelling behavior of a novel hybrid gelatin hydrogel with carbon nanotubes. A novel hybrid gelatin hydrogel with carbon nanotubes was synthesized by a physical mixing method. The structure of the novel hydrogel obtained was characterized by SEM. Besides, the swelling behavior of the synthesized hydrogel was measured at two different temperatures. The results indicate that carbon nanotubes added could maintain the stability of the hybrid hydrogel without cross‐linking at 37 °C. This suggests that the hybrid gelatin hydrogel with carbon nanotubes could be used in biomedical field. Besides, its application in protein separation is discussed.
SEM image of the gelatin‐MWNTs hybrid gel at 10 000 × magnification. 相似文献
Two emerging material classes are combined in this work, namely polymeric carbon nitrides and microporous polymer networks. The former, polymeric carbon nitrides, are composed of amine‐bridged heptazine moieties and showed interesting performance as a metal‐free photocatalyst. These materials have, however, to be prepared at high temperatures, making control of their chemical structure difficult. The latter, microporous polymer networks have received increasing interest due to their high surface area, giving rise to interesting applications in gas storage or catalysis. Here, the central building block of carbon nitrides, a functionalized heptazine as monomer, and tecton are used to create microporous polymer networks. The resulting heptazine‐based microporous polymers show high porosity, while their chemical structure resembles the ones of carbon nitrides. The polymers show activity for the photocatalytic production of hydrogen from water, even under visible light illumination.
Summary: The recrystallization behavior of high density polyethylene (HDPE) single crystals with vacuum evaporated metal chromium or carbon on their surface has been investigated by transmission electron microscopy (TEM) and electron diffraction (ED) techniques. The results indicate that the particle‐coated HDPE single crystals can retain their single crystal structure after complete melting and subsequent recrystallization, with the heat‐treated temperature as high as 200 °C. This phenomenon is attributed to a surface fixing effect of vacuum evaporated Cr or carbon on the single crystals.
A bright‐field electron micrograph and the corresponding electron diffraction pattern of recrystallized Cr‐coated HDPE single crystals. 相似文献
The synthesis of water soluble star‐block copolypeptides and their encapsulation properties are described. The star‐block copolypeptides, obtained by ring‐opening polymerization of amino acid N‐carboxyanhydrides, consist of a PEI core, a hydrophobic polyphenylalanine or polyleucine inner shell, and a negatively charged polyglutamate outer shell. The encapsulation study showed that these water soluble, amphiphilic star‐block copolypeptides could simultaneously encapsulate versatile compounds ranging from hydrophobic to anionic and cationic hydrophilic guest molecules.
Multi‐walled carbon nanotubes (MWNT) purified by acidic solution were processed with PMMA via an in‐situ polymerization. Experimental evidences indicate the role of radical initiator (AIBN) and MWNT, showing increases of polymerization rate and MWNT diameter. Induced radicals on the MWNT by AIBN were found to trigger the grafting of PMMA. Moreover, the solvent cast film showed a better nanoscopic dispersion of MWNT and possibilities of CNT composites in engineering applications.
Fractured surface of multi‐walled carbon nanotube composite with PMMA prepared by in‐situ bulk polymerization. 相似文献
A series of π‐conjugated polymers linked by benzocarborane (1,2‐(buta‐1′,3′‐diene‐1′,4′‐diyl)‐1,2‐dicarbadodecaborane) were synthesized via Sonogashira–Hagihara polycondensation reaction. The opened molecular structure of diiodo monomer containing benzocarborane resulted in fast polymerization and high molecular weights. The obtained polymers were fully characterized by 1H, 13C, and 11B NMR spectroscopies. UV‐vis absorption and photoluminescence studies revealed the acceptor‐profile of benzocarborane. Unlike the polymers linked by o‐carborane, these polymers exhibited strong luminescence in the solution state, presumably because the inductive effect of carborane is dominant, rather than cage‐π interactions.
The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.
Summary: Electro‐active shape‐memory composites were synthesized using conducting polyurethane (PU) composites and multi‐walled carbon nanotubes (MWNTs). Surface modification of the MWNTs (by acid treatment) improved the mechanical properties of the composites. The modulus and stress at 100% elongation increased with increasing surface‐modified MWNT content, while elongation at break decreased. MWNT surface modification also resulted in a decrease in the electrical conductivity of the composites, however, as the surface modified MWNT content increased the conductivity increased (an order of 10−3 S · cm−1 was obtained in samples with 5 wt.‐% modified‐MWNT content). Electro‐active shape recovery was observed for the surface‐modified MWNT composites with an energy conversion efficiency of 10.4%. Hence, PU‐MWNT composites may prove promising candidates for use as smart actuators.
The electro‐active shape‐recovery behavior of PU‐MWNT composites. The pictured transition occurs within 10 s when a constant voltage of 40 V is applied. 相似文献
Summary: Multiwalled carbon nanotube (MWNT) nanocomposites dispersed in a poly(methyl methacrylate) (PMMA) matrix were prepared via suspension polymerization, in which radicals induced on the outer wall of the MWNTs by 2,2′‐azoisobutyronitrile initiate the grafting of PMMA. The synthesized MWNT/PMMA nanocomposite particles were found to have a spherical shape and exhibit a high electrical conductivity, mainly as a result of the carbon nanotubes. A suspension was prepared with MWNT/PMMA particles in insulating silicone oil and its electrorheological properties were investigated by controlling applied direct current (DC) electric field strengths.
Flow curve possessing a region analogous to the coexistence curve. 相似文献
Nanoscale fibers with embedded, aligned, and percolated non‐functionalized multiwalled carbon nanotubes (MWCNTs) were fabricated through electrospinning dispersions based on melt‐compounded thermoplastic polyurethane/MWCNT nanocomposite, with up to 10 wt.‐% MWCNTs. Transmission electron microscopy indicated that the nanotubes were highly oriented and percolated throughout the fibers, even at high MWCNT concentrations. The coupling of efficient melt compounding with electrospinning eliminated the need for intensive surface functionalization or sonication of the MWCNTs, and the high aspect ratio as well as the electrical and mechanical properties of the nanotubes were retained. This method provides a more efficient technique to generate one‐dimensional nanofibers with aligned MWCNTs.
Multiwalled carbon nanotubes (MWNTs) have been introduced into blends of polycarbonate (PC) and poly(styrene‐acrylonitrile) (SAN) by melt mixing in a microcompounder. Co‐continuous blends are prepared by either pre‐compounding low amounts of nanotubes into PC or SAN or by mixing all three components together. Interestingly, in all blends, regardless of the way of introducing the nanotubes, the MWNTs were exclusively located within the PC phase, which resulted in much lower electrical resistivities as compared to PC or SAN composites with the same MWNT content. The migration of MWNTs from the SAN phase into the PC phase during common mixing is explained by interfacial effects.
Multiwalled carbon nanotubes in the form of bucky papers were modified using Ar/O2 plasma and thereafter melt‐mixed into polycarbonate. The effect of plasma modification on the nanotubes was followed by XPS, indicating the formation of carboxylic or ester groups at the nanotube surfaces. In the melt‐mixed nanocomposites, the modified nanotubes exhibited a better macrodispersion and better phase adhesion to the matrix as evidenced by morphological investigations. The electrical percolation threshold was not altered and occurred below 0.5 wt.‐% nanotubes. The mechanical properties were improved by having higher values of stress at yield, stress beyond the yield point, and strain at break illustrating the effect of both better dispersion and enhanced phase adhesion.
A novel pH‐responsive polymer vesicle obtained by the aqueous self‐assembly of carboxy‐terminated hyperbranched polyesters is reported. The synthesis is very simple, just a one‐step esterification of the commercially available hydroxy‐terminated hyperbranched polyester of Boltorn Hx (x = 20, 30, 40) with succinic anhydride. The vesicle size can be controlled from 200 nm to 10 µm by simply adjusting the solution pH as well as the degrees of branching (or generation).
New multifunctional copoly(2‐oxazoline) nanoparticles were prepared for cell studies. The polymer contains double‐bond side chains as potential reaction sites for “thio”‐click reactions as well as a fluorescein label covalently bound to the polymer backbone. Using the nanoprecipitation technique, spherical nanoparticles of 200–800 nm were obtained. Confocal laser scanning microscopy measurements revealed the cellular uptake of the nanoparticles.
Novel poly(ethylene glycol) (PEG) derivatives having both carboxylic acid, and sugar side chains were synthesized. These polymers were used to coat DNA/poly(ethyleneimine) complexes, and effectively protected them against albumin-induced aggregation. They presented carbohydrate moieties on the DNA complex surfaces as a cell-binding ligand, and the galactose-bearing polymer remarkably enhanced the poly(ethyleneimine)-mediated gene transfection on HepG2 cells.
Synthesis of poly(ethylene glycol) derivatives having both carboxylic acid and sugar pendant groups. 相似文献
The ability to control the dispersion of carbon nanotubes in polymers is key to most applications of nanotube‐polymer composites. This feature article describes recent advances in methods used to disperse carbon nanotubes and considers how these methods affect dispersion on different length scales. It is becoming increasing clear that perfect dispersion is not desired for many applications, in particular for electrical conductivity, and controlling the dispersion is key for proper function of the composite in its intended application.
A simple and direct method for derivatization of solid polysaccharides is presented. The novel methodology is based on the combination of organic acid‐catalyzed esterification or etherification and photochemical thiol‐ene click derivatization of a heterogeneous polysaccharide. The solid cellulose was “organoclick” modified with aryl, alkyl and polyester groups, respectively. The modification allows for a highly modular and metal free surface modification of solid polysaccharides.
