A new, nickel‐coated graphite resistance‐change‐based method for gel‐point determination for epoxy‐based thermoset resins is presented and compared with DSC and rheological methods. Gelation times determined by this new method are in very good agreement with conventional techniques; this new method is potentially simpler and less time consuming than existing ones.
Ultra‐thin fibers, consisting of blends of a PPE derivative and polystyrene, with average diameters ranging from 430 to 1 200 nm, were produced by electrospinning. The electrospinnability was significantly improved by adding pyridinium formate to the spinning solution. FT‐IR spectroscopy was used to confirm the composition of the electrospun fibers and their morphology was probed by SEM. The optical properties of the as‐prepared solutions, pristine and annealed fibers, and corresponding spin‐coated and solution‐cast films were investigated by UV‐vis spectroscopy. A comparison of the PL emission spectra revealed aggregation of PPE molecules in the electrospun materials but the extent of aggregation can be reduced if the materials are annealed above the glass transition temperature.
Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using 1H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.
This paper reports on a web of superamphiphobic fluoro‐compound fibers that forms as a result of a typical electrospinning method without any additional treatment. An electrospun web of poly(2,2,2‐trifluoroethyl methacrylate) fibers exhibits superamphiphobicity when the water and hexadecane contact angles both exceed 150°. The morphology of a web is modulated by changing the polymer solution concentration from 24 to 30 wt.‐% with other fixed processing conditions. The fiber diameter length depends mainly on the polymer concentration. A web formed from a 26 wt.‐% solution has the smallest and most uniform fiber diameter; it also has the highest robustness parameter on wetting, thus the highest water and hexadecane contact angles. This result offers the possibility of simple industrial production of an amphiphobic surface.
1,3,5‐Benzenetrisamide‐based supramolecular nucleating agents for poly(butylene terephthalate) (PBT) are reported. 1,3,5‐Benzenetrisamides combine excellent thermal stability with chemical resistance, basic requirements for the use in high‐melting thermoplastics. To establish structure–property relationships, the central core and peripheral substituents are varied systematically. Dissolution and crystallization behavior of the additives in the PBT melt and the crystallization temperature of PBT are investigated as a function of the additive concentration. Efficient nucleating agents can increase the crystallization temperature of PBT by 10.6 °C to 199.1 °C. A visualization of supramolecular nano‐objects formed in the polymer melt is provided.
This paper demonstrates how the electric‐field‐assisted thermal annealing of octadecylamine‐functionalized SWNT/PMMA films induces an increase in the composite transversal conductivity of several orders of magnitude and a decrease in the lateral conductivity. This difference has been rationalized in terms of the nanotube alignment into the polymer matrix along the electric field direction. This result provides an initial understanding of how electric fields can be used to control the bulk physical properties of such nanocomposites.
Oriented precursors of MFCs consisting of HDPE and PA6 or PA12 are studied during strain‐controlled slow load‐cycling. In the PA6‐containing blends a strongly retarded nanostrain response is detected. Compatibilization induces nanostrain heterogenization. Stress fatigue is lower in the PA12 blends, but hardly decreased by the compatibilizer. Selective migration of the compatibilizer into a disordered semi‐crystalline fraction of the HDPE matrix can explain the findings. The semi‐crystalline HDPE entities in PA6 blends appear more disordered than in PA12‐blends. An analysis of the HDPE nanostructure evolution during cycling reveals epitaxial strain crystallization. Uncompatibilized PA6 blends cycled about high pre‐strain show plastic flow but nanoscopic shrinkage in the semi‐crystalline stacks.
A facile and easily industrialized approach for preparing highly dispersed MMT/polymer nanocomposites is developed by combining the latex compounding method and a spray‐drying process. Clay particles are successfully delaminated into layers, and layer re‐stacking is effectively prevented. HR‐TEM and XRD results confirm that MMT layers achieve exfoliated or nearly exfoliated dispersion in both MMT/styrene‐butadiene rubber and MMT/PS nanocomposites. Compared with melt‐blended MMT/SBR composites, MMT/SBR nanocomposites prepared by this new strategy exhibit extremely high dynamic modulus.
Thermo‐responsive PNIPAAm/PLLA nanofibrous films with tunable surface morphologies and better biocompatibility were prepared by electrospinning technique. The electrospun composite films possessed a “bead‐on‐string” structure. The wettability of nanofibrous films was observed by water CA measurements. The results showed that the electrospinning process and addition of PLLA did not change the thermo‐sensitivity of PNIPAAm. The wettability of electrospun PNIPAAm/PLLA composite films could switch from superhydrophilic to superhydrophobic when the temperature increased from 20 to 50 °C. Electrospinning is a promising way to create stimuli‐responsive surfaces with potential application in the design and tactics of controllable drug delivery system.
An in situ process for the production of polyamide‐6 nanocompounds is investigated as an alternative to melt compounding. During the in situ production, the layered silicates are dispersed in the monomer caprolactam before the polymerisation in a twin screw extruder, leading to an intercalation of the silicates. The production of a polyamide compound containing 0, 2 and 4 wt.‐% nanoscale silicates was successful. An improvement of the elastic modulus of approximately 30–60% was reached. The figure shows the TEM micrograph of a nanocompound containing 2 wt.‐% nanoclay at a magnification of 30 000×.
The controlled deposition of electrospun nanofibers at the micro‐scale is studied. Several collectors with microscopic patterns are prepared using photolithography. Nanofiber deposition is influenced by the geometry, the size, and the distance between micro‐patterns. Within certain conditions, membranes with multiple “micro spider‐webs” or perpendicularly interconnected microgrids are obtained. Dielectric micro‐holes having a conductive bottom can be filled by the nanofiber. This kind of micro‐molding is rationalized using simulations that show the influence of the collector relative permittivity on the electric field at the pattern vicinity. “Micro‐woven” membranes of PCL with good mechanical properties can be produced, allowing their use for biomedical applications in tissue engineering.
Summary: Contact‐mode AFM adhesion strength measurements were employed in order to investigate the capability of PBBMA FR as an adhesion promoter in PP composites. The reactive FR exhibited superior coupling properties in comparison to conventional coupling agents such as PP‐g‐ma introduced in reinforced PP composites.
AFM image showing the recess carved out by the AFM tip in a PBBMA layer deposited on glass treated with APS. 相似文献
A method that combines UV irradiation and pausing was developed to manipulate the regularity and the length scales of the morphology generated by phase separation in full‐interpenetrating polymer networks of polystyrene and poly(methyl methacrylate). Upon increasing the pause time of photopolymerization and photo‐crosslink processes, the morphology gradually changes from hexagonal‐like packing to random structures. The width of the loss tan δ obtained for these phase‐separated materials changes with the morphological regularity, suggesting a potential technique for fabrication of mechanical bandgap materials.
The influence of Ca‐stearate‐coated CaCO3 and talc on the quiescent and flow‐induced crystallization of iPP is studied using different methods. Comparison of rheometry and DSC shows that rheometry is an interesting tool to monitor crystallization kinetics. It is observed that the Ca‐stearate coating degrades at commonly used annealing temperatures, influencing the crystallization behavior of the CaCO3‐containing polymer. WAXD indicates that the CaCO3 does not significantly influence the degree of crystallinity. As shear intensifies, both the pure and particle‐containing polymers crystallize faster; however, their behavior also becomes increasingly similar. There are indications that shear influences the organization of the CaCO3 aggregates.
Developing co‐continuity in a polymer blend determines a multiphase system with enhanced properties which originate from the synergism of its constituents. Filling a blend with nanoparticles is a promising route to guide its morphology and eventually affect the co‐continuity transition. We add different kinds of nanoparticles to an HDPE/PEO blend to study how they affect the morphology of the blend as function of their surface properties and form factor. We find that PEO drop size is drastically reduced by particles adsorbed at the HDPE/PEO interface. However, we show that a drastic shifting of the co‐continuity threshold may only be achieved when particles affect the rheology of the interface.
The effect of nanoplatelets on the rheological behavior of epoxy monomers with variations in nanoplatelet exfoliation level and aspect ratio was investigated. The results show that the presence of exfoliated nanoplatelets in epoxy can significantly influence viscosity and lead to shear‐thinning phenomena, especially when the aspect ratio of the nanoplatelets is high. By employing the Krieger‐Dougherty model, the effectiveness of nanoplatelets in altering epoxy rheological behavior was quantitatively described and compared with experimental findings. Possible physical reasons for the observed rheological behaviors are discussed. The implication of the present study for polymer nanocomposites processing is also addressed.
Film‐insert‐molded (FIM) tensile specimens were prepared under various molding conditions to investigate the effects of wall temperature and packing pressure on the residual stress distribution and thermoviscoelastic deformation. The warpage of the specimen increased with increasing mold‐wall temperature difference and decreased with increasing packing pressure. The FIM specimens produced with unannealed films showed the warpage reversal phenomenon (WRP) during annealing and the degree of WRP was affected significantly by the molding conditions and thermal shrinkage of the film. The warpage of the specimen was predicted by three‐dimensional flow and stress analyses and the prediction was in good agreement with the experimental results.
The influence of the flow history experienced during injection molding on the mechanical properties of amorphous polymers is investigated. It is demonstrated that flow‐induced molecular orientation only causes a small anisotropic effect on the yield stress, which can be regarded as insignificant with respect to its absolute value. Its influence on the post‐yield strain‐hardening response is also shown to be imperceptible, in contrast to a orientation which is applied during deformation below the glas transition.
Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.
The fabrication of tissue engineering scaffolds based on the polymerization of crosslinked polylactide using leaching and batch foaming to generate well‐controlled and interconnected biodegradable polymer scaffolds is reported. The scaffold fabrication parameters are studied in relation to the interpore connectivity, pore morphology, and structural stability of the crosslinked PLA scaffold. In vitro cell culture and in vitro degradation are used to analyze the biocompatibility and biodegradability of the scaffolds. The new crosslinked PLA thermoset scaffolds are highly suitable for bone tissue engineering applications due to their complex internal architecture, thermal stability, and biocompatibility.
