There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Strategies for compatibilization of polymer blends

Carbon nanotubes (CNTs) are regarded as ideal filler materials for polymeric fiber reinforcement due to their exceptional mechanical properties and 1D cylindrical geometry (nanometer-size diameter and very high aspect ratio). The reported processing conditions and property improvements of CNT reinforced polymeric fiber are summarized in this review. Because of CNT polymer interaction, polymer chains in CNTs’ vicinity (interphase) have been observed to have more compact packing, higher orientation, and better mechanical properties than bulk polymer. Evidences of the existence of interphase polymers in composite fibers, characterizations of their structures, and fiber properties are summarized and discussed. Implications of interphase phenomena on a broader field of fiber and polymer processing to make much stronger materials are now in the early stages of exploration. Beside improvements in tensile properties, the presence of CNTs in polymeric fibers strongly affects other properties, such as thermal stabi...

Polymer/Carbon Nanotube Nano Composite Fibers–A Review

This paper reports the use of multiwalled carbon nanotubes (MWCNT) to reinforce and toughen gel-spun ultra high molecular weight polyethylene (UHMWPE) fibers. By adding 5 wt% MWCNT, ultra strong fibers with tensile strengths of 4.2 GPa and strain at break of ∼5% can be produced. In comparison with the pure UHMWPE fiber at the same draw ratios, these values represent increases of 18.8% in tensile strength and 15.4% in ductility. In addition, a 44.2% increase in energy to fracture has also been observed. The mechanism of reinforcement has been studied using a combination of high resolution scanning electron microscopy (SEM) and micro-Raman spectroscopy. Carbon nanotube alignment along the tensile draw direction has been observed at high elongation ratios. Such alignment induces strong interfacial load transfer both at small and large strains to enhance the stiffness and tensile strength of the composite fiber. Consequently, the mechanical properties of the composite fiber follow closely with the rule of mixtures. Our work also reveals potential for positive deviation from rule of mixtures if the CNT alignment can be further optimized.

Ultra-strong gel-spun UHMWPE fibers reinforced using multiwalled carbon nanotubes

Polymer blends are mixtures of at least two polymers and/or copolymers comprising more than 2 wt% of each macromolecular component. Most blends are immiscible, and need to be compatibilized. The compatibilization must not only ensure improvement in performance, but it must be reproducible, insensitive to forming stresses and repeated processing. This review on compatibilization of polymer blends is prepared in three parts : (i) description of the interface/interphase; (ii) compatibilization by addition of a copolymer (with a special emphasis on the use of block copolymers) ; and (iii) reactive compatibilization.

Interphase and compatibilization of polymer blends

We report, herein, on the structures, melting/crystallization, electrical, and dielectric properties of poly (vinylidene fluoride) (PVDF) nanocomposites reinforced with a neat multiwalled carbon nanotube (MWCNT). For our purposes, PVDF/MWCNT nanocomposite films with a wide range of MWCNT contents (0.0–20.0 wt%) are prepared via ultrasonicated solution-mixing and melt-compression methods. It is found that MWCNTs become well dispersed in nanocomposites by wrapping them with PVDF chains. The relative content of β-phase to α-phase crystals of a PVDF matrix is higher for the nanocomposite films with higher MWCNT content; although, the overall crystallinity of the nanocomposites is almost identical, irrespective of the MWCNT content. The electrical conductivity and dielectric permittivity of the nanocomposites as a function of frequency are strongly dependent on the MWCNT content. The electrical percolation threshold of PVDF/MWCNT nanocomposites is formed between 2.0 and 5.0 wt% MWCNT. The neat PVDF and nanocomposites with low MWCNT contents of 0.2 and 1.0 wt% are electrically insulating materials (∼10−9 S/cm at 102 Hz) with low dielectric permittivity of 9–28; while the nanocomposites with high MWCNT contents of 5.0–20.0 wt% have relatively high electrical conductivity values (10−4∼10−2 S/cm at 102 Hz). In contrast, the nanocomposite with 2.0 wt% MWCNT has a huge dielectric permittivity of ∼6520 at 102 Hz, although it has relatively low electrical conductivity of ∼10−8 S/cm at 102 Hz. The huge dielectric permittivity of the nanocomposite with 2.0 wt% MWCNT could be caused by charge accumulation at the interfacial layers between PVDF chains and MWCNTs in the vicinity of the electrical percolation threshold. 
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Structures, electrical, and dielectric properties of PVDF-based nanocomposite films reinforced with neat multi-walled carbon nanotube

Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion as the block copolymer is added. Thermal analysis with the aid of physical aging reveals that the block copolymer is located at the interface

Compatibilizing effect of a styrene-methyl methacrylate block copolymer on the phase behavior of poly(2,6-dimethyl-1,4-phenylene oxide) and poly(styrene-co-acrylonitrile) blends

A conducting polymer composite was prepared by the postpolymerization of pyrrole in a polyacrylonitrile (PAN) matrix film. To enhance the electrostatic interaction between the two phases, a small amount of a sulfonate or a carboxylate (COO−) group was incorporated into the PAN structure. The presence of electrostatic interaction between the conducting polypyrrole and the anion-containing PAN copolymer was elucidated by examination of the morphology and the electrical properties of the composite. The aromatic sulfonate-containing matrix provided the composite with the best results in the electrical conductivity, the environmental stability of conductivity, and the morphological property. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2641–2648, 1998

Ionic interactions in polyacrylonitrile/polypyrrole conducting polymer composite

The electronically conductive copolymer of PSPMS-g-PPy (poly(styrene-co-pyrrolylmethyl-styrene)-g-polypyrrole) was synthesized by the electrochemical method. In this copolymerization, a processable polymer film that has pyrrole moiety in its backbone was used as a copolymer precursor. The precursor was obtained by modifying PSCMS (poly(styrene-co-chloromethylstyrene)) with potassium pyrrole. 1 H NMR spectroscopic analysis indicated that 4.7% of the styrene units in the precursor have pyrrole substituents. Electrolysis of the spin-coated precursor film on platinum electrodes showed optimum copolymerization in a mixture electrolyte consisting of acetonitrile, dichloromethane (80:20 by volume), 0.1 M pyrrole, and 0. M lithium perchlorate. Constant potential electrolysis showed that pyrrole groups in the precursor were oxidized to form PPy; that is, they acted as grafting centers at which the PPy grew. SEM results and conductivity measurements supported the formation process of PPy copolymer. The maximum conductivity of the final products was in the range of 10 -2 S/cm.

Electrochemical Preparation of Polypyrrole Copolymer Films from PSPMS Precursor

A series of composite fibers composed of multi-walled carbon nanotube (MWCNT) and poly(vinyl alcohol) (PVA) are prepared by varying co-flowing wet-spinning conditions such as spinning geometry and PVA concentration, which affect aligning shear stress for MWCNTs during the wet-spinning. Then, structural features, mechanical and electrical performances of MWCNT/PVA composite fibers are investigated as a function of the aligning shear stress of the wet-spinning process. SEM images of the composite fibers exhibit that MWCNTs are wetted effectively with PVA chains. Polarized Raman spectra confirm that the alignment of MWCNTs is enhanced along the composite fiber axis with increasing the aligning shear stress of the spinning process. Accordingly, initial moduli and tensile strengths of the composite fibers are significantly increased with the increment of the aligning shear stress. In addition, it is found that electrical conductivities of MWCNT/PVA composite fibers increase slightly with the aligning shear stress, which is associated with the formation of efficient electrical conduction paths caused by well-aligned MWCNTs along the composite fiber axis.

Doo Hyun Baik

Papers

Structures, electrical, and dielectric properties of PVDF-based nanocomposite films reinforced with neat multi-walled carbon nanotube

Compatibilizing effect of a styrene-methyl methacrylate block copolymer on the phase behavior of poly(2,6-dimethyl-1,4-phenylene oxide) and poly(styrene-co-acrylonitrile) blends

Ionic interactions in polyacrylonitrile/polypyrrole conducting polymer composite

Electrochemical Preparation of Polypyrrole Copolymer Films from PSPMS Precursor

Effects of wet-spinning conditions on structures, mechanical and electrical properties of multi-walled carbon nanotube composite fibers