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Conductive polymer composites possessing a low percolation‐threshold concentration as a result of double percolation of a conductive filler and its host phase in an immiscible polymer blend afford a desirable alternative to conventional composites. In this work, blends of high‐density polyethylene (HDPE) and ultrahigh molecular weight polyethylene (UHMWPE) were used to produce ternary composites containing either carbon black (CB), graphite (G), or carbon fiber (CF). Blend composition had a synergistic effect on electrical conductivity, with pronounced conductivity maxima observed at about 70–80 wt % UHMWPE in the CB and G composites. A much broader maximum occurred at about 25 wt % UHMWPE in composites prepared with CF. Optical and electron microscopies were used to ascertain the extent to which the polymers, and hence filler particles, are segregated. Differential scanning calorimetry of the composites confirmed that the constituent polymers are indistinguishable in terms of their thermal signatures and virtually unaffected by the presence of any of the fillers examined here. Dynamic mechanical analysis revealed that CF imparts the greatest stiffness and thermal stability to the composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1013–1023, 2002

We successfully formed an inclusion complex between nylon-6 and R-cyclodextrin and attempted to use the formation and subsequent disassociation of the nylon-6/R-cyclodextrin inclusion complex to manipulate the polymorphic crystal structures, crystallinity, and orientation of nylon-6. Formation of the inclusion complex was verified by Fourier transform infrared (FTIR) spectroscopy, wideangle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and CP/MAS 13 C NMR. After obtaining the inclusion complex of nylon-6 and R-cyclodextrin, the sample was treated in an acid environment to remove the host R-cyclodextrin and coalesce the nylon-6 guest polymer. Examination of as-received and IC coalesced nylon-6 samples showed that the R-form crystalline phase of nylon-6 is the dominant component in the coalesced sample. X-ray diffraction patterns demonstrate that the γ-form is significantly suppressed in the coalesced sample. Along with the change in crystal form, an increase in crystallinity of ∼80% was revealed by DSC, and elevated melting and crystallization temperatures were also observed for the coalesced nylon-6 sample. FTIR spectroscopy revealed a significant degree of orientaion for the nylon-6 chains coalesced from their R-cyclodextrin inclusion complex crystals. Thermogravimetric analysis indicated that nylon-6 has an ∼30 °C higher thermal degradation temperature after modification by threading into and being extracted from its R-cyclodextrin inclusion complex.

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Low-molecular-weight liquid poly(ethylene glycol) (PEG) spontaneously forms an inclusion compound (IC) when combined with R-cyclodextrin (R-CD) powder at room temperature. This process can be followed with wide-angle X-ray diffraction (WAXD). The WAXD data shows that the R-CD crystals undergo a solid-state crystal-crystal transformation from the cage to the channel crystal structure upon IC formation over a period of about 8 h. The time dependence of the 2θ ) 20°R-CD channel structure X-ray peak can be described by a simple first-order kinetic model. The effects of changing the temperature, PEG:R-CD molar ratio, PEG molecular weight, and vacuum-drying the CD have been studied. The barrier opposing the PEG inclusion-induced solid-state transformation of R-CD from the cage to the channel crystal structure appears to be dominated by changes in the packing/interactions of R-CDs, rather than the loss in the conformational entropy experienced by the PEG chains during the inclusion process.

The diffusion of fluorescein into nylon-66 fibers has been studied for the first time by laser scanning confocal microscopy (LSCM). LSCM makes it possible to noninvasively obtain high-resolution three-dimensional images of the spatial distribution of dyes (fluorescein) in fibers dyed for various length of times. Integration over the dye distribution yields the total amount of dye in the fiber, which is found to be in close agreement with that determined by UV−vis spectrophotometry after dissolving the fibers. Thus, the diffusion coefficients determined noninvasively by LSCM ((6.9 ± 1.0) × 10-11 cm2/s) and the destructive traditional means ((7.8 ± 1.9) × 10-11 cm2/s) also agree. The LSCM method has several significant advantages. Among these are its speed, nondestructive nature, and the ability not only to determine the total dye content of the fiber but also to image the dye distribution profile across the fiber diameter. This latter ability is demonstrated to be important to understanding the visual appearance of dyed fibers and fabrics. Two fibers, one ring-dyed and one uniformly dyed, each with the same over all dye content, show remarkably different shades of color. The ring-dyed fiber is lighter, an observation confirmed by the reflectivities measured for each fiber, which were in the ratio ring-dyed/uniformly dyed = 2/1. LSCM observation of dyed fibers provides us not only with a means to measure the dye diffusion coefficient in the fiber, but also the time-dependent, three-dimensional distribution of dye molecules.