Search

Electric field induced orientation of polymer chains in macroscopically aligned electrospun polymer nanofibers is described. PEO polymer backbones within the polymer nanofibers were successfully oriented along the nanofibers axes through electrospinning leading to conclusion that a high degree of orientation of the polymer backbone occurs along the fiber axis.

A novel method is presented that is capable of collecting time-resolved vibrational spectroscopic information with sub-100-[micro]s temporal resolution. Unlike previous step scan FT-IR approaches, the phenomena under study do not necessarily need to be repeatable. The methodology described herein is based on the planar array infrared (PA-IR) technique, which utilizes a spectrograph for wavelength dispersion and a mid-infrared focal plane array (FPA) detector for simultaneous detection of multiple wavelengths. Unlike previous PA-IR approaches, a rolling mode FPA is employed. This unique data readout mode, where data are read out of the array two rows at a time, is exploited to generate increased temporal resolution. The capabilities of this technique are demonstrated using the example of the electric field-induced Freedericksz transition of a nematic liquid crystal. It is shown that the orientational dynamics of a single transition can be tracked over a spectral range of 154 [cm.sup.-1] with a temporal resolution of 99.17 [micro]s while requiring a total experimental time of less than 1 s.

An investigation of the longitudinal acoustic mode (LAM) in a series perfluoro-n-alkanes under pressure has been carried out using Raman spectroscopy in conjunction with a diamond anvil cell. Perfluoro-n-alkanes are shown to undergo a phase transition from a helical to a planar zigzag structure at 5 kbar. This conformational change with pressure results in an abrupt increase in the LAM frequency. Since the chain axis elastic modulus of a planar zigzag molecule is larger than that of a helical one, such a conformational change leads to stiffening of the backbone giving rise to the observed change in the LAM frequency. [ABSTRACT FROM AUTHOR]

Presents a study that observed Curie transition in vanadium-fluorine-terbium-Iron random copolymer of fixed chemical composition has been investigated as a function of processing history. Analysis of the solution cast and melt crystallized materials using differential scanning calorimetry and wide angle x-ray diffraction; Thermal analysis; Wide angle x-ray diffraction.

ABSTRACT Nanocomposites of low-density polyethylene/polyhydroxybutyrate (LDPE/PHB) containing organomodified montmorillonite (OMMT) and/or LDPE grafted maleic anhydride (LDPE- g-MAH) were prepared with a wide range of composition ratios using a vertical co-rotating twin-screw microCompounder. To infer the effect of OMMT and LDPE- g-MAH on the thermal stability of prepared nanocomposites, all samples were characterized by thermogravimetric analysis while changing clay and compatibilizer contents. Accordingly, two commonly used kinetic models (Coats-Redfern and Horowitz-Metzger) were employed to correlate the thermal stability of the samples with kinetic parameters, including activation energy and pre-exponential factor. Furthermore, morphological features of LDPE/PHB in the presence or absence of OMMT and LDPE- g-MAH were studied using scanning electron microscopy, transmission electron microscopy, and wide-angle X-ray diffraction analysis. It was found that for a specific OMMT composition ratio (1 wt %), the thermal stability is enhanced due to an exfoliated structure. However, for samples containing more organoclay (>=3 wt %), the thermal stability was reduced showing the competition between the barrier effect of organoclay platelets and the catalyzing effect of ammonium salts. Moreover, when using LDPE- g-MAH as compatibilizer, it acted as a good coupling agent in all compositions in LDPE major phase systems in contrast to PHB major phase samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45922. [ABSTRACT FROM AUTHOR]

Research is presented concerning the development of a colloidal crystal templating method for the deposition of metallic films, which are structured and porous, on flat substrates. The convenience of the method is discussed.

Research was conducted to examine the self-assembly of low molar mass molecules that have strong intermolecular interactions and the manipulation of the phase structures formed by segregated block copolymers through stepwise crystallization. X-ray diffraction results were compared with the layer spacing calculated from the 00l lines. Different chain conformations and packings were taken into account, but the X-ray diffraction results agreed best with fully extended chains oriented normal to the layers with the ethylene oxide core in a planar zigzag conformation.

ABSTRACT Electrospun poly(vinylidene fluoride) (PVDF) nanofibers were collected on aluminum foil across a gap with widths that varied in size from 2 to 10 mm. Scanning electron microscopy (SEM) images on fiber bundles showed that in all cases, fibers in the gap were macroscopically aligned across the gap. However, single fiber selected area electron diffraction (SAED) patterns and polarized Fourier Transform Infrared (FTIR) spectra demonstrated that fibers deposited across the gap were also highly aligned at the molecular level with the polymer backbones oriented along the fiber axis and that the extent of molecular orientation increased with the gap width. A possible explanation for this observation is based on the repulsion of similarly charged nanofibers and the simultaneous attraction of these fibers to the oppositely charged gap edges. This provides a plausible model for understanding the deposition kinetics and subsequent molecular orientation as a function of gap size when electrospinning using this method of fiber collection. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 617-623 [ABSTRACT FROM AUTHOR]