John F. Rabolt

Electrospun fibers were produced using a variety of solvents to investigate the influence of polymer/solvent properties on the fiber surface morphology. Electrospinning is a novel processing technique for the production of fibers with diameters in the range of a few nanometers to tens of micrometers. We have been able to produce polymeric fibers with a high surface area through the introduction of a micro- and nanostructured surface structure, which we refer to as a “porous” morphology. These features could be introduced in several different polymeric fibers increasing their range of application significantly. The pores vary from densely packed, well-formed nanopores with diameters in the range 20−350 nm to larger flat pores of about 1 μm. The increased surface area of polymeric fibers was correlated with high volatility solvents used in the electrospinning process. The effect of processing parameters on the fiber surface morphology was also investigated using optical microscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM).

Synthesis of suspensions of nanosize particles of Fe3O4 was carried out in bulk aqueous solutions without the presence of surfactants. The Fe3O4 nanoparticles were oxidized to γ-Fe2O3 by direct aeration of the suspension at 100 °C. The shape and size distribution and crystallinity of the Fe3O4 nanoparticles were assessed by transmission electron microscopy and selected area electron diffraction. Very uniform and stable colloidal suspensions of the Fe3O4 nanoparticles in water could be synthesized. Oxidation of the colloidal system leads to γ-Fe2O3 nanoparticles of much larger size than Fe3O4.

ABSTRACT: Electrospinning is a technique used to produce micron to submicron diameter polymeric fibers. The surface of electrospun fibers is important when considering end-use applications. For example, the ability to introduce porous surface features of a known size is required if nanoparticles need to be deposited on the surface of the fiber or if drug molecules are to be incorporated for controlled release. Surface features, or pores, became evident when electrospinning in an atmosphere with more than 30% relative humidity. Increasing humidity causes an increase in the number, diameter, shape, and distribution of the pores. Increasing the molecular weight of the polystyrene (PS) results in larger, less uniform shaped pores. This work includes an investigation of how humidity and molecular weight affect the surface of electrospun PS fibers. The results of varying the humidity and molecular weight on the surface of electrospun PS fibers were studied using optical microscopy, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM) coupled with image analysis.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionSynthesis and Characterization of Nanometer-Size Fe3O4 and γ-Fe2O3 ParticlesYoung Soo Kang, Subhash Risbud, John F. Rabolt, and Pieter StroeveCite this: Chem. Mater. 1998, 10, 6, 1733Publication Date (Web):May 28, 1998Publication History Published online28 May 1998Published inissue 1 June 1998https://pubs.acs.org/doi/10.1021/cm970904shttps://doi.org/10.1021/cm970904scorrectionACS PublicationsCopyright © 1998 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views1653Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (30 KB) Get e-Alertsclose Get e-Alerts

Polymer and life science applications of a technique that combines atomic force microscopy (AFM) and infrared (IR) spectroscopy to obtain nanoscale IR spectra and images are reviewed. The AFM-IR spectra generated from this technique contain the same information with respect to molecular structure as conventional IR spectroscopy measurements, allowing significant leverage of existing expertise in IR spectroscopy. The AFM-IR technique can be used to acquire IR absorption spectra and absorption images with spatial resolution on the 50 to 100 nm scale, versus the scale of many micrometers or more for conventional IR spectroscopy. In the life sciences, experiments have demonstrated the capacity to perform chemical spectroscopy at the sub-cellular level. Specifically, the AFM-IR technique provides a label-free method for mapping IR-absorbing species in biological materials. On the polymer side, AFM-IR was used to map the IR absorption properties of polymer blends, multilayer films, thin films for active devices such as organic photovoltaics, microdomains in a semicrystalline polyhydroxyalkanoate copolymer, as well as model pharmaceutical blend systems. The ability to obtain spatially resolved IR spectra as well as high-resolution chemical images collected at specific IR wavenumbers was demonstrated. Complementary measurements mapping variations in sample stiffness were also obtained by tracking changes in the cantilever contact resonance frequency. Finally, it was shown that by taking advantage of the ability to arbitrarily control the polarization direction of the IR excitation laser, it is possible to obtain important information regarding molecular orientation in electrospun nanofibers.