JUAN P. HINESTROZA, PH.D.
CORNELL UNIVERSITY

The ability of detecting and measuring electrostatic charges and charge distributions with nanoscale resolution can enable the fiber industry to devise new strategies to solve electrostatic buildup and dissipation problems present during fiber processing operations. While these problems are centuries old, existing knowledge in this area is mainly empirical and Edisonian. Most existing analytical techniques rely upon measuring the average charge over many centimeters (and in the best case hundreds of micrometers) from the surface of the fibers. While the average bulk charge may be zero far from the surface, the local charge and charge densities a few nanometers from the surface can be several orders of magnitude higher. The presence of these highly charged domains (As shown in Figure 1) do affect the coverage, dispersion, and diffusion of surface finishes, dyes, and anti-static additives over the textile fibers. Today a comprehensive understanding of the electrostatic behavior of high curvature low energy surfaces relevant to fiber operations does not exist and one of the goals of our research group is aimed at building basic knowledge of static buildup and dissipation at the molecular level and its relevance to textile systems. Our group uses a combination of electrostatic force EFM and chemical force microscopy CFM techniques to understand charge trapping and detrapping mechanisms in Fibers. Our group uses EFM to locate and quantify the presence of electrical charges with nanoscale precision while minimizing the curvature effect of the sample while we used CFM to identify specific chemical functional groups or molecular structures that could be responsible for charge trapping and detrapping mechanisms.

The deleterious effect of solvent exposure on the performance of electret filters has been a topic of controversy during previous years. Electret based filters are considered to be the most efficient in capturing submicron sized particles while providing minimal pressure drop. It is believed that exposure to some solvents may have a negative effect of the filtration performance of electret filters. While solvent-induced charge degradation of the fibers is usually suggested as the root cause of this phenomenon, there has not been a direct measurement capable of validating this hypothesis. Recently, it was demonstrated that Electrostatic Force Microscopy (EFM) could indeed be used to directly probe solvent-induced charge degradation in electret filter media. In fact, Electrostatic force gradient images, obtained by monitoring the shifts in phase and frequency between the oscillations of the biased AFM cantilever and those of the piezoelectric driver, can be used to quantify the extent of charge degradation caused by the immersion of the fibers into a widely commercial solvent as shown in Figure 2.

Currently our group, in partnership with Warren Jasper at NCSU, is aiming at correlating the observations at a nanoscale made with our AFM and CFM microscopes with those of macroscopic tests commonly used in the Textile and Fiber Industries. Several challenges need to be surpassed before we can claim success as at this level of granularity, the geometrical and electrical effects of the EFM probe and the surface on which the specimen is mounted play significant roles in distorting the E-field. According to Maxwell’s seminal work at the end of the 19th century, the mapping of the E-field or the vector potential will be sufficient to solve for the charge distribution. Although in theory this is straight forward, solutions to Poisson’s equation for arbitrary boundary conditions such as those present in fiber-based systems are not trivial and expensive computational methods are required. Information about our work in the area of Textiles Nanotechnology can be found at http://www.HinestrozaResearch.com

College of Textiles
P.O. Box 8301
Raleigh, NC 27695-8301
Telephone: (919) 515-6646
FAX: (919) 515-3733
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Last Site Revision:
February 2, 2006