Focused Ion Beam Characterization of Bicomponent Polymer Fibers

Abstract

Previous work has shown that focused ion beam (FIB) can be effectively utilized for the cross-sectional analysis of polymers such as core-shell solid micro-spheres [1] and hollow latex nanospheres [2]. While these have clearly demonstrated the precise location selection and milling control provided by the FIB technique, the samples studied consisted of only a single polymer. In this work, FIB is used to investigate bicomponent polymeric fiber systems by taking advantage of the component's differing physical properties. An approach for cross sectioning and thus revealing the morphology with respect to the polymeric components in a bicomponent polymeric fiber crosssection with the island-in-the-sea (I/S) structure is presented. The I/S fibers investigated were fabricated using the spunbonding process and are composed of bicomponent combinations of polypropylene (PP), polylactic acid (PLA), polyethylene terephthalate (PET), or nylon 6 (PA6).Bicomponent I/S fibers [3] were coated with approximately 30 nm of palladium-gold using a Denton Desk II sputter coater. An FEI Quanta 200 3D Dual Beam system was used for crosssectioning and imaging. The fibers were cross-sectioned by using a 30keV Ga + ion beam for both the mass removal and cross-section polishing steps of the process. Initial mass removal was carried out using a water injection system to chemically enhance material removal [4]. The injection of the water vaper into the vacuum chamber resulted in an increase of chamber pressure of about 1 order of magnitude (from about 5E-6 Torr to 5E-5 Torr). Prior to the mass removal step, a platinum strip was deposited onto a selected area across the width of the fiber to protect the surface of the fiber by preventing unwanted etching of the fiber surface. An approximately 20x20 µm 2 area with a depth equals to the fiber diameter (~10µm) was removed in the mass removal step by using a 20nA beam and a rectangle raster pattern. Beam currents of 5nA, 1nA and 100pA were subsequently used for cross-section polishing using a cleaning cross-section milling pattern to provide line-by-line material removal. Finally, a 30pA beam with a dwell time of 55µs and a 1024x768 pixels scan resolution was directed perpendicular to the cross section surface to provide a secondary electron (SE) image. An example of an I/S fiber cross-section is presented in Figure 1. Differential sputtering of the respective polymers gave rise to the necessary topographical contrast since sputtering occurred over the cross-section surface during ion induced secondary electron imaging. This differential sputtering combined with the contrast generated by ion-induced secondary electron microscopy provided the ability to differentiate the structure of the bicomponent fiber.Various spunbonding process parameters govern the final I/S fiber structure and properties. Previous studies on revealing the cross-section morphology utilizing oxygen plasma [5][6] and scanning electron microscopy (SEM) can also provide structural information. However, the sample preparation and ...

Far‐reaching geometrical artefacts due to thermal decomposition of polymeric coatings around focused ion beam milled pigment particles

“…Dual beam instruments that combine focused ion beam with a scanning electron microscope (FIB-SEM) are extensively used for characterization of various materials ranging from semiconductors to biological tissue (Stevie et al, 2005;Volkert & Minor, 2007;Bassim et al, 2014), but have not been applied to analysis of organic corrosion barrier coatings. In the past, FIB-SEM has been used for site specific cross sectioning and/or lamella extraction for transmission electron microscope imaging (White et al, 2001;Lins et al, 2002;Loos et al, 2002;Beach et al, 2005;Brunner et al, 2006Brunner et al, , 2008Brostow et al, 2007;Kawahara et al, 2008;Martínez et al, 2008;Wong et al, 2010;Firpo et al, 2015;Qin et al, 2015), destructive tomography (Kato et al, 2007;Lin et al, 2012;Olea-Mejía et al, 2012) and nanofabrication (Aubry et al, 2002;Niihara et al, 2005;Lee et al, 2012;Schmied et al, 2012;Orthacker et al, 2014;Schmied et al, 2014) of polymers and polymeric composites. Out of these examples, only a few studies have been dedicated to characterization of pristine organic coatings and paints (Lins et al, 2002;Brunner et al, 2006Brunner et al, , 2008Brostow et al, 2007;Lin et al, 2012;Chen et al, 2013;Doutre et al, 2014).…”

Interconnected, microporous hollow fibers for tissue engineering: Commercially relevant, industry standard scale‐up manufacturing

“…Applications range from membrane separation, liquid and gas filtration, desalination, and biomedical separation processes . Fabrication of hollow fibers has been described in the literature, including processing parameters and resultant effects on physical and mechanical properties . Specific to the fabrication method and processing parameters, both physical and mechanical properties can be tailored to meet the requirements of a specific application.…”

“…Micropores allow a diffusion path for nutrients into the scaffold and removal of cellular waste products. Micropores can be created after the spinning process via cold stretching, thermally induced phase separation (TIPS), or by introducing a secondary sacrificial component into the base polymer . Subsequent removal of the sacrificial component leaves a microporous network throughout the fiber wall generated by the primary polymer.…”

“…Closed slit designs typically allow for better control of fiber diameter as well as elimination of grooves on the surface where the polymer streams converge . These designs also allow for the inclusion of either a gas stream in the center lumen to form the hollow channel, or a secondary sacrificial polymer that can be subsequently removed to form the hollow channel …”

“…The EastONE islands were removed by subjecting the filaments to mechanical agitation in de‐ionized water and subsequently sonicating for two hours at 69°C . Wong et al verified that the EastONE component was removed via focused ion beam characterization, resulting in filaments with 12 hollow channels and microporous fiber walls (Fig. ).…”