We report a new method to precisely locate inorganic nanoparticles at polymeric fiber crossing sites. Polymeric fibers are aligned by a previously reported non-electrospinning Spinneret based Tunable Engineered Parameters (STEP) polymeric fiber manufac- turing technique. Cross-hatch pattern (perpendicular) of polymeric fibers embedded with inorganic nanoparticles (e.g.: Fe(NO 3) 3 or Bi(NO 3) 3) were fabricated on top of each other and the fiber compositions re-acted during annealing process, thus, producing a desired phase (e.g.: BiFeO 3) only at the crossing site. Our method of-fers an easy way to mass arrange and locate nanoparticles at designed positions on virtually all types of substrates.
Nanomaterials have attracted much interest because of their novel properties compared to bulk materials [1,2]. Different manufacturing processes such as sol-gel [
In this work, we report an alternative and simple way to achieve patterning of nanomaterials. Spinneret based Tunable Engineered Parameters (STEP) non-electrospinning fiber manufacturing platform has recently been developed to deposit polymeric nano/microfibers [10,11]. This technique can continuously deposit uniform diameter micro/nano polymer fibers with control on fiber dimensions (diameter: sub 100 nm—microns, length: mmcm, orientation: parallel and orthogonal) in single and multiple layers at user defined spacing. Furthermore, STEP allows deposition of single and multiple-layer fibrous structures in planar, and customized three-dimensional configurations. These polymer networks can be used as inorganic nanomaterial carriers, through mixing of metal oxide ion solutions with polymer solutions before spinning. Post fiber fabrication, the networks are subjected to high heat, which ablates the base polymer and initiates a chemical reaction at intersection of two or more different types of fibers, thus, resulting in the formation of a new phase only at specific locations.
Two different polymer solutions: polystyrene (PS) (Mw = 2,257,000, Scientific Polymer, USA) dissolved in Xylene at 7 wt%; and polyvinylpyrrolidone (PVP) (SigmaAldrich, USA) dissolved in a mixture solvent (6 ml ethyl alcohol and 5 ml H2O) at 6 wt% were used in this study. A metal source of 0.202 g Fe(NO3)3·9H2O or 0.243 g Bi(NO3)3·5H2O was added into PVP solution.
The solution was pumped through the micropipette at a flow rate of 20 ml/hour using a syringe pump (Fisher Scientific Inc, USA). STEP based resultant fibers were collected on the substrate (4 - 8 mm in width) in aligned configurations at 1000 RPM and cris-cross structures were fabricated by depositing fibers on top of previously deposited layers. SrTiO3 signal crystal substrates were used to collect fibers.
Scanning electron microscopy (SEM) images were obtained using a LEO (Zeiss) 1550 high-performance Schottky field-emission SEM operated at 5 kV. Oxford INCA Energy E2H X-ray Energy Dispersive Spectrometer (EDS) system with Silicon Drifted detector attached to SEM was used to take DES data. A FEI Helios 600 NanoLab focused ion beam SEM or FIB was used to lift-out transmission electron microscope (TEM) samples. A Philips EM420 transmission electron microscope was then used to obtain cross sectional images.
The STEP technique offers a simple and cost-effective way, to spin aligned polymer fibers with well-controlled separation distances. Smooth and uniform diameter 500 nm diameter parallel PS fibers were deposited at 2 microns separation distances (
Since only the intersection regions have both Bi and Fe elements, EDS line scans were used to confirm the
elemental ratio of the reactant phase in the fibers. Three such line scans were taken from different fiber cross sections as shown in
To further study the fiber intersection regions, we used a FIB to lift-out annealed fiber cross section areas and obtain cross sectional images using transmission electron microscope (TEM). TEM samples were made by liftingout regions shown as broken line in
left some spaces. A high resolution image of the middle reveals denser region, with fewer holes. The contrast in
In conclusion, an application to locate nanoparticles using STEP platform has been demonstrated based on a fiber-fiber intertexture composite construction. EDS and TEM were used to study and analyze fiber intersection regions. It is an easy and inexpensive way by which to locate nanoparticles at preferred spatial positions. Compared to these vapor deposition methods our method just costs approximately 10%. Though this study demonstrates fibers as carriers of two inorganic nanomaterials in the network, it is easily expandable to accommodate multiple fiber types of different diameters and carriers in the same network, thus leading to complex patterns and arrangements of fused nanomaterials at desired locations in planar and nonplanar sites for applications ranging from advanced materials to sensor systems.
The authors gratefully acknowledge the financial support from the Ministry of Science and Technology of China through a 973-Project under Grant No.2012CB619401 and National Science Foundation (USA) under DMR- 0757502. The authors are also thankful to Institute for Critical Technology and Applied Sciences (ICTAS) along with Nanoscale Characterization and Fabrication Laboratory (NCFL) at Virginia Tech for SEM and TEM work.