ABSTRACT HATIBOGLU, BILGE. Mechanical Properties of Individual Polymeric Micro and Nano Fibers using Atomic force Microscopy (AFM). (Under the direction of Dr. Behnam Pourdeyhimi and Dr. Juan P. Hinestroza.) Being the raw materials, fibers have the biggest importance in textiles industry. With the invention of the first man-made fiber, nylon, in 1930s, fiber industry gained a new aspect. During the recent years, fibers gained another aspect with the term “nanotechnology”. Now, today’s science is focused on the nano materials. Analyzing and finding new applications for them are some of the concerns. Textile industry is affected from the fiber part of the nanomaterials. The introduction of the nanofibers added a lot of interesting applications to textiles. Drug delivery, tissue engineering, reinforcement for composite materials, filtration are some of the interesting applications of nanofibers. Having a lot of exciting applications, nanofibers require to be examined well. However, since they are fairly small materials, it is not very easy to analyze them. In this thesis, we aimed to develop a method to analyze mechanical properties of individual micro and nanofibers using a technique called Atomic Force Microscopy (AFM). After finding a useful approach to prepare individual islands-in-the-sea form fibers for the further analysis, we also set up AFM and developed an experimental approach to examine individual PET and Nylon-6 micro and nanofibers’ mechanical properties. MECHANICAL PROPERTIES OF INDIVIDUAL POLYMERIC MICRO AND NANO FIBERS USING ATOMIC FORCE MICROSCOPY (AFM) by Bilge Hatiboglu A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science Textile Engineering Raleigh, North Carolina 2006 Approved By: Dr. Behnam Pourdeyhimi Dr. Juan P. Hinestroza Chair of Advisory Committee Co-chair of Advisory Committee Dr. Orlando Rojas Dr. Phillip Russell Member of Advisory Committee Member of Advisory Committee BIOGRAPHY Bilge Hatiboglu was born on July 20th, 1981 in Merzifon, Turkey. On completing her elementary and high school study in Merzifon, Bilge entered college at Istanbul Technical University, Istanbul, Turkey, in the year 1999 to proceed towards her Bachelor’s degree in textile engineering. She graduated with distinction in 2004 and, upon graduation she entered the Master of Science program in Textile Engineering, at North Carolina State University in 2004. While she was working on her masters program, she worked as a research assistant under Dr. Behnam Pourdeyhimi and Dr. Juan P. Hinestroza on a project funded by Nonwovens Corporative Research Center. ii ACKNOWLEDGEMENTS I would like to express my gratitude to my advisors Dr. Behnam Pourdeyhimi and Dr. Juan P. Hinestroza for giving me the opportunity to work with them and for their continuous patience and guidance. This work would not have been possible without their knowledge and support. I also appreciate the support given by the other members of my advisory committee, Dr. Phillip Russell and Dr. Orlando Rojas. I also appreciate the financial support provided by Nonwovens Cooperative Research Center. I would like to thank Chuck Mooney, Mike Salmon, David Nackashi, Roberto Garcia and Dale Batchelor for their help and support with the experimental work. I extented my great appreciation to Jeffrey Krauss. My special thanks go to Umut Kivanc Sahin and Erkmen Ercan for their support and encouragement throughout this work. My last but not least gratitude goes to my parents and my sister for being with me, supporting me and trusting me at every moment of my life… Without all of you, this degree would not be possible. Thank you all once more… iii TABLE OF CONTENTS LIST OF TABLES……………………………………………………………..…….....vii LIST OF FIGURES……………………………………………………………………viii 1. INTRODUCTION……………………………………..…………………………….1 2. LITERATURE REVIEW…………………………………………………………...3 2.1. Fibers………………………………………………………………………….3 2.1.1. Natural Fibers……………………………………………………….4 2.1.2. Man-Made Fibers…………………………………………………...4 2.2. General Fiber Properties……………………………………………………...4 2.2.1. Geometric Characteristics…………………………………………..5 2.2.2. Physical Properties………………………………………………….5 2.2.3. Chemical Properties………………………………………………...6 2.2.4. Mechanical Properties………………………………………………6 2.3. Properties of Polyamide-6 (Nylon-6) and Polyester (PET)…………………..7 2.3.1. Nylon-6 Fibers……………………………………………………...7 2.3.2. PET Fibers………………………………………………………...10 2.4. Microfibers…………………………………………………………………..12 2.5. Nanofibers…………………………………………………………………...13 2.5.1. Fabrication of Nanofibers…………………………………………16 2.5.1.1. Drawing………………………………………………….14 2.5.1.2. Template Synthesis……………………………………...14 2.5.1.3. Phase Separation………………………………………...15 2.5.1.4. Bicomponent Extrusion…………………………...…….15 iv 2.5.1.5. Self-Assembly…………………………………………...18 2.5.1.6. Electrospinning………………………………………….18 2.5.1.7. Other Techniques………………………………………..20 2.5.2. Applications of Nanofibers………………………………………..20 2.5.2.1. Filters……………………………………………………21 2.5.2.2. Biomedical Applications………………………………...22 2.5.2.3. Protective Clothing……………………………………...24 2.5.2.4. Reinforcement for Composite Materials………………..24 2.5.2.5. Sensors…………………………………………………..25 2.5.3. Analytical Techniques………………………………………...…..25 2.5.3.1. Scanning Electron Microscopy (SEM).………………....25 2.5.3.2. Transmission Electron Microscopy (TEM)…..…………31 2.5.3.3. Atomic Force Microscopy (AFM)……………………....35 3. EXPERIMENTAL APPROACH…………………………………………………...47 3.1. Materials…………………………………………………………………….47 3.2. Instruments…………………………………………………………………..49 3.2.1. Focused Ion Beam (FIB)…………………………………………..49 3.2.2. Scanning Electron Microscopy (SEM)……………………………50 3.2.3. Dynamic Mechanic Analyzer (DMA)…………………………….52 3.2.4. Atomic Force Microscopy (AFM)………………………………...54 3.3. Experimental Procedures……………………………………………………59 3.3.1. First Approach…………………………………………………….60 3.3.2. Second Approach…………………………………………………61 v 3.3.3. Third Approach……………………………………………………61 3.3.4. Final Approach…………………………………………………….64 4. RESULTS AND DISCUSSION……………………………………………………..66 4.1. Cross-sectioning and imaging islands-in-the-sea form fibers……………….66 4.2. Method Validation…………………………………………………………..71 4.3. AFM Imaging and Indentations……………………………………………..72 4.4. Determination of the tip radius……………………………………………...78 4.5. Determination of the cantilevers’ size………………………………….…...79 4.6. Determination of the cantilevers’ spring constant…………………………..80 4.7. Data processing and obtaining Force vs. Displacement curves……………..81 4.8. Calculation of elastic modulus values……………………………………….99 4.9. Results for PET micro and nanofibers……………………………………..103 4.10. Results for Nylon-6 micro and nanofibers………………………………..105 4.11. Results for Nylon-6 hollow micro and nanofibers………………………..107 5. SUMMARY AND CONCLUSIONS………………………………………………108 6. REFERENCES……………………………………………………………………...110 7. APPENDIX………………………………………………………………………….115 vi LIST OF TABLES Page Table 2.1 Effect of drawing on Elastic modulus of Nylon-6 fibers [3]…………………...8 Table 2.2 Typical Properties of nylon fibers [3]…………………………………………10 Table 2.3 Typical properties of Polyester fibers [3]……………………………………..11 Table 4.1 Elastic modulus values [GPa] of the PET film, obtained under different testing conditions………………………………………………..71 Table 4.2 An example of the variation on the same cantilevers’ spring constants because of the size, RF and QF………………………………………..81 vii LIST OF FIGURES Page Figure 2.1 Cross-sections of bicomponent fibers………………………………………..16 Figure 2.2 Classical bilateral bicomponent spinning (A, B: Polymers) [12]…………….17 Figure 2.3 Pipe-in-pipe mixers [12]……………………………………………………...17 Figure 2.4 Schematic figure of Elecrtospinnig process [13]……………………………..19 Figure 2.5 Fractional efficiency (Filtration Efficiency vs. particle size) for a standard cellulose media and nanofiber filter media [22]………………………..22 Figure 2.6 SEM images of nickel titanate fibers: a)as-prepared composite fibers, b) fibers calcinated at 1273 K [28]……………………………………….27 Figure 2.7 SEM images of the V2O5 fibers [29]…………………………………………27 Figure 2.8 SEM images of elastomeric nanofiber membranes under two different levels of biaxial strain a) 100%, b) 0 % [24]………………………......28 Figure 2.9 SEM photograph of PVA/lithium chloride/manganese acetate composite fiber samples [30]…………………………………………………….29 Figure 2.10 SEM images of a) polyaniline nanofibers b) polyaniline nanofibers and polyaniline/CeO2 composite microspheres [32]…………………………….30 Figure 2.11 TEM image of polyaniline nanofibers [32]…………………………………31 Figure 2.12 TEM images of a) Twisted nantubes; b) and c) Aligned, nanotubes in PEO nanofibers [35]…………………………………………………………..32 Figure 2.13 TEM image of an individual Collagen-r-PCL composite nanofiber a) collagen as the shell material, and PCL the support b) is the TEM image of a pure PCL nanofiber [34]……………………………..33 Figure 2.14 Transmission electron micrographs of a) PA6 fiber, a segment almost constant in diameter b) PLA nanofiber fibers with modulations [37]…………...34 Figure 2.15 AFM images of PA6 nanofibres a) regular fiber b) plasma treated fiber (for 60 seconds) [40]……………………………………………………….35 viii Figure 2.16 a) NCAFM image (25 ím _ 25 ím) of dendrimer 1 nanofibers prepared by drop-casting a 2.0 _ 10-6 M dendrimer 1 solution in THF on a silicon surface in a saturated environment of THF, b) NCAFM image (25 ím _ 25 ím) of dendrimer 1 nanofibers repared by drop-casting a 2.0 _ 10-6 M dendrimer 1 solution in THF in a saturated environment of THF:H2O ) 90:10 (v/v) on a silicon surface, c) NCAFM image (50 ím _ 50 ím) of dendrimer