Micro/Nano Mechanical Systems Lab Class#16

Transcription

1 Microsystems Laboratory Micro/Nano Mechanical Systems Lab Class#16 Liwei Lin Professor, Dept. of Mechanical Engineering Co-Director, Berkeley Sensor and Actuator Center The University of California, Berkeley, CA Liwei Lin, University of California at Berkeley 1

2 Outline Microsystems Laboratory The rest of the semester Near-field Electrospinning Liwei Lin, University of California at Berkeley 2

3 Rest of the Semester Microsystems Laboratory 3/8 Other possible MEMS/NEMS labs 3/13 MD simulation lab (no lecture) 3/15 project proposal (1-2 pages ppt) 3/20 3/22 MD simulation lab (no lecture) 4/3 project design/progress (5 pages ppt) 4/5 review for quiz 4/10 quiz 4/12 quiz solution 4/17, 4/19, 4/24, 4/26 final presentations

4 Outline Microsystems Laboratory Electrospinning - Overview Near-Field Electrospinning Applications PVDF Nanogenrators Liwei Lin, University of California at Berkeley 4

5 Electrospinning Microsystems Laboratory Mechanical spinning Electrospinning early patent in 1934 Syringe Spinning KV Polymer solution Needle cm Stretching Whipping Random, Continuous Nanofiber < 50nm Collector Liwei Lin, University of California at Berkeley

6 What are the Limitations? Microsystems Laboratory Diameter of nanofiber Thinner fibers Alignment Longer distance, Lower concentration, Higher conductivity Whipping Higher Voltage D. Li et al, 2004 A. Theron et al, 2001 J. Kameoka et al, 2004 Liwei Lin, University of California at Berkeley

7 Near-Field Electrospinning Electrode-to-collector distance: m Drive voltage: V Tip diameter: 25 m or smaller Microsystems Laboratory High Voltage h Probe Tip Polymer Solution Liquid Jet Collector Liwei Lin, University of California at Berkeley

8 Results & Limitations Microsystems Laboratory 3~7 wt % Polyethylene oxide (PEO) Nanofiber diameter: 50nm 2 m Manual control Liwei Lin, University of California at Berkeley

9 Potential Microsystems Laboratory Machine-controlled electrospinning Liwei Lin, University of California at Berkeley

10 Comparisons Microsystems Laboratory Conventional Electrospinning Near-Field Needle Spinneret Metal probe tip Several hundred µm Spinneret Diameter 25 µm or smaller Continuous supply Polymer Supply Dip pen KV Applied Voltage As low as 600 V Very long Nanofiber Length Several cm cm Electrode-to-collector Distance µm Controllability Liwei Lin, University of California at Berkeley

11 Microsystems Laboratory Continuously NEFS Setup Direct writing of large area patterns Steel needle with 70 m opening Modified NFES process Original Modified

12 Microsystems Laboratory

13 Continuous NEFS Results Microsystems Laboratory Direct writing of large area patterns (last week) Liwei Lin, University of California at Berkeley

14 Large Area Deposition Microsystems Laboratory A single nanofiber in a designed trajectory 4X4 cm2 area 15 min deposition period for a total length of 108 m, nanofiber has a diameter of 700 nm 100 m Liwei Lin, University of California at Berkeley

15 Application (I) - NanoSensors Direct-write suspended nanofibers on MEMS Microsystems Laboratory conductive polymer by NFES Current [μa] nm Nanofiber Liwei Lin, University of California at Berkeley Bias [V]

16 Microsystems Laboratory Application (II) - NanoAssembly Direct-write patterning of nanoparticles Mixing nanoparticles in nanofibers Removing nanofibers and growing nanowires/tubes 5 & 20nm Au nanoparticles Liwei Lin, University of California at Berkeley

17 Microsystems Laboratory Application (III) Fluidic Connector Direct-write fluidic connector (analogy to wire bonding) h 3h Liwei Lin, University of California at Berkeley

18 Fabrication Process Microsystems Laboratory Conformal coating of fluidic channel material after electrospinning & remove sacrificial nanofiber by etching or evaporation A B Sacrificial PEO nanofiber Coat Hydrophilic & Channel Chip Chip Chip Chip C Open etch holes D Remove nanofiber Chip Chip Chip Chip Liwei Lin, University of California at Berkeley

19 Fabrication Results Microsystems Laboratory Suspended nanofiber overhanging two separated chips with Parylene coating Chip Parylene Chip Nanofiber Nanofiber Chip Suspended nanofibers Parylene coating Liwei Lin, University of California at Berkeley

20 Microsystems Laboratory Application (IV) Bio Scaffolds High (favorable) surface-to-volume ratio with appropriate porosity, malleability to conform to a wide variety of sizes, textures, and shapes. Murine calvaria cells (MC3T3-E1) seeded onto an electrospun PLLA + collagen SUNY Stony Brook Liwei Lin, University of California at Berkeley Ordered nanofiber by NFES might lead to preferred cell growth & differentiation, localized control, functional tissue?

21 Microsystems Laboratory Application (V) - Composites Embedded high-modulus fibrous materials (e.g., glass fibers, carbon fibers, carbon nanotubes) for material reinforcement Embedding sensors & drug carriers. Liwei Lin, University of California at Berkeley

22 Other Applications Microsystems Laboratory Filtration, sensing, Liwei Lin, University of California at Berkeley

23 Electrospun Piezoelectric Nanogenerators Prof. Liwei Lin Berkeley Sensor and Actuator Center Department of Mechanical Engineering University of California, Berkeley 2012 University of California

24 Outline Background Berkeley Sensor and Actuator Center (BSAC) What s electrospinning? Near Field Electrospinning (NFES) Process design Orderly nanofiber deposition Direct Write Piezoelectric Nanogenerator Conclusion 2012 University of California

25 2012 University of California

26 2012 University of California

27 How Does It Work? Piezoelectric Property of PVDF Mechanical Strain Electrical Potential PVDF exists in several forms:, and crystalline phases phase is primarily responsible for piezoelectric proper es Dipole orientation Poling process Bulk or thin film PVDF Stretching and strong electric field Electrospinning In situ poling process Electrospinning of PVDF from its solutions promoted the formation of phase. In contrast, only the and phases were detected in the spin coated samples from the same solutions Non polar phase (Before NFES) Net dipole moment Polar phase (After NFES) Carbon Fluorine Hydrogen omitted 2012 University of California

28 2012 University of California

29 What s the Challenge? Conventional electrospinning Random orientation The polarities of these nanofibers mostly cancel out each other and the net piezoelectric output is close to zero Near field electrospinning Orderly nanofiber patterns with controlled direction of polarity 2012 University of California

30 PVDF Nanogenerator Fabrication process Spacing between electrodes: 100~500 m Fiber diameter: 500nm~3 m A Polymer jet Syringe needle High Voltage B Poling axis High Voltage Electrode Plastic substrate (NFES direction) Substrate moving direction Substrate moving direction Experimental setup Inside a Faraday cage (Not to scale) 2012 University of California

31 Mechanism Piezoelectric Response V + R L q R NG C NG V i R L 1. R L i 1. Start stretching 2. Hold stretching 3. Start releasing 4. End of release V + V R L _ + + V + V R L _ + i 2012 University of California

32 Effect of Strain Rate The current generated by strain in poling direction Current (na) Fast strain rate (0.04 sec) i q d EA 33 d 33 :piezoelectric constant E: Young s modulus A: cross sectional area Current output depends on strain rate Charge depends on applied strain 0.17 sec 0.33 sec Time (sec) 2012 University of California Slow strain rate (0.10 sec) Charge (pc)

33 Voltage (mv) Effect on Stretching Frequency Higher frequency Higher electric output Hz 3 Hz 4 Hz Stretching Release C u rren t (n A ) Hz 3 Hz 4 Hz Stretching Release Time (sec) Time (sec) 2012 University of California

34 Validation of Piezoelectric Response Different materials under the same experimental setup Voltage (mv) PVDF single nanofibers Stretching Release Time (sec) Voltage (mv) PEO nanofiber Stretching Release Time (sec) PVDF random nanofibers mats Voltage (mv) Stretching Release Time (sec) 2012 University of California

35 Long Term Stability Test 0.04% strain applied at a frequency of 0.5Hz for 100 min Voltage (mv) Current (na) Time (min) Time (min) Voltage (mv) Current (na) Time (sec) Time (sec) 2012 University of California

36 High Energy Conversion Efficiency? Voltage (mv) Energy conversion efficiency W e /W m Total electric energy generated during stretching W e = VI dt Total elastic energy applied during stretching W m = 1/8 D 2 L 0 E 2 Voltage Current Time (sec) Current (na) Energy conversion efficiency (%) University of California 5 0 Fiber diameter (μm) PVDF fiber Film PVDF Film fiber Film thickness (μm)

37 Other Related Works in Lin Lab 1 3D Electrospinning 2012 University of California

38 Fabrication Results grid patterns 3D Electrospinning 2012 University of California

39 Cylinder & Flower Wall width 2012 University of California

40 Other Related Works in Lin Lab 2 Direct write graphene FET 2012 University of California

41 Transistors, Junctions & Devices n or p type FET & pn junction A complimentary inverter made of p-gfet and n- GFET (npn junction in this case) is constructed 2012 University of California