Micro/Nano Mechanical Systems Lab –Class#16Micro/Nano Mechanical Systems Lab –Class#16 Liwei Lin Professor, Dept. of Mechanical Engineering Co-Director, Berkeley Sensor and Actuator

Microsystems LaboratoryUC-Berkeley, ME Dept.

1Liwei Lin, University of California at Berkeley

Micro/Nano Mechanical Systems Lab – Class#16

Liwei Lin

Professor, Dept. of Mechanical Engineering Co-Director, Berkeley Sensor and Actuator CenterThe University of California, Berkeley, CA94720

e-mail: [email protected]://www.me.berkeley.edu/~lwlin



Outline

The rest of the semesterNear-field Electrospinning


3/8 – Other possible MEMS/NEMS labs3/13 – 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 quiz4/10 – quiz4/12 – quiz solution4/17, 4/19, 4/24, 4/26 – final presentations

Rest of the Semester



Outline

Electrospinning - OverviewNear-Field ElectrospinningApplicationsPVDF Nanogenrators


Liwei Lin, University of California at Berkeley

ElectrospinningMechanical spinning Electrospinning – early

patent in 1934

SpinningSpinning

10―30 KV

Syringe

PolymersolutionNeedle

Collector

10―50 cm

Stretching

Whipping

Random, ContinuousNanofiber < 50nm



What are the Limitations? Diameter of nanofiber

Alignment

Thinner fibersThinner fibersLonger distance,

Lower concentration,Higher conductivity

Longer distance,Lower concentration,Higher conductivity Higher VoltageHigher Voltage

WhippingWhipping

D. Li et al, 2004D. Li et al, 2004 J. Kameoka et al, 2004

J. Kameoka et al, 2004A. Theron et al, 2001A. Theron et al, 2001



Near-Field Electrospinning Electrode-to-collector distance: 500–1000mDrive voltage: 600–1500 VTip diameter: 25 m or smaller

Collector

High Voltage

Probe Tip

Polymer Solution

Liquid Jet h



Results & Limitations 3~7 wt % Polyethylene oxide (PEO)Nanofiber diameter: 50nm– 2mManual control



Potential Machine-controlled electrospinning



Comparisons Conventional Electrospinning Near-Field

Needle Spinneret Metal probe tip

Several hundred µm Spinneret Diameter 25 µm or smaller

Continuous supply Polymer Supply Dip pen

10–30 KV Applied Voltage As low as 600 V

Very long Nanofiber Length Several cm

10–50 cm Electrode-to-collector Distance 500–1000 µm

Controllability


Continuously NEFS SetupDirect writing of large area patterns

• Steel needle with 70m opening• Modified NFES process

ModifiedModifiedOriginalOriginal




Continuous NEFS ResultsDirect writing of large area patterns (last week)



Large Area Deposition• 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

100m100m



Application (I) - NanoSensorsDirect-write suspended nanofibers on MEMS

conductive polymer by NFES

conductive polymer by NFES

-6.00

-4.00

-2.00

0.00

2.00

4.00

6.00

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

Bias [V]

Curr

ent [

μA]

100nm Nanofiber



Application (II) - NanoAssemblyDirect-write patterning of nanoparticles

Mixing nanoparticles in nanofibers

Mixing nanoparticles in nanofibers

Removing nanofibers and growing nanowires/tubesRemoving nanofibers and growing nanowires/tubes

5 & 20nm Au nanoparticles



Application (III) – Fluidic ConnectorDirect-write fluidic connector (analogy to wire

bonding)

3h

h



Fabrication ProcessConformal coating of fluidic channel material after

electrospinning & remove sacrificial nanofiber by etching or evaporation

A B

C D

Sacrificial PEO nanofiber

Chip ChipChip Chip

Coat Hydrophilic & Channel

Chip Chip

Open etch holes

Chip ChipChip Chip

Remove nanofiber

Chip ChipChip Chip



Fabrication ResultsSuspended nanofiber

overhanging two separated chips with Parylene coating

Suspended nanofibersSuspended nanofibers

Chip

Chip Nanofiber

Parylene coatingParylene coating

Chip

Nanofiber

Parylene



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.

SUNY – Stony Brook

Murine calvaria cells (MC3T3-E1) seeded onto an electrospunPLLA + collagen

Ordered nanofiber by NFES might lead to preferred cell growth & differentiation, localized control, functional tissue?



Application (V) - Composites Embedded high-modulus fibrous materials (e.g., glass

fibers, carbon fibers, carbon nanotubes) for material reinforcement

Embedding sensors & drug carriers.



Other ApplicationsFiltration, sensing, …

©2012 University of California

Electrospun Piezoelectric Nanogenerators

Prof. Liwei Lin

Berkeley Sensor and Actuator CenterDepartment of Mechanical Engineering

University of California, Berkeley


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




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)

Polar phase(After NFES)

Net dipole moment

Carbon Fluorine Hydrogenomitted



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


PVDF Nanogenerator• Fabrication process

– Spacing between electrodes: 100~500m– Fiber diameter: 500nm~3m

• Experimental setup– Inside a Faraday cage

(Not to scale)

Plastic

substr

ate

Electro

de

Plastic

substr

ate

Electro

de

A BSyringe needle

HighVoltagePolymer jet

Substrate moving direction

High Voltage

Substrate moving direction

Poling axis

(NFES direction)


Mechanism ‐ Piezoelectric Response

1. Start stretching2. Hold stretching

3. Start releasing4. End of release

V‐V+

+ ‐

RL

RL1.

2.

i

V‐V+

RL

3.

_ +

RL

4.

i

_ +

CNG

RNGqRL

V+

V‐

i


-4-3-2-101234

0 1 2 3 4Time (sec)

Cur

rent

(nA

)

-300

-200

-100

0

100

200

300

Cha

rge

(pC

)

Fast strain rate (0.04 sec)

Slow strain rate (0.10 sec)

0.17 sec 0.33 sec

Effect of Strain Rate• The current generated by strain in poling direction

d33:piezoelectric constant E: Young’s modulus A: cross sectional area

– Current output depends on strain rate– Charge depends on applied strain

33i q d EA


Effect on Stretching Frequency• Higher frequency → Higher electric output

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

0 10 20 30 40Time (sec)

Cur

rent

(nA

)

2 Hz 3 Hz 4 Hz

Stretching

Release

-20

-15

-10

-5

0

5

10

15

0 10 20 30 40Time (sec)

Volta

ge (m

V)

2 Hz 3 Hz 4 Hz

Stretching

Release


Validation of Piezoelectric Response• Different materials under the same experimental setup

‐40

‐30

‐20

‐10

0

10

20

30

40

0 10 20 30 40

Voltag

e (m

V)

Time (sec)

Stretching

Release

PVDF single nanofibers

‐10

‐5

0

5

10

0 10 20 30

Voltag

e (m

V)

Time (sec)

Stretching

Release

PEO nanofiber

‐10

‐5

0

5

10

0 10 20 30

Voltag

e (m

V)

Time (sec)

Stretching

Release

PVDF random nanofibers mats


Long Term Stability Test• 0.04% strain applied at a frequency of 0.5Hz for 100 min

-6

-4

-2

0

2

4

2409 2414 2419 2424

Time (sec)

Cur

rent

(nA

)

-15

-10

-5

0

5

10

15

1421 1426 1431 1436

Time (sec)

Volta

ge (m

V)

-15

-10

-5

0

5

10

15

0 20 40 60 80 100

Time (min)

Volta

ge (m

V)

-6

-4

-2

0

2

4

0 20 40 60 80 100

Time (min)

Cur

rent

(nA

)


High Energy Conversion Efficiency?• Energy conversion efficiency

We/Wm• Total electric energy generated during stretching

We= VI dt• Total elastic energy applied during stretching

Wm= 1/8D2L0E2

0

5

10

15

20

25

0 50 100 150Film thickness (μm)

Ener

gy c

onve

rsio

n ef

ficie

ncy

(%)

0 2 4 6 8Fiber diameter (μm)

PVDF FilmPVDF fiberPVDF fiberPVDF Film

-0.5

0.0

0.5

1.0

1.5

2.0

0 0.25 0.5 0.75 1Time (sec)

Volta

ge (m

V)

-0.5

0

0.5

1

1.5

Curr

ent (

nA)

VoltageCurrent


Other Related Works in Lin Lab ‐ 1

3D Electrospinning


Fabrication Results – grid patterns

3D Electrospinning


Cylinder & Flower

Wall width


Other Related Works in Lin Lab ‐ 2Direct‐write graphene FET


Transistors, Junctions & Devicesn or p type FET & pn junction

A complimentary inverter made of p-GFET and n-GFET (npn junction in this case) is constructed

Documents

Micro/Nano Mechanical Systems Lab –Class#16Micro/Nano Mechanical Systems Lab –Class#16 Liwei Lin Professor, Dept. of Mechanical Engineering Co-Director, Berkeley Sensor and Actuator