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MEEN 489MEEN 489--502 502 Nanotechnology Issues in Nanotechnology Issues in ManufacturingManufacturing

Nanotechnology ConceptsNanotechnology Concepts28 October 200428 October 2004Dr. CreasyDr. Creasy

In this lecture we review the types of nanoparticles, platelets, and fibers of interest.

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Earth, Soccer, and C60Earth, Soccer, and C60

Earth d = 12.7 MmEarth d = 12.7 Mm

Soccer ball Soccer ball d = 0.22 md = 0.22 m

C60 d = 0.7 nmC60 d = 0.7 nm

101077/10/10--11 = 10= 1088

1010--11/10/10--99 = 10= 1088

We can check the scale of Buckminster Fullerene particles with this comparison:A regulation size soccer ball is 220 mm in diameter. The combination of hexagonal and pentagonal structures that form the soccer ball are identical to those that form a fullerene at the atomic scale. The diameter of the scoccerball compared to the diameter of the earth is approximately the same as the diameter of C60 compared to the scoccer ball.

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Early Report: Nanoparticle Early Report: Nanoparticle Hazards? (SMU, Dallas TX)Hazards? (SMU, Dallas TX)

Nanoparticle (fullerenes) effects on lipid Nanoparticle (fullerenes) effects on lipid peroxidationperoxidation in the brains of fish.in the brains of fish.

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Clean Water Fullerenes @ 0.5 PPM

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Althought fullerenes have not yet found an application. They are used to studythe effect of loose nanoparticles on living creatures.One recent university study found that fullerenes caused a rapid increase in the rate of tissue degradation in fish when present at 0.5 parts per million.

Studies like this one must be conducted in advance of large scale production of nanoconstituents.

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What is the Young’s Modulus What is the Young’s Modulus of a Carbon Nanotube?of a Carbon Nanotube?

5 TPa? (5000 5 TPa? (5000 GPaGPa))1 TPa? (1000 1 TPa? (1000 GPaGPa))720 720 GPaGPa at 9at 9--12% 12% StrainStrain

E = E = σσ//εε = FL= FL00/A/A∆∆LL

Pitch fiber 830 Pitch fiber 830 GPaGPa; ; 0.5% strain0.5% strainIM7 fiber 303 IM7 fiber 303 GPaGPa; ; 2% strain.2% strain.

The previous discussion concerned nanoparticles, that is, components that havenanoscale features in all three dimensions. If we keep a nanometer size in two

dimensions and let the third approach more familiar minron sizes, we wouldhave something like the carbon nanotube.Researchers are looking at possible electrical, chemical, and structural applications of carbon nanotubes. In the case of structural applications, we haveno clear determination of the modulus of a carbon nanotube! An early paperpresented a calculation of the Young’s modulus at 5 teraPascal. However, a subsequent analysis showed that, since one must define a cross sectional area. the first calculation had used a tube thickness that did not account for the cloudof electrons around the nucleus of each carbon atom. That analysis dropped theYoung;’s modulus to 1 teraPascal, which is still a tremendously stiff material.However, for those of us hoping to use nanotubes in composite materials, Pipesnoted that the tube does not fill up with resin as shown the lower left image.Since the fiber is empty, we must use the entire cross section instead of the wallthickness as the area. This drops the tube stiffness to 720 GPa. Large, but in thesame range as conventional carbon fibers. However, the strain to failure of the tubes are much larger so they might still be worth using.

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MontmorilloniteMontmorillonite ClaysClays

1 nm thick.1 nm thick.1 x 1 µm plate.1 x 1 µm plate.

Intercalation.Intercalation.

http://www.psrc.usm.edu/macrog/mpm/cohttp://www.psrc.usm.edu/macrog/mpm/composit/nano/struct2_1.htmmposit/nano/struct2_1.htm

Platelets: Nanoscale in 1 Platelets: Nanoscale in 1 Dimension and Microscale in a Dimension and Microscale in a PlanePlane

If we now allow two of the dimensions of our particles to reach micron size, we have a platelet. Clay particles have found some success in increasing the stiffness of thermoplastics. There is much work to do in effectively separating and distributing the platelets through the polymer.These clays are much like the solid here in College Station. They swell and shrink by great amounts as a fluid in introduced and removed. Each platelet is a ceramic structure that is about 1 nm thick. These are ionically bonded with a free space, which is called a gallery, between platelets.The platelets are separated by introducing oligimers (short chain polymers) thatare compatible with the clay at one end of the chain and compatible with the polymer along the chain and at the other chain end.

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Exfoliation Maximizes the Exfoliation Maximizes the EffectEffect

This slide shows exfoliated platelets. The short chains are swollen, perhaps bytreatment with solvents and the separated platelets can be blended with the matrix polymer.

The sketch of the oligimer at the lower right shows an end group with a net positive charge. This can bond ionically with a negatively charged site on the clay.

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Why Use Clay Platelets?Why Use Clay Platelets?

Adding 5 w/0 clay to Adding 5 w/0 clay to nylonnylon--6 provides 6 provides unique performance unique performance enhancement.enhancement.

40% higher tensile 40% higher tensile strengthstrength68% higher tensile 68% higher tensile modulusmodulusHeat distortion Heat distortion temperature temperature increased from 65° increased from 65° (nylon(nylon--6) to 152°C 6) to 152°C

And clay is cheap because it is dug from the ground.

If you want it, you can buy two rail car loads of clay tomorrow.

It could be a long time before two rail car loads of nanotubes are ever produced.

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Switch to PDF FileSwitch to PDF File

Problems in dispersion of Problems in dispersion of nanoparticlesnanoparticles..

The PDF file shows the problems in dispersing nanoscale components in a polymer melt.

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Polymer ActuatorsPolymer ActuatorsPeter Peter SommerSommer--LarsenLarsen

““Light, flexible, Light, flexible, noiseless actuators noiseless actuators with stroke, force and with stroke, force and efficiency similar to efficiency similar to --or better than or better than -- that that of human muscles; of human muscles; such is the promise of such is the promise of polymer actuators.”polymer actuators.”

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Why Polymers?Why Polymers?

Compared with Silicon Compared with Silicon Devices...Devices...Many cycles might be Many cycles might be possiblepossibleFlexibleFlexibleTailored compliance Tailored compliance = 1/stiffness= 1/stiffnessLess friction (beware Less friction (beware of sticky polymers)of sticky polymers)

Also, polymers could have a softer touch than metal or ceramic devices.

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A Thermally Actuated Polymer Micro Robotic GripperA Thermally Actuated Polymer Micro Robotic Gripperfor Manipulation of Biological Cellsfor Manipulation of Biological CellsHoHo--Yin Chan1 and Wen J. LiYin Chan1 and Wen J. Li

This polymer microactuator can grasp single cells without damaging them.

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Chan & Li Use µChan & Li Use µFabFabMethods to Make Methods to Make AcutatorAcutator

Combine metal and Combine metal and polymer on a silicon polymer on a silicon surface.surface.BimaterialBimaterial Strip: Use Strip: Use difference in thermal difference in thermal expansion to bend expansion to bend the strip.the strip.The polymer is The polymer is paryleneparylene, which is , which is vapor deposited vapor deposited dimerdimer..

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Polymer Flexure Adds Polymer Flexure Adds Function without Joints...Function without Joints...

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Capture of Capture of ZebrafishZebrafishEmbryoEmbryo

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Polymer Provides a Polymer Provides a Compliant Capture SurfaceCompliant Capture Surface

This system is thermally actuated. It is like a bimetallic strip. The activation temperature must be compatible with the cells studied.

As the size of the device grows smaller, we must use other means to activatethem. Electric motors and solenoids lose their effectiveness. For example, a solenoid must have a good number of turns of conductor in order to generate a driving force. As the component shrinks it becomes more difficultto make a coiled conductor.

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Why Dielectric Actuation?Why Dielectric Actuation?

Many elastomers Many elastomers have good dielectric have good dielectric strength and could strength and could provide actuation.provide actuation.

The issue is the The issue is the compliant electrode compliant electrode layer.layer.

However, small scales make electrostatic devices possible. Opposite charges on the top and bottom surfaces of a sheet of material have a large effect if the thickness of the sheet is small and the dielectric constant of the material is largeenough to support the charge density neeeded for actuation.

Also, recall that silicon based mems devices shown earlier in the semester aredriven by oscillating static charges on comb drives.

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Acrylic ElastomerAcrylic Elastomer

This acrylic elastomer extends to 4 times its initial width when it is compressedby an electrostatic charge.

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Maxwell Pressure for a Maxwell Pressure for a Compliant CapacitorCompliant Capacitor

For large pressure we need large For large pressure we need large dielectric constant and large electric field dielectric constant and large electric field strength in an elastomer.strength in an elastomer.

The pressure generated is equal to the product of the materials dielectric constant, the permittivity of free space, and the square of the electric field.

E, the electric field, is equal to the applied voltage V divided by the thicknessof the polymer sheet, z. Note that z is reduced by the actuation, so E rises, but it must never exceed the breakdown limit of the polymer.

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A Silicone Rubber ActuatorA Silicone Rubber Actuator

Pelrine et al. SiliconeElastic Energy Density (J/cm3) 0.22Maxwell Pressure (MPa) 1.36Strain (%) 32Young's Modulus (MPa) 1Electric Field Strength (V/µm) 235Dielectric Constant (1 kHz) 2.8

The electric field strength shows that devices must be a few microns think ifwe want to avoid using thousands of volts for the system.

The following finite element analysis demonstrates this scale effect.

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A 10 mm CubeA 10 mm Cube

Apply ±1 VApply ±1 V

Apply a 2 v differential charge at the top and bottom surfaces of a 10mm cubeof silicone will not provide any performance.

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Increase Voltage to Increase Voltage to ±1.175MV±1.175MV

The dielectric limit for a 10 mm cube would support an applied voltage of ±1,175,000 volts.

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Nodal ForcesNodal Forces

Range from 0.185 N Range from 0.185 N in the corners to in the corners to 0.685 N in the center.0.685 N in the center.

FEA shows that the forces generated at each node ranges from 0.185 ot 0.685 newtons.

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3D Symmetry Boundary 3D Symmetry Boundary ConditionsConditions

One plane each of X One plane each of X and Y symmetry.and Y symmetry.The bottom Z surface The bottom Z surface cannot move in Z.cannot move in Z.

We can look at the deformation of the cube when subjected to this greatelectric field. Symmetry conditions were set to keep the model stable in virtual space.

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PerformancePerformance

Compression Stress: Compression Stress: 0.67 MPa0.67 MPaMovieMovie---->>

10mm 10mm cube.avicube.avi

When the mesh was fully refined, the compression stress reach 670 kPa.The movie shows the deformation.

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Performance 1 mm thickPerformance 1 mm thick

MovieMovie1mm 1mm sheet.avisheet.avi

If we change the cube into a 10 mm by 10 mm by 1 mm thick sheet, we reduce the total voltage to ± 118 kV and get better performance.

The thickness is reduced by 69% and the sheet extends by 45%.

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ScalingScalingCell size Thickness Load Condition Displacement ZZ, XY Stress

(MPa)2.5 mm 10 mm -+1.175E6 V -6.09 mm (60%)

4.23 mm (42%)

-0.540

1 mm 10 mm -+1.175E6 V -6.75 mm (67%)

5.54 mm (55%)

-0.673

0.5 mm 10 mm -+1.175E6 V -6.82 mm (68%)5.85 mm (58%) -0.682

0.25 mm 1 mm ±117,500 V -0.686 mm (69%)2.24 mm (45%)

-0.685

25 µm 100 µm ±11,750 V -68.7 µm (69%)0.224 mm (45%)

-0.684

2.5 µm 10 µm ±1,175 V

0.25 µm 1 µm ±117.5 V

This table shows the results of the analysis. The first column is the mesh size in the finite element model. The second column is the thickness of the elastomer. The third column shows the maximum potential that we can applyto the elastomer at each thickness.

The fourth and fifth columns show the displacement in Z, X, and Y, and the generated stress.

The last two rows are left as a homework assignment.

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Gripper: Short ModelGripper: Short Model

±1175 V±1175 VFixed bottom surface.Fixed bottom surface.10 µm thick.10 µm thick.Movie:Movie:

Gripper1.aviGripper1.avi

We can start to design and analyze active devices that use this mechanism.

If we want to make a gripper that uses this activation method, we can combinethe electrostatic model with the elastic model and find the resulting behavior.

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Gripping ActionGripping Action

The movie shows the gripping action dynamically. However, further analysisis needed to find the effective gripping strength at the tips of the ‘fingers.’

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Bending CylinderBending Cylinder

1 mm diameter1 mm diameter10 µm thick active 10 µm thick active layerslayers

We can progress to more complex elements. Consider a complex extrusion ofa fiber that contains multiple electrostatic actuators. These are coextruded in meso to micro scale dies and then drawn down to smaller sizes if appropriate.

This cylinder contains four regions of actuation within an elastomer.

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Bending CylinderBending Cylinder

100 µm diameter100 µm diameter10 µm thick active 10 µm thick active layerslayers

These active regions may be powered in unison, in combination, or individually.

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500 µm Long Bending 500 µm Long Bending ElementElement

Places enough Places enough material away from material away from clamped BC to allow clamped BC to allow free motion.free motion.All elements All elements deactivated so that a deactivated so that a free element could be free element could be tested.tested.

A short length of this active filament cannot overcome a gripped end conditionand perform a function. However, at a length of 500 microns the cylinder canbend. Longer lengths would bend to a greater extemt.

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Trial ActivationTrial Activation

This model shows the effect of ‘firing’ a single actuator.

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Single Actuator ActiveSingle Actuator Active

Displacement is 0.124 mm.Displacement is 0.124 mm.Movie: Movie:

CylinderSingleActiveElement.aviCylinderSingleActiveElement.avi

The movie shows the displacement.

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Two Actuators Improve Two Actuators Improve BendingBending

Vector sum of deflections Vector sum of deflections increases magnitude of bending increases magnitude of bending by 42%by 42%Displacement is 0.172 mmDisplacement is 0.172 mmMovie:Movie:

CylinderTwoActiveElements.aviCylinderTwoActiveElements.avi

Two neighboring actuators generate more bending from the vector sum of the displacements.

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Four Actuators Extend the Four Actuators Extend the ElementElement

Element gets 8% Element gets 8% longer.longer.Displacement is Displacement is 0.040 mm0.040 mmCross section is Cross section is more rectangular.more rectangular.Movie:Movie:

CylinderFourActive.aviCylinderFourActive.avi

When all four actuators are charged the cylinder extends rather than bends.