Lightweight Multifunctional Structural Materials: Near Term and Future Systems

1. Lightweight Multifunctional Structural Materials: Near Term and Future Systems Enrique V. Barrera Department of Mechanical Engineering and Materials Science Rice University Tuesday, May 17, 2010

2. Philosophy of Developing Advanced Materials With Nanotubes Nanotubes as Reinforcements Fully Integrated Nanotube Composites Time Dependent and Reversible Properties of Nanotubes Synergism Nanotubes as Templates for Advanced Properties

3. Air Force funded Ultra-high Strength produced by: Fully integrating nanotubes, Time dependent behavior, Synergistic interactions, and Use of nanotubes as templates. Numerous ideas developed in the field will likely be employed.

5. SWNTs as Ideal Reinforcements • Single-Walled Carbon Nanotubes tend to have < 4.0-wt.% metal impurities. • SWNT • SWNT Diameter ~ 1.2 nm • SWNT length ~ 1.0 - 10.0 mm • Tensile Strength > 100 GPa • Elastic Modulus ~ 1.4 TPa • Thermal Conductivity 1750 - 5800 W/mK • SWNT bundles ~ 10 - 100 SWNTs • SWNT bundle length 10.0 mm SEM TEM http://www.cnanotech.com

6. How should we go about it? Philosophy of Developing Advanced Materials With Nanotubes Calculations indicate that conventional composite materials development will not fully utilize the full potential of carbon nanotubes. To achieve a new ultra high strength material several engineering aspects of nanotubes must be learned. Fully Integrated Nanotube Composite Need for Functionalization and smart processing “Processing” w/VGCFs, SWNT Ropes, SWNTs Arrival at “Multi- Functional” applications We can produce conducting polymers, materials for thermal management, and multifunctional materials in route to high strength nanotube materials.

7. Typical composites construction based on the volume fraction rule. Note similarities in strain to failure. Usually the matrix fails after the fiber. However, Nanotubes have 5% elongation to failure. (1) Composite approaches throw away a significant contribution from the nanotubes. Analysis with this approach would produce a material with a 10,000% increase in *strength. Still a very good result but not fully using SWNT. (2) *ideal bonding along the nanotube. Composites Development is Not the Way to Go. Fiber Composite s Matrix e smax =50-150 GPa s E= 1 TPa SWNT sf(e) Epoxies: 1-2% elong. e

8. (2) Interfaces in Nanotube Composites Can we assume complete bonding? 1. Nanotubes can be looked at as either carbide formers or non carbide formers. 2. The interfacial area for nanotubes is four orders of magnitude larger than for micron size fiber reinforced composites (3000 cm2/cm3). 3. The interface can act as sites for nucleation of the polymer and, therefore, can influence crystallization and polymer matrix properties. 4. Furthermore, because of the nanotube sizes, the space between nanotubes is also very small (often times nanoscale). 5. The shear strength of the nanotube/matrix interface is 500 MPa, the shear strength of a rope is 6 MPa, and the normal stress of the interface is 23 MPa. 6. VGCFs and MWNTs can be functionalized at defect sites. For SWNT functionalization C bonds must be broken with care!! 7. Coatings are a future option. sN t

9. *The Critical Length of Nanotubes and Interface Strength What are the lengths of nanotubes? Ropes are microns long. sf(e) Critical length of a fiber Fiber strength lc Fiber diameter Matrix shear strength (assuming 20 MPa) Instead of tm , mP >> For strengthening. m Interface Friction P Shrinkage Pressure mP ≈ 1/10(tm ) *Assuming complete bonding. For polymers: (3) SWNTs are less than 0.3 mm long. NTs are not long enough!

13. Two Approaches: Use of designed functionalizations Highnanotube concentration composites

15. Conventional Polymer Composites Conventional Polymers Composite Laminates, etc. Hybrid Polymers, Block Copolymers And New Resins Self-assembly quantum Functionalization Nanotech Functionalization Chemistry Size Mechanical, Chemical, and Bio Assembly Bio-inspired Nanomaterials

17. O O H H O O H H H H C C H H C C C C H H H H C C C C H H C C H H 2 2 2 2 2 2 2 2 N N O H H C C C C H H C C H H 2 2 2 2 H C C H C H H H C C H H C C C C H H O O H H 2 2 2 2 2 2 O O H H N N Fully Integrated Nanotube Composite Sidewall amine functionalization of nanotubes using peroxide O O + HOCCH2CH2. CH2CH2C-OH O [CH2CH2-C-NH- -CH2- -NH2]n || || SWNT || A new curing agent Nanotubes become integral to the epoxy. The epoxy is (reformulated). Fully Integrated Nanotube Composite

18. No Nanotubes Present Interface delamination is common Clean fiber surface after debonding – poor interface Without SWNT Fractography of composites without nanotubes by SEM observation • Shear fracture failure is dominated by a high degree of fiber/matrix interfacial debonding in typical vinyl ester composites - a typical delamination failure in composite laminates with brittle resin system • Less resin deformation • Featured with smooth and clean fiber surface after interfacial debonding • Weak adhesion between matrix and fiber

19. Incipient Wetting of Nanotubes  SWNTs / Epoxy Spray Sizing • Procedure • Solvent / SWNTs / Epoxy • Spray on Fiber Reinforcements • Immediate Curing Epoxy with SWNTs & Solvent at one time SWNTs in Epoxy / Solvent Evaporating Solvent Curing on Surface Glass fiber mat Epoxy / SWNTs Sized glass fiber mat JongDae Kim

20. Pristine SWNT coated Resin adhesion on fiber and scalloped surface J. Zhu, et al.

21. Synergism for Mechanical Behavior • Maximum increase is obtained for 0.025% VGCF + 0.025% CNT • Possible synergistic effect.

22. 1.E+06 Unfilled PP 10% VGCF 30% VGCF 1.E+05 Pre sheared PP 20% VGCF 1.E+04 Viscosity* (Pa s) 1.E+03 1.E+02 0.01 0.1 1 10 100 1000 W (rad/sec) w/K. Lozano Nanotube Polymer Mixing High shear and moderate torque lead to high dispersion. Bench Mixing Banbury Spinning Change in viscosity shows the percolation threshold Shear thinning Similar behavior seen for clay, MWNT, and SWNT Composites

23. Complex Viscosity of All Samples Complex viscosity at 175°C of all the samples tested. Four ways to reduce process viscosity.

24. SWNT purification and functionalization Metals on Nanotubes: Copper Tin Gold Silver Nickel Powder Metallurgy Metal deposition on SWNTs Metal coated SWNTs dispersion Ni and SWNTs co-deposition Co deposition on SWNTs and fine diamond powder Composite Sintering Ni on NTs Disperse nickel coated SWNTs onto the fiber mat Drilling tool application Electromagnetic Levitation

25. EMI SE Results • 3X surface conductivity with 1 wt% SWNTs • 10X surface conductivity with 1 wt% Ni coated SWNTs • Higher mechanical properties expected from functionalized Ni coated SWNTs • Comparable EMI SE with and without Ni coating but can be improved with improved SWCNT coverage

26. EMI SE Test Results • Carbon fiber leads to 60 db EMI SE. • 1 wt% SWNT improved average SE by 33% • 3 wt% SWNT improved SE by 42% • Noise from non-homogeneity of the samples • Improved dispersion is important to obtain uniform SE • Near term application is directed toward improving surface conductivity

28. Lightweight Structures: Metals and Alloys: Titanium • Fractured surfaces reveal the presence of nanotubes. • SEM of fractured samples revel stable nanotubes in titanium that were processed in the melt (>1450ºC).

29. Comparison of TiO2 and TiC to TiSWNTs: Early Samples Ti oxide appears to be present. Ti carbide does not form

30. Stable and Dispersed NTs on Ti • Nanotubes survive the high temperature melt processing of titanium. No carbides or oxides occur. 39

31. Hardness: Structural Enhancement • Vickers Microhardness method • Strength increase with increasing nanotube content wt% Hard. %Increase 0 307 0.5 356 20 1.5 404 33 2.5 535 74 4.5 885 188 44

32. Nano enabled FIBER COMPOSITES: Top layer(s) for Lightning Strike Protection. Excellent mechanical properties in directions of the fiber (x and y axis). Mid-plane strengthening perpendicular to the fibers (z axis). Thermal management that is anisotropic. Sensing capabilities (distributed). y z x “System on Panel” POLYMER (Epoxy, Vinyl-ester, etc.) FRPC Unidirectional or Woven Fiber (Carbon Fiber, Glass Fiber, Kevlar, etc.)