Abstract
Protective applications in extreme environments demand materials with superior modulus, strength, and specific energy absorption (SEA) at lightweight. They must also have the ability to attenuate intense stress waves and absorb kinetic energy from impact while providing thermally stable functionality. However, these properties typically have a trade-off. Hierarchically architected materials—such as the architected vertically aligned carbon nanotube (VACNT) foams—offer the potential to overcome these trade-offs and achieve synergistic enhancement in mechanical properties because of their multiscale origins of bulk properties derived from structural features that span nano to millimeter scales. Such architected materials with complex hierarchical structures require careful investigation of the effects of multitier design parameters and their interactions on the resultant bulk mechanical properties. Here, we adopt a full-factorial design of experiments (DOE) approach to identify an optimal set of design parameters to achieve synergistic enhancement in SEA, compressive strength, and modulus at lightweight in VACNT foams with mesoscale cylindrical architecture. We exploit size effects from geometrically-confined synthesis and highly interactive morphology of the CNTs to enable higher-order design parameter interactions that intriguingly disrupt the diameter-to-thickness (D/t)-dependent scaling laws found in common architected materials having steel and composite tubular structures. We show that exploiting complementary hierarchical mechanisms in architected material design can lead to superior and synergistic enhancement of mechanical properties and performance desirable for extreme protective applications.
| Original language | English |
|---|---|
| Article number | 101899 |
| Journal | Extreme Mechanics Letters |
| Volume | 57 |
| DOIs | |
| State | Published - Nov 2022 |
| Externally published | Yes |
Funding
This research is supported by the U. S. Office of Naval Research under PANTHER program, United States award number N000142112044 through Dr. Timothy Bentley. We also acknowledge partial support from the Army Research Office, United States award number W911NF2010160 through Dr. Denise Ford. The authors acknowledge the use of facilities and instrumentation at the Wisconsin Centers for Nanoscale Technology (WCNT) partially supported by the National Science Foundation (NSF), United States through the University of Wisconsin Materials Research Science and Engineering Center, United States ( DMR-1720415 ). We thank all the staff of WCNT, particularly Mr. Quinn Lenord for his assistance in photolithography. This research is supported by the U. S. Office of Naval Research under PANTHER program, United States award number N000142112044 through Dr. Timothy Bentley. We also acknowledge partial support from the Army Research Office, United States award number W911NF2010160 through Dr. Denise Ford. The authors acknowledge the use of facilities and instrumentation at the Wisconsin Centers for Nanoscale Technology (WCNT) partially supported by the National Science Foundation (NSF), United States through the University of Wisconsin Materials Research Science and Engineering Center, United States (DMR-1720415). We thank all the staff of WCNT, particularly Mr. Quinn Lenord for his assistance in photolithography. First, a standard 100 mm diameter (100 crystal orientation) p-type silicon wafer was spin-coated with 10μm thick S1813 photoresist at 3000 rpm for 30 s and pre-baked on a hot plate at 110°C for 45 s to remove any solvents. After spin coating, the wafer was partially diced through the thickness (30% of the thickness of the wafer) into 5mm×5mm squares. Next, the diced wafer was exposed to ultra-violet (UV) light through a chrome/soda-lime photomask to transfer the micropattern. The photomask is designed with cylindrical micropatterns of various combinations of Din, t, and g and manufactured by Photo Sciences (Torrance, CA). After 8 s of exposure with 405 nm UV light (exposure dose of 10mW/cm2), the unexposed photoresist is removed in the 30 s MF321 developer bath. After the developer bath, a 20 nm chromium thin film is evaporated using a metal evaporator. The remaining photoresist (exposed to UV light previously) is removed in an acetone bath, leaving a chromium film on the substrate, which prevents the growth of CNTs in the designated areas on the substrate (inverse of the architecture). We synthesize architected VACNTs on diced patterned substrates using a floating catalyst thermal chemical vapor deposition (tCVD) process. We use a syringe pump to inject a feedstock solution of ferrocene (catalyst precursor) in toluene (carbon source) ([w/v]=0.01g/ml) at a rate of 0.8 ml/min into a furnace tube maintained at a temperature of 827°C (1100K). A mixture of argon (95%) and hydrogen (5%) flowing at 800 sccm carries toluene vapors inside the furnace, where nanotubes grow on the patterned silicon wafer. After synthesis, we remove the architected VACNT film from the furnace and cut it into squares of 5mm×5mm—each square having an architecture with a specific combination of Din, t, and g—for mechanical characterization.
Keywords
- Architected materials
- Design of experiments
- Property conflict
- Size effects
- Structural hierarchy
- Vertically aligned carbon nanotube foams
