Creation and Evaluation of Polymer/Multiwall Carbon Nanotube Films for Structural Vibration Control and Strain Sensing Properties

Multifunctional materials both with damping properties and strain sensing properties are very important. They promise to be more weight-efficient, and provide volume-efficient performance, flexibility and potentially, less maintenance than traditional multi-component brass-board systems. The goal of this dissertation work was to design, synthesize, investigate and apply polyaniline/Multiwall carbon nanotube (PANI/MWCNT) and polyurethane (PU) /MWCNT composites films for structural vibration control and strain sensors using free layer damping methods and static and dynamic strain sensing test methods. The PANI/MWCNT was made by in situ polymerization of PANI in the presence of MWCNT, then frit compression was used to make circular and rectangular PANI/MWCNT composite films. PU/MWCNT composites were made by the layer-by-layer method. Free end vibration test results showed both of PANI/MWCNT and PU/MWCNT have better damping ratios than each of their components. Static sensing test indicated that though there appears to be residual strain in both composite sensors after the load is removed, both the sensor and the foil strain gage react linearly when re-engaged. A drift test of the sensor showed that it is stable. The dynamic sensing test results showed that over the range of 10-1000 Hz, the PANI/MWCNT composite sensor was consistently superior to foil strain gage for sensing purposes since the highest peak consistently corresponded to the input frequency and was much higher, for example, at 20 Hz, 820 times higher than those of the strain gage. Using the same criterion, the PU/Buckypaper composite sensor was comparable to or superior to the foil strain gage for sensing purposes over the range of 10 Hz to 200 Hz. The relationship of loss factor, η, and beam coverage length, L1/L, is discussed for single sided and double sided attachment. For both PANI/MWCNT and PU/MWCNT, the loss factor, η, was found to increase as coverage length, L1/L, increases. The loss factor, η, was found to have a maximum as with coverage length, L1/L, as the coverage length continues to increase. The trend for double sided attachment was found to follow the trends discussed by Rao (2004) and Levy and Chen (1994) for viscoelastic material constrained damping