Date/Time: 04-03-2018 - Tuesday - 05:00 PM - 07:00 PM
Peter Knapp1 SungWoo Nam1 2 Cheol Park3

1, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
2, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
3, NASA Langley Research Center, Hampton, Virginia, United States

Soft, functional composites based on suspensions of nanoscale active elements embedded in a compliant matrix have potential to create a new class of mechanical, electrical and optical materials for use in actuators, stimuli-responsive materials, and structures with controlled mechanical properties. The primary limitation preventing the development of these materials is difficulty in integrating the active materials of interest with matrix materials with appropriate properties without compromising functionality. Boron Nitride Nanotubes (BNNTs), insulating analogues of carbon nanotubes, exhibit thermal, chemical, and mechanical stability, electroactive functionality, and radiation shielding ability; making them an ideal base for composites. Of particular interest are BNNT’s high strength, which may allow them to reinforce traditional soft materials, piezoelectric properties which allow them to be used as actuators, high band gap and dielectric properties which allow them to be used in optical nanostructures and anisotropic specific thermal conductivity. Unfortunately, as synthesized BNNTs take the form low density fluff that must be suspended in a matrix for use. Polydimethylsiloxane (PDMS), a silicon based organic polymer appears to be an ideal matrix material as it demonstrates high elasticity, permitting piezoelectric driven flexure, optical clarity, allowing it to be used in optical structures, and contrast in thermal and dielectric properties with BNNT allowing for development of anisotropic materials. To date, successful integration of BNNT’s and PDMS has not been realized due to the chemical incompatibility of the two materials. While the dispersion and hydrogen bonding solubility parameters of both BNNTs and PDMS are similar, the difference in polar values prevents BNNTs from dispersing in PDMS. We have overcome this limitation utilizing a co-solvent mixing procedure with tetrahydrofuran (THF) followed by simultaneous stirring and evaporation under a nitrogen purge. THF has an intermediate polar coefficient of solubility allowing the BNNTs and PDMS to begin to mix. Subsequent prolonged stirring accompanied with a slow nitrogen purge to remove THF and thicken the mixture produces a stable dispersion with varying concentrations (0.3 – 2 wt%) of BNNTs that can be cast into arbitrary forms. The resulting composites show no apparent clustering of BNNTs, which would compromise properties and demonstrate tunable, wavelength dependent optical absorption. Preliminary tension testing has yielded mixed results indicating an increase in ultimate tensile strength but decrease in Young’s modulus, opposite to what was expected with the addition of BNNTs to PDMS, further testing is being pursued to confirm and explain this effect. Future exploration of alignment and texturing of nanotubes as well as probing of electromechanical and thermal properties could yield a novel soft material composite for sensing and actuation.

Meeting Program

5:00 PM–7:00 PM Apr 3, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E