Sung-Goo Lee

Bundling dynamics regulates the active mechanics and transport in carbon nanotube networks and their nanocomposites

High-density carbon nanotube networks (CNNs) continue to attract interest as active elements in nanoelectronic devices, nanoelectromechanical systems (NEMS) and multifunctional nanocomposites. The interplay between the network nanostructure and its properties is crucial, yet current understanding remains limited to the passive response. Here, we employ a novel superstructure consisting of millimeter-long vertically aligned single walled carbon nanotubes (SWCNTs) sandwiched between polydimethylsiloxane (PDMS) layers to quantify the effect of two classes of mechanical stimuli, film densification and stretching, on the electronic and thermal transport across the network. The network deforms easily with an increase in the electrical and thermal conductivities, suggestive of a floppy yet highly reconfigurable network. Insight from atomistically informed coarse-grained simulations uncover an interplay between the extent of lateral assembly of the bundles, modulated by surface zipping/unzipping, and the elastic energy associated with the bent conformations of the nanotubes/bundles. During densification, the network becomes highly interconnected yet we observe a modest increase in bundling primarily due to the reduced spacing between the SWCNTs. The stretching, on the other hand, is characterized by an initial debundling regime as the strain accommodation occurs via unzipping of the branched interconnects, followed by rapid rebundling as the strain transfers to the increasingly aligned bundles. In both cases, the increase in the electrical and thermal conductivity is primarily due to the increase in bundle size; the changes in network connectivity have a minor effect on the transport. Our results have broad implications for filamentous networks of inorganic nanoassemblies composed of interacting tubes, wires and ribbons/belts.

Thermally conductive polyamide 6/carbon filler composites based on a hybrid filler system

Abstract We explored the use of a hybrid filler consisting of graphite nanoplatelets (GNPs) and single walled carbon nanotubes (SWCNTs) in a polyamide 6 (PA 6) matrix. The composites containing PA 6, powdered GNP, and SWCNT were melt-processed and the effect of filler content in the single filler and hybrid filler systems on the thermal conductivity of the composites was examined. The thermal diffusivities of the composites were measured by the standard laser flash method. Composites containing the hybrid filler system showed enhanced thermal conductivity with values as high as 8.8 W (m · K)−1, which is a 35-fold increase compared to the thermal conductivity of pure PA 6. Thermographic images of heat conduction and heat release behaviors were consistent with the thermal conductivity results, and showed rapid temperature jumps and drops, respectively, for the composites. A composite model based on the Lewis–Nielsen theory was developed to treat GNP and SWCNT as two separate types of fillers. Two approaches, the additive and multiplicative approaches, give rather good quantitative agreement between the predicted values of thermal conductivity and those measured experimentally.

Preparation and Characterization of Expanded Graphite Intercalation Compound/ UV-Crosslinked Acrylic Resin Pressure Sensitive Adhesives

The expanded graphite intercalated compound (xGIC)/pressure sensitive adhesives (PSAs) were prepared by syrup process and in situ process. The effects of xGIC filler on the morphology and property of acrylic resin based UV-crosslinked PSA were investigated. The xGICs showed more uniform dispersion in acrylic matrix and the degree of filler connection was more prominent in the syrup process than in situ process. The peel strength and tackiness of UV-crosslinked PSAs were strongly dependent on the amount of the filler and the peel strength decreased with increasing xGIC. The thermal conductivity of PSAs was explained in terms of filler dispersion, wetting, and matrix infiltration. The thermal conductivity of PSA was 0.46 W/mK by adding 20 wt% of xGIC, which was 287% improvement compared to the unfilled PSA. It is speculated that 2-dimensional xGIC fillers effectively formed the thermal pathway.

Pressure-Sensitive Adhesive Composites with a Hydrophobic Form of Graphene Oxide for Enhanced Thermal Conductivity

Pressure-sensitive adhesive (PSA) composites containing oleylamine functionalized graphene oxide (OA-f-GO) fillers were prepared. The effects of the surface modification of graphene oxide (GO) on the morphology of the PSA composites and on its thermal and adhesive properties were investigated. In contrast to GO fillers, the OA-f-GO fillers were found to be uniformly dispersed in the PSA matrix without any agglomeration and voids. The hydrophobization of GO resulting from the oleylamine functionalization improved the compatibility of the GO sheets with the PSA matrix. The thermal conductivity of the OA-f-GO (5 wt%)/PSA composites at UV energy of 2,000 mJ/cm2 was 55%, 140%, and 300% greater than the thermal conductivities of the OA-f-GO (5 wt%)/PSA composites, GO (5 wt%)/PSA composites, and bare PSA at UV energy of 800 mJ/cm2, respectively. In addition, the higher peel strength of the OA-f-GO/PSA composites compared to that of the GO/PSA composites was explained by the better wetting of hydrophobic OA-f-GO fillers in the PSA matrix.