Bounphanh Tonpheng

Microstructural and property changes in high pressure treated carbon nanotube/polybutadiene composites

In a comprehensive investigation of carbon nanotube (CNT) filled liquid and solid polybutadienes of molecular weights 2600 and 100000, respectively, we report results of thermal conductivity (κ), glass transition temperature (Tg), interfacial interaction and microstructure before and after simultaneous high-pressure and high-temperature (HP&HT) treatment. The HP&HT treatment changed polybutadiene from a liquid or solid to a highly cross-linked, ebonite-like, state. Concurrently, the microstructure changed from randomly dispersed CNTs to a web-like structure of coated and/or wrapped CNTs, with a permanent shift in their D*-band by as much as ∼16 cm−1. Moreover, κ of the recovered state of a 2.9 wt% –COOH functionalized multi-wall carbon nanotube (MWCNT) composite increased by ∼34% predominantly due to an irreversible densification and a consequentially increased phonon velocity. Results prior to treatment show that single-wall carbon nanotube (SWCNT) fillers promote κ better (17%/wt%) than –SH functionalized MWCNT fillers (8%/wt%), which is accounted for by their higher aspect ratio, whereas their about twice as high κ appears to be unimportant. The SWCNTs also raise Tg slightly more than MWCNTs and, in particular, under the most densified conditions and for the high molecular weight polybutadiene, which may be due to more favorable conditions for coating/wrapping.

Thermal Conductivity and Heat Capacity of a Nylon- 6/Multi-wall Carbon Nanotube Composite Under Pressure

The thermal conductivity, κ, of nylon-6 increased 22% whereas the heat capacity per unit volume, ρcp, decreased 10% by adding 2.1 wt% Multi-Wall Carbon Nanotubes MWCNTs. Simultaneously, the glass t ...

Polyisoprene single-wall carbon nanotube composites synthesized under high pressure

The mechanical and thermal properties of high-pressure-synthesized composites of polyisoprene (PI) and single-walled carbon nanotubes (SWCNTs) (1 wt%) have been measured using a tensile tester and the transient hot-wire method. PI–SWCNT composites were prepared by ultrasonic mixing in toluene to obtain good dispersion of the nanotubes within the polymer matrix, which was verified by atomic force microscopy. The mixtures were dried for several days under dynamic vacuum and subsequently treated at a high pressure (∼0.5 GPa) and temperature (513 K) to improve the SWCNT–polymer interaction. As a result of the high-pressure treatment, PI becomes crosslinked, yielding an elastomeric PI–SWCNT composite. Preliminary results show that the tensile strength and Youngs modulus of the composite are 2.8 and five times higher, respectively, than those of pure high-pressure-treated PI, and that the thermal conductivity increased ∼30% by adding 1 wt% SWCNTs.

In situ high-pressure vulcanization and thermal properties of polyisoprene

Liquid cis-1,4-poly(isoprene) (PI) has been vulcanized under high pressures without using additives. Moreover, the thermal conductivity and heat capacity per unit volume of both unvulcanized (liquid state at room temperature) and vulcanized (rubbery state) PI have been measured, and found to be the same in both states. However, the relaxation behavior associated with the glass transition differs. The unvulcanized PI exhibits two clearly resolved relaxation processes near the glass transition whereas these tend to combine into one process in the vulcanized PI. Moreover, at the same pressure temperature co-ordinate, the relaxation time of the vulcanized sample (∼1 s at 220 K at atmospheric pressure) is longer than that of the unvulcanized sample.