Nano shish kebabs control pore size in buckypaper
18 Feb 2012
1
The shish kebab purportedly originated in medieval times when soldiers from Iran grilled meat on their swords over open fires. Now materials researchers from Drexel University in Philadelphia, Pennsylvania, have adapted the concept of the shish kebab on the nanoscale to control the pores size in ''buckypaper.''
Traditional buckypaper consists of a thin film of pure carbon nanotubes.
''We decorate a pure carbon nanotube with a polymer single crystal so that each tube will turn into a shish kebab,'' says Christopher Li, of the A J Drexel Technology institute. ''We use the carbon nanotube as the shish [skewer], and we put a kebab [polyethylene single crystal] on it at various intervals, and we use these nanostructures to make buckypaper with a controlled pore size.''
They call the product nanohybrid shish kebab (NHSK) paper.
Traditional buckypaper is porous, but the pores are so small that doping the paper with functional groups to make it more electrically conductive is limited. This makes it less than ideal as a material for use in batteries and supercapacitors - applications for which buckypaper is being investigated.
With NHSK paper, the kebabs serve as spacers to separate the carbon nanotubes; pore size is controlled by the spacers, which opens up the range of functional groups that can be placed in the pores to enhance conductivity.
The researchers fabricated the NHSK paper by ultrasonication of single-walled carbon nanotubes SWCNTs) in dichlorobenzene to separate the SWCNTS from the entangled bundles in which they usually reside.
Polyethylene pellets were dissolved separately in dichlorobenzene and mixed with the SWCNT solution at 130°C. When cooled to 88.5°C, the polyethylene crystallised onto the SWCNTs to form the shish kebab precursor units. Free-standing NHSK paper resulted after filtering, rinsing, and drying in a vacuum dessicator for two days. For five batches with varying polyethylene contents, the average polyethylene kebab crystal diameter ranged from 17 to 94 nm, and the mean spacing between the kebabs was 35 to 68 nm.
This study, reported recently in ACS Nano, showed that conductivity of the NHSK paper increased with increasing wt per cent of SWCNTs, ranging from a conductivity of 2.64 S/cm for 13 wt per cent SWCNTs to 1930 S/cm for 100 wt per cent SWCNTs. An average pore size of 31 nm was measured for kebab-crystal spacing of approximately 50 nm.
''You can put different functional groups within the pores so you can do nano-electrochemistry - without these pores your options are limited,'' Li says.
Of particular interest in this stage of the research was the wetting angle in contact with water, which reached 152.3 degrees for a 25 wt per cent SWCNT paper, making it superhydrophobic. Li says that the superhydrophobicity could enable the researchers to control the charging speed of batteries.
''This research shows that we can use this shish-kebab instead of the carbon nanotube itself to build a three dimensional membrane with controlled pore size, so this opens up a whole playground for using it for electrochemical devices,'' Li concludes.
Traditional buckypaper consists of a thin film of pure carbon nanotubes.
''We decorate a pure carbon nanotube with a polymer single crystal so that each tube will turn into a shish kebab,'' says Christopher Li, of the A J Drexel Technology institute. ''We use the carbon nanotube as the shish [skewer], and we put a kebab [polyethylene single crystal] on it at various intervals, and we use these nanostructures to make buckypaper with a controlled pore size.''
They call the product nanohybrid shish kebab (NHSK) paper.
Traditional buckypaper is porous, but the pores are so small that doping the paper with functional groups to make it more electrically conductive is limited. This makes it less than ideal as a material for use in batteries and supercapacitors - applications for which buckypaper is being investigated.
With NHSK paper, the kebabs serve as spacers to separate the carbon nanotubes; pore size is controlled by the spacers, which opens up the range of functional groups that can be placed in the pores to enhance conductivity.
The researchers fabricated the NHSK paper by ultrasonication of single-walled carbon nanotubes SWCNTs) in dichlorobenzene to separate the SWCNTS from the entangled bundles in which they usually reside.
Polyethylene pellets were dissolved separately in dichlorobenzene and mixed with the SWCNT solution at 130°C. When cooled to 88.5°C, the polyethylene crystallised onto the SWCNTs to form the shish kebab precursor units. Free-standing NHSK paper resulted after filtering, rinsing, and drying in a vacuum dessicator for two days. For five batches with varying polyethylene contents, the average polyethylene kebab crystal diameter ranged from 17 to 94 nm, and the mean spacing between the kebabs was 35 to 68 nm.
This study, reported recently in ACS Nano, showed that conductivity of the NHSK paper increased with increasing wt per cent of SWCNTs, ranging from a conductivity of 2.64 S/cm for 13 wt per cent SWCNTs to 1930 S/cm for 100 wt per cent SWCNTs. An average pore size of 31 nm was measured for kebab-crystal spacing of approximately 50 nm.
''You can put different functional groups within the pores so you can do nano-electrochemistry - without these pores your options are limited,'' Li says.
Of particular interest in this stage of the research was the wetting angle in contact with water, which reached 152.3 degrees for a 25 wt per cent SWCNT paper, making it superhydrophobic. Li says that the superhydrophobicity could enable the researchers to control the charging speed of batteries.
''This research shows that we can use this shish-kebab instead of the carbon nanotube itself to build a three dimensional membrane with controlled pore size, so this opens up a whole playground for using it for electrochemical devices,'' Li concludes.
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