Processing of loose carbon nanotubes into isolated, high density submicron channels.

Loose multi-wall carbon nanotubes (MWNTs) were processed into a bundle of 19,600 individual channels with an individual channel diameter of 0.4 microm using a fiber drawing process. First, a powder of sodium silicate solution containing purified MWNTs was created. A glass capillary tube was filled with the powder and drawn into fibers. The fibers were cut into segments, bundled and redrawn multiple times to create fibers with multiple channels containing MWNTs. This processing approach created thousands of uniformly ordered channels containing dispersed MWNTs in a glass matrix while simultaneously aligning the MWNTs. The bulk resistivity of the MWNT-silicate channel has been improved by 38% after two consecutive draws as a result of the increased MWNT fraction.

Effects of catalyst introduction methods using PAMAM dendrimers on selective electroless nickel deposition on polyelectrolyte multilayers.

We studied the effects of catalyst introduction methods using poly(amidoamine) (PAMAM) dendrimers on the nickel patterning of polyelectrolyte multilayer (PEM)-coated substrates. Three different approaches to palladium catalyst introduction using microcontact printing as the patterning technique were utilized and compared. The catalyst introduction methods are (1) direct catalyst stamping, (2) directed assembly using PAMAM dendrimer stamping, and (3) catalyst encapsulation and reduction to nanoparticles within PAMAM dendrimers before stamping. After patterning, the sample surfaces were placed in an electroless bath where nickel was selectively plated onto the patterns. The patterned surfaces were characterized using optical microscopy, atomic force microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The metal plating rates on different homogeneous surfaces that simulate the patterned surfaces were measured using a quartz crystal microbalance. In addition, the effect of PEM film thickness (i.e., number of bilayers) on the selectivity of nickel patterning was investigated.

Wrinkle-free nanomechanical film: control and prevention of polymer film buckling.

For the first time, we report on methods to control and prevent polymer films from buckling. Buckled morphologies were created by thermally cycling or mechanically compressing a poly(dimethylsiloxane) substrate coated with a polyelectrolyte multilayer film. By variation of the dimensions of the surface topography relative to the buckling wavelength (e.g., pattern size is less than, equal to, and greater than the buckling wavelength), the orientation and the local morphology of the buckled films were controlled. On the basis of the information obtained, we demonstrate how to alleviate the unavoidable buckling by incorporating nanoparticles into the film. In addition, we studied the effect of the silica layer that results from oxygen plasma treatment and the critical temperature for permanent film buckling.

Patterned and controlled polyelectrolyte fractal growth and aggregations.

Two-dimensional patterned and controlled polyelectrolyte aggregations (e.g., tree-like ramified structures) created by microcontact printing have been demonstrated and discussed. Polyelectrolyte-micropatterned aggregations on surfaces were controlled by the micropattern size and shape of PDMS stamps. The formation of aggregates was dependent on the ink and surface conditions, and the aggregates consisted of two distinct layers; strongly adsorbed, primary uniform layers and weakly adsorbed, secondary aggregation layers positioned on top of the primary layers. The adsorption of the primary layers was strong enough not to be washed away, while the aggregated secondary layers were easily removed by washing. The aggregation of secondary layers showed typical tree-like ramified structures of fractal growth and aggregation. Directional and confined stamping led to directing and confining the growth of the fractal polyelectrolyte clusters, respectively. The micropatterned primary uniform layers were not removed by extensive washing, and they were identified by selective nickel plating and charged particle selective adsorption in which the surface formed positive and negative micropatterns. These functional and patterned surfaces have great potentials for advanced devices and sensors.