Organic nanocomposite structure tailored by controlling droplet coalescence during inkjet printing.

Inkjet printing offers a low-cost, high-throughput avenue for producing functional organic materials through rapid translation of desktop discoveries to industrial roll-to-roll processes. Here, we report a simple, but effective strategy to control droplet coalescence during inkjet printing, as a major variable, to tailor the nanoscale morphology of organic composite materials produced upon evaporation of all-liquid inks. During deposition, the spacing between ink droplets was controlled to systematically vary the extent of droplet coalescence. Our results show that decreasing coalescence increased the solvent evaporation rate, supersaturation of the solutes, and nucleation density of the precipitating organic crystals. This phenomenon was utilized to tailor the average size of pentaerythritol tetranitrate (PETN) crystals dispersed in an adhesive binder matrix from ~0.2 to upwards of 100 µm. The results suggest that controlling the extent of droplet coalescence can be used as an effective means to tailor the composite morphology of printed organic materials at the nanoscale.

Effects of disordered hemispherical micropatterns on Staphylococcus epidermidis biofilm formation.

Surfaces which have physical patterns in the scale of bacteria cells have been shown to influence the microorganism's adhesion and biofilm formation characteristics. Layer-by-layer self-assembly was utilized to create disordered hemispherical patterns on poly(dimethylsiloxane) with a feature size of 0.5 microm, 1.0 microm and 2.0 microm. The effects of pattern size on the retention and biofilm formation of Staphylococcus epidermidis were examined as a function of culture time. The 1.0 microm pattern significantly reduced biofilm surface coverage by approximately 30% after 5 h of culture in comparison to that on an unpatterned surface while the effect of the 0.5 and 2.0 microm patterns was negligible. On the 1.0 microm surface, bacteria initially adhered on the unpatterned areas of the disordered surface and subsequently developed into biofilms by spreading across the unpatterned areas while avoiding those covered by the pattern. The results suggest that the size of surface patterns is an important factor in altering bacteria adhesion and biofilm formation characteristics.