Hongming Dong

An experimental study of drop-on-demand drop formation

The dynamics of drop-on-demand (DOD) drop formation have been studied experimentally using an imaging system with an interframe time of 1μs and a spatial resolution of 0.81μm∕pixel. Using a piezoelectrical actuated inkjet printhead with the nozzle orifice diameter of 53μm, experiments were conducted over a range of viscosities (1.0–5.0cP) and surface tensions (35–73mN∕m). The effects of the driving signal, which controls the piezoelectric transducer that produces the pressure pulse to drive the liquid from the reservoir through the orifice, have been examined along with those of liquid properties. The main stages of DOD drop formation, including ejection and stretching of liquid, pinch-off of liquid thread from the nozzle exit, contraction of liquid thread, breakup of liquid thread into primary drop and satellites, and recombination of primary drop and satellites, are analyzed based on the experimental results. The breakup time of liquid threads was found to be dependent mainly on the capillary time based...

Visualization of drop-on-demand inkjet: Drop formation and deposition

An apparatus developed for visualizing drop-on-demand (DOD) drop formation and impaction on substrates is described. Using a pulsed laser, a low-speed charge coupled device camera, and signal generators, an imaging system based on flash photography is shown to be able to obtain sharp images with a temporal resolution of 200ns and a spatial resolution of 0.81μm∕pixel. Several steps are taken to minimize the “first drop problem” so that excellent reproducibility is achieved; drop formation is reproducible with a positional variation of 1μm. The visualization system coupled with a motorized stage allows imaging of the impaction of micron-size drops on surfaces. A wave form generator and an amplifier are used to produce the required wave form for a given printhead and ejected liquid. Demonstration of the system for study of DOD micron-size drop formation and impaction on a substrate is presented. The effects of signal wave form on DOD drop formation are demonstrated using a Trident printhead driven by four di...

Waterborne oil-modified polyurethane coatings via hybrid miniemulsion polymerization

As part of a wider effort to develop a new class of waterborne coatings, hybrid miniemulsion polymerization was carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of oil-modified polyurethane resin. Latexes with different ratios of resin to acrylic monomers were synthesized. The monomer emulsions prepared for hybrid miniemulsion polymerization showed excellent shelf-life stability (>5 months) and the polymerization was run free of coagulation. Solvent extraction indicated that the grafting efficiency of polyacrylics was greater than 29% for all the samples produced. A 13C solution NMR spectrum showed that a substantial fraction of the original carbon double bonds (>61%) in oil-modified polyurethane remained after polymerization for film curing. Films obtained from the latexes presented good adhesion properties and fair hardness properties.

Drop-on-demand drop formation of polyethylene oxide solutions

The dynamics of drop-on-demand (DOD) drop formation for solutions containing polyethylene oxide (PEO) have been studied experimentally. Using a piezoelectrical actuated inkjet printhead with the nozzle orifice diameter of 53 μm, experiments were conducted for a series of PEO aqueous solutions with molecular weights ranging from 14 to 1000 kg/mol, polydispersity from 1.02 to 2.5, and concentrations from 0.005 to 10 wt. %. The addition of a small amount of PEO can have a significant effect on the DOD drop formation process, increasing breakup time, decreasing primary drop speed, and decreasing the number of satellite drops in some cases. The effects depend on both molecular weight and concentration. At lower molecular weights (14 and 35 kg/mol), the effect of PEO over the dilute solution regime is insignificant even at concentrations large enough that the solution does not fall in the dilute regime. As PEO molecular weight increased, the effects became significant. For monodispersed PEO solutions, breakup t...