Per Dahlsten

Surface energy patterning for inkjet printing in device fabrication

For application of device fabrication by inkjet printing, an accurate and high resolution patterning method is required. However, high resolution inkjet printing, which limited by the inkjet nozzles and the ink movements, is one of the most challenging issues at present. An enhanced control of ink flow and spread by surface energy patterning on substrates can be used to improve the resolution and quality of the inkjet printed devices. Our strategy is depositing a hydrophobic pattern on a hydrophilic substrate, and thereafter inkjet printing the functional ink on top of the surface energy pattern. High surface energy contrast patterns on polyimide were got by microcontact printing, which can make ink moving from hydrophobic area to hydrophilic polyimide substrate. Inkjet printed silver patterns with 15 μm thin gaps were obtained by the surface energy pattern. This visible and easy processing pattern can be used widely in inkjet printing for higher resolution, more precise pattern, and smaller devices.

Influence of long-term aqueous exposure on surface properties of plasma-sprayed oxides Cr2O3 and Cr2O3–25 wt% TiO2

The influence of water exposure on the surface properties of plasma-sprayed Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) was studied. It was shown that both plasma-sprayed materials contained Cr(VI) hydrous oxide phases, which dissolved rapidly at the beginning of water exposure. The dissolution continued slowly during the whole water exposure time. The Cr(VI) dissolution was accompanied by a rapid increase in surface IEP value. Both Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) showed similar dissolution, zeta potential, and surface oxidation states. Thus the addition of TiO(2) did not influence the surface properties of the plasma-sprayed Cr(2)O(3).

Electrokinetic behavior of melamine-formaldehyde latex particles at moderate electrolyte concentration.

The electrokinetic behavior of micrometer-sized melamine-formaldehyde latex particles in 10(-3)-10(-1)M monovalent electrolyte dispersions was investigated by electrophoresis and electroacoustics. Specific adsorption of the electrolytes was identified as a shift of the isoelectric point (pH(iep)) with an increased ionic strength. All salts had an equal dependence on the ionic strength. The pH(iep) was correlated with the anion sequence predicted by the hard-soft acid-base (HSAB) principle, Hofmeister series, and Born charging. The Born and the Hofmeister anion scale were successful in producing a systematic dependency of the isoelectric point (pH(iep)), particularly in high (10(-1)M) and low (10(-3)M) MF electrolyte dispersions. No clear trend could be found for the pH(iep) dependence on the anion HSAB scale.

Influence of charge exchange in acidic aqueous and alcoholic titania dispersions on viscosity.

Charging effects resulting from adsorption of acid, acid anions, and protons on titania (anatase) surfaces in anhydrous or mixed alcohol-water dispersions is summarized. The suddenly enhanced conductivity as compared to titania-free solutions has previously been modeled and explained as surface-induced electrolytic dissociation (SIED) of weak acids. This model and recently published results identifying concurrent surface-induced liquid (solvent) dissociation (SILD) are evaluated with experimentally determined conductivity and pH of solutions, zeta-potential of particles, and viscosity of dispersions. Titania (0-25wt%)-alcohol (methanol, ethanol, and propanol) dispersions mixed with (0-100wt%) water were acidified with oxalic, phosphoric, and sulfuric acids. It was found that the experimental results could in many cases be condensed to master curves representing extensive experimental results. These curves reveal that major properties of the systems appear within three concentration regions were different mechanisms (SILD, surface-induced liquid dissociation; SIAD, surface-induced acid dissociation) and charge rearrangement were found to be simultaneously active. In particular, zeta-potential - pH and viscosity - pH curves are in acidified non-polar solvents mirror images to those dependencies observed in aqueous dispersions to which hydroxyl is added. The results suggest that multiple dispersion and adsorption equilibria should be considered in order to characterize the presented exceptionally extensive and complex experimental results.

Interaction between oxalic acid and titania in aqueous ethanol dispersions.

The charging effects resulting from adsorption of oxalic acid and oxalate anions on titania (anatase) surfaces in anhydrous or mixed water-ethanol suspensions is summarized. The suddenly enhanced electrical conductance with respect to titania free solutions has previously been explained in terms of surface-induced electrolytic dissociation (SIED) of weak acids. A recently published model has previously been found to successfully characterize the complex SIED effect. The model is evaluated experimentally by recording the conductance and pH of the dispersion and the zeta potential of the particles. The experimental results can be condensed to master curves, which reveal the major properties of the systems and facilitate further modeling of extensive experimental results. The equilibrium and transport properties of solutions and particles were related, but different mechanisms was found to be active in each case. The results suggest that at least three adsorption equilibria should be considered in order to improve the model.

Surface Charge and Conductance in Dispersions of Titania in Nonaqueous and Mixed Solvents

The nature and speciation of ions, and their affinities to mineral surfaces are well-known for aqueous solutions, and less well-known for mixed water-organic and nonaqueous solutions. Weak acids show strong preferential adsorption of anions on titania, and support a high negative surface charge on titania particles in organic solvents in spite of the very low degree of dissociation of these acids. The interaction between solutions of weak acids in organic solvents and titania particles results in enhanced electrical conductance with respect to the original solutions (in the absence of titania). This phenomenon is explained in terms of surface-induced electrolytic dissociation of weak acids. In mixed water-organic solvents the conductance behavior gradually shifts from water-like behavior (titania depresses the conductance) to opposite behavior (titania enhances the conductance). A quantitative model was proposed to explain the complex effect of the electrolyte and titania concentration on the conductance of the dispersion and zeta potential of the particles.