Ink-Drop Dynamics on Chemically Modified Surfaces

Measuring the Shape, Stiffness, and Interface Tension of Droplets with the Scanning Ion Conductance Microscope

Imaging and probing liquid-liquid interfaces at the micro- and nanoscale are of high relevance, for example, in materials science, surface chemistry, and microfluidics. However, existing imaging techniques are limited in resolution, average over large sample areas, or interact with the sample. Here, we present a method to quantify the shape, stiffness, and interface tension of liquid droplets with the scanning ion conductance microscope (SICM), providing submicrometer resolution and the ability to perform noncontact mechanical measurements. We show that we can accurately image the three-dimensional shape of micrometer-sized liquid droplets made of, for example, decane, hexane, or different oils. We then introduce numerical models to quantitatively obtain their stiffness and interface tension from SICM data. We verified our method by measuring the interface tension of decane droplets changing under the influence of surfactants at different concentrations. Finally, we use SICM to resolve the dissolution dynamics of decane droplets, showing that droplet shape exhibits different dissolution modes and stiffness continuously increases while the interface tension remains constant. We thereby demonstrate that SICM is a useful method to investigate liquid-liquid interfaces on the microscale with applications in materials or life sciences.

Three-Dimensional Morphology and Contour Quality of Conductive Lines Printed by High-Viscosity Paste Jetting

The utilization of high-viscosity paste jetting technology has the potential to significantly expand the range of available materials and enhance the three-dimensional forming efficiency compared to inkjet printing. In this study, the three-dimensional morphology and contour quality of lines printed using high-viscosity silver paste were investigated. Four types of lines were identified based on differences in the printing shape, and contour fluctuation evaluation indices were defined in both the transverse and longitudinal directions to establish quantitative distinction principles. Based on the research of inkjet printing, a modified theoretical model relating the dimensionless line width and droplet spacing was established considering the cross-sectional characteristics of the lines printed by high-viscosity paste jetting. With the establishment of mathematical models, distinction criteria between various line shapes were obtained and the printable range of uniform lines was determined. Finally, based on response surface methodology, the influences of single droplet jetting parameters, the line printing speed, and their interactions on the line contour fluctuation were analyzed. This study involved theoretical and experimental research on the line morphology and contour quality, which can provide support for control of the line printing quality in high-viscosity paste jetting technology.

Development of Binder-Free Pigment Inks for Direct Inkjet Printing on Cotton Fabric without Pretreatment

Inkjet printing technology is widely used in the textile digital printing application today though the current technology still requires pretreatment and postwashing procedures before and after printing. Additional chemical treatment generates a large amount of wastewater and complicates the process. Among the many potential approaches for reducing chemical waste, pigments with self-dispersing capability were prepared and formulated into binder-free inkjet inks that require no pretreatment or after-washing process when printing cotton fabrics. The new self-dispersing pigment inks were tested and evaluated on cotton fabrics. The distribution of particles was between 122.2 and 188.5 nm, and inks have excellent storage capability. Printed fabrics' light fastness and acid/alkali resistance are about grade 5, and printed cotton's washing and rubbing fastness are above grade 3. The mechanism and performance of ink drops were investigated by LF-NMR and ink-drop observation methods. This work provides a possible solution for reducing wastewater in the textile industry.