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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 23: Complex Fluids and Soft Matter 1 (joint session DY/CPP)

CPP 23.1: Vortrag

Mittwoch, 7. September 2022, 09:30–09:45, H18

Writing in Water — •Thomas Palberg and Nadir Möller — Institut für Physik, Johannes Gutenberg Universität Mainz

Writing is an ancient cultural technique, typically performed by leaving some trace in or on a solid surface. We here explore the possibilities of leaving the trace in a liquid medium close to a surface and obtain lines or letters with high contrast and durability. Ion exchange (IEX) resin beads are used as mobile proton or hydroxyl ion sources. Moving them across the substrate in low-salt water, leaves a pH trace. Added autonomously swimming particles are able to follow this trace, mimicking hunter and prey dynamics or mate tracing, but without leaving a visible testimony. Written lines are realized by adding larger amounts of micron-sized passive particles, which settle to the like-charged substrate. Being phoretically drawn to or repelled from the pH traces, they form a well-visible trail behind the source. Trails of cationic IEX are white on black, those of anionic IEX are black on white. Their diffusive fading is slowed by continued phoretic flows and trails are stable up to hours. Sources moving autonomously just scribble. Sources propelled straight by gravity leave high-contrast lines. Deliberate tilting sequences for the substrate, then, facilitate writing.