For 1st time, scientists write words in liquid water

As a matter of fact,

I'll be reading at the Decatur GA Oublic Library on the 19th as the 5th reader in the Written in Water series.

Scientists used a process called 'diffusioosmosis' to write words that lingered in liquid water. Scientists have discovered a way to write directly into liquid water, creating clear and long-lasting patterns which float below the surface of the fluid.



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Breaking barriers in communication! Scientists achieve a remarkable feat by writing words in liquid water for the first time. This groundbreaking accomplishment could revolutionize various fields, from data storage to environmental monitoring. Imagine the possibilities for transmitting messages in water-rich environments or even underwater communication networks. This discovery is not just a drop in the ocean; it's a wave of innovation, fit for a king WhatsApp era of connectivity.

See: https://arxiv.org/abs/2304.05357
Traditional writing techniques comprise carving and engraving as well as printing and writing with ink. Earliest human drawings date back some 30 000 years, possibly even much longer.1] As a visible language, writing appeared in the Middle East between 3400 and 2600 before the Common Era.2, 3] These techniques continue to coexist as means of storing and transporting information, nowadays accompanied by various multimedia techniques for displaying.4] In addition, various novel techniques extend and complement these traditional techniques, including (electron) lithography, optical tweezing, direct printing, or force microscopic manipulation.5-12] Remarkably, the size of glyphs and letters covers the range from a few hundred meters13] down to the atomic scale14] and even below.15] In the more classical approaches, one creates a local, line-shaped variation of the material density in or on an extended substrate acting as background: A line is carved out or some ink is deposited. A solid substrate stabilizes the density variation by strong intermolecular forces, keeping it in shape. The same principle has been applied to write on surfaces submerged in a fluid. For instance, scanning probe lithography was used to carve or deposit lines within or onto self-assembled monolayers submerged in fluids containing suitable chemicals.16, 17] In addition, sophisticated micron-sized structures have been printed using two-photon polymerization.18, 19] UV-polymerization and crosslinking were also used to write on a solid surface within a liquid starting from a dispersion of reactive chemicals to manufacture patterns with superb thermoresponsive mechanical properties.20] There are now even commercial scuba diver slates available for underwater writing on a substrate. Importantly, however, all these approaches still rely on a substrate i) for fixing the written structures and ii) for providing mechanical support. In contrast, “writing into a fluid” requires a mechanism that does not depend on such localization measures. The mechanism must also be intrinsically robust against rapid line dispersion, which would cause short lifetimes of any drawn lines. In fact, even in a quiescent (convection-free) fluid, the moving pen would transfer kinetic energy to the fluid, provoking line dispersion by locally created eddies. While such local eddies are rather unimportant when the pen is much smaller than the written letters, as, e.g., in skywriting,21] the creation of fine, durable, and freely-floating lines remains challenging. In fact, to write fully reconfigurable lines into a liquid at the microscale, an approach fundamentally different from underwater ink deposition or line carving and a new type of micro-pen are required. To develop such an approach, we exploit the following ideas.

Incidentally, a mobile fluid offers an alternative way of writing lines by particle transport toward a prescribed pattern. Imagine to start from a homogenous density of ink particles in a quiescent fluid and to use a pen that attracts the ink particles toward itself and/or its trajectory. If the resulting accretion process is sufficiently efficient and fast as compared to the subsequent dispersion of the ink particles, an increase in ink density may result past the pen, and a line is written. As key ingredients, this approach requires a sufficient range of particle-transporting attraction, a slow line dispersion, and a suitable way of pen-steering.

To meet the first requirement, the directed transport of colloidal particles by chemical, thermal, or light-intensity gradients can be exploited. A key example is phoretic effects, where, in general, the imposed gradient leads to a difference in chemical potential along a particle surface and drives a slip flow of the adjacent fluid along the surface, which, in turn, evokes directed motion of the particle.22-26] Using a large chemical-loaded “beacon” falling under gravity, Banerjee et al. created a colloidal over-density evolving along the trajectory within a few minutes.27] Here, colloidal motion relied on the local strength and direction of the gradient of electrolyte concentration. While these pioneering experiments demonstrate the possibility of writing freely buoyant lines within a fluid, they lack the option of deliberate pen steering.

In this work, we demonstrate a generic method for writing lines and letterings into a liquid rather than onto a solid. This method uses an ion-exchange resin bead (IEX) as a fully steerable micro-pen and exploits the presence of a solid substrate only for line assembly but not for fixing the ink. Instead, lines are written near a substrate but are not attached to it yielding freely floating long-lived lines which can be reconfigured and allow us to recycle the ink for writing new lines before optionally fixing them to the substrate.20, 28, 29] To achieve this, we exploit an effective way to transport colloids along extended surfaces: The ion-exchange resin bead (pen) evokes a so-called diffusio–osmotic (DO) flow.22, 30, 31] Such a flow emerges because the ion-exchange process induces a nonuniform concentration profile that causes a stress (force) on the solvent within the interfacial layer of the substrate resulting in a solvent flow towards the IEX.32] This flow then advects colloidal tracers towards the IEX, which can be viewed as an effective attraction between the IEX and the tracers.33] In the past, DO flows have been successfully employed with fixed sources,32-38]self-propelling sources,39, 40] and combinations of sources and sinks41] to create centrally symmetric or asymmetric assemblies of tracer particles at the source. Here, we exploit this mechanism to dynamically assemble a line of tracer particles (ink) in the wake of a moving ion-exchange resin bead. Once assembled, those tracers will disperse only very slowly by thermal diffusion in the eddy-free fluid. Moreover, the ongoing pen-induced DO flows focus ink particles toward the center of the written lines supporting their durability and sharpness.

Our results exemplify a generic pathway for writing and drawing fine, free-floating but durable lines in a liquid medium. Our approach is modular and allows combinations of different inks, drives, steering, and, optionally, fixation techniques. This could be used in the future for structuring liquids with deliberate line-based patterns, decorate, and thus visualize chemical tracers, or create desired initial states for future colloid experiments.

See: https://onlinelibrary.wiley.com/doi/10.1002/smll.202303741?af=R
Any kind of written form that can be produced using continuous lines can be readily reproduced, as other simulations have shown. Moreover, interruptions, such as breaks between separate letters, could also be achieved because, for example, the ion exchange process could be switched on and off at will using light exposure techniques. Even erasure and correction of what has been written is possible.
Hartmann352