Kinetics of Nanoscale Self-Assembly Measured on Liquid Drops by Macroscopic Optical Tensiometry: From Mercury to Water and Fluorocarbons

Haimov, Boris; Яковлев, А. В.; Glick-Carmi, Rotem; Bloch, Leonid; Rich, Benjamin B.; Müller, Marcus; Pokroy, Boaz

doi:10.1021/jacs.5b10446

Cited by 8 publications

(27 citation statements)

References 61 publications

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“…This result is significant compared to a previous study on ST kinetics in droplet systems. [43] In our next system, we showed an example of compartmentalization by creating a complex droplet, containing an aqueous HPTS solution encapsulated inside an outer organic layer. These droplets exhibited a light-stimulated self-propulsion away from the light.…”

Section: Discussionmentioning

confidence: 98%

Self‐Propulsion of Droplets via Light‐Stimuli Rapid Control of Their Surface Tension

Yucknovsky

Rich

Westfried

et al. 2021

Adv Materials Inter

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Such systems can mimic the motion of living cells as similar stimuli are present in nature, and can also result in our fundamental understanding of early origin of life events.The movement of droplets is linked with nonuniform surface tension (ST), resulting in fluid flow, known as the Marangoni effect. [18][19][20] This effect is based on an asymmetric exposure of the droplet surface to a chemical cue, i.e., chemotaxis, whereas ion or pH gradients are most common. [21][22][23] The asymmetry in the droplet/solution interface creates a nonuniform change in the ST. Light is a convenient tool to control the asymmetry and ST of droplets, and accordingly the motion of droplets. To use light as stimuli, there is a need for photochromic molecules next to the droplets, undergoing a photochemical process. To date, the commonly used families of photochromic molecules for mediating dynamic processes, e.g., droplet motion are azobenzenes that undergo trans-cis photoisomerization, [24,25] and spiropyran and its derivatives that overgo photocleavage primary to the proton release, resulting in minute-length reaction timescales. [26][27][28][29][30][31][32] Therefore, a yet-to-beresolved challenge in the use of such photochromic molecules is the associated timescales and especially the reversibility of the dynamic process.Herein, we propose a new approach to chemophototaxis for gaining fast subsecond responses not only to turning on the light, but also for the reversible process of turning the light off, which is based on the use of Brønsted-Lowry photoacids and photobases. This class of organic molecules undergoes a dramatic change in their dissociation equilibrium constant (pKa) upon light excitation. [33] Thus, only in their electronically excited state do photoacids and photobases behave as strong acids and bases. The above-mentioned spiropyrans are also referred to as photoacids since their photocleavage process from spiropyran to merocyanine involves the release of a proton, however, there is a large difference in terms of mechanism and timescales relative to Brønsted-Lowry photoacids. In this context, we hypothesize that the fast excited-state proton transfer (ESPT) of Brønsted-Lowry photoacids and photobases can induce rapid chemical changes on the surface of pH-sensitive droplets and initiate their motion. We show here a variety of different droplet systems involving the use of photoacids and photobases either within the droplet, on its surface, or in solution, whereas we use light to self-propel and to guide the movement of the droplet. Nature demonstrates many examples of response and adaptation to external stimuli. Here, this study focuses on self-propulsion (motion) while presenting several self-propelling droplet systems responsive to pH gradients. Light is used as the gating source to gain reversibility, avoid the formation of chemical wastes, and control the self-propulsion remotely. To achieve light-stimuli ultrafast response, photoacids and photobases are used, capable of donating or capturing a proton, respect...

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Section: Discussionmentioning

confidence: 98%

Self‐Propulsion of Droplets via Light‐Stimuli Rapid Control of Their Surface Tension

Yucknovsky

Rich

Westfried

et al. 2021

Adv Materials Inter

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“…If one studies monolayer formation on droplets, 1 evaporative colloidal deposition, 2,3 the buoyancy of suspended particles on an interface, 4 or the aggregation of colloidal nanoparticles by capillary condensation, 5 most likely, the behavior of the system can be explained in terms of capillarity theory. 6,7 At the heart of this approach lies the approximation that bulk and surface properties of large planar bodies can be extrapolated to describe small and curved systems.…”

Section: Introductionmentioning

confidence: 99%

Nanocapillarity and Liquid Bridge-Mediated Force between Colloidal Nanoparticles

et al. 2018

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In this work, we probe the concept of interface tension for ultrathin adsorbed liquid films on the nanoscale by studying the surface fluctuations of films down to the monolayer. Our results show that the spectrum of film height fluctuations of a liquid–vapor surface may be extended to ultrathin films provided we take into account the interactions of the substrate with the surface. Global fluctuations of the film height are described in terms of disjoining pressure, whereas surface deformations that are proportional to the interface area are accounted for by a film thickness-dependent surface tension. As a proof of concept, we model the capillary forces between colloidal nanoparticles held together by liquid bridges. Our results indicate that the classical equations for capillarity follow very precisely down to the nanoscale provided we account for the film height dependence of the surface tension.

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“…This result is significant comparing to a previous study on ST kinetics in droplet systems. 36 In our next system, we showed an example of compartmentalization by creating a complex droplet, containing an aqueous HPTS solution encapsulated inside an outer organic layer. These droplets exhibited a light-stimulated self-propulsion away from the light.…”

Section: Discussionmentioning

confidence: 98%

“…This result is significant comparing to a previous study on ST kinetics in droplet systems. 36 In our next system, we…”

Section: Discussionmentioning

confidence: 99%

Self-Propulsion of Droplets via Light-Stimuli Rapid Control of Their Surface Tension

Yucknovsky¹,

Rich²,

Westfried³

et al. 2021

Preprint

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Biology demonstrates many examples of response and adaptation to external stimuli, and here we focus on self-propulsion (motion) while presenting several self-propelling droplet systems responsive to pH gradients. We use light as the gating source to gain reversibility, avoid the formation of chemical wastes, and control the self-propulsion remotely. To achieve light-stimuli ultra-fast response, we use photoacids and photobases, capable of donating or capturing a proton, respectively, in their excited-state. We control the movement and directionality of the droplet’s self-propulsion by introducing the photo-acid/base either in bulk solution, on the surface of the droplet, or inside the droplet. We show that proton transfer between the photo-acid/base and the droplet results in a rapid change in the droplet’s surface tension, which induces the self?propulsion movement. The high versatility of our systems together with a record-breaking ultra?fast response to light makes them highly attractive for the design of various controlled cargo?carrier systems.<br>

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Kinetics of Nanoscale Self-Assembly Measured on Liquid Drops by Macroscopic Optical Tensiometry: From Mercury to Water and Fluorocarbons

Cited by 8 publications

References 61 publications

Self‐Propulsion of Droplets via Light‐Stimuli Rapid Control of Their Surface Tension

Self‐Propulsion of Droplets via Light‐Stimuli Rapid Control of Their Surface Tension

Nanocapillarity and Liquid Bridge-Mediated Force between Colloidal Nanoparticles

Self-Propulsion of Droplets via Light-Stimuli Rapid Control of Their Surface Tension

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