Dual Droplet Functionality: Phototaxis and Photopolymerization

Abstract

The use of phototaxis to move droplets in liquids offers the opportunity to emulate natural processes such as the controlled transport of materials in fluidic environments and to undertake chemistry at specific locations. We have developed a photoactive organic droplet whose movement in aqueous solution is driven by a photoinitiator, as a result of a light induced reaction within the droplet generating a Marangoni flow. The photoinitiator not only drives the droplet motion but can also be used to initiate polymerization following transfer of the droplet to a specific location and its merging 2 with a secondary, monomer-containing droplet. The same light is used to control the transport of the droplet and the polymerization. The efficacy of this droplet transport and reactor system has been demonstrated by the site specific underwater polymerization of N-isopropylacrylamide to repair a leaking vessel and the adhesion of two materials together.

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

“…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.…”

“…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.…”

Collective Behaviors of Active Matter Learning from Natural Taxes Across Scales

“…[ 30 ] Light‐induced Marangoni flow can serve as the mediation for phototaxis motion, for example, within photoactive microdroplets under 365 nm laser irradiation. [ 286 ] Electric field is programmable with respect to its voltage, frequency, and conductive surfaces. In a nonuniform electric field, 2D patterning of heterogeneous particles can be performed on ITO glass substrates because of electrowetting and dielectrophoresis (DEP) between two parallel plates (Figure 10F).…”

Application of Super Photoacids in Controlling Dynamic Processes: Light-Triggering the Self-Propulsion of Oil Droplets

“…Previously, we have used oil droplets as a convenient model for an artificial system capable of stimuli-responsiveness and motion. While there are many examples where chemical or physical signals, such as a change in pH or light, were used as a stimulus for a droplet’s self-propulsion, − we were the first to use Brønsted photoacids to control their motion. Brønsted photoacids are organic molecules that undergo a dramatic drop of p K a in their electronically excited state. − Accordingly, such photoacids can be considered as a transient source of proton donors only upon their light excitation.…”