Influence of Polarity Change and Photophysical Effects on Photosurfactant-Driven Wetting

Abstract

Photosurfactants have shown considerable promise for enabling stimuli-responsive control of the properties and motion of fluid interfaces. Recently, a number of photoswitch chemistries have emerged to tailor the photoresponsive properties of photosurfactants. However, systematic studies investigating how photoresponsive surfactant behavior depends on the photochemical and photophysical properties of the switch remain scarce. In this work, we develop synthetic schemes and surfactant designs to produce a well-controlled library of photosurfactants to comparatively assess the behavior of photoswitch chemistry on interfacial behavior. We employ photoinduced spreading of droplets at fluid interfaces as a model for such studies. We show that although photosurfactant response is largely guided by expected trends with changes in polarity of the photoswitch, interfacial behavior also depends nontrivially and sometimes counter-intuitively on the kinetics and mechanisms of photoswitching, particularly at the interface of two solvents, as well as on complex interactions with other surfactants. Understanding these complexities enables the design of new photosurfactant systems and their optimization toward responsive functions including triggered spreading, dewetting, and destabilization of droplets on solid and fluid surfaces.

Donor–Acceptor Stenhouse Adduct‐Polydimethylsiloxane‐Conjugates for Enhanced Photoswitching in Bulk Polymers

“…[ 11–15 ] Their tunable absorption in the spectral range between 450 and 750 nm [ 16–21 ] enables DASA activation at wavelengths suitable for biological applications. [ 22 ] DASA‐functionalized polymers were already investigated for potential applications in a number of areas ranging from photo‐/hydrochromic, [ 23–25 ] photopatternable, [ 26–29 ] or wettability switching [ 30–34 ] surfaces and objects, to smart drug delivery, [ 35–40 ] chemical sensing, [ 41–45 ] and photoactuation. [ 46 ] Systems operating in suspension, including polymer‐based micelles, [ 35,38,39,47 ] polymersomes [ 37 ] and other polymer nanoparticles, [ 36,40,43 ] as well as DASA immobilization in polymer films, [ 23,31,46 ] polymer networks, [ 24 ] polymer nanofibers [ 45 ] and on functionalized polymeric surfaces [ 26,30,33,48 ] were reported.…”

Depinning of Multiphase Fluid Using Light and Photo-Responsive Surfactants

“…All MC isomers are completely transformed back to SP in the right-hand image of Figure 1 e. In previous work, we explored the photowetting behaviors of SP-DA-PEG and revealed the excellent reversibility and stability of SP-DA-PEG at oil/water interfaces by examining both the kinetics and the interfacial tensions. 29 Compared with many previously reported photoresponsive surfactants, the ease of synthesis and well-studied properties of SP-DA-PEG make it an ideal candidate for the manipulation of fluid systems explored in this work.…”

“…In this study, we introduce the use of photoresponsive surfactants to promote bubble and droplet departure from a solid surface. We employ a photoresponsive surfactant that we recently designed and synthesized, 29 which is capable of achieving fast, reversible, and significant interfacial changes of different solvents, thanks to its large polarity change under illumination. To highlight the potential of this approach, we demonstrate the removal of droplets and bubbles pinned on a solid substrate using dilute (0.1 mM) photoresponsive surfactants and low-intensity (0.25 mW/mm 2 ) lights.…”

Large-Scale Dewetting via Surfactant-Laden Droplet Impact

“…13−16 The existence of a surface tension gradient due to the inhomogeneity of surfactant distribution in the liquid gives rise to Marangoni stress, driving liquid to the high surface tension area. 17,18 Marangoni stress induced by a surfactant alters the interfacial dynamics and produces many unique phenomena, which are extremely important in various industrial and biomedical fields. In the coating field, if a surfactant is distributed nonuniformly, Marangoni stress will deform the surface of the film and result in a defective coating.…”

“…The critical thickness, H cri , is determined by liquid and interfacial properties via H cri = 2­(γ/ ρg ) 0.25 sin­(θ/2), where γ is the surface tension at the liquid–gas interface, ρ is the liquid density, g is the acceleration of gravity, and θ is the static contact angle . For an unstable liquid film, a dry hole can be formed under certain external disturbances, and it will spread outward spontaneously, which finally causes the dewetting phenomenon. − On hydrophilic surfaces, liquid dewetting can also occur if they are exposed to external stimuli such as air blowing and mixing with low surface energy liquids, which may include alcohol, isopropyl alcohol, and some surfactants. − The existence of a surface tension gradient due to the inhomogeneity of surfactant distribution in the liquid gives rise to Marangoni stress, driving liquid to the high surface tension area. , …”