Photoswitchable Dissipative Two-Dimensional Colloidal Crystals.
TL;DR: This work describes the first reversible photocontrol of two-dimensional colloidal crystallization at the air/water interface, where millimeter-sized assemblies of microparticles can be actuated through the dynamic adsorption/desorption behavior of a photosensitive surfactant added to the suspension.
Abstract: Control over particle interactions and organization at liquid interfaces is of great importance both for fundamental studies and practical applications. Rendering these systems stimulus-responsive is thus a desired challenge both for investigating dynamic phenomena and realizing reconfigura-ble materials. Here, we describe the first reversible photo-control of two-dimensional colloidal crystallization at the air/ water interface, where millimeter-sized assemblies of micro-particles can be actuated through the dynamic adsorption/ desorption behavior of a photosensitive surfactant added to the suspension. This allows us to dynamically switch the particle organization between a highly crystalline (under light) and a disordered (in the dark) phase with a fast response time (crystallization in % 10 s, disassembly in % 1 min). These results evidence a new kind of dissipative system where the crystalline state can be maintained only upon energy supply.
Summary (1 min read)
- To their knowledge, this is the first time that such a dynamic photoresponse of a large colloidal assembly at the air/ water interface is reported.
- The authors thus conclude that the colloidal structure was not controlled by the relative composition of cis/trans AzoTAB isomers in the bulk, instead they propose that it was mediated by the adsorption/desorption dynamics of AzoTAB.
- D) Height of the twelfth peak in the RDF curves as a function of irradiation time for samples irradiated with UV (violet circles) or blue light (blue triangles).
- One minute of irradiation efficiently crystallized the whole particle assembly , whereas 2 min in the dark were enough for the system to switch back to the disordered state .
Conflict of interest
- The authors declare no conflict of interest.
- Each cycle consisted of irradiation with blue light (440 nm, 63 Wm 2) for 1 min and dark conditions for 2 min.
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Q1. What contributions have the authors mentioned in the paper "Photoswitchable dissipative two-dimensional colloidal crystals" ?
Here, the authors describe the first reversible photocontrol of two-dimensional colloidal crystallization at the air/ water interface, where millimeter-sized assemblies of microparticles can be actuated through the dynamic adsorption/ desorption behavior of a photosensitive surfactant added to the suspension. This allows us to dynamically switch the particle organization between a highly crystalline ( under light ) and a disordered ( in the dark ) phase with a fast response time ( crystallization in 10 s, disassembly in 1 min ). Precise regulation of the interactions governing the assembly of colloidal particles at fluid interfaces is the subject of vivid interest in the scientific community, either for the design of novel materials or for studies of more fundamental phenomena. 5 ] Specifically, while reconfigurable structures are sought for the development of innovative devices, dissipative systems are also studied to understand how matter organizes itself. Alternatively, light appears as a valuable stimulus for the study of dynamic assembly. Light was also shown to control the crystallization of colloids, either with active particles, 23 ] photoresponsive particles, light-sensitive substrates, 25 ] or non-responsive colloids. To their knowledge, the only report on the photocontrol of colloidal crystallization at a liquid interface was recently achieved using optical trapping at the interface of an oil-in-water drop and led to ordered, yet very small, assemblies. Here, the authors describe the first system where extended 2D colloidal crystallization is induced on-demand using light as an input. The system is composed of inherently passive anionic microparticles mixed with small amounts of a cationic photosensitive surfactant. The light-induced dynamic adsorption/desorption behavior of the surfactant from the air/water interface allows us to tune the particle– particle interaction with light. The authors analyze both structural and dynamic features of the colloidal assemblies in response to different irradiation profiles, and perform cycles of crystallization/disassembly to assess the reversibility of the process. Strikingly, their experiments demonstrate the dissipative, outof-equilibrium nature of the ordered colloidal assemblies, since the crystals are only formed when continuous energy supply is provided by light irradiation, whereas energy removal leads to a rapid disassembly of the colloidal structure. The authors recently showed that micromolar amounts of conventional cationic surfactants ( for example, dodecyltrimethylammonium bromide, DTAB ) induced the adsorption of anionic particles by decreasing the adsorption barrier at the air/water interface. At such low surfactant concentrations ( CMC/ 1000–CMC/100, where CMC is the critical micellar concentration ), the particles adsorbed with a low contact angle ( 308 ) and remained highly charged, forming disordered assemblies or polycrystalline patches in a particleand surfactant-concentration-dependent manner. Here, to explore the possibility to dynamically switch particle assemblies at the air/water interface at constant composition, the authors used anionic polystyrene particles ( diameter 5. 1 mm ) at a fixed concentration ( 0. 01 mgmL ) and 10 mm of the AzoTAB photosensitive surfactant ( Figure 1A ). The particles were brought to the air/water interface of a suspension in a cylindrical cell by flipping it up and down using their previously described protocol ( Figure 1 C, top panel ).