Self‐Regulated Smectic Emulsion with Switchable Lasing Application

Abstract

be a two-step process, since the separated liquids need specific mechanical treatments such as sonication or gas bubbling to return to the initial emulsion form, [8,9] restricting the practical applications. Moreover, the switchable emulsifiers need to be specially designed according to the physical and chemical properties of the host/guest liquids and switching triggers, which makes this method complicated, time consuming, and expensive. Finally, although it has been demonstrated that self-emulsification methods can produce emulsions with small droplet size, i.e., sub-micrometer, without any mechanical energy input, these processes typically require high concentration of surfactants and are not reversible. [14][15][16] An ideal switchable emulsion should fulfill several requirements. First, the guest liquid should be able to be emulsified in the host medium without the need of a specific emulsifier, since the presence of surfactants would compromise the purity of the involved liquids and potentially decrease the performance of the system in its active form. Second, for high reproducibility and reliability, the system should be capable of reversibly producing droplets of uniform size so that every single droplet in the emulsion performs its particular function in the same way. Third, the system should be able to undergo rapid and infinitely reversible on-off switching without any mechanical treatment. In order to realize this, the host and the guest liquids would need to be semimiscible with a degree of miscibility that could be modulated through physical parameters, such as temperature of the guest material. Since semimiscibility requires a mild hydrophobic interface between the two constituents, nonaqueous systems such as oil-in-oil emulsions seem to be appropriate candidates. Yet, oil-in-oil emulsions are usually unstable due to the low surface tension at the oil-oil interface, for instance, ≈3 mN m −1 for hydrocarbon and silicon oils. [17] Stabilizing oil-in-oil emulsions without the use a specifically designed stabilizer is still a challenge. [18] In this paper, we propose a method to fabricate highly stable switchable emulsions that fulfill the requirements mentioned above. The method consists in mixing silicon oil with a semifluorinated liquid crystal (LC) that display two different smectic phases (SmA and SmE) when decreasing temperature from the isotropic phase. We show that emulsification and demulsification processes occur at the smectic A and isotropic phases respectively, enabling fast switching between the two states via temperature. The elasticity and chemistry of the LC guarantees the stability of the emulsified state without the use of any surfactant. Interestingly, we observe two different kinds of A structurally reversible smectic liquid crystal (LC) emulsion made of semifluorinated rod-type molecules in silicon oil, which is controlled by simple heating and cooling, is presented. Without adding any kind of additives, such as surfactants, polymers or emulsifiers, and without using any special t...

Electron microscopy analysis of soft materials with freeze‐fracture techniques

“…Kim et al 44 observed a phase transition when LC molecules containing perfluoroalkyl groups formed an emulsion in silicone oil (Figure 6a). When the LC molecules are cooled in an isotropic liquid state and transition to a smectic state, they form spherical and myelin‐like structures.…”

“…(a) The LC dispersed in the silicone oil undergoes a phase change and spontaneously forms a myelin structure. (scale bars = 20 μm) 44,74 . (b) FF‐SEM and x‐ray diffraction analysis of fracture plane for Q 230 cubic phase of lipid‐water system (scale bar = 200 nm) 45 .…”

“…Because the replica has high electrical conductivity, it is free from damage caused by electron beams and easy to analyze solutions with high viscosity. Taking these advantages, FF-TEM analysis can be used to observe various soft materials such as polymers, 43,44 liquid crystals (LCs), [44][45][46] and biomaterials. 11,12,47…”

Tunable Microlasers Modulated by Intracavity Spherical Confinement with Chiral Liquid Crystal

“…Based on the unique features, LCs have been extensively used in biosensing, temperature detection, and whispering‐gallery mode (WGM) laser resonators. [ 19–24 ] As the chiral dopant increases in CLC droplets, the number of periodic refractive index variation (periodic shells) increases to form higher structural confinement and chirality. Recent studies have further applied CLC microdroplets to obtain spherical or lateral confinement of optical modes.…”

DNA Self-Switchable Microlaser

“…Switchable interfaces have offered tremendous opportunities over the past decade, including bioelectronics, − optical devices, ,, laser switches, − biomedical sensors, , and fundamental biology. − In particular, the concept of “switchable biointerfaces” can be referred to as interfaces that change their microscopic properties in response to biological stimuli or biomolecular interactions. Contrary to artificially designed interfaces, switchable biointerfaces that take advantage of a biological system and biorecognition have demonstrated high functionality far beyond that obtained from nanomaterials. − Among all biomolecules, DNA is one of the most potent biomaterials known for its controllable synthesis and specificity of base-pair interactions. − Besides biomedical applications, the programmability and self-assembly of DNA structures offer versatile ways to construct DNA biointerfaces and tailor optical responses. − The stimuli-responsive properties of DNA molecules thus enable the development of program-switchable DNA interfaces. , …”