Contact-Mediated Nucleation of Subcooled Droplets in Melt Emulsions: A Microfluidic Approach

The production of melt emulsions is mainly influenced by the crystallization step, as every single droplet needs to crystallize to obtain a stable product with a long shelf life. However, the crystallization of dispersed droplets requires high subcooling, resulting in a time, energy and cost intensive production processes. Contact-mediated nucleation (CMN) may be used to intensify the nucleation process, enabling crystallization at higher temperatures. It describes the successful inoculation of a subcooled liquid droplet by a crystalline particle. Surfactants are added to emulsions/suspensions for their stabilization against coalescence or aggregation. They cover the interface, lower the specific interfacial energy and form micelles in the continuous phase. It may be assumed that micelles and high concentrations of surfactant monomers in the continuous phase delay or even hinder CMN as the two reaction partners cannot get in touch. Experiments were carried out in a microfluidic chip, allowing for the controlled contact between a single subcooled liquid droplet and a single crystallized droplet. We were able to demonstrate the impact of the surfactant concentration on the CMN. Following an increase in the aqueous micelle concentrations, the time needed to inoculate the liquid droplet increased or CMN was prevented entirely.

Liquid-Liquid Nanogenerator basing on Aqueous-Aqueous Interface

Solid nanogenerators often have a limited charge transfer due to the low contact area. Compared with solid-solid or solid-liquid nanogenerators, liquid-liquid nanogenerators can effectively increase the transferred charge. Limited by the fluidity of the liquid, the precise manipulation of the liquid morphology remains a challenge. In this work, using the surface tension of the droplet to fix the shape, we designed a new liquid-liquid triboelectric nanogenerator by using the immiscible aqueous-aqueous interface, achieving the contact surface charge transfer of 129 nC of a single droplet. This liquid-liquid nanogenerator has been proven to be applicable in humid environments, and the two-phase materials have good biocompatibility and can be used as a good carrier for drugs. Therefore, this nanogenerator is useful for future design of implantable devices and the design of a new type of bionic fully self-powered system has great potential. Meanwhile, such design established the foundation of aqueous electronics and more creation can be achieved by using this route.

Influence of laser hardening on laser induced periodic surface structures on steel substrates

Laser-induced periodic surface structures (LIPSS) are used to structure surfaces for functionalization. Thus, hydrophilic states are generated using LIPSS. However, these nanostructures do not withstand mechanical loads and therefore cannot be used for most tribological applications. Within this work the approach of laser hardening of LIPSS is investigated. It is shown that laser hardening leads to an alteration of prior structured surfaces. That effects the wetting behaviour. The higher the laser power during hardening, the more increases the contact angle of a single droplet on the surface and the more the surface lacks in terms of wetting behaviour. This phenomenon is attributed to changes in LIPSS’ aspect ratio. A high ratio leads to low contact angles and is shifted to low values when the laser power increases resulting in high contact angles. Hence, it is concluded that the thermal load during laser hardening, and it’s influence on the wettability must be taken into account when LIPSS are subjected to laser hardening.