ABSTRACT
Boiling, one of the most common phase-change heat transfer methods, is widely used in nuclear power plants, spacecraft, integrated circuits, and other situations, where rapid and efficient heat transfer is crucial. However, boiling heat transfer is efficient only in a specific surface temperature range when a droplet impacts a superheated surface. Here, we enhance the boiling heat transfer and extend this temperature range by adding a tiny amount of surfactant. We find that surfactants can weaken the Kelvin effect of boiling bubbles, and thus reduce the onset of boiling driven temperature and significantly enhance the maximum vaporization rate of the droplet effectively. In particular, different from previous studies, we find that the surfactants at lower concentrations can increase the Leidenfrost temperature of the droplets. All the above effects jointly expand the temperature range of effective boiling heat transfer. This study sheds new light on the role of surfactants in the boiling process and offers a new medium to promote heat-transfer applications.
ABSTRACT
Microbial infections have become a great threat to human health and one of the main risks arises from direct contact with the surfaces contaminated by pathogenic microbes. Herein, a kind of hexagonal column interpenetrated spheres (HCISs) are fabricated by non-covalent assembly of plant gallic acid with quaternary ammonium surfactants. Different from one-time burst release of conventional antimicrobial agents, the HCIS acts like a "antimicrobial molecular bank" and releases the antimicrobial ingredients in a multistage way, leading to long-lasting antimicrobial performance. Taking advantage of strong hydrophobicity and adhesion, HCISs are applicable to various substrates and endowed with anti-water washing property, thus showing high in vitro antimicrobial efficiency (>99 %) even after being used for 10 cycles. Meanwhile, HCISs exhibit broad-spectrum antimicrobial activity against bacteria and fungi, and have good biocompatibility with mammalian cells. Such a low-cost and portable long-lasting antimicrobial agent meets the growing anti-infection demand in public spaces.
Subject(s)
Anti-Bacterial Agents/pharmacology , Antifungal Agents/pharmacology , Biocompatible Materials/pharmacology , Polyphenols/pharmacology , Surface-Active Agents/pharmacology , Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/chemistry , Antifungal Agents/chemical synthesis , Antifungal Agents/chemistry , Biocompatible Materials/chemical synthesis , Biocompatible Materials/chemistry , Candida albicans/drug effects , Cations/chemistry , Cations/pharmacology , Escherichia coli/drug effects , Microbial Sensitivity Tests , Molecular Structure , Particle Size , Polyphenols/chemistry , Staphylococcus aureus/drug effects , Surface-Active Agents/chemistryABSTRACT
Improving water droplet deposition on superhydrophobic surfaces is essential in many agricultural and industrial spraying processes. Adding surfactants is generally considered a simple way to enhance the wetting ability of droplets on surfaces. However, finding effective surfactants for the deposition and spread of high-speed impacting droplets on superhydrophobic surfaces remains a challenge. Here, we propose a model to predict the deposition results of impacting droplets on superhydrophobic surfaces by studying the droplets containing a series of asymmetric double-chain quaternary ammonium ionic surfactants with different chain lengths. By introducing the molecular diffusion rate, the ability of molecules to reduce surface tension, as well as the stability of aggregates into the model, the impact outcomes of surfactant droplets on the superhydrophobic surface are described and predicted. This study provides a beneficial blueprint for the selection of surfactants and the control of droplet impact behavior on superhydrophobic surfaces.
