Nanobubbles (NBs) have a widespread application in antimicrobial activity, wastewater treatment, and ecological restoration due to numerous peculiar characteristics, such as small diameter, long-term stability, and ability to produce hydroxyl radicals. Despite significant applications, only limited comprehensive investigations are available on the role of surfactants and pH in NBs characteristics. Therefore, this study examines the effects of different surfactants (i.e., anionic, cationic, and nonionic) and pH medium on bulk NB formation, diameter, concentration, bubble size distribution (BSD), ζ-potential, and stability. The effect of surfactant at concentrations above and below the critical micelle concentration was investigated. NBs were generated in deionized (DI) water using a piezoelectric transducer. The stability of NBs was assessed by tracking the variation in diameter and concentration over time. In a neutral medium, the diameter of NBs is smaller than in other surfactant or pH mediums. The diameter, concentration, BSD, and stability of NBs are strongly influenced by the ζ-potential rather than the solution medium. BSD curve shifts to a smaller bubble diameter when the magnitude of ζ-potential is high in any solution. In pure water, surfactant, and pH mediums, NBs have existed for a long time. NBs have a shorter life span in environments with a pH ≤ 3. Surfactant adsorption on the surface of NBs increases with increasing surfactant concentration up to a certain limit, beyond which it declines substantially. The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to interpret the NBs stability, resulting in a total potential energy barrier that is positive and greater than 45.55 k B T for 6 ≤ pH ≤ 11, whereas for pH < 6, the potential energy barrier essentially vanishes. Moreover, an effort has also been made to explicate the plausible prospect of ion distribution and its alignment surrounding NBs in cationic and anionic surfactants. This study will extend the in-depth investigation of NBs for industrial applications involving NBs.

No abstract

Most soft actuators producing joint-like deformations rely on the expansion of materials or on the use of multiple chambers in equilibrium while requiring additional structures for inter-connecting the joints. This paper introduces a new soft pneumatic actuator where a constriction placed on an inflatable tube allows the tube to bend around the constriction through the formation of a crease around the constriction. The bending of the tube then changes as the shape of the crease change under a change in pressure without relying on the expansion of the material. This results in an actuator that has a single chamber where multiple constrictions can be placed and freely re-arranged to form different structures as their insertion is nonpermanent. The constriction is also able to induce lateral bending deformations such that the actuator can assume a helical configuration using multiple constrictions spaced over the length of the actuator. The performance of different constriction designs in terms of bending angle without any payloads and with additional payloads is presented followed by their implementation in three different designs of morphing decorative flowers. The actuator itself does not produce a large force and its range of motion is quite limited, but it has a unique set of properties that make it ideal for visual and creative applications as well as educational purposes.