Soft robotics are attractive to researchers and developers due to their potential for biomimicry applications across a myriad of fields, including biomedicine (e.g., surgery), the film industry (e.g., animatronics), ecology (e.g., physical ‘animats’), human–robot interactions (e.g., social robots), and others. In contrast to their rigid counterparts, soft robotics offer obvious actuation benefits, including their many degrees of freedom in motion and their potential to mimic living organisms. Many material systems have been proposed and used for soft robotic applications, involving soft actuators, sensors, and generators. This review focuses on dielectric elastomer (DE)-based actuators, which are more general electro-active polymer (EAP) smart materials. EAP-based soft robots are very attractive for various reasons: (a) energy can be efficiently (and readily) stored in electrical form; (b) both power and information can be transferred rapidly via electrical phenomena; (c) computations using electronic means are readily available. Due to their potential and benefits, DE-based actuators are attractive to researchers and developers from multiple fields. This review aims to (1) provide non-experts with an “easy-to-follow” survey of the most important aspects and challenges to consider when implementing DE-based soft actuators, and (2) emphasize current solutions and challenges related to the materials, controls, and portability of DE-based soft-actuator systems. First, we start with some fundamental functions, applications, and configurations; then, we review the material models and their selection. After, we outline material limitations and challenges along with some thermo-mechano-chemical treatments to overcome some of those limitations. Finally, we outline some of the control schemes, including modern techniques, and suggest using rewritable hardware for faster and more adaptive controls.

The Environmental Protection Agency (EPA) of the United States recently released the first-ever federal regulation on per- and polyfluoroalkyl substances (PFASs) for drinking water. While this represents an important landmark, it also brings about compliance challenges to the stakeholders in the drinking water industry as well as concerns to the general public. In this work, we address some of the most important challenges associated with measuring low concentrations of PFASs in drinking water in the field in real drinking water matrices. First, we review the “continuous monitoring for compliance” process laid out by the EPA and some of the associated hurdles. The process requires measuring, with some frequency, low concentrations (e.g., below 2 ppt or 2 ng/L) of targeted PFASs, in the presence of many other co-contaminants and in various conditions. Currently, this task can only (and it is expected to) be accomplished using specific protocols that rely on expensive, specialized, and laboratory-scale instrumentation, which adds time and increases cost. To potentially reduce the burden, portable, high-fidelity, low-cost, real-time PFAS sensors are desirable; however, the path to commercialization of some of the most promising technologies is confronted with many challenges, as well, and they are still at infant stages. Here, we provide insights related to those challenges based on results from ab initio and machine learning studies. These challenges are mainly due to the large amount and diversity of PFAS molecules and their multifunctional behaviors that depend strongly on the conditions of the media. The impetus of this work is to present relevant and timely insights to researchers and developers to accelerate the development of suitable PFAS monitoring systems. In addition, this work attempts to provide water system stakeholders, technicians, and even regulators guidelines to improve their strategies, which could ultimately translate in better services to the public.

Dielectric elastomers (DEs) find applications in many areas, particularly in the field of soft robotics. When modeling and simulating DE-based actuators and sensors, a substantial portion of the literature assumes the selected DE material to behave in some perfectly hyperelastic manner, and the vast majority have assumed invariant permittivity. However, studies on simple planar DEs have revealed instabilities and hastened breakdowns when a variable permittivity is allowed. This is partly due to the intertwined electromechanical properties of DEs rooted on their labyrinthine polymeric microstructures. This work focuses on studying the effects of a varying (with stretch) permittivity on the out-of-plane deformation of a circular DE, using a model derived from principles of strain-induced polymer birefringence. In addition, we utilize the Edward–Vilgis model, which attempts to account for effects related to crosslinking, and length extension, slippage, and entanglement of polymer chains. Our approach reveals the presence of “stagnation” regions in the electromechanical behavior of the DE actuator material. These stagnation regions are characterized by both electrical and mechanical critical electrostrictive coefficient ratios. Mechanically, certain values of the electrostrictive coefficient ratio predict cases where deformation does not occur in response to a change in voltage. Electrically, certain cases are predicted where changes in capacitance cannot be measured in response to changes in deformation. Thus, some combined conditions of loading and material properties could limit the effectiveness of DE membranes in either actuation or sensing. Therefore, our results reveal mechanisms that could be useful to designers of actuators and sensors and unveil an opportunity for exploring new theoretical materials with potential novel applications. Furthermore, since there are known analogous formulations between electrical and optical properties, criticality principles studied in this article could be extended to optomechanical coupling.

In this work, the degradation of mono‐ and polyfluorinated phenolic compounds was demonstrated by a series of crude plant peroxidases, including horseradish root (HRP) and six members of the Cucurbita genus. Highly active samples were identified using a library screening approach in which more than 50 crude plant samples were initially evaluated for defluorination activity toward 4‐fluorophenol. The highest concentrations were observed in the HRP, pumpkin skin (PKS), and butternut squash skin (BNS), which consistently gave the highest intrinsic rates of decomposition for all the substrates tested. Although HRP exhibited a significant decrease in activity with increased fluorination of the phenolic substrate, PKS showed only minor reductions. Furthermore, in silico studies indicated that the active site of HRP poorly accommodates the steric bulk of additional fluorines, causing the substrate to dock farther from the catalytic heme and thus slowing the catalysis rate. We propose that the PKS active site might be larger, allowing closer access to the perfluorinated substrate, and therefore maintaining higher activity compared to the HRP enzyme. However, detailed kinetic characterization studies of the peroxidases are recommended. Conclusively, the high catalytic activity of PKS and its high yield per gram of tissue make it an excellent candidate for developing environmentally friendly biocatalytic methods for degrading fluorinated aromatics. Finally, the success of the library approach in identifying highly active samples for polyfluorinated aromatic compound (PFAC) degradation suggests the method may find utility in the quest for other advanced catalysts for PFAS degradation.

Static mixers (SM) have become standard equipment in the process industries. They are widely used in applications that involve chemical reactions, heat transfer, blending of fluids, or a combination of these. Compared to mechanically agitated vessels, SMs consume less energy, require less maintenance, and can provide mixing with shorter residence time. Assessment of the performance of SM provides a means to categorize and rank the available devices and new designs, which in turn facilitates selection for specific applications. Applying the second law efficiency (SLE) principle, we derived and proposed a novel mixing parameter, the M number, which is a dimensionless ratio of mixing level to energy loss. The parameter is compared to an industry-standard method of mixing evaluation that relies on the coefficient of variation (CoV) change across the mixer. Both CoV and the M number are used to evaluate mixing performance from computational fluid dynamics (CFD) results for a static mixer for various inlet conditions. Unlike the CoV-based parameters considered, the M number offers the advantages of accounting for energy loss and the natural mixing effects of the system. In addition, an empirical relationship is obtained that relates the M number to the Reynolds number (Re). Potential applications for the M number are discussed and its limitations are noted. Work in progress includes investigation with other SM.