Himanshu Mishra

California Institute of Technology | CIT · Department of Applied Physics & Materials Science

Numerous natural and engineering scenarios necessitate the entrapment of air pockets or bubbles on submerged surfaces. Current technologies for bubble entrapment rely on perfluorocarbon coatings, limiting their sustainability. Herein, we investigated the efficacy of doubly reentrant cavity architecture towards realizing gas-entrapping microtextured...

Numerous natural and industrial processes entail the spontaneous entrapment of gas/air as rough/patterned surfaces are submerged under water. As the wetting transitions ensue, the gas diffuses into the water leading to the fully water‐filled state. However, the standard models for wetting do not account for the microtexture's topography on collecti...

Zare and co-workers have recently claimed that hydrogen peroxide is spontaneously generated on the air-water interface of sprayed microdroplets, i.e., that H2O2 forms without an external energy source or co-reactant or catalyst. Specifically, they find that the H2O2(aq) concentration in sprayed microdroplets increases by a factor of 3.5 (or 2.5) as...

In response to the challenge of nutrient-deficient sandy soils and water scarcity due to excessive evaporative water loss in arid regions, we developed and tested two complementary soil amendment technologies: Superhydrophobic sand (SHS) mulch and an enriched date palm biochar. In a greenhouse pot experiment, we investigated the independent and syn...

Liquid droplets hanging from solid surfaces are commonplace, but their physics is complex. Examples include dew or raindrops hanging onto wires or droplets accumulating onto a cover placed over warm food or windshields. In these scenarios, determining the force of detachment is crucial to rationally design technologies. Despite much research, a qua...

Liquid droplets hanging from solid surfaces are commonplace, but their physics is complex. Examples include dew or raindrops hanging onto wires or droplets accumulating onto a cover placed over warm food or windshields. In these scenarios, determining the force of detachment is crucial to rationally design technologies. Despite much research, a qua...

Polymer filaments form the foundation of biology from cell scaffolding to DNA. Their study and fabrication play an important role in a wide range of processes from tissue engineering to molecular machines. We present a simple method to deposit stretched polymer fibers between micro-pillars. This occurs when a polymeric drop impacts on and rebounds...

Abstract Irrigated agriculture in arid and semi‐arid regions is a vital contributor to the global food supply. However, these regions endure massive evaporative losses that are compensated by exploiting limited freshwater resources. To increase water‐use efficiency in these giga‐scale operations, plastic mulches are utilized; however, their non‐bio...

Polymer filaments form the foundation of biology from cell scaffolding to DNA. Their study and fabrication play an important role in a wide range of processes from tissue engineering to molecular machines. We present a simple method to deposit stretched polymer fibers between micro-pillars. This occurs when a polymeric drop impacts on and rebounds...

Recent reports on the formation of hydrogen peroxide (H2O2) in water microdroplets produced via pneumatic spraying or capillary condensation have garnered significant attention. How covalent bonds in water could break under such mild conditions challenges our textbook understanding of physical chemistry and water. While there is no definitive answe...

Recent reports on the production of hydrogen peroxide (H2O2) on the surface of condensed water microdroplets without the addition of catalysts or additives have sparked significant interest. The underlying mechanism is thought to be ultrahigh electric fields at the air–water interface; smaller droplets present larger interfacial areas and produce h...

Irrigated agriculture in arid and semi-arid regions is a vital contributor to the global food supply; however, these regions endure massive evaporative losses that are compensated by unsustainable freshwater withdrawals. Plastic mulches have been used to curtail evaporation, improve water-use efficiency, and ensure food and water security, but they...

Recent reports on the formation of hydrogen peroxide (H$_2$O$_2$) in water microdroplets produced via pneumatic spraying or capillary condensation have garnered significant attention. How covalent bonds in water could break under such conditions challenges our textbook understanding of physical chemistry and the water substance. While there is no d...

Recent reports on the production of hydrogen peroxide (H$_2$O$_2$) on the surface of condensed water microdroplets without the addition of catalysts or additives have sparked significant interest. The underlying mechanism is speculated to be ultrahigh electric fields at the air-water interface; smaller droplets present higher interfacial area and p...

Liquid marbles refer to droplets that are covered with a layer of non-wetting particles. They are observed in nature and have practical significance. These squishy objects bounce, coalesce, break, inflate, and deflate while the liquid does not touch the substrate underneath. Despite the considerable cross-disciplinary interest and value of the rese...

Post-harvest storage of grains is crucial for food and feed reserves and facilitating seeds for planting. Ironically, post-harvest losses continue to be a major food security threat in the developing world, especially where jute bags are utilized. While jute fabrics flaunt mechanical strength and eco-friendliness, their water-loving nature has prov...

The cover image is based on the Full Paper A First‐Principles Approach for Treating Dye Wastewater by Adriano Santana et al., https://doi.org/10.1002/qua.26501.

Liquid marbles refer to liquid droplets that are covered with a layer of non-wetting particles. They are observed in nature and have practical significance. However, a generalized framework for analyzing liquid marbles as they inflate or deflate is unavailable. The present study fills this gap by developing an analytical framework based on liquid-p...

The Leidenfrost phenomenon entails the levitation of a liquid droplet over a superheated surface, cushioned by its vapor layer. For water, superhydrophobic surfaces are believed to suppress the Leidenfrost point ($\it{T}$$_{\rm L}$)-the temperature at which this phenomenon occurs. The vapor film obstructs boiling heat transfer in heat exchangers, t...

p>Harrington’s thumb rule states that for every 1% increase in seed moisture content (SMC), seed lifetime decreases by 50%. Thus, to avoid post-harvest grain losses, stored seeds must be insulated from water. Although the jute bags typically used to store grains afford an ecofriendly, durable, and low-cost storage solution, their hydrophilic nature...

Excessive evaporative loss of water from the topsoil in arid-land agriculture is compensated via irrigation, which exploits massive freshwater resources. The cumulative effects of decades of unsustainable freshwater consumption in many arid regions are now threatening food-water security. While plastic mulches can reduce evaporation from the topsoi...

In article number 2001268, Himanshu Mishra and co‐workers present a comprehensive report on the strengths and weaknesses of biomimetic doubly reentrant cavities in the context of pressure‐induced wetting transitions underwater. They pinpoint the contributions of surface make‐up, hydrostatic pressure, and cavity profile and aspect ratio through a br...

The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science. A clear understanding of these mechanisms could, for instance, aid the rational design of triboelectric generators and micro- and nano-fluidic devices. Here, we investigate the origins of the exc...

Numerous materials are employed for the removal of contaminants from wastewaters. However, the regeneration/reuse of these materials is still seldom practiced. Quantitative insights into intermolecular forces between the contaminants and the functional surfaces might aid the rational design of reusable materials. Here, we compare the efficacies of...

Superomniphobic surfaces, which repel droplets of polar and apolar liquids, are used for reducing frictional drag, packaging electronics and foods, and separation processes, among other applications. These surfaces exploit perfluorocarbons that are expensive, vulnurable to physical damage, and have a long persistence in the environment. Thus, new a...

The removal of water-soluble organics from aqueous feeds is required in numerous practical applications, including bioresource processing, fermentation, and wastewater treatment. To this end, direct contact membrane distillation (DCMD) has been proposed as a separation technology. DCMD utilizes hydrophobic membranes – typically, comprising perfluor...

Nuclear quantum effects (NQEs) in water arise due to delocalization, zero-point energy (ZPE), and quantum tunneling of protons. Whereas quantum tunneling is significant only at low temperatures, proton delocalization and ZPE influence the properties of water at normal temperature and pressure (NTP), giving rise to isotope effects. However, the cons...

The air–water interface serves as a crucial site for numerous chemical and physical processes in environmental science and engineering, such as cloud chemistry, ocean-atmosphere exchange, and wastewater treatment. The development of “surface-selective” techniques for probing interfacial properties of water therefore lies at the forefront of researc...

The recent application of electrosprays to characterize the air-water interface, along with the reports on dramatically accelerated chemical reactions in aqueous electrosprays, have sparked a broad interest. Herein, we report on complementary laboratory and in silico experiments tracking the oligomerization of isoprene, an important biogenic gas, i...

Rough/patterned/textured surfaces with nano/micro cavities that broaden below the surface – known as ‘re-entrant’ – can be omniphobic (macroscopic contact angle greater than 90° for both water and oils). The existing theoretical models that explain the effects of texture on wetting are complex and do not provide a simple procedure for predicting th...

Wetting of rough surfaces involves time-dependent effects, such as surface deformations, non-uniform filling of surface pores within or outside the contact area, and surface chemistries, but the detailed impact of these phenomena on wetting is not entirely clear. Understanding these effects is crucial for designing coatings for a wide range of appl...

In tropospheric chemistry, secondary organic aerosol (SOA) is deemed an end product. Here, on the basis of new evidence, we make the case that SOA is a key reactive intermediate. We present laboratory results on the catalysis by carboxylate anions of the disproportionation of NO2 'on water': 2NO2 + H2O = HONO + NO(9-) + H+ (R1), and supporting quan...

We will summarize recent advances in First-principles based methods for predicting interfacial entropy and free energy with applications to reactions at surfaces of water contg. various electrolytes. At Caltech, we have recently adapted an electrospray ionization mass spectrometer to selectively probe physicochem. phenomena on liq. surfaces. Thus,...

Recent experiments in our laboratory have shown that the probability of gaseous HNO 3 deprotonation on the surface of water is dramatically enhanced by anions. Herein, we report a quantum chemical study of how a HNO 3 molecule transfers its proton upon approaching water clusters containing or not a chloride ion. We find that HNO 3 always binds to t...

Differences in the extent of protonation of functional groups lying on either side of water-hydrophobe interfaces are deemed essential to enzymatic catalysis, molecular recognition, bioenergetic transduction, and atmospheric aerosol-gas exchanges. The sign and range of such differences, however, remain conjectural. Herein we report experiments show...

Extraction of boron from aqueous solutions using selective resins is important in a variety of applications including desalination, ultrapure water production, and nuclear power generation. Today's commercial boron-selective resins are exclusively prepared by functionalization of styrene-divinylbenzene (STY-DVB) beads with N-methylglucamine to prod...

Proton transfer (PT) through and across aqueous interfaces is a fundamental process in chemistry and biology. Notwithstanding its importance, it is not generally realized that interfacial PT is quite different from conventional PT in bulk water. Here we show that, in contrast with the behavior of strong nitric acid in aqueous solution, gas-phase HN...

Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially va...

In a global process linking the Earth's climate with its ecosystems, massive photosynthetic isoprene (ISOP) emissions are converted to light-scattering haze. This phenomenon is imperfectly captured by atmospheric chemistry models: predicted ISOP emissions atop forest canopies would deplete the oxidizing capacity of the overhead atmosphere, at varia...

Key chemical and biological processes are driven by proton transfer (PT) across water interfaces with hydrophobic media. What distinguishes PT 'on water' from conventional PT 'in water', however, remains unclear. Here we show that nitric acid, a strong acid 'in water', does not dissociate on the surface of water unless anions are present therein. W...

A scalable electrochemical process for addressing the thermomechanical compliance and contact resistance at metal/thermoelectric (M/TE) interfaces by integrating TE films with carbon nanotube (CNT) arrays is presented. Thermomechanical compliance and thermal contact characteristics of TE/CNT/M and TE/M contacts are compared. A process-flow for patt...

Nano/microparticles have been used widely in drug delivery applications. The majority of the particles are prepared by the conventional emulsion methods, which tend to result in particles with heterogeneous size distribution with sub-optimal drug loading and release properties. Recently, microfabrication methods have been used to make nano/micropar...

Thermomechanical compliance, electrical and thermal contact resistances in miniaturized thermoelectric devices Miniaturized thermoelectric (TE) heat-pumps seem to be the ideal candidate for localized heat-flux dissipation challenges in microelectronics . It is unfortunate that despite of sustained research in this field, the realization of widespre...

Interestingly, an esoteric branch of pure mathematics called “functional analysis”, more general and profound than variational calculus and originally developed by mathematicians, can be employed to explain clearly how the finite element machinery works. In a very abstract way, finite element results can be portrayed as “shadows” or orthogonal proj...

Moderate electrical contact resistance between two metal substrates has been reported when one of the two surfaces was covered with a multiwall carbon nanotube (MWCNT) film1. The motivation behind this work is to study the effects on electrical contact resistance of depositing MWCNT films on both mating surfaces. We have measured the electrical con...