Low Adhesion Force Research Articles

Optimization of Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines menisci morphology and percolation behavior of water through the porous fiber matrix of the Gas Diffusion Layer (GDL), and the transport characteristics of droplets according to the energy landscape of the medium. The hydrophobic GDL, which shows promise for improved water management, can be classified as non-wetting (NW), and mixed-non-wetting (MNW, i.e. PTFE coated). The mixed-non-wetting behavior is caused by the hydrophobic coating which allows parts of the meniscus contact line to deform freely in contact with the fibers, while other parts of the meniscus remain pinned due to coating defects. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume, setting it apart from both NW and wetting GDL. The main transport mechanism for NW media is by droplet gliding along the fibers, made possible by low adhesion forces. “Clamshell” droplets are energetically favored at high contact angles, optimal design would require small volume droplets yielding low adhesion forces for this morphology. On the other hand, if MNW conditions are present, optimal design should aim for a small droplet volume and high breakthrough pressure as shown in present simulations. The numerical model employed herein captures the meniscus evolution and the corresponding breakthrough pressure for MNW and wetting media, and various degree of pinning. The model predicts up to 50% higher breakthrough pressure when 20% of the meniscus perimeter is pinned, for the MNW medium when compared to the wetting (non-coated) counterpart, results being supported by recent experimental studies.

Self-assembling of chimeric mussel-inspired bio-adhesives originated from Mytilus californianus and Anabaena flos-aquae: A new approach to develop underwater adhesion

Bio-adhesives play a pivotal role in a wide range of medical applications. However, there are some problems about their application in different pH values and low adhesion force under wet conditions. Here, we report new recombinant fusion protein achieved by mussel foot proteins (Mfps) of Mytilus Californianus and gas vesicle protein A (GvpA) of Anabaena flos-aquae by genetic engineering methods. Transmission electron microscopy verified that these chimeric proteins self-assembled into β-sheet rich fibres because of GvpA amyloid structure. Also, in comparison to other studies, their adhesion forces were significantly increased, especially in the alkaline environments based on Mfp-3 and Mfp-5, confirmed by the colloidal probe atomic force microscope. This study illustrates that copolymer of Mfp-5-GvpA:GvpA-Mfp-3 can be used as a sturdy underwater adhesive with tolerance to auto-oxidation, especially at basic conditions.

Construction of hierarchically hollow micro-nanostructured surface on polyester via in-situ chlorosilane polymerization and its superhydrophobicity

Superhydrophobic fibers based on hierarchically hollow structured surface were prepared for the first time via in-situ growth on polyester, filaments-on-spheres (SF) structures, filaments-and-spheres-on-spheres (FASS) structures and spheres-on-spheres (SS) structures were constructed, exhibiting excellent superhydrophobicity with water contact angles of 158.7 ± 3.4°, 158.5 ± 0.9°, 152.7 ± 3.6° and sliding angles of 1.0 ± 0.7°, 2.3 ± 0.4°, 4.5 ± 0.6°, respectively. More than that, extremely low adhesive force of 74.48 μN was attained. The mechanism of in-situ formation of hollow hierarchical structures on polyester was proposed, and surface chemistry was verified by carrying out X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Moreover, the effect of water absorption on the hydrolysis of chlorosilane was also investigated, showing that wet fabric soaking in solution was of pivotal importance to the hydrolysis condensation polymerization and as-obtained hierarchical structures.

Tails stabilize landing of gliding geckos crashing head-first into tree trunks

Animals use diverse solutions to land on vertical surfaces. Here we show the unique landing of the gliding gecko, Hemidactylus platyurus. Our high-speed video footage in the Southeast Asian rainforest capturing the first recorded, subcritical, short-range glides revealed that geckos did not markedly decrease velocity prior to impact. Unlike specialized gliders, geckos crashed head-first with the tree trunk at 6.0 ± 0.9 m/s (~140 body lengths per second) followed by an enormous pitchback of their head and torso 103 ± 34° away from the tree trunk anchored by only their hind limbs and tail. A dynamic mathematical model pointed to the utility of tails for the fall arresting response (FAR) upon landing. We tested predictions by measuring foot forces during landing of a soft, robotic physical model with an active tail reflex triggered by forefoot contact. As in wild animals, greater landing success was found for tailed robots. Experiments showed that longer tails with an active tail reflex resulted in the lower adhesive foot forces necessary for stabilizing successful landings, with a tail shortened to 25% requiring over twice the adhesive foot force.

The co‐effect of microstructures and mucus on the adhesion of abalone from a mechanical perspective

Reliable and reversible adhesion underwater is challenging due to the water molecules and weak layers of contaminants at the contact interface, which requires to deepen the understanding of wet adhesion of biological surfaces. Herein, the co-effect of microstructures and mucus of abalone foot on wet adhesion is investigated from both experimental and theoretical perspectives. The morphologies, adhesion force and coefficient of friction indicate that the mucus in adhesion zone is crucial for successful attachment of abalone based on capillary forces and viscous forces, and the mucus in non-adhesion zone with lower adhesion force and friction coefficient may behave as a lubricant for the locomotion. The theoretical calculation manifests that the microstructures may help abalone to form multiple liquid bridges with the secreted mucus, and significantly increase the wet adhesion force of abalone. These findings will bring profound views into the underlying mechanisms of biological surface adhesion.

Optically Manipulated Microtools to Measure Adhesion of the Nanoparticle-Targeting Ligand Glutathione to Brain Endothelial Cells.

Targeting nanoparticles as drug delivery platforms is crucial to facilitate their cellular entry. Docking of nanoparticles by targeting ligands on cell membranes is the first step for the initiation of cellular uptake. As a model system, we studied brain microvascular endothelial cells, which form the anatomical basis of the blood-brain barrier, and the tripeptide glutathione, one of the most effective targeting ligands of nanoparticles to cross the blood-brain barrier. To investigate this initial docking step between glutathione and the membrane of living brain endothelial cells, we applied our recently developed innovative optical method. We present a microtool, with a task-specific geometry used as a probe, actuated by multifocus optical tweezers to characterize the adhesion probability and strength of glutathione-coated surfaces to the cell membrane of endothelial cells. The binding probability of the glutathione-coated surface and the adhesion force between the microtool and cell membrane was measured in a novel arrangement: cells were cultured on a vertical polymer wall and the mechanical forces were generated laterally and at the same time, perpendicularly to the plasma membrane. The adhesion force values were also determined with more conventional atomic force microscopy (AFM) measurements using functionalized colloidal probes. The optical trapping-based method was found to be suitable to measure very low adhesion forces (≤ 20 pN) without a high level of noise, which is characteristic for AFM measurements in this range. The holographic optical tweezers-directed functionalized microtools may help characterize the adhesion step of nanoparticles initiating transcytosis and select ligands to target nanoparticles.

Near-infrared light accurately controllable superhydrophobic surface from water sticking to repelling

Great attention has been paid to superhydrophobic surface with tunable water adhesion behaviors, but many challenges still remain for developing a surface with accurate regional control of the superwetting behaviors to realize on-demand responses. Herein, a superhydrophobic surface with accurately controllable water adhesion performance for local areas has been developed, by integrating carbonyl iron particles (CIPs) into a shape memory polymer (SMP) to get photothermal-responsive pillar array. The morphologies of the programmed surface can be remotely and accurately regulated through near-infrared (NIR) light irradiation, hence resulting in the accurate control of surface superwetting behaviors. By adjusting the intensity and targeted area of the NIR irradiation, the controllable surface deformation even in a minimal area of ~0.95 mm2 can be achieved. Among those, the surface with bent microstructures demonstrates high water adhesion force (98 μN) with a high water rolling-off angle (even the surface was overturned to 180°), whereas the superhydrophobic surface with the recovered micro/nanostructure arrays exhibits relatively low water adhesion force (25 μN) with an extremely low rolling-off angle (4°). We have proven that these programmable superhydrophobic surfaces can not only accurately adjust the droplet adhesive force in the target area, but also serve as ideal platforms for distinct microfluidic microreactors. These unique characteristics endow the NIR light remotely controlled superhydrophobic surfaces with special advantages for abroad applications in liquid droplet manipulations, micro reactions, biochemical detections, etc.

Fabrication of mechanically stable UV-curing superhydrophobic coating by interfacial strengthening strategy

UV-curing superhydrophobic coatings, which have high efficiency and energy saving characteristics, have wide application prospects, but still face some challenges, such as limited mechanical stability and low adhesive force. Herein, a durable UV-curing superhydrophobic polyurethane acrylic (PUA) coating was prepared via an interfacial strengthening strategy. Nano-SiO2 grown in situ on the surfaces of carboxylated carbon nanotubes (CNTs) were used to strengthen the interfacial interaction between the particles and reduce the barrier effect of the nanoparticles on the resin monomers. The CC bonds on the CNTs@SiO2 particle surface, which were grafted with 3-methacryloxypropyltrimethoxysilane (MPS), improved the lateral film-forming properties of the coating as the PUA monomers polymerized with the unsaturated CC bonds. Additionally, the longitudinal bonding between the coating and metal surface was enhanced by the addition of MPS, which acted as a bridge that connected the CC bonds of PUA to the hydroxyl group on the metal surface. Because of the aforementioned interfacial strengthening in both the vertical and horizontal directions, the superhydrophobic PUA/MPS/CNTs@SiO2 coating exhibited excellent adhesion (0 grade) and maintained superhydrophobicity even after 1500 cycles of abrasion. In addition, the prepared superhydrophobic coating also possessed good UV-resistance, self-cleaning properties, and could withstand impact by water droplets (4.4 m/s) and sand.

Transcriptomic Analysis Identified ARHGAP Family as a Novel Biomarker Associated With Tumor-Promoting Immune Infiltration and Nanomechanical Characteristics in Bladder Cancer.

Bladder cancer (BCa) is a common lethal urinary malignancy worldwide. The role of ARHGAP family genes in BCa and its association with immuno-microenvironment remain largely unknown. ARHGAP family expression and immune infiltration in BCa were analyzed by bioinformatics analysis. Then, we investigated cell proliferation, invasion, and migration in vivo and in vitro of the ARHGAP family. Furthermore, atomic force microscopy (AFM) was employed in measuring cellular mechanical properties of BCa cells. The results demonstrated that ARHGAP family genes correlate with a tumor-promoting microenvironment with a lower Th1/Th2 cell ratio, higher DC cell infiltration, higher Treg cell infiltration, and T-cell exhaustion phenotype. Silencing ARHGAP5, ARHGAP17, and ARHGAP24 suppressed BCa cell proliferation, migration, and metastasis. Knocking down of ARHGAPs in T24 cells caused a relatively higher Young’s modulus and lower adhesive force and cell height. Taken together, ARHGAP family genes promote BCa progressing through establishing a tumor-promoting microenvironment and promoting cancer progression.

Reusing ground tire rubber powder as thermoplastic elastomers with excellent superhydrophobicity and self-cleaning performance

A simple, effective and inexpensive method was proposed to reuse ground tire rubber (GTR) powder by preparing a superhydrophobic surface via a molding process. The obtained superhydrophobic surface was based on low-density polyethylene (LDPE) / ground tire rubber (GTR) thermoplastic elastomers (TPEs) where the styrene-butadiene-styrene block copolymer (SBS) was used as compatibilizer and series sandpapers were used as templates. The mechanical properties, hydrophobic properties, surface morphology and self-cleaning property were investigated systematically. The results showed that both of the mechanical properties and superhydrophobicity could be greatly improved with a certain amount of SBS. The superhydrophobic surface based on molded LDPE/SBS/GTR (weight ratio = 40/15/60) TPE exhibited excellent superhydrophobicity (with a contact angle of 164.6° ± 3.0° and a tilt angle of 4.4° ± 1.9°). Furthermore, abundant tearing microstructure could be found obviously by morphology observation. Optical images indicated the surface possessed of low adhesion force and self-cleaning property.

Mycelial pellets for alleviation of membrane fouling in membrane bioreactor

In this study, mycelial pellets (MPs) were employed as efficient and sustainable bio-carriers to alleviate membrane fouling in membrane bioreactor (MBR). The comparative study was performed in lab-scale MBR in the absence and presence of MPs addition under continuous operation for 80 days. The results demonstrated efficient removal of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) for both systems, while MPs addition led to lower rate at which transmembrane-pressure was increased, lower filtration resistance, thinner bio-cakes and fewer contents of extracellular polymeric substances (EPS) and soluble microbial products (SMP) in bio-cakes of membrane surface. Adding MPs into MBR could enhance biomass retention and EPS content in suspended liquid, thus accelerating the granulation of activated sludge, which should be responsible for mitigation of membrane fouling. According to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the total surface free energy between membrane and foulants was always attractive, but total interfacial interaction especially acid-based (AB) interaction in the presence of MPs was weaker than that in the absence, confirming lower adhesion force induced by MPs. Furthermore, high throughput sequencing analysis of bio-cakes illustrated that a smaller relative abundance of EPS producer including the classes Gammaproteobacteria, Alphaproteobacteria and Actinobacteria, and a higher abundance of SMP decomposer including the class Chloroflexia were observed. The relevant mechanisms were underlined schematically to explain the function of MPs in mitigating membrane fouling process, which could be attributed to formation of biofilm with MPs serving as bio-carriers followed by promoted sludge granulation. This study provides a proof-in-concept demonstration of using MPs as bio-carriers to mitigate membrane fouling, making wastewater treatment by MBR more efficient, more reliable and more sustainable.

A facile one-step route to fabricate bio-inspired superhydrophobic matrix with high corrosion inhibition to Cu metal

Bio-inspired by nature, superhydrophobic surface provides opportunities in the field of material protection. In this research, a single one-step electrodeposition procedure has fabricated superhydrophobic (SHP) coating based on Ca-myristic acid complex onto Cu substrate. The as-fabricated superhydrophobic surfaces possess extremely low surface adhesive force to water phase and excellent self-cleaning and antifouling ability. Using different electrochemical approaches including scanning Kelvin probe (SKP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve techniques, the coating is revealed to protect Cu substrate from corrosion. After being soaked in 3.5wt% NaCl solution for 120 h, corrosion current density of SHP Cu is still much lower (1/27.5) than that of bare Cu. In addition, through 5.0wt% NaCl salt spray experiment, the corrosion current density of SHP Cu decreases to 5.49×10−5 mA/cm2, which is much lower than that of the bare Cu (1.02×10−6 mA/cm2). Therefore, the SHP coating can be potentially used to protect Cu from corrosion in harsh environment.

Tunable adhesion of an elastic pillar by pressurizing inner cavity

This work studies the effect of a cavity with inner pressure on the adhesion of circular pillars with a flat tip in contact with a rigid smooth surface. The inner cavity of pillars is pressurized positively before the contact. The effect of the cavity on the adhesion is examined for different cavity diameters and different membrane thicknesses over the cavity. The shape of the tip of the pillars is changed in accordance with the cavity dimension and the positive cavity pressure, which allows the change of an adhesive contact type from a flat-punch adhesive contact to a spherical adhesive contact that results in tunable adhesion strength of circular pillars. The results demonstrate that having an inner cavity reduces the adhesion, where the cavity diameter is more effective than the membrane thickness over the cavity on the reduction of the adhesive force. Applying pressure to the inner cavity of the pillars changes the sphericity, which alters the adhesive force accordingly. The sphericity [Formula: see text]0.1 almost has no effect on the tunable adhesion strength, where the higher sphericity results in the reduction of the adhesive force from high adhesive force to low adhesive force linearly with a tunable efficiency between 95% and 98%.

Superamphiphilic TiO2 Composite Surface for Protein Antifouling.

Unwanted protein adsorption deteriorates fouling processes and reduces analytical device performance. Wettability plays an important role in protein adsorption by affecting interactions between proteins and surfaces. However, the principles of protein adsorption are not completely understood, and surface coatings that exhibit resistance to protein adsorption and long-term stability still need to be developed. Here, a nanostructured superamphiphilic TiO2 composite (TiO2 /SiO2 ) coating that can effectively prevent nonspecific protein adsorption on water/solid interfaces is reported. The confined water on the superamphiphilic surface enables a low adhesion force and the formation of an energy barrier that plays a key role in preventing protein adsorption. This adaptive design protects the capillary wall from fouling in a harsh environment during the bioanalysis of capillary electrophoresis and is further extended to applications in multifunctional microfluidics for liquid transportation. This facile approach is not only perfectly applied in channels with complicated configurations but may also offer significant insights into the design of advanced superwetting materials to control biomolecule adhesion in biomedical devices, microfluidics, and biological assays.

A novel ceramic microfiltration membrane fabricated by anthurium andraeanum-like attapulgite nanofibers for high-efficiency oil-in-water emulsions separation

Anthurium andraeanum-like Fe3O4-attapulgite (FATP) fibers were prepared by anchoring nano-Fe3O4 particles on the surface of attapugite (ATP) via chemical coprecipitation. Then a novel ceramic microfiltration membrane with superhydrophilic and underwater superoleophobic performance was fabricated based on the FATP fibers. Ascribed to the hydrophilic performance of Fe3O4 and micro-nano structure of FATP fibers, the underwater oil contact angles of the FATP membrance for various types of oils are larger than 158° and the membrane also possesses rather low adhesion force with oil droplets. After 3 cycles of oil-in-water (O/W) emulsion separation, the steady flux of FATP membrane is 209 L m−2 h−1, 44% higher than that of ATP membrane. Moreover, the FATP membrane is stable and easy to clean, its oil rejection maintains at 98.7% and flux can recover by 86.5% using hot water as cleaning agent. The as-developed anthurium andraeanum-like structure in membrane surface provides promising guidance to improve the O/W purification performance of membrane.

The adhesive behavior of the polyethylene component in the “GP-ice” for studying the ice propulsion of the promising Arctic icebreakers

The maritime constituent is the crucial component of the Artic transport and logistics system. In the modern period of the development of science and technology, the ice model experiment in the experimental model basin is the main instrument of the research engineer, who creates and develops the existing arctic vessels forms. The article is dealt with the one of the aspects of the composite model ice (“GP-ice”) consisting of the polyethylene granules frozen into natural ice. The crucial factor providing the modelling conditions is the model ice strength reduction due to lower adhesion forces on the granules. The aim of this investigation was to assess the reliability of the existing data and to obtain the one’s own results in terms of the adhesion strength value at the normal fracture. The experimentation procedure in the NNSTU small ice tank is presented. The adhesive compound strength of the high-pressure polyethylene and ice at the normal fracture was determined. The analysis of results, which has satisfactory statistical characteristics, is presented. As the experiments results, the dependence of the adhesion strength value on the temperature inside the heat chamber (-20, -10) was revealed. The influence of the frozen surface boundaries was also significant and had a negatively impact on the results of the samples separation of a smaller dimension-type. In further the obtained results will be used in the mathematical models of the “GP-ice” deformation and fracture, as well as for improving the ice cover composite model for testing the promising Arctic icebreakers forms in the experimental model ice basin.

(Invited) Micro-Transfer-Printing at X-FAB: Demonstration of a New Technology for Wafer-Level Packaging

Introduction Within this publication micro-transfer-printing (µTP) will be introduced as a promising new technology for 3D wafer-level packaging (WLP). The main advantage of µTP arises from the substantial parallel chip transfer from the source wafer to a target device by a visco-elastic stamp. To execute and develop this versatile technology a pilot line has been installed in the X-FAB MEMS Foundry GmbH clean room facilities within a funded EU project (MICROPRINCE). To demonstrate the general process capabilities recent results on the preparation and integration of silicon-based ICs, optical filters and III/V semiconductors shall be discussed. Contents The general principle of µTP is based on the utilization of an elastomer stamp to transfer devices or arrays of devices from their native substrate (source) to a non-native target material [1]. A mandatory requirement for this transfer is that the stamp, typically made of polydimethylsiloxane (PDMS), provides tunable adhesion properties to the printable chiplet [2]. Thereby, high adhesion during the “pick-up” as well as low adhesion forces during the “placing” steps can be achieved.The general process flow for micro-transfer-printing is illustrated in Figure 1 .Therein, the main advantage of µTP, namely the extensive parallelization of the chip placement (schematics a.-e.), can be recognized. Such a parallelization offers the possibility of a major process time reduction.Prior to the transfer operation, the source wafer has to be prepared for the printing process. This involves the formation of reliable anchor and tether structures which carry the printable chiplets after the release etch. Another crucial requirement on these structures is that they provide a controlled micro-fracture and release the transfer chiplets to the stamp [3]. An example of a print-ready optical filter device is furthermore illustrated in Figure 1g.The target on the other hand has to be coated with an adhesion providing polymer (see red layer in Figure 1d.-f.) for which bisbenzocyclobutene (BCB) is applied at X-FAB.After the printing itself, a post-processing comprising the patterning of applied adhesion media, a wiring via a Cu redistribution layer (RDL) and a passivation is required to allow the functionality of active devices (see Figure 1f.). Figure 1h shows two 3D-integrated demonstrator devices which have been printed on a XL035 technology from X-FAB and which were afterwards connected via a Cu-RDL layer. Within the printing experiments of these chiplets a print yield of about 99.9% with a placement accuracy of down to 3σ ≤ 0.78µm has been achieved. Conclusions By this publication the Micro-transfer-printing (µTP) technology and its technical implementation will be introduced. To build up and develop µTP processes a pilot line has been installed in the X-FAB MEMS Foundry GmbH via a funded ECSEL project called “MICROPRINCE”. To execute the µTP technology for 3D integration several process steps have to be executed to prepare a source wafer for the printing operation, transfer the chiplets to a non-native target and connect them afterwards during the prost-processing. The process sequence itself will be explain in more detail within the presentation on examples of optical filters, silicon ASICs as well as III/V semiconductor chiplets. Acknowledgements This work is funded by ECSEL JU under grant agreement No 737465 and by the BMBF No ESECS16204. Further, the authors like to thank all X-FAB internal and external MICROPRINCE partners for their support.

Running-in behavior of a H-DLC/Al2O3 pair at the nanoscale

Diamond-like carbon (DLC) film has been developed as an extremely effective lubricant to reduce energy dissipation; however, most films should undergo running-in to achieve a super-low friction state. In this study, the running-in behaviors of an H-DLC/Al2O3 pair were investigated through a controllable single-asperity contact study using an atomic force microscope. This study presents direct evidence that illustrates the role of transfer layer formation and oxide layer removal in the friction reduction during running-in. After 200 sliding cycles, a thin transfer layer was formed on the Al2O3 tip. Compared with a clean tip, this modified tip showed a significantly lower adhesion force and friction force on the original H-DLC film, which confirmed the contribution of the transfer layer formation in the friction reduction during running-in. It was also found that the friction coefficient of the H-DLC/Al2O3 pair decreased linearly as the oxygen concentration of the H-DLC substrate surface decreased. This phenomenon can be explained by a change in the contact surface from an oxygen termination with strong hydrogen bond interactions to a hydrogen termination with weak van der Waals interactions. These results provide new insights that quantitatively reveal the running-in mechanism at the nanoscale, which may help with the design optimization of DLC films for different environmental applications.

Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application

Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Re...

Effects of flow-interruption on the bacteria transport behavior in porous media

Attachment is an important strategy for microorganisms to survive, grow, and perform biogeochemical functions in soil and groundwater systems. This study investigated the effect of flow-interruption (FI) that is common in subsurface environments on bacterial attachment/detachment using a metal-reducing bacterium Shewanella oneidensis strain (MR1) as an example. Column experiments and one dimensional bacterial transport models were performed by varying flow interruption duration, fluid ionic strength, and solid grain surface electrostatic properties with a goal to understand the effect of FI on bacterial attachment/detachment. The results indicated that MR1 generally behaved as colloidal particles in transport and attachment/detachment under continuous flow conditions. However, the FI events induced a significant release of MR1 in both injection and elution phases, showing a peak MR1 concentration, which was higher than that in the injecting solution, immediately after the FI events. The peak MR1 concentrations were higher in systems with lower adhesive forces between bacteria and solid grains, a lower attachment site capacity in porous media, and a longer FI duration. The diffusive release of the previously attached bacteria during the FI events and the momentum force when flow re-started immediately after the FI events were likely the mechanisms leading to bursting release of bacteria with the release concentrations higher than that in the influent solutions. The results have important implication for understanding bacterial migration and attachment, and their subsequent functions, especially in dynamic hydraulic environments such as in hyporheic zones or in soils subject to dynamic changes in infiltration rates under for example extreme precipitation and drought conditions.