Conical Pores Research Articles

Overcoming the Energy vs Power Dilemma in Commercial Li-Ion Batteries via Sparse Channel Engineering.

Improvements in both the power and energy density of lithium-ion batteries (LIBs) will enable longer driving distances and shorter charging times for electric vehicles (EVs). The use of thicker and denser electrodes reduces LIB manufacturing costs and increases energy density characteristics at the expense of much slower Li-ion diffusion, higher ionic resistance, reduced charging rate, and lower stability. Contrary to common intuition, we unexpectedly discovered that removing a tiny amount of material (<0.4 vol %) from the commercial electrodes in the form of sparsely patterned conical pores greatly improves LIB rate performance. Our research revealed that upon commercial production of high areal capacity electrodes, a very dense layer forms on the electrode surface, which serves as a bottleneck for Li-ion transport. The formation of sparse conical pore channels overcomes such a limitation, and the facilitated ion transport delivers much higher power without reduction in the practically attainable energy. Diffusion and finite element method-based simulations provide deep insights into the fundamentals of ion transport in such electrode designs and corroborate the experimental findings. The reported insights provide a major thrust to redesigning automotive LIB electrodes to produce cheaper, longer driving range EVs that retain fast charging capability.

Synaptic Response of Fluidic Nanopores: The Connection of Potentiation with Hysteresis.

Iontronic fluidic ionic/electronic components are emerging as promising elements for artificial brain-like computation systems. Nanopore ionic rectifiers can be operated as a synapse element, exhibiting conductance modulation in response to a train of voltage impulses, thus producing programmable resistive states. We propose a model that replicates hysteresis, rectification, and time domain response properties, based on conductance modulation between two conducting modes and a relaxation time of the state variable. We show that the kinetic effects observed in hysteresis loops govern the potentiation phenomena related to conductivity modulation. To illustrate the efficacy of the model, we apply it to replicate rectification, hysteresis and conductance modulation of two different experimental systems: a polymer membrane with conical pores, and a blind-hole nanoporous anodic alumina membrane with a barrier oxide layer. We show that the time transient analysis of the model develops the observed potentiation and depression phenomena of the synaptic properties.

Dynamic light scattering unveils stochastic degradation in large-pore mesoporous silica nanoparticles

Mesoporous Silica Nanoparticles (MSNs) have been increasingly investigated as versatile drug delivery carriers. A particular challenge for the systemic use of MSNs lies in the control of their degradation, which has not been fully understood until now. We implemented standard dynamic light scattering (DLS) experiments and introduced a novel DLS technique in a confocal volume to track the dynamics of large-pore MSN degradation in situ. This unique DLS technique, which involves a small observation volume, was chosen for its ability to count particle by particle during the degradation process, a method that has not been commonly used in nanoparticle research. The experiments were performed in different media compositions at low particle concentrations, below the silica solubility limit. MSNs with large conical pores were prepared and studied as they offer the possibility to incorporate and release large-sized biomolecules. Large-pore MSNs followed a singular degradation mechanism following a stochastic-like behavior, a finding that challenges the common idea that all nanoparticles (NPs) degrade similarly and homogeneously over time. We showed that some NPs are observed intact over a prolonged period while most other NPs have already vanished or been transformed into swollen NPs. Thus, a heterogeneous degradation process occurs, while the total concentration of NPs undergoes an exponential decay. These large conical pores MSNs will be utilized as reliable biomolecule nanocarriers by predicting the factors underlying the NP hydrolytic stability.

Dynamic Response of Ionic Current in Conical Nanopores.

Ionic current rectification (ICR) of charged conical nanopores has various applications in fields including nanofluidics, biosensing, and energy conversion, whose function is closely related to the dynamic response of nanopores. The occurrence of ICR originates from the ion enrichment and depletion in conical pores, whose formation is found to be affected by the scanning rate of voltages. Here, through time-dependent simulations, we investigate the variation of ion current under electric fields and the dynamic formation of ion enrichment and depletion, which can reflect the response time of conical nanopores. The response time of nanopores when ion enrichment forms, i.e., at the "on" state is significantly longer than that with the formation of ion depletion, i.e., at the "off" state. Our simulation results reveal the regulation of response time by different nanopore parameters including the surface charge density, pore length, tip, and base radius, as well as the applied conditions such as the voltage and bulk concentration. The response time of nanopores is closely related to the surface charge density, pore length, voltage, and bulk concentration. Our uncovered dynamic response mechanism of the ionic current can guide the design of nanofluidic devices with conical nanopores, including memristors, ionic switches, and rectifiers.

Translocation of polymers through a wide-open conical pore

The transport of biomolecules across a cell membrane is an important phenomenon that plays a pivotal role in the functioning of biological cells. In this paper, we investigate such processes by modeling the translocation of polymers through a conical channel, directed from the wider opening to the narrow end of the conical channel. We use the molecular dynamics approach to study the problem. The effect of the different conical pore geometry and polymer lengths on translocation dynamics is determined from the behavior of the total translocation time, τ, and the waiting time distributions, w(s). The escape of polymer segments from the narrow end of the conical channel is tracked by studying the escape velocity profile (〈v i 〉). To demonstrate the asymmetric pore effects on the translocation dynamics, we compare the translocation process from both the terminals: the wider-opening and the narrow-end of the conical channel. We find striking differences in the translocation dynamics for both processes, which are in agreement with the experimental study. We have accounted for the effect of various rigidity, and increasing length of a polymer chain, on both types of processes. This computational study can be used to underline the translocation process from different conical pores.

Single Condensation Droplet Self-Ejection from Divergent Structures with Uniform Wettability.

Coalescence-induced condensation droplet jumping has been extensively studied for anti-icing, condensation heat transfer, water harvesting, and self-cleaning. Another phenomenon that is gaining attention for potential enhancements is the self-ejection of individual droplets. However, the mechanism underlying this process remains elusive due to cases in which the abrupt detachment of an interface establishes an initial Laplace pressure difference. In this study, we investigate the self-ejection of individual droplets from uniformly hydrophobic microstructures with divergent geometries. We design, fabricate, and test arrays of truncated, nanostructured, and hydrophobic microcones arranged in a square pattern. High-speed microscopy reveals the dynamics of a single condensation droplet between four cones: after cycles of growth and stopped self-propulsion, the suspended droplet self-ejects without abrupt detachments. Through analytical modeling of the droplet in a conical pore as an approximation, we describe the slow isopressure growth phases and the rapid transients driven by surface energy release once a dynamic configuration is reached. Microcones with uniform wettability, in addition to being easier to fabricate, have the potential to enable the self-ejection of all nucleated droplets with a designed size, promising significant improvements in the aforementioned applications and others.

Neuromorphic responses of nanofluidic memristors in symmetric and asymmetric ionic solutions.

We show that ionic conduction properties of a multipore nanofluidic memristor can be controlled not only by the amplitude and frequency of an external driving signal but also by chemical gating based on the electrolyte concentration, presence of divalent and trivalent cations, and multi-ionic systems in single and mixed electrolytes. In addition, we describe the modulation of current rectification and hysteresis phenomena, together with neuromorphic conductance responses to voltage pulses, in symmetric and asymmetric external solutions. In our case, memristor conical pores act as nanofluidic diodes modulated by ionic solution characteristics due to the surface charge-regulated ionic transport. The above facts suggest potential sensing and actuating applications based on the conversion between ionic and electronic signals in bioelectrochemical hybrid circuits.

Influence of conical graded porous architecture on the mechanical, failure behavior and fluid-flow properties for bone scaffold application

IntroductionThe advanced design of the controllable hierarchical gradient architecture of functionally graded porous scaffold is gaining increasing attention in tissue engineering (TE). This paper proposed a new design gradient concept of Schwartz-Primitive (Sch-P) conical graded porous architecture by integrating linear and radial graded patterns. Materials and Methods: Four types of gradient pattern structures with similar 80 % porosity were designed and fabricated using polylactic acid (PLA) pro via material extrusion. The structural compression test was performed to evaluate the mechanical properties in order to validate the computational analysis. In addition to that, computational fluid dynamics (CFD) was conducted to predict the permeability and fluid-induced wall shear stress (WSS) of porous structures. Results: The experimental result shows that conical graded structures exhibit the highest mechanical strength in terms of elastic modulus (64.84 MPa), yield stress (1.83 MPa), and total energy absorption (1.115 J/m3) compared to linear, radial, and uniform structures. The unique smooth surfaces of the conical pores arrangement resulted in excellent strength with a localized fracture in the shape of a chevron and global fracture in a layer-by-layer failure mechanism. Indeed, the permeability values for conical graded meets the fluid permeability of actual cancellous bone. Conclusion: The findings highlighted that conical graded structure offered superior mechanical characteristics with improved energy absorption and failure behavior as well as fluid-flow properties. It indicates that conical graded meets all the mechanical and biological requirements to mimic the cancellous bone, especially in load-bearing applications.

Synaptical Tunability of Multipore Nanofluidic Memristors.

We demonstrate a multipore nanofluidic memristor with conical pores showcasing a wide range of hysteresis and memristor properties that provide functionalities for brainlike computation in neuromorphic applications. Leveraging the interplay between the charged functional groups on the pore surfaces and the confined ionic solution, the memristor characteristics are modulated through the electrolyte type, ionic concentrations, and pH levels of the aqueous solution. The multipore membrane mimics the functional characteristics of biological ion channels and displays synaptical potentiation and depression. Furthermore, this property can be inverted in polarity by chemically varying the pH level. The ability to modulate memory effects by ionic conductivity holds promise for enhancing signal information processing capabilities.

Electrochemical impedance spectroscopy of membranes with nanofluidic conical pores

Electrochemical impedance spectroscopy (EIS) constitutes a useful tool in membrane science and technology because it provides valuable structural and functional information. The different arcs observed in the impedance spectra permit to decouple and understand distinct physico-chemical phenomena occurring under operating conditions. By using EIS techniques, we have characterized here multipore asymmetric membranes with conical pores that exhibit a broad range of ionic conduction properties, including current rectification. These properties can be modulated by tuning the electrical interaction between the charges functionalized on the pore surface and the nanoconfined ionic solution. In particular, the membrane electrical response is studied as a function of the amplitude and frequency of the external voltage signal, the electrolyte type and concentration, and the solution pH. Remarkably, significant chemical inductance effects are observed. The scalability and biocompatibility of these pores suggest good potential for use in hybrid biodevices and interfaces.

Iontronic Nanopore Model for Artificial Neurons: The Requisites of Spiking.

Brain-inspired neuromorphic computing is currently being investigated for effective artificial intelligence (AI) systems. The development of artificial neurons and synapses is imperative to creating efficient computational biomimetic networks. Here we propose the minimal configuration of an effective iontronic spiking neuron based on a conical nanofluidic pore ionic diode. The conductance is composed of a Boltzmann open channel probability and a blocking inactivation function, forming the structure of a memristor. The presence of a negative resistance and the combination of activation-deactivation dynamics cause a Hopf bifurcation. Using the characteristic frequencies of small perturbation impedance spectroscopy, we discuss the conditions of spiking, in which the system enters a limit cycle oscillation. We arrive at the conclusion that an excitable neuron-like system can be made with a single active channel instead of the more complex combination of multiple channels that occurs in the Hodgkin-Huxley neuron model.

Electrochemical performance and impedance of a conical pore in the low–Pt PEM fuel cell catalyst layer

AbstractA model for the transient electrochemical performance of a conical pore in the cathode catalyst layer of a low–Pt PEM fuel cell is developed. The pore is separated from the Pt surface by a thin ionomer film. A transient equation for the oxygen diffusion along the pore coupled to the proton conservation equation in the ionomer film is derived. Numerical solution of the static equations shows superior electrochemical performance of a conical pore as compared to cylindrical pore with equivalent electrochemically active surface area. Equations for the pore impedance are derived by linearization and Fourier–transform of transient equations. The conical pore impedance is calculated and compared to the impedance of equivalent cylindrical pore. It is shown that the pore shape affects the frequency dependence of impedance.

ALTERNATIVE ESTIMATION OF THE SOIL WATER RETENTION CURVE BASED ON THE ARYA-PARIS MODEL

ABSTRACT: The physical and chemical characteristics of a soil determine its hydraulic properties, such as hydraulic conductivity, infiltration, and moisture. Due to the usefulness of a soil's moisture retention characteristic curve, several methodologies have been developed to obtain it. Mathematical models for the prediction of this hydraulic property constitute a type of methodologies that is economical and very affordable. One of the most practical models is the model of Arya and Paris (1981), which, however, requires an adjustment parameter, which limits its applicability in some cases, and, in addition, underestimates the moisture content by not considering the water remaining in the soil menisci. The present study proposes an alternative model based on the model of Arya and Paris, but that attempts to circumvent the disadvantages mentioned above, assuming a pore network formed by conical pores. The predictions of the moisture retention curve of our alternative model were compared with those of the original model through the root mean square error, using experimental data from 100 soils of three different textural classes, taken from the UNSODA database. The results by texture indicate that the alternative model generally produces better estimates for all three textures; however, for 17% of the soils the Arya and Paris model performed better. Keywords: water retention curve, retention, soil, porosity, volume.

Tetraalkoxysilane-Assisted Self-Emulsification Templating for Controlled Mesostructured Silica Nanoparticles.

Although mesoporous silica nanoparticles (MSNs) have been intensively investigated, their mesostructure and formation mechanism are still a topic of debate. Here, we show that MSNS are generated at the interface of the biphasic water-surfactant-triethanolamine-tetraalkoxysilane (TAOS) quaternary system. The spontaneous microemulsification of the hydrophobic TAOS generates microdroplets and direct micelles that both determine the particle size and the pore size. We confirmed also that the dendritic morphology with conical pores is an intermediate species, which readily transforms into regular MSNs concomitantly with the collapse of the microemulsion due to the continuous consumption of TAOS. The prominent effect of the microemulsion on the mechanism growth as a primary template is thoroughly investigated and named here tetraalkoxysilane-assisted self-emulsification templating.

Dry reforming of methane over Ni/SiO2 catalysts: Role of support structure properties

Dry reforming of methane (DRM) can take advantage of greenhouse gases (CH4 and CO2) to reduce their impact on the ecological environment. However, the biggest hurdle for the DRM reaction is design of catalysts with strong sintering and carbon deposition resistance. Furthermore, understanding the role of supports is vital for the logical construction of dry reforming catalysts. Here, the effect of support pore structure on DRM catalyst is elucidated by impregnating nickel with inverted conical mesoporous silica spheres (MSS), ordered mesoporous silica (MCM-41), and commercial silica (SiO2). A series of characterizations showed that the MSS with inverted-tapered pore structure was favorable for the active components to disperse in the confinement channel, thereby improving the dispersibility of the active metals. In addition, the inverted-tapered pores were more favorable for the contact between reactant molecules and active sites. Compared with 10Ni/MCM-41 and 10Ni/SiO2, the catalyst 10Ni/MSS exhibited the best initial CH4 conversion (85.1 %) and CO2 conversion (90.5 %). The stability test showed that the MSS carrier effectively prevented Ni nanoparticle sintering and carbon deposition. Kinetic studies showed that the unique inverted conical pore structure significantly reduced the apparent activation energies for CH4 and CO2 splitting. These findings provide a new perspective for designing Ni-based dry reforming catalysts.

Influence of shape and charged conditions of nanopores on their ionic current rectification, electroosmotic flow, and selectivity

The electrokinetic behaviors, including ionic current rectification (ICR), selectivity, and electroosmotic flow (EOF) of a nanopore play important role in applications such as nano sensing, salinity gradient power, and desalination of sea water. Since those behaviors can be influenced significantly by the shape and charged conditions of a nanopore, the influence of these factors on its performance is studied in detail by comparing the behavior of six types of nanopore (conical, cylindrical, cigar, funnel, hourglass, and dumbbell-shaped pores), each of them can be unipolarly or bipolarly charged. In addition to examining their performance under various conditions, the associated mechanisms are also discussed. We show that the internal volume of a nanopore is the most important factor influencing its ICR behavior. However, the selectivity of a nanopore depends both on its internal volume and the fraction of its narrow region. The bipolar and unipolar nature of a nanopore can yield interesting velocity profile, which is also influenced by the salt concentration and nanopore geometry.

Pore characteristics and fractal characterization variability of typical middle- and high-rank coal reserves: A case study of middle- and high-rank coal samples in western Guizhou

This article focused on the study of pore structure characteristics of Songhe and Linhua coal samples based on mercury injection experiments and high-pressure isothermal adsorption experiments. The results show that the pore structure of coal samples in the two mining areas is obviously different under the influence of metamorphic degree. The pores of Songhe mine coal samples, which are characteristic of middle-rank coal reserves, are predominantly open cylindrical pores with good connectivity to medium-to-large pores but poor absorption capacity. The tiny and medium pores of Linhua coal samples, which are characteristic of high-level coal reserves, have poor connectivity, dominated by conical pores with mostly closed and semi-closed pores. The pore size distribution of the middle-rank coal sample is multi-peaked, with better developed pore sizes, while the pore size distribution of the Linhua coal sample is bi-peaked, with micro and small pores developed. The pore fractal shape of high-rank coal reserves is higher than that of middle-rank coal reserves, and the complexity of permeable pore space and diffusive pore space of high-order coal reservoirs is higher than that of middle-order coal reservoirs.

Verification of A New Filter for Isolation of Circulating Tumor Cells by Only Blood Filtration.

Since circulating tumor cells (CTCs) are precursors of metastatic lesions, extracting CTCs from whole blood is useful in obtaining information for cancer treatment. One of the CTC isolation methods is the size selection method; however, since the conventional methods are expensive and cumbersome, we developed an affordable and simple filter, whose usefulness is verified in this study. The new filter [hereafter, soft micropore filter (S-MPF)] is made up of a polyethylene film with a thickness of 15 μm and conical pores having a diameter of 8-10 μm, which are opened uniformly (opening rate, 20%). This filter can filter whole blood by free-falling under gravity. The possibilities of the filter's usage for model CTC isolation, immunostaining, short-term cell culture, and gene mutation detection in extracted model CTCs were verified. S-MPF was able to extract model CTCs with an isolation rate of up to 15%. These model CTCs were detected by cytology, immunostaining, and culture by short-term incubation of filtered cells. Furthermore, genetic mutations were identified in the cultured cells. In addition, CTC isolation from the peripheral blood of patients with lung cancer was demonstrated by setting the volume of collected blood to 15 ml to prevent a low recovery rate. The S-MPF can be used to extract model CTCs quickly and easily. Moreover, cytological diagnosis, immunostaining, short-term culture, and gene mutation search are possible with this filter. Given its proven applicability in clinical samples, this filter can be used in clinical settings.

High-Efficient Fog Harvest from a Synergistic Effect of Coupling Hierarchical Structures.

Fog harvesting is an important method to solve the water shortage in arid and semi-arid areas by collecting water from air. Improving fog harvesting efficiency is still a big challenge to be overcome. Herein, under the inspiration of natural creatures, a novel harvesting structure that couples a hierarchical microchannel (HMC) needle with the Janus membrane by taking a conical pore as their junction is proposed. Such an HMC-conical pore-Janus membrane system can improve the harvesting efficiency by regulation of liquid behavior in the whole fog harvesting process involving droplet capture from air, high speed transport on the microchannel, and droplet detachment from Janus. The synergistic effects of the hierarchical channel-conical pore-Janus structure are exploited in terms of capture, transport, and detachment capabilities, and their underlying mechanism to enhance fog harvesting efficiency is built. Compared with the traditional harvesting structure, the proposed hierarchical channel-conical-Janus coupling mode was demonstrated to improve fog harvesting efficiency by 90%. Such a coupled system has potential applications in efficient fog harvesting systems, microfluidic devices, and liquid manipulation.

Electroosmotic transport and current rectification of viscoelastic electrolyte in a conical pore nanomembrane

Nanomembranes have received a wide range of applications in water treatment, gas separation, molecular and supramolecular separations. Nanopores offer the separation of the components even at nano- or picomolar concentrations. In addition, DNA translocation, DNA sequencing of nucleotides, single molecular analyses for biomedical nanoscopic devices are perhaps the unique feature of nanomembranes that convectional membranes may not achieve. Despite such an overwhelming application, the theoretical understanding of electroosmotic transport in nanopores is still in infancy and it is limited to simple Newtonian-like fluids. This work has numerically investigated the ionic current rectification (ICR) in a conical nanopore filled with viscoelastic electrolyte. ICR quantifies the unequal upstream and downstream ionic flow rates during the forward and reverse potential bias. This is similar to a semiconductor transistor’s current potential (I−V) response. The ICR exhibits several potential applications in the design of biosensors for the measurement and analysis of biofluids such as blood, lymph, and plasma, micro-scale pumping devices, ion-selective membranes, etc. The electroosmotic flow (EOF) in the conical nanopore of Carreau fluid is investigated by solving a set of Poisson, Nernst–Planck, and momentum equations to account for the electric potential, transport of ionic species, and velocity field. The behaviors of ICR in Carreau fluid are examined by varying the shear-thinning index (0.6≤n≤1), Debye length (1≤κRt≤50), Deborah number (1≤De≤100), and applied electric potential (−50≤V≤50). The electroosmotic flow is observed to be significantly stronger in shear-thinning fluids. All else being equal, the volumetric flow rate increases several folds in shear-thinning fluids. Shear-thinning fluid behavior enhances the magnitude of the current in the conical nanopore.