Hydrogels with multiple characteristic pore dimensions: From transport properties to multifunctional materials

We are developing in-plane nanofluidic devices with multiple pores in series for resistive-pulse measurements of nanoscale particles. Here, we report an approach to calculate the effective diameters of the T = 3 and T = 4 capsids of hepatitis B virus (HBV) capsids from resistive-pulse measurements without using a particle calibration standard and by approximating the noncylindrical cross section of the in-plane nanopore with an equivalent diameter. Because HBV capsids resemble porous protein shells, the capsids displace less electrolyte during translocation and have current pulses with smaller amplitudes than solid particles with similar diameters. To determine an effective volume and, subsequently, an effective diameter for the HBV capsids, we measured the relative pulse amplitudes, nanopore and nanochannel dimensions, device resistance, and electrolyte resistivity. When pore dimensions are precisely measured, effective diameters of the T = 3 and T = 4 HBV capsids were calculated without a calibration standard to be 25.2 ± 0.3 and 28.1 ± 0.3 nm, respectively. If pore dimensions are not completely characterized, one of the capsids can be used as a calibration standard to determine the effective diameter of the other capsid. The effective diameters of the T = 3 and T = 4 capsids were 25.1 ± 0.1 and 28.0 ± 0.2 nm, respectively, when measured across nanopores with equivalent diameters from 68 to 105 nm. Accurate determination of the effective diameters for the T = 3 and T = 4 capsids makes them attractive as calibration standards for resistive-pulse sensing because of their narrow size distributions.

Organic shale is characteristics of multi-component and multiple pore, making flow mechanism of water imbibition in shale very complicated. In this study, firstly, the micro pore structure and pore size of shale were quantitatively characterized by scanning electron microscope. Secondly, a new experimental device for spontaneous imbibition of water under the conditions of formation temperature and confining pressure was designed. Finally, A new imbibition index was proposed to evaluate the contribution of multiscale pores to shale water imbibition. The experimental results of shale samples from the Longmaxi formation (LF) in the Sichuan Basin indicate that the water imbibition in shale was divided into three stages: diffusion stage, transition stage, and balance stage. The diffusion stage was the stage when most of the water imbibition takes place, and the transition stage was the time when the induced micro-fractures were generated. The water imbibition of shale was inhibited under the condition of temperature and pressure of shale reservoirs. Compared with the conventional spontaneous imbibition, the capillary pressure and osmotic pressure were the main imbibition forces in the transition stage. The micro-fractures induced by hydration provide a new channel for water imbibition and promote the further improvement of imbibition capacity. The research results provide effective guidance for the optimization of flowback system.

In petrophysics, characteristic lengths are used to relate fundamental transport properties of porous media. However, these characteristic lengths have mostly been defined and tested in fully saturated conditions, with few exceptions. This contribution revisits the seminal work of Johnson-Koplik-Schwartz (JKS) length, which represents an effective pore size controlling various transport-related properties of porous media, such as permeability and electrical conductivity. A novel closed-form equation is presented to predict the behavior of this characteristic length in partially saturated media for different saturation states. Using previous models in the literature that predict the intrinsic and relative electrical conductivities under partially saturated conditions, we infer the JKS length as functions of water saturation and properties associated with the pore-size distribution of the considered porous medium. The proposed method allows for the direct estimation of effective and relative permeability through electrical conductivity measurements. This creates new opportunities for remotely characterizing partially saturated media. We believe that this new model has potential for various applications in reservoir (CO2 or hydrogen storage) and vadose zone studies.

The transport properties of porous media exhibit complex multiscale behaviours, which are governed by nonlinear interaction of structural heterogeneity, and which present significant challenges for theoretical understanding and practical modelling. To address this complexity, we propose a fractal-based framework to quantitatively link structural parameters with transport behaviours, focusing specifically on electrical current flow in porous media. Our approach develops a tortuosity model based on self-similarity principles in order to describe the geometric structure, and to assess the transport properties, such as permeability and electrical conductivity.At the single-capillary level, key microstructural properties, such as pore geometry and connectivity, and transport properties, including permeability and electrical conductivity, can be quantified using metrics such as fractal dimension, tube number, and characteristic length. These parameters capture both structural complexity and scaling behaviour. Taking electrical conductivity as an example, a two-dimensional porous medium with a grid resolution of 16,384 × 16,384 is generated using the Quartet Structure Generation Set (QSGS) method and partitioned into smaller scales (e.g., 1024, 512, 256, and 128) to explore multiscale behaviour and scaling effects. Finite difference methods are employed to calculate the electrical field distributions and derive the effective electrical conductivity. These results are then mapped to the parameters of the self-similar tortuosity model, providing insights into its ability to capture the complex relationships between structure and transport properties.Statistical analysis reveals that the measured fractal dimensions follow a Weibull distribution across scales, characterised by its distinctive shape and scale parameters. By contrast, characteristic length and tube number values exhibit scale-dependent variations that influence their respective distribution patterns. Tube number conforms to a lognormal distribution, reflecting its intrinsic variability. These findings enable the development of more accurate and computationally efficient multiscale models, with potential applications in areas such as fluid flow, heat transfer, and the design of advanced porous materials.

Fibrous materials can efficiently dissipate acoustic energy, and their intrinsic properties are determined by fiber geometries (microscale). In this study, the effect of cross-sections of fibers on the transport and acoustic properties of fibrous materials was investigated. First, fibers of various cross-sections were modeled by adjusting their open porosity. The representative elementary volumes of fiber structures were generated to describe the periodic unit-cell structures. Next, the transport properties (such as static airflow resistivity, high-frequency limit of the dynamic tortuosity, viscous characteristic length, thermal characteristic length, and static thermal permeability) of fibrous materials were calculated by solving numerical problems using the finite element method. These properties of fibrous materials with complex cross-sections were compared with those with circular cross-sections. Finally, the sound absorption coefficients were predicted using the Johnson-Champoux-Allard-Lafarge (JCAL) model and rigid frame approximation, and the differences in sound-absorbing behavior were analyzed. This study can provide insights into the design of lightweight fibrous materials while maintaining optimal sound absorption performance.

We here extend the theory of microporomechanics by Dormieux et al. to multiple pore spaces. As an application, we reveal, on the basis of a recently validated multiscale elastic model for bone tissues by Fritsch and Hellmich, the effects of multiple pore pressures in various, scale-separated pore spaces, on the overall behavior of the multiporous composite material. Thereby, our focus is on the lacunar pore space, and on its interplay with the pore spaces found further below: not only those between the mineral crystals (of some 10 nm characteristic pore size) but also those of the collagen molecules building up (micro-)fibrils (with a little more than 1 nm distance between these molecules). Our results clearly show that the interplay between pore pressure and skeleton deformation depends strongly on the loading direction and on the characteristic size of the pores—hence, we can conclude that the consideration of these strongly hierarchical and anisotropic effects in whole-organ simulations including fluid...

In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high temperatures on solar absorption are rarely considered in practical research. Therefore, this study presents a porous zinc and silver sulfide solar absorber with high-temperature radiative cooling capabilities. The solar absorption rate and radiative cooling efficiency in the high-temperature range (636 K–1060 K) are computed using the finite-difference time-domain method. Furthermore, the impact of parameters such as characteristic length, porosity, incident angle, and pore shape factor on both the absorption rate and efficiency of the solar absorber is analyzed. The mechanism is further examined from the perspective of microscopic thermal radiation. The results show that, in the high-temperature range, the solar absorption rate increases with higher porosity and incident angles, reaching its peak when the characteristic length is 1 μm. These findings highlight the significant potential of the solar absorber for efficient solar energy harvesting in photo-thermal conversion applications within a specific high-temperature range.

There has been considerable interest in preparing ionic circuits capable of manipulating ionic and molecular transport in a solution. This direction of research is inspired by biological systems where multiple pores with different functionalities embedded in a cell membrane transmit external signals and underlie all physiological processes. In this manuscript, we describe the modeling of ion transport through small arrays of nanopores consisting of 3, 6, and 9 nanopores and an integrated gate electrode placed on the membrane surface next to one pore opening. We show that by tuning the gate voltage and strategically placing nanopores with nonlinear current-voltage characteristics, the local signal at the gate affects ionic transport through all nanopores in the array. Conditions were identified when the same gate voltage induced opposite rectification properties of neighboring nanopores. We also demonstrate that an ionic diode embedded in a nanopore array can modulate transport properties of neighboring pores even without a gate voltage. The results are explained by the role of concentration polarization and overlapping depletion zones on one side of the membrane. The modeling presented here is intended to become an inspiration to future experiments to create nanopore arrays that can transduce signals in space and time.

Understanding the impact of synthesis parameters on the pore structure properties of fly ash-based geopolymers

The transport and sound absorption properties of random close packings of monodisperse spherical particles are explored following a multiscale approach. First, the discrete element method is used to simulate the free fall of the monodisperse particles in a bounded domain to create virtual samples that are representative of real samples. Different particle diameters ranging from 1 to 16 mm are studied. From the virtual samples, representative volume elements (RVEs) are defined. Local partial differential equations governing the transport properties are numerically solved on the RVEs. From the discretized RVEs and the numerical solutions, eight transport properties (porosity, tortuosity, and viscous and thermal static tortuosities, permeabilities, and characteristic lengths) are derived. Micro-macro relationships between these properties and the particle diameter are developed. They are validated against experimental measurements of the open porosity and sound absorption coefficients. The relationships are used to analyze the salient sound absorption features of such media, notably the resonant sound absorption behavior. Expressions allowing identification of the optimal particle diameter for a given thickness, or conversely, the optimal thickness for a given particle diameter, for achieving 100% absorption at the first resonant absorption are derived.

The ability of fibrous media to mitigate sound waves is controlled by their transport properties that are themselves greatly affected by the geometrical characteristics of their microstructure such as porosity, fiber radius, and fiber orientation. Here, the influence of these geometrical characteristics on the anisotropic transport properties of random fiber structures is investigated. First, representative elementary volumes (REVs) of random fiber structures are generated for different triplets of porosity, fiber radius and fiber orientation. The fibers are allowed to overlap and are motionless (rigid-frame assumption). The fiber orientation is derived from a second order orientation tensor. Second, the transport equations are numerically solved on the REVs which are seen as periodic unit cells (PUCs). These solutions yield the transport properties governing the sound propagation and dissipation in the respective fibrous media. These transport properties are the tortuosity, the viscous and thermal static permeabilities, and the viscous characteristic length. Finally, relations are proposed to estimate the transport properties and the thermal characteristic length when the geometry of the fiber structures is known.

Study on the pore structure of eco-regenerated mortar using corn cob based on nuclear magnetic resonance

Pore space microstructure transitions in porous media are investigated by means of simulations of pore networks subject to a random compaction mechanism. With critical path analysis we track the characteristic pore length of the media. This pore length becomes singular at transition porosities, exhibiting kinks and even discontinuities if compaction is strong. The transitions arise from the appearance of new modes in the pore size distribution. Different modes control the transport properties in different porosity intervals where the characteristic pore length is continuous. These continuous pieces of pore length correspond to structurally different media. A transition occurs when the pore fraction controlling flow equals the critical percolation probability of the underlying lattice representing the pore space. To prove the validity of the transitions discovered by simulation we develop an analytical description of the pore-size distribution of media under compaction by using a detailed balance of pore populations. Analytical transition porosities agree precisely with simulations. At the first pore space microstructure transition the change in characteristic length l P exhibits a critical scaling Δl P α (λc − λ) υ , with υ = 1 and λ a compaction factor. Within this approach many aspects of the pore space microstructure transitions observed in the simulations are explained.

New multifunctional materials that include fluid passages are being developed. These materials hold promise for future high-performance aerospace structures. The fluid in the passages can enhance heat transfer, control deformation, provide resin for healing or remodeling, disclose damage, and modify stiffness and damping. This paper presents an engineering model for synthetic vascular materials that have fluid passages much smaller than a characteristic structural length such as panel thickness. A class of idealized materials is modeled as a two-phase continuum with a solid phase and a fluid phase occupying every volume. In order to simulate fully multifunctional synthetic vascular materials, the model permits the solid and fluid phases to exchange mass, momentum and energy. Balance equations and the entropy inequality for general mixtures are taken from existing continuum mixture theory. These are augmented with certain definite types of solid-fluid interactions in order to enable adequately general, but workable, engineering analysis. The thermomechanical characteristics of this restricted class of multifunctional materials are delineated. By demanding that the law of increase of entropy be satisfied for all processes, much is deduced about the acceptable forms of constitutive equations. The paper concludes with a study of the uniaxial tension behavior of an idealized vascular material.

Effect of particle size distribution on the evolution of porous, microstructural, and dimensional characteristics during sinter-crystallisation of a glass-ceramic glaze