Velocity, stress and concentration fields revealed by micro-PIV and SAXS within concentration polarization layers during cross-flow ultrafiltration of colloidal Laponite clay suspensions

In situ multiscale characterization of cellulose nanocrystals orthotropic organization achieved by combining ultrasound and frontal ultrafiltration

Combining frontal ultrafiltration (FU) and ultrasound (US) processes, an orthotropic organization of cellulose nanocrystals (CNCs) suspensions was achieved and characterized at multiscale, from the nanometer length scale by small angle X-ray scattering (SAXS) and dichroism, to the micrometer length scale by small angle light scattering (SALS). A dedicated channel cell has been developed to simultaneously generate a vertical acoustic force via a vibrating blade at the top and a transmembrane pressure force through the membrane at the bottom. Three specific orientations in three successive layers were revealed in a one-step FU-US process. In a first layer at the bottom, the CNCs were concentrated under the action of transmembrane pressure with their director aligned parallel to the horizontal membrane surface. In a second upper layer a random orientation of the CNCs was detected. Finally, in the upper part of the channel, a third layer of CNCs with their director vertically oriented was revealed. Near the membrane surface, transmembrane pressure forces dominate, leading to highly concentrated CNCs deposition with enough consistency to avoid any change in orientation induced by the US at the top of the channel. At increasing distances from the membrane, acoustic radiation forces become predominant, reorienting the CNCs vertically.

Rayleigh streaming phenomena at the physical origin of cellulose nanocrystals orientations during combined ultrasound and ultrafiltration processes

Rayleigh acoustic streaming, a phenomenon resulting from the interaction of ultrasound (US) with a fluid, was revealed for the first time during simultaneous frontal filtration and US processes on a cellulose nanocrystal (CNC) suspension. According to in situ small-angle X-ray scattering (SAXS) and particle image velocimetry (PIV) measurements, channel-type filtration cells coupled with US were developed to simultaneously generate a vertical acoustic force via an ultrasonic vibrating blade at the top and to concentrate the CNCs under a transmembrane pressure force at the bottom. SAXS measurements under different transmembrane pressures demonstrated a change in CNCs orientation as a function of the distance from the membrane surface to the vibrating blade. These measurements led to the appearance of an orthotropic organization: CNCs were vertically oriented near the vibrating blade, then had an isotropic organization in the middle, and exhibited horizontal orientations near the membrane surface. This orthotropic organization appeared above a threshold in transmembrane pressure of ∼0.6 × 105 Pa. Concurrently, in situ micro-PIV measurements revealed the formation of Rayleigh acoustic streaming in the CNCs suspension, for the same threshold in transmembrane pressure and same US conditions, thereby highlighting the origin of the orthotropic organization. We propose that this threshold allows for sufficient accumulation of CNCs near the membrane surface, thus enabling confined flow, to generate acoustic streaming. This work highlights the interplay between acoustic streaming and orientations of CNC particles, thereby advancing understanding of the manipulation of liquid crystal-like suspensions in microfluidic applications.

Mechanistic exploration of licorice reconciling Medicine:Huangqi Guizhi Wuwu decoction and Shaoyao Gancao decoction compatibility as an example

ETHNOPHARMACOLOGICAL RELEVANCE

Glycyrrhiza uralensis Fisch. (GU) is a pivotal botanical in traditional Chinese medicine (TCM), because of its ability to reconcile various herbs, and its crucial role in numerous formulas. Huanggui Shaogan decoction (HSGD) is an empirical formula, developed by Huangqi Guizhi Wuwu decoction (HGD) and Shaoyao Gancao decoction (SGD), and prepared by adding GU to HGD. However, the mechanisms of GU reconciling medicine remain incompletely characterized.

AIM OF THE STUDY

This study aimed to explain mechanisms of GU reconciling medicine based on the differences of components, pharmacological efficacy, and the existence of the components.

METHODS

Differential components between HSGD and HGD were systematically identified using LC‒MS/MS coupled with chemometric analysis. The existence states and binding affinities of these differential components were further characterized via ultrafiltration separation. The therapeutic potential of HSGD was validated in a murine model of oxaliplatin-induced peripheral neuropathy (OIPN).

RESULTS

Twenty-two differential chemical components between HSGD and HGD were identified, including flavonoids, saponins, gingerol, and monoglycoside. The transmittance of flavonoids and gingerols increased in HSGD. However, the transmittance of astragalus saponins decreased, which may be due to micelle association and the increase in molecular clusters. HSGD could enhance the mechanical pain threshold, alleviate cold nociceptive hypersensitivity, relieve dorsal root ganglia neuron injury, and decrease the expression of nerve growth factor, 5-hydroxytryptamine, substance P, and calcitonin gene-related peptide better. The differential correlation analysis revealed the relationship between differential components and pharmacological indicators. The above results indicated that different herbs combinations had a greater impact on the dissolution and molecular state of the components of Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao.

CONCLUSION

The study highlights the solubilizing effect of GU within HSGD, and it also improves the efficacy of the treatment of OIPN, which underpins its compatibility rationality. It provided an inspiration for the study of other TCM formulas.

A Novel Modeling Optimization Approach for a Seven-Channel Titania Ceramic Membrane in an Oily Wastewater Filtration System Based on Experimentation, Full Factorial Design, and Machine Learning

This comprehensive study looks at how operational conditions affect the performance of a novel seven-channel titania ceramic ultrafiltration membrane for the treatment of produced water. A full factorial design experiment (23) was conducted to study the effect of the cross-flow operating factors on the membrane permeate flux decline and the overall permeate volume. Eleven experimental runs were performed for three important process operating variables: transmembrane pressure (TMP), crossflow velocity (CFV), and filtration time (FT). Steady final membrane fluxes and permeate volumes were recorded for each experimental run. Under the optimized conditions (1.5 bar, 1 m/s, and 2 h), the membrane performance index demonstrated an oil rejection rate of 99%, a flux of 297 L/m2·h (LMH), a 38% overall initial flux decline, and a total permeate volume of 8.14 L. The regression models used for the steady-state membrane permeate flux decline and overall permeate volume led to the highest goodness of fit to the experimental data with a correlation coefficient of 0.999. A Multiple Linear Regression method and an Artificial Neural Network approach were also employed to model the experimental membrane permeate flux decline and analyze the impact of the operating conditions on membrane performance. The predictions of the Gaussian regression and the Levenberg-Marquardt backpropagation method were validated with a determination coefficient of 99% and a Mean Square Error of 0.07.

Chiral nematic nanocomposites with pitch gradient elaborated by filtration and ultraviolet curing of cellulose nanocrystal suspensions

An innovative method combining frontal filtration with ultraviolet (UV) curing has been implemented to design cellulosic nanocomposite films with controlled anisotropic textures from nanometric to micrometric length scales. Namely, an aqueous suspension containing poly (ethylene glycol) diacrylate polymer (PEGDA) as a photocurable polymer and cellulose nanocrystals (CNCs) at a 70/30 mass ratio was processed by frontal filtration, followed by in-situ UV-curing in a dedicated cell. This procedure allowed designing nanocomposite films with highly oriented and densely-packed CNCs, homogeneously distributed in a PEGDA matrix over a thickness of ca. 500 μm. The nanocomposite films were investigated with small-angle X-ray scattering (SAXS), by raster-scanning along their height with a 25 μm vertically-collimated X-ray beam. The CNCs exhibited a high degree of orientation, with their director aligned parallel to the membrane surface, combined with an increase in the degree of alignment as concentration increased towards the membrane surface. Scanning electron microscopy images of fractured films showed the presence of regularly spaced bands lying perpendicular to the applied transmembrane pressure, highlighting the presence of a chiral nematic (cholesteric) organization of the CNCs with a pitch gradient that increased from the membrane surface to the bulk.

Orthotropic organization of a cellulose nanocrystal suspension realized via the combined action of frontal ultrafiltration and ultrasound as revealed by in situ SAXS

HYPOTHESIS

Rodlike cellulose nanocrystals (CNCs) exhibit significant potential as building blocks for creating uniform, sustainable materials. However, a critical hurdle lies in the need to enhance existing or devise novel processing that provides improved control over the alignment and arrangement of CNCs across a wide spatial range. Specifically, the challenge is to achieve orthotropic organization in a single-step processing, which entails creating non-uniform CNC orientations to generate spatial variations in anisotropy.

EXPERIMENTS

A novel processing method combining frontal ultrafiltration (FU) and ultrasound (US) has been developed. A dedicated channel-cell was designed to simultaneously generate (1) a vertical acoustic force thanks to a vibrating blade at the top and (2) a transmembrane pressure force at the bottom. Time-resolved in situ small-angle X-ray scattering permitted to probe the dynamical structural organization/orientation of CNCs during the processing.

FINDINGS

For the first time, a typical three-layer orthotropic structure that resembles the articular cartilage organization was achieved in one step during the FU/US process: a first layer composed of CNCs having their director aligned parallel to the horizontal membrane surface, a second intermediate isotropic layer, and a third layer of CNCs with their director vertically oriented along the direction of US wave propagation direction.

Geometrical Influence on Particle Transport in Cross-Flow Ultrafiltration: Cylindrical and Flat Sheet Membranes

Cross-flow membrane ultrafiltration (UF) is used for the enrichment and purification of small colloidal particles and proteins. We explore the influence of different membrane geometries on the particle transport in, and the efficiency of, inside-out cross-flow UF. For this purpose, we generalize the accurate and numerically efficient modified boundary layer approximation (mBLA) method, developed in recent work by us for a hollow cylindrical membrane, to parallel flat sheet geometries with one or two solvent-permeable membrane sheets. Considering a reference dispersion of Brownian hard spheres where accurate expressions for its transport properties are available, the generalized mBLA method is used to analyze how particle transport and global UF process indicators are affected by varying operating parameters and the membrane geometry. We show that global process indicators including the mean permeate flux, the solvent recovery indicator, and the concentration factor are strongly dependent on the membrane geometry. A key finding is that irrespective of the many input parameters characterizing an UF experiment and its membrane geometry, the process indicators are determined by three independent dimensionless variables only. This finding can be very useful in the design, optimization, and scale-up of UF processes.

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications.

Role of concentration polarization in cross flow micellar enhanced ultrafiltration of cadmium with low surfactant concentration

Concentration polarization is an important issue in micellar enhanced ultrafiltration (MEUF) of wastewater containing heavy metal ions at low surfactant concentrations. In this paper, we studied removal of Cd(Ⅱ) by cross flow MEUF at low sodium dodecyl sulfate (SDS) concentration levels, and the role of concentration polarization in flux decline and Cd(Ⅱ) rejection was emphasized. Concentration polarization resistance and SDS concentration near membrane were calculated to characterize concentration polarization. The results showed that SDS concentration near membrane was 13 mM when feed concentration was merely 0.8 mM. By combining phase diagram of SDS, structures of SDS micelles in concentration polarization layer were deduced and thin layer structure transformed to porous structure formed by accumulated globular micelles when SDS concentration increased. Although micelles formed in concentration polarization layer was responsible for flux decline, they also provided adsorption sites for Cd(Ⅱ).