Changes In Zeta Potential Research Articles

Effects of High-Intensity Ultrasound Treatments on the Physicochemical and Structural Characteristics of Sodium Caseinate (SC) and the Stability of SC-Coated Oil-in-Water (O/W) Emulsions.

The effects of high-intensity ultrasound treatment (0, 3, 6, 9 min) on physicochemical and structural characteristics of SC and the storage, thermal and freeze–thaw stability of SC O/W emulsions were investigated. The results showed that ultrasound treatment reduced the particle size of SC, although there were no obvious changes in zeta potential, profiles and weights. Ultrasound treatment improved surface hydrophobicity and fluorescence intensity of SC and changed ultraviolet–visible (UV–Vis) spectroscopy but had no influence on the secondary structure of SC. This indicates that ultrasounds might destroy the tertiary structure but leave most of the integral secondary structure. A scanning electron microscope (SEM) also showed that ultrasound-treated SC presented small aggregates and a loose structure. The physicochemical and structural changes of SC benefited the ability of protein adsorbing oil droplets and emulsion stability. Under stresses such as storage, thermal and freeze–thawing, the oil droplets of treated emulsions were still uniform and stable, especially at 6 min and 9 min. Overall, the high-intensity ultrasounds made the SC present small aggregates and a loose structure improving the SC O/W emulsions stability under storage, thermal and freeze–thawing environment and have great potential to stabilize the SC prepared O/W emulsions.

Mannose-Anchored Nano-Selenium Loaded Nanostructured Lipid Carriers of Etravirine for Delivery to HIV Reservoirs.

The present investigation aims to develop and explore mannosylated lipid-based carriers to deliver an anti-HIV drug, Etravirine (TMC) and Selenium nanoparticles (SeNPs), to the HIV reservoirs via the mannose receptor. The successful mannosylation was evaluated by the change in zeta potential and lectin binding assay using fluorescence microscopy. Electron microscopy and scattering studies were employed to study the structure and surface of the nanocarrier system. The presence of selenium at the core-shell of the nanocarrier system was confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. Further, the in vitro anti-HIV1 efficacy was assessed using HIV1 infected TZM-bl cells followed by in vivo biodistribution studies to evaluate distribution to various reservoirs of HIV. The results exhibited higher effectiveness and a significant increase in the therapeutic index as against the plain drug. The confocal microscopy and flow cytometry studies exhibited the efficient uptake of the coumarin-6 tagged respective formulations. The protective effect of nano selenium toward oxidative stress was evaluated in rats, demonstrating the potential of the lipidic nanoparticle-containing selenium in mitigating oxidative stress in all the major organs. The in vivo biodistribution assessment in rats showed a 12.44, 8.05 and 9.83-fold improvement in the brain, ovary, and lymph node biodistribution, respectively as compared with plain TMC. Delivery of such a combination via mannosylated nanostructured lipid carriers could be an efficient approach for delivering drugs to reservoirs of HIV while simultaneously reducing the oxidative stress induced by such long-term therapies by co-loading Nano-Selenium.

Vilazodone-phospholipid mixed micelles for enhancing oral bioavailability and reducing pharmacokinetic variability between fed and fasted states

Despite the effectiveness and high tolerability of vilazodone (VLZ) as an antidepressant, its use is still limited due to its poor solubility and food dependent absorption. This study aims to load VLZ-phospholipid complex into self-assembled micelles forming VLZ-PL mixed micelles (VLZ-PL-MM), that can enhance VLZ solubility, improve its bioavailability and reduce the pharmacokinetic variability between the fed and fasting conditions. The effect of surfactant type and concentration was assessed using four different non-ionic surfactants (Brij 58, Tween 80, Labrasol and Pluronic F127) in four different weight ratios between the drug-complex and surfactant (1:0.5, 1:1, 1:2 and 1:3 w/w). Two VLZ-PL-MM formulae prepared using Brij 58 and Labrasol in 1:3 w/w ratio were selected as optimised ones since they have the highest encapsulation efficiency (100.83 and 93.87%, respectively), a particle size below 250 nm (206.73 and 221.33 nm, respectively) and negative zeta potential values (−29.63, −17.20 mV, respectively). Lyophilisation of these formulations using 3% sucrose was successful with no statistical changes in particle size and zeta potential upon rehydration. Both formulations elicited faster and higher in-vitro drug release profiles compared to the pure drug and the marketed tablet. In addition, both selected formulae improved ex-vivo permeation across rabbit intestinal membrane compared to the pure drug and the marketed tablet, with marked superiority of the one prepared using Brij 58. The results of the in-vivo study in male albino rabbits revealed similar AUC0-24 values after the oral administration of the best achieved VLZ-PL-MM system under fed and fasted conditions (769.89 and 741.55 ng.h mL−1, respectively). On the other hand, the marketed product showed significantly lower values of the AUC0-24 relative to the VLZ-PL-MM system and there was a marked enhancement of absorption of drug from the marketed product in presence of food (244.24 and 174.96 ng.h mL−1 under fed and fasted conditions, respectively). In addition, VLZ concentrations in the brain after 24 h obtained from the selected VLZ-PL-MM were significantly higher than those obtained from marketed tablet under fed and fasted conditions. Thus, the phospholipid mixed micelles formulation enhances the oral bioavailability of the poorly soluble drug and reduces the pharmacokinetic variability between fasting and fed conditions.

How docetaxel entrapment, vesicle size, zeta potential and stability change with liposome composition–A formulation screening study

Limitations of the anticancer drug product Taxotere® have encouraged researchers to entrap the active ingredient docetaxel (DTX) into nanocarriers such as liposomes. However, until now no DTX-liposome formulation has reached the clinic. Hence, in the present study, different Soy-PC based DTX-liposome formulations were screened in an attempt to identify lipid-compositions with promising DTX-entrapment (DTX-EE). Various other quality attributes, such as vesicle size and morphology, poly dispersity index (PDI), zeta potential (ZP), stability and in vitro drug release were also investigated. In an initial study, the inclusion of charged lipids within the liposome bilayer was observed to have a positive effect on DTX-EE. Thus, cationic DOTAP (1,2-Dioleoyl-3-trimethylammonium-propane) and anionic DMPG (1,2-Dimyristoyl-sn-glycero-3-phospho-(1′-rac-glycerol) lipids were selected for further investigations. With anionic DMPG, only a temporary rise in EE was gained with ≥ 20% (w/w) DMPG in Soy-PC lipid-based liposomes, whereas a concentration-dependent increase in EE was observed with cationic DOTAP. A DTX-EE > 95% was obtained with only 5% (w/w) DOTAP in Soy-PC, while neutral liposomes formed from Soy-PC alone, gave 41.5% DTX-EE. In the stability study, a DOTAP concentration > 10% (w/w) in Soy-PC was found to facilitate a stable DTX-EE > 90% after 12 weeks storage. The positive effect of cationic lipids on the EE was confirmed when replacing cholesterol (CHOL), initially shown to suppress DTX-entrapment, with cationic 3ß-[N-(N',N'-dimethylaminoethane)-carbamoyl]Cholesterol (DC-CHOL). Here, DTX-EE was improved from 29.8% to 92.0% (w/w) with 10% (w/w) CHOL and DC-CHOL in Soy-PC, respectively. Finally, PEGylation of DOTAP-liposomes with DSPE-PEG2000 and DSPE-PEG750 reduced the DTX-EE relative to DOTAP-liposome with no PEGylation. As with the DMPG-liposomes, a temporarily raised affinity between DTX and liposomes was obtained with anionic DSPE-PEGylation of Soy-PC liposomes, however, this effect was not maintained after 4 weeks storage. However, in a dialysis set-up, cationic DOTAP-liposomes released DTX to a higher extent than PEGylated liposomes. Thus, the optimal formulation with regard to storage stability and in vivo performance need to be investigated further, applying conditions that are closer to mimic the in vivo-situation. Applying the Dual Asymmetric Centrifugation (DAC) method in liposome production appears favourable due to its good reproducibility. The observed increase in DTX entrapment with cationic lipids or PEGylation appears scalable into pilot manufacturing scale.

Design of nanostructured lipid carriers and solid lipid nanoparticles for enhanced cellular uptake

In this study PEG-free and zeta potential changing lipid-based nanocarriers providing enhanced cellular uptake were developed. Nanostructured lipid carriers (NLC), consisting of paraffin wax, caprylic/ capric triglyceride, cetyltrimethylammoniumchloride and either soy lecithin or polyglycerol-4 laurate and solid lipid nanoparticles (SLN) with the same composition but without the liquid lipid content were developed. All formulations exposed a positive surface charge and were then coated with the polyphosphate Graham’s salt. Phosphate release from these formulations was evaluated by incubation with intestinal alkaline phosphatase as well as on a Caco-2 monolayer and zeta potentials were measured. Additionally, cellular uptake studies were performed.Within 5 h, a remarkable amount of phosphate was released from all formulations incubated with intestinal alkaline phosphatase. Enzymatically induced phosphate release with intestinal alkaline phosphatase led to a zeta potential shift up to Δ 26 mV. Results of phosphate release and zeta potential change were confirmed on Caco-2 cells. Cellular uptake studies on Caco-2 cells showed an up to 5.6-times higher uptake compared to cells with inhibited phosphatase. According to these results, polyphosphate coating is a powerful tool to obtain lipid-based nanocarriers for enhanced cellular uptake.

Study of the coagulation-flocculation treatment of flowback water from shale gas hydraulic fracturing by using combination of dithiocarbamate compound-polyacrylamide

In this paper, a dithiocarbamate-type flocculant DTC-TETA was prepared by using triethylenetetramine as the material and combination of DTC-TETA and polyacrylamide was used for the coagulation-flocculation of flowback water from shale gas hydraulic fracturing (FWSG). The coagulation-flocculation process was optimized by using turbidity as index and the recommended process was as follows: DTC-TETA dosage 200 mg/L, anionic polyacrylamide AN905 dosage 1 mg/L, flocculation stirring speed 200 rpm, flocculation stirring time 3 min and settlement time 5 min. The turbidity of FWSG can be reduced to be 13 NTU from the initial turbidity of more than 2000 NTU under the recommended process. The performance of DTC-TETA was much better than that of polyaluminum chloride and the Fe2+ in FWSG also can be removed. The function mechanism of DTC-TETA was investigated through the studies of zeta potential change of suspended solids and structural characteristics of flocs. The results confirmed that the flocs were developed by the network formed by the coordination reaction between DTC-TETA and Fe2+, which can filter out suspended solids. This study signifies that both suspended solids and Fe2+ ion can be removed by using DTC-TETA as flocculant, which is a new choice for the FWSG treatment.

Antioxidant potential of biosynthesized zinc oxide nanoparticles from Sargassum polycystum aqueous extract

The exploitation of marine sources is exponentially increasing in past few decades due to fact that the seaweeds have many biological and commercial applications. This study aims in the biosynthesis of zinc oxide nanoparticles from aqueous extract of seaweed Sargassum polycystum. The surface morphology and optical properties of the zinc oxide nanoparticles were analysed with X- Ray diffraction, Zeta potential and UV spectral changes. X-ray diffraction analysis showed that the zinc oxide nano particles were polydispersed with the mean size of 32.5±1.5 nm. The nanoparticles were mostly spherical in crystalline form. The zinc oxide nanoparticles showed the absorption properties in the ultraviolet range. The nanoparticles were assessed for enzymic and non enzymic antioxidant properties and were found to have greater antioxidant potency. The antioxidant activity of S. polycystum may be due to the phytochemicals present which is involved in many biological applications.

Interaction between secondary lipid oxidation products and hemoglobin with multi-spectroscopic techniques and docking studies

This study aimed to explore the effect of secondary lipid oxidation products (SLOPs) on hemoglobin (Hb) in chicken model. The fluorescence quenching technique and molecular docking were employed, and the apparent binding constants Ksv and the binding site numbers of SLOPs with Hb were calculated. The results revealed that three SLOPs (hexanal, benzaldehyde, and 2-pentanone) obviously promoted the oxidation of Hb, which is consistent with the change of Hb hydrophobicity, particle size, polydispersity index and zeta potential. The SLOPs strongly quenched the intrinsic fluorescence of Hb and triggered the alterations in the Hb structure. Hydrophobic interaction was the main force between SLOPs and Hb. Among the three SLOPs, hexanal demonstrated more stronger oxidation on Hb, which is closely related to its hydrophobic ability and structure characteristic, especially 10 μM hexanal is more prone to form an obvious unfolded structure and caused molecular aggregation than lower concentrations.

Fabrication of High-Acyl Gellan-Gum-Stabilized β-Carotene Emulsion: Physicochemical Properties and In Vitro Digestion Simulation

The β-carotene emulsion system using high-acyl gellan gum (HA) as an emulsifier was fabricated and systematically studied. The stability and stabilizing mechanism of the emulsion using medium-chain triglyceride as oil phase with a water-oil mass ratio of 9:1 under different physicochemical conditions of heat, pH, and ions were investigated by analyzing mean particle size (MPS), emulsion yield (EY), and dynamic stability. The effects of the HA-β-carotene emulsion system on the bioaccessibility of β-carotene in vitro were conducted. During the simulated oral digestion stage (SODP) and simulated gastric digestion stage (SGDP), the emulsion systems stabilized with different HA contents showed good stability, and the changes of MPS and zeta potential (ZP) were within 2.5 μm and 3.0 mV, respectively. After entering the simulated intestinal digestion phase (SIDP), β-carotene was released from oil droplets and formed micelles with bile salts, phospholipids, etc. HA-β-carotene emulsion can enhance the release rate of free fatty acid (FFA), which ultimately affects the β-carotene bioaccessibility. These results indicate that HA can be used to prepare carotene emulsion and improve its bioavailability. The study provides a reference for the application of HA as a natural emulsifier and the delivery of β-carotene.

Pyrite activated peroxymonosulfate combined with as a physical-chemical conditioner modified biochar to improve sludge dewaterability: analysis of sludge floc structure and dewatering mechanism.

In this study, we proposed an advanced oxidation process of pyrite (FeS2) and peroxymonosulfate (PMS) and prepared a modified polyaluminum chloride biochar (P-BC). The motivation is to use the combination of FeS2 + PMS + P-BC to improve waste activated sludge (WAS) dewaterability. The method to improve the sludge dewatering effect with the combination of FeS2 + PMS + P-BC is as follows: in the first step, pour 0.75 g/g TSS FeS2 and 0.6 g/g TSS PMS into the sludge, and stir for 15 min. Then, add P-BC and stir for 5 min; complete the entire WAS processing process. The vacuum filtration test was used to evaluate the dehydration effect. The water content (Wc) and specific resistance to filtration (SRF) of the raw sludge can be reduced from the original values of 92% and 2.36 × 1013 m/kg to 67% and 9.89 × 1011 m/kg, respectively. The results showed that the combination of FeS2 + PMS + P-BC can effectively improve the sludge dewatering effect through oxidation. A laser particle size analyzer is used to observe changes in sludge particle size. The median diameter of sludge particles increased from 55.37 to 64.56 μm. A zeta analyzer to is used observe changes in sludge zeta potential. The zeta potential of sludge particles increased from − 15.8 to 0.4 mV. In the analysis of extracellular polymeric substances (EPS) of sludge, it was found that protein (PN) and polysaccharide (PS) in EPS decreased significantly. To further analyze the phenomenon of PN and PS drop, excitation-emission-matrix spectra (3D-EEM) was used. To observe the changes of sludge functional group, X-ray photoelectron spectroscopy was used. It was found that FeS2 + PMS + P-BC can destroy the functional groups of sludge, such as O–H, C–C, and O═C—NH– related to proteins and polysaccharides.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-022-21074-4.

The Efficiency of Lemon Essential Oil-Based Nanoemulsions on the Inhibition of Phomopsis sp. and Reduction of Postharvest Decay of Kiwifruit.

Essential oils (EOs) have excellent antibacterial activity and are generally recognized as safe (GRAS) for use in food preservatives. However, the application of EOs is limited because of their strong volatility and easily oxidized. Encapsulation of EOs into nanoemulsions could effectively prevent oxidative deterioration. In this study, lemon essential oil-based nanoemulsion (LEO/NE) was prepared by high-pressure homogenization. FT-IR and encapsulation efficiency analysis indicated that LEO was effectively encapsulated in the nanoemulsion. The results of zeta potential changes after 35 d storage indicated that LEO/NE exhibits good stability at room temperature. The effect of LEO/NE on the main soft rot pathogens of kiwifruit Phomopsis sp. was investigated, and the results showed that LEO/NE significantly inhibited spore germination and mycelia growth of Phomopsis sp. by promoting ROS accumulation, intracellular antioxidant enzyme activities, and cell apoptosis. The preservation experiment was carried out by inoculating Phomopsis sp. spores into fresh kiwifruit, and the LEO/NE effectively inhibited soft rot development in kiwifruit in a LEO dose dependent manner. LEO/NE with 1% LEO loading amount has a good effect on preventing postharvest decay of kiwifruit caused by Phomopsis sp.

In-Membrane Nanostructuring of Cationic Amphiphiles Affects Their Antimicrobial Efficacy and Cytotoxicity: A Comparison Study between a De Novo Antimicrobial Lipopeptide and Traditional Biocides.

Cationic biocides have been widely used as active ingredients in personal care and healthcare products for infection control and wound treatment for a long time, but there are concerns over their cytotoxicity and antimicrobial resistance. Designed lipopeptides are potential candidates for alleviating these issues because of their mildness to mammalian host cells and their high efficacy against pathogenic microbial membranes. In this study, antimicrobial and cytotoxic properties of a de novo designed lipopeptide, CH3(CH2)12CO-Lys-Lys-Gly-Gly-Ile-Ile-NH2 (C14KKGGII), were assessed against that of two traditional cationic biocides CnTAB (n = 12 and 14), with different critical aggregation concentrations (CACs). C14KKGGII was shown to be more potent against both bacteria and fungi but milder to fibroblast host cells than the two biocides. Biophysical measurements mimicking the main features of microbial and host cell membranes were obtained for both lipid monolayer models using neutron reflection and small unilamellar vesicles (SUVs) using fluorescein leakage and zeta potential changes. The results revealed selective binding to anionic lipid membranes from the lipopeptide and in-membrane nanostructuring that is distinctly different from the co-assembly of the conventional CnTAB. Furthermore, CnTAB binding to the model membranes showed low selectivity, and its high cytotoxicity could be attributed to both membrane lysis and chemical toxicity. This work demonstrates the advantages of the lipopeptides and their potential for further development toward clinical application.

Peculiarities of electrophoretic deposition and morphology of deposited films in non-aqueous suspensions of Al2O3–Al nanopowder

The paper presents the results of a comprehensive study of the electrokinetic properties of non-aqueous suspensions of the Al2O3–Al nanopowder obtained by the method of electric explosion of wires (EEW) with 0.3 wt.% of metallic aluminum in its composition. The dependence of zeta potential on the concentration of the Al2O3–Al suspension is revealed. The nature of long-term changes in zeta potential and pH in suspensions is established. Appearance of bubbles in the deposited coatings due to the interaction of metallic aluminum particles with the liquid suspension medium during electrochemical reactions on the electrodes is defined as the main feature of the electrophoretic deposition (EPD) process in the Al2O3–Al suspensions. The influence of the suspension preparation method on the deposited coatings’ morphology is demonstrated.

Quality Assessment of Extemporaneously Compounded Carvedilol Oral Suspension for Pediatric Patients at the Hospital Pharmacy

Aims: The aim of this study was to evaluate different quality control parameters and the stability of the carvedilol compounded extemporaneous suspensions over three months at room temperature.
 Methodology: The carvedilol compounded extemporaneous suspensions were prepared in our lab in a manner consistent with how they are prepared for pediatric patients at the hospital pharmacy. The suspensions were stored at room temperature and analyzed immediately and at 1, 2 and 3 months. Suspensions were monitored for changes in organoleptic properties, pH, particle size, zeta potential, viscosity, sedimentation volume, drug content and drug dissolution.
 Results: The results demonstrated that the carvedilol compounding protocol used in this study was reliable and able to prepare 1.67 mg/mL of carvedilol suspension by using carvedilol commercially available tablets and Ora-blend as a suspending vehicle. Also, the extemporaneously compounded suspension maintained acceptable quality attributes when stored for three months at room temperature.
 Conclusion: The extemporaneously compounded suspension enables pediatricians to administer a variable dose, which adapts to every patient’s needs, and gives the possibility of treatment when the liquid dosage form is not available.

Enhanced bioaccessibility and stability of iron through W/O/W double emulsion-based solid lipid nanoparticles and coating with water-soluble chitosan

W/O/W double emulsion-based iron-solid lipid nanoparticles (Fe-SLNs) and water-soluble chitosan-coated Fe-SLNs (WSC-Fe-SLNs) were developed to increase the bioaccessibility and stability of iron. Fe-SLNs exhibited a small diameter (158.17 ± 0.72 nm) and adequate zeta potential (−34.31 ± 0.41 mV) to maintain stable dispersion. The coating with WSC resulted in an increase in particle diameter (up to 226.13 ± 1.97 nm) and change of zeta potential to positive value (+47.83 ± 1.24 mV) because of the amine groups of chitosan. The lipid peroxidation of the Fe-SLNs and WSC-Fe-SLNs was substantially lower than that of pure iron. Both Fe-SLNs and WSC-Fe-SLNs were also able to protect the encapsulated iron in simulated gastric fluid, while effectively releasing almost 80% of the iron in simulated intestinal fluid. The Fe-SLNs and WSC-Fe-SLNs showed a great potential as functional materials to apply to various food industries through enhancement of physical stability and bioaccessibility of the encapsulated iron.

Synergistic effect of aminosilane and K2CO3 on improving Chemical Mechanical Polishing performance of SiO2 dielectric layer

Chemical Mechanical Polishing (CMP) is a widely used surface treatment process in integrated circuit manufacturing for global planarization of the surface layers of various materials. The CMP slurry is regarded as one of the key determinants of planarization performance, considering the synergistic effect of its abrasive and other chemical components. As the component size is decreased to the molecular or even atomic scale, ways to achieve a high material removal rate of the SiO2 dielectric layer while maintaining high surface topography quality have become a challenge for the integrated circuit manufacturing industry. In this work, the synergistic effect of aminosilane and K2CO3 in the SiO2 CMP process was identified. A material removal rate of 248 nm/min and surface roughness of 0.374 nm was achieved under a pH of 11, SiO2 abrasive of 12 wt%, K2CO3 concentration of 0.12 M, and 3-aminopropyltriethoxysilane (APTES) concentration of 60 ppm. Through X-ray photoelectron spectroscopy (XPS), it was found that APTES can be adsorbed on the surface of SiO2 film through chemical bonding. Further, it was proved by fourier infrared spectroscopy (FTIR) that APTES could be combined with abrasive particles and coated on the surface of abrasive to realize the modification. The changes in particle size and zeta potential of the slurry were measured with a laser particle size analyzer. The studies suggested that under the influence of K2CO3, the hydration reaction on the SiO2 surface was intensified, the chemical bonding between APTES and the silanol (Si–OH) dangling bond on both surface of abrasive and SiO2 film was established, which enhanced the chemical reaction on the wafer surface. Finally, a material removal model of SiO2, characterized by the synergistic effect of APTES and K2CO3 was proposed based on the study.

Chitosan-coated bovine serum albumin nanoparticles for topical tetrandrine delivery in glaucoma: in vitro and in vivo assessment

Glaucoma is one of the leading causes of blindness. Therapies available suffer from several drawbacks including low bioavailability, repeated administration and poor patient compliance with adverse effects thereafter. In this study, bovine serum albumin nanoparticles (BSA-NPs) coated with chitosan(CS) were developed for the topical delivery of tetrandrine (TET) for glaucoma management. Optimized nanoparticles were prepared by desolvation. pH, BSA, CS and cross-linking agent concentrations effects on BSA-NPs colloidal properties were investigated. CS-BSA-NPs with particle size 237.9 nm and zeta potential 24 mV was selected for further evaluation. EE% exceeded 95% with sustained release profile. In vitro mucoadhesion was evaluated based on changes in viscosity and zeta potential upon incubation with mucin. Ex vivo transcorneal permeation was significantly enhanced for CS coated formulation. In vitro cell culture studies on corneal stromal fibroblasts revealed NPs biocompatibility with enhanced cellular uptake and improved antioxidant and anti-proliferative properties for the CS-coated formulation. Moreover, BSA-NPs were nonirritant as shown by HET-CAM test. Also, bioavailability in rabbit aqueous humor showed 2-fold increase for CS-TET-BSA-NPs compared to TET with a sustained reduction in intraocular pressure in a rabbit glaucoma model. Overall, results suggest CS-BSA-NPs as a promising platform for topical ocular TET delivery in the management of glaucoma.

A FRACTAL MODEL OF POWER-LAW FLUID THROUGH CHARGED FIBROUS POROUS MEDIA BY USING THE FRACTIONAL-DERIVATIVE THEORY

The study characterizes power-law fluid through charged fibrous porous media with spatial fractional-derivative and fractal geometry. Seepage flow of power-law fluid across fractal fibrous porous media in the presence of electric double layers (EDLs) is investigated based on the capillary bundle model. The acquired velocity distribution equation in a narrow capillary is then transformed into the form of series with appropriate Taylor approximation. After that, an analytical formula for dimensionless permeability is derived based on the generalized Darcy’s law. The effects of diverse parameters, including the fractal dimension of pore area, porosity, fractional order and Zeta potential on dimensionless permeability, are discussed. It can be seen from the results that lower fractional order has an amplification effect on dimensionless permeability with the change in Zeta potential. The results provide some theoretical guidance for revealing the seepage mechanism of a power-law fluid in charged porous media.

Loquat fruit-based carbon quantum dots as an “ON-OFF” probe for fluorescent assay of MnO4− in waters based on the joint action of inner filter effect and static quenching

As one kind of high nutrition fruits, abandoned loquat causes great waste due to short storage period. For resource utilization, we herein fabricated the loquat fruit-based carbon quantum dots (CQDs) by a facile/green hydrothermal method. The as-fabricated CQDs showed spherical shape with an average size of 4.46 nm, and richness in functional hydroxyl and carboxyl moieties on their surface. Under daylight and UV light, the as-fabricated CQDs displayed light yellow and blue color, respectively, with a fluorescence quantum yield of 10.36%. Upon the addition of MnO4−, the fluorescence intensity of loquat-based CQDs was prominently quenched in a concentration-dependent manner, suggesting the feasibility for constructing a sensitive “ON-OFF” nanoprobe. By virtue of changes in UV-Vis absorption, fluorescence lifetime, Stern-Volmer constant and zeta potential, the MnO4−-triggered quenching mechanisms were attributable to the joint action of inner filter effect and static quenching. Under optimized conditions, the CQDs supplied wide linear range of 0.2–150 μM, low detection limit of 0.06 μM, and high recovery of 96.0–106.0% for MnO4− in environmental waters. Especially, it exhibited the superior selectivity and anti-inference capacity for other commonly existed cations and anions in waters. In contrast to China authentic indirect iodometry method and previously reported approaches, the newly developed “ON-OFF” nanoprobe possesses comparable or even better analytical performance. As far as our information goes, it is the first report on the loquat fruit-based CQDs for successful application in the assay of trace-level MnO4− in environmental waters, thereby showing great potential in conventional monitoring.

Adsorption of CTAB on Sapphire-c at High pH: Surface and Zeta Potential Measurements Combined with Sum-Frequency and Second-Harmonic Generation.

The adsorption of cetyltrimethylammonium bromide (CTA+Br-) on sapphire-c surfaces was studied at pH 10 below the surfactants' critical micelle concentration. The evolution of interfacial potentials as a function of CTAB concentration was characterized by surface and zeta potential measurements and complemented by molecular dynamic (MD) simulations as well as by second-harmonic (SHG) and vibrational sum-frequency generation (SFG) spectroscopy. The changes in interfacial potentials suggest that the negative interfacial charge due to deprotonated surface aluminols groups is neutralized and can be even overcompensated by the presence of CTA+ cations at the interface. However, SFG intensities from strongly hydrogen-bonded interfacial water molecules as well as SHG intensities decrease with both increasing CTAB concentration and the magnitude of the surface potential. They do not suggest a charge reversal at the interface, while the change in zeta potential is actually consistent with an apparent charge inversion. This can be qualitatively explained by results from MD simulation, which reveal adsorbed CTA+ cations outside a first strongly bound hydration layer of water molecules, where they can locally distort the structural order and replace some of the interfacial water molecules adjacent to the first layer. This is proposed to be the origin for the significant loss in SFG and SHG intensities with increasing CTAB concentration. Moreover, we propose that CTA+ can act as a counterion and enhance the occurrence of deprotonated surface aluminols that is consistent with the decrease in surface potential.