Long-term Dispersion Stability Research Articles

Long-Term Physical Stability of Amorphous Solid Dispersions: Comparison of Detection Powers of Common Evaluation Methods for Spray-Dried and Hot-Melt Extruded Formulations

Although physical stability can be a critical issue during the development of amorphous solid dispersions (ASDs), there are no established protocols to predict/detect their physical stability. In this study, we have prepared fenofibrate ASDs using two representative manufacturing methods, hot-melt extrusion and spray-drying, to investigate their physical stability for one year. Intentionally unstable ASDs were designed to compare the detection power of each evaluation method, including X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and dissolution study. Each method did not provide the same judgment results on physical stability in some cases because of their different evaluation principles and sensitivity, which has been well-comprehended only for one-component glass. This study revealed that the detection powers of each evaluation method significantly depended on the manufacturing methods. DSC was an effective method to detect a small amount of crystals for both types of ASDs in a quantitative manner. Although the sensitivity of XRPD was always lower compared to that of DSC, interpretation of the data was the easiest. SEM was very effective for observing the crystallization of the small amount of drug for hot-melt extruded products, as the drug crystal vividly appeared on the large grains. The dissolution performance of spray-dried products could change even without any indication of physical change including crystallization. The advantage/disadvantage and complemental roles of each evaluation method are discussed for deeper understanding on the physical stability data of ASDs.

One-Pot Synthesis of Alkyl Functionalized Reduced Graphene Oxide Nanocomposites as the Lubrication Additive Enabling Enhanced Tribological Performance.

Recently, aiming for the enhanced dispersibility of graphene-based nanomaterials in lubricating oil matrices to serve as highly efficient lubricant additives, numerous modification approaches have been extensively studied. However, these previous modification routes usually involve a tedious multistep modification process or multitudinous toxic reagents, restricting their extensive practical application. In this work, novel graphene oxide (GO) nanoadditives (RGO-g-BO) featuring excellent durable dispersion capability and remarkable tribological performance were successfully prepared via an environmentally friendly one-step approach consisting of surface grafting of long-chain bromooctadecane (BO) and in situ chemical reduction. Benefiting from the greatly improved lipophilicity (resulting from the introduction of hydrophobic long-chain alkane groups and chemical reduction), along with the miniaturization effect, RGO-g-BO exhibits superior long-term dispersion stability in the finished oil. Moreover, the tribological properties results demonstrated that the finished oil filled with RGO-g-BO nanolubricants achieved an outstanding friction-reducing and antiwear performance. Particularly, under the optimum content of RGO-g-BO (as low as 0.005 wt%), the friction coefficient as well as the wear volume of the composite finished oil were greatly reduced by 13% and 53%, respectively, as compared with nascent finished oil. Therefore, in view of the advantages of low-cost, one-step facile synthesis, desirable dispersion capability, and remarkable tribological performance, RGO-g-BO holds great prospects as a highly efficient lubrication additive in the tribology field.

Polycarboxylate superplasticizer modified 3D graphene as long-term-efficient water-based lubricating additive under heavy load conditions

At present, due to the excellent properties of graphene, which can significantly enhance the performance of lubricants, researchers are conducting extensive studies on it. However, the poor dispersion of graphene limits its application in lubrication, which becomes an urgent problem for researchers to solve. Moreover, with the concept of green environmental protection becoming more and more popular, the research on water-based lubricants is of great significance. Therefore, we modify three-dimensional graphene (3DG) by polycarboxylate superplasticizer (PCE) to prepare a water-based lubrication nano-additive with long-term dispersion stability, named PCEG. PCEG nanomaterials can stably disperse in water for more than three months, which effectively solves this problem. Tests show that friction coefficient and wear volume of the lubricant with 0.5 wt% PCEG are reduced by 31.1 % and 23.1 %, respectively, compared to the base fluid at 20 N (2.7 GPa) heavy load conditions. The enhanced lubrication performance is attributed to the fact that PCEG, which has excellent dispersion stability, forms a strong adsorption and continuous dense lubrication film on the friction surface. In addition, it fills and polishes the grooves and pits, thus improving the friction-reduction and anti-wear properties. This study not only greatly solves the problem of poor dispersion stability of graphene and develops a nano-lubricant that is consistently effective under heavy load conditions, but also provides an important reference value for the subsequent development of high-performance and stable graphene-based lubricants.

Design and tribological performance of graphene nanofluids dispersed by dragging effect of bicomponent gelator

Nanofluids have excellent lubrication and high thermal conductivity. However, the agglomeration and sedimentation produced by the large surface energy of nanoparticles in base liquid threaten the long-term dispersion stability and impact the wide application of nanofluid. In this work, based on the self-assemble behavior and continuous network structure formed by low molecular weight organic gelator, the uniform clusters were formed through regulating the kinetics behavior in the gelling process. The dragging effect was demonstrated by oleic acid - sodium dodecyl sulfate (OA-SDS) bicomponent gelator and graphene oxide (GO) nanosheets. The results showed that GO nanofluids dispersed by OA-SDS were stable for more than 12 months. The well-dispersed GO nanofluid exhibited better anti-friction and anti-wear properties under both immersion and electrostatic minimum quantity lubrication conditions. Moreover, the lower contact angle, surface tension and droplet size of nanofluids after charging improved the wettability on the frictional interface. The GO adsorption film formed on the friction interface protected the tribochemical reaction film of iron oxide and prevented the occurrence of sintering of base oil.

Investigation of thermo-optical properties and photothermal conversion performance of MWCNT, Fe3O4, and ATO nanofluid for volumetric absorption solar collector

For the use of volumetric absorption solar thermal collector (VASTC), the thermo-optical properties, photothermal conversion characteristics and economics of MWCNT (Multi-walled carbon nanotube) (0.0005–0.004 wt%), Fe3O4 (0.025–0.1 wt%), and antimony-doped tin oxide (ATO) (0.05–0.25 wt%) nanofluids (NFs) were comprehensively investigated. As a result, The improvement of thermal conductivity, specific heat, and viscosity of MWCNT, Fe3O4, and ATO NFs was insignificant in the concentration range where optical absorbance can improve. The photothermal conversion efficiency (ηPTC) and receiving efficiency (ηrec) were significantly improved according to the increase in the concentration. Among NFs, the 0.002 wt% MWCNT, 0.075 wt% Fe3O4, and 0.1 wt% ATO NFs had maximum ηPTC (93.3%, 90%, and 89.2%) and ηrec (83.7%, 81.4%, and 77.7%). Regarding dispersion stability, the optical transmittance of MWCNT, Fe3O4, and ATO NFs slightly increased, and long-term dispersion stability is required for the use of VASTC. Economically, the cost required per unit photothermal conversion energy (CUPTE) of 0.002 wt% MWCNT NF is 0.102–0.538 $/g, which is cheaper than 0.075 wt% Fe3O4 and 0.1 wt% ATO NFs. Overall, MWCNTs can be used as working fluid for VASTC due to their excellent optical absorption and low price once long-term dispersion stability is achieved.

Transforming water-soluble carbon dots with high particle size regularity as the high-performance oil-based lubricant additives by one-step surface modification

Developing high-performance carbon dot (CD)-based lubricant additives towards non-polar base oils is always challenging because it is an arduous task to gain hydrophobic CDs with high quality. In this work, with the aid of the chemical reaction between hydroxyl groups and lauroyl chloride molecules, the water-soluble CDs-OH derived from the solvothermal method with particularly high particle size regularity were transformed as the oil-soluble CDs-LA by the one-step surface modification process. As expected, the CDs-LA capped by abundant long alkyl chain groups exhibited excellent long-term dispersion stability in non-polar base oil of polyalphaolefin (PAO4) and hence could be served as the additives of PAO4 directly. Under the same test conditions, the tribological performance of CDs-LA was obviously superior to the hydrophobic CDs obtained by the pyrolysis method, implying that the high particle size regularity was beneficial for making full use of the lubrication functions of CDs. Loading 1.7 wt% of CDs-LA made the friction and wear of PAO4 reduced by 32.2 % and 76.4 %, respectively. When the duration prolonged from 20 min to 200 min, the friction reduction of base oil triggered by CDs-LA further enlarged to 46.9 %. The friction-reducing and anti-wear performance of CDs-LA under high loads was also satisfactory. The worn surface analysis results demonstrated that the robust and homogenous boundary lubrication films composed of FexOy and CDs have generated on the rubbing surfaces lubricated by CDs-LA/PAO4 dispersion, well accounting for the outstanding friction reduction and wear resistance functions of CDs-LA.

Polymer-inducing chemical degradation of amorphous solid dispersions driven by drug-polymer interactions for physical stabilization

Intermolecular interactions between active pharmaceutical ingredients (APIs) and carrier polymers are important for the long-term physical stability of amorphous solid dispersions (ASDs). However, the negative impact of intermolecular interactions on chemical stability has rarely been reported. In this study, the relationship between intermolecular interactions and physical and chemical stability was investigated using two ASDs composed of API and hydroxypropyl methylcellulose acetate succinate (HPMCAS) with different stabilities: ASD1 was physically stable but chemically unstable, whereas ASD2 was physically unstable but chemically stable. Ionic-bonding between the pyridine nitrogen in the API and succinyl group in HPMCAS was found in both ASDs. The additional interaction between the succinyl group in HPMCAS and the hydroxyl group in the API was suggested only in ASD1. It was concluded that the additional interaction contributed to the physical stability of ASD1; however, it accelerated the chemical reaction between the succinyl and hydroxyl groups to generate succinyl ester owing to its close proximity. This study shows that the intermolecular interaction between the API and carrier polymer is not always beneficial for chemical stability. Understanding the molecular states of APIs and polymers in ASDs is important for their successful development.

Microfluidic controllable synthesis and size-dependent flow boiling heat transfer of silica nanofluids

Microchannel flow boiling heat transfer with nanofluids is an effective approach to enhance the heat transfer performance of high-power electronics. However, conventional nanofluids are plagued by laborious fabrication procedures, poor stability, and uncontrollable nanoparticle sizes, which compromise the overall heat transfer efficiency. To address these challenges, a facile microfluidic synthesis strategy is developed to prepare highly stable and size-controllable silica nanofluids in a continuous, efficient, and high-throughput methodology. The introduction of silica nanofluid aims to facilitate surface bubble formation and delay coalescence, ultimately enhancing the critical heat flux (CHF) and heat transfer coefficient (HTC) for efficiently cooling silica chips. Through the specifically designed spiral microchannel reactor, nanofluids with controllable nanoparticle sizes ranging from several tens of nanometers to a few hundreds of nanometers can be synthesized with long-term (>30 days) dispersion stability at both room temperature (25 °C) and high temperature (75 °C). Importantly, with negligible changes in pressure drop, the CHF and HTC of the synthesized nanofluids increase by maximum of 55 % and 63 % respectively compared to the basic fluid. Furthermore, our results suggest that smaller-sized nanoparticles outperform larger ones at higher flow rates. These findings not only provide important guidelines for the controllable preparation of nanofluids, but also shed new light on the rational design of efficient nanosystems for two-phase cooling.

In-situ deposition of silver nanoparticles on cuprous oxide hollow spheres for sensitive and recyclable SERS sensing in solution based on electromagnetic and chemical enhancement

In order to achieve widespread application of surface-enhanced Raman spectroscopy (SERS) technique for practical sensing illegal additives in food, it is crucial to construct a reliable SERS substrate that offers both high sensitivity and reusability. This work utilized a simple and rapid in-situ deposition method to deposit Ag nanoparticles onto hollow Cu2O nanospheres, resulting in the formation of Cu2O/Ag nanocomposites with photocatalytic and SERS properties. These nanocomposites were employed as a hopeful SERS analysis for effective sensing of colorant additives in fruit juice, including methylene blue (MB) and rhodamine 6G (R6G). Impressively, the nanocomposites exhibited an exceptional detection limit of 10−9 M for the color agents and demonstrated a strong linear relationship between SERS intensities and the logarithmic concentration (R2 ≥ 0.95). The hollow structure of Cu2O provided low density and long-term dispersion stability in solution, which are beneficial for real-time monitoring the additives in liquid food. The excellent SERS performance can be attributed to the electromagnetic effect of Ag metals and the chemical enhancement of Cu2O semiconductors, as confirmed by the N 1 s XPS spectra from MB. Furthermore, the Cu2O/Ag nanocomposites efficiently degraded dye molecules under UV light irradiation within a short period of 45 min. So, the nanocomposites exhibited practical recyclability, as demonstrated by their consistent performance over five cycles of SERS sensing. These findings highlight their significant potent for SERS sensing trace pollutants and ecological restoration by photocatalytic reaction in the future.

Facile construction of graphene oxide/CeO2 nanohybrid for enhancing tribological properties of green rapeseed oil

The ultra-small size and long-term dispersion stability of nanomaterials are the key factors affecting the anti-friction and wear-resistant effect on lubricating oil. In this study, the CeO2 nanoparticles with size of about 8.1 nm were in-situ anchored on the surface of graphene oxide (GO) nanosheets to obtain GO/CeO2 nanohybrid through a facile solvothermal method. The microstructure and chemical composition of the GO/CeO2 were characterized by FESEM, HRTEM, XRD, and XPS. The as-prepared GO/CeO2 could keep outstanding dispersion in rapeseed oil for 60 days, suggesting the ultra-small CeO2 decorating GO had long-term dispersion stability in rapeseed oil. Moreover, the effect of GO/CeO2 on the lubricating behaviors of rapeseed oil were explored using a ball-on-disc friction tester. Results showed that the GO/CeO2 nanohybrid decreased the average coefficient of friction and wear rate of rapeseed oil more significantly than single GO or CeO2 nanoparticles. At the addition of 0.1 wt% GO/CeO2, the friction coefficient of rapeseed oil decreased by 36.5 % and wear rate decreased by 62.4 %. In addition, the lubricating mechanisms of GO/CeO2 nanohybrid in rapeseed oil were proposed. This study could provide a novel strategy for the construction of ultra-small CeO2 nanoparticles and promote the develop high-performance green lubricant additive of GO/CeO2 nanohybrid.

Investigations of stable surface-modified gold nanofluids optical filters based on optical optimization for photovoltaic/thermal systems

Nanofluid filters have become increasingly popular for solar photovoltaic/thermal (PV/T) systems due to their tunable optical and thermal properties, especially for some plasmonic nanofluids. However, towards optimizing the characteristics of the plasmonic nanofluids filters, by identifying the best nanofluid parameters and improving their long-term dispersion stability, more researches need to be conducted. In this work, the effects of nanoparticles concentration, optical thickness and nanoparticle size on performance of Au nanofluids filtered PV/T systems are investigated theoretically. The PV/T systems can obtain optimal merit function (MF) of 1.367 and 1.357 for Au/water nanofluid and Au/ethylene glycol (EG) nanofluid, respectively. Then, surface-modified Au nanoparticles capped with polyethylene glycol (PEG) or polyvinylpyrrolidone (PVP) polymers are prepared and dispersed in water and EG, respectively. The stability of the stabilizer coated Au nanofluids upon long-term ambient storage, continuous heating, cyclic flowing and solar radiation is discussed. Au + PVP/EG nanofluids exhibit more excellent thermal stability than that of Au + PVP/water. To study the effectiveness of the optimal Au + PVP/EG nanofluids filtered PV/T system, indoor flowing experiments are conducted. The optimal MF of 1.95 and exergy efficiency of 13.98% is achieved filtered by Au + PVP/EG nanofluid with concentration of 29.2 ppm when mass flow rate is 2 mL/min.

Laser Generation of Colloidal Nanoparticles in Liquids: Key Processes of Laser Dispersion and Main Characteristics of Nanoparticles

The processes of laser dispersion of materials for high-performance generation of colloidal nanoparticles in liquids have been considered. Various laser and material parameters affecting this process have been studied. Efficiencies and ergonomics of the generation of colloidal nanoparticles with the help of laser systems having nano-, pico-, and femtosecond pulse durations have been compared using optical and mass criteria by the example of laser ablation of a chemically inert model material (gold) in distilled water without the use of chemical stabilizers. The main characteristics of gold and silver nanoparticles obtained by ablation in water using pulsed laser radiation of different durations have been comprehensively compared. The types of colloidal interactions between nanoparticles in aqueous media have been discussed, and the contributions of structural and ion-electrostatic interactions to the long-term stability of gold and silver nanoparticle dispersions have been analyzed.

LASER GENERATION OF COLLOIDAL NANOPARTICLES IN LIQUIDS: KEY PROCESSES OF LASER DISPERSION AND MAIN CHARACTERISTICS OF NANOPARTICLES

The processes of laser dispersion of materials for high-performance generation of colloidal nanoparticles in liquids have been considered. Various laser and material parameters affecting this process have been studied. Efficiencies and ergonomics of the generation of colloidal nanoparticles with the help of laser systems having nano-, pico-, and femtosecond pulse durations have been compared using optical and mass criteria by the example of laser ablation of a chemically inert model material (gold) in distilled water without the use of chemical stabilizers. The main characteristics of gold and silver nanoparticles obtained by ablation in water using pulsed laser radiation of different durations have been comprehensively compared. The types of colloidal interactions between nanoparticles in aqueous media have been discussed, and the contributions of structural and ion-electrostatic interactions to the long-term stability of gold and silver nanoparticle dispersions have been analyzed.

Double-template-regulated biomimetic construction and tribological properties of superdispersed calcium borate@polydopamine/cellulose acetate-laurate nanocomposite

Herein, a novel superdispersed calcium borate@polydopamine/cellulose acetate-laurate nanocomposite (CTAB-CB@PDA/CAL) is successfully synthesized by a double-template-regulated biomimetic mineralization strategy using PDA/CAL as a hard template and cetyltrimethylammonium bromide (CTAB) as a soft template and surface hydrophobic modifier. The results show that CB can grow uniformly on the CAL surface, and CTAB can improve the hydrophobicity of CTAB-CB@PDA/CAL due to the synergistic effect of the double templates, which contributes to the enhanced dispersibility and long-term dispersion stability of CTAB-CB@PDA/CAL in poly-alpha-olefin (PAO) base oil. Furthermore, CB can rapidly enter the friction interface due to the long substituents of CTAB and CAL, so CTAB-CB@PDA/CAL used as a lubricant additive in PAO base oil exhibits superior tribological performance compared to CB, CB/CAL, and CB@PDA/CAL.

Synthesis of Eco-Friendly Carbon Dots as Self-Repairing Additives of Polyalphaolefin by Means of a Green Solvation Effect.

The eco-friendly menthol-modified carbon dots (CDs-Menth) were synthesized for the first time and exhibited the particularly promising application potential as additives of polyalphaolefin (PAO4). On the one hand, the CDs-Menth could be well dispersed into PAO4 with excellent and long-term dispersion stability via a convenient and green mean, that is, the solvation effect of petroleum ether. This mean was far more advanced to current strategies such as chemical modifications and adding dispersants. On the other hand, the CDs-Menth as additives possessed not only the duty-bound merits such as the distinguished friction-reducing, anti-wear, and load-carrying functions, but also an amazing ability of self-repairing effect. The repairing rate of lower disc in the ball-on-disc friction pair lubricated with CDs-Menth/PAO4 lubricant (2.5 wt %) was about 19.3% if the friction duration was prolonged from 20 to 120 min. Meanwhile, the wear volume reduction for PAO4 caused by CDs-Menth remarkably increased from 43.5 to 74.6%. By virtue of the self-repairing effect, the CDs-Menth could form the tough and tensile boundary lubrication films on the rubbing surfaces, not only tremendously reducing the friction and wear of friction pair, but also hopefully protecting the friction interfaces from the potential oxidation and corrosion.

Facile and scalable preparation of carbon dots with Schiff base structures toward an efficient corrosion inhibitor

Carbon dots (CDs) have been demonstrated to be a novel, green and effective corrosion inhibitor. Nevertheless, it still remains an enormous challenge to obtain CDs corrosion inhibitors by an energy-efficient and time-saving way. Meanwhile, there is no investigation to evaluate the inhibition effect of CDs with Schiff base structures. To surmount the barrier, a facile and scalable approach is elaborately designed to prepare CDs with Schiff base structures (Sc-CDs) by Schiff base reaction using o-phenylenediamine (o-PD) and p-benzoquinone (p-BQ) as precursors at 50 °C for 2 h, and their corrosion inhibiting properties for Q235 carbon steel in 1 M HCl solution are systematacially investigated by weight loss test, electrochemical impedance spectra (EIS) and potentiodynamic polarization (PDP) measurement for the first time. Significantly, Sc-CDs with a long-term dispersion stability in HCl solution reveal a prominent inhibition efficiency of >96 % only at 200 mg/L incorporation. And according to the analyses of electrochemistry, adsorption isotherm and corrosion morphology, the inhibition mechanism of Sc-CDs is rationally attributed to the protective film established by Sc-CDs chemical and physical adsorptions. This work not only provides a facile, scalable, energy-efficient and time-saving approach to synthesize CDs, but also firstly evidences significant inhibition capacities of CDs with Schiff base structures. These findings would dramatically stimulate the development of truly low-cost and high-efficiency CDs corrosion inhibitors.

Green synthesis of biomass-derived carbon dots as an efficient corrosion inhibitor

Metallic corrosion threatens the safety and reliability of metallic facilities and equipment, and exacerbates the issues of environmental pollution and economic losses. However, it is still a challenge to obtain green inhibitors employing sustainably renewable and economical materials. Herein, biomass-derived carbon dots (CDs) are prepared via green hydrothermal treatment only using lichi leaves as the raw material, and their corrosion inhibition properties for Q235 carbon steel in 1 M HCl are systematically investigated using weight loss test, electrochemical impedance spectra (EIS) and potentiodynamic polarization (PDP) measurement for the first time. Specifically, the as-obtained eco-friendly lichi leaves-derived CDs (LCDs) possess numerous O- and N-containing functional groups. And these groups endow LCDs almost unchanged intensities of photoluminescence (PL) and ultraviolet–visible (UV–vis) peaks for two weeks in 1 M HCl solution, demonstrating a long-term dispersion stability of LCDs. On the premise, LCDs at only 200 mg/L concentration reveal an eminent corrosion inhibition ability with a high inhibition efficiency of 98.06% for Q235 carbon steel immersed in 1 M HCl. Meanwhile, they enable the surface roughness (Sa) value of steel surface to starkly reduce by 73.7% (from 12.428 to 3.264 μm) by comparison with that of blank HCl solution. Furthermore, based on analyses of adsorption isotherm and corrosion morphology, their inhibition mechanism is attributed to the protective film formed by LCDs chemical and physical adsorptions. This work firstly substantiates the remarkable inhibition capacities of biomass-derived CDs and provides their green synthesis approach, beneficial to stimulate the advancement of green and efficient corrosion inhibitors.

Processing method determines the long-term stability of particle dispersions in concentrated nanoparticle/polymer suspensions.

Since the degree of particle dispersion can determine the physical properties of polymer nanocomposites (PNCs), plenty of studies have focused on the intrinsic parameters of PNCs such as the concentration/size/chemistry of nanoparticles/polymers relevant to the particle microstructure. While the consideration of these parameters is based on PNCs being in their equilibrium states, PNCs can be kinetically trapped in a nonequilibrium state during the multiple steps of processing. In other words, processing conditions can contribute more significantly to particle dispersion and the properties of PNCs beyond the effects of the intrinsic parameters. Hence, a systematic understanding of the nonequilibrium behaviour of PNCs is required to achieve the desired properties. In this work, we prepared concentrated suspensions with two different preparation pathways. The two different pathways yield different polymer conformations particularly near the particle surface despite the same composition of particles/polymers as the systems are trapped in a nonequilibrium state. Accordingly, the particle microstructures are also greatly changed by the preparation pathway. We found that even in the presence of solvents, these preparation pathway-dependent nonequilibrium effects on particle microstructures persist after several months of aging and ultimately determine the long-term stability of the particle dispersion.

Zwitterionic Silica-Based Hybrid Nanoparticles for Filtration Control in Oil Drilling Conditions

Water-based drilling fluids (WBDFs) that are susceptible to high temperature and saline pollution always exhibit poor ability to control fluid loss and seriously threaten the operation security of oil well drilling; especially, ultradeep well WBDFs that can simultaneously tolerate high salinity and temperature of over 200 °C are difficult to obtain. Herein, a zwitterionic silica-based hybrid nanomaterial (ZSHNM) with a spherical morphology (50–150 nm) was synthesized, and its filtration performance was thoroughly investigated. ZSHNM showed an extraordinary long-term (≥10 months) dispersion stability even at high concentrations in water and possessed remarkable tolerance to high temperature and salinity. Typically, merely adding 2 wt % ZSHNM in WBDFs could achieve an excellent filtration performance even at 240 °C, and with 11 wt % CaCl2 or 36 wt % NaCl added, it showed the best performance to our knowledge. The results suggested that the sodium bentonite (Na-Bent) dispersion could be well stabilized in the presence of ZSHNM even at high temperature and with the presence of cations. Additionally, the silicate core could improve the thermal stability of ZSHNM, whereas the zwitterionic shell could form complexes with cations and further mitigate the aggregation of Na-Bent particles. Thus, the particle size distribution in WBDFs could be finely regulated similar to that in neat Na-Bent dispersion. Furthermore, given the zwitterionic ZSHNM filled in the micro–nanopores among the Na-Bent particles, a compact and low-permeability filter cake was readily formed and ultimately reduced the drilling fluid loss during the filtration process. This work provided a versatile strategy to address the high temperature and high salinity tolerance of WBDFs synchronously, thereby pioneering a new way to develop high-performance drilling additives for ultradeep and complex wells.

Stability investigation of propylene glycol-based Ag@SiO2 nanofluids and their performance in spectral splitting photovoltaic/thermal systems

One main challenge facing nanofluid filters in PV/T systems is their long-term dispersion stability. This work studies the stability of the Ag@SiO2 nanoparticles suspended in propylene glycol (PG)-based fluids for use as optical filters. These nanofluid filters are subjected to high temperature heating test and thermal cycling test to analyze their thermal stability and identify appropriate base fluids. The results of UV–Vis spectroscopy and visual inspection show that both the most concentrated Ag@SiO2/PG + water nanofluid and Ag@SiO2/PG nanofluid exhibit excellent thermal stability when heated to 95 °C and 120 °C, respectively and no agglomeration is observed for exposure to thermal cycling test. A theoretical model with the measured transmittance of the identified Ag@SiO2 nanofluids as the input is introduced to evaluate performance of the nanofluid filtered PV/T system by varying the nanoparticles concentration, optical path-length and concentration ratio. The results indicate that Ag@SiO2/PG + water filter and Ag@SiO2/PG filter for PV/T systems using silicon cells show the capability to increase the economic value of more than 30% at optimum nanoparticles concentration of 12.7 mg/L and optical path-length of 35 mm and 40 mm, respectively, when the concentration ratio varies from 1 to 30 suns.