表面活性剂对水基纳米流体固液相变特性的影响

引言蓄冷是利用谷电生产冷能并储存起来以满足峰电时空调负荷需求的一种节能技术,能达到移峰填谷、稳定电力需求的目的。冰蓄冷是一种常用蓄冷技术,即利用具有较大凝固潜热水作为相变材料工质。     

Particle size effects in the thermal conductivity enhancement of copper-based nanofluids

We present an analysis of the dispersion characteristics and thermal conductivity performance of copper-based nanofluids. The copper nanoparticles were prepared using a chemical reduction methodology in the presence of a stabilizing surfactant, oleic acid or cetyl trimethylammonium bromide (CTAB). Nanofluids were prepared using water as the base fluid with copper nanoparticle concentrations of 0.55 and 1.0 vol.%. A dispersing agent, sodium dodecylbenzene sulfonate (SDBS), and subsequent ultrasonication was used to ensure homogenous dispersion of the copper nanopowders in water. Particle size distribution of the copper nanoparticles in the base fluid was determined by dynamic light scattering. We found that the 0.55 vol.% Cu nanofluids exhibited excellent dispersion in the presence of SDBS. In addition, a dynamic thermal conductivity setup was developed and used to measure the thermal conductivity performance of the nanofluids. The 0.55 vol.% Cu nanofluids exhibited a thermal conductivity enhancement of approximately 22%. In the case of the nanofluids prepared from the powders synthesized in the presence of CTAB, the enhancement was approximately 48% over the base fluid for the 1.0 vol.% Cu nanofluids, which is higher than the enhancement values found in the literature. These results can be directly related to the particle/agglomerate size of the copper nanoparticles in water, as determined from dynamic light scattering.     

Synthesis of Silica Nanofluid and Application to CO2 Absorption

Abstract

This study focused on the synthesis of stable nanofluids and their direct application to the CO₂ absorption process. A sol-gel process was used as the synthesis method of nanoparticles in nanofluid. The particle size and stability were determined by SEM image and zeta potential of the nanofluid. Three types of nanofluids containing approximately 30 nm, 70 nm, and 120 nm particles were synthesized and all nanofluids had a stable zeta potential of approximately ? 45 mV. Addition of nanoparticles increased the average absorption rate of 76% during the first 1 minute and total absorption amount of 24% in water. The capacity coefficient of CO₂ absorption in the nanofluid is 4 times higher than water without nanoparticles, because the small bubble sizes in the nanofluid have large mass transfer areas and high solubility.     

Suspensions of Iron Oxide Nanoparticles Stabilized by Anionic Surfactants

Two common anionic surfactants, sodium oleate (SO) and sodium dodecyl benzene sulfonate (SDBS) were used to re‐suspend iron oxide nanoparticles in aqueous solutions. At certain SO concentrations, the SO formulations produced highly stable suspensions. In contrast, SDBS‐stabilized nanoparticles exhibited poor stability at all concentrations. The adsorption isotherm of SO on iron oxide nanoparticles revealed that stable suspensions were obtained when the equilibrium SO concentration (after adsorption) reached its critical micelle concentration (CMC). At this “optimal” condition, the maximum SO adsorption was reached, and the zeta‐potential of the particles was highly negative (～ ?50 mV). According to the SO isotherm, this optimal formulation coincided with the formation of a highly compact SO bilayer. The SDBS isotherm, on the other hand, revealed that SDBS is not strongly adsorbed on the surface of iron oxide nanoparticles and that is likely that a patchy, loosely packed bilayer, is formed on the surface of the iron oxide nanoparticles when the equilibrium SDBS concentration reaches its CMC. The DLVO theory confirmed the connection between formulation conditions and the corresponding stability. This works confirmed that the formation of a surfactant bilayer is an important element in producing stable nanoparticle suspensions with anionic surfactants. It was also confirmed that for anionic surfactants, electrostatic repulsions are an important factor in establishing an energy barrier against flocculation. This work also introduced two more elements into the design of nanoparticle suspensions. The first element is that, in order to ensure the best possible dispersion, the surfactant concentration in solution at equilibrium with the adsorbed surfactant should be close or slightly above its CMC. The second element is that the molecular structure of the surfactant should facilitate the formation of closely packed bilayers.     

Synthesis and characterization of β-TCP/CNT nanocomposite: Morphology,microstructure and in vitro bioactivity

In this study, β-TCP/CNT nanocomposite has been synthesized by solution precipitation method. Then, the effects of the different percentage of CNT (CNT1β-TCP, CNT3β-TCP, CNT5β-TCP) and surfactant (CNT1β-TCP1SDBS, CNT1β-TCP2SDBS, CNT1β-TCP3SDBS) on β-TCP/CNT nanocomposite powder were studied. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) analyses were used to characterize the samples. The observations revealed that the microstructure of 1 wt% CNT could provide dispersion without agglomeration in nanocomposite powder; however, a higher concentration of CNT powder in the nanocomposite resulted in the formation of Ca₂PO₇ phase. Implementing 2 wt% of SDBS as a surfactant modified the shape, size, and distribution of CNT particles on nanocomposites. Finally, the nanocomposite sample was immersed in simulated body fluid (SBF) to evaluate the in vitro bioactivity. It obviously showed an apatite layer on the surface after 7 days of immersion in SBF. Taken together, this nanocomposite might be potentially to be used as bone repair biomaterial.     

Preparation of polyacrylonitrile nanoparticles via dispersion polymerization of acrylonitrile using a poly(N-vinyl pyrrolidone)-cobalt complex in an aqueous system

Monodisperse spherical polyacrylonitrile (PAN) nanoparticles were successfully prepared for the first time by dispersion polymerization of acrylonitrile (AN) in water using well-defined poly(N-vinyl pyrrolidone) (PVP) that was end-capped by a cobalt(II) acetylacetonate (Co(acac)₂) complex (PVP-Co(acac)₂) as both a macroinitiator and a colloidal stabilizer. The well-defined PVP-Co(acac)₂ (M_n = 14,000 g/mol, PDI = 1.25) was synthesized by the bulk cobalt-mediated radical polymerization of N-vinyl pyrrolidone at 20 °C using 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) as an initiator and Co(acac)₂ as a regulating agent. The PVP macroradicals generated at 30 °C by the homolytic cleavage of the C–Co bonds in PVP-Co(acac)₂ initiated the dispersion polymerization of AN, as well as successfully stabilized the growing PAN particles. The average diameters of PAN nanoparticles synthesized with 20, 30, 40, and 50 wt% of PVP-Co(acac)₂ at 30 °C for 24 h were 263.5, 163.1, 157.3, and 143.5 nm, respectively. The PAN nanoparticles had a slightly crumpled spherical appearance, and the degree of crystallinity of the PAN nanoparticles prepared using 30 wt% of PVP-Co(acac)₂ was 31.2%. The mol% of VP units in the PAN nanoparticles was about 6 mol%, and the PVP chains were present on the surface of the PAN nanoparticles as a stabilizing layer. The PVP hairy chains could successfully stabilize very small Ag nanoparticles on the surface of the PAN nanoparticles.     

Influence of process parameters on the formation of Silicalite-1 zeolite particles

Silicalite-1 particles with minimum twinning have been synthesized inside the polar core of non-ionic surfactant/co-surfactant-stabilized water-in-oil (w/o) type emulsions at 150° ± 1 °C within a short reaction time of 5 h. The non-ionic surfactants of varying hydrophilic–lipophilic balance (HLB) values, i.e. sorbitan monooleate (Span 80, HLB: 4.3), sorbitan monolaurate (Span 20, HLB: 8.6), polyoxyethylene (4) lauryl ether (Brij 30, HLB: 9.7) and polyoxyethylene sorbitan monooleate (Tween 80, HLB: 15), the cationic surfactant, i.e. cetyl trimethyl ammonium bromide (CTAB), surfactant concentration, co-surfactant, synthesis temperature and time have been found to play significant role in controlling size and characteristics of Silicalite-1. It has been observed that the crystallinity and size of Silicalite-1 can be tailored by adjusting the interactions between the polar surfactant head groups at the w/o interface and the growing crystallographic surfaces (or silicate/TPA ions) in the aqueous medium of the emulsion.     

N,N-二甲基甲酰胺/液体石蜡非水乳液体系的稳定性研究

将Tween 80,PluronicL64和聚醚胺JEFFAMINE M-2070(M-2070)分别与Span 85复配制得了N,N-二甲基甲酰胺(DMF)/液体石蜡非水乳液体系,从亲水亲油平衡值(HLB)、液滴粒径和稳定时间等方面研究了二元表面活性剂复配对非水乳液稳定性的影响;在Tween 80和Span 85复配基础上,将十二烷基苯磺酸钠(SDBS)、十六烷基三甲基溴化铵(CTAB)和聚乙烯吡咯烷酮(PVP)分别添加到非水乳液体系中,从粒径和乳液稳定时间2个方面考察了三元表面活性剂复配对乳液稳定性的影响。结果表明,Tween 80和Span 85复配可得到较稳定的非水乳液;添加CTAB后,非水乳液的稳定性反而降低;添加PVP后,非水乳液的稳定性有一定程度地加强;而添加SDBS后,乳液的稳定性大大增强。     

Effect of triblock copolymer non-ionic surfactants on the rheology of 3 mol% yttria stabilised zirconia nanosuspensions

The effect of three different molecular weights of a triblock copolymer non-ionic surfactant composed of poly(ethylene oxide) and poly(propylene oxide) have been investigated on the zeta potential, stability and rheology of a commercial nanosuspension of 3 mol% yttria stabilised zirconia (3YSZ). Whilst the surfactants showed some evidence of being adsorbed onto the nanoparticle surfaces, it was in insufficient quantities to achieve complete coverage and measurement of the total organic carbon content suggested that the bulk of the surfactants remained in the liquid medium. As a result, there was only a small effect on the zeta potential. Nevertheless, the stability of the suspension was not affected up to solids contents as high as 54 wt%. Whilst the viscosity of the nanosuspension increased slightly with increasing surfactant concentration due to the presence of the polymer molecules, for the lowest molecular weight surfactant the effect was relatively small. Finally, it was observed that if the ionic strength of the suspension was reduced via the removal of free electrolytes in the suspension by dialysis, the viscosity decreased significantly. The reverse behaviour was also observed when extra NH₄Cl electrolyte was added to the nanosuspension.     

Size-controlled synthesis of nano α-alumina particles through the sol–gel method

Nano α-alumina particles were synthesized by a sol–gel method using aqueous solutions of aluminum isopropoxide and 0.5 M aluminum nitrate. 1/3-benzened disoulfonic acid disodium salt (SDBS) and sodium bis-2-ethylhexyl sulfosuccinate (Na(AOT)) were used as surfactant stabilizing agents. Solution was stirred for different periods (24, 36, 48 and 60 h) at 60 °C. The samples were then analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Introduction of surfactant stabilizing agents and different stirring times will affect the size and shape of particle formed and also the degree of aggregation. SDBS, however, produced better dispersion, finer particles and spherical shape nanoparticles, compared to Na(AOT). The finest particle size (20–30 nm) was obtained at 48 h stirring time with SDBS surfactant.     

The Phase Transformation Mechanism of Bentonite-Stabilized and Cetyltrimethylammonium Bromide-Stabilized Emulsions and Application in Reversible Emulsification Oil-Based Drilling Fluids

We obtained a reversible emulsion system induced by bentonite solid particles and surfactant Cetyltrimethylammonium bromide (CTAB, whose critical micelle concentration (CMC) value is 9.21 × 10⁻⁴ mol L⁻¹). In this study, the zeta potential and contact angle were used to characterize surface wettability of bentonite solid particles in the process of phase transmission behavior. The adsorption amount was calculated at different CTAB concentrations, and then the adsorption isotherm of surfactant CTAB at bentonite solid particles was also studied to confirm the adsorption behavior and adsorption layer structure. The electrical conductivity and microscopic analysis were employed to characterize the phase inversion behavior of emulsion. The results show that the wettability of bentonite particles can be reversed by changing the CTAB concentration, and then the two phase transition behavior of bentonite emulsion can be induced. Additionally, the surfactant CTAB can be used in oil-based drilling fluid systems for the inversion of the emulsion type. The research on the performance of the reversible emulsion oil-based drilling fluid system shows that it has a good thermal stability and a small amount of fluid loss, and successfully reduces the damage of the traditional oil-based drilling fluids on oil well completion.     

Synthesis and characterization of nanosized polypyrrole–polystyrene composite particles

Nanosized polypyrrole–polystyrene (PPy–PS) composite particles were synthesized by the polymerization of pyrrole on PS nanoparticles in the presence of FeCl₃. The PS nanoparticles were prepared from microemulsion polymerizations using the cationic nonpolymerizable surfactant cetyltrimethylammonium bromide (CTAB), the nonionic polymerizable surfactant ω‐methoxy[poly(ethylene oxide)₄₀]undecyl α‐methacrylate (PEO–R–MA‐40), or the cationic polymerizable surfactant ω‐acryloyloxyundecyltrimethylammonium bromide (AUTMAB). For the latexes stabilized by CTAB, the resulting PPy–PS composite particles exhibited relatively poor colloidal stability and the pressed pellets exhibited relatively low electrical conductivities (～10^?7–10^?3 S cm^?1). However, for the latexes stabilized by polymerizable surfactants, the resulting PPy–PS composite particles exhibited relatively good colloidal stability and relatively high conductivities (～10^?5–10^?1 S cm^?1). The effect of polymerizable surfactants on the colloidal stability of composite particles and the conducting mechanism of the composites are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1360–1367, 2004     

A study on the synthesis of acrylic composite particles and investigation of their characterization

Core-shell latexes were synthesized by sequential emulsion polymerization of methyl methacrylate (MMA), styrene (St), and ethyl acrylate (EA) in the presence of anionic surfactant, and the characteristics of these latexes were evaluated. The core latex had to be synthesized carefully to avoid the formation of secondary particles. The sequential polymerization method adopted for this synthesis took advantage of stabilizing particles grown during shell polymerization. In core-shell latex polymerization, to suppress the generation of new particles and to minimize the gelation during the shell polymerization, the amount of surfactant (Sodium dodecyl benzene sulfonate: SDBS) should be reduced to the minimum, 0.01 wt% and 0.02 wt% of SDBS to amount of monomer, respectively, when the Polymethyl methacrylate (PMMA) and Polystyrene (PSt) core latexes are prepared. In addition, the monomer pre-emulsion method is better than monomer-add method. The core-shell structure for composite latex synthesized was demonstrated by Particle Size Analysis (PSA), Differential Scanning Calorimeter (DSC), Transmission Electron Microscope (TEM), formability of film, and hydrolysis under NaOH solution.     

The stabilisation of aqueous suspensions of coal particles

Dilute suspensions of coal particles having average diameters of 1 μm have been prepared from coals from the Shanxi Province, the People's Republic of China, and from the UK. The suspensions were stable only in the presence of surfactant repellants. Measurements of zeta potentials showed suspensions stabilised by non-ionic and ionic surfactants to behave very differently. The effects of the concentrations of repellant and of electrolyte, of the rank and maceral group composition of the coal and of the pH of the medium are contrasted for suspensions stabilised by a polyether, by CTAB and by a lignosulphonic acid. The non-ionic, polyether repellant which formed monolayers on the coal surface, each molecule being bound at more than one site, probably to oxygen groups, readily stabilised the colloidal system by pushing the zeta shear plane away from the coal surface. Larger concentrations of the ionic repellants were needed to confer stability, which they did by the formation of complex charged species on the coal surface.     

Investigation of thermal conductivity and rheological properties of nanofluids containing graphene nanoplatelets

In the present study, stable homogeneous graphene nanoplatelet (GNP) nanofluids were prepared without any surfactant by high-power ultrasonic (probe) dispersion of GNPs in distilled water. The concentrations of nanofluids were maintained at 0.025, 0.05, 0.075, and 0.1 wt.% for three different specific surface areas of 300, 500, and 750 m²/g. Transmission electron microscopy image shows that the suspensions are homogeneous and most of the materials have been well dispersed. The stability of nanofluid was investigated using a UV-visible spectrophotometer in a time span of 600 h, and zeta potential after dispersion had been investigated to elucidate its role on dispersion characteristics. The rheological properties of GNP nanofluids approach Newtonian and non-Newtonian behaviors where viscosity decreases linearly with the rise of temperature. The thermal conductivity results show that the dispersed nanoparticles can always enhance the thermal conductivity of the base fluid, and the highest enhancement was obtained to be 27.64% in the concentration of 0.1 wt.% of GNPs with a specific surface area of 750 m²/g. Electrical conductivity of the GNP nanofluids shows a significant enhancement by dispersion of GNPs in distilled water. This novel type of nanofluids shows outstanding potential for replacements as advanced heat transfer fluids in medium temperature applications including solar collectors and heat exchanger systems.     

Natural citric acid assisted synthesis of CuO nanoparticles: Evaluation of structural,optical, morphological properties and colloidal stability for gas sensor applications

In the present research, natural ingredient lemon juice was selected as a fuel to prepare nanoparticles under combustion method. The structural properties of nanophase copper oxide nanoparticles (CuO NPs) synthesized by a natural citric acid aided combustion process were studied using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). According to the SEM and TEM images, the manufactured product is made up of spherical nanoparticles with a limited size distribution. According to the XRD pattern, the average crystallite size of monoclinic structured CuO nanoparticles was 10.4 nm for as-prepared samples and 20.5 nm for annealed samples. The zeta potential value confirms the negative surface charge of the samples and the values show the excellent stability (-58.1 mV) for as-prepared sample and the good particles stability (-38.3 mV) was exhibited for heat treated sample. The optical band gap of CuO nanoparticles is 2.01 eV and it decreases to 1.28 eV under heat treatment. The sensitivity and selectivity of the samples were tested under different operating temperatures (OT) and different gas concentrations (GC). Recovery-response time plots confirm that the CuO nanoparticles are promising materials for gas sensor fabrications.     

Surfactant-assisted combustion synthesis of agglomerated-free,size- and shape-controlled magnetic iron oxide nanoparticles for biomedical applications

An advanced version of the solution combustion synthesis (SCS) method was developed to prepare iron oxide (IO) nanoparticles, through controlling the agglomeration, size and shape of nanoparticles by assisting a cationic surfactant, “cetyltrimethylammonium bromide (CTAB)” and ethanol. Various IO nanoparticles were prepared in the presence of different CTAB:ethanol molar compositions of 0:0, 0.27:0, 0.55:0, 0.27:17.1, 0.55:17.1 and 0.82:17.1. The morphological evolution from agglomerated-shape particles to the well-dispersed as well as the size- and shape-controlled particles depended directly on the CTAB:ethanol molar composition. A shift from ferromagnetic behavior to superparamagnetic was observed by the application of CTAB along with ethanol, where the lowest blocking temperature (T_b, 60 K), highest saturation magnetization (M_s, 83.5 emu g⁻¹), zero coercivity and remanance magnetization were revealed for the particles prepared by CTAB:ethanol molar compositions of 0.55:17.1. These particles showed an acceptable specific absorption rate (SAR) value (320 W g⁻¹) as well as no obvious hemolytic and cytotoxic effects. This work provides new insights into advancing the SCS method and thus controlling the morphology, size and shape of metal oxide nanoparticles.     

Superior enhancement of imbibition recovery by novel surfactant mixtures with a large hydrophobic group combined with nanosilica

Low interfacial tension (IFT) drainage and imbibition are effective methods for improving oil recovery from reservoirs that have low levels of oil or are tight (i.e., exhibit low oil permeability). It is critical to prepare a high efficient imbibition formula. In this work, a novel 2,4,6-tris(1-phenylethyl)phenoxy polyoxyethylene ether hydroxypropyl sodium sulfonate (TPHS) surfactant was synthesized and evaluated for imbibition. Its structure was confirmed by Fourier transform infrared spectroscopy and the interfacial tension (IFT) of the crude oil/0.07% TPHS solution was 0.276 mN/m. When 0.1 wt% TPHS was mixed with 0.2 wt% alpha olefin sulfonate (AOS), the IFT was lowered to 6 × 10⁻² mN/m. The synergy between nanoparticles (NPs) and TPHS/AOS mixed surfactant was studied by IFT, contact angle on sandstone substrates, zeta potential, and spreading dynamics through microscopic methods. The results show that the surfactant likely adsorbs to the NP surface and that NP addition can help the surfactant desorb crude oil from the glass surface. With the addition of 0.05 wt% SiO₂ NPs (SNPs), the imbibition oil recovery rate increased dramatically from 0.32%/h to 0.87%/h. The spontaneous imbibition recovery increased by 4.47% for original oil in place (OOIP). Compared to flooding by TPHS/AOS surfactant solutions, the oil recovery of forced imbibition in the sand-pack increased by 12.7% OOIP, and the water breakthrough time was delayed by 0.13 pore volumes (PV) when 0.05% SNPs were added. This paper paves the way for enhanced oil recovery in low-permeability sandstone reservoirs using novel TPHS/AOS surfactants and SNPs.     

三种表面活性剂对Fe3O4纳米颗粒的形貌影响

选用十六烷基三甲基溴化铵(CTAB)、聚乙烯吡咯烷酮(PVP)、十二烷基磺酸钠(SDS)3种表面活性剂,研究了这3类不同表面活性剂和不同添加量对Fe3O4纳米颗粒的形貌调控作用,利用透射电镜(TEM)对样品进行表征分析,并给出了机理解释。结果表明:1)3种不同的表面活性剂的加入都获得球形或近球形的纳米颗粒。根据TEM及沉积时间的综合分析,3种活性剂的平均粒径比较:SDS相似文献   

Synthesis of high proton conducting nanoparticles by emulsion polymerization

High ion-exchange capacity (IEC) sulfonated polystyrene nanoparticles were synthesized by an emulsion copolymerization of styrene, divinyl benzene and sulfonated styrene (SS). The effects of varying the counterion of the sulfonated styrene monomer, the SS concentration, the surfactant and the addition of a crosslinking agent on the ability to stabilize the emulsion nanoparticles to high IEC were studied. Water-insoluble nanoparticles, 20-160 nm in diameter, with IEC as high as 5.2 meq/g were achieved using sulfonated styrene with a quaternary alkyl ammonium cation, a non-ionic surfactant and a crosslinking agent in the emulsion formulation. That IEC corresponds to fully sulfonated crosslinked polystyrene.