微通道中原位分散技术可控制备氧化铜纳米流体及复合薄膜前体

疏水纳米颗粒分散于有机体系中形成的纳米分散体,具有独特的理化性质和重要的应用价值。其中,纳米颗粒的单分散性、均匀性和稳定性是决定纳米分散体性能的关键。以Cu O纳米分散体作为纳米流体和复合薄膜前体这一典型体系为研究对象,通过设计平板型微通道实现了Cu O纳米分散体制备过程中的液滴聚并和改性Cu O纳米颗粒的原位分散。制备了颗粒体积分数达2%、平均粒径约30 nm的Cu O-基础油纳米流体,该纳米流体具有良好的稳定性和达到0.184 W·m~(–1)·K~(–1)的较高热导率;制备的Cu O-PDMS(聚二甲基硅氧烷)复合薄膜具有较强的抗菌性能和颗粒复合层稳定性。通过系统性实验研究,证明了原位分散方法在强化改性颗粒高效分散中的重要作用,确定了颗粒性能及分散行为对分散体性能的影响规律。     

“超重力+”法可控制备透明纳米分散体及应用

纳米颗粒的分散是纳米材料应用的核心难题之一。新一代纳米材料——单分散纳米颗粒材料分散在溶剂中可形成具有良好透明性或明显丁达尔效应的纳米分散体,较传统纳米粉体材料更易于分散,展现出更优异的纳米效应及应用性能,是国际前沿研究方向。其中,低成本规模化可控制备高固含量、高稳定、高透明的纳米分散体仍面临巨大挑战。针对此问题,本文作者课题组面向终端工程应用需求,提出基于颗粒表面主动设计和修饰调控表面特性,利用超重力强化分子混合结晶过程的方法,有机耦合表面改性-分离过程,率先提出了超重力反应结晶-改性分离耦合的新方法,即“超重力+”法制备透明纳米分散体。本文总结了近年来本文作者课题组在透明纳米分散体“超重力+”法可控制备与应用方面的成果,并对下一步研究方向进行了展望。     

纳米炭载PbO·CuO复合催化剂的制备及其应用

采用三元溶胶-凝胶技术和超临界干燥法制备出纳米炭载PbO·CuO复合催化剂,用扫描电镜和元素分析仪对其颗粒表面进行形貌表征和元素分析;将其应用至交联改性双基推进剂中,研究了该复合催化剂对推进剂燃烧性能及火焰结构的影响,并与同配比的微米级PbO/CuO/CB混合催化剂进行了对比。结果表明,采用该方法制备的纳米炭载PbO·CuO复合催化剂颗粒分布均匀,单组分含量可以有效控制,PbO和CuO均匀负载在纳米炭上,颗粒尺寸为30~60nm,可有效改善交联改性双基推进剂的燃烧性能;当PbO、CuO、CB的摩尔比为5∶10∶3时,推进剂在10~20 MPa内的燃速压强指数可降至0.36;与含微米级PbO/CuO/CB混合催化剂的推进剂相比,含纳米炭载PbO·CuO复合催化剂的推进剂火焰燃面更不规则,火焰亮度和亮黄丝线明显增加,燃烧更为剧烈,表明纳米炭载PbO·CuO复合催化剂对交联改性双基推进剂催化效果明显优于微米级PbO/CuO/CB混合催化剂。     

改性纳米SiO_2/聚氨酯复合乳液的研究

通过原位聚合或直接共混合成了由吐温-80改性的纳米SiO2与聚氨酯的复合乳液,并用粒度分析、UV-Vis和DSC等技术进行了表征.结果表明:原位聚合法制得的复合乳液涂膜的性能提升比直接共混明显,加入适量通过吐温-80改性的SiO2纳米粒子可以使制备的水性聚氨酯分散体粒径分布均匀,稳定性好,而且能够同时增加涂膜的拉伸强度、断裂伸长率以及耐候性.     

丙烯酸树脂及其涂料

201306001具有自清洁性能的含纳米分散体的丙烯酸涂料[刊,英]／FarbodAlimohammadi等／／Journal of Coatings Technology and Research-2012．9（6）．-687～693将表面功能化改性的气相二氧化硅纳米复合分散体加入丙烯酸涂料中,并采用扫描电镜（SEM）观察表明该分散体在聚合物基料中分散良好。     

PBAT/纳米蒙脱土复合薄膜的制备及水蒸气阻隔性能研究

利用双十八烷基二甲基氯化铵(D1821)对纳米蒙脱土(MMT)进行预处理和改性,得到MMT-D1821,然后采用涂膜法和流延法制备了聚己二酸-对苯二甲酸丁二醇酯(PBAT)/MMT-D1821复合薄膜。对PBAT/未改性MMT及PBAT/MMT-D1821复合薄膜的微观形貌、水蒸气阻隔性能和力学性能进行了研究。结果表明:与未改性MMT相比,MMT-D1821在PBAT基体中的分散状态得到改善,PBAT/MMT-D1821复合薄膜的水蒸气阻隔性能及力学性能均比PBAT/未改性MMT复合薄膜明显提升;采用涂膜法制备的复合薄膜较之流延法得到的薄膜具有更好的水蒸气阻隔性能。     

聚氨酯/还原氧化石墨烯聚对苯二胺薄膜的制备与性能

采用Hummers法制备氧化石墨烯（GO）,并在其表面原位聚合聚对苯二胺(PPDA),再经水合肼还原得到还原氧化石墨烯聚对苯二胺(RGO-PPDA)复合体,并用其改性热塑性聚氨酯(TPU)薄膜,最终通过溶液涂膜制得TPU/RGO-PPDA复合薄膜。通过傅里叶变换红外光谱仪、X射线衍射仪、扫描电子显微镜、透射电子显微镜、X射线光电子能谱仪对RGO-PPDA纳米复合体进行表征,并利用氧气透过仪、高阻计对TPU/RGO-PPDA复合薄膜的性能进行测试,并与TPU/GO-PPDA复合薄膜性能进行对比。结果表明,GO上原位聚合PPDA,显著改善了GO的亲油性,这有利于GO在氮氮二甲基甲酰胺(DMF)中的分散,进而有利于实现在TPU基体中的均匀分散;当RGO-PPDA含量为0.8 %(质量分数,下同)时,TPU/RGO-PPDA复合薄膜的氧气透过率降低了73.28 %,导电性能提升了8个数量级,表现出良好的阻隔抗静电性能。     

非共价改性纳米颗粒稳定Pickering乳液的制备及可逆调控

用具有氧化还原活性分子乙酰基二茂铁吖嗪(Fc⁺A)对磁性纳米颗粒Fe₃O₄@SiO₂进行非共价疏水改性,将改性颗粒作为乳化剂制备Pickering乳液。通过TEM、SEM、FTIR、XRD、接触角测量、光学显微镜等对纳米颗粒及Pickering乳液的结构、形貌和性能进行表征。结果表明：制备的核壳结构纳米颗粒粒径为150 nm左右,分散均匀;Fc⁺A成功修饰到纳米颗粒表面,且随Fc⁺A浓度的增加,改性颗粒的接触角明显增大;Fc⁺A浓度为12.5 mmol/L,乳化剂浓度为0.3%(质量),油水比为4∶6,搅拌速率为10000 r/min,得到的Pickering乳液具有良好的稳定性。而且,所得乳液具双重响应性,通过氧化还原和磁场可实现对乳液稳定性的可逆调控。     

PDA包覆铝粉及其在HTPB中的分散稳定性

通过原位多巴胺(DA)聚合法在铝粉表面包覆聚多巴胺(PDA),制备了Al@PDA复合颗粒;采用SEM表征不同DA质量浓度下Al@PDA的表面形貌。用XRD测试铝粉包覆前后的晶型;采用XPS分析Al@PDA的表面元素组成;通过沉降法研究了铝粉和Al@PDA在HTPB中的分散稳定性;通过制备固化胶并切片取样观察固体颗粒在HTPB中的分散情况。结果表明,当DA质量浓度为3.5g/L时对铝粉的包覆效果最好,在铝粉表面形成牢固的PDA薄膜;包覆前后Al的晶型没有改变;XPS在Al@PDA表面检测到的C-OH、C=O组分和π-π共轭结构证实了PDA包覆层的存在。沉降24h后Al-HTPB体系出现分层,而Al@PDA-HTPB体系仍然颜色均一,表明Al@PDA在HTPB中的分散稳定性明显优于原料铝粉。     

纳米TiO_2表面改性及在PUA复合涂层中的应用

以硬脂酸和钛酸酯偶联剂为复合改性剂对纳米TiO2进行表面改性,并通过原位分散和光固化方法制备了改性纳米TiO2/聚氨酯丙烯酸酯(PUA)复合涂层。讨论了纳米TiO2的改性条件及改性效果,并通过SEM、DSC和力学性能测试等手段考察了改性纳米TiO2对PUA性能的影响。结果表明,当钛酸酯为0.00234 mol/L、硬脂酸为0.0352 mol/L、温度45℃、时间1.5 h时,纳米TiO2的表面改性效果较好;改性后的纳米TiO2在PUA中的分散稳定性得到提高,且改性纳米TiO2/PUA复合涂层的力学性能,尤其是耐冲击力和拉伸强度得到了提高。     

Enhancement of Thermal Conductivity with CuO for Nanofluids

The enhancement of the thermal conductivity of ethylene glycol in the presence of copper oxide (CuO) is investigated. CuO nanofluids are prepared in a two‐step method. No surfactant is employed as a dispersant. The volume fraction of CuO nanoparticles suspended in ethylene glycol liquid is below 5 vol.‐%. The crystalline phases of the CuO powders are measured with x‐ray diffraction patterns (XRD). CuO nanoparticles are examined using scanning electron microscopy (SEM) to determine their microstructure. The thermal conductivities of the CuO suspensions are measured by a modified transient hot wire method. The viscosity was measured with a viscosity instrument. The results show that CuO nanofluids with low concentrations of nanoparticles have considerably higher thermal conductivities than the identical ethylene glycol base liquids without solid nanoparticles. The thermal conductivity ratio improvement for CuO nanofluids is approximately linear with the volume fraction of nanoparticles. For CuO nanoparticles at a volume fraction of 0.05 (5 vol‐.%) thermal conductivity was enhanced by up to 22.4 %. CuO nanofluids thus have good potential for effective heat transfer applications.     

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.     

An Investigation on the Thermal Effusivity of Nanofluids Containing Al(2)O(3) and CuO Nanoparticles

The thermal effusivity of Al(2)O(3) and CuO nanofluids in different base fluids, i.e., deionized water, ethylene glycol and olive oil were investigated. The nanofluids, nanoparticles dispersed in base fluids; were prepared by mixing Al(2)O(3), CuO nanopowder and the base fluids using sonication with high-powered pulses to ensure a good uniform dispersion of nanoparticles in the base fluids. The morphology of the particles in the base fluids was investigated by transmission electron microscopy (TEM). In this study, a phase frequency scan of the front pyroelectric configuration technique, with a thermally thick PVDF pyroelectric sensor and sample, was used to measure the thermal effusivity of the prepared nanofluids. The experimental results of the thermal effusivity of the studied solvents (deionized water, ethylene glycol and olive oil) showed good agreement with literature values, and were reduced in the presence of nanoparticles. The thermal effusivity of the nanofluid was found to be particularly sensitive to its base fluid and the type of nanoparticles.     

Effect of particle size on the thermal conductivity of nanofluids containing metallic nanoparticles

A one-parameter model is presented for the thermal conductivity of nanofluids containing dispersed metallic nanoparticles. The model takes into account the decrease in thermal conductivity of metal nanoparticles with decreasing size. Although literature data could be correlated well using the model, the effect of the size of the particles on the effective thermal conductivity of the nanofluid could not be elucidated from these data. Therefore, new thermal conductivity measurements are reported for six nanofluids containing silver nanoparticles of different sizes and volume fractions. The results provide strong evidence that the decrease in the thermal conductivity of the solid with particle size must be considered when developing models for the thermal conductivity of nanofluids.     

Enhancements of thermal conductivities with Cu,CuO, and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system

In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.     

Microwave-assisted synthesis of hybrid colloids for design of conducting films

We report synthesis of colloids with polymer core and inorganic shell consisting of silver nanoparticles (AgNPs) which can be used as building blocks for the preparation of conducting composite films. Polymer colloids based on copolymer of styrene and butyl acrylate with variable film formation temperature and functional surface have been prepared by surfactant-free emulsion polymerization. Polymer particles with average size between 140 nm and 220 nm and narrow size distribution were used as templates for deposition of AgNPs by microwave-assisted reduction of silver precursors in aqueous medium. The loading of the AgNPs on the polymer particle surface has been increased up to 60 wt.-%. Obtained hybrid colloids were used for preparation of composite films. The electrical conductivity of the composite films starts to increase if the AgNPs loading on the polymer particle surface is above 20 wt.-%.     

Preparation and properties of copper-oil-based nanofluids

In this study, the lipophilic Cu nanoparticles were synthesized by surface modification method to improve their dispersion stability in hydrophobic organic media. The oil-based nanofluids were prepared with the lipophilic Cu nanoparticles. The transport properties, viscosity, and thermal conductivity of the nanofluids have been measured. The viscosities and thermal conductivities of the nanofluids with the surface-modified nanoparticles have higher values than the base fluids do. The composition has more significant effects on the thermal conductivity than on the viscosity. It is valuable to prepare an appropriate oil-based nanofluid for enhancing the heat-transfer capacity of a hydrophobic system. The effects of adding Cu nanoparticles on the thermal oxidation stability of the fluids were investigated by measuring the hydroperoxide concentration in the Cu/kerosene nanofluids. The hydroperoxide concentrations are observed to be clearly lower in the Cu nanofluids than in their base fluids. Appropriate amounts of metal nanoparticles added in a hydrocarbon fuel can enhance the thermal oxidation stability.     

Heat transfer in nanoparticle suspensions: Modeling the thermal conductivity of nanofluids

This work reviews experimental data and models for the thermal conductivity of nanoparticle suspensions and examines the effect of the properties of the two phases on the effective thermal conductivity of the heterogeneous system. A model is presented for the effective thermal conductivity of nanofluids that takes into account the temperature dependence of the thermal conductivities of the individual phases, as well as the size dependence of the thermal conductivity of the dispersed phase. We demonstrate that this model can be used to calculate the thermal conductivity of nanofluids over a wide range of particle sizes, particle volume fractions, and temperatures. The model can also be used to validate experimental thermal conductivity data for nanofluids containing semiconductor or insulator particles and confirm the size dependence of the thermal conductivity of nanoparticles. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

The Effect of Size and Concentration of Nanoparticles on the Mass Transfer Coefficients in Irregular Packed Liquid–Liquid Extraction Columns

This investigation explored the effects of nanofluids on mass transfer enhancement using an irregularly packed liquid–liquid extraction column and the chemical systems of water–acetic acid–toluene. SiO₂ nanoparticles with sizes of 10, 30, or 80 nm are dispersed in toluene–acetic acid to produce nanofluids with different volume fractions of 0, 0.01, 0.05, and 0.1 vol.%. The effects of nanoparticle size and concentration on dispersed phase mass transfer coefficient were discussed based on the experimental data. This is for the first time that the effect of nanoparticle size is studied in liquid–liquid extraction systems. It was found that the mass transfer enhancement was more significant in nanofluids with smaller particles. It was also observed that mass transfer coefficient is larger in nanofluids compared to that in dispersed phase without nanoparticles, with a peak enhancement at a nanoparticle volume fraction of 0.05 vol.% for 10-nm particles and 0.01 vol.% for 30- and 80-nm particles. The maximum mass transfer coefficient enhancement was approximately 42% at 0.05% concentration of nanoparticles using smaller particles (10 nm). Finally, a novel correlation for prediction of effective diffusivity in the presence of nanoparticles has been proposed, which is a function of nanoparticle size and its concentration. The main advantage of this approach is that the principal effect of these two parameters is considered in correlation without which the experimental data could not be fitted with an acceptable accuracy.     

氧化铝有机纳米流体的流动传热基础特性

以氧化铝为纳米粒子、丙二醇和水为基础液体制备了氧化铝有机纳米流体,分别测量了它的沸点、热导率、比热容和黏度。以1％～5％（体积分数）的氧化铝纳米流体作为冷介质,测试了在车用机油冷却器中的传热系数和流动阻力。试验结果表明,纳米粒子能够显著强化基础液体在机油冷却器中的换热能力,粒子体积分数和流体温度是影响纳米流体热物性的重要因素。氧化铝纳米流体的沸点高于120℃,比热容随体积分数增加而降低,热导率、黏度和在机油冷却器中的传热系数均随粒子体积分数的增加而提高。在试验Ⅱ中,5％（体积分数）纳米流体的平均传热系数比基础液体提高了124.56％,而流动阻力增幅较小。