纳米微粒对低温保护剂溶液结晶性质的影响

为了研究纳米微粒对低温保护剂溶液结晶性质的影响,实验利用差示扫描量热仪(DSC)测量了加入不同粒径、不同质量分数的HA纳米微粒的乙二醇(EG)低温保护剂溶液的成核温度和结晶焓。实验结果表明:纳米微粒加入EG溶液后,成核温度明显升高,并且随着纳米微粒粒径的和质量浓度的增大而升高显著;加入一定质量浓度(>0.2%)的纳米微粒后,同浓度的低温保护剂溶液的结晶焓稳定地升高。成核温度与结晶焓的升高说明,纳米微粒能够促进低温保护剂溶液的结晶。     

纳米微粒对低温保护剂溶液玻璃化性质的影响

利用差示扫描量热仪(DSC)研究了加入羟基磷灰石(HA)纳米微粒对低温保护剂溶液玻璃化的影响,实验得到了不同粒径和不同质量浓度的HA纳米微粒加入PVP溶液的玻璃化转变温度与反玻璃化温度.实验结果表明加入纳米微粒能显著的影响低温保护剂溶液的玻璃化性质.且随着纳米微粒质量分数的增加,溶液的玻璃化转变温度与反玻璃化温度均显著...     

纳米低温保护剂水合及玻璃化性质的DSC研究

利用差示扫描量热仪（DSC）研究了羟基磷灰石（HA）纳米微粒对丙三醇溶液冻结过程中水合性质及玻璃化性质的影响．实验结果表明在中高浓度HA纳米颗粒对溶液水合性质影响显著．与未加纳米颗粒的溶液相比,溶液结晶量减少,未冻水含量增大．在较低浓度溶液中,加入纳米颗粒后玻璃化温度变化不明显,但反玻璃化温度明显升高;当溶液浓度达到6...     

醇类低温保护剂水溶液过冷和水合性质研究

利用差示扫描量热仪研究了乙二醇、丙三醇、1,3丙二醇、1,3丁二醇和2,3丁二醇水溶液的过冷行为和水合性质,得出了这些性质与线性多元醇溶液浓度的关系.研究发现,在低浓度过冷度与浓度之间没有明显关系;而在中高浓度则具有相似的变化规律,即随着溶液浓度增大而增大.各低温保护剂在水合性质上所表现出的差异性,体现了保护剂的官能团(羟基、甲基)所起到的重要作用.     

HA纳米微粒对PEG-600低温保护剂反玻璃化结晶的影响

为了研究羟基磷灰石HA纳米微粒对低温保护剂反玻璃化结晶的影响,本文利用DSC和低温显微镜研究了含有不同粒径(20nm、40nm、60nm)和不同质量浓度(0.1%、0.2%、0.4%、0.8%)HA纳米微粒的PEG-600(50%,w/w)溶液反玻璃化过程中的结晶现象.试验结果表明:与未添加纳米微粒的PEG-600溶液相比,加入40nm、0.4%纳米微粒的HA-PEG600溶液的反玻璃化温度升高了7℃;加入20nm、0.4%和40nm、0.8%纳米微粒的HA-PEG600溶液的冰晶生长速率分别降低了35%和提高了50%;纳米低温保护剂溶液的冰晶形貌从大圆形变成了小圆形、枝晶或小圆形中夹带枝晶.     

HA纳米微粒对PEG-600低温保护剂玻璃化性质的影响

为了研究羟基磷灰石HA纳米微粒对低温保护剂玻璃化性质的影响,利用DSC测量了含有不同粒径(20nm,40nm,60nm)和不同质量浓度(0.1%,0.2%,0.4%,0.8%)HA纳米微粒的PEG-600(50%,w/w)溶液的玻璃化温度。试验结果表明:加入40nm,0.8%HA的PEG-600溶液的玻璃化转变温度最大,熔融温度最小,稳定性也最高。与未加纳米微粒的PEG-600溶液相比,玻璃化转变温度提高了5℃,熔融温度降低了4.5℃,稳定性提高了近30%。加入60nm,0.8%HA的PEG-600溶液的玻璃化转变温度和反玻璃化温度都是最小,而熔融温度最大,稳定性也最低。与未加纳米微粒的PEG-600溶液相比,反玻璃化温度降低了4.5℃,稳定性降低了14%。     

纳米微粒对PVP低温保护剂比热的影响

为了研究纳米微粒对低温保护剂热力学性质的影响,本实验利用差示扫描量热仪(DSC)测量了加入不同质量分数的HA纳米微粒的PVP低温保护剂溶液的比热值.实验结果表明:纳米微粒加入PVP溶液后比热值明显减小,而且HA纳米微粒质量浓度越高,溶液的比热值越小.由于比热容与热扩算系数成反比关系,比热的降低能提高溶液的传热效率,进一...     

低温纳米复合相变蓄冷材料热物性研究

低温相变蓄冷的关键是蓄冷材料的开发.本文针对啤酒工艺对冷源温度的要求,选择BaCl2共晶盐水溶液为相变蓄冷材料基液,在基液中添加粒径为20nm的TiO2纳米粒子,形成具有蓄冷功能的纳米复合材料.对其热物性如导热系数、相变潜热、相变温度、过冷度及粘度进行了实验测量和分析.结果表明,在TiO2纳米粒子的质量分数为1%的情况下,纳米复合蓄冷材料的导热系数比基液提高了11.28%,过冷度从3.97℃降为1.21℃,同时粘度增加了21.7%,相变潜热略有降低.     

稀土纳米发光材料的燃烧法制备及光谱性质

用燃烧法制备了不同粒径的La2O3:Eu3 纳米微粒,研究了影响La2O3:Eu3 纳米微粒大小的实验条件,发现粒径大小随甘氨酸(Gly)与稀土离子比例的增大而减小.制备的纳米微粒由谢乐公式计算的粒径尺寸为12～28 nm.测量了样品的高分辨光谱.运用激光选择激发,研究了光谱在不同发光中心上的变化,表面态对于这些变化起着主要作用.     

微槽道纳米流体饱和沸腾CHF特性研究

以水和三种不同质量分数(0.2%、0.5%和1.0%)的Al2O3纳米流体作为实验工质,在三种不同尺寸微槽道中进行饱和沸腾传热实验,研究沸腾传热过程中临界热流密度(Critical Heat Flux,简称CHF)的变化特性。主要分析了微通道水力半径、纳米流体浓度、进口过冷度和临界热力学干度等因素对CHF的影响。实验结果发现:在水力半径较小的槽道内CHF发生得比较早;CHF随纳米流体浓度的增大而增大;CHF随进口过冷度增大有细微增大的趋势;CHF随临界热力学干度的增大而减小。文中还将实验结果与现有的、工况条件与本实验相近的理论模型进行了拟合比较,发现理论模型能较好预测本实验。     

Glassy dynamics of water at interface with biomolecules: A Mode Coupling Theory test

We study the slow dynamics of hydration water upon cooling in two different biological aqueous solutions, one containing a molecule of lysozyme and another with trehalose molecules. In particular we test if the glassy behaviour of these solutions fulfils the predictions of the popular Mode Coupling Theory of glassy dynamics. In particular we test the Time Temperature Superposition Principle and the matching of the exponents of the theory. Our results confirm that this theory is able to describe the dynamical behaviour of supercooled water also in non ideal cases as the ones under investigation in the region of mild supercooling.     

The effect of silica nanoparticles on the pore structure of hydrating cement paste: a spatially resolved low-field NMR study

ABSTRACT

The hydration process of four different cement-based materials at different depths inside the sample was investigated using localised nuclear magnetic resonance relaxation measurements. All the samples are based on white Portland cement (CEM I 42.5 R), with a water-to-cement ratio of 0.5. One sample is a simple cement paste and the other three additionally contain 5% (by mass of cement) silica nanoparticles (50–200?nm size), silanised silica nanoparticles (with silane A 174) or silica fume (80% silica; 0.15?µm average size). The localised transverse relaxation measurements were performed using a single-sided NMR instrument. The relaxation rates were monitored for 48?h during the hydration process at different depths inside the sample. The results showed that the presence of nanoparticles influences not only the speed of hydration overall, but also the homogeneity of the materials.     

Structure and photoluminescence of VAC-functionalized ZnO nanoparticles by plasma polymerization

A plasma polymerization method was used to modify the surfaces of ZnO nanoparticles, and the effects of plasma surface modification on photoluminescence (PL) property of ZnO nanoparticles were studied. High-resolution transmission electron microscopy images revealed that a thin film of vinyl acetate (VAC) polymer layer (∼4 nm) was uniformly deposited on the surfaces of the ZnO nanoparticles. The chemical structure of the polymer layer was identified by Fourier transform infrared (FTIR) experiments. The photoluminescence (PL) intensity of the ZnO nanoparticles was found to be significantly decreased by the deposited plasma films. For the particle of smaller size, the ultrathin film indicated better ultraviolet (UV) shielding ability.     

Structural and physical aspects of the formation of salt crystals from solutions

The peculiarities of the crystallization of about 100 solutions of different salts have been experimentally studied. A correlation is established between the maximum attainable supercooling temperature of the solution and the structure of the crystals formed. It is found that the highest supercoolings are characteristic of solutions of acentric crystals.     

铜管表面水合物晶体生长特性研究

实验研究了浓度分别为5 wt%、15 wt%、20 wt%、30 wt%的四丁基溴化铵(TBAB)溶液在外径为21mm的铜管外表面的结晶特性.实验首先以15 wt%TBAB溶液为例,观察其降温结晶过程,得到了TBAB水合物晶体在不同阶段生长的特征.然后对不同浓度、不同过冷度条件下的TBAB溶液进行降温结晶实验,观察并测...     

Dehydration process in NaCl solutions under various external electric fields

Ionic motions at solid-liquid interface in supersaturated NaCl solutions have been investigated by molecular dynamics (MD) simulation for understanding crystal growth processes. The density profile in the vicinity of the interfaces between NaCl(100) and the supersaturated NaCl solution was calculated. Diffusion coefficients of water molecules in the solution were estimated as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the interfaces was different from those of bulk solution owing to electric fields depending on the surface charge. Therefore, the electric field was applied to the supersaturated solutions and dehydration phenomenon occurring in the process of the crystal growth was discussed. As the electric field increased, it was observed that the Na⁺ keeping strongly hydration structure broke out by the electric force. In supersaturated concentration, the solution structure is significantly different from that of dilution and has a complicated structure with hydration ions and clusters of NaCl. If the electric fields were applied to the solutions, the breakout of hydration structure was not affected with increasing the supersaturated ratio. This reason is that the cluster structures are destroyed by the electric force. The situation depends on the electric field or crystal surface structure.     

Photoluminescence of CdS nanoparticles embedded in a starch matrix

CdS nanoparticles were synthesized by precipitation in aqueous solution using starch as the capping molecule, and the effect of the pH of the solution on the optical absorption, photoluminescence, and size of the nanoparticles was studied. Absorption spectra, obtained by photoacoustic spectroscopy, indicated that the band gap energy of the crystalline nanoparticles decreased from 2.68 eV down to 2.48 eV by increasing the pH of the solution from 9 up to 14. The X-ray diffraction analysis revealed that the CdS nanoparticles were of zinc blende structure, and that the particle size increased from 1.35 nm up to 2.45 nm with increasing pH. In addition, temperature-dependent photoluminescence (PL) measurements of the capped material showed a blue-shift of the emission peak for temperatures higher than 150 K, indicating the influence of starch on the formation of defect levels on the surface of the CdS nanoparticles.