Pal Bhupender, Mallick Soumya Suddha, Pal Bonamali
School of Chemistry and Biochemistry, Thapar University, Patiala 147004, Punjab, India.
Department of Mechanical Engineering, Thapar University, Patiala 147004, Punjab, India.
J Nanosci Nanotechnol. 2018 May 1;18(5):3283-3290. doi: 10.1166/jnn.2018.14624.
The long term dispersion stability for an improved thermal conductivity is a challenging issue that needs to be solved for heat transfer applications. Hence, this research investigated that a thin layer of SiO2 coating (2-5 nm) over WO3 nanostructures (SiO2@WO3) of different shapes exhibit superior dispersion (0.01%) stability for longer duration (∼3 days) as evident by steady zeta potential (-30 ↔ -60.70 mV), no significant change in particle-size (139 ↔ 147 nm) distribution, density (1.001 ↔ 0.988 g/cm3) and refractive index (1.335 ↔ 1.332) etc., are indicator for colloidal stability relative to bare WO3 nanoparticles and bulk SiO2 aqueous suspension which quickly settles down within 1-2 hours after 30 min sonication at 23 °C. Thin Si-OH layer over WO3 surface imparts superior hydrophilicity, larger surface area for effective solute-solvent (SiO2@WO3-H2O) interaction for improved colloidal stability showing no sedimentation and color change of SiO2@WO3 dispersion (0.01%) even after 3 days due to repulsive interaction between negatively charged Si-O- particles. Thereby, thermal conductivity is found to be quite stable (0.631 ↔ 0.618 W/m K) up to 3 days, whereas aqueous suspension of bare WO3 and SiO2 particles quickly settle down and thermal conductivity rapidly decreased to a value of 0.584 W/m K for de-ionized water further indicates the significance of SiO2 coating. Depending on the thickness of SiO2 layer and volume fraction of SiO2@WO3, a maximum of 8-10% increment of thermal conductivity was achieved where anisotropic WO3 displayed always more (∼5%) thermal conductivity than typical spherical nanoparticles.
对于改善热导率而言，实现长期分散稳定性是一个具有挑战性的问题，这是传热应用中需要解决的。因此，本研究调查了不同形状的WO₃纳米结构（SiO₂@WO₃）上的一层薄SiO₂涂层（2 - 5纳米）在较长时间（约3天）内表现出优异的分散稳定性（0.01%），这可通过稳定的zeta电位（-30 ↔ -60.70 mV）、粒径（139 ↔ 147纳米）分布、密度（1.001 ↔ 0.988克/立方厘米）和折射率（1.335 ↔ 1.332）等无显著变化来证明，相对于裸WO₃纳米颗粒和本体SiO₂水悬浮液而言，这些是胶体稳定性的指标，裸WO₃纳米颗粒和本体SiO₂水悬浮液在23℃下超声处理30分钟后，1 - 2小时内就会迅速沉降。WO₃表面的薄Si - OH层赋予其优异的亲水性，更大的表面积有利于溶质 - 溶剂（SiO₂@WO₃ - H₂O）进行有效相互作用，从而改善胶体稳定性，即使3天后SiO₂@WO₃分散液（0.01%）也没有沉降和颜色变化，这是由于带负电荷的Si - O - 颗粒之间的排斥相互作用。由此发现，热导率在长达3天的时间内相当稳定（0.631 ↔ 0.618瓦/米·开尔文），而裸WO₃和SiO₂颗粒的水悬浮液迅速沉降，去离子水的热导率迅速降至0.584瓦/米·开尔文，这进一步表明了SiO₂涂层的重要性。根据SiO₂层的厚度和SiO₂@WO₃的体积分数，热导率最多可提高8 - 10%，其中各向异性的WO₃的热导率总是比典型的球形纳米颗粒高约5%。
