基于棕榈酸改性纳米TiO2超疏水涂层的制备

Preparation of Nano TiO2 Superhydrophobic Coating Based on Palmitic Acid Modification

目前超疏水表面制备方法众多,但其改性机理及疏水机理研究仍不够完善。通过棕榈酸改性纳米TiO_(2)制备一种高效超疏水表面并分析其改性和疏水的机理。试验上按不同改性配比制得悬浮液,通过两步喷涂法将悬浮液喷涂到铝基表面制备得到超疏水表面,并采用傅里叶红外光谱仪和扫描电子显微镜进行表征与分析。研究中采用分子动力学模拟方法构建棕榈酸改性纳米TiO_(2)模型和润湿模型,使用COMPASS Ⅱ力场进行分子动力学模拟,通过体系构型以及均方根位移和径向分布函数的计算结果对改性机理、不同改性配比效果及微观润湿行为进行分析研究。经试验与模拟的验证,不同的改性配比形成不同的微纳结构对表面润湿性有着极大的影响,通过表征测试筛选得到最佳改性配比,成功改性制备得到接触角为164.4°的超疏水表面。经分析可知,棕榈酸与纳米TiO_(2)通过氢键吸附发生脱水缩合反应产生酯键,成功将亲水性的纳米TiO_(2)改性为超疏水性,改性配比制备的表面不仅表面能低,而且形成层次分明的微纳结构使得表面超疏水性能更佳。通过宏观试验与微观分子动力学模拟相结合的方法研究分析得到PA改性纳米TiO_(2)机理、不同改性配比对表面润湿性影响和疏水机理,进一步完善制备超疏水表面的相关机理研究,在超疏水表面制备及研究方面具有参考意义。

Several methods are available for preparing superhydrophobic surfaces.However,their practical applications are limited owing to imperfections in their modification and hydrophobicity mechanisms.Therefore,investigating the mechanisms underlying the formation of superhydrophobic surfaces is crucial.Additionally,the preparation method and material selection for superhydrophobic surfaces have a significant impact on cost and environmental considerations.In this study,we chose palmitic acid(PA)-modified titanium dioxide(TiO_(2)),which has a low surface energy and is environmentally friendly and cost-effective.Our objective was to prepare a highly efficient superhydrophobic surface using this material and analyze its modification and hydrophobicity mechanisms.Experimentally,we prepared suspensions with varying modification ratios and applied them to polished aluminum surfaces using a two-step spraying method.The chemical reactions between TiO_(2) nanoparticles and PA were analyzed using a Fourier infrared spectrometer.Scanning electron microscopy was used to characterize the morphologies of the superhydrophobic surfaces.A contact angle meter was used to evaluate the wetting performance of the samples by measuring their surface contact and rolling angles.To further investigate the modification mechanism and effect of different modification ratios on the surface wetting behavior,we utilized a molecular dynamics simulation method.Different models consisting of varying numbers of molecule-modified nano-TiO_(2)(101),were constructed.Additionally,various surface-wetting models have been developed to simulate different wettabilities.The COMPASS II force field was then employed for molecular dynamics simulations to analyze and study the modification mechanism and microscopic wetting behavior through system configuration.The root-mean-square displacement and radial distribution functions were calculated to obtain meaningful results.Overall,this research aims to elucidate of the mechanism underlying superhydrophobic surface modification and provide insights into the influence of different modification ratios on the wetting behavior at the molecular level.Validation using macroscopic experiments and microscopic molecular dynamics simulations confirmed that different modification ratios result in distinct micro-nanostructures with significant impact on surface wettability.Through characterization tests,the optimal modification ratio was identified to be 0.2 g of the PA weight and 1 g of TiO_(2) weight.At this ratio,a superhydrophobic surface was successfully prepared,exhibiting a contact angle of 164.4°and a rolling angle of 2°.Meticulous analysis revealed that bonding between PA and nano-TiO_(2) occurred via hydrogen bonding,followed by subsequent dehydration condensation reactions that culminated in the formation of ester bonds.When the head of the PA molecules is grafted onto the TiO_(2) surface,the tail is expelled and oscillates in a swaying motion.This unique adsorption mechanism creates a hydrophobic film composed predominantly of alkyl chains,which effectively transforms the inherent hydrophilic properties of the surface.Notably,the optimal modification ratios not only yield surfaces with low surface energy but also facilitate the development of a hierarchical micro-nanostructured surface,thereby augmenting the superhydrophobic characteristics.By combining macroscopic experiments and microscopic molecular dynamics simulations,this study analyzed the mechanism of PA-modified nano-TiO_(2),along with the impact of different modification ratios on surface wettability and hydrophobicity.These findings further refine our understanding of superhydrophobic surfaces,which hold immense significance for their preparation and research.Nevertheless,one limitation became apparent in this study,primarily concerning the opaque white appearance of the coating derived from PA-modified TiO_(2).Unfortunately,this monochromatic attribute significantly restricts extensive application.Consequently,the development of a coating with the ability to assume a diverse range of colors or achieve transparency would undoubtedly yield substantial benefits,facilitating a more versatile utilization of superhydrophobic surfaces.This aspect should be further explored in future studies to enhance the applicability of these surfaces in various practical settings.