Lee Min-Kyo, Park Young-Chun
School of Computer Science and Electrical Engineering , Handong Global University , Pohang 37554 , Republic of Korea.
Langmuir. 2019 Feb 12;35(6):2066-2077. doi: 10.1021/acs.langmuir.8b03258. Epub 2019 Jan 29.
The contact angle relaxation of TiO surfaces is an important problem that must be understood, particularly for long-lasting hydrophilicity under dark conditions. The relaxation of sputtered anatase TiO thin films over a long time (∼22 days) in an atmospheric environment was observed using quantitative XPS analysis. A new peak was identified as HO within a donor-acceptor complex at ∼2.57 eV above the lattice oxygen peak. This donor-acceptor complex turns out to be a key factor for long lasting hydrophilicity, and our model is presented. Adventitious carbon contamination was not the main cause of the contact angle relaxation. Instead, samples with lower amounts of donor-acceptor complexes ( I/ I ≤ ∼5%) underwent contact angle relaxation over time, and samples with a high density of donor-acceptor complexes ( I/ I ≥ ∼10%) showed good hydrophilicity (contact angle ≤20°) over 22 days. Larger amounts of basic Ti-OH relative to acidic OH ( I/ I ≥ 1) resulted in greater amounts of donor-acceptor complexes ( I/ I ≥ ∼10%). Thus, basic Ti-OH groups interact with HO by forming a strong electrostatic donor-acceptor complex, leading to long-lasting hydrophilicity. Indeed, TiO was transformed to show long lasting hydrophilicity by high-density oxygen plasma treatment by forming sufficient Ti-OH groups and HO molecules in the donor-acceptor complexes. Contact angle relaxation is closely related to the interactions between water molecules and the TiO surface in the dark. It is suggested that the relaxation depends on the number of electrostatic donor-acceptor complexes. This study provides new insight by linking theoretical studies with the experimental contact angle at the TiO surface in an ambient environment and is the first study that provides the presented relaxation mechanism.
TiO表面的接触角弛豫是一个必须理解的重要问题，特别是对于在黑暗条件下的持久亲水性而言。使用定量XPS分析观察了溅射的锐钛矿TiO薄膜在大气环境中长时间（约22天）的弛豫情况。在高于晶格氧峰约2.57 eV处的供体-受体复合物中，一个新的峰被鉴定为HO。事实证明，这种供体-受体复合物是持久亲水性的关键因素，并提出了我们的模型。杂质碳污染不是接触角弛豫的主要原因。相反，供体-受体复合物含量较低（I/I≤约5%）的样品随时间发生接触角弛豫，而供体-受体复合物密度高（I/I≥约10%）的样品在22天内表现出良好的亲水性（接触角≤20°）。相对于酸性OH，碱性Ti-OH含量更高（I/I≥1）会导致更多的供体-受体复合物（I/I≥约10%）。因此，碱性Ti-OH基团通过形成强静电供体-受体复合物与HO相互作用，导致持久亲水性。实际上，通过高密度氧等离子体处理，TiO通过在供体-受体复合物中形成足够的Ti-OH基团和HO分子而转变为具有持久亲水性。接触角弛豫与黑暗中水分子与TiO表面之间的相互作用密切相关。有人认为，弛豫取决于静电供体-受体复合物的数量。本研究通过将理论研究与环境中TiO表面的实验接触角联系起来提供了新的见解，并且是第一项提供所提出的弛豫机制的研究。
