Theory of Polymers and Soft Matter (TPS), Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Langmuir. 2011 Jul 19;27(14):8678-86. doi: 10.1021/la200203s. Epub 2011 Jun 23.
For the first time, atomistically detailed molecular dynamics calculations revealed molecular ordering of the water-oxidized atactic polystyrene (aPS) interface. Both ordering of the water molecules and the phenyl rings occur. In addition, the natural roughness of the surface has been simulated and compared to experimental values. The composition of the simulated aPS films is based on spin-coated aPS films that have been oxidized and characterized experimentally. The aPS surfaces are oxidized with ultraviolet-ozone radiation and have been characterized by XPS, AFM, and water contact angle measurements. XPS measurements show that the oxygen content in the sample increases rapidly with exposure and reaches saturation near 24 at. % of oxygen. The molecular dynamics simulations show smoothening of an hydrophobic aPS surface upon transition from vacuum to water. The smoothening decreases with increasing hydrophilicity. The calculations reveal ordering of oxidized phenyl rings for aPS surfaces in water. The order increases with increasing hydrophilicity. Additionally, we investigated the water structure near the aPS-water interface as a function of the surface hydrophilicity. With increasing hydrophilicity, the density of water at the aPS-water interface increases. The water density profile is steeper in the presence of hydrophobic aPS. The water shows an ordered layer near both the hydrophobic and hydrophilic surfaces; the position of this layer shifts toward the interface with increasing hydrophilicity.
首次通过原子级详细的分子动力学计算揭示了水氧化无规聚苯乙烯(aPS)界面的分子有序性。水分子和苯基环都发生了有序排列。此外，还模拟了表面的自然粗糙度并与实验值进行了比较。模拟的 aPS 薄膜的组成基于已经过实验氧化和表征的旋涂 aPS 薄膜。用紫外线-臭氧辐射氧化 aPS 表面，并通过 XPS、AFM 和水接触角测量进行了表征。XPS 测量表明，样品中的氧含量随暴露迅速增加，并在接近 24 原子%的氧时达到饱和。分子动力学模拟表明，aPS 表面从真空过渡到水时会变得更加光滑。随着亲水性的增加，平滑度降低。计算结果表明，aPS 表面在水中的氧化苯基环有序排列。亲水性增加，有序性增加。此外，我们还研究了 aPS-水界面附近的水结构随表面亲水性的变化。随着亲水性的增加，aPS-水界面处的水密度增加。在疏水性 aPS 存在的情况下，水的密度分布曲线更陡峭。水在疏水性和亲水性表面附近都显示出有序层；随着亲水性的增加，该层向界面移动。
