不同链长直链烷基硫醇自组装的吸附动力学

Adsorption Kinetics of Alkanethiols Self-assembled Monolayer with Different Alkyl Chains

本文利用电化学方法,并结合接触角和原子力显微镜表征手段对直链烷基硫醇自组装的吸附动力学进行了研究。分别考察了短链正六烷基硫醇、中链正十二烷基硫醇和长链正十八烷基硫醇三种链长硫醇分子的组装动力学,每种链长考察了四个浓度。实验结果表明:硫醇自组装由快速吸附和缓慢重组两个过程组成,其组装过程符合扩散控制的Langmuir模型。表观吸附动力学常数kobs与吸附动力学常数ka都显示了浓度相关性,由此估算出烷基硫醇链每增加一个CH2单元,吸附自由能变化约0.09kJ/mol。

In this paper,the adsorption kinetics for the formation of self-assembled monolayer of alkanethiols has been investigated by electrochemical method, contact angle and atomic force microscopy. Three alkyl chains, including short hexanethiol, middle dodecanethiol, and long octadecanethiol, and four concentrations for each thiol are examined. The experimental results indicate that the adsorption of thiol consists of two process, a fast adsorption and a slowly reorganizations. The adsorption process is demonstrated to follow a diffusion-controlled Langmuir model. The apparent adsorption rate constant kobs and the adsorption rate constant k. are all related to the concentration. According to our results, the adsorption free energy of difference per CH2 unit is 0.09 kJ/mol.