The hydrolysis of methyl ester (–CO2Me) and tert-butyl ester (–CO2tBu) functionalized SAMs as a function of subphase temperature and pH is described. Contact angle measurements show that the methyl ester functionalized monolayer does not hydrolyse in pH 1–13 aqueous solutions heated up to 80 °C. In contrast, the –CO2tBu functionalized monolayer hydrolysed below pH 5. The rate and the extent of the hydrolysis were dependent on the temperature and pH of the aqueous solution. Using the Cassie equation, the activation energy for the hydrolysis of CO2tBu-phenyl functionalized SAM was determined as 75 ± 7 kJ mol−1 from the contact angle measurements. Furthermore, the adhesion properties of –CO2tBu and –COOH functionalized SAMs were investigated by depositing –NR2 and –COOH functionalized polystyrene nanoparticles onto the surfaces at pH 3 and 9. By AFM, it was observed that the particles bind preferentially to the –COOH functionalized SAM and the adhesion was pH dependent, with the largest coverage being observed at pH 3. Using the acquired understanding of the hydrolysis of –CO2tBu functionalized SAM and the particle adhesion properties, a simple and facile approach towards fabricating a particle density gradient on this surface is demonstrated. An acid gradient SAM (20 mm long) was prepared by mounting one end of a –CO2tBu functionalized SAM onto the hot side of a Peltier element (80 °C) in pH 1 aqueous solution. The substrate was subsequently immersed into a colloidal solution of –NR2 functionalized polystyrene nanoparticles, removed and rinsed. By AFM, the particle density was shown to be dependent on the surface coverage of –COOH moieties of the underlying SAM. The density started at 104 particles µm−2 on the hydrolysed end down to 0 particles µm−2 on the non-hydrolysed end.
本研究描述了甲基酯(-CO2Me)和叔丁基酯(-CO2tBu)官能化 S
AM 的
水解与亚相温度和 pH 值的函数关系。接触角测量结果表明,在 pH 值为 1-13 的
水溶液中加热至 80 °C,甲酯官能化单层不会
水解。与此相反,-CO2tBu 功能化单层在 pH 值低于 5 时发生
水解,
水解速度和程度取决于
水溶液的温度和 pH 值。通过接触角测量,利用卡西方程确定了 CO2tBu-苯基官能化 S
AM 的
水解活化能为 75 ± 7 kJ mol-1。此外,通过在 pH 值为 3 和 9 的表面沉积-NR2 和-COOH 功能化聚
苯乙烯纳米颗粒,研究了-CO2tBu 和-COOH 功能化 S
AM 的粘附特性。通过原子力显微镜(A
FM)观察到,颗粒优先结合到 -COOH 功能化 S
AM 上,并且粘附与 pH 值有关,在 pH 值为 3 时观察到最大的覆盖率。利用对 -CO2tBu 功能化 S
AM 的
水解和颗粒粘附特性的理解,展示了在该表面上制造颗粒密度梯度的简单易行的方法。在 pH 值为 1 的
水溶液中,将 -CO2tBu 功能化 S
AM 的一端安装在珀尔帖元件的热面(80 °C)上,制备了酸梯度 S
AM(20 毫米长)。随后将基底浸入 -NR2 功能化聚
苯乙烯纳米颗粒的胶体溶液中,取出并冲洗。原子力显微镜显示,颗粒密度取决于底层 S
AM 的 -COOH 分子的表面覆盖率。
水解端的密度从 104 微米-2 开始,到非
水解端的 0 微米-2。