Fabrication of a nanoparticle gradient substrate by thermochemical manipulation of an ester functionalized SAM
Fabrication of a nanoparticle gradient substrate by thermochemical manipulation of an ester functionalized SAM
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通过酯功能化 SAM 的热化学操作制造纳米颗粒梯度基底
DOI：
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发表时间：
2007
期刊：
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通讯作者：
J. Preece
中科院分区：
文献类型：
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作者：
P. Iqbal;K. Critchley;J. Bowen;D. Attwood;D. Tunnicliffe;S. Evans;J. Preece
研究了甲酯(-CO2Me)和叔丁酯(-CO2tBu)功能化自组装膜的水解亚相温度和pH。接触角测量表明，甲酯功能化的单分子膜在加热到80°C的pH 1-13的水溶液中不发生水解，而-CO2tBu功能化的单分子膜在pH 5以下发生水解。根据Cassie方程，根据接触角测定，确定了CO2tBu-苯基官能团化SAM的水解活化能为75±7kJ·−~(-1)。此外，通过在-CO2tBu和-COOH功能化的聚苯乙烯纳米颗粒表面沉积-NR2和-COOH功能化的聚苯乙烯纳米颗粒，研究了-CO2tBu和-COOH功能化自组装膜的黏附性能。原子力显微镜观察到-CO2tBu和-COOH功能化的自组装膜优先结合在-COOH功能化的自组装膜上，并且这种黏附是pH依赖的，在pH值为3时达到最大的覆盖率。根据对-CO2tBu功能化的自组装膜的水解性和颗粒黏附特性的了解，我们展示了一种在该表面制备颗粒密度梯度的简便方法。将-CO2tBu功能化的SAM的一端安装在pH为1的Peltier元件(80°C)的热面上，制备了一种长20 mm的酸梯度SAM。随后将底物浸入-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，颗粒密度依赖于底层SAM的-COOH部分的表面覆盖率。水解端的密度从104µm−2开始，非水解端的密度从0微米−2开始。
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.