Sanders Wesley, Anderson Mark R
Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060-0212, USA.
Langmuir. 2008 Nov 18;24(22):12766-70. doi: 10.1021/la801512g. Epub 2008 Oct 24.
Electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM) measurements are used to examine the ability of applied potential to drive the ionic self-assembly of poly(diallyldimethylammonium) chloride (PDDA) onto a substrate modified with a monolayer of 3-mercaptopropionic acid (3-MPA). The potential of zero charge (PZC) of the gold electrode modified with a monolayer of 3-MPA was found by differential capacitance measurements to be -0.12 (+/-0.01) V versus Ag-AgCl. Changing the substrate potential to values positive (-0.01 V vs Ag-AgCl) of the PZC induces interfacial conditions that are favorable for the electrostatic deposition of cationic polymers onto the surface of 3-MPA monolayers. This result is also consistent with experimental observations obtained when the 3-MPA-modified substrate is exposed to 0.10 mol L (-1) NaOH solutions. When potentials equal or negative to the PZC are applied to the substrate, no significant accumulation of the PDDA is found by either QCM or EIS measurement. This result is consistent with results obtained when the 3-MPA modified substrate is exposed to 0.10 mol L (-1) HCl solutions where no PDDA adsorption is expected because the monolayer is neutral under these conditions. Changes in the impedance and quartz crystal frequency obtained after potential is applied to the substrate are interpreted in terms of the applied potential creating interfacial conditions that are favorable for the deprotonation of the terminal carboxylic acid groups and the subsequent electrostatic assembly of the polycation onto the negatively charged monolayer.
采用电化学阻抗谱（EIS）和石英晶体微天平（QCM）测量方法，研究施加电势驱动聚二烯丙基二甲基氯化铵（PDDA）在由3-巯基丙酸（3-MPA）单层修饰的基底上进行离子自组装的能力。通过微分电容测量发现，由3-MPA单层修饰的金电极的零电荷电势（PZC）相对于Ag-AgCl为-0.12（±0.01）V。将基底电势改变为高于PZC的值（相对于Ag-AgCl为-0.01 V）会诱导出有利于阳离子聚合物静电沉积到3-MPA单层表面的界面条件。当3-MPA修饰的基底暴露于0.10 mol L⁻¹ NaOH溶液时获得的实验观察结果也与此结果一致。当将等于或低于PZC的电势施加到基底上时，通过QCM或EIS测量均未发现PDDA有明显积累。该结果与3-MPA修饰的基底暴露于0.10 mol L⁻¹ HCl溶液时获得的结果一致，在这些条件下预计不会有PDDA吸附，因为单层在这些条件下呈中性。根据施加的电势所产生的界面条件来解释将电势施加到基底后所获得的阻抗和石英晶体频率的变化，该界面条件有利于末端羧酸基团去质子化以及随后聚阳离子在带负电荷的单层上的静电组装。
