Edmondson Steve, Vo Cong-Duan, Armes Steven P, Unali Gian-Franco, Weir Michael P
Dainton Building, Department of Chemistry, The University of Sheffield, Brook Hill, Sheffield, S3 7HF, UK.
Langmuir. 2008 Jul 15;24(14):7208-15. doi: 10.1021/la7039898. Epub 2008 Jun 13.
The layer-by-layer (L-b-L) deposition of oppositely charged polyelectrolytic macroinitiators has been demonstrated on planar silica substrates. The build-up of the macroinitiator multilayers was monitored by ellipsometry (up to 21 layers) and dual polarization interferometry (up to 17 layers) and good agreement was found between these techniques. The increase in L-b-L thickness was approximately linear, with an average thickness of 2.3 A per layer of deposited macroinitiator. Surface-initiated ATRP of a model nonionic methacrylic monomer, 2-hydroxyethyl methacrylate (HEMA) in a 1:1 methanol/water mixture was conducted at ambient temperature. Increasing the number of macroinitiator layers led to a significant increase in PHEMA brush thickness up to 110 nm, which is attributed to the greater surface grafting density. PHEMA brush thicknesses obtained after 22 h showed a linear dependence on the number of layers of deposited macro-initiator, with all layers exhibiting near-identical growth kinetics. X-ray photoelectron spectroscopy was used to monitor L-b-L assembly and also to confirm PHEMA growth. This technique indicated the loss of small counterions from the multilayers during L-b-L deposition and confirmed an increase in the surface density of bromoester initiator groups as the number of deposited macroinitiator layers was increased. For 17 macroinitiator layers, the bromoester initiator density is estimated to be approximately 4.9 +/- 0.2 nm (-2) from the DPI data. This is comparable to that calculated for ATRP initiator monolayers obtained by either thiol or silane chemistry. Ellipsometry suggested that the macroinitiator multilayers were weakly hydrated prior to the in situ HEMA polymerization. AFM studies indicated that the PHEMA brushes had appreciable surface roughness, but this roughness became negligible compared to the brush thickness with increasing macroinitiator layers.
已证实在平面二氧化硅基底上可进行带相反电荷的聚电解质大分子引发剂的逐层（L-b-L）沉积。通过椭偏仪（最多21层）和双偏振干涉仪（最多17层）监测大分子引发剂多层膜的形成，发现这些技术之间具有良好的一致性。L-b-L厚度的增加近似呈线性，每沉积一层大分子引发剂的平均厚度为2.3 Å。在室温下，在1:1甲醇/水混合物中对模型非离子甲基丙烯酸单体甲基丙烯酸2-羟乙酯（HEMA）进行表面引发的原子转移自由基聚合（ATRP）。增加大分子引发剂层数会导致聚甲基丙烯酸2-羟乙酯（PHEMA）刷厚度显著增加，最高可达110 nm，这归因于更高的表面接枝密度。22小时后获得的PHEMA刷厚度与沉积的大分子引发剂层数呈线性关系，所有层均表现出近乎相同的生长动力学。利用X射线光电子能谱监测L-b-L组装过程，并确认PHEMA的生长。该技术表明在L-b-L沉积过程中多层膜中存在小抗衡离子的损失，并证实随着沉积的大分子引发剂层数增加，溴酯引发剂基团的表面密度增加。对于17层大分子引发剂，根据双偏振干涉数据估计溴酯引发剂密度约为4.9±0.2 nm⁻²。这与通过硫醇或硅烷化学方法获得的ATRP引发剂单层计算值相当。椭偏仪表明，在原位HEMA聚合之前，大分子引发剂多层膜的水合程度较弱。原子力显微镜研究表明，PHEMA刷具有明显的表面粗糙度，但随着大分子引发剂层数增加，与刷厚度相比，这种粗糙度变得可以忽略不计。
