Department of Chemical Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1.
J Phys Chem B. 2013 Jan 10;117(1):441-9. doi: 10.1021/jp3101688. Epub 2012 Dec 21.
Poly(acrylic acid-co-N,N'-methylenebisacrylamide) hydrogel films were synthesized by copolymerizing acrylic acid (AAc) with N,N'-methylenebisacrylamide (MBA) as a cross-linker via photo polymerization in the spacing confined between two glass plates. NMR spectroscopy was utilized to determine the cross-linking density. We found that the cross-linking density determined by NMR is higher than that expected from the feed concentrations of cross-linkers, suggesting that MBA is more reactive than AAc and the heterogeneous nature of the cross-linking. In addition to the swelling tests, indentation tests were performed on the hydrogel films under water to investigate effects of the cross-linking density on the adhesion and mechanical properties of the hydrogel films in terms of adhesive pull-off force and Hertz-type elastic modulus. As the cross-linker concentration increased, the effective elastic modulus of the hydrogel films increased dramatically at low cross-linking densities and reached a high steady-state value at higher cross-linking densities. The pull-off force decreased with increasing cross-linker concentration and reached a lower force plateau at high cross-linking densities. An optimal "trade-off" cross-linking density was determined to be 0.02 mol fraction of MBA in the hydrogel, where balanced elastic modulus and adhesive pull-off force can be obtained.
聚（丙烯酸-co-N,N'-亚甲基双丙烯酰胺）水凝胶膜是通过在两块玻璃板之间的间隔内通过光聚合将丙烯酸（AAc）与 N,N'-亚甲基双丙烯酰胺（MBA）共聚合成的作为交联剂。NMR 光谱用于确定交联密度。我们发现 NMR 确定的交联密度高于从交联剂的进料浓度预期的交联密度，表明 MBA 比 AAc 更具反应性，并且交联具有非均相性质。除了溶胀测试外，还在水下对水凝胶膜进行了压痕测试，以研究交联密度对水凝胶膜的粘附和力学性能的影响，包括剥离粘附力和赫兹型弹性模量。随着交联剂浓度的增加，水凝胶膜的有效弹性模量在低交联密度下急剧增加，并在更高的交联密度下达到高稳态值。剥离力随交联剂浓度的增加而降低，并在高交联密度下达到较低的力平台。确定了一个最佳的“权衡”交联密度，即水凝胶中 MBA 的 0.02 摩尔分数，在该交联密度下可以获得平衡的弹性模量和剥离粘附力。
