Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
ACS Appl Mater Interfaces. 2011 Dec;3(12):4714-21. doi: 10.1021/am201132x. Epub 2011 Nov 22.
Poly(N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel assemblies (aggregates) were synthesized via polymerization of the cross-linker N,N'-methylenebisacrylamide (BIS) in the presence of microgels in solution. In this case, the microgels were entrapped in the polymerized cross-linker network. The aggregates were investigated for their ability to remove the organic, azo dye molecule 4-(2-hydroxy-1-napthylazo) benzenesulfonic acid sodium salt (Orange II) from water at both room and elevated temperatures. These results were compared with unaggregated microgels that were previously reported (Parasuraman, D.; Serpe, M. J. ACS. Appl. Mater. Interfaces 2011, 3, 2732.). It was found that the removal efficiency increased at elevated temperature, most likely due to the thermoresponsive nature of the pNIPAm-based aggregates, which expel water of solvation and deswell at higher temperature and reswell when they are cooled back to room temperature. Furthermore, increasing the number of cycles the aggregates are heated and cooled enhanced the percent removal of the dye from water. We also evaluated the effect of increasing cross-linker concentration on the removal efficiency, where we found the removal efficiency to increase with increasing cross-linker concentration in the aggregates. The maximum removal efficiency reached by the microgel aggregates at elevated temperatures was calculated to be 73.1%. This enhanced uptake is due to the presence of larger internal volume between the microgels in the aggregates, which the individual microgels lack. Control studies reveal that the structure and hydrophobicity of the aggregates lead to the enhanced uptake efficiencies and is not due to the presence of BIS alone. We determined that aggregates leak 75.6% of the dye that was originally removed from solution. The removal of Orange II by the aggregates at room temperature was fit by a Langmuir sorption isotherm.
聚（N-异丙基丙烯酰胺）-共-丙烯酸（pNIPAm-co-AAc）微凝胶组装体（聚集物）是通过在溶液中的微凝胶存在下聚合交联剂 N,N'-亚甲基双丙烯酰胺（BIS）合成的。在这种情况下，微凝胶被包埋在聚合的交联剂网络中。研究了聚集物从水中去除有机偶氮染料分子 4-（2-羟基-1-萘基偶氮）苯磺酸钠盐（橙 II）的能力，实验在室温及升高的温度下进行。这些结果与之前报道的未聚集的微凝胶（Parasuraman，D.；Serpe，M. J. ACS. Appl. Mater. Interfaces 2011, 3, 2732.）进行了比较。结果发现，升高温度会增加去除效率，这很可能是由于基于 pNIPAm 的聚集物的温敏性质所致，在较高温度下，聚集物会排出溶剂化水并溶胀，当冷却回室温时，聚集物会再溶胀。此外，增加聚集物加热和冷却的循环次数会增强染料从水中的去除率。我们还评估了增加交联剂浓度对去除效率的影响，发现随着聚集物中交联剂浓度的增加，去除效率也会增加。微凝胶聚集物在升高温度下达到的最大去除效率计算为 73.1%。这种增强的摄取是由于聚集物中微凝胶之间存在更大的内部体积，而单个微凝胶则缺乏这种体积。对照研究表明，聚集物的结构和疏水性导致了增强的摄取效率，而不是由于单独存在 BIS。我们确定聚集物会泄漏从溶液中最初去除的染料的 75.6%。室温下橙 II 的去除通过朗缪尔吸附等温线拟合。
