State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 199 Ren'ai Road, Suzhou 215123, P. R. China.
State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 199 Ren'ai Road, Suzhou 215123, P. R. China.
J Colloid Interface Sci. 2020 Apr 15;566:394-400. doi: 10.1016/j.jcis.2020.01.076. Epub 2020 Jan 21.
Poly(N-isopropylacrylamide) microgels are used extensively in the design of drug carriers, surfaces for control of cell adhesion, and optical devices. Particle size is a key factor and has a significant influence in many areas.
In this work, precise control of the particle size of poly(N-isopropylacrylamide) microgels was achieved by controlling the separation distance of the poly(N-isopropylacrylamide) chains. Dibromoalkanes of different size were used as an adjustable "molecular ruler" to measure molecular dimensions in poly(N-isopropylacrylamide) nanoaggregates at the critical crosslinking temperature.
We find that the chain separation distance decreases as the temperature increases with a sharp decrease over the 55-to-65 °C interval. Based on the observed relationships between chain separation and crosslinker, the particle size of poly(N-isopropylacrylamide) microgels can be regulated by changing the length of the "molecular ruler" (crosslinker) at the same temperature. Furthermore, for partly crosslinked poly(N-isopropylacrylamide) microgels that contain free crosslinkable sites, the particle size can be reduced still more by further crosslinking ("re-crosslinking") with crosslinkers of different size. It is shown that the particle size can be regulated by adjusting the length of "molecular ruler" and the degree of crosslinking. This work provides a "molecular level" method for precise control of poly(N-isopropylacrylamide) microgel particle size.
聚（N-异丙基丙烯酰胺）微凝胶被广泛应用于药物载体、控制细胞黏附的表面和光学器件的设计中。粒径是一个关键因素，在许多领域都有重要影响。
在这项工作中，通过控制聚（N-异丙基丙烯酰胺）链的分离距离，实现了聚（N-异丙基丙烯酰胺）微凝胶粒径的精确控制。使用不同大小的二溴烷烃作为可调“分子标尺”，在临界交联温度下测量聚（N-异丙基丙烯酰胺）纳米聚集体中的分子尺寸。
我们发现，随着温度的升高，链分离距离减小，在 55 到 65°C 的区间内急剧下降。基于链分离与交联剂之间的观察到的关系，在相同温度下通过改变“分子标尺”（交联剂）的长度可以调节聚（N-异丙基丙烯酰胺）微凝胶的粒径。此外，对于含有游离可交联位点的部分交联聚（N-异丙基丙烯酰胺）微凝胶，通过用不同大小的交联剂进一步交联（“再交联”）可以进一步减小粒径。结果表明，通过调节“分子标尺”的长度和交联度可以调节粒径。这项工作提供了一种用于精确控制聚（N-异丙基丙烯酰胺）微凝胶粒径的“分子水平”方法。
