Precise regulation of particle size of poly(N-isopropylacrylamide) microgels: Measuring chain dimensions with a “molecular ruler” Journal Articles uri icon

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  • HYPOTHESIS: 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. EXPERIMENTS: 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. FINDINGS: 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.


  • Xue, Hui
  • Zhao, Ziqing
  • Chen, Rui
  • Brash, John
  • Chen, Hong

publication date

  • April 2020