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Chin. Phys. B, 2019, Vol. 28(6): 064701    DOI: 10.1088/1674-1056/28/6/064701
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS Prev   Next  

Effects of thiocyanate anions on switching and structure of poly(N-isopropylacrylamide) brushes

Xin-Jun Zhao(赵新军)1,2, Zhi-Fu Gao(高志福)3
1 Xinjiang Laboratory of Phase Transitions and Microstructures of Condensed Matter Physics, Yili Normal University, Yining 835000, China;
2 Laboratory of Micro-Nano Electro Biosensors and Bionic Devices, Yili Normal University, Yining 835000, China;
3 Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150, Science 1-Street, Urumqi 830011, China
Abstract  

In this work, we investigate the effects of thiocyanate anions on the switching and the structure of poly (N-isopropylacrylamide) (PNIPAM) brushes using a molecular theory. Our model takes into consideration the PNIPAM-anion bonds, the electrostatic effects and their explicit coupling to the PNIPAM conformations. It is found that at low thiocyanate anion concentration, as the anion concentration of thiocyanate increases, thiocyanate anions are more associated with PNIPAM chains through the PNIPAM-anion bonds, which contributes to stronger electrostatic repulsion and leads to an increase of lower critical solution temperature (LCST). By analyzing the average volume fractions of PNIPAM brushes, it is found that the PNIPAM brush presents a plateau structure. Our results show that the thiocyanate anions promote phase segregation due to the PNIPAM-anion bonds and the electrostatic effect. According to our model, the reduction of LCST can be explained as follows:at high thiocyanate anion concentration, with the increase of thiocyanate concentration, more ion bindings occurring between thiocyanate anions and PNIPAM chains will result in the increase of the hydrophobicity of PNIPAM chains; when the increase of electrostatic repulsion is insufficient to overcome the hydrophobic interaction of PNIPAM chains, it will lead to the reduction of brush height and LCST at high thiocyanate anion concentration. Our theoretical results are consistent with the experimental observations, and provide a fundamental understanding of the effects of thiocyanate on the LCST of PNIPAM brushes.

Keywords:  molecular theory      PNIPAM brushes      effect of thiocyanate anions  
Received:  13 November 2018      Revised:  26 February 2019      Accepted manuscript online: 
PACS:  47.27.eb (Statistical theories and models)  
  05.65.+b (Self-organized systems)  
Fund: 

Project supported by the Joint Funds of Xinjiang Natural Science Foundation (Grant No. 2019D01C333), the National Natural Science Foundation of China (Grant Nos. 11847610 and 21764015), the National Basic Research Program of China (Grant No. 2015CB857100).

Corresponding Authors:  Xin-Jun Zhao     E-mail:  zhaoxinjunzxj@163.com

Cite this article: 

Xin-Jun Zhao(赵新军), Zhi-Fu Gao(高志福) Effects of thiocyanate anions on switching and structure of poly(N-isopropylacrylamide) brushes 2019 Chin. Phys. B 28 064701

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