Acta Chimica Sinica ›› 2021, Vol. 79 ›› Issue (4): 500-505.DOI: 10.6023/A20110529 Previous Articles     Next Articles



于淼a,b, 赵武a,b, 张凯a,b, 郭鑫a,b,*()   

  1. a 四川大学 机械工程学院 成都 610065
    b 创新方法与创新设计四川省重点实验室 成都 610065
  • 投稿日期:2020-11-18 发布日期:2020-12-18
  • 通讯作者: 郭鑫
  • 基金资助:
    创新方法工作专项(2020IM020400); 四川科技厅重点研发项目(2019YFG0373); 中央高校基本业务费项目(2019SCU12075)

Single-Molecule Mechanism of pH Sensitive Smart Polymer

Miao Yua,b, Wu Zhaoa,b, Kai Zhanga,b, Xin Guoa,b,*()   

  1. a School of Mechanical Engineering, Sichuan University, Chengdu 610065, China
    b Innovation Method and Creative Design Key Laboratory of Sichuan Province, Chengdu 610065, China
  • Received:2020-11-18 Published:2020-12-18
  • Contact: Xin Guo
  • About author:
  • Supported by:
    Special Fund for Innovative Method Work(2020IM020400); Sichuan Science and Technology program(2019YFG0373); Fundamental Research Funds for the Central Universities(2019SCU12075)

As an important part of smart materials, the volume, mass, or elasticity of pH-sensitive polymers can shift with pH values. Based on the feature, the pH-sensitive polymers can be used in many fields such as biology, chemistry and micro/ nano electromechanical system. Previous researches are based on the development and utilization of the known properties of functional smart materials, the mechanism of pH-sensitivity at the single-molecule level is still unclear. Based on the single molecule force spectroscopy, the single-chain mechanics of a typical pH-sensitive polymer, polyacrylic acid (PAA), in the buffer solution with different pH values have been studied. In order to reduce the influence of other factors on the experimental results, the buffer solution used in the experiment is disodium hydrogen phosphate citric acid with adjusted salt ion concentration of 0.5 mol/L, and the pH value is the only variable in the experiment (from 2 to 8). PAA is dissolved in deionized water (DI water) to a concentration of 5 mg/L, then used for the polymer physisorption on a silanized glass substrate, which has undergone piranha solution cleaning and then immersed in the (3-aminopropyl)- triethoxysilane (APTES) solution (2 mmol/L, CH2Cl2 solution) for 20 mins. After that, the sample is rinsed with abundant DI water to remove the loosely adsorbed polymer and dried by air flow. The single molecule force spectroscopy experiments were carried on a commercial atomic force microscope (Asylum Research, MFP-3D). The experimental results show that as the pH value increases, the single PAA chain undergoes from collapsed conformation to fully extended conformation, and the energy required for the transformation between different conformations during the stretching process is calculated. In addition, according to the chain shrinkage rate under different loads, the shrinkage work of single PAA chain under the change of pH is calculated. Based on the characteristic of the conformation changes of single PAA chain with pH value, a new molecular motor (switch) design concept was proposed. It can be expected that the result of this work can provide theoretical basis and data support for the design of multi response polymer and novel smart sensors.

Key words: single molecular force spectroscopy, pH-sensitive polymer, conformational change, molecular motor, molecular switch, smart sensor