EuF_3-NaYF_4纳米晶/PNIPAm三元复合凝胶的荧光温敏行为与影响机制

Thermosensitive Fluorescent Behavior and Mechanism of EuF_3-NaYF_4 Nanocrystals/PNIPAm Ternary Complex Hydrogel

分别采用水热法制备EuF3与NaYF4纳米晶,与N-异丙基丙烯酰胺(NIPAm)混合后进行自由基聚合,一步法合成EuF3-NaYF4纳米晶/聚N-异丙基丙烯酰胺(PNIPAm)三元复合凝胶.对纳米晶与复合凝胶的结构与荧光性能进行了表征.重点研究了三元复合凝胶的荧光温敏行为,并对其影响机制进行了探讨.结果表明,EuF3与NaYF4纳米晶在PNIPAm凝胶基体中的体相掺杂,同样产生了明显的能量传递.两种纳米晶相对含量的变化,对复合凝胶的荧光温敏性能有重要影响.

In this work, EuF3 and NaYF4 nanocrystals were prepared by liquid-solution-solid （LSS） method respectively, high-resolution transmission electron microscopy （HRTEM） images revealed that the as-prepared NaYF4 nanocrystals were monodisperse nanoparticles with the size about 30 nm; while the as-prepared EuF3 were polydisperse nanoparticles with the size of 5～20 nm. And they were used to prepare a series of novel ternary complex hydrogels of EuF3-NaYF4 nanocrystals/poly（N-isopropyl acrylamide） （PNIPAm） by free radical polymerization. In a typical synthesis, 2 mg the as-prepared EuF3 and NaYF4 nanocrystals, 201.6 mg reactants of N-isopropyl acrylamide （NIPAm）, N,N＇-methylenebisacrylamide （BIS） and azodiisobutyronitrile （AIBN） （mNIPAm∶mBIS∶mAIBN=200/0.2/1.4） and 4 mL CHCl3 were mixed and added into a 10 mL sealing tube. The tube was placed into an ultrasonic oscillator for about 10 min to obtain a uniform mixture, and then oxygen was removed by bubbling N2 and successfully exerting vacuum on the tube for about 5 min. After the operation was repeated three times, the tube was sealed and kept at 60 ℃ for 3 h. After that, the crude complex hydrogels were synthesized. Finally, the crude hydrogels were immersed into deionized water to remove the remained monomers and impurities. The total time of soaking was about 7 d, and the deionized water was replaced every 10 h. Following the above procedure, all of the mentioned EuF3-NaYF4/PNIPAm complex hydrogels were obtained. The structure and fluorescent properties of the complex hydrogels were investigated by differential scanning calorimeter （DSC）, photoluminescence （PL）, Fourier transform infrared （FTIR）, X-ray diffraction （XRD）. And the thermosensitive fluorescent behavior of the complex hydrogels was investigated and the mechanism was discussed in detail. The results suggested that, in the PNIPAm hydrogel matrix, energy can be transferred between the bulk doped EuF3 nanocrystals and NaYF4 nanocrystals. Either the relative content of two kinds of nanocrystals or the ambient temperature plays an important role in the thermosensitive fluorescent behavior of the complex hydrogels.