Glass transition temperature of single-chain polystyrene particles end-grafted to oxide-coated silicon
Glass transition temperature of single-chain polystyrene particles end-grafted to oxide-coated silicon
复制标题
端接枝到氧化物涂层硅上的单链聚苯乙烯颗粒的玻璃化转变温度
DOI：
10.1063/1.5140627
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发表时间：
2020-02-14
影响因子：
4.4
通讯作者：
Wang, Xinping
中科院分区：
文献类型：
--
作者：
Li, Yawei;Lin, Decai;Wang, Xinping
采用基于 PeakForce QNM 原子力显微镜 (AFM) 粘附力测量的方法研究了端接枝到不同直径 D-0（3.4 nm-8.8 nm）和摩尔质量 M-n（8-123 kg/mol）的 SiO2-Si 基底上的聚苯乙烯（PS）单链颗粒的玻璃态动力学。随着温度升高，AFM 尖端在加载后拉出单链时所经历的粘附力 F-ad 在升高的温度下表现出逐步增加，我们根据以前的工作将其确定为 T-g。我们的结果表明，接枝单链的 T-g 以与 Fox-Flory 方程一致的方式随 M-n 增加，但量化 T-g 的 M-n 依赖性的系数仅为本体 PS 值的 (36 +/- 6)%。此外，M-n -> 无穷大极限下的 T-g 值比本体 T-g 低约 25 摄氏度，但比悬浮在溶液中 D-0 接近 100 nm 的（未束缚的）PS 纳米颗粒高 15 摄氏度以上。我们的研究结果与我们的单链的 T-g 是一致的，该单链的 T-g 主要受界面的同时影响（降低 T-g）和端接枝（增强 T-g）的影响。后者被认为通过依赖链连接性的机制对玻璃化转变动力学施加影响，并且不随链长度而变化。由 AIP Publishing 许可发布。
A method based on the PeakForce QNM atomic force microscopic (AFM) adhesion measurement is employed to investigate the glassy dynamics of polystyrene (PS) single-chain particles end-grafted to SiO2-Si substrates with different diameters, D-0, of 3.4 nm-8.8 nm and molar masses, M-n, of 8-123 kg/mol. As temperature was increased, the adhesion force, F-ad, experienced by the AFM tip on pulling off the single chains after loading demonstrated a stepwise increase at an elevated temperature, which we identified to be T-g based on previous works. Our result shows that T-g of our grafted single chains increases with M-n in a manner consistent with the Fox-Flory equation, but the coefficient quantifying the M-n dependence of T-g is only (36 +/- 6)% the value of bulk PS. In addition, the value of T-g in the M-n -> infinity limit is about 25 degrees C below the bulk T-g but more than 15 degrees C above that of (untethered) PS nanoparticles with D-0 approximate to 100 nm suspended in a solution. Our findings are consistent with T-g of our single chains being dominated by simultaneous effects of the interfaces, which depress T-g, and end-grafting, which enhances T-g. The latter is believed to exert its influence on the glass transition dynamics by a mechanism reliant on chain connectivity and does not vary with chain length. Published under license by AIP Publishing.