Zhang Chuan, Guo Yunlong, Priestley Rodney D
Department of Chemical and Biological Engineering and ‡Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544, United States.
Department of Chemical and Biological Engineering and Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544, United States.
ACS Macro Lett. 2014 Jun 17;3(6):501-505. doi: 10.1021/mz500204q. Epub 2014 May 13.
We report the effect of isochoric confinement on the characteristic length of the glass transition (ξ) for polystyrene (PS) and poly(4-methylstyrene) (P4MS). Utilizing silica-capped PS and P4MS nanoparticles as model systems, ξ values are determined from the thermal fluctuation model and calorimetric data. With decreasing nanoparticle diameter, ξ decreases, suggesting a reduction in the number of segmental units required for cooperative motion at the glass transition under confinement. Furthermore, a direct correlation is observed between ξ and the isochoric fragility () in confined polymers. Due to a nearly constant ratio of the isochoric to isobaric fragility in confined polymer nanoparticles, a correlation between ξ and also implies a correlation between ξ and the volume contribution to the temperature dependence of structural relaxation. Lastly, we observe that when the fragility and characteristic length are varied in the same system the relationship between the two properties appears to be more correlated than that of across different bulk glass-formers.
我们报告了等容限制对聚苯乙烯（PS）和聚（4-甲基苯乙烯）（P4MS）玻璃化转变特征长度（ξ）的影响。利用二氧化硅包覆的PS和P4MS纳米颗粒作为模型系统，根据热涨落模型和量热数据确定ξ值。随着纳米颗粒直径减小，ξ减小，这表明在限制条件下玻璃化转变时协同运动所需的链段单元数量减少。此外，在受限聚合物中观察到ξ与等容脆性（）之间存在直接相关性。由于受限聚合物纳米颗粒中等容脆性与等压脆性的比值几乎恒定，ξ与之间的相关性也意味着ξ与结构弛豫温度依赖性的体积贡献之间存在相关性。最后，我们观察到，当在同一系统中改变脆性和特征长度时，这两个性质之间的关系似乎比不同本体玻璃形成剂之间的关系更相关。
