Salgueiro W, Somoza A, Silva L, Consolati G, Quasso F, Mansilla M A, Marzocca A J
IFIMAT-UNCentro, Pinto 399, B7000GHG Tandil, Argentina.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 May;83(5 Pt 1):051805. doi: 10.1103/PhysRevE.83.051805. Epub 2011 May 27.
A systematic study on the evolution of free volume as a function of the temperature in vulcanized at 433 K natural rubber (NR) and styrene butadiene rubber (SBR) in 25-75, 50-50, 75-25 NR-SBR (percent content of pure NR and SBR, respectively) blends was studied by positron annihilation lifetime spectroscopy. All samples were prepared with sulfur and TBBS (n-t-butyl-2-benzothiazole sulfenamide) as accelerator. The glass transition temperatures of the samples studied were determined by differential scanning calorimetry (DSC) and from lifetime data. In general, a sigmoidal-like complex behavior of the long-lived lifetime component, linked to the nanohole free volume, as a function of the temperature was found. For SBR, the slope of the ortho-positronium lifetime against temperature curves could be well-fitted using a linear function. For blends and also for NR, two different linear functions were necessary. This last behavior is explained in terms of the supercooled process involving a reconfiguration of the elastomeric chains. In the case of blends, the state of cure of NR and SBR in each NR-SBR sample was also taken into account in the discussion of the results obtained. Besides, thermal expansion coefficients of the free volumes in the transition and glassy region of all compounds were estimated. The differences observed in the values of this parameter are discussed by taking into account the morphology and formulation of each blend, the crosslink densities, and the role of the interphases formed between both NR and SBR elastomers.
采用正电子湮没寿命谱对433 K硫化的天然橡胶（NR）和丁苯橡胶（SBR），以及25 - 75、50 - 50、75 - 25（分别为纯NR和SBR的百分比含量）的NR - SBR共混物中自由体积随温度变化的情况进行了系统研究。所有样品均以硫磺和促进剂TBBS（N - 叔丁基 - 2 - 苯并噻唑次磺酰胺）制备。通过差示扫描量热法（DSC）和寿命数据确定了所研究样品的玻璃化转变温度。一般来说，发现与纳米孔自由体积相关的长寿命寿命成分随温度呈现出类似S形的复杂行为。对于SBR，邻 - 正电子素寿命随温度曲线的斜率可以用线性函数很好地拟合。对于共混物以及NR，则需要两个不同的线性函数。最后这种行为是根据涉及弹性体链重新排列的过冷过程来解释的。在共混物的情况下，在讨论所得结果时还考虑了每个NR - SBR样品中NR和SBR的硫化状态。此外，还估算了所有化合物在转变区和玻璃态区自由体积的热膨胀系数。通过考虑每种共混物的形态和配方、交联密度以及NR和SBR弹性体之间形成的界面相的作用，对该参数值中观察到的差异进行了讨论。
