Influence of C60 fullerenes on the glass formation of polystyrene
Influence of C60 fullerenes on the glass formation of polystyrene
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DOI：
10.1016/j.polymer.2015.05.001
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发表时间：
2015-06
期刊：
影响因子：
4.6
通讯作者：
A. Sanz;Him Cheng Wong;A. Nedoma;J. Douglas;J. Cabral
中科院分区：
文献类型：
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作者：
A. Sanz;Him Cheng Wong;A. Nedoma;J. Douglas;J. Cabral
我们通过差示扫描量热法（DSC）和介电光谱法（DS）研究了富勒烯c60对聚苯乙烯（PS）的热性能和玻璃形成的影响，当c60的质量分数达到30%时。通过显微观察、小角中子散射（SANS）和广角x射线散射（WAXS）实验，初步确定了PS/C60纳米复合材料的混溶性阈值和分散性阈值，发现该阈值分别为1质量%和4质量% C60。c60的加入提高了快速沉淀的PS复合材料的玻璃化转变温度（Tg），达到c60浓度的“阈值”（与分散性估计一致，≃4 wt%）。在这个浓度之外，tgregrets逐渐趋向于整洁的PS值。我们对分子质量为270 kg/mol的PS复合材料进行了全面的研究，并证明了c60ontgg对2和20 kg/mol的PS基质的影响的普遍性。由于分散质量下降，热退火或缓慢蒸发复合材料在很大程度上逆转了这些影响。在C60的存在下，复合材料的动态脆性增加，但与tgforps的标度保持不变。同样，物理老化实验表明，玻璃状态下的松弛焓降低，这主要是由于tg随C60的增加而增加。c60对ps α-弛豫的减缓与先前Debye-Waller测量显示的局部“软化”和脆性增加形成对比。这种效果与抗塑剂添加剂相反，抗塑剂添加剂既使材料在玻璃状态下变硬，又使材料变硬，模拟表明，这可能是由于包装挫折感的增加。最后，我们回顾了纳米颗粒对tgof PS的影响，并讨论了不同类型纳米颗粒对tgshift的非普适性。
We investigate the impact of fullerene C60on the thermal properties and glass formation of polystyrene (PS) by differential scanning calorimetry (DSC) and dielectric spectroscopy (DS), for C60concentrations up to 30% mass fraction. The miscibility and dispersibility thresholds of PS/C60nanocomposites are first estimated by a combination of microscopy, small angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS) experiments, and these thresholds were found to be ≃1 mass% and ≃4 mass% C60, respectively. The addition of C60increases the glass-transition temperature (Tg) of rapidly precipitated PS composites, up to a ‘threshold’ C60concentration (≃4 wt%, in agreement with the dispersibility estimate). Beyond this concentration, theTgreverts gradually towards the neat PS value. We present a comprehensive study for composites based on PS of molecular mass 270 kg/mol, and demonstrate the generality of the impact of C60onTgfor PS matrices of 2 and 20 kg/mol. Thermal annealing or slowly evaporated composites largely reverse these effects, as the dispersion quality decreases. The dynamic fragilitymof the composite is found to increase in the presence of C60, but the scaling ofmwithTgfor PS is retained. Similarly, physical ageing experiments show a reduction of relaxation enthalpy in the glass regime, which is largely accounted for by the increase ofTgwith C60. The slowing down of the PSα-relaxation with C60contrasts with the local ‘softening’ indicated by former Debye-Waller measurements and increase in fragilitym. This effect is opposite to that of antiplasticizer additives, which both stiffen the material in the glassy state and reduceTg, and simulations suggest this could be due to an increase in packing frustration. Finally, we review observations on the effect of nanoparticles on theTgof PS and discuss the non-universal nature ofTgshifts by various types of nanoparticles.