Beckingham Bryan S, Ho Victor, Segalman Rachel A
Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States.
ACS Macro Lett. 2014 Jul 15;3(7):684-688. doi: 10.1021/mz500262d. Epub 2014 Jul 2.
Herein, we detail the formation of a rigid amorphous fraction in poly(3-(2'-ethyl)hexylthiophene) (P3EHT) at high relative crystallinity, yielding a more complete picture of the solid-state structure. In the differential scanning calorimetry (DSC) heating scans of isothermally crystallized P3EHT a distinct endothermic peak appears slightly above the crystallization temperature. This previously undescribed endothermic feature of P3EHT's thermal behavior is observed consistently ∼20 °C above the crystallization temperature-shifting to higher temperatures with increasing crystallization temperature-and increases in magnitude with both time and crystallization temperature. Here, we determine the origins of this endothermic peak with DSC and temperature-modulated DSC (TMDSC). TMDSC reveals that the annealing peak observed in the total heat flow (THF)-heat flow equivalent to that of conventional DSC-is a consequence of an enthalpic relaxation observable as an endothermic peak in the nonreversible heat flow (NHF) and a glass transition evident as a step increase in the reversible heat flow (RHF). In conjunction with conventional DSC observations, these results indicate that the observed annealing peak is a consequence of the formation of distinct amorphous regions-a mobile amorphous fraction (MAF) and a rigid amorphous fraction (RAF)-during the isothermal crystallization process and not the melting of a distinct crystallite population or melt recrystallization.
在此，我们详细阐述了聚（3 - （2'- 乙基）己基噻吩）（P3EHT）在高相对结晶度下刚性非晶部分的形成，从而更完整地描绘了其固态结构。在等温结晶的P3EHT的差示扫描量热法（DSC）加热扫描中，在略高于结晶温度处出现一个明显的吸热峰。P3EHT热行为的这一先前未描述的吸热特征在结晶温度以上约20°C处始终观察到，随着结晶温度的升高向更高温度移动，并且其幅度随时间和结晶温度而增加。在此，我们用DSC和温度调制DSC（TMDSC）确定了这个吸热峰的起源。TMDSC表明，在总热流（THF）中观察到的退火峰——与传统DSC的热流相当——是由焓松弛导致的，在不可逆热流（NHF）中表现为吸热峰，在可逆热流（RHF）中表现为明显的台阶式增加，即玻璃化转变。结合传统DSC的观察结果，这些结果表明，观察到的退火峰是等温结晶过程中形成不同非晶区域——可移动非晶部分（MAF）和刚性非晶部分（RAF）——的结果，而不是不同微晶群体的熔化或熔体再结晶。
