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1.聚合物分子工程国家重点实验室 复旦大学高分子科学系 上海 200438
2.高分子化学与物理教育部重点实验室 北京大学化学与分子工程学院 北京 100871
Published:2018-9,
Received:18 December 2017,
Revised:16 January 2018,
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Yi-xin Liu, Er-qiang Chen. Thickening Kinetics of Monolayer Crystals of Low Molecular Weight Poly(ethylene oxide) Fractions on Mica Surfaces. [J]. Acta Polymerica Sinica 0(9):1212-1220(2018)
Yi-xin Liu, Er-qiang Chen. Thickening Kinetics of Monolayer Crystals of Low Molecular Weight Poly(ethylene oxide) Fractions on Mica Surfaces. [J]. Acta Polymerica Sinica 0(9):1212-1220(2018) DOI: 10.11777/j.issn1000-3304.2017.17333.
采用附有热台的原子力显微镜(AFM)原位跟踪研究了2种低分子量聚氧乙烯(PEO)样品的单层片晶在云母表面的增厚行为. 实验发现表面平整的一次折叠链片晶在其熔点以下等温退火时,其内部陆续出现增厚区域(增厚粒子). 单个增厚粒子可在厚度和侧向尺寸2个维度同时生长. 其中,增厚粒子的厚度随时间的变化曲线呈S形,并具有显著的温度相关性. 基于在厚度维度满足成核机理的假设,可推导出厚度与时间的对数成正比关系. 据此关系可进一步求得片晶侧表面自由能,结果与文献报道一致,并且对于2种PEO样品的结果也相近,确认了我们提出的机理的合理性. 增厚粒子侧向尺寸随时间线性生长,生长速率与退火温度正相关,推测与片晶中的链滑移有关.
The thickening of monolayer crystals of low molecular weight poly(ethylene oxide) (PEO) fractions on mica surface are
in situ
monitored by an atomic force microscopy (AFM) coupled with a hot stage. Two PEO fractions
with different molecular weights (HPEO2K
M
n
= 2000; HPEO3K
M
n
= 3000)
have been examined. It is found that thickening domains continuously emerge when smooth once-folded-chain crystals are annealed isothermally below their melting temperature. A single thickening domain can grow in thickness and lateral size simutaneously. The growth of the thickness of the thickening domain follows a sigmoidal curve and depends significantly on the annealing temperature. It is found that the thickness of the thickening domain grows linearly with the logarithm of time. Such linear relation implies that its underlying mechanism should be nucleation and growth
as confirmed by a theoretical derivation of the thickness of the thickening domain as a function of time based on this mechanism. For each annealing temperature
a linear regression between the thickness of the thickening domain and the logarithm of time is performed and the obtained reciprocal of the slope linearly depends on the reciprocal of the annealing temperature. Then the surface free energy of the lateral surface of the folded-chain crystals can be inferred from the relation between the reciprocal of the slope and the annealing temperature. In this study
the value of the lateral surface free energy is found to be 1.25 and 1.22 kJ/mol for HPEO2K and HPEO3K
respectively. These values agree well with each other and also with reported values
which further validates our proposed mechanism. The lateral size of the thickening domain grows linearly with time as long as its thickeness approaches the extended-chain crystal. Such type of growth resembles the direct growth of the polymer crystals from the melt. However
its reltation between the growth rate and the annealing temperature is quite different from that of the growth of polymer crystals: the growth rate increases with the annealing temperature in the thickening case while it decreases with the crystallization temperature in the crystallization case. It indicates that there is an activation process rather than a nucleation process during thickening
which has been attributed to the chain sliding diffusion within the folded-chain crystals.
薄膜结晶片晶增厚生长动力学
Thin film crystallizationFolded-chain crystalThickeningGrowth kinetics
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