Structure and component dynamics in binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with water and tetrahydrofuran: A diffraction, calorimetric, and dielectric spectroscopy study.
Structure and component dynamics in binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with water and tetrahydrofuran: A diffraction, calorimetric, and dielectric spectroscopy study.
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聚（2-（二甲基氨基）乙基甲基丙烯酸酯）与水和四氢呋喃的二元混合物的结构和组分动力学：衍射、量热和介电光谱研究。
DOI：
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发表时间：
2016
影响因子：
4.4
通讯作者：
J. Colmenero
中科院分区：
文献类型：
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作者：
G. Goracci;A. Arbe;Á. Alegría;Yixi Su;Urs Gasser;J. Colmenero
我们结合X射线衍射、中子衍射和极化分析、小角中子散射、差示扫描量热法和宽带介电谱研究了聚甲基丙烯酸二甲氨基乙酯与水或四氢呋喃(THF)在不同浓度下的二元混合物的结构和动力学。水性混合物的特征是高度非均相的结构，其中水团簇与聚合物基质的主链和侧基的基本纳米分离共存。当四氢呋喃分子/单体的浓度小于或等于一个时，四氢呋喃分子均匀地分布在聚合物纳米结构域中。对于较高的四氢呋喃含量，发现了一种更不均匀的情况，但没有证据表明存在溶剂簇合物。在四氢呋喃混合物中，我们观察到玻璃化转变温度显著降低，该温度随溶剂用量的增加而提高，但在较高的四氢呋喃浓度时似乎达到饱和。四氢呋喃的加入显著降低了聚合物的β驰豫活化能。四氢呋喃分子的存在似乎阻碍了这一过程的一个缓慢成分，该成分在干燥状态下是活跃的。这些含水混合物呈现出非常广泛的玻璃化转变特征，显示出与结构研究相一致的高度非均相行为。关于溶剂动力学，在玻璃态深处，所有数据都可以用阿累尼乌斯温度依赖关系来描述，活化能相当相似。然而，四氢呋喃的特征时间值比水小约三个数量级。水动力学在玻璃化转变的起始区显示出向越来越高的表观活化能转变的交叉，支持其解释是由于周围基质的结构和松弛冻结的结果。在THF中没有这种交叉(至少在这里访问的宽动态窗口中)是由于在聚合物基质中这些分子的松弛中缺乏协作性效应。
We have combined X-ray diffraction, neutron diffraction with polarization analysis, small angle neutron scattering,differential scanning calorimetry, and broad band dielectric spectroscopy to investigate the structure and dynamics of binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with either water or tetrahydrofuran (THF) at different concentrations. Aqueous mixtures are characterized by a highly heterogeneous structure where water clusters coexist with an underlying nano-segregation of main chains and side groups of the polymeric matrix. THF molecules are homogeneously distributed among the polymeric nano-domains for concentrations of one THF molecule/monomer or lower. A more heterogeneous situation is found for higher THF amounts, but without evidences for solvent clusters. In THF-mixtures, we observe a remarkable reduction of the glass-transition temperature which is enhanced with increasing amount of solvent but seems to reach saturation at high THF concentrations. Adding THF markedly reduces the activation energy of the polymer β-relaxation. The presence of THF molecules seemingly hinders a slow component of this process which is active in the dry state. The aqueous mixtures present a strikingly broad glass-transition feature, revealing a highly heterogeneous behavior in agreement with the structural study. Regarding the solvent dynamics, deep in the glassy state all data can be described by an Arrhenius temperature dependence with a rather similar activation energy. However, the values of the characteristic times are about three orders of magnitude smaller for THF than for water. Water dynamics display a crossover toward increasingly higher apparent activation energies in the region of the onset of the glass transition, supporting its interpretation as a consequence of the freezing of the structuralrelaxation of the surrounding matrix. The absence of such a crossover (at least in the wide dynamic window here accessed) in THF is attributed to the lack of cooperativity effects in the relaxation of these molecules within the polymeric matrix.