Relationship between Temperature-Induced Changes in Internal Microscopic Structures of Poly(N-isopropylacrylamide) Microgels and Organic Dye Uptake Behavior
Relationship between Temperature-Induced Changes in Internal Microscopic Structures of Poly(N-isopropylacrylamide) Microgels and Organic Dye Uptake Behavior
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DOI：
10.1021/la501838c
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发表时间：
2014-07-29
期刊：
影响因子：
3.9
通讯作者：
Suzuki, Daisuke
中科院分区：
文献类型：
--
作者：
Kureha, Takuma;Sato, Takaaki;Suzuki, Daisuke
温度引起的变化的聚（N-异丙基丙烯酰胺）（pNIPAm）微凝胶的内部结构进行了评估，通过小角X射线散射（SAXS），结果被用来解释有机染料吸收的微凝胶。使用两种有机染料：阳离子罗丹明6 G（R6 G）和阴离子赤藓红进行上染实验。在SAXS调查中，微凝胶的内部结构，其特征在于在相关长度，xi，和距离，d*，这源于两个相邻链的异丙基的局部包装。随着温度的升高，微凝胶的体积相变温度（VPTT），相关长度，xi，增加和距离，d*，减少。同时，尽管微凝胶的体积减小，但pNIPAm微凝胶吸收的染料的量增加。结果表明，由于异丙基基团的疏水缔合作用，pNIPAm分子链之间的距离更近，导致疏水结构域的增长。因此，染料和pNIPAm之间的疏水相互作用可能伴随着结构域的形成。随着温度的进一步升高，VPTT以上，相关长度，xi，减少，然后没有定义，因为Ornstein-Zernike型的贡献消失，和距离，d*，没有很大的变化。同时，每单位体积的微凝胶的染料的吸收量也没有很大的变化，其表现类似于距离d*。这可能是由于微凝胶的内部结构没有发生很大的变化，因为异丙基基团相互接触。这一观点得到了不含疏水异丙基的非温敏微凝胶的摄取研究结果的支持。
Temperature-induced changes in the internal structures of poly(N-isopropylacrylamide) (pNIPAm) microgels were evaluated by small-angle X-ray scattering (SAXS), and the results were used to explain organic dye uptake by the microgels. The dye uptake experiments were conducted using two organic dyes: cationic rhodamine 6G (R6G) and anionic erythrosine. In the SAXS investigation, the internal structures of the microgels were characterized in terms of the correlation length, xi, and the distance, d*, which originated from the local packing of the isopropyl groups of two neighboring chains. With increasing temperature up to the volume phase transition temperature (VPTT) of the microgels, the correlation length, xi, was increased and the distance, d*, was decreased. At the same time, the amounts of the dyes taken up by the pNIPAm microgels were increased, despite a decrease in the volume of the microgels. The results indicated that the pNIPAm chains were closer to each other due to the hydrophobic association of isopropyl groups, which resulted in the growth of the hydrophobic domains. Thus, the hydrophobic interactions between the dyes and pNIPAm were probably accompanied by the domain formation. With a further increase of temperature above the VPTT, the correlation length, xi, was decreased and then not defined because the Ornstein-Zernike type contribution disappeared, and the distance, d*, was not largely changed. At the same time, the uptake amounts of the dyes per unit volume of the microgels were also not largely changed, which behaved similar to the distance, d*. It was probably due to the fact that the internal structures of the microgels were not largely changed because the isopropyl groups were in contact with each other. The view was supported by the result of the uptake study of the nonthermoresponsive microgels which did not have the hydrophobic isopropyl groups.