Self-assembly of short chain Poly-N-isopropylacrylamid (PNIPAM) induced by superchaotropic Keggin Polyoxometalates: from globules to sheets.,Journal of the American Chemical Society

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Self-assembly of short chain Poly-N-isopropylacrylamid (PNIPAM) induced by superchaotropic Keggin Polyoxometalates: from globules to sheets.
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2019-04-05 , DOI: 10.1021/jacs.8b12181
Thomas Buchecker _{1,

2} , Philipp Schmid _{1,

2} , Isabelle Grillo ₃ , Sylvain Prévost ₄ , Markus Drechsler ₅ , Olivier Diat ₂ , Arno Pfitzner ₁ , Pierre Bauduin ₂

Affiliation

We show here for the first time that short chain poly( N-isopropylacrylamide) (PNIPAM), one of the most famous thermoresponsive polymers, self-assembles in water to form (i) discrete nanometer-globules and (ii) micrometric sheets with nm-thickness upon addition of the well-known Keggin-type polyoxometalate (POM) H3PW12O40 (PW). The type of self-assembly is controlled by PW concentration: at low PW concentrations, PW adsorbs on PNIPAM chains to form globules consisting of homogeneously distributed PWs in PNIPAM droplets of several nm in size. Upon further addition of PW, a phase transition from globules to micrometric sheets is observed for PNIPAMs above a polymer critical chain length, between 18 and 44 repeating units. The thickness of the sheets is controlled by the PNIPAM chain length, here from 44 to 88 repeating units. The PNIPAM sheets are electrostatically stabilized PWs accumulated on each side of the sheets. The shortest PNIPAM chain with 18 repeating units produces PNIPAM/PW globules with 5-20 nm size but no sheets. The PW/PNIPAM self-assembly arises from a solvent mediated mechanism associated with the partial dehydration of PW and of the PNIPAM, which is related to the general propensity of POMs to adsorb on neutral hydrated surfaces. This effect, known as superchaotropy, is further highlighted by the significant increase in the lower critical solubilization temperature (LCST) of PNIPAM observed upon the addition of PW in the mM range. The influence of the POM nature on the self-assembly of PNIPAM was also investigated by using H4SiW12O40 (SiW) and H3PMo12O40 (PMo), i.e. changing the POM's charge density or polarizability in order to get deeper understanding on the role of electrostatics and polarizability in the PNIPAM self-assembly process. We show here that the superchaotropic behavior of POMs with PNIPAM polymers enables the formation and the shape control of supramolecular organic-inorganic hybrids.

中文翻译：

由超离液 Keggin 多金属氧酸盐诱导的短链聚-N-异丙基丙烯酰胺（PNIPAM）的自组装：从球状体到片状。

我们在这里首次展示了短链聚（N-异丙基丙烯酰胺）（PNIPAM），最著名的热敏聚合物之一，在水中自组装形成（i）离散的纳米球和（ii）具有 nm - 添加众所周知的 Keggin 型多金属氧酸盐 (POM) H3PW12O40 (PW) 后的厚度。自组装的类型受 PW 浓度控制：在低 PW 浓度下，PW 吸附在 PNIPAM 链上形成由均匀分布的 PW 组成的小球，小球由大小为几纳米的 PNIPAM 液滴组成。在进一步添加 PW 后，对于 PNIPAM 超过聚合物临界链长度（18 到 44 个重复单元），观察到从小球到微米片的相变。片材的厚度由 PNIPAM 链长度控制，此处为 44 到 88 个重复单元。PNIPAM 片材是静电稳定的 PW，堆积在片材的每一侧。具有 18 个重复单元的最短 PNIPAM 链产生 PNIPAM/PW 小球，大小为 5-20 nm，但没有片。PW/PNIPAM 自组装源于与 PW 和 PNIPAM 的部分脱水相关的溶剂介导机制，这与 POM 吸附在中性水合表面上的一般倾向有关。这种被称为超离液性的效应通过在添加 mM 范围内的 PW 后观察到的 PNIPAM 的下临界溶解温度 (LCST) 显着增加而进一步突出。还通过使用 H4SiW12O40 (SiW) 和 H3PMo12O40 (PMo) 研究了 POM 性质对 PNIPAM 自组装的影响，即改变 POM' s 电荷密度或极化率，以便更深入地了解静电和极化率在 PNIPAM 自组装过程中的作用。我们在这里展示了具有 PNIPAM 聚合物的 POM 的超离液行为能够形成和控制超分子有机 - 无机杂化物的形状。

更新日期：2019-04-05

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