Surface-initiated mechano-ATRP as a convenient tool for tuning of bidisperse magnetorheological suspensions toward extreme kinetic stability,Polymer Chemistry

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Surface-initiated mechano-ATRP as a convenient tool for tuning of bidisperse magnetorheological suspensions toward extreme kinetic stability
Polymer Chemistry ( IF 4.1 ) Pub Date : 2021-08-24 , DOI: 10.1039/d1py00930c
Martin Cvek ₁ , Jozef Kollar ₂ , Miroslav Mrlik ₁ , Milan Masar ₁ , Pavol Suly ₁ , Michal Urbanek ₁ , Jaroslav Mosnacek _{2,

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Affiliation

A concept initially intended for mechanically controlled atom transfer radical polymerization (hereinafter referred to as “mechano-ATRP”) was extended in order to modify magnetic nanoparticles (NPs) with poly(methyl acrylate) (PMA) grafts, resulting in NPs@PMA hybrids which served as efficient additives in magnetorheological (MR) suspensions. In a novel procedure, magnetic NPs with an ATRP initiator anchored on their surfaces were added into a mechano-ATRP mixture, bringing about surface-initiated growth of the PMA chains after exposure to ultrasonication (35 kHz, 45 °C). The reaction proceeded with low concentration (at hundreds of “ppm”) of the CuBr₂ catalyst, thereby providing the PMA chains with low dispersity of molar masses and high monomer conversions. Investigation was conducted as to the effect of hexagonal micro-ZnO and cubic-phase BaTiO₃ piezoelectric transducers on the feasibility of the process. The presence of PMA on the surfaces of NPs@PMA hybrids was proven by infra-red spectroscopy, as well as thermal and magnetization analyses. The NPs@PMA hybrids were subsequently applied as additives to fabricate a bidisperse MR suspension, in which they unexpectedly enhanced accessible shear stress and yield stress values by up to ∼840 Pa under a magnetic field (of up to 432 kA m⁻¹). Notably, the MR suspension supplemented with the NPs@PMA hybrids synthesized by mechano-ATRP exhibited no sign of sedimentation when left undisturbed for 2 days, although sedimentation of the reference sample occurred within a few hours. Such enhancements were attributed to the effects of friction, formation of a 3D gel-like network and the reduced density of the NPs@PMA hybrids.

中文翻译：

表面引发的机械-ATRP 作为将双分散磁流变悬浮液调整为极端动力学稳定性的便捷工具

最初用于机械控制原子转移自由基聚合（以下称为“机械-ATRP”）的概念得到扩展，以便用聚（丙烯酸甲酯）（PMA）接枝物改性磁性纳米粒子（NPs），从而产生 NPs@PMA 杂化物用作磁流变 (MR) 悬浮液中的有效添加剂。在一种新的程序中，将表面固定有 ATRP 引发剂的磁性 NP 添加到机械-ATRP 混合物中，在暴露于超声处理（35 kHz，45 °C）后导致 PMA 链的表面引发生长。反应在低浓度（数百“ppm”）的 CuBr _{2 下进行}催化剂，从而提供具有低摩尔质量分散性和高单体转化率的 PMA 链。研究了六方微ZnO 和立方相BaTiO ₃压电换能器对该工艺可行性的影响。红外光谱以及热分析和磁化分析证明了 PMA 在 NPs@PMA 杂化物表面的存在。NPs@PMA 杂化物随后被用作添加剂来制造双分散 MR 悬浮液，其中它们在磁场（高达 432 kA m ^-1）。值得注意的是，补充有机械-ATRP 合成的 NPs@PMA 杂化物的 MR 悬浮液在不受干扰 2 天时没有表现出沉降的迹象，尽管参考样品的沉降发生在几小时内。这种增强归因于摩擦的影响、3D 凝胶状网络的形成以及 NPs@PMA 杂化物的密度降低。

更新日期：2021-08-24

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