Multi-stage freezing of HEUR polymer networks with magnetite nanoparticles.
Multi-stage freezing of HEUR polymer networks with magnetite nanoparticles.
复制标题
使用磁铁矿纳米颗粒对 HEUR 聚合物网络进行多级冷冻。
作者：
A. Campanella;O. Holderer;K. Raftopoulos;C. Papadakis;M. Staropoli;M. Appavou;P. Müller‐Buschbaum;H. Frielinghaus
我们观察到当疏水磁性纳米粒子(MNPs)被嵌入到疏水改性的乙氧基氨酯(Heur)水凝胶中时，水凝胶的链段动力学发生了变化。用介电弛豫谱(DRS)和中子自旋回波谱(NSE)研究了纳米复合水凝胶的动力学。Heur聚合物网络疏水结构域中的磁性纳米颗粒增加了这些结构域的大小和距离。尺寸的增加会导致疏水区域附近的聚合物被稀释，从而使靠近“中心”的最小聚合物水滴具有更高的流动性。这反映在DR数据中检测到的β过程的激活能降低。随着距离的增加，最大的亲水性聚合物水滴的尺寸增加。因此，最大水滴的节段动力学变慢了。在短时间尺度，即10(-9)S；τ<；10(-3)S，节段性动力学的抑制反映在DRS数据中检测到的α松弛过程和NSE数据中的节段性运动的松弛速率Γ随着磁性纳米粒子浓度的增加而减小。只有纯水凝胶在低温下才能看到小水滴的逐步(多阶段)冻结。另一方面，玻璃化转变温度(Tg)随着MnP负载量的增加而降低，表明长时间尺度下的链段动力学加速(τ∼100 S)。因此，可以通过改变MNP浓度来调节水凝胶的Tg。从NSE数据中提取了静态不均匀对总散射函数Sst(Q)的贡献，揭示了一种比引起总散射函数S(Q)的凝胶结构更有序的凝胶结构，其松弛关联长度ξNse=(43±5)ä，大于静态调查的起伏关联长度ξSANS=(17.2±0.3)ä。
We observe a change in the segmental dynamics of hydrogels based on hydrophobically modified ethoxylated urethanes (HEUR) when hydrophobic magnetite nanoparticles (MNPs) are embedded in the hydrogels. The dynamics of the nanocomposite hydrogels is investigated using dielectric relaxation spectroscopy (DRS) and neutron spin echo (NSE) spectroscopy. The magnetic nanoparticles within the hydrophobic domains of the HEUR polymer network increase the size of these domains and their distance. The size increase leads to a dilution of the polymers close to the hydrophobic domain, allowing higher mobility of the smallest polymer blobs close to the "center". This is reflected in the decrease of the activation energy of the β-process detected in the DRS data. The increase in distance leads to an increase of the size of the largest hydrophilic polymer blobs. Therefore, the segmental dynamics of the largest blobs is slowed down. At short time scales, i.e. 10(-9) s < τ < 10(-3) s, the suppression of the segmental dynamics is reflected in the α-relaxation processes detected in the DRS data and in the decrease of the relaxation rate Γ of the segmental motion in the NSE data with increasing concentration of magnetic nanoparticles. The stepwise (multi-stage) freezing of the small blobs is only visible for the pure hydrogel at low temperatures. On the other hand, the glass transition temperature (Tg) decreases upon increasing the MNP loading, indicating an acceleration of the segmental dynamics at long time scales (τ∼ 100 s). Therefore, it would be possible to tune the Tg of the hydrogels by varying the MNP concentration. The contribution of the static inhomogeneities to the total scattering function Sst(q) is extracted from the NSE data, revealing a more ordered gel structure than the one giving rise to the total scattering function S(q), with a relaxed correlation length ξNSE = (43 ± 5) Å which is larger than the fluctuating correlation length from a static investigation ξSANS = (17.2 ± 0.3) Å.
二嵌段共聚物薄膜中磁场引导磁赤铁矿纳米粒子的纳米和微观结构
影响因子：
9.5
作者：
E.Metwalli;M.A.Niedermeier;M.Opel;J.Ning;J.Perlich;S.V.Roth;P.Müller- Buschbaum
通讯作者：
P.Müller- Buschbaum