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Physical properties of macromolecule-metal oxide nanoparticle complexes: Magnetophoretic mobility, sizes, and interparticle potentials.

机译：大分子金属氧化物纳米粒子复合物的物理性质：磁致动性，尺寸和粒子间电势。

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Magnetic nanoparticles coated with polymers hold great promise as materials for applications in biotechnology. In this body of work, magnetic fluids for the treatment of retinal detachment are examined closely in three regimes; motion of ferrofluid droplets in aqueous media, size analysis of the polymer-iron oxide nanoparticles, and calculation of interparticle potentials as a means for predicting fluid stability. The macromolecular ferrofluids investigated herein are comprised of magnetite nanoparticles coated with tricarboxylate-functional polydimethylsiloxane (PDMS) oligomers. The nanoparticles were formed by reacting stoichiometric concentrations of iron chloride salts with base. After the magnetite particles were prepared, the functional PDMS oligomers were adsorbed onto the nanoparticle surfaces.; The motion of ferrofluid droplets in aqueous media was studied using both theoretical modeling and experimental verification. Droplets (∼1-2 mm in diameter) of ferrofluid were moved through a viscous aqueous medium by an external magnet of measured field and field gradient. Theoretical calculations were made to approximate the forces on the droplet. Using the force calculations, the times required for the droplet to travel across particular distances were estimated. These estimated times were within close approximation of experimental values.; Characterization of the sizes of the nanoparticles was particularly important, since the size of the magnetite core affects the magnetic properties of the system, as well as the long-term stability of the nanoparticles against flocculation. Transmission electron microscopy (TEM) was used to measure the sizes and size distributions of the magnetite cores. Image analyses were conducted on the TEM micrographs to measure the sizes of approximately 6000 particles per sample. Distributions of the diameters of the magnetite cores were determined from this data. A method for calculating the total particle size, including the magnetite core and the adsorbed polymer, in organic dispersions was established. These estimated values were compared to measurements of the entire complex utilizing dynamic light scattering (DLS). Better agreement was found for narrow particle size distributions as opposed to broader distribution.; The stability against flocculation of the complexes over time in organic media were examined via modified Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations. DLVO theory allows for predicting the total particle-particle interaction potentials, which include steric and electrostatic repulsions as well as van der Waals and magnetic attractions. The interparticle potentials can be determined as a function of separation of the particle surfaces. At a constant molecular weight of the polymer dispersion stabilizer, these calculations indicated that dispersions of smaller PDMS-magnetite particles should be more stable than those containing larger particles. The rheological characteristics of neat magnetite-PDMS complexes (i.e., no solvent or carrier fluid were present) were measured over time in the absence of an applied magnetic field to probe the expected properties upon storage. The viscosity of a neat ferrofluid increased over the course of a month, indicating that some aggregation occurred. However, this effect could be removed by shearing the fluids at a high rate. This suggests that the particles do not irreversibly flocculate under these conditions.
机译：涂有聚合物的磁性纳米颗粒有望作为生物技术中的材料。在这项工作中，将在三种情况下仔细检查用于治疗视网膜脱离的磁性液体。介质中铁磁流体液滴的运动，聚合物-氧化铁纳米粒子的尺寸分析以及粒子间电势的计算，作为预测流体稳定性的一种手段。本文研究的大分子铁磁流体由包覆有三羧酸盐官能化聚二甲基硅氧烷（PDMS）低聚物的磁铁矿纳米颗粒组成。通过使化学计量浓度的氯化铁盐与碱反应形成纳米颗粒。磁铁矿颗粒制备后，功能性PDMS低聚物被吸附到纳米颗粒表面。使用理论模型和实验验证研究了铁磁流体在水介质中的运动。铁磁流体的液滴（直径约1-2 mm）通过测量磁场和磁场梯度的外磁体移动通过粘性水性介质。进行理论计算以近似液滴上的力。使用力计算，可以估算出液滴跨特定距离传播所需的时间。这些估计的时间非常接近实验值。纳米颗粒尺寸的表征特别重要，因为磁铁矿芯的尺寸会影响系统的磁性能，以及纳米颗粒抗絮凝的长期稳定性。透射电子显微镜（TEM）用于测量磁铁矿芯的尺寸和尺寸分布。在TEM显微照片上进行图像分析，以测量每个样品大约6000个颗粒的大小。从该数据确定磁铁矿芯的直径分布。建立了一种计算有机分散体中包括磁铁矿芯和吸附的聚合物在内的总粒径的方法。将这些估计值与利用动态光散射（DLS）对整个复合物的测量结果进行比较。对于较窄的粒度分布而不是较宽的分布，发现了更好的一致性。通过改进的Derjaguin-Landau-Verwey-Overbeek（DLVO）计算来检查复合物在有机介质中随时间的絮凝稳定性。 DLVO理论允许预测粒子间的总相互作用势，其中包括空间和静电排斥力以及范德华力和磁引力。颗粒间的电势可以根据颗粒表面的分离来确定。在聚合物分散稳定剂的分子量恒定的情况下，这些计算表明，较小的PDMS-磁铁矿颗粒的分散体应比包含较大颗粒的分散体更稳定。在没有施加磁场的情况下，随时间测量纯磁铁矿-PDMS复合物（即不存在溶剂或载液）的流变特性，以探测储存时的预期性能。纯铁磁流体的粘度在一个月的过程中增加，表明发生了一些聚集。但是，可以通过高速剪切流体来消除这种影响。这表明颗粒在这些条件下不会不可逆地絮凝。

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