Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized Nanoparticles.
Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized Nanoparticles.
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DOI：
10.1021/acs.macromol.6b00987
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发表时间：
2016-07-26
期刊：
影响因子：
5.5
通讯作者：
Armes SP
中科院分区：
文献类型：
--
作者：
Akpinar B;Fielding LA;Cunningham VJ;Ning Y;Mykhaylyk OO;Fowler PW;Armes SP
设计了一系列模型空间稳定的二嵌段共聚物纳米颗粒来帮助开发分析方案，以确定两个关键参数：有效颗粒密度和空间稳定剂层厚度。前一个参数对于基于分析（超）离心技术的高分辨率粒度分析是必不可少的（例如，圆盘离心光沉积测定法，DCP），而后者参数在确定作为胶体稳定性机制的空间稳定化的有效性方面具有根本重要性。使用RAFT水乳液聚合通过聚合诱导自组装（比萨）制备二嵌段共聚物纳米颗粒：该方法提供相对窄的粒度分布，并且使得能够分别通过疏水性和亲水性嵌段的平均聚合度的系统变化独立地调节平均粒径和稳定剂层厚度。疏水性核形成嵌段是聚（甲基丙烯酸2，2，2-三氟乙酯）[PTFEMA]，其被选择用于其相对高的密度。亲水性稳定剂嵌段是聚（单甲基丙烯酸甘油酯）[PGMA]，其是在宽温度范围内保持水溶性的众所周知的非离子聚合物。制备了四个系列的PGMAx-PTFEMAy纳米颗粒（x = 28、43、63和98，y = 100-1400），并通过透射电子显微镜（TEM）、动态光散射（DLS）和小角X射线散射（SAXS）进行表征。发现PGMA稳定剂和成核PTFEMA的聚合度对平均粒径（20 ~ 250 nm）有很强的影响。此外，SAXS用于确定溶剂化PGMA稳定剂嵌段的1.46至2.69 nm的回转半径。因此，计算这些空间稳定颗粒的平均有效密度，并确定为介于1.19 g cm-3（对于较小颗粒）和1.41 g cm-3（对于较大颗粒）之间;这些值显著低于PTFEMA的固态密度（1.47 g cm-3）。由于分析离心需要颗粒和水相之间的密度差，因此确定有效颗粒密度对于获得可靠的粒度分布显然至关重要。此外，通过考虑叠加在粒度分布上的固有密度分布，重新计算选定的DCP数据。因此，发现真实的粒度分布比使用错误的单一密度值计算的粒度分布略窄，较小的颗粒对此伪影特别敏感。
A series of model sterically stabilized diblock copolymer nanoparticles has been designed to aid the development of analytical protocols in order to determine two key parameters: the effective particle density and the steric stabilizer layer thickness. The former parameter is essential for high resolution particle size analysis based on analytical (ultra)centrifugation techniques (e.g., disk centrifuge photosedimentometry, DCP), whereas the latter parameter is of fundamental importance in determining the effectiveness of steric stabilization as a colloid stability mechanism. The diblock copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using RAFT aqueous emulsion polymerization: this approach affords relatively narrow particle size distributions and enables the mean particle diameter and the stabilizer layer thickness to be adjusted independently via systematic variation of the mean degree of polymerization of the hydrophobic and hydrophilic blocks, respectively. The hydrophobic core-forming block was poly(2,2,2-trifluoroethyl methacrylate) [PTFEMA], which was selected for its relatively high density. The hydrophilic stabilizer block was poly(glycerol monomethacrylate) [PGMA], which is a well-known non-ionic polymer that remains water-soluble over a wide range of temperatures. Four series of PGMAx–PTFEMAy nanoparticles were prepared (x = 28, 43, 63, and 98, y = 100–1400) and characterized via transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). It was found that the degree of polymerization of both the PGMA stabilizer and core-forming PTFEMA had a strong influence on the mean particle diameter, which ranged from 20 to 250 nm. Furthermore, SAXS was used to determine radii of gyration of 1.46 to 2.69 nm for the solvated PGMA stabilizer blocks. Thus, the mean effective density of these sterically stabilized particles was calculated and determined to lie between 1.19 g cm–3 for the smaller particles and 1.41 g cm–3 for the larger particles; these values are significantly lower than the solid-state density of PTFEMA (1.47 g cm–3). Since analytical centrifugation requires the density difference between the particles and the aqueous phase, determining the effective particle density is clearly vital for obtaining reliable particle size distributions. Furthermore, selected DCP data were recalculated by taking into account the inherent density distribution superimposed on the particle size distribution. Consequently, the true particle size distributions were found to be somewhat narrower than those calculated using an erroneous single density value, with smaller particles being particularly sensitive to this artifact.