North S M, Jones E R, Smith G N, Mykhaylyk O O, Annable T, Armes S P
Department of Chemistry, University of Sheffield , Dainton Building, Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
Lubrizol Limited , Hexagon Tower, P.O. Box 42, Blackley, Manchester M9 8ZS, U.K.
Langmuir. 2017 Feb 7;33(5):1275-1284. doi: 10.1021/acs.langmuir.6b04541. Epub 2017 Jan 24.
The present study focuses on the use of copolymer nanoparticles as a dispersant for a model pigment (silica). Reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization was used to synthesize sterically stabilized diblock copolymer nanoparticles. The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA). The mean degrees of polymerization for the PDMA and PBzMA blocks were 71 and 100, respectively. Transmission electron microscopy (TEM) studies confirmed a near-monodisperse spherical morphology, while dynamic light scattering (DLS) studies indicated an intensity-average diameter of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average diameter of 29 ± 0.5 nm and a mean aggregation number of 154. Aqueous electrophoresis measurements confirmed that these PDMA-PBzMA nanoparticles acquired cationic character when transferred from ethanol to water as a result of protonation of the weakly basic PDMA chains. Electrostatic adsorption of these nanoparticles from aqueous solution onto 470 nm silica particles led to either flocculation at submonolayer coverage or steric stabilization at or above monolayer coverage, as judged by DLS. This technique indicated that saturation coverage was achieved on addition of approximately 465 copolymer nanoparticles per silica particle, which corresponds to a fractional surface coverage of around 0.42. These adsorption data were corroborated using thermogravimetry, UV spectroscopy and X-ray photoelectron spectroscopy. TEM studies indicated that the cationic nanoparticles remained intact on the silica surface after electrostatic adsorption, while aqueous electrophoresis confirmed that surface charge reversal occurred below pH 7. The relatively thick layer of adsorbed nanoparticles led to a significant reduction in the effective particle density of the silica particles from 1.99 g cm to approximately 1.74 g cm, as judged by disk centrifuge photosedimentometry (DCP). Combining the DCP and SAXS data suggests that essentially no deformation of the PBzMA cores occurs during nanoparticle adsorption onto the silica particles.
本研究聚焦于使用共聚物纳米颗粒作为一种模型颜料（二氧化硅）的分散剂。采用可逆加成-断裂链转移（RAFT）醇分散聚合法合成了空间稳定的二嵌段共聚物纳米颗粒。空间稳定剂嵌段为聚甲基丙烯酸2-（二甲氨基）乙酯（PDMA），成核嵌段为聚甲基丙烯酸苄酯（PBzMA）。PDMA和PBzMA嵌段的平均聚合度分别为71和100。透射电子显微镜（TEM）研究证实了近乎单分散的球形形态，而动态光散射（DLS）研究表明强度平均直径为30 nm。小角X射线散射（SAXS）报告体积平均直径为29±0.5 nm，平均聚集数为154。水性电泳测量证实，由于弱碱性PDMA链的质子化，这些PDMA-PBzMA纳米颗粒从乙醇转移到水中时获得了阳离子特性。通过DLS判断，这些纳米颗粒从水溶液中静电吸附到470 nm二氧化硅颗粒上，在亚单层覆盖时导致絮凝，在单层覆盖或以上时导致空间稳定。该技术表明，每颗二氧化硅颗粒添加约465个共聚物纳米颗粒时达到饱和覆盖，这对应于约0.42的表面覆盖分数。使用热重分析、紫外光谱和X射线光电子能谱对这些吸附数据进行了佐证。TEM研究表明，阳离子纳米颗粒在静电吸附后在二氧化硅表面保持完整，而水性电泳证实，在pH值低于7时发生表面电荷反转。通过盘式离心光沉降法（DCP）判断，相对较厚的吸附纳米颗粒层导致二氧化硅颗粒的有效颗粒密度从1.99 g/cm显著降低至约1.74 g/cm。结合DCP和SAXS数据表明，在纳米颗粒吸附到二氧化硅颗粒上的过程中，PBzMA核基本上没有变形。
