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SAXS studies of the thermally-induced fusion of diblock copolymer spheres: formation of hybrid nanoparticles of intermediate size and shape
Chemical Science ( IF 8.4 ) Pub Date : 2020-03-27 , DOI: 10.1039/d0sc00569j
E. J. Cornel 1, 2, 3, 4 , P. S. O'Hora 4, 5 , T. Smith 4, 5 , D. J. Growney 4, 5 , O. O. Mykhaylyk 1, 2, 3, 4 , S. P. Armes 1, 2, 3, 4
Affiliation  

Dilute dispersions of poly(lauryl methacrylate)–poly(benzyl methacrylate) (PLMA–PBzMA) diblock copolymer spheres (a.k.a. micelles) of differing mean particle diameter were mixed and thermally annealed at 150 °C to produce spherical nanoparticles of intermediate size. The two initial dispersions were prepared via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate in n-dodecane at 90 °C. Systematic variation of the mean degree of polymerization of the core-forming PBzMA block enabled control over the mean particle diameter: small-angle X-ray scattering (SAXS) analysis indicated that PLMA39–PBzMA97 and PLMA39–PBzMA294 formed well-defined, non-interacting spheres at 25 °C with core diameters of 21 ± 2 nm and 48 ± 5 nm, respectively. When heated separately, both types of nanoparticles regained their original dimensions during a 25–150–25 °C thermal cycle. However, the cores of the smaller nanoparticles became appreciably solvated when annealed at 150 °C, whereas the larger nanoparticles remained virtually non-solvated at this temperature. Moreover, heating caused a significant reduction in mean aggregation number for the PLMA39–PBzMA97 nanoparticles, suggesting their partial dissociation at 150 °C. Binary mixtures of PLMA39–PBzMA97 and PLMA39–PBzMA294 nanoparticles were then studied over a wide range of compositions. For example, annealing a 1.0% w/w equivolume binary mixture led to the formation of a single population of spheres of intermediate mean diameter (36 ± 4 nm). Thus we hypothesize that the individual PLMA39–PBzMA97 chains interact with the larger PLMA39–PBzMA294 nanoparticles to form the hybrid nanoparticles. Time-resolved SAXS studies confirm that the evolution in copolymer morphology occurs on relatively short time scales (within 20 min at 150 °C) and involves weakly anisotropic intermediate species. Moreover, weakly anisotropic nanoparticles can be obtained as a final copolymer morphology over a restricted range of compositions (e.g. for PLMA39–PBzMA97 volume fractions of 0.20–0.35) when heating dilute dispersions of such binary nanoparticle mixtures up to 150 °C. A mechanism involving both chain expulsion/insertion and micelle fusion/fission is proposed to account for these unexpected observations.

中文翻译:

SAXS研究二嵌段共聚物球的热诱导融合:形成中等大小和形状的杂化纳米粒子

将具有不同平均粒径的聚(甲基丙烯酸月桂酯)-聚(甲基丙烯酸苄酯)(PLMA-PBzMA)二嵌段共聚物球体(也称为胶束)的稀释分散液混合,并在150°C下进行热退火,以制得中等大小的球形纳米颗粒。两种初始分散液是通过在90°C下在十二烷中进行甲基丙烯酸苄酯的可逆加成-断裂链转移(RAFT)分散聚合制备的。形成核的PBzMA嵌段的平均聚合度的系统变化使得可以控制平均粒径:小角X射线散射(SAXS)分析表明PLMA 39 –PBzMA 97和PLMA 39 –PBzMA 294在25°C时形成清晰明确的非相互作用球,其芯直径分别为21±2 nm和48±5 nm。分别加热时,两种类型的纳米颗粒在25–150–25°C的热循环中恢复其原始尺寸。但是,较小的纳米颗粒的核在150°C退火时变得明显溶剂化,而较大的纳米颗粒在此温度下实际上仍未溶解。此外,加热导致PLMA 39 –PBzMA 97纳米粒子的平均聚集数显着降低,表明它们在150°C时会部分解离。PLMA 39 –PBzMA 97和PLMA 39 –PBzMA 294的二元混合物然后在广泛的组成范围内研究了纳米颗粒。例如,对1.0%w / w等体积的二元混合物进行退火导致形成中等平均直径(36±4 nm)的单个球体。因此,我们假设单个PLMA 39 –PBzMA 97链与较大的PLMA 39 –PBzMA 294纳米颗粒相互作用形成杂化纳米颗粒。时间分辨SAXS研究证实,共聚物形态的演化发生在相对较短的时间范围内(在150°C下20分钟以内),并且涉及弱各向异性的中间物种。此外,可以在有限的组成范围内(例如,对于PLMA 39 –PBzMA 97的体积分数为0.20–0.35),将此类二元纳米颗粒混合物的稀分散液加热至150°C。提出了一种涉及链排出/插入和胶束融合/裂变的机制来解释这些意外的现象。
更新日期:2020-03-27
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