Weber C H M, Chiche A, Krausch G, Rosenfeldt S, Ballauff M, Harnau L, Göttker-Schnetmann I, Tong Q, Mecking S
Physikalische Chemie II, University of Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany.
Nano Lett. 2007 Jul;7(7):2024-9. doi: 10.1021/nl070859f. Epub 2007 Jun 12.
We present a complete analysis of the structure of polyethylene (PE) nanoparticles synthesized and stabilized in water under very mild conditions (15 degrees C, 40 atm) by a nickel-catalyzed polymerization in aqueous solution. Combining cryogenic transmission electron microscopy (cryo-TEM) with X-ray scattering, we demonstrate that this new synthetic route leads to a stable dispersion of individual PE nanoparticles with a narrow size distribution. Most of the semicrystalline particles have a hexagonal shape (lateral size 25 nm, thickness 9 nm) and exhibit the habit of a truncated lozenge. The combination of cryo-TEM and small-angle X-ray scattering demonstrates that the particles consist of a single crystalline lamella sandwiched between two thin amorphous polymer layers ("nanohamburgers"). Hence, these nanocrystals that comprise only ca. 14 chains present the smallest single crystals of PE ever reported. The very small thickness of the crystalline lamella (6.3 nm) is related to the extreme undercooling (more than 100 degrees C) that is due to the low temperature at which the polymerization takes place. This strong undercooling cannot be achieved by any other method so far. Dispersions of polyethylene nanocrystals may have a high potential for a further understanding of polymer crystallization as well as for materials science as, e.g., for the fabrication of extremely thin crystalline layers.
我们对在非常温和的条件下（15摄氏度，40个大气压）于水溶液中通过镍催化聚合合成并稳定化的聚乙烯（PE）纳米颗粒的结构进行了全面分析。结合低温透射电子显微镜（cryo-TEM）和X射线散射技术，我们证明了这种新的合成路线能够导致具有窄尺寸分布的单个PE纳米颗粒的稳定分散。大多数半结晶颗粒呈六边形（横向尺寸25纳米，厚度9纳米），呈现出截顶菱形的形态。cryo-TEM和小角X射线散射的结合表明，这些颗粒由夹在两个薄的非晶态聚合物层之间的单个结晶薄片组成（“纳米汉堡”）。因此，这些仅包含约14条链的纳米晶体是有史以来报道的最小的PE单晶。结晶薄片的极薄厚度（6.3纳米）与极端过冷（超过100摄氏度）有关，这是由于聚合发生的低温所致。到目前为止，任何其他方法都无法实现这种强烈的过冷。聚乙烯纳米晶体的分散体对于进一步理解聚合物结晶以及材料科学可能具有很高的潜力，例如用于制造极薄的结晶层。
