Baier Jennifa, Koetz Joachim, Kosmella Sabine, Tiersch Brigitte, Rehage Heinz
Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 25, 14476 Potsdam, Germany.
J Phys Chem B. 2007 Jul 26;111(29):8612-8. doi: 10.1021/jp068995g. Epub 2007 May 25.
This paper is focused on the characterization of polyelectrolyte-modified inverse microemulsions and their use as templates for the synthesis of magnetite nanoparticles. It is shown that the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) of low molar mass can be incorporated into the individual inverse microemulsion droplets (L2 phase) consisting of heptanol, water, and an amphoteric surfactant with a sulfobetaine head group. Up to a polymer concentration of 20% by weight in the aqueous phase and for different molecular weights of the polymer, an isotropic phase still exists. At a PDADMAC concentration of 10% the area of the isotropic L2 phase is shifted in direction to the water corner. In the percolated area of the L2 phase, i.e., at higher water content, a temperature-dependent change in the conductivity can by observed, and bulk water can be detected by means of differential scanning calorimetry measurements. The unusual temperature-dependent behavior of the polymer-modified system, i.e., the conductivity decrease with increasing temperature, can be explained by temperature-sensitive polyelectrolyte-surfactant interactions, influencing the droplet-droplet interactions. These PDADMAC-modified microemulsions can be successfully used as a template for the formation of ultrafine magnetite particles, in contrast to the nonmodified microemulsion, where the process is misdirected due to the "disturbing" effect of the surfactants. However, in the presence of PDADMAC the surfactant head groups were masked, and therefore magnetite can be synthesized. During the process of magnetite formation the PDADMAC controls the particle growing and stabilizes spherical magnetite particles with a diameter of 17 nm, which can be redispersed without a change in size.
本文着重于聚电解质改性反相微乳液的表征及其作为合成磁铁矿纳米颗粒模板的应用。结果表明，低摩尔质量的阳离子聚电解质聚二烯丙基二甲基氯化铵（PDADMAC）可以掺入由庚醇、水和具有磺基甜菜碱头基的两性表面活性剂组成的单个反相微乳液滴（L2相）中。在水相中聚合物浓度高达20%（重量）且聚合物分子量不同时，仍存在各向同性相。当PDADMAC浓度为10%时，各向同性L2相的区域向水角方向移动。在L2相的渗滤区域，即水含量较高时，可以观察到电导率随温度的变化，并且可以通过差示扫描量热法测量检测到大量水。聚合物改性体系不寻常的温度依赖性行为，即电导率随温度升高而降低，可以用对温度敏感的聚电解质 - 表面活性剂相互作用来解释，这种相互作用影响了液滴间的相互作用。与未改性的微乳液不同，这些PDADMAC改性的微乳液可以成功用作形成超细磁铁矿颗粒的模板，在未改性微乳液中，由于表面活性剂的“干扰”作用，过程会被误导。然而，在PDADMAC存在下，表面活性剂头基被掩盖，因此可以合成磁铁矿。在磁铁矿形成过程中，PDADMAC控制颗粒生长并稳定直径为17 nm的球形磁铁矿颗粒，这些颗粒可以重新分散而尺寸不变。
