Sommer Cornelia, Deen G Roshan, Pedersen Jan Skov, Strunz Pavel, Garamus Vasil M
Department of Chemistry and iNANO Interdisciplinary NanoScience Center, University of Aarhus, Langelandsgade 140, DK-8000 Arhus C, Denmark.
Langmuir. 2007 Jun 5;23(12):6544-53. doi: 10.1021/la070181j. Epub 2007 May 5.
The phase behavior and structure of a four-component microemulsion system forming droplets with an oil core surrounded by the non-ionic C12E5 surfactant in water and "decorated" by long PEO chains using the block copolymer/surfactant Brij 700 has been studied. The surfactant-to-oil volume ratio, the coverage density of the droplets with decorating molecules, and the temperature were varied. For a surfactant-to-oil volume ratio of 2, the solutions form isotropic and clear solutions at room temperature, and the addition of Brij molecules stabilize the micelles: the transition to an opaque phase is shifted to higher temperatures as the surface coverage increases. At a surfactant-to-oil ratio of 1, the isotropic microemulsion phase is confined to a very narrow range of temperature, which location is shifted to increasing temperature, as the amount of Brij at the surface of the droplet is increased. For large surface coverages, the lower emulsification boundary varies roughly linearly with the surface coverage. The structure of the droplet phase was investigated by small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). For a surfactant-to-oil ratio of 2, the SANS data revealed a transition from rodlike to spherical particles when Brij molecules are added to the system, which induces a larger curvature of the surfactant film. For a surfactant-to-oil ratio of 1, the droplets are nearly spherical at all surface coverages. The intermicellar interactions effects become increasingly more pronounced as Brij is added, due to the introduction of the highly swollen corona. A quantitative analysis of some of the SAXS data was done using an advanced model based on Monte Carlo simulations. It demonstrates the strong chain-chain interactions within the corona and confirms the increased interparticle interactions, as the coverage density is increased.
研究了一种四组分微乳液体系的相行为和结构，该体系形成的液滴具有油核，被水中的非离子型C12E5表面活性剂包围，并使用嵌段共聚物/表面活性剂Brij 700用长PEO链“修饰”。改变了表面活性剂与油的体积比、用修饰分子修饰的液滴的覆盖密度以及温度。对于表面活性剂与油的体积比为2的情况，溶液在室温下形成各向同性的澄清溶液，添加Brij分子可稳定胶束：随着表面覆盖率的增加，向不透明相的转变温度升高。在表面活性剂与油的比例为1时，各向同性微乳液相局限于非常窄的温度范围，随着液滴表面Brij量的增加，该温度范围向升高的温度移动。对于大的表面覆盖率，较低的乳化边界大致随表面覆盖率呈线性变化。通过小角中子散射（SANS）和小角X射线散射（SAXS）研究了液滴相的结构。对于表面活性剂与油的比例为2的情况，SANS数据显示当向体系中添加Brij分子时，从棒状颗粒向球形颗粒转变，这会导致表面活性剂膜的曲率增大。对于表面活性剂与油的比例为1的情况，在所有表面覆盖率下液滴几乎都是球形的。由于引入了高度溶胀的冠层，随着Brij的添加，胶束间相互作用效应变得越来越明显。使用基于蒙特卡罗模拟的先进模型对一些SAXS数据进行了定量分析。结果表明，随着覆盖密度的增加，冠层内存在强链-链相互作用，并证实了颗粒间相互作用增强。
