Formation and stability of nanoemulsions with mixed ionic-nonionic surfactants.
Formation and stability of nanoemulsions with mixed ionic-nonionic surfactants.
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DOI：
10.1039/b912460h
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发表时间：
2009-10
期刊：
影响因子：
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通讯作者：
Lijuan Wang;R. Tabor;J. Eastoe;Xuefeng Li;R. Heenan;Jinfeng Dong
中科院分区：
文献类型：
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作者：
Lijuan Wang;R. Tabor;J. Eastoe;Xuefeng Li;R. Heenan;Jinfeng Dong
采用一种简单、低能的两步稀释方法，用离子-非离子表面活性剂二元混合物制备纳米乳液。该体系由水/DDAB-C(12)E(5)/癸烷组成。通过稀释位于双连续微乳液或层状液晶相区的浓缩物，得到纳米乳液。采用对比变化小角中子散射（SANS）和动态光散射（DLS）对制备的纳米乳进行了研究。SANS谱图表明，加入阳离子DDAB表面活性剂后，C(12)E(5)纳米液滴除了静电排斥作用增加外，基本没有结构变化。有趣的是，SANS表明，表面活性剂混合物的组成(DDAB摩尔比(m(DDAB)/(m(DDAB) + m（C（12)E（5)）为0.40）和液滴体积分数（phi）在0.006 ~ 0.120之间）对首选液滴尺寸几乎没有影响。在1 d的测试期间，SANS没有观察到纳米乳液滴的结构和半径发生明显变化，尽管仅用C(12)E(5)稳定的体系中液滴数量强度明显下降。然而，随着时间的推移，DLS粒径的变化明显增加，液滴体积分数越高，变化幅度越大。由DLS和SANS数据确定的纳米乳表观液滴尺寸之间的差异可归因于发生在SANS灵敏度范围之外的远程液滴相互作用。结果表明，絮凝作用是纳米乳不稳定的主要机制。结果表明，加入带电荷的DDAB可显著延缓纳米乳液的絮凝速度，这可能是由于液滴之间的静电斥力增强，从而提高了纳米乳液的稳定性。
A simple, low-energy two-step dilution process has been applied with binary mixtures of ionic-nonionic surfactants to prepare nanoemulsions. The systems consist of water/DDAB-C(12)E(5)/decane. Nanoemulsions were obtained by dilution of concentrates located in bicontinuous microemulsion or lamellar liquid crystal phase regions. The nanoemulsions generated were investigated both by contrast-variation small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS profiles show that C(12)E(5) nanodroplets suffer essentially no structural change on incorporation of the cationic DDAB surfactant, except for increased electrostatic repulsive interactions. Interestingly, SANS indicated that the preferred droplet sizes were hardly affected by the surfactant mixture composition (up to a DDAB molar ratio (m(DDAB)/(m(DDAB) + m(C(12)E(5))) of 0.40) and droplet volume fraction, phi, between 0.006 and 0.120. No notable changes in the structure or radius of nanoemulsion droplets were observed by SANS over the test period of 1 d, although the droplet number intensity decreased significantly in systems stabilized by C(12)E(5) only. However, the DLS sizing shows a marked increase with time, with higher droplet volume fractions giving rise to the largest changes. The discrepancy between apparent nanoemulsion droplet size determined by DLS and SANS data can be attributed to long-range droplet interactions occurring outside of the SANS sensitivity range. The combined SANS and DLS results suggest flocculation is the main mechanism of instability for these nanoemulsions. The flocculation rate is shown to be significantly retarded by addition of the charged DDAB, which may be due to enhanced electrostatic repulsive forces between droplets, leading to improved stability of the nanoemulsions.