摘要
Highly monodisperse polystyrene nanoparticles with mean diameters of less than 100 nm are synthesized via aqueous emulsion polymerization using an amphoteric initiator (VA-057) in the presence of sub-millimolar concentrations of anionic surfactant. Since the net charge on the initiator is almost zero at neutral pH, the resultant latex particle size is mainly determined by surfactant adsorption. Polymerizations were performed in the presence of a range of anionic surfactants with differing critical micelle concentrations (CMC) by varying the concentrations of surfactant, initiator and monomer, and also the ionic strength. Sodium dodecyl benzene sulfonate (SDBS), sodium hexadecyl sulfate (SHS), and sodium octadecyl sulfate (SOS) have relatively low CMCs and so enable formation of highly monodisperse nanoparticles at relatively low (sub-millimolar) surfactant concentrations, CS (i.e. below the CMC in each case). Empirically, it was found that the particle number, Np, and coefficient of variation of the particle size, CV, were strongly dependent on the CS/CMC ratio: Np increased almost in proportion with the square of this ratio, while the CV exhibited a minimum at approximately CS/CMC = 0.20. Higher ionic strength reduced the particle size, which is consistent with the above relationship because the addition of salt lowers the CMCs of ionic surfactants. Polymer latex particles produced using such formulations form highly regular, close-packed colloidal arrays.
摘要译文
第i个平均直径小于100纳米的通过使用一种两性剂（VA-057）的子毫摩尔浓度的阴离子表面活性剂的存在下的水性乳液聚合合成。由于在引发剂的净电荷几乎为零，在中性pH下，将得到的胶乳颗粒尺寸主要由表面活性剂吸附测定。聚合反应在一个范围内的阴离子表面活性剂的存在下，通过改变表面活性剂的浓度进行具有不同的临界胶束浓度（CMC）引发剂和单体，并且还离子强度。十二烷基苯磺酸钠（SDBS），十六烷基硫酸钠（SHS）和钠十八烷基硫酸（SOS）具有相对低的CMC等能够形成高度单分散的纳米颗粒在相对低的（子毫摩尔）表面活性剂浓度，CS（即低于CMC在每种情况下）。凭经验，发现粒子数N p和系数的粒径，CV的变化，强烈依赖于在CS / CMC比：N P增加几乎正比与该比的平方，而CV表现出最小约为CS / CMC \x3d 0.20。较高的离子强度降低了粒径，这是与上述的关系是一致的，因为在加入盐的降低离子表面活性剂的CMC的。使用这样的制剂生产的聚合物胶乳颗粒形成规则性高，密堆积胶体阵列。
Haruyuki Ishii; Motohiro Ishii; Daisuke Nagao; Mikio Konno. Advanced synthesis for monodisperse polymer nanoparticles in aqueous media with sub-millimolar surfactants[J]. Polymer, 2014,55(12): 2772–2779