Arriagada FJ, Osseo-Asare K
Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, 16802
J Colloid Interface Sci. 1999 Mar 15;211(2):210-220. doi: 10.1006/jcis.1998.5985.
The effect of ammonia concentration on the region of existence of single-phase water-in-oil microemulsions has been investigated for the system polyoxyethylene (5) nonylphenyl ether (NP-5)/cyclohexane/ammonium hydroxide. The presence of ammonia decreases the size of the microemulsion region. A minimum concentration of surfactant (estimated at about 1.1 wt%) is required for solubilization of the aqueous phase; this value is not significantly affected by ammonia concentration. As indicated by fluorescence spectral data, the transition between bound and free water occurs when the water-to-surfactant molar ratio is about 1 and the presence of ammonium hydroxide does not appear to have a significant effect on this. Ultrafine (30-70 nm diameter), monodisperse silica particles produced by hydrolysis of tetraethoxysilane (TEOS) in the microemulsion show a complex dependence of the particle size on the water-to-surfactant molar ratio (R) and on the concentration of ammonium hydroxide. At relatively low ammonia concentration in the aqueous pseudophase (1.6 wt% NH3) the particle size decreases monotonically with increase in R. However, for higher ammonia concentrations (6.3-29.6 wt% NH3) a minimum in particle size occurs as R is increased. These trends are rationalized in terms of (a) the effects of the concentration, structure, and dynamics of the NP-5 reverse micelles on the hydrolysis and condensation reactions of TEOS, and (b) the effects of ammonia concentration on the stability of the microemulsion phase, the hydrolysis/condensation reactions of TEOS, and the depolymerization of siloxane bonds. Copyright 1999 Academic Press.
对于聚氧乙烯（5）壬基苯基醚（NP - 5）/环己烷/氢氧化铵体系，研究了氨浓度对单相油包水微乳液存在区域的影响。氨的存在减小了微乳液区域的大小。水相增溶需要最低浓度的表面活性剂（估计约为1.1 wt%）；该值不受氨浓度的显著影响。如荧光光谱数据所示，当水与表面活性剂的摩尔比约为1时，束缚水和自由水之间发生转变，氢氧化铵的存在似乎对此没有显著影响。通过在微乳液中水解四乙氧基硅烷（TEOS）制备的超细（直径30 - 70 nm）、单分散二氧化硅颗粒显示，颗粒尺寸对水与表面活性剂的摩尔比（R）和氢氧化铵浓度具有复杂的依赖性。在水假相中氨浓度相对较低（1.6 wt% NH₃）时，颗粒尺寸随R的增加单调减小。然而，对于较高的氨浓度（6.3 - 29.6 wt% NH₃），随着R的增加，颗粒尺寸出现最小值。这些趋势可以通过以下方面来解释：（a）NP - 5反胶束的浓度、结构和动力学对TEOS水解和缩合反应的影响，以及（b）氨浓度对微乳液相稳定性、TEOS水解/缩合反应和硅氧烷键解聚的影响。版权所有1999年学术出版社。
