可聚合细乳液的配制和稳定性机理,Macromolecules

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可聚合细乳液的配制和稳定性机理
Macromolecules ( IF 5.1 ) Pub Date : July 22, 1999 , DOI: 10.1021/ma990299+
Katharina Landfester ₁ , Nina Bechthold ₁ , Franca Tiarks ₁ , Markus Antonietti ₁

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可以通过在细乳液中聚合来合成尺寸范围为30-180 nm的聚苯乙烯胶乳，其中粒径与表面活性剂十二烷基硫酸钠（SDS）的量有关，该量相对于单体在0.5至50 wt％之间变化。使用浊度和表面张力测量来表征超声作用下的微乳化和液滴尺寸的稳定状态。由于似乎通过碰撞引起的液滴融合和超声裂变的速率方程建立了尺寸平衡，因此细乳液在不同量的表面活性剂下实现了最小的液滴尺寸。即，它们被“极稳定的”相对于碰撞（τ _2个工序）。针对完整的奥斯特瓦尔德熟化稳定性（τ ₁通过加入疏水基获得的疏水基，该疏水基在很宽的结构范围内变化。这种疏水剂的效率主要是由非常低的水溶性决定的。临界稳定的细乳液液滴的生长通常比聚合时间慢。因此，在理想情况下，可以获得液滴与颗粒的1：1副本，并且临界稳定状态被冻结。确定了这些颗粒具有SDS分子的临界表面覆盖率，并且在很大程度上取决于粒径：粒径越小，表面活性剂所需的表面覆盖率越高。这些系统的良好可及性允许在胶乳的宏观表面张力与颗粒的微观覆盖范围之间建立一般关系，这对于所有胶乳而言都是正确的。最后，将细乳液中的聚合特性与大乳液和微乳液中相应工艺的特性进行了比较。

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Formulation and Stability Mechanisms of Polymerizable Miniemulsions

Polystyrene latexes in a size range of 30−180 nm can be synthesized by polymerization in miniemulsions where the particle size responds to the amount of the surfactant sodium dodecyl sulfate (SDS) which was varied between 0.5 and 50 wt % with respect to monomer. Turbidity and surface tension measurements were used to characterize the miniemulsification by ultrasonication and the approach to a steady state of droplet size. Since size equilibrium seems to be established by a rate equation of collision-induced droplet fusion and ultrasound fission, miniemulsions realize the minimal droplet size for the distinct amount of surfactant; i.e., they are “critically stabilized” with respect to collisions (τ₂ process). Complete stability against Ostwald ripening (τ₁ process) is obtained by the addition of a hydrophobe, which was varied over a broad structural range. The efficiency of this hydrophobic agent is given mainly by a very low water solubility. The growth of the critically stabilized miniemulsion droplets is usually slower than the polymerization time; therefore in ideal cases, a 1:1 copy of droplets to particles is obtained, and the critically stabilized state is frozen. The critical surface coverage of these particles with SDS molecules was determined and depends strongly on the particle size: the smaller the particle size, the higher the required surface coverage with surfactant. The good accessibility of these systems allows to establish a general relation between the macroscopic surface tension of the latex and the microscopic coverage of the particles which is expected to hold true for all latexes. Finally, the characteristics of polymerization in miniemulsions were compared with those of the corresponding processes in macro- and microemulsions.

更新日期：2017-01-31

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