酯化淀粉乳化剂制备的高效氯氟氰菊酯O/W乳液的稳定机制

Stability Mechanism of Lambda-Cyhalothrin O/W Emulsion Prepared with Esterified Starch as Emulsifier

通过测定辛烯基琥珀酸淀粉钠的用量、盐离子、pH值和温度等因素对油滴Zeta电位及表面吸附量的影响,分析了以酯化淀粉辛烯基琥珀酸淀粉钠为乳化剂制备的5%高效氯氟氰菊酯水乳剂的稳定机制。结果表明,辛烯基琥珀酸淀粉钠质量分数为7%时,Zeta电位达到最大值,油滴表面吸附量接近饱和;Na+、Mg2+和Al3+压缩油滴表面的双电层,降低Zeta电位,削弱静电排斥作用,增加辛烯基琥珀酸淀粉钠分子柔性,提高辛烯基琥珀酸淀粉钠表面吸附量,且随着Na+、Mg2+、Al3+离子强度依次增大,压缩双电层能力依次增强,Zeta电位降低和表面吸附量增加程度依次增大;pH值影响辛烯基琥珀酸淀粉钠在水中的解离,在碱性范围内解离出较多羧酸根,静电排斥力较大,Zeta电位较高,但表面吸附量有所降低;温度升高,辛烯基琥珀酸淀粉钠在水溶液中溶解度增大,呈舒展状态,且辛烯基琥珀酸淀粉钠从油滴表面逃逸的趋势增加,油滴表面Zeta电位和表面吸附量均随着温度升高而降低,在低温区差别不大,温度越高二者变化越明显。辛烯基琥珀酸淀粉钠通过吸附于油滴表面为其提供较强的静电斥力和空间位阻作用而维持O/W乳液稳定。

The stability mechanism of 5% （w/w） lambda-cyhalothrin 0/W emulsion prepared with octenyl succinic anhydride （OSA）-modified starch as emulsifier was studied. For this purpose, the effects of 0SA- modified starch content, inorganic ions, pH value and temperature on the Zeta potential of oil droplets and surface loads（F） of modified starch were investigated. When the 0SA-modified starch content was 7% （mass fraction）, Zeta potential could reach the maximum, and Г appear to reach saturation level; Na ＋ , Mg2＋ and Al3 ＋ were able to decrease Zeta potential by compressing the electronic double layer thickness of oil droplet surface, which could lead to the enhancement of molecular flexibility due to the weakened electrostatic exclusion and make F enlarger. With the increasing of ionic strength, the capacity of compressing the electronic double layer thickness of oil droplet surface was subsequently enhanced by Na ＋ , Mg2＋ and Al3 ＋ , and the degrees of Zeta potential reduction and F increment were obvious in the sequence of Na ＋ , Mg2 ＋ and Al3 ＋. As the pH affected the ionization of OSA-modified starch in water, in the range of alkaline, strong electrostatic repulsive force was provided by more ionized carboxylic ions and the Zeta potential increased while the F decreased. As temperature increased, the solubility or escaping tendency of OSA-modified starch increased, so the Zeta potential and Г decreased, furthermore the difference was not obvious at low temperatures, but at higher temperature it was, the less the Zeta potential and surface load （F） was. The OSA-modified starch that was adsorbed at the oil droplets surface was able to stabilize the emulsion by very strong electrostatic exclusion and steric-hindrance double effect.