High Internal Phase Emulsions Stabilized Solely by Functionalized Silica Particles
High Internal Phase Emulsions Stabilized Solely by Functionalized Silica Particles
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仅通过功能化二氧化硅颗粒稳定的高内相乳液
DOI：
10.1002/anie.200990003
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Ikem V
中科院分区：
文献类型：
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作者：
Ikem V
高内相乳液(HIPE)在食品、化妆品、制药和石油工业中的广泛应用非常重要。[1]如果连续相是可聚合的，HIPE可以用作模板[2]，用于合成具有潜在应用的高孔聚合物，作为组织工程中的低重量结构或支架。[3]HIPE的特征在于最小内相体积比为0.74，[2]虽然Lissant首先将这一最小值定义为0.70。[4]由连续有机相和内部水相(w/o乳液)组成的HIPE通常由大量的表面活性剂稳定。[5]颗粒稳定的乳液，也称为Pickering乳液，最近引起了人们的极大兴趣。[6]与表面活性剂不同，颗粒由于其高附着能而不可逆地吸附在乳液的界面上，这使它们成为很好的乳化剂。[7]颗粒在两相界面上的吸附能力主要取决于颗粒的润湿性。[8]亲水颗粒，如金属氧化物，倾向于稳定O/W乳液(连续水相和内部有机相)，而疏水颗粒，如碳，倾向于稳定W/O乳液。[9]然而，通过将表面活性剂分子吸附到颗粒表面[10]或通过硅烷化来改变颗粒的润湿性是可能的。[11]以前关于颗粒稳定乳液的所有报道都涉及内相浓度低于70vol%的乳液。Kralchevsky等人[12]建立了一个热力学模型，预测粒子稳定的乳液将在内部相体积分数为0.5以上发生相转化，但补充说，从实验上讲，动力学因素意味着在体积分数为0.70时观察到相转化。Binks和Lumsden[11]进一步指出，颗粒稳定的乳液相在体积分数为0.65和0.70之间反转，这意味着主相变为连续相。在这里，我们报道了用二氧化硅纳米颗粒(SPS)稳定体积分数高达0.92的Pickering w/o HIPEs，这种纳米颗粒已经通过油酸(OA)的吸附疏水。研究了粒子浓度对乳状液稳定性、液滴大小和乳状液内相体积分数上限的影响。此外，我们还聚合了Pickering HIPE制备了高孔聚Pickering HIPE(PPH)，并通过吸附OA对亲水性SPS(直径为20-100 nm)进行了功能化。通过热重分析(TGA)确定官能化SPS的OA含量为3.5wt%。Binks和Lumsdon[11]通过使用二氯二甲基硅烷疏水的SPS的高能乳化方法制备了w/o乳液，并观察到在60%到70vol%的内相水平下，乳液从w/o到o/w的灾难性反转。这里感兴趣的问题是，如果乳状液只是通过搅拌产生的，那么OA功能化的SPS是否会成为HIPE相转化的机械障碍。我们制备了含苯乙烯/聚乙二醇二甲基丙烯酸酯(PEGDMA；1：1)为油相的HIPEs 1-4(表1，条目1-4)，内部体积分数为70，75，80或85
High internal phase emulsions (HIPEs) are important for a wide range of applications in the food, cosmetic, pharmaceutical, and petroleum industries.[1] If the continuous phase is polymerizable, HIPEs can be used as templates [2] for the synthesis of highly porous polymers with potential applications as low-weight structures or scaffolds in tissue engineering.[3] HIPEs are characterized by a minimum internal phase volume ratio of 0.74,[2] although Lissant first defined this minimum as 0.70.[4] HIPEs consisting of a continuous organic phase and an internal aqueous phase (w/o emulsions) are commonly stabilized by large amounts of surfactants.[5] Particle-stabilized emulsions, also known as Pickering emulsions, have recently attracted much interest.[6] Unlike surfactants, particles irreversibly adsorb at the interface of emulsions because of their high energy of attachment, which makes them good emulsifiers.[7] The ability of particles to adsorb at the interface between the two phases is primarily dependent on the wettability of the particles.[8] Hydrophilic particles such as metal oxides tend to stabilize o/w emulsions (a continuous aqueous phase and an internal organic phase) while hydrophobic particles such as carbon tend to stabilize w/o emulsions.[9] Nevertheless, it is possible to modify the wettability of particles by adsorbing surfactant molecules onto the particle surfaces [10] or by silanation.[11] All previous reports on particle-stabilized emulsions deal with emulsions that have internal phase levels below 70 vol%. Kralchevsky et al.[12] developed a thermodynamic model predicting that particle-stabilized emulsions will phase invert above internal phase volume fractions of 0.5, but added that, experimentally, kinetic factors mean that phase inversion is observed at volume fractions of 0.70. Binks and Lumsden [11] further stated that particle-stabilized emulsions phase invert between volume fractions of 0.65 and 0.70, which means the major phase becomes the continuous phase. We report herein the stabilization of Pickering w/o HIPEs with volume fractions of up to 0.92 by using silica nanoparticles (SPs), which have been hydrophobized by adsorption of oleic acid (OA). We studied the influence of the particle concentration on the emulsion stability, the droplet size, and the upper limit of the internal phase volume fraction within the emulsion. Furthermore, we polymerized the Pickering HIPEs to produce highly porous poly-Pickering HIPEs (PPH).Hydrophilic SPs (20–100 nm in diameter) were functionalized by adsorption of OA. The OA content of the functionalized SPs was determined by thermogravimetric analysis (TGA) to be 3.5 wt%. Binks and Lumsdon [11] prepared w/o emulsions by a high energy emulsification method using dichlorodimethylsilane-hydrophobized SPs, and observed a catastrophic inversion of the emulsions from w/o to o/w at internal phase levels between 60 and 70 vol%. The question of interest here is if OA-functionalized SPs will act as a mechanical barrier for the phase inversion of HIPEs if the emulsions are produced simply by stirring. We prepared HIPEs 1–4 (Table 1, entries 1–4) containing styrene/poly (ethylene glycol) dimethacrylate (PEGDMA; 1: 1) as the oil phase with 70, 75, 80, or 85 vol% internal