非离子-阴离子Bola型表面活性剂和纳米SiO2颗粒协同稳定的双重响应型O/W乳状液

Dual-responsive oil-in-water emulsions co-stabilized by a nonionic-anionic Bola surfactant and silica nanoparticles

合成了一种非离子-阴离子Bola型智能表面活性剂,通过pH-响应可以在非离子型CH_(3)O(EO)_(5)-R_(11)-COOH(pHpKa)之间转换。单独使用时,非离子型和Bola型分别表现为不良乳化剂和优良乳化剂。与纳米SiO_(2)颗粒复配使用时,非离子型能与SiO_(2)颗粒协同稳定O/W(正癸烷)型Pickering乳状液,其中表面活性剂通过氢键作用吸附到颗粒表面产生原位疏水化作用,提高了颗粒的表面活性,并且这种Pickering乳状液具有pH-和温度-双重响应性,能够通过改变pH或者温度使乳状液在稳定和破乳之间实现多次转换。另一方面,Bola型CH_(3)O(EO)5-R_(11)-COONa能够与纳米SiO_(2)颗粒协同稳定分散液包油(oil-in-dispersion)乳状液,该乳状液具有良好的耐温性,但对调节pH时产生的盐较为敏感。然而与破乳后能完全返回水相便于回收再利用的同系物CH_(3)O(EO)7-R_(11)-COOH相比,具有较短EO链的CH_(3)O(EO)_(5)-R_(11)-COOH无论处于非离子型还是Bola型状态仍具有相当的油溶性,破乳后不能完全返回水相,表明EO数大小对这类新型智能表面活性剂的性能有显著的影响。

A smart nonionicanionic Bola surfactant was synthesized which could be switched between nonionic form CH_(3)O(EO)_(5)-R_(11)-COOH(pH<pKa=6.6)and Bola form CH_(3)O(EO)5-R_(11)-COON a(pH>pKa)a s triggered by pH.Individually,the nonionic/Bola forms behaved as poor/good emulsifiers,respectively.When the nonionic form was mixed with silica nanoparticles,they could co-stabilize n-decanein-water Pickering emulsions,where the silica nanoparticles were hydrophobized in situ to be surface-active by adsorption of the surfactant via hydrogen bonding.The Pickering emulsions could be switched between stable and unstable statuses many times as triggered by either pH or temperature.On the other hand,the Bola form could co-stabilize oil-in-dispersion emulsions with silica nanoparticles,which were resistant to heating but were sensitive to the salt formed during pH alternation.However,in contrast to the CH_(3)(EO)_(7)-R_(11)-COONa which could completely transfer to aqueous phase after demulsification,its analogue with shorter EO chain,i.e.,CH_(3)(EO)_(5)-R11-COONa,was still partially oil-soluble either in nonionic form or in bola form,suggesting a significant effect of EO number on the performance of these novel smart surfactants.