Yuan Zaiwu, Hao Jingcheng, Hoffmann Heinz
Key Laboratory of Colloid and Interface Chemistry (Shandong University), Ministry of Education, Jinan 250100, PR China.
J Colloid Interface Sci. 2006 Oct 15;302(2):673-81. doi: 10.1016/j.jcis.2006.06.059. Epub 2006 Jul 3.
Acidic surfactants, single- and bi-2-methylheptanol polyethenoxy ether phosphate esters, H2PO3(OCH2CH2)nOCH2CH2CH2CH2CH2CH(CH3)2 (u-MHPEPE) and HPO3[(OCH2CH2)nOCH2CH2CH2CH2CH2CH(CH3)2]2 (d-MHPEPE), where n approximately 4, were synthesized. Phase behavior of u- and d-MHPEPE (u- and d-MHPEPE mixtures were abbreviated as MHPEPE) mixtures in aqueous solutions and vesicle formation were determined. Surface tension measurements showed that u-MHPEPE and MHPEPE have low surface tensions at critical micelle concentrations. gamma(cmc)=29.0 mNm(-1) and cmc=16.0 mmolL(-1) for u-MHPEPE, MHPEPE has two transition points suggesting the mixtures of u- and d-MHPEPE with gamma(cmc1)=30.5 mNm(-1) and cmc1=4.0 mmolL(-1), and gamma(cmc2)=27.3 mNm(-1) and cmc2=42.0 mmolL(-1). These values, specific gamma(cmc), are much lower than those of traditionally cationic or anionic surfactants such as cetyltrimethylammonium bromide (CTAB, gamma(cmc)=37.1 mNm(-1) at cmc=0.92 mmolL(-1)) and sodium dodecyl sulfate (SDS, gamma(cmc)=39.0 mNm(-1) at cmc=8.1 mmolL(-1)). Rich phase behavior was observed with increasing MHPEPE concentration, an isotropic L(1)-phase (micelle solution), an unstable emulsion-region (with time, the samples separate into two-phase), a transparently bluish and birefringent Lalpha-phase up to 200 mmol L(-1) with unilamellar and multilamellar vesicles. These unilamellar and multilamellar vesicles were demonstrated by using staining transmission electron microscopy (staining-TEM), which were compared to freeze-fracture TEM (FF-TEM). The vesicle-phase is stable for at least 1 year. Vesicle formation possibly could be explained in harmonization of the hydrophobic force of acidic surfactant tails, the hydrogen bonding (H-bonding) and the electrostatic interaction among polar headgroups of PEO ether phosphate ester. Phase transition from the flow birefringent unilamellar vesicles induced by addition of HCl, NaCl, NaOH, and increasing temperature has been observed. Surprisingly, for u-MHPEPE or d-MHPEPE in water, we just observed L1-phase (micelle solution) with increasing u-MHPEPE or d-MHPEPE concentration.
合成了酸性表面活性剂，单-和双-2-甲基庚醇聚乙氧基醚磷酸酯，即H2PO3(OCH2CH2)nOCH2CH2CH2CH2CH2CH(CH3)2（u-MHPEPE）和HPO3[(OCH2CH2)nOCH2CH2CH2CH2CH2CH(CH3)2]2（d-MHPEPE），其中n约为4。测定了u-MHPEPE和d-MHPEPE（u-和d-MHPEPE混合物简称为MHPEPE）混合物在水溶液中的相行为以及囊泡形成情况。表面张力测量表明，u-MHPEPE和MHPEPE在临界胶束浓度时具有较低的表面张力。u-MHPEPE的γ(cmc)=29.0 mN/m(-1)，cmc=16.0 mmol/L(-1)，MHPEPE有两个转变点，表明u-和d-MHPEPE混合物的γ(cmc1)=30.5 mN/m(-1)，cmc1=4.0 mmol/L(-1)，以及γ(cmc2)=27.3 mN/m(-1)，cmc2=42.0 mmol/L(-1)。这些特定的γ(cmc)值远低于传统阳离子或阴离子表面活性剂，如十六烷基三甲基溴化铵（CTAB，在cmc=0.92 mmol/L(-1)时γ(cmc)=37.1 mN/m(-1)）和十二烷基硫酸钠（SDS，在cmc=8.1 mmol/L(-1)时γ(cmc)=39.0 mN/m(-1)）。随着MHPEPE浓度增加，观察到丰富的相行为，有各向同性的L(1)相（胶束溶液）、不稳定的乳液区（随着时间推移，样品会分离成两相）、在高达200 mmol/L(-1)时呈现透明蓝色且双折射的Lα相，伴有单层和多层囊泡。通过染色透射电子显微镜（染色-TEM）证实了这些单层和多层囊泡，并与冷冻断裂TEM（FF-TEM）进行了比较。囊泡相至少稳定1年。囊泡形成可能可以通过酸性表面活性剂尾部的疏水力、氢键（H键）以及聚环氧乙烷醚磷酸酯极性头基之间的静电相互作用的协同作用来解释。观察到通过添加HCl、NaCl、NaOH以及升高温度诱导流动双折射单层囊泡发生相转变。令人惊讶的是，对于水中的u-MHPEPE或d-MHPEPE，随着u-MHPEPE或d-MHPEPE浓度增加，我们仅观察到L1相（胶束溶液）。
