脂肪酰基氨基酸表面活性剂亲/疏水基结构对界面性质的影响

Influence of hydrophilic and hydrophobic groups of fatty acyl amino acid surfactants on the interfacial properties

摘要:

基于绿色合成方法,利用月桂酸甲酯、肉豆蔻酸甲酯、棕榈酸甲酯分别与丙氨酸、丝氨酸、苏氨酸反应制备了9种脂肪酰基氨基酸表面活性剂。通过表/界面张力测试及界面扩张流变实验探究了亲水/疏水基的协同作用对界面行为的影响。结果表明,相比于丙氨酸,丝氨酸、苏氨酸表面活性剂α取代基中的羟基有助于增强分子间氢键作用、提高界面活性并促进表面活性剂分子在界面上紧密排列。同时,脂肪酰基链长的增长可使得氨基酸α取代基对表面活性剂界面性质的影响更加显著,而氨基酸α极性取代基有利于长链脂肪酰基表面活性剂的亲水亲油平衡,改善其界面性能。由于羟基和长链脂肪酰基的协同增效,棕榈酰基丝氨酸表面活性剂(C16Ser)的CMC可降至3.9×10_-4^mol/L,水溶液表面张力可降至27.60 mN/m,分子最小截面积低至0.87 nm₂^,界面扩张模量可达47.6 mN/m。氨基酸的羟基与长脂肪酰基在提高界面性能方面相互配合,呈现出良好的协同效应。

Abstract:

Based on a green synthesis method, 9 fatty acyl amino acid surfactants were prepared by reacting methyl laurate, methyl myristate and methyl palmitate with alanine, serine and threonine, respectively. The effects of the synergistic interaction of hydrophilic/hydrophobic groups on the interfacial behavior were investigated by surface/interfacial tension measurement and interfacial dilatational rheological experiments. The results showed that, compared with that of alanine, the hydroxyl groups in the α-substituents of the serine and threonine surfactants contributed to the enhancement of intermolecular hydrogen bonding, the improvement of interfacial activity, and the close arrangement of surfactant molecules at the interface. Meanwhile, the increase of fatty acyl chain length made the effect of amino acid α-substituents on the interfacial properties of surfactants more significant. In turn, the polar α-substituent of amino acid facilitated the hydrophilic-lipophilic balance of long-chain fatty acyl surfactants and improved their interfacial properties. Due to the synergistic effect of hydroxyl group and long chain fatty acyl group, the CMC of palmitoyl serinate surfactant declined to 3.9×10_^-4 mol/L, the surface tension of aqueous solution was reduced to 27.60 mN/m, the minimum surface area occupied per surfactant molecule at surface decreased to 0.87 nm₂^{, and the interfacial dilatation}al modulus was enhanced as high as to 47.6 mN/m. Hydroxyl group of amino acid and long fatty acyl group showed a good synergistic effect in enhancing the interfacial properties,.