表面活性剂Surfactant

按亲水基的电性分为阴离子型（脂肪酸钠肥皂、十二烷基硫酸钠 SDS、直链烷基苯磺酸钠 LAS）、阳离子型（季铵盐，有杀菌和柔顺作用）、两性型（甜菜碱）和非离子型（脂肪醇聚氧乙烯醚）。表面活性剂分子在水面定向排列，疏水尾朝向空气，从而降低表面张力；浓度超过临界胶束浓度后在溶液内部聚集成胶束，把油污包裹在疏水内核中，实现去污和增溶。亲水亲油平衡值（HLB）用于选择乳化剂类型。

By the charge of the head group surfactants are anionic (sodium fatty-acid soaps, sodium dodecyl sulfate SDS, linear alkylbenzene sulfonate LAS), cationic (quaternary ammonium salts, which are antibacterial and soften fabrics), zwitterionic (betaines) or non-ionic (fatty alcohol ethoxylates). Molecules line up at the water surface with tails toward the air, lowering surface tension; above the critical micelle concentration they gather into micelles that wrap oily dirt in their hydrophobic cores, cleaning and solubilising it. The hydrophilic–lipophilic balance (HLB) guides the choice of emulsifier.

约公元前 2800 年巴比伦人已用动物脂肪和草木灰制造肥皂。1916 年德国因一战油脂短缺发明了第一种合成洗涤剂（烷基萘磺酸盐）。1930 年代脂肪醇硫酸盐和烷基苯磺酸盐出现，二战后合成洗涤剂迅速取代肥皂。1960 年代支链烷基苯磺酸盐难以生物降解、使河流泛起泡沫，被可降解的直链型（LAS）取代。

Babylonians made soap from animal fat and wood ash by about 2800 BCE. Germany, short of fats in the First World War, invented the first synthetic detergent, alkylnaphthalene sulfonate, in 1916. Fatty alcohol sulfates and alkylbenzene sulfonates appeared in the 1930s, and synthetic detergents displaced soap after the Second World War. In the 1960s branched alkylbenzene sulfonates, which resist biodegradation and foamed up rivers, were replaced by biodegradable linear ones (LAS).

表面活性剂用于洗涤剂和个人护理品、食品乳化（卵磷脂、单甘酯）、农药和涂料分散、石油三次采油、矿物浮选、纺织印染、药物增溶和纳米材料合成模板。肺泡表面活性物质缺乏会导致早产儿呼吸窘迫综合征。

Surfactants are used in detergents and personal care, food emulsifiers (lecithin, monoglycerides), dispersing pesticides and paints, enhanced oil recovery, mineral flotation, textile dyeing, drug solubilisation and as templates for nanomaterials. A lack of lung surfactant causes respiratory distress syndrome in premature babies.