洗涤剂的去污作用

洗涤剂的去污原理是复杂的，影响洗涤剂去污作用的因素几乎涉及各个方面，因而我们不可能对洗涤去污作用的影响因素做全面系统的分析。在此，仅就与洗涤剂的去污作用紧密相关的表面活性剂的性能进行探讨。

一、表面张力和表面活性剂

按照物理化学定义，在体系内部物理化学性质完全相同的部分称为相。相与相之间的接触面称为界面，习惯上通常将气体与固体、气体与液体之间的界面称为表面。

物体表面的分子与相内部的分子，受力情况是不同的。例如在水相内部，水分子受到周围水分子的吸引力是平衡的，而在水与空气界面上的水分子，其受到空气的吸引力要比受到水的吸引力小得多。因此，表面层的水分子处于受力不平衡状态，它受到一种指向相内部的拉力使表面收缩（例如荷叶上的水成珠状）。这种作用于表面而指向相内部的表面收缩力称之为表面张力。

将不同性质的物质溶于水时，水的表面张力会发生变化，物质能使水的表面张力降低的性质称之为表面活性。在溶液中，既使浓度很低也可以显著降低溶液表面张力的物质即称之为表面活性剂，织物用洗涤剂中即含有各种各样的表面活性剂。

常用表面活性剂的分子是由长链的疏水（又叫亲油）基团和亲水的离子基团或极性基团组成的。这种由亲油基和亲水基两部分结合在一起的双亲结构组成的表面活性剂分子，常用表示。其中，表示亲油基，表示亲水基。

表面活性剂在水中浓度达到一定程度后，其分子中的亲油基相互靠在一起，以尽可能减少亲油基与水的接触面积。这种由若干表面活性剂分子相互靠在一起，把亲油基包围在内部而只把亲水基伸向水中所组成的分子聚合集体称之为胶束。由于胶束与水之间没有排斥作用，故表面活性剂分子以胶束状态存在时，可以稳定地分散在水中。

表面活性剂在溶液中开始形成胶束的浓度称为临界胶束浓度。在这个浓度范围内，表面活性剂的许多性质如表面张力、去污力等都显著发生变化。超过这个范围，随着表面活性剂浓度的增加，溶液的性质不再有显著的变化。因此，洗涤液中表面活性剂的浓度应保持在稍高于临界胶束浓度，才能既充分发挥表面活性剂的去污作用又不至于造成浪费。

二、表面活性剂的润湿渗透作用

被洗织物与洗涤液接触时，原来的固-气和液-气表面消失，取而代之以新的固-液表面。当溶液沿着纤维铺展时，会渗到纤维的空隙里并将空气驱赶出去。这种现象和过程叫做润湿和渗透。织物用洗涤剂中的表面活性剂即具有优异的帮助溶液快速润湿织物和渗透到纤维内部的功能。

润湿是洗涤去污的前奏曲。有利于润湿，才有可能使黏附在织物上的污垢脱离、去除。然而由于织物的表面积很大，而且织物由无数纤维组成，在纤维间形成毛细管结构，洗涤液要完全润湿织物并渗透到纤维内部，需要较长的时间。为此，织物水洗时常需要把待洗织物用水浸泡（预洗），必要时还应适量加入少量洗涤剂，以尽可能地润湿织物，从而为洗涤去污奠定良好的基础。

三、表面活性剂的乳化作用

本来是两种不相混溶的液体（如水和油），其中的一种以极微小的粒子（1—10μm）均匀地分散到另一种溶液中的作用，称作乳化。诚然，单靠油和水是得不到稳定的乳化液的。

我们知道，表面活性剂分子同时带有亲水基和亲油基。当其加入油水体系时，表面活性剂的亲油基插入油中，而亲水基一端则伸向水中，并在油滴表面定向排列，组成一层亲水性分子膜，从而减小了油滴之间的吸引力，使得油在较小的搅拌力作用下，既能在水中分散成油滴，同时防止油滴重新恢复油水分离的原状。

洗涤剂的乳化作用对于织物上油污的去除起着十分重要的作用。织物洗涤时，洗涤剂水溶液在织物表面铺展润湿，并渗入纤维内部，从而逐渐占据纤维表面把油污顶替下来。原来铺展在织物表面的油污逐渐蜷缩成油滴，在物理机械力作用下，油滴脱离织物进入水中并被洗涤剂乳化，稳定分散在洗涤液中。同时，被乳化、分散的油污也不易聚集到一起或重新沉积在织物上。

值得指出的是，仅靠洗涤剂的润湿和乳化作用并不足以有效地完成洗涤作用。

四、表面活性剂的分散悬浮作用

把固体污垢的极小微粒分散到洗涤液中形成悬浮分散体，是织物洗涤剂的另一重要洗涤作用。

洗涤剂的分散悬浮作用与乳化作用的原理基本相同。洗涤液中的表面活性剂在润湿固体污垢和织物表面的同时，也会吸附在污垢和织物表面。由于吸附层的形成，加大了污垢微粒与织物表面间的距离，从而削弱了它们分子间的引力。在机械外力作用下，颗粒状固体污垢很容易从织物上脱落下来，并稳定地分散悬浮在洗涤液中。所以，在去除固体污垢过程中，除了洗涤剂的作用外，机械力的作用是不能忽视的。

对于在水中带负电荷的污垢微粒，由于一般织物在水中也带负电荷，所以阴离子性洗涤剂吸附到污垢微粒和织物纤维表面之后，增加了它们表面所带的负电荷数量，从而加大了织物与污垢微粒之间的静电排斥力（同性相斥），这不仅有利于污垢微粒自被洗物中除去，同时与织物分离了的污垢粒子也不易再沉积到织物表面。正因为如此，洗涤剂中含有大量阴离子表面活性剂对去除固体微粒状污垢是大有益处的。

也有的污垢微粒在水中带正电荷。这些带正电荷的污垢与阴离子洗涤剂发生化学吸附，使污垢微粒的电荷降至零，同时表面呈现疏水性。此时，洗涤液中其他活性剂分子则会和已呈现疏水性污垢微粒发生憎水（或者叫亲油）吸附，在原来的吸附层上又吸附了第二层表面活性剂分子。第二层表面活性剂分子的亲水基朝向水中，使污垢微粒变成亲水性的，并带有负电荷。发生这种情况，对洗涤去污同样是有利的。

非离子表面活性剂可以吸附于一般带电的固体表面，使疏水的污垢粒子表面变得亲水，使织物的亲水性进一步得到增加，这无疑有利于润湿和洗涤去污。同时，由于污垢粒子周围形成较厚的水化吸附层，造成了防止污垢粒子互相接近的空间障碍，使污垢粒子不易发生再沉积，因而也可达到优异的洗涤效果。

五、表面活性剂的增溶作用

提高难溶或不溶性物溶解度的作用叫增溶。增溶作用的发生，和表面活性剂在溶液中形成胶束是分不开的，织物水洗过程中，由于洗涤介质是水，因而表面活性剂的亲水基均向外朝向水中，而亲油基则朝内聚拢在一起。洗涤液中当表面活性剂浓度较大，溶液中存在较多胶束时，不溶于水的物质因其性质各异而加溶于胶束的不同部位。因此，增溶现象可以理解成是表面活性剂胶束对亲油物质的溶解过程，是表面活性剂胶束的一种特殊作用。洗涤剂溶液中表面活性剂浓度越高，生成的胶束数量越多，增溶量越大。

增溶作用与乳化作用不同。乳化是两种互不相溶的液体，其中一种液体分散到另一种液体中后，得到的不稳定、不连续、不透明的多相体系。而增溶得到的增溶液是均匀、稳定、透明的单相体系。表面活性剂胶束对油污的增溶作用，实际上是使脱离了织物表面的油性污垢再溶解于洗涤液中，从而使油污不可能再沉积在织物上。

增溶作用的典型应用是水洗用去油渍剂。在表面活性剂的水溶液中，加入少量溶解油脂性污垢的溶剂，它被增溶于表面活性剂的胶束中。利用这种混合液，能有效地去除织物上的油脂性污垢。干洗助剂是表面活性剂增溶作用具体应用的另一个实例。干洗助剂中，在表面活性剂内加入少量协助去除织物上水性污垢的水，它被增溶于亲油基向外朝向溶剂、亲水基向内的表面活性剂逆胶束中，从而利于干洗过程中去除织物上的水溶性污垢。

六、表面活性剂的泡沫作用

“泡”是液体薄膜包围着的气体。气体分散在液体中的状态称为气泡。若液体容易成膜且不易破坏，则这种液体搅拌时就会产生许多泡沫。

表面活性剂的水溶液都有程度不同的发泡作用。泡沫对污垢有强烈的吸附作用，对防止污垢在织物上的再沉积有很大益处，因而于洗涤去污有一定的内在联系，然而泡沫过多也使织物不容易漂洗干净。习惯上人们常把起泡作用与洗涤作用混为一谈，认为洗涤剂质量的优劣取决于泡沫的多少，实际并非如此。经验和研究都已证明，洗涤作用与泡沫作用并无直接关系。尽管如此，泡沫在洗涤剂的使用过程中还是不可缺少的。

织物洗涤用表面活性剂中，阴离子表面活性剂如烷基苯磺酸钠（代号LAS）、脂肪醇聚氧乙烯醚硫酸钠（代号AES）等，特别是AES的发泡性能好，而非离子表面活性剂的发泡性能相比较差。

通过上述讨论我们可以知道，洗涤剂中的表面活性剂具有润湿、乳化、吸附、渗透、分散、悬浮、起泡、增溶等多种功能，织物的洗涤去污过程，即是上述功能综合作用的结果。除上述功能外，表面活性剂还具有柔软、抗静电、抗菌消毒等功能。

上述讨论，是针对以水作为洗涤介质的水洗过程中，表面活性剂的各种功能对洗涤去污的作用和影响。而以四氯乙烯等溶剂作为洗涤介质的干洗，其影响洗涤作用或者说影响洗涤质量的因素则与干洗所用的洗涤设备、洗涤工艺、溶剂质量、污垢性质、织物受污垢污染的程度、干洗助剂的选择应用等多种因素有关。在诸多影响干洗洗涤效果的因素中，尤以洗涤设备、溶剂质量、干洗工艺和干洗助剂的选择应用对织物干洗效果的影响最为明显。

The principle of detergent cleaning is complex, and the factors that affect the cleaning effect of detergent involve almost all aspects. Therefore, it is impossible for us to conduct a comprehensive and systematic analysis of the factors that affect the cleaning effect of detergent. Here, only the performance of surfactants closely related to the cleaning effect of detergents will be discussed.

1、 Surface tension and surfactants

According to the definition of physical chemistry, the parts within a system that have identical physical and chemical properties are called phases. The contact surface between phases is called the interface, and it is customary to refer to the interface between gas and solid, gas and liquid as the surface.

The molecules on the surface of an object and the molecules inside the phase are subjected to different forces. For example, inside the aqueous phase, the attraction of water molecules to surrounding water molecules is balanced, while at the interface between water and air, water molecules are much less attracted by air than by water. Therefore, the water molecules in the surface layer are in an unbalanced state of force, and they are subjected to a tensile force directed towards the interior of the phase, causing the surface to contract (such as water droplets on lotus leaves). The surface contraction force that acts on the surface and points towards the interior of the phase is called surface tension.

When substances with different properties are dissolved in water, the surface tension of water will change. The property of substances that can reduce the surface tension of water is called surface activity. In a solution, substances that can significantly reduce the surface tension of the solution even at low concentrations are called surfactants, and textile detergents contain various types of surfactants.

The molecules of commonly used surfactants are composed of long-chain hydrophobic (also known as oleophilic) groups and hydrophilic ionic or polar groups. This type of surfactant molecule is composed of a amphiphilic structure consisting of two parts: an oleophilic group and a hydrophilic group. It is commonly referred to as. Among them, represents lipophilic group and represents hydrophilic group.

After the concentration of surfactants in water reaches a certain level, the lipophilic groups in their molecules come together to minimize the contact area between the lipophilic groups and water. This type of molecular aggregation composed of several surfactant molecules that are placed together, enclosing the lipophilic group inside while only extending the hydrophilic group into the water, is called a micelle. Due to the lack of repulsion between micelles and water, surfactant molecules can be stably dispersed in water when they exist in the form of micelles.

The concentration at which surfactants begin to form micelles in solution is called the critical micelle concentration. Within this concentration range, many properties of surfactants, such as surface tension and cleaning power, undergo significant changes. Beyond this range, as the concentration of surfactants increases, the properties of the solution no longer undergo significant changes. Therefore, the concentration of surfactants in the washing solution should be kept slightly higher than the critical micelle concentration in order to fully utilize the cleaning effect of surfactants without causing waste.

2、 Wetting and Permeation of Surfactants

When the washed fabric comes into contact with the washing solution, the original solid gas and liquid gas surfaces disappear and are replaced by new solid liquid surfaces. When the solution spreads along the fibers, it will seep into the gaps of the fibers and drive out the air. This phenomenon and process are called wetting and permeation. Surfactants in fabric detergents have excellent functions in helping solutions quickly wet fabrics and penetrate into fibers.

Wetting is the prelude to washing and cleaning. Beneficial for wetting, it is possible to detach and remove dirt adhered to the fabric. However, due to the large surface area of the fabric and the countless fibers it is composed of, capillary structures are formed between the fibers. It takes a long time for the washing solution to completely wet the fabric and penetrate into the fibers. For this reason, fabric washing often requires soaking the fabric to be washed in water (pre washing), and if necessary, adding a small amount of detergent to wet the fabric as much as possible, laying a good foundation for washing and cleaning.

3、 Emulsification effect of surfactants

Originally, it was two immiscible liquids (such as water and oil), one of which dispersed uniformly in extremely small particles (1-10 μ m) into the other solution, known as emulsification. Indeed, stable emulsions cannot be obtained solely through oil and water.

We know that surfactant molecules carry both hydrophilic and oleophilic groups. When it is added to the oil-water system, the lipophilic group of the surfactant is inserted into the oil, while one end of the hydrophilic group extends into the water and is oriented and arranged on the surface of the oil droplets, forming a hydrophilic molecular film, thereby reducing the attraction between oil droplets. This allows the oil to disperse into oil droplets in the water under less stirring force, while preventing the oil droplets from returning to their original state of oil-water separation.

The emulsifying effect of detergents plays a crucial role in removing oil stains from fabrics. When washing fabrics, the detergent solution spreads and wets the surface of the fabric, and penetrates into the fibers, gradually occupying the surface of the fibers to replace the oil stains. The oil stains that originally spread on the surface of the fabric gradually curled up into oil droplets. Under the action of physical and mechanical forces, the oil droplets detached from the fabric and entered the water, where they were emulsified by the detergent and stably dispersed in the washing solution. Meanwhile, emulsified and dispersed oil stains are also less likely to gather together or re deposit on fabrics.

It is worth noting that relying solely on the wetting and emulsifying effects of detergents is not sufficient to effectively complete the washing process.

4、 Dispersion and Suspension of Surfactants

Dispersing tiny particles of solid dirt into the washing solution to form a suspended dispersion is another important washing function of fabric detergents.

The principle of dispersion and suspension of detergents is basically the same as that of emulsification. Surfactants in detergent not only wet solid dirt and fabric surfaces, but also adsorb onto them. Due to the formation of the adsorption layer, the distance between dirt particles and the fabric surface is increased, thereby weakening their intermolecular attraction. Under the action of mechanical external force, granular solid dirt is easily detached from the fabric and stably dispersed and suspended in the washing solution. So, in the process of removing solid dirt, besides the role of detergent, the effect of mechanical force cannot be ignored.

For dirt particles with negative charges in water, since most fabrics also carry negative charges in water, anionic detergents adsorb onto the surface of dirt particles and fabric fibers, increasing the amount of negative charges carried on their surfaces. This increases the electrostatic repulsion (repulsion) between the fabric and dirt particles, which not only facilitates the removal of dirt particles from the washed fabric, but also makes it difficult for dirt particles separated from the fabric to deposit on the fabric surface. Because of this, detergents containing a large amount of anionic surfactants are highly beneficial for removing solid particulate dirt.

Some dirt particles also carry positive charges in water. These positively charged dirt and anionic detergents undergo chemical adsorption, reducing the charge of the dirt particles to zero, while the surface exhibits hydrophobicity. At this point, other active agent molecules in the washing solution will undergo hydrophobic (or oleophilic) adsorption with the already hydrophobic dirt particles, and a second layer of surfactant molecules will be adsorbed on the original adsorption layer. The hydrophilic groups of the second layer of surfactant molecules face towards the water, making the dirt particles hydrophilic and negatively charged. This situation is also beneficial for washing and cleaning.

Non ionic surfactants can adsorb onto generally charged solid surfaces, making hydrophobic dirt particles hydrophilic and further increasing the hydrophilicity of fabrics, which undoubtedly benefits wetting and cleaning. At the same time, due to the formation of a thick hydration adsorption layer around the dirt particles, a spatial barrier is created to prevent the dirt particles from approaching each other, making it difficult for the dirt particles to re deposit, thus achieving excellent washing effect.

5、 Solubilization effect of surfactants

The effect of increasing the solubility of insoluble or poorly soluble substances is called solubilization. The occurrence of solubilization is inseparable from the formation of micelles by surfactants in solution. During fabric washing, due to the washing medium being water, the hydrophilic groups of surfactants tend to face outward towards the water, while the lipophilic groups tend to gather inward. When the concentration of surfactants in the washing solution is high and there are many micelles in the solution, substances that are insoluble in water will dissolve in different parts of the micelles due to their different properties. Therefore, the solubilization phenomenon can be understood as the dissolution process of lipophilic substances by surfactant micelles, which is a special function of surfactant micelles. The higher the concentration of surfactants in detergent solution, the more micelles are generated and the greater the solubilization capacity.

Solubilization is different from emulsification. Emulsification is an unstable, discontinuous, and opaque multiphase system obtained by dispersing one of two immiscible liquids into another. The solubilized solution obtained is a homogeneous, stable, and transparent single-phase system. The solubilization effect of surfactant micelles on oil stains is actually to dissolve the oily dirt that has detached from the fabric surface in the washing solution, making it impossible for the oil stains to deposit on the fabric again.

The typical application of solubilization is as an oil stain remover for water washing. In the aqueous solution of surfactants, a small amount of solvent that dissolves oily dirt is added, and it is solubilized in the micelles of surfactants. By using this mixture, it is possible to effectively remove oily dirt from fabrics. Dry cleaning agents are another example of the specific application of surfactant solubilization. In dry cleaning aids, a small amount of water is added to the surfactant to assist in removing water-based dirt from the fabric. It is solubilized in the surfactant reverse micelles with lipophilic groups facing outward towards the solvent and hydrophilic groups facing inward, which facilitates the removal of water-soluble dirt from the fabric during the dry cleaning process.

6、 Foam effect of surfactant

Bubble "is a gas surrounded by a liquid film. The state in which gas is dispersed in a liquid is called a bubble. If the liquid is easy to form film and is not easy to destroy, many foam will be produced when the liquid is stirred.

The aqueous solution of surfactants has varying degrees of foaming effect. Foam has a strong adsorption on dirt, which is very beneficial to prevent the re deposition of dirt on the fabric. Therefore, it has certain internal connection with washing and decontamination. However, too much foam also makes the fabric difficult to rinse clean. Traditionally, people often confuse foaming and washing, and think that the quality of detergent depends on the number of foam, which is not the case. Both experience and research have proved that the washing effect is not directly related to the foam effect. Nevertheless, foam is indispensable in the use of detergents.

Among the surfactants used for fabric washing, anionic surfactants such as sodium alkylbenzenesulfonate (LAS) and sodium fatty alcohol polyoxyethylene ether sulfate (AES) have good foaming performance, while nonionic surfactants have relatively poor foaming performance.

Through the above discussion, we can know that surfactants in detergents have multiple functions such as wetting, emulsification, adsorption, permeation, dispersion, suspension, foaming, and solubilization. The washing and stain removal process of fabrics is the result of the comprehensive effects of these functions. In addition to the above functions, surfactants also have functions such as softness, anti-static, antibacterial and disinfection.

The above discussion is aimed at the various functions and effects of surfactants on washing and stain removal during the water washing process using water as the washing medium. The factors that affect the washing effect or washing quality of dry cleaning using solvents such as tetrachloroethylene as the washing medium are related to various factors such as the washing equipment used, washing process, solvent quality, dirt properties, degree of fabric contamination by dirt, and the selection and application of dry cleaning aids. Among the many factors that affect the dry cleaning effect, the selection and application of washing equipment, solvent quality, dry cleaning process, and dry cleaning agents have the most significant impact on the dry cleaning effect of fabrics.