Why surfactants reduce surface tension

The basic condition for a molecule that can be used as a surfactant is to have hydrophilic and hydrophobic groups. When the surfactant is prepared into a solution, the active agent molecules on its surface tend to orient the hydrophilic groups towards the aqueous phase, and the hydrophobic groups towards the air phase, that is, the subject said that they are neatly arranged on the surface of the water. As a result of this arrangement, a layer of hydrophobic groups is distributed on the surface of the water.

The hydrophobic group means that its surface energy is relatively low, so the aqueous solution of the surfactant has a low surface tension.

Surfactants exist in two forms in water, one is adsorbed on the surface of the solution, and the other is self-assembled into micelles by hydrophobic action in water. The surface tension is reduced because it is adsorbed on the surface of the solution. The surface tension of the solution has a direct relationship with the surface adsorption capacity, the process of surfactant adsorption at the gas-liquid interface is actually the process of the water molecules in the gas-liquid interface being gradually replaced by the lipophilic chain segment of the surfactant, and the process of changing the chemical composition of the solution surface, when the concentration of surfactant increases, the lipophilic groups at the gas-liquid interface increase, so the surface tension of the aqueous solution decreases with the increase of the concentration of surfactant.

The reason why the surface tension of the aqueous solution of the mature Gemini surfactant is low is that the spacing between the twin heads is smaller, which is conducive to the surfactant to be arranged more closely on the surface of the solution and make it show excellent surface activity.

Surfactant.

It has lipophilic and hydrophilic groups, and after being dissolved in water, the hydrophilic group is affected by water molecules.

Attraction, even enough to pull a short non-polar hydrocarbon chain into the water, while the lipophilic group is repelled by the water molecules. In order to overcome this.

Surfactants have lipophilic and hydrophilic groups, and when dissolved in water, the hydrophilic group is attracted by water molecules, even enough to pull a short non-polar hydrocarbon chain into the water, and the lipophilic group is repelled by the water molecules. In order to overcome this unstable state, the only way to overcome this unstable state is to occupy the surface of the dissolved air front fluid, and extend the lipophilic to the gas phase and the hydrophilic to the aqueous phase. Directional single-molecule adsorption is formed, which reduces the tension at the gas-water and oil-water interfaces and exhibits surface activity.

Then I'll go ahead and elaborate:

First of all, at the liquid-solid interface, the centripetal contraction force of the molecules on the surface of the liquid is generated, which is called the resultant force of the surface tension, in order to reduce this force, it is necessary to form or add a force in the opposite direction to counter it, and the surfactant is hydrophilic at one end and hydrophobic at the other end, so in addition to the internal tension, it also produces the opposite repulsion force to the hydrophobic group, and the existence of this force can naturally reduce the surface tension. I don't know if this explanation is acceptable. Please advise, 2, for the solution, the solute will affect the surface tension of the solution, and the Gibbs derivation relationship is as follows:

（dσ/dc）t * c/rt

The first half of the equation is the isothermal derivative. It's not good to show it here. where is the surface excess, is the surface tension, t is the thermodynamic temperature, r is the gas Changshu, and c is the solution concentration.

When (ddc) >0, <0, such species are defined as non-surfactants; Otherwise, it is called surfactant. It is called a surfactant because it reduces the surface tension, which is the definition...0. Why does surfactant cause a significant decrease in surface tension?

Why surfactants make the surface tension significantly decrease, the parental structure goes without saying.

Downstairs is not my question, why the formation of directional single molecule adsorption, can make the tension of gas-water and oil-water, the interface decrease?

And that definition, it's just a chicken-and-egg thing.

The direction of the surface tension is tangent to the liquid surface, not centripetal. Therefore, the sentence "Therefore, in addition to the surface tension to the interior, the fighting limb also produces the opposite repulsion force to the hydrophobic group" is not true. Moreover, why does the directional arrangement of amphiphilic molecules generate force?

Where does the force come from?

Okay, understood. Surface tension refers to the force between the liquid and the gas, which can cause the liquid to form a thin and powerful film on the surface, which is the scene we often see when washing rice and vegetables. The purpose of reducing the surface tension of Bohu is to make better use of the properties of liquids in industrial applications and daily life, so that they can wet the surface of other materials, provide conditions for chemical reactions, crystal growth, etc.

Actives are a class of substances that can reduce surface tension.

First of all, anionic surfactants are active agents that can reduce surface tension. For example, sodium lauryl sulfate (SDS) is an anionic surfactant that allows water to better wet solid surfaces. In addition, SDS can also provide the necessary ions for electrophoresis and is commonly used in protein electrophoresis.

In addition, sodium dodecylbenzene sulfonate (SDBS) is another anionic surfactant, which is also often used in detergents, emulsifiers, drug controlled release, etc.

Secondly, cationic surfactants are also a common type of active agent that can reduce surface tension by interacting with anionic surface molecules. The more common cationic surfactants include trimethyl hexametaphosphate (CTAB) and cetyl trimethylammonium bromide (CTAB). CTAB is commonly used in the synthesis of nanoparticles, colloidal stabilization and other fields, while TDTMA is often used in sewage treatment, purification of oily wastewater, dispersion of emulsions, etc.

In addition, there are non-ionic surfactants, which are characterized by their difficulty in interacting with ionic surface molecules and are commonly used in additives such as dyes, colloids, and lubricants. For example, dodecyl ethoxylates (BRIj 35) and dodecyl ethoxylates (Tween 20) are common nonionic surfactants, which are widely used in ultrasonic cracking, crystal growth, and controlled drug release.

In summary, there are many types of active agents to reduce surface tension, including anionic, cationic, and nonionic surfactants. They have different advantages and uses in different fields and applications, and it is necessary to select the appropriate active agent for use according to the actual needs. <>

Surfactants are a class of substances that can only exhibit specific properties in solution systems. When the concentration of the solution does not reach the critical capsule concentration (CMC), there are two states of surfactant molecules, some surfactant molecules are adsorbed and arranged in a directional manner at the liquid interface, the hydrophilic group points to the aqueous solution, and the lipophilic group points to the air outside the liquid surface, the reason is that the force is different on the liquid surface of the molecule or inside the liquid, if the molecule is in the solution, the forces on all aspects are different, among which there is attraction and cohesion, and it is different at the liquid surface, the surfactant molecule is subject to the gravitational force inside the liquid, That is, the gravitational force of water molecules to the hydrophilic group and the gravitational force of the air are different, and the former is much larger than the latter, and there is only repulsion and no gravitational force between the lipophilic group and the water molecule at the same time, so the molecules are pushed to the water surface and arranged on the liquid surface, when the number of molecules arranged is large enough, a single molecular film will be formed on the surface of the liquid, this phenomenon is the result of directional adsorption, and most of the liquid-air interface is replaced by the surfactant molecule air interface, so that when creating a new interface per unit area, it is necessary to form less energy than the water-air interface, This is why surfactants reduce surface tension or interfacial tension.

Obviously, the more the same surfactant molecules accumulate at the liquid surface, the higher the concentration, the more the surface tension decreases, until the entire liquid surface is completely covered by the surfactant molecules, and the surface tension is reduced to a minimum.

Due to the different chemical structure of surfactants, the minimum value that can be achieved to reduce the surface tension effect will not be the same, in two immiscible liquids, such as oil and water liquid interface, the surfactant will occur more than the directional adsorption phenomenon, and the hydrophilic group and lipophilic group of the surfactant have achieved a good directional adsorption effect respectively, the more significant the directional adsorption effect is at this time, the effect of reducing tension or interfacial tension is more likely to be observed, for some additives, such as, wetting agent, penetrantIt is very important to reduce the surface tension of the surface tension. Because it determines the wetting, osmotic and developing effects of the preparation on the agent when used.

It is more important to reduce the interfacial tension of other additives such as dispersants, emulsifiers, and relievable solubilizers, because the smaller the interfacial tension, the easier it is for the whole system to be dispersed and emulsified, and thus the stronger the ability to automatically form a suspension or emulsifier. Different surfactants play a very important role in formulation screening, which directly determines the success of formulation screening of formulations.

1. Surfactants are a class of compounds with surface reactive properties. After being dissolved in liquids (especially water), it can significantly reduce the surface tension or interfacial tension of the solution, and can improve the solubilization, emulsification, dispersion, penetration, wetting, foaming and washing ability of the solution. Xinweishun focuses on the research and development of environmentally friendly surfactants, which are mainly used to make synthetic detergents, emulsifiers, demulsifiers, penetrants, foaming agents, defoamers, wetting agents, dispersing agents, flotation agents, softeners, antistatic agents, waterproofing agents and other additives.

2. Widely used in textile, food, medicine, pesticides, cosmetics, construction, mining and other industrial fields. Surfactants have a common characteristic, that is, the presence of both hydrophilic and lipophilic groups (also known as hydrophobic groups) in the molecule. Hydrophilic groups are usually groups that are easily ionized after being dissolved in water, such as carboxylates, sulfonates, sulfates, etc., as well as hydroxyl or polyoxyvinyl groups that are not ionized in water.

The lipophilic group can attract and dissolve with oils, and is usually a hydrocarbon group with a long carbon chain composed of petroleum or oil, which can be aliphatic hydrocarbons or aromatic hydrocarbons. If the hydrophilic base has strong performance, it will be soluble in water, and conversely, if the lipophilic base has strong performance, it will be soluble in oil.

3. Change the interface properties between the two-phase substances, which can play the functions of wetting, penetration, cleaning, dispersion, emulsification, solubilization, foaming, defoaming, etc. Surfactants can be divided into anionic, cationic, zwitterionic and nonionic surfactants according to their structure. Anionic surfactants can be dissociated into anions and cations in water, and anions play a role in reducing surface tension.

1. Wetting and osmotic effect: The reason why surfactant has wetting and osmotic effect is because it can significantly reduce the surface tension of water.

2. Emulsification: Two immiscible liquids, one of which is dispersed in the other phase in the form of droplets, this effect is called emulsification. Emulsification tends not to occur spontaneously or persistently.

3. Dispersion: The system formed by evenly dispersing insoluble solid substances in the liquid Bisun head body with tiny particles is called dispersion or suspension, which is called dispersion, and the surfactant that can make the dispersion occur smoothly is called dispersant.

4. Foaming: The state of gas dispersed in the liquid is called bubbles, the dispersion system formed by a large number of bubbles gathered together is called foam, and the ability to promote the formation of foam is called foaming. Foams are similar to emulsions and suspensions, except that the inner phase is a gas instead of a liquid and a solid.