𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : 𝐒𝐮𝐫𝐟𝐚𝐜𝐞 𝐒𝐜𝐢𝐞𝐧𝐜𝐞 𝐟𝐨𝐫 𝐅𝐨𝐫𝐦𝐮𝐥𝐚𝐭𝐨𝐫𝐬

𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

𝐒𝐮𝐫𝐟𝐚𝐜𝐞 𝐒𝐜𝐢𝐞𝐧𝐜𝐞 𝐟𝐨𝐫 𝐅𝐨𝐫𝐦𝐮𝐥𝐚𝐭𝐨𝐫𝐬

Wetting & Contact Angle — From Surface Tension to Real Performance

In real applications, everything comes down to one simple question:

Does the liquid spread… or does it bead?

When a liquid touches a surface:

• It can spread and form a uniform film

• Or remain as a droplet with limited contact

This behavior is described by:

𝐂𝐨𝐧𝐭𝐚𝐜𝐭 𝐀𝐧𝐠𝐥𝐞 (θ)

✔ 𝐋𝐨𝐰 𝐚𝐧𝐠𝐥𝐞 → 𝐠𝐨𝐨𝐝 𝐰𝐞𝐭𝐭𝐢𝐧𝐠 → 𝐬𝐩𝐫𝐞𝐚𝐝𝐢𝐧𝐠

 ✔ 𝐇𝐢𝐠𝐡 𝐚𝐧𝐠𝐥𝐞 → 𝐩𝐨𝐨𝐫 𝐰𝐞𝐭𝐭𝐢𝐧𝐠 → 𝐛𝐞𝐚𝐝𝐢𝐧𝐠

What controls this?

It’s a balance between:

• Liquid surface tension (γLV)

• Surface energy of the substrate (γSV)

In simple terms: if γLV < γSV, the liquid spreads; if γLV > γSV, it beads.

What’s really happening

The system always tends to minimize energy:

If spreading reduces energy → it spreads

If not → it minimizes contact (forms a droplet)

From a thermodynamic perspective, wetting is favored when the total interfacial energy of the system decreases, which depends on the balance between liquid–vapor, solid–vapor, and solid–liquid interactions.

Why this matters in formulation

A formulation may show a “good” surface tension value, but if it does not match the surface energy of the substrate, wetting will be limited—leading to defects such as cratering, dewetting, poor adhesion, and non-uniform film formation.

Dynamic behavior (critical in real processes)

Wetting is not only determined by equilibrium conditions, but also by how fast the system responds.

In real applications, newly created interfaces require surfactant molecules to:

• 𝐝𝐢𝐟𝐟𝐮𝐬𝐞 𝐟𝐫𝐨𝐦 𝐭𝐡𝐞 𝐛𝐮𝐥𝐤

 • 𝐚𝐝𝐬𝐨𝐫𝐛 𝐚𝐭 𝐭𝐡𝐞 𝐢𝐧𝐭𝐞𝐫𝐟𝐚𝐜𝐞

 • 𝐨𝐫𝐢𝐞𝐧𝐭 𝐩𝐫𝐨𝐩𝐞𝐫𝐥𝐲

These processes are governed by molecular mobility, diffusion rates, and interfacial kinetics.

If they are too slow, even a well-designed formulation may fail to wet the surface under dynamic conditions.

🔬 Role of additives

Surface additives help by:

✔ 𝐥𝐨𝐰𝐞𝐫𝐢𝐧𝐠 𝐬𝐮𝐫𝐟𝐚𝐜𝐞 𝐭𝐞𝐧𝐬𝐢𝐨𝐧 (γ𝐋𝐕)

 ✔ 𝐢𝐦𝐩𝐫𝐨𝐯𝐢𝐧𝐠 𝐬𝐩𝐫𝐞𝐚𝐝𝐢𝐧𝐠

 ✔ 𝐚𝐝𝐚𝐩𝐭𝐢𝐧𝐠 𝐭𝐡𝐞 𝐥𝐢𝐪𝐮𝐢𝐝 𝐭𝐨 𝐥𝐨𝐰-𝐞𝐧𝐞𝐫𝐠𝐲 𝐬𝐮𝐛𝐬𝐭𝐫𝐚𝐭𝐞𝐬

Their performance depends not only on their ability to reduce equilibrium surface tension, but also on their adsorption kinetics and molecular architecture at the interface.

🔥 Key insight

Wetting is where surface tension becomes real performance — it is not just about lowering surface tension, but about matching the liquid to the surface to ensure proper spreading and interfacial interaction.

source : Ernesto Muñiz Mata

#SurfaceScience #CoatingsTechnology #FormulationChemistry #Surfactants #InterfacialScience