Contents

Surface energy components

Pronunciation: /ˈsɜːrfɪs ˈɛnərdʒi kəmˈpoʊnənts/

Surface energy components are the parts of a surface free energy or surface tension that come from different kinds of molecular interaction. The usual split is into a dispersive part and a polar part, or into Lifshitz-van der Waals, acid and base parts.

Also called

Surface tension components Dispersive and polar components Disperse and polar parts

Related terms

Surface free energy models Equation of State (SFE model) Fowkes method

Topics

Surface energy Dispersive component Polar component
Book a 15 minute demo Read the surface energy measurement guide

At a glance

What the components are, and why the split matters more than the total.

What it is

Every molecule attracts its neighbours through dispersion forces. Some also attract through dipoles and hydrogen bonds. Components put a number on each kind.

  • Dispersive (γᵈ): London dispersion forces, present in all materials
  • Polar (γᵖ): dipole and hydrogen bonding forces combined
  • Acid γ⁺ and base γ⁻: the polar part split by electron acceptor and donor

Why it matters

Two surfaces can share a total of 40 mJ/m² and still bond very differently. Adhesion is strongest when the components of adhesive and substrate match, polar with polar and dispersive with dispersive. Plasma or corona treatment usually raises the polar part while the dispersive part barely moves, which is why tracking components catches changes a total can miss.

Worked example

Our shared hypothetical polymer, analysed with OWRK using water at 75° and diiodomethane at 50° (20 °C):

  • γSᵈ = 34.3 mJ/m², γSᵖ = 6.7 mJ/m²
  • γS = 34.3 + 6.7 = 41.0 mJ/m²
  • Polar fraction = 6.7 / 41.0 = 0.16, so about 16% polar

Track the polar fraction as well as the total when you compare treatments. The surface free energy calculator reports both parts from your own angles.

How it is measured

Components of a solid come from contact angles of two or more liquids whose own components are known, put through a model such as OWRK or van Oss-Chaudhury-Good. The surface energy measurement guide covers liquid choice and the procedure.

Expert view

“Droplet adhesion is three-dimensional. Two side-view angles give an estimate; the whole story is how the angle and the contact line vary all the way around the drop.”

Dr. Alidad Amirfazli, Co-founder and Scientific Advisor, Droplet Lab

What the terms mean

Three ways of splitting the same surface energy.

Dispersive and polar (Fowkes, OWRK)

γ = γᵈ + γᵖ. Two numbers per material, found with one nonpolar and one polar liquid. The most widely reported split.

Lifshitz-van der Waals and acid base (van Oss-Chaudhury-Good)

γ = γᴸᵂ + 2√(γ⁺ γ⁻). Three numbers per material, found with three liquids. Shows whether a surface donates or accepts electrons.

No components (Equation of State)

Only the total γ is used. Neumann and coworkers argue that the split is not needed for most low energy solids.

Probe liquid components used across our model pages, 20 °C: water 72.8 = 21.8 dispersive + 51.0 polar mN/m; diiodomethane 50.8 = 50.8 dispersive + 0 polar mN/m.

γᵈ Dispersive component, mJ/m² (mN/m for liquids)
γᵖ Polar component, mJ/m²
γᴸᵂ Lifshitz-van der Waals component, mJ/m²
γ⁺, γ⁻ Electron acceptor (acid) and donor (base) parameters, mJ/m²

Key equations

How components add up and how they combine across an interface.

Equation: γ = γᵈ + γᵖ

Variable legend:

  • γ: total surface energy or surface tension (mJ/m² or mN/m)
  • γᵈ, γᵖ: dispersive and polar components

Interpretation: The total is the sum of its parts. For water, 21.8 + 51.0 = 72.8 mN/m.

When to use: Use it to report a result in a way that shows which kind of interaction dominates.

Assumptions:

  • The interactions are independent and simply add

Common mistakes:

  • Reporting only the total, which hides treatment effects

Equation: Wa = 2 [√(γSᵈ γLᵈ) + √(γSᵖ γLᵖ)]

Variable legend:

  • Wa: work of adhesion between solid and liquid (mJ/m²)
  • S and L subscripts: solid and liquid

Interpretation: Like pairs with like. A polar liquid gains nothing from a solid with no polar component, however large its dispersive part.

When to use: Use it to see why matching components improves wetting and adhesion.

Assumptions:

  • Geometric mean combining rule, as in Fowkes and OWRK

Common mistakes:

  • Mixing component values for liquids from different reference tables

Equation: γᴬᴮ = 2 √(γ⁺ γ⁻)

Variable legend:

  • γᴬᴮ: acid base component (mJ/m²)
  • Water by convention: γ⁺ = γ⁻ = 25.5, so γᴬᴮ = 51.0 mN/m

Interpretation: A surface needs both acid and base character to have a sizeable acid base component of its own.

When to use: Use it when the van Oss-Chaudhury-Good model is chosen.

Assumptions:

  • Acid and base interactions combine crosswise

Common mistakes:

  • Equating γ⁻ alone with the polar component

How to read it

What component values tell you about a surface.

Components are model results, not direct measurements, so they depend on the liquid set and the reference values used. Keep both fixed when you compare samples. Our note on reproducible surface energy calculation from contact angles explains which choices to lock down, and typical values sit in our surface free energy of common polymers and substrates dataset.

Reading component values

If you see It usually means Check next
Polar part close to zero A nonpolar surface such as PTFE, polyethylene or polypropylene Whether a treatment step was skipped
Polar part rises after plasma, corona or flame Polar groups were added to the outer layer How fast it decays over hours or days
Dispersive part shifts a lot Contamination or a different material at the surface Cleaning, handling and the diiodomethane angle
Large γ⁻ but small γ⁺ A basic, electron donating surface Whether that matches the expected chemistry

Common misconceptions

Where surface energy components are most often misread.

Components are fixed material properties

They depend on the model and the liquid reference values. Water has been assigned dispersive values from about 22 to 26 mN/m or more in different tables, which shifts every result. Standards such as ISO 19403-2 for paints and varnishes ask you to report the evaluation method and liquid data.

A higher total always means better adhesion

Matching components matters more. A water based coating needs a polar part on the substrate; a total built mostly from dispersive forces may still fail. On coated surfaces, as in thin film and nanocoating surface characterization, track the polar part separately.

Related terms

Where surface energy components fit among related ideas.

Broader term

  • Surface free energy (SFE)
  • Surface free energy models

Models that use components

  • Fowkes method
  • OWRK method
  • van Oss-Chaudhury-Good method

Related terms

  • Equation of State (SFE model)
  • Work of adhesion
  • Surface tension

FAQ

Short answers to the questions people ask most about surface energy components.

What is the difference between the dispersive and polar component?

The dispersive component comes from London dispersion forces, which act between all molecules. The polar component comes from permanent dipoles and hydrogen bonds, which only some materials have. Water is about 30% dispersive and 70% polar, while diiodomethane and most hydrocarbons are essentially all dispersive.

Why does plasma treatment increase the polar component?

Plasma, corona and flame treatments add oxygen containing groups such as hydroxyl and carbonyl to the outer molecular layer. These groups form dipole and hydrogen bonding interactions, so the polar component rises. The dispersive part changes little. Over time the polar part often falls again as the surface reorganises or picks up contamination.

What polar fraction is good for printing or bonding?

It depends on the ink or adhesive, because components should match. As a rough guide, surfaces with almost no polar component, such as untreated polyolefins, wet poorly with water based products. Set your own limit by comparing component values with real print or peel test results on your materials.

References

Primary sources and further reading.

1. Fowkes, F. M. (1964). Attractive forces at interfaces. Industrial and Engineering Chemistry, 56(12), 40 to 52. https://doi.org/10.1021/ie50660a008
2. Owens, D. K., and Wendt, R. C. (1969). Estimation of the surface free energy of polymers. Journal of Applied Polymer Science, 13(8), 1741 to 1747. https://doi.org/10.1002/app.1969.070130815
3. van Oss, C. J., Chaudhury, M. K., and Good, R. J. (1988). Interfacial Lifshitz-van der Waals and polar interactions in macroscopic systems. Chemical Reviews, 88(6), 927 to 941. https://doi.org/10.1021/cr00088a006
4. Surface energy measurement guide
5. Surface free energy models
6. Fowkes method
7. Equation of State (SFE model)