nonDLVO

Non-DLVO refers to interparticle forces that are not captured by classical DLVO theory, which combines electrostatic double-layer repulsion and van der Waals attraction to describe colloidal stability. In many real systems, additional short- and medium-range forces modify interaction profiles and stability. These non-DLVO forces arise from solvent structure, molecular adsorbates, and entropic effects, and they can be either repulsive or attractive.

Key components include hydration or solvation forces, which originate from structured water layers on surfaces and decay over a fraction of a nanometer to a few nanometers; hydrophobic forces, which can promote attraction between nonpolar surfaces in water; and steric forces from adsorbed polymers or surfactants that create a soft repulsive layer. Depletion forces, caused by non-adsorbing polymers in the solution, can also induce attraction at small separations. Polymer bridging, where the same polymer adsorbs to two surfaces, can lead to attraction. Specific ion effects (Hofmeister series) alter surface charge and solvent structure, producing ion-specific non-DLVO contributions. Additional forces include solvent- or ion-induced structural forces and image-charge related interactions.

Non-DLVO interactions are especially important for proteins, clays, emulsions, and nanoparticle suspensions, particularly at short separations (sub-nanometer to several nanometers) and in concentrated or high-ionic-strength environments. Experimental techniques such as the surface force apparatus, atomic force microscopy with colloid probes, and force measurements on thin films reveal these contributions.

Understanding non-DLVO forces is essential for accurately predicting colloidal stability, adhesion, wetting, and rheology in complex fluids, where DLVO alone fails to describe observed behavior.