Enthalpy of mixing

The enthalpy of mixing corresponds to the amount of heat released or absorbed when two substances—liquids, solids, or polymers—are combined. This thermodynamic parameter allows for the evaluation of compatibility between components and the anticipation of interaction phenomena (attraction, repulsion, dissolution, molecular association).
In formulation, it is an essential indicator for optimizing the stability , miscibility , and performance of finished products , whether food, cosmetic, pharmaceutical, or polymeric.

Principle and analytical method

The analysis of the enthalpy of mixing is performed by isothermal titration calorimetry (ITC) , a high-precision technique that directly measures the heat exchanges associated with the mixing reaction.
The principle is based on:

• the progressive injection of one component (solute or polymer) into another (solvent or matrix) at constant temperature;
• real-time detection of heat emitted or absorbed;
• the integration of these signals to determine the molar enthalpy of mixing (ΔHmix).

Thermal conductivity analysis (TCA) allows for the characterization of the strength of molecular interactions (hydrogen bonds, van der Waals forces, electrostatics) and the identification of optimal formulation conditions.
For further studies, explore differential scanning calorimetry (DSC) , useful for determining thermal transitions and polymer compatibility, or thermogravimetric analysis (TGA) for evaluating the thermal stability of materials.

Industrial applications

The study of enthalpy of mixing applies to many fields:

• Cosmetics industry : evaluation of the compatibility between emulsifiers, oils, polymers or hydrophilic/lipophilic actives in emulsions and gels.
• Food and nutraceuticals : prediction of the stability of liquid or powder formulations, measurement of the interaction between proteins, polysaccharides and lipids.
• Materials and polymers : characterization of mixtures of polymers, solvents or plasticizers to optimize miscibility and prevent phase separations.
• Packaging and the environment : study of the interactions between packaging materials and the products contained, or of organic mixtures in environmental environments.
• Animal nutrition and plants : assessment of the compatibility of additives and excipients in complex food formulations.

This analysis is a valuable tool for formulators, as it allows them to adjust the proportions of ingredients, prevent physical instabilities, and optimize the texture or durability of products.

Analytical interest and related analyses

The enthalpy of mixing is often combined with other thermal and physicochemical studies for a complete understanding of the interactions:

• Dynamic mechanical analysis (DMA) to evaluate the viscoelastic properties of materials;
• Measurement of interfacial tension to characterize adhesion or wetting phenomena;
• Analysis of the rheology of powders to study the flow and mixing behavior of granular products.

These complementary analyses allow a multidimensional approach to complex formulations and facilitate the development of stable and high-performance products.

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