Formulation Analysis: 4 Factors Affecting Stability
A formulation is loosely defined as the structured mix of ingredients in a finished product. Typical components include a continuous phase, a dispersed phase, stabilizing agents, and various additives which combine to perform a virtually limitless range of functions. However, the sheer versatility offered by formulation engineering is also associated with numerous challenges. The complex chemistry underlying the process meant that formulations were confined to biochemical and life sciences applications for decades: agrochemicals, complex mechanical lubricants, pharmaceuticals, etc. Yet innovations in formulation analysis have opened new avenues for commercial markets to exploit the benefits of finely-tailored emulsions and colloidal systems.
What is Formulation Analysis?
Formulation analysis is a circular process concerned with research and development (R&D), quality assurance and control (QA/QC), and optimization of colloids intended for use in any number of downstream applications. It is carried out concurrently throughout the development cycle of most colloidal systems to determine vital properties that may be indicative of success, including:
- The affinity between distinct components; i.e. the dispersibility of solid particles in a continuous solvent.
- Dispensability; i.e. how well the formulation works with different applicators.
- Shelf life and stability in sub-optimal conditions.
Each of these essential properties is underlined by one crucial factor: colloidal stability.
Formulation analysis typically evaluates colloidal stability by measuring chemically- or physically-driven migration phenomena in emulsions. If the distinct phases remain in a state of dispersed equilibrium for a predicted length of time, the formulation can be considered suitably stable and fit for purpose. However, instability of colloidal systems is practically unavoidable given the broad range of destabilizing mechanisms that can impact their thermodynamic properties in the short- and long-term.
What Affects Formulation Stability?
Colloidal systems typically display at least one form of particle migration or size change as they age. With the increasing complexity of commercial formulations, it is not uncommon to observe several instability phenomena under different test parameters: agitation, temperature, etc. This dynamic interplay of factors makes it impossible to eliminate instability mechanics from formulations which will be subjected to different thermomechanical conditions during storage, transport, and eventual application.
Formulation analysis must contend with countless factors affecting stability, but these are four of the most common phenomena that chemists must screen for to ensure the success of commercial products:
- Flocculation—Aggregation: Inter-molecular interactions between the dispersed phase within the continuous phase can cause particles to cluster together and form heterogeneous assemblies. Formulation analysis will often prescribe additional additives to overcome the Van der Waals or electrostatic forces encouraging flocculation.
- Coalescence: Similar to aggregation, coalescence is a form of phase separation where dispersed media comes together to form a distinct mass. Unlike flocculation, where particles remain distinct and may be re-dispersed via an application of force, coalescence is often irreversible.
- Creaming: This occurs when a formulation separates into two or more distinct emulsions, with one (the cream) containing a higher disperse phase content than the other(s).
- Sedimentation: Depends on the buoyancy of the dispersed phase and can be used to describe any form of instability mechanic where particles separate from the continuous phase and sink to the bottom.
Formulation Analysis with Particulate Systems
Particulate Systems has extensive experience in formulation analysis for complex chemistries and consumer goods alike. We utilize the industry-leading Turbiscan® system to optically-interrogate samples via static multiple light scattering, acquiring accelerated aging tests of emulsions under simulated use, storage, or outlying conditions. Unlike alternative tools used in formulation analysis, the Turbiscan® applies no mechanical stress to samples. This ensures that stability indices are indicative of the emulsion in its native state, providing the most accurate method of formulation analysis currently possible.Posted on