Rheology: Beyond Simple Viscosity
Physics
Viscosity is merely resistance to flow. Yield stress is the minimum force required to initiate flow. If you want to suspend beads or bubbles, you need yield stress, not just high viscosity.
Core Analysis
Formulation and regulation are intrinsically linked. An ingredient that provides excellent yield stress might be restricted to 0.1% in the final formula due to toxicological concerns. Always cross-reference functional desires with regulatory constraints.
| Parameter | Critical Value | Impact |
|---|---|---|
| Temperature | >45°C | Accelerates degradation kinetics |
| pH Range | 4.5 - 5.5 | Optimal for skin microbiome & organic acids |
| Water Activity (aw) | < 0.6 | Microbes cannot proliferate |
Frequently Asked Questions
Why does my lotion thin out when pumped?
Because it is shear-thinning (pseudoplastic). The shear force applied by the pump temporarily aligns the polymer networks, reducing viscosity.
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