Cosmetic Rheology & Non-Newtonian Fluid Dynamics: Shear-Thinning & Yield Stress (Engineering Review 2009)
The flow behavior of a cosmetic product dictates shelf-life stability, pigment suspension, and sensory payoff upon skin application.
Engineering Mechanism & Kinetic Flowchart
Yield Stress (τ₀) and Gravitational Stability
Yield stress is the minimum finite force required to initiate flow. In mineral sunscreens, foundation creams, and clay emulsions, an engineered yield stress prevents dispersed pigments and oil droplets from sedimenting under gravity (Stokes' Law), ensuring physical integrity across a 3-year shelf life without phase separation.
Thixotropy and Hysteresis Loop Analysis
Thixotropic fluids undergo time-dependent, reversible breakdown under constant shear, followed by progressive structural recovery once agitation ceases. In rotational rheometry, the area between ascending and descending shear curves (the hysteresis loop) quantifies the breakdown kinetics, preventing post-application dripping while guaranteeing a velvety after-feel.
Process Engineering & Scale-Up Implications
Measuring elastic (G') and loss (G'') moduli using cone-and-plate oscillatory rheometers allows formulation chemists to predict viscoelastic gel transitions, optimizing rotor-stator homogenizer speeds during pilot plant scale-up.
Pharmacist-Biochemist · Specialist in Cosmetic Engineering & Dermato-Pharmacology · Published on July 06, 2009 at 18:30
O conteúdo deste artigo possui caráter exclusivamente informativo, educativo e de divulgação científica, baseado em literatura farmacêutica revisada por pares e diretrizes de Farmácia Baseada em Evidências. As informações não constituem recomendação terapêutica, diagnóstico clínico ou prescrição farmacêutica individualizada. Não substitui a consulta com um médico ou farmacêutico habilitado. Consulte sempre um profissional de saúde antes de iniciar, alterar ou descontinuar qualquer tratamento.
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