Effect of D-Mannitol on the Microstructure and Rheology of Non-Aqueous Carbopol Microgels.

Simona Migliozzi,Luca Mazzei,Panagiota Angeli

doi:10.3390/ma14071782

Abstract

D-mannitol is a common polyol that is used as additive in pharmaceutical and personal care product formulations. We investigated its effect on the microstructure and rheology of novel non-aqueous Carbopol dispersions employing traditional and time-resolved rheological analysis. We considered two types of sample, (i) fresh (i.e., mannitol completely dissolved in solution) and aged (i.e., visible in crystalline form). The analysis of the intracycle rheological transitions that were observed for different samples revealed that, when completely dissolved in solution, mannitol does not alter the rheological behaviour of the Carbopol dispersions. This highlights that the chemical similarity of the additive with the molecules of the surrounding solvent allows preserving the swollen dimension and interparticle interactions of the Carbopol molecules. Conversely, when crystals are present, a hierarchical structure forms, consisting of a small dispersed phase (Carbopol) agglomerated around a big dispersed phase (crystals). In keeping with this microstructural picture, as the concentration of Carbopol reduces, the local dynamics of the crystals gradually start to control the integrity of the microstructure. Rheologically, this results in a higher elasticity of the suspensions at infinitesimal deformations, but a fragile yielding process at intermediate strains.

Highlights

Formulated products with complex textures are part of everyday life; examples include cosmetic and healthcare products, drug delivery devices, building materials, food, and inks
We first assessed the effect of mannitol on the final swollen dimensions of Carbopol particles by analysing the trend of the relative zero-shear viscosity with Carbopol concentration (c) in the three different solvents
We investigated the effect of the addition of D-mannitol, a common additive in pharmaceutical and personal care product formulations, on the rheological behaviour of non-aqueous Carbopol dispersions while using traditional and time-resolved rheological analysis

Summary

Introduction

Formulated products with complex textures are part of everyday life; examples include cosmetic and healthcare products, drug delivery devices, building materials, food, and inks. Among the commercially available molecules, Carbopol polymers are one of the most popular microgels employed industrially and in research These molecules consist of high molecular weight polymers of polyacrylic acids, which swell upon dispersion in a polar solvent, creating a transparent suspension of soft elastic particles. Thanks to their nontoxicity, stability, high thickening properties, and transparency, Carbopol gels have been widely used in cosmetics, pharmaceuticals [5,6,7], and other commercial and industrial applications [8], as well as model yield stress fluids in academia [9,10,11].

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