Simple Method for Rheological Determination of Surfactant Layer Thickness, Adsorbed on Soft Rubber Particles
Natural rubber latex is a colloidal suspension of particles, which is very important for many industrial applications. These latex particles are not only polydispersed but also very soft and deformable, which makes the prediction of rheological properties much difficult. Herein, the rheology of natu...
| Autores: | , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión aceptada para publicación |
| Fecha de publicación: | 2019 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/195100 |
| Acceso en línea: | http://hdl.handle.net/10261/195100 |
| Access Level: | acceso abierto |
| Palabra clave: | Surfactant Adsorption Rheology Natural rubber latex Thickness of adsorbed layer |
| Sumario: | Natural rubber latex is a colloidal suspension of particles, which is very important for many industrial applications. These latex particles are not only polydispersed but also very soft and deformable, which makes the prediction of rheological properties much difficult. Herein, the rheology of natural rubber latex has been studied at high particle concentrations, analyzing the effects of surfactant addition on colloidal stability. A hydrophobically modified inulin surfactant (INUTEC NRA) was selected for this study, since previous works had shown that this inulin surfactant imparts good colloidal stability to polystyrene latex particles. The most important objective was studying the influence of the surfactant on the particle adsorbed layer and determining the thickness of the adsorbed surfactant layer. The results showed that relative viscosity increased as a function of latex volume fraction and this increase became extremely sharp as the volume fraction approached the maximum packing volume fraction, as expected. This variation in viscosity with volume fraction has a complex behavior, which could not be analysed using conventional models based on hard-rigid spheres, such as Krieger-Dougherty (K-D) or Maron-Pierce (M-P). Herein, we describe a simple semiempirical method to determine the surfactant adsorbed layer thickness, based on the linear dependence of intrinsic viscosity with 1/(max-2, where is the volume fraction of rubber particles and max is the maximum volume fraction at which viscosity tends to infinity. The difference in maximum packing fraction, with and without surfactant, allows the calculation of the adsorbed layer thickness, ≈2.8 nm, which is a good estimate for the thickness of surfactant molecules adsorbed on latex particles. This surfactant thickness has been confirmed by direct measurements using Dynamic Light Scattering (DLS), which gave a value of 3.1 nm. Viscoelastic oscillatory measurements have also been performed, showing that natural rubber particle suspensions are predominantly elastic above =0.63 latex volume fractions. The elastic modulus has been analyzed as a function of surfactant concentration, confirming that stability of latex particles is mainly controlled by surfactant concentration. |
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