Viscoelastic Properties and Sulfur Distribution at the Nanoscale in Binary Elastomeric Blends: Toward Phase-Specific Cross-Link Density Estimations

João P Cosas Fernandes,Marc Weydert,Robert Quintana,Beatriz Basterra-Beroiz,Nathalie Valle,Carlos E Federico,Esther Lentzen

doi:10.1021/acsapm.1c00032

Abstract

Immiscible blends of elastomers present high technological interest, and the selection of the vulcanization system is important for the optimization of properties for different technical applications. In particular, the effect of the curing agents on the distribution of cross-links in each phase is key for the full comprehension of the structure–property relationships. Aiming at the understanding of the phase-specific network structure in rubber blends, this work presents an innovative strategy for the quantitative characterization of the local viscoelastic properties of immiscible rubber blends by atomic force microscopy (AFM) measurements. A systematic study on the quantitative nanomechanical characterization by AFM of unfilled single natural rubber (NR) matrixes with different degrees of cross-link densities ultimately allows for the estimation of the phase-specific cross-link density of the NR phase in NR/butadiene rubber (BR) blends, prepared with varying vulcanization systems. Complementary chemical information by high-resolution secondary ion mass spectrometry imaging is able to reveal differences in sulfur contents in each elastomeric phase of the blends.

Highlights

Blends of elastomers or thermoplastics containing elastomer particles present high technological interest as they are often used as a basis for compound formulations for a variety of applications, such as damping materials, flexible pressure sensors, food packaging and membranes, biomedical applications, as well as in the tire and aerospace industries.[1]
The aim of this study is to develop a methodology for understanding the phase-specific network structure in elastomeric blends, by estimating the phase-specific cross-link density from mechanical, viscoelastic properties, and chemical distributions at the nanoscale
A strategy for cantilever selection for atomic force microscopy (AFM) AM−FM nanoviscoelastic analysis based on master curves generated from rheometry experiments was presented

Summary

Introduction

Blends of elastomers or thermoplastics containing elastomer particles present high technological interest as they are often used as a basis for compound formulations for a variety of applications, such as damping materials, flexible pressure sensors, food packaging and membranes, biomedical applications, as well as in the tire and aerospace industries.[1] In elastomeric blends, rubber curatives may have different degrees of solubility in each matrix, which consume vulcanizing agents at different rates due to their different degrees of unsaturation, leading to a potentially uneven distribution of cross-links.[2] in immiscible binary blends, it is important that the selected vulcanization system leads to optimized compound properties upon vulcanization of the two phases. The substantial developments of the past years in characterization techniques made the identification of nanomechanical properties and chemical analysis in the submicron scale possible. Methods were proposed where the cantilever is driven at two of its flexural resonance frequencies, one being modulated by amplitude (amplitude modulation (AM)) and the other by frequency

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