Measuring the interactions between carbon black nanoparticles and latex thin films in aqueous media using AFM force spectroscopy

Abstract

AFM force spectroscopy was utilised to measure the interactions between latex and carbon black nanoparticles in neutral ultrapure water and basic ultrapure water with 0.7% ammonia (pH of 11.6 ± 0.05) by weight added. For the first time, carbon black nanoparticles were adhered to AFM tips with epoxy using force spectroscopy techniques and characterised using SEM and AFM. The carbon-functionalised tips were then utilised to interact with thin films (prepared from concentrated and field latex suspensions) in the two liquid media. The results demonstrated that both attractive (during tip approach) and adhesive (during tip retraction) forces were considerably greater between the latex and carbon nanoparticles when the experiments were carried out in ultrapure water compared to ultrapure water with 0.7% ammonia. This was because the basic ammonia solution increased the negative surface charges of the latex and carbon particles which was confirmed by zeta potential measurements. Therefore, in the ammonia solution, only repulsion was observed on the tip approach and only small amounts of adhesion were observed on the tip retraction. Furthermore, the results demonstrated that despite the different processing and treatment of the concentrated and field latex samples, their interactions with the carbon black nanoparticles were similar in each medium. This study directly measures the interactions between carbon black nanoparticles and natural rubber latex, which has a significance for the manufacturing of automotive tyres and other polymer/carbon composites.