Quantitative Characterisation of the Inner Structure of Core-Shell Latex Particles by 1H Solid-State NMR

Abstract

Solid-state 1H NMR spin diffusion experiments are used to characterise the inner morphology and the core coverage of core-shell latex particles. From the spin-diffusion curve a specific surface is calculated as a function of the amount of mobile phase selected by an adjustable dipolar filter. In this paper, a parameter η is introduced to compare the specific surfaces of actual core-shell particles with an idealistic model without any interphase between mobile and rigid phases. With a simple mathematical model it is possible to fit the variation of η versus the radius of the particle. The quantitative results obtained lead to the localisation of the interphase, the measure of its thickness and give an idea of the profile of molecular mobility along the radius of the particle. Five samples are analysed with this new methodology to test the accuracy and the sensitivity of the method. The influence of the core-shell ratio and the synthesis conditions on the interphase structure and the core coverage factor are discussed. Comparison between freeze-dried and spray-dried samples and air-dried films shows measurable evolution of the interphase morphology of the particles upon drying. The measurements also suggest very close packing of the core-shell particles during the film formation process.