Microheterogeneities of core‐shell latexes probed by ¹H spin diffusion and transmission electron microscopy

Abstract

A core-shell latex built up of polybutadiene as a mobile component and polystyrene as a rigid component is investigated. Solid-state NMR spectroscopy and transmission electron microscopy are used to characterize the morphology and possible heterogeneities of the latex particles (average particles sizes 70-100 nm). NMR spectroscopy allows the determination of average domain distances much below the particle size due to standard electron microscopy. These differences are explained by an additional microstructure of the core-shell particles. Indeed, electron micrographs at high resolution confirm the existence of heterogeneities within the polybutadiene core of the latex. The presented investigations demonstrate the power of a combined application of solid-state NMR spectroscopy and transmission electron microscopy for the characterization of core-shell latexes.

Quantitative measurement of core coverage in core-shell particles by solid-state1H NMR spin-diffusion experiments

“…3, the calculated particle diameter from the spin-diffusion data for the normal core-shell particle structure lies in the range of the particle diameter measured by DLS and UC, respectively. This contrasts with observations of heterogeneites in the core of other systems on length scales about one order of magnitude smaller than the particle size [11][12][13] . The detected NMR particle diameter of 60 nm is of course not exactly the DLS value of 90 nm.…”

“…Of course all these conclusions are only valid if the spin-diffusion experiment detects the global particle structure and not some small heterogeneities inside the particle 7,11,12,15) . Only then is quantitative information about the specific surface provided which can be used either to determine core coverages or to distinguish different particle morphologies.…”

“…This results in spin-diffusion curves featuring a superimposition of several different magnetisation exchange processes. Spin-diffusion experiments showing such superimposed magnetisation exchange processes are not suited to the characterisation of the overall morphology of latex particles 12) . Fig.…”

“…110 8C). If the measurements are performed at lower temperatures, heterogeneities inside the seed copolymer are detected 12) . This results in spin-diffusion curves featuring a superimposition of several different magnetisation exchange processes.…”

“…During a spin-diffusion experiment, the magnetisation of one part of the system is selected while the magnetisation of the other part is suppressed. Subsequently, the diffusive flow of magnetisation from the first to the second phase is monitored and analysed to detect domain sizes in a range of 1 -100 nm 11,12) . Consequently, it is possible to detect both heterogeneities in one phase or interphases between two phases, and thus probe the entire morphology of heterogeneous polymers 11) as well as the water layer surrounding the particle 13) .…”