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

Abstract

SUMMARY:The shell material core coverages of two-phase core-shell particles are determined quantitatively by NMR spin-diffusion experiments. A simple relation is derived between the specific surface (ratio of core surface and core volume) and the core coverage of acrylic core-shell particles in the solid state. Through calibration with a reference sample of known core coverage, the core coverage of the other samples can then be evaluated. The values of core coverages determined by spin-diffusion become more accurate as the core coverage becomes smaller. In a series of poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) coreshell latices, the core coverage was found to vary between 43 and 80%. Additionally, information about the global particle morphologies is derived from a quantitative comparison of the specific surface and the particle diameter measured by dynamic light scattering.

Quantitative Characterisation of the Inner Structure of Core-Shell Latex Particles by1H Solid-State NMR

“…We decided to limit the number of cycles to six to avoid the loss of signal due to the existence of imperfect 90 8 pulses. [20] As we can see in Figure 4b, indeed the values of the g curve are superior to 1 and show a maximum for a radius of the particle around 28 nm. The two edges of the curve tend to reach a value of 1 as we move the selection towards the mobile core (small radius) or to the rigid shell (big radius).…”

“…Used to compare the different samples, e9 represents a normalised interphase thickness as percentage of the outer radius of the particle. A10 40 14 13 10 -B20 45 17 17 18 13 C20 45 19 16 --D20 45 16 12 --E30 39 16 15 13 shell of one particle may then be in contact with the core of another [20] contributing to the increase in its apparent core-coverage factor f app measured by NMR. Table 4 shows the specific surface and the apparent core-coverage factor measured at 353 K for the 5 samples.…”

“…This indicates that in both cases the geometry of the assembling is identical. It is possible to apply a correction [20] on the apparent core-coverage factor to calculate the real one of the isolated particle. A conversion between apparent and real core-coverage factors can be made using the following equation:…”

“…[16 -19] The core coverage of similar particles was also determined. [20] The aim of this paper is to present a new solid-state NMR methodology that enables us to localise and quantify the interphase in a core-shell system and to measure its thickness. Hence it gives an idea of the molecular mobility profile along the radius of the spherical particles.…”

Determination of Polyisoprene‐block‐poly(methyl methacrylate) Domain Sizes Using 1H Spin Diffusion

“…[14,15,26] Our results are in line with other recent examples from the literature where it has been found that the NMR methods somewhat underestimate domain sizes. [7,[35][36][37] It is not clear at present what mechanisms may be responsible for the discrepancies, but it cannot be excluded that the microphase separation leads to increased dynamics at the interface that interfere with the spin diffusion processes. [32,33] Conclusion Solid-state NMR techniques were used to study microphase separated PI-b-PMMA diblock copolymers.…”