Resolving the different bulk moduli within individual soft nanogels using small-angle neutron scattering.

Abstract

The bulk modulus, <i>K</i>, quantifies the elastic response of an object to an isotropic compression. For soft compressible colloids, knowing <i>K</i> is essential to accurately predict the suspension response to crowding. Most colloids have complex architectures characterized by different softness, which additionally depends on compression. Here, we determine the different values of <i>K</i> for the various morphological parts of individual nanogels and probe the changes of <i>K</i> with compression. Our method uses a partially deuterated polymer, which exerts the required isotropic stress, and small-angle neutron scattering with contrast matching to determine the form factor of the particles without any scattering contribution from the polymer. We show a clear difference in softness, compressibility, and evolution of <i>K</i> between the shell of the nanogel and the rest of the particle, depending on the amount of cross-linker used in their synthesis.