Soft nanoparticles have received great interest lately due to their potential use in a range of applications, including drug delivery, all polymer nanocomposites, and self-healing materials. These soft nanoparticles are generally formed via extensive branching and/or internal crosslinking of macromolecules to form nanoscale particle-like structures. Moreover, their unique properties often require particle like behavior, yet the correlation of crosslink density to particle like behavior is poorly defined. Will a single crosslink in a long polymer chain form a ‘nanoparticle’? Is there a limiting percent of crosslinking that is needed to transition a polymer chain to a soft nanoparticle? From a broader perspective, the definition of what makes a construct a ‘nanoparticle’ is also not clearly defined. In this presentation, we will discuss our small angle neutron scattering studies that seek to clearly define the transition from a polymer chain to a nanoparticle vis internal crosslinking. A combination of analyses of the SANS curves, including the dimensionless Kratky plot, the fractal dimension, and the ratio of Rg/RH, provides insight into the particle-like properties of the examined polymer constructs. These results show that the primary characteristic that delineates a polymeric chain from a nanoparticle is not its size, but the presence of a surface, which can be detected via these analyses. Using the idea that a nanostructure requires the presence of a surface to be a nanoparticle leads to the surprising conclusion that crosslinking densities as low as 0.8%, or 1 crosslink for every 125 monomers, is sufficient to realize very strong particle-like characteristics.

When does a macromolecule transition from a polymer chain to a nanoparticle?

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