Size and shape fluctuations of ultrasoft colloids

TL;DR

This study investigates the size and shape fluctuations of ultrasoft colloids, specifically dendrimers, using advanced neutron scattering techniques to understand their dynamic behavior and structural basis.

Contribution

It introduces a novel approach combining SANS and neutron spin echo to quantify size and shape fluctuations in ultrasoft colloids, revealing a crossover in fluctuation behavior.

Findings

Size fluctuation is suppressed at higher dendrimer concentrations.

Shape fluctuation increases beyond a certain concentration.

Dynamic crossover is linked to inter- and intra-particle dynamics.

Abstract

Ultrasoft colloidal particle fluctuates due to its flexibility. Such fluctuation is essential for colloidal structure and dynamics, but is challenging to quantify experimentally. We use dendrimers as a model system to study the fluctuation of ultrasoft colloids. By considering the dynamic polydispersity in the small-angle neutron scattering (SANS) model, and introducing the fluctuation of invasive water into the contrast in SANS, we reveal the fluctuating amplitudes of the size and shape of the dendrimer of generation 6 at finite concentrations. The size fluctuation is suppressed while the shape fluctuation increases as the weight fraction of dendrimers passes 11%. With neutron spin echo data, we suggest that such crossover originates from the competition between the inter- and intra-particle dynamics. Further investigation on lower-generation samples shows a contrary result, which suggests a structural basis for these dynamic phenomena.