Nanoparticle and Polymer Diffusion Measured by ToF-SIMS

Existing methods of measuring NP diffusion include dynamic light scattering (DLS) and Rutherford backscattering (RBS) but are greatly limited in the materials they can evaluate and the accessible length scales. Here, we apply time-of-flight secondary ion mass spectroscopy (ToF-SIMS) to separately measure NP and polymer diffusion. For nanoparticle diffusion, we fabricate trilayer polymer-nanocomposite-polymer samples and measure the cross-section with ToF-SIMS to extract the NP distribution in 3D. Processing the 3D data corrects for sample tilt, deconvolutes the beam resolution, and integrates the data to extract a 1D NP concentration profile, to which a diffusion equation is fit. By comparing diffusion coefficients measured by our ToF-SIMS method and RBS for the same poly(2-vinylpyridine) (P2VP) and silica NP system, we validate our experimental methodology. Polymer diffusion was similarly measured using a trilayer sample of polystyrene (PS)-deuterated PS-PS; the PS diffusion coefficients for 69k and 423k are in excellent agreement with prior results. This work establishes ToF-SIMS as a reliable and versatile tool for measuring diffusion coefficients.