Microfluidic Approach to Study Bubble Nucleation in Polymeric Foams for the Development of DFT-based Models

Bubble nucleation sets the structural foundation of a foam, yet remains poorly understood. Single-component classical nucleation theory predicts erroneous nucleation barriers, particularly when applied to foaming of multicomponent liquids used to produce lightweight, functional materials. Multicomponent theories are limited by lack of (1) thermodynamic and (2) nucleation rate data for validation. For the first, we used gravimetry-axisymmetric drop shape analysis (G-ADSA) in the Di Maio lab (U Naples) to measure equilibrium compositions and interfacial tension of polymer-CO2 mixtures up to 8MPa, which validated PC-SAFT and DFT models from the Wang group (Caltech) that enable string method calculations of the nucleation barrier. For the second, we developed a microfluidic hydrodynamic-focusing apparatus that linearly decreases pressure from 10MPa to as low as 0.1MPa within 100ms while observing bubble nucleation and growth. The instrument, designed for use with optical microscopy, X-ray scattering, thermography and FTIR, will be described. This approach to validating multicomponent theories of bubble nucleation can be extended to study complex effects of additives on foaming and enable design of foam composition and processing conditions to achieve desired material properties.