Fabrication of flat and sizeable nanocellular polymethyl methacrylate (PMMA) foam with tunable thermal conductivity

Abstract

Polymeric nanocell foam is a promising material that faces manufacturing challenges. Producing sizable and thick foams for properties testing has been challenging. This study aims to scale up and understand the foaming mechanism of nanocellular foams by controlling the saturation temperature, pressure, and molecular weight distribution of the matrix to fine‐tune the glass transition temperature of the polymer/gas mixture. The hot‐press foamed samples possess a 100 × 70 × 6 ~ 8 mm3 dimension and a cell size of less than 200 nm. Bimodal structures can also be created by controlling the critical processing parameters. Introducing 37% microcells into unimodal nanocellular foam reduced the relative density from 0.29 to 0.19. The thermal conductivity of the foams was tuned by controlling the cell size distribution. Unimodal nanofoams have the lowest thermal conductivity for foams of the same density due to the Knudsen effect and tortuosity. The measured thermal conductivity is in agreement with theoretical models.Highlights PMMA nanofoam with a dimension of 100 × 70 × 6–8 mm3 and cell size below 200 nm. The morphology of nanofoams was tuned to be unimodal and bimodal. The foam density of the bimodal nanofoams was lowered below 0.238 g/cm3. The thermal conductivity of foams was tuned by controlling the cell structure.