Adjustment of Coatings Morphology and Particle Distribution of Layered Silicates by Freeze-Drying for Improved Gas Barriers

Abstract

Freeze-drying of layered silicates modified with dodecylamine (DDA) is a highly effective technique for the preparation of barrier pigments that significantly mitigate the permeation of oxygen, water vapor, and hydrogen through polymer films containing these particles. In contrast to oven-dried modified silicates, the delamination of the particles is markedly enhanced. Additionally, the solvent used in the coating preparation is critical to the delamination and exfoliation processes. By applying Hansen solubility parameters, it is feasible to predict suitable solvents that facilitate these processes. The concentration of DDA employed for silicate modification influences the morphological characteristics of the particles. A maximum interlayer spacing of 2.15 nm is attained at a silicate-to-DDA weight ratio of 2.25:1. The permeation rates of oxygen, water vapor, and hydrogen through coatings devoid of particles, as well as those containing varying amounts of oven-dried and freeze-dried clay particles, are systematically investigated. The permeation is found to be minimal in systems incorporating freeze-dried particles, with a notable reduction by four orders of magnitude observed when compared to the coating without any filler. Notably, for hydrogen, even low concentrations (0.1–2%) of modified layered silicates also lead to a reduction of permeation by up to four orders of magnitude.