On the effect of particle surface chemistry in film stratification and morphology regulation.

Archana Samanta,Romain Bordes

doi:10.1039/d0sm00317d

Abstract

Combinations of colloids and binders are often used to formulate functional coatings. In these mixtures, competition between particle migration, polymer chain diffusion, evaporation and sedimentation affects their respective spatial location and therefore can govern the surface features. In addition to this, the surface chemistry of the nanoparticles (NPs) and the resulting interparticle interactions can play a significant role in dictating the morphology and the properties of resultant films. Hence it would be possible to tune the surface and bulk topology of the films by controlling these parameters. A combination of various acrylic binders with two types of silica sols, bare (BSiO2) and modified silica (MSiO2), differing in their ability to gel, were formulated and dried under controlled conditions. Factors influencing the mobility and migration of binder and silica particles were evaluated with respect to particle concentration and drying rate. MSiO2 films showed prominent pores with gradual increase in Si% across the cross-section of the films, whereas, BSiO2 films had no pores and showed a uniform Si content across the cross-section of the films. This difference is explained by the variation in gelation between BSiO2 compared to MSiO2, that hindered the NPs migration and affects the infiltration and stratification process. This study paves a path forward to achieve desired surface and bulk porosity from colloidal silica coatings by effective control of chemistry of particles along with process parameters.

Highlights

Complex colloidal coatings are widely used for fabrication of functionalized surfaces and interfaces, as a thin layer of these deposited particles has the advantage of significantly altering the surface properties of the material while keeping the bulk properties intact
The mechanisms of film formation is well understood for binary mix of colloids where the particles retain their structure after film formation,[22,41,42,43] this paper discusses the influence of silica surface chemistry, formulation constituents, and temperature on the film forming behavior of silica–binder systems where the binder forgoes its initial morphology after the film formation process
Two types of silica nanoparticles were considered, one that could undergo gelling during the film forming process, and one that was modified to resist salt induced gelling (MSiO2)

Summary

Introduction

Complex colloidal coatings are widely used for fabrication of functionalized surfaces and interfaces, as a thin layer of these deposited particles has the advantage of significantly altering the surface properties of the material while keeping the bulk properties intact. Properties such as surface hardness, corrosion resistance, self-cleaning, super-hydrophobicity, thermal insulation, and others[1] are commonly achieved through this approach.

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