Evidence of stratification in binary colloidal films from microbeam X-ray scattering: Toward optimizing the evaporative assembly processes for coatings


Type
Article
Change log
Authors
Routh, AF 
Carr, Amanda 
Liu, Weiping 
Yager, Kevin G 
Bhatia, Surita 
Abstract

Colloidal films have many important applications where a layered configuration is desirable, including flexible electronics, anti-reflective coatings, and anti-microbial paints. We report stratification during evaporative film formation in binary colloidal dispersion, probed using a novel microbeam small-angle X-ray scattering (SAXS) technique. To our knowledge, SAXS approaches have not been used to experimentally obtain quantitative data of concentration profiles in multicomponent colloidal films. We measured the local scattering of a film at different vertical locations using a microfocused X-ray beam and determined particle concentrations at different film depths using a linear combination analysis of the mixed film and pure film scattering data. Using small particle size ratios ranging from 2.55 to 1.25, we experimentally observed and quantify three distinct stratification configurations: inverted small on- top, large-on-top, and no stratification. Our results show some agreement with a previously proposed stratification state diagram, although there are some limitations. Experimental verification of these stratification phenomena is critical to fully understanding the physics of particle movement and structure development during film formation, which is crucial for optimizing evaporative assembly processes for coatings.

Description
Keywords
SAXS, films, evaporative assembly, stratification, coatings, colloids
Journal Title
ACS Applied nano materials
Conference Name
Journal ISSN
2574-0970
2574-0970
Volume Title
1
Publisher
American Chemical society
Sponsorship
Financial support for this work was provided by the National Science Foundation through award CBET-1335787 and a Department of Education Graduate Assistance in Areas of National Need (GAANN) fellowship for A. J. C., Award P200A160163. This research used beamline 11-BM, CMS, of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.