title: Effects of freezing and thawing on the microstructure of latex paints.
abstract: Freeze-thaw (FT) cycles can aggregate particles in aqueous paint suspensions. To understand the mechanism of particle aggregation, cryogenic scanning electron microscopy (cryoSEM) was used to visualize the microstructure after the freezing and thawing steps of the FT cycle. After the freezing step, cryoSEM images show that the microstructure contains ice crystals and particle-rich regions. Adding propylene glycol, a FT stabilizing additive, leads to formation of larger ice crystals. After thawing, the dispersion structure revealed by cryoSEM shows that the particles redisperse only in the paint with the highest amount of propylene glycol. The other paints contain clusters that are different from the particle-rich regions found after the freezing step. Increasing the thawing rate leads to a more dispersed microstructure even in the absence of propylene glycol. Analysis of the cryoSEM results shows that particle aggregation into these clusters occurs during the thawing stage, and slow thawing conditions lead to more aggregation. The cryoSEM results reported here are used to propose a mechanism of aggregation of particles in the paint.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455, United States.
authors.forename: Manish
authors.initials: M
authors.lastname: Mittal
authors.affiliation: Dow Coating Materials R&D, The Dow Chemical Company, Midland, MI 48674, United States.
authors.forename: John A
authors.initials: JA
authors.lastname: Roper
authors.affiliation: Core R&D Analytical Sciences, The Dow Chemical Company, Spring House, PA 19477, United States.
authors.forename: Catheryn L
authors.initials: CL
authors.lastname: Jackson
authors.affiliation: Dow Coating Materials R&D, The Dow Chemical Company, Spring House, PA 19477, United States.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Monaghan
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455, United States. Electronic address: lfrancis@umn.edu.
authors.forename: Lorraine F
authors.initials: LF
authors.lastname: Francis
mesh_terms: D005615:Freezing; D008855:Microscopy, Electron, Scanning; D015394:Molecular Structure; D010316:Particle Size; D019946:Propylene Glycol / Q000737:chemistry*; D013499:Surface Properties; D013535:Suspensions / Q000737:chemistry*
chemical_list: D013535:Suspensions; D019946:Propylene Glycol