High resolution cryogenic scanning electron microscopy (cryo-SEM) was used to study
the physics of latex film formation. Fast freezing, controlled freeze-drying and
annealing under vacuum, followed by room-temperature and cryogenic SEM
demonstrated that van der Waals force alone can compact a latex coating under
conditions devoid of surface tension and capillary forces. Rewetting tests of the
annealed coatings shed light on distinguishing elastic and viscoelastic deformation.
Key factors affecting the freeze-thaw (F/T) stability of polymer latexes were studied.
The nanostructural changes during freeze-thaw cycles were visualized by cryo-SEM.
Reducing Tg and modulus of the polymer, latex particle size, amount of protective
functional groups, molecular weight and addition of coalescent all lead to reduced F/T
stability. Both the freezing and thawing rates have strong impact on F/T stability.
Both functional acid monomer type and degree of neutralization in pre-emulsion greatly
influence the ability of the latex and titanium dioxide (TiO2) particles to interact with
each other which prevents TiO2 particle aggregation. Latexes incorporated with
vinylphosphonic or itaconic acid show better TiO2 efficiency than latexes with acrylic
acid or methacrylic acid. For acid monomers with high water solubility, higher degree
of neutralization in pre-emulsion yields in general lower TiO2 efficiency.
Cryo-SEM was employed to further understand the nature of nanostructure deduced by
small angle x-ray scattering (SAXS) for poly(butadiene-b-ethylene oxide) diblock
copolymers solutions, as a function of copolymer concentration and block copolymer
composition. The SAXS measurements and cryo-SEM images reveal a new type of
network morphology, comprised of a random arrangement of interconnected cylinders,
in addition to the other classical structures.
University of Minnesota Ph.D. dissertation, Novermber 2008. Major: Materials science and engineering. Advisors: L. E. Scriven and H. Ted Davis
Cryo-SEM Study of Nanostructure Development of latex dispersions and block copolymer solutions.
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