5.5 Drying of low-Tg latex film: studies by OCT-Gravimetry-Video method
(Room 243-245)
10 Apr 18
11:30 AM
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12:00 PM
Tracks:
Session 5: Architectural Coatings I
Waterborne latex coatings are gaining larger popularity and development due to their low volatile organic compound (VOC) emissions and improved performances of applications. However, the drying process of latex film formation is inhomogeneous (i.e. spatial distribution of latex particles is non-uniform and evolving with time), causing defects of dried coatings, which still lacks mechanistic understandings. This research uses Optical Coherence Tomography (OCT)-Gravimetry-Video method to non-invasively study the drying inhomogeneity of latex films, including packing of particles, cracking and skin layer formation. This method combines OCT, digital balance and video camera together to simultaneously monitor the local internal structure, the global water evaporation rate, and the visual appearance of film as a function of drying time. Results showed the packing profile of particles that started accumulating from the top down to the bottom of film, which was affected by the particle size. After packing stage, for high Tg particles, “shear banding” and cracking structures appeared; for low Tg particles, skin layer formed and thickened with time. The effects of water-soluble additives, especially surfactants, on the cracking, skin formation and drying time of films will also be reported.