In Situ Monitoring of Dispersion Film Formation Using Tapping-Mode Atomic Force Microscopy
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O10.19.1
In Situ Monitoring of Dispersion Film Formation Using Tapping-Mode Atomic Force Microscopy Jing Li*, Wenbin Liang, Steve Chum Analytical Sciences Laboratory* and Plastic R&D, The Dow Chemical Company 2301 N. Brazosport Blvd., B1470, Freeport, TX 77566 ABSTRACT The coalescence process of poly (ethylene-co-vinyl acetate) (EVA) and poly (ethyleneco-octene) (EO) dispersion particles was monitored in situ using tapping-mode atomic force microscopy (TMAFM) equipped with a miniature hot stage. This work describes the effect of particle size on the film formation temperature based on direct experimental observation, clarifying further the debate about particle size effect on minimum film formation temperature (MFFT). The results suggest that semicrystalline polyolefin particles have similar deformation temperature dependence. Smaller particles tend to deform faster than larger particles, which is attributed to their smaller mass. Furthermore, morphology changes and mechanical property development associated with the film formation process are also discussed. The TMAFM technique is shown to be very useful in gaining insight into the film formation mechanism, which will provide guidance in future practical applications with polyolefin dispersions. INTRODUCTION Film formation from polymer dispersions has been a subject of great interest in recent years [1]. Despite new advances, formation of void-free film from discrete particles, especially semicrystalline polymer particles, and the mechanisms involved in deformation of small polymeric particles are still the subjects of active research. In particular, the particle size of polymer dispersions has been found to affect film formation temperature by some investigators [2], while Sperry [3] and others [4] observed the contrary. Such questions have been debated for decades due to lack of accurate experimental data support [5]. There is a need to develop a new analytical technique that will help to answer a number of fundamental questions concerning polyolefin dispersion film formation processes, such as particle size and temperature effect on latex film formation. Tapping-mode atomic force microscopy (TMAFM) is a viable technique because it provides high-resolution imaging and measurement of surface topography and properties on a molecular scale. Most importantly, combining hot stage with TMAFM [6] allows the researcher to monitor in situ the surface morphology changes in real time and study the temperature and particle size effects on the latex particle deformation process. This work studies the film formation processes of semicrystalline polyolefin dispersions using TMAFM and attempts to clarify the effect of particle size on the film formation mechanism and associated mechanical properties of the resulting films. EXPERIMENTAL Two polyolefin dispersion samples made of poly (ethylene-co-vinyl acetate) (EVA) and poly (ethylene-co-octene) (EO) latices were used in this study. Basic properties of the polymer resins and the dispersions are shown in Table 1. Films of aqueous
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