Amorphous Deposit Formed by Evaporation of Poly(Ethylene Glycol) Aqueous Droplet

Crystallization of poly(ethylene glycol) (PEG) greatly debase the quality of printing and coating during drying, where it is used as a dispersant. In this work, we have investigated the drying process of aqueous droplet of poly(ethylene glycol) (PEG) as a function of molecular weight (M_w). It shows that PEG would crystallize on a hydrophilic surface but form an amorphous deposit on a hydrophobic surface at a humidity (RH) of 40% when M_w ≤5000 g/mol. However, PEG would crystallize regardless of the surface and RH when M_w is above 10 000 and 20 000 g/mol. By regulating PEG concentration, molecular weight, and RH, the droplet can be dried into an amorphous deposit for over 24 h. Raman spectroscopy and low-field nuclear magnetic resonance (LF-NMR) indicate that the water molecules bound to PEG chains (M_w ≤5000 g/mol) under slow drying inhibit their crystallization.