The Influence Of Ions On Film Formation And Film Stability Of Waterborne Polyurethane Latex

Polymer nanofilms are a new type of material with nano-scale thickness in macroscopic dimensions,which are not only ultra-light,but also have good flexibility and biocompatibility.Most of the polymer nanofilms are solution-formed,with a flat surface after complete evaporation of the solvent.However,the large amount of solvent consumption and evaporation is environmentally hazardous and limits the use of polymer nanofilms on a large scale.Compared to solution-based films,polyurethane latex offer advantages in terms of environmental friendliness and high film quality.The effect of different ions and different ion concentrations on the stability of latex has been studied in many studies,but the effect of different ions and different ion concentrations on the film formation of latex is relatively little studied.In this paper,different concentrations of Li Cl,Na Cl,NH₄Cl,Na F,Na Br,Na I and Na SCN were added to waterborne polyurethane latex to prepare nano-films by spin-coating,and the effects of different ions and different ion concentrations on the preparation and stability of polyurethane nano-films were systematically investigated.The specific research contents and results include:（1）The effect of different ion concentrations on the preparation of nanofilms was systematically investigated.The results show that as the ion concentration increases,the latex particles fuse earlier in the film formation process and form a mesh structure.With the continuous evaporation of water,the mesh structure compresses to form a film with a non-uniform surface,forming a large number of nano-scale holes that do not easily flow directionally to form micron-scale holes.In contrast,with conventional latex film formation,the fusion of latex particles occurs close to the surface of the substrate,resulting in a relatively intact nano-film that is prone to directional flow due to the hydrophobic nature of the substrate,which ultimately manifests itself as larger holes in the nano-film.（2）The influence of different ions on the preparation of nanofilms was systematically investigated.The results show that in the Hofmeister Series,kosmotropes similar to F^-,which have a high hydration capacity,help the polyurethane to form hydrophobic structures and the latex particles are in an under-fused state during the film formation process.Chaotropes similar to I^-,which are weakly hydrated,are more disordered in the hydrophobic structure of the polyurethane and the latex particles are in an over-fused state during film formation.（3）The effect of different ion concentrations on the stability of nanofilms was systematically investigated.The results show that for nanofilms made with similar additions of Na Cl,the dense holes in the nanofilms increase the fluctuations in the thickness direction of the nanofilms as the ions concentration increases,amplifying the capillary wave fluctuations at specific wavelengths present on the fluid surface,and therefore the nanofilms become more rapidly de-wetting and less stable.For nanofilms made with Na I and Na SCN,on the other hand,as the ions concentration increases,the nanofilm de-wetting rate decreases and stability increases.（4）The effect of different ions on the stability of nanofilms was systematically investigated.The results show that chaotropes similar to I^-significantly reduce the residual stress in the nanofilms and the nanofilm stability increases.In addition,the formation of more hydrogen-bonded carbonyl groups in polyurethane nanofilms also contributes to the stability of the nanofilms.