Improved Tribological Performance of Polydopamine/Polytetrafluoroethylene Thin Coatings With Silica Nanoparticles Incorporated into the Polydopamine Underlayer

Polytetrafluoroethylene (PTFE) is a solid lubricant with low friction coefficient. However, it lacks durability as a thin coating. Prior studies have shown that a polydopamine (PDA) underlayer enhances the coating durability. In this study, 100, 200, and 300 µL of aqueous silica nanoparticle (NP) dispersions were added to a 15 mL PDA deposition solution. Stainless steel substrates were coated with PDA + silica in the mixed dispersions and then coated with PTFE layers to form thin PDA + silica/PTFE coatings. The coatings were tested in ball-on-flat linear reciprocating motion under dry contact conditions. The durability of the PDA/PTFE coating was improved by 70% when 100 µL of aqueous silica NP dispersion was added. The significant improvement in the durability was attributed to the increased adhesion of the PTFE coating to the PDA underlayer, the fragmented wear debris, and the enhanced counterface transfer film. These samples also showed enhanced resistance under linearly increasing load scratch testing with lower coefficient of friction (COF) and higher delamination resistance when compared to samples without silica.

Development of a Polyacrylate/Silica Nanoparticle Hybrid Emulsion for Delaying Nutrient Release in Coated Controlled-Release Urea

Polyacrylate/silica hybrid emulsions were prepared by blending aqueous silica nanoparticles with polyacrylate emulsion, which were used for coating urea granules. After incorporating 1.0 wt.% silica nanoparticles into polyacrylate emulsion, preliminary solubility of CRU was decreased from 38.3% to 2.2%, and the release duration was extended from 8 to 27 days. The hybrid coating remarkably delayed the release of urea via improving wear-resistance due to the enhanced hardness, reducing water vapor permeability because of the tortuous diffusion pathway, and less breakage of CRU granules resulted from higher glass transition temperature. Meanwhile, the processibility was improved, which prevented particle agglomeration during coating. Therefore, aqueous silica nanoparticles have potential application in polymer emulsion coated controlled-release fertilizers.

Deconvolution of BIL-SFG and DL-SFG spectroscopic signals reveals order/disorder of water at the elusive aqueous silica interface

Through the prism of the rather controversial and elusive silica/water interface, ab initio DFT-based molecular dynamics simulations of the structure and non-linear SFG spectroscopy of the interface are analysed.