UNDERSTANDING “COFFEE-RINGS” ON MOLECULARLY SMOOTH AND CHEMICALLY MODIFIED SUBSTRATES USING AQUEOUS SOLUTIONS OF GOLD NANOPARTICLES STABILIZED BY POLY(VINYL ALCOHOL)
MetadataShow full item record
While gold nanoparticles (AuNPs) have many potential applications, a common obstacle to their use is their propensity to aggregate together. We propose a solution to this issue through conjugation with poly(vinyl alcohol) (PVOH), a biocompatible and water-soluble polymer. PVOH stabilizes AuNPs in solution, and also can act as a spacer for 2D self-assemblies of AuNPs. The binding mechanisms of PVOH onto AuNPs were studied using dynamic light scattering and through the construction of Langmuir adsorption isotherms. Self-assembled 2D arrays of AuNPs have important applications in numerous areas of science and technology including printing, catalysis, molecular sensing, and microassay manufacturing. A simple and effective way to form this type of array would be to deposit sessile drops containing AuNPs onto desired substrates. However, colloids in solution typically form non-uniform deposit patterns upon solvent evaporation, commonly known as “coffee rings.” Deposit patterns on substrates of varying wettabilities were studied using optical microscopy and atomic force microscopy to gain insight into the mechanisms of droplet drying. It was found that the deposit pattern on superhydrophilic substrates is a highly regular, monodisperse layer of AuNPs. It was also found that on hydrophobic surfaces, the contact area of the droplet, ring thickness, and ring width were all functions of the receding contact angle of the substrate. Through these studies, it was discovered that relative humidity plays an important role in deposit pattern formation. Under high humidity, drying occurs more slowly, and deposits form more regularly. In the future, these studies will be performed in controlled humidity environments.