title: Stability and dewetting of metal nanoparticle filled thin polymer films: control of instability length scale and dynamics.
abstract: We investigate the influence of gold nanoparticle addition on the stability, dewetting, and pattern formation in ultrathin polymer-nanoparticle (NP) composite films by examining the length and time scales of instability, morphology, and dynamics of dewetting. For these 10-50 nm thick (h) polystyrene (PS) thin films containing uncapped gold nanoparticles (diameter approximately 3-4 nm), transitions from complete dewetting to arrested dewetting to absolute stability were observed depending on the concentration of the particles. Experiments show the existence of three distinct stability regimes: regime 1, complete dewetting leading to droplet formation for nanoparticle concentration of 2% (w/w) or below; regime 2, partial dewetting leading to formation of arrested holes for NP concentrations in the range of 3-6%; and regime 3, complete inhibition of dewetting for NP concentrations of 7% and above. Major results are (a) length scale of instability, where lambdaH approximately hn remains unchanged with NP concentration in regime 1 (n approximately 2) but increases in regime 2 with a change in the scaling relation (n approximately 3-3.5); (b) dynamics of instability and dewetting becomes progressively sluggish with an increase in the NP concentration; (c) there are distinct regimes of dewetting velocity at low NP concentrations; (d) force modulation AFM, as well as micro-Raman analysis, shows phase separation and aggregation of the gold nanoparticles within each dewetted polymer droplet leading to the formation of a metal core-polymer shell morphology. The polymer shell could be removed by washing in a selective solvent, thus exposing an array of bare gold nanoparticle aggregates.
authors.affiliation: Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Pin 721 302, West Bengal, India.
authors.forename: Rabibrata
authors.initials: R
authors.lastname: Mukherjee
authors.forename: Soma
authors.initials: S
authors.lastname: Das
authors.forename: Anindya
authors.initials: A
authors.lastname: Das
authors.forename: Satinder K
authors.initials: SK
authors.lastname: Sharma
authors.forename: Arup K
authors.initials: AK
authors.lastname: Raychaudhuri
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Sharma
mesh_terms: D004548:Elasticity; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D053761:Nanocomposites / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D014783:Viscosity; D017155:Wettability
chemical_list: D011108:Polymers; D006046:Gold