The stability of thin polymer films as controlled by changes in uniformly sputtered gold

Abstract

Type of publicationArticle (peer-reviewed) Link to publisher's versionhttp://dx.doi.org/10.1039/c3sm27130gAccess to the full text of the published version may require a subscription. The stability of polystyrene thin films of low molecular weight on a solid substrate is shown to be controlled by the presence of uniformly distributed gold sputtered at the air-polymer interface. Continuous gold coverage causes the formation of wrinkles. High coverage and Au nanoparticle (NP) density leads to the development of a spinodal instability while low coverage and NP density retards the nucleation dewetting mechanism that beads up the thin polymer film into drops when no coverage is 10 present. Heating at temperature larger than the polymer glass transition temperature for extended periods allows the gold NPs to coalesce and rearrange. The area of polymer surface covered by NPs decreases as a result and this drives the films from unstable to metastable states.When the gold NPs are interconnected by polymer chains a theoretically predicted spinodal instability that patterns the film surface is experimentally observed. Suppression of the instability and a return to a flat film occurs when the 15 polymer interconnections between particles are broken. While the polymer films maintain their physical continuity changes in their chemical surface composition and thickness are observed. The observed film metastability is nevertheless in agreement with theoretical prediction that includes these surface changes. Rights

Stability of Ultrathin Nanocomposite Polymer Films Controlled by the Embedding of Gold Nanoparticles

“…In contrast, in the Au NP covered region of the same sample In those cases the pattern wavelength increases with the heating time. 18 The difference arises from the NP embedding that occurs in the samples studied here. In the earlier work 18,19 NP embedding was not observed, but NP surface aggregation was present.…”

“…Heating a thin polystyrene film (h PS10 = 25 nm) at 170 ºC for t = 1440 min allows for nucleation dewetting development 1,18 in the uncovered polymer region (i.e. for Si/SiO x /Polymer/Air).…”

“…Inf.). [18][19][20][21] The deposition led to uniformly distributed NPs (Figure 1a) on the polymer surface in the central region of the samples (see Figure S2) allowing a direct comparison between Si/SiO x /Polymer/Air (Figure 1b) and Si/SiO x /Polymer/AuNP/Air regions (Figure 1c-g). The mean radius value of the NPs was R p ≈ 1.55 nm and the fractional Au coverage was C f ≈ 0.14.…”

“…18,19 Based on these previous studies, we expect for the particular case of ultra-thin polystyrene films (25 nm ≤ h poly ≤ 30 nm) covered by a Au layer with nominal thickness of 1 nm presented 4 here that a spinodal instability should develop as the initial coverage is above the critical threshold. 18 Indeed, this phenomenon takes place. However, in the current work the film and the pattern dynamics differ from the previous cases investigated as the Au NPs do not remain at the film surface, but embed in the film.…”

“…[6][7][8][9][10][11][12][13][14][15][16][17] In general, the stability against dewetting for Au NP-covered thin polymer films can be predicted by the total interaction potential between the air-polymer and polymer-substrate interfaces. In a previous paper, 18 we have shown that the total potential Φ controlling the system stability is a combination of the van der Waals interaction between the two polymer interfaces Φ poly (h poly ) and the interaction between the Au NPs with a mean radius R p and the underlying layers Φ AuNP (h poly , R p ). The influence of each term is weighted by the changes in the amount of Au present at the air-polymer interface i.e.…”