Delamination and Wrinkling of Flexible Conductive Polymer Thin Films

Abstract

Polymer based conductive and transparent thin films are an important class of functional materials at the heart of flexible organic electronic devices. These flexible films are prone to degradation and to mechanical instability leading to the formation of blisters, wrinkles, and cracks. This is detrimental to their use especially in the case of multilayer devices. Here, it is shown that a simple water or solvent drop deposited on such films gives rise to a buckling instability and the formation of several folds due to the tendency of these films to swell in contact with the solvent. A phase diagram of the instability portraying its domain of existence, and thus the means to inhibit it, is proposed. By depositing drops on such films and observing the instability, material parameters such as the elastic modulus of the thin films or their energy of adhesion to the substrate can be estimated reliably. Further, the instability can be harnessed to pattern surfaces at low cost giving rise to percolated and more conductive pathways in the conductive polymer films under scrutiny.

Drop Spreading and Confinement in Swelling-Driven Folding of Thin Films

“…Upon evaporation of the solvent, the film deswelled, but the folds did not disappear (Figure b) indicating that reverse sliding is prevented, either by film–substrate adhesion or by film self-adhesion over the self-contacting region along the underside of the fold. Similar folding has been observed in swollen hydrogels, − other polymer films, − in strained, crosslinked polymer brushes, in metal films on solvent-swollen substrates, and in growing bacterial biofilms . The signature feature of such folding is a high degree of localization, i.e., some regions of the film show high localized curvature and large out-of-plane deflection, whereas the rest of the film remains conformal with the flat substrate.…”

“…Thin films under compression can undergo a variety of instabilities including creases, wrinkles, localized folds, ridges, and delamination buckles. − The resulting structures have a wide variety of applications, including microscale patterning, surface property enhancement, and responsive materials . This article is about an unusual type of buckling behavior wherein a film resting on a rigid substrate, upon swelling with a solvent, forms highly localized folds. − The chief concern of this article is to explore finite-size effects, i.e., situations when only a small region of the film is allowed to swell.…”

Controlling morphology, adhesion, and electrochromic behavior of PEDOT films through molecular design and processing

“…Likewise, the PEDOT-Crown film produced by cyclic voltammetry (Figure S6d) is smoother than the corresponding PEDOT film (Figure S6b), but in this case, it is worth noting that the increased average PEDOT film thickness is skewed by the high degree of noise, which is attributed to puckering of the poorly-adhered thick film to ITO, as seen in Figure S2. 13,19 Therefore, this observed reduction in wrinkling for the PEDOT-Crown films is further evidence that the crown polymer achieves superior adhesion to ITO than is the case for PEDOT.…”

“…11 Furthermore, its well-established electrochromic switching between darkand sky-blue has enabled the development of PEDOTbased electrochromic devices. 12 Despite these advantages, there are still many obstacles yet to overcome in order to realize the full potential of PEDOT as an ideal bioelectronic or electrochromic material; noted problems associated with PEDOT include decay in stability over time 12 ; poorly controlled surface morphology 13 ; and weak substrate adhesion, 14 attributed to the lack of suitable chemical interactions between the substrate and polymer. 15 Much work has already been done to procure solutions to these issues; thus far mostly focusing on refining deposition method, or incorporating a variety of comonomers, dopants or additives.…”

Universal aspects of droplet spreading dynamics in Newtonian and non-Newtonian Fluids

“…Droplet impacts are routinely studied 1 to understand a wide range of phenomena ranging from spraying, coating, printing [2][3][4][5] to self cleaning and anti-icing. 6 Typical examples abound from every day life or in industrial applications: a droplet of rain impacting a glass pane, 7 the deposition of a molten metal droplet for electronic printing, [8][9][10] or droplet impacts of polymers or surfactants solutions usually used for a more controlled deposition.…”