Spontaneous Surface Flattening via Layer-by-Layer Assembly of Interdiffusing Polyelectrolyte Multilayers

Abstract

We report a facile means to achieve planarization of nonflat or patterned surfaces by utilizing the layer-by-layer (LbL) assembly of highly diffusive polyelectrolytes. The polyelectrolyte pair of linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) is known to maintain intrinsic diffusive mobility atop or even inside ionically complexed films prepared by LbL deposition. Under highly hydrated and swollen conditions during the sequential film buildup process, the LbL-assembled film of LPEI/PAA undergoes a topological self-deformation for minimizing surface area to satisfy the minimum-energy state of the surface, which eventually induces surface planarization along with spontaneous filling of surface textures or nonflat structures. This result is clearly different from other cases of applying nondiffusive polyelectrolytes onto patterned surfaces or confined structures, wherein surface roughening or incomplete filling is developed with the LbL assembly. Therefore, the approach proposed in this study can readily allow for surface planarization with the deposition of a relatively thin layer of polyelectrolyte multilayers. In addition, this strategy of planarization was extended to the surface modification of an indium tin oxide (ITO) substrate, where surface smoothing and enhanced optical transmittance were obtained without sacrificing the electronic conductivity. Furthermore, we investigated the potential applicability of surface-treated ITO substrates as photoelectrodes of dye-sensitized solar cells prepared at room temperature. As a result, an enhanced photoconversion efficiency and improved device characteristics were obtained because of the synergistic role of polyelectrolyte deposition in improving the optical properties and acting as a blocking layer to prevent electron recombination with the electrolytes.

Humidity‐Triggered Self‐Healing of Microporous Polyelectrolyte Multilayer Coatings for Hydrophobic Drug Delivery

“…Especially important is the charge distribution of polyelectrolytes, which has been investigated primarily to understand the buildup mechanism of PEM films . The highly charged polyelectrolytes tend to be kinetically trapped within the films due to their extended polyion size and strong charge binding between ion pairs . In this PEM system, both PEI (p K a ≈ 6.5) and PAA (p K a ≈ 4.5–5.5) are weak polyelectrolytes with low charge density, and they are assembled into a network that is not tightly cross‐linked and therefore is easily disturbed .…”

Nanopatterned conductive polymer films as a Pt, TCO-free counter electrode for low-cost dye-sensitized solar cells

“…1b). 27 A nanopatterned PEDOT thin lm was fabricated via the spincoating of a PEDOT oligomer solution 18 on top of the PS/PET substrates with a hole pattern, followed by thermal polymerization at 70 C for various polymerization times. The homogeneous EDOT oligomer solution was spin-coated on the nanopatterned PS/PET substrates (Fig.…”

Hydrophobically modified polyelectrolyte for improved oxygen barrier in nanobrick wall multilayer thin films

“…Figure shows the exponential growth of these quadlayer recipes, as measured by profilometry, which is expected when using multiple weak polyelectrolytes . The seemingly exponential growth of these films is attributable to the interdiffusion of PEI (or PEI‐Py) and PAA …”