Thickness Gradient in Polymer Coating by Reactive Layer-by-Layer Assembly on Solid Substrate

Abstract

The study describes a simple yet robust methodology for forming gradients in polymer coatings with nanometer-thickness precision. The thickness gradients of 0–20 nm in the coating are obtained by a reactive layer-by-layer assembly of polyester and polyethylenimine on gold substrates. Three parameters are important in forming thickness gradients: (i) the incubation time, (ii) the incubation concentration of the polymer solutions, and (iii) the tilt angle of the gold substrate during the dipping process. After examining these parameters, the characterization of the anisotropic surface obtained under the best conditions is presented in the manuscript. The thickness profile and nanomechanical characterization of the polymer gradients are characterized by atomic force microscopy. The roughness analysis has demonstrated that the coating exhibited decreasing roughness with increasing thickness. On the other hand, Young’s moduli of the thin and thick coatings are 0.50 and 1.4 MPa, respectively, which assured an increase in mechanical stability with increasing coating thickness. Angle-dependent infrared spectroscopy reveals that the C–O–C ester groups of the polyesters exhibit a perpendicular orientation to the surface, while the CC groups are parallel to the surface. The surface properties of the polymer gradients are explored by fluorescence microscopy, proving that the dye’s fluorescence intensity increases as the coating thickness increases. The significant benefit of the suggested methodology is that it promises thickness control of gradients in the coating as a consequence of the fast reaction kinetics between layers and the reaction time.

Scaled Production of Functionally Gradient Thin Films Using Slot Die Coating on a Roll-to-Roll System

“…More specifically, the gradient structure of an organic electrically conductive material, poly­(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), was developed in application areas such as wearable smart electronics and optoelectronics . Further, polyethylenimine (PEI) is a synthetic cationic material, and the gradient structure has been used in many applications such as nanofiltration membranes and cell adhesion . However, the gradient structures in these applications mostly exist through the thickness and/or use lab-scale methods that are not scalable and inefficient.…”

“… 21 Further, polyethylenimine (PEI) is a synthetic cationic material, and the gradient structure has been used in many applications such as nanofiltration membranes 22 and cell adhesion. 23 However, the gradient structures in these applications mostly exist through the thickness and/or use lab-scale methods that are not scalable and inefficient.…”

Improved ionic current rectification utilizing cylindrical nanochannels coated with polyelectrolyte layers of non-uniform thickness

“…As such, we make use of PEL thickness asymmetry, which is different from PEL charge asymmetry used in bipolar channels; 64 in fact, our method is based on a new grafting technique developed recently for a layer-by-layer PEL coating that allows for a thickness gradient. 65 The efficacy of the proposed design is compared with PEL-covered conical nanochannels by numerically solving the governing equations including the Poisson, Nernst–Planck, and Stokes–Brinkman equations. It is shown that the proposed design can provide a higher degree of ICR than conical nanochannels over a wide range of ion concentrations, and its efficiency is more pronounced for higher values of the PEL-fixed charge concentration.…”

Highly Efficient Conversion of Salinity Difference to Electricity in Nanofluidic Channels Boosted by Variable Thickness Polyelectrolyte Coating

“…While the findings reported herein appear to be somewhat conceptual, recent advancements in surface engineering, fabrication, and functionalization in general indeed evidence their practicality. Specifically, the development of a simple yet robust methodology of forming gradients in polymer coatings with nanometer thickness precision by a reactive layer-by-layer assembly via modulating the incubation time, the incubation concentration of the polymer solutions, and the tilt angle of the substrate during the dipping process is a promising point in this respect. Our proposed method shares some features with previous research works exploiting geometrical asymmetry, with ,, or without PEL coating, to enhance RED power generation.…”