Spin-speed independent thickness and molecular adsorption behaviour of polyelectrolyte multilayers

Abstract

The science behind the buildup mechanism of polyelectrolyte multilayers is important for developing devices for various engineering applications. Here we, study the dependency of thickness of polyelectrolyte multilayer films, fabricated using spin-assisted layer-by-layer self-assembly of polyelectrolytes technique, with respect to varying spin-speed while keeping all other parameters of the fabrication process-window constant. The thickness measurements were performed using variable angle spectroscopic ellipsometry and atomic force microscopy. The experimentally observed results were validated mathematically using a Flory type theory. In addition, the biomolecular adsorption studies on these polyelectrolyte multilayer films fabricated at various spin-speeds, were also quantitatively analyzed using fluorescence microscopy studies. It was seen that the effect of spin-speed on the thickness of polyelectrolyte multilayers was negligible. In addition, it was also observed that the bio-molecular adsorption modalities onto these substrates were also independent of the spin-speed. This finding prompts to develop low-cost alternative technologies for various biomedical engineering applications, like functionalized substrates for centrifugal assay for fluorescence-based cell adhesion, wherein stability of films against strong mechanical forces generated during spinning can play an important role.

Simplifying Molecular Transport in Polyelectrolyte Multilayer Thin Films

“…[ 113,147–149 ] But, ellipsometry require specialized substrates and complex modelling for data interpretation. [ 150 ]…”

Fluorescence Signal Enhancement by a Spray-Assisted Layer-by-Layer Technique on Aluminum Tape Devices for Biosensing Applications

“…Further researchers have noticed a significant difference in the surface properties of polymeric films fabricated using DA-, SA-, and SP-LbL methods, which is due to the difference in adsorption mechanisms involved. In DA-LbL, the polyelectrolyte deposits on the substrate as a result of electrostatic interactions, followed by rearrangement of adsorbed polymeric chains. , On the other hand, in SA-LbL, polyelectrolyte deposition and rearrangement occur simultaneously as a result of the high spinning speed. Here, elimination of loosely bound polyelectrolyte chains with water during rinsing also takes a short time as a result of the high spin speed. , In addition, the centrifugal and air shear forces involved in SA-LbL increase the electrostatic interactions, resulting in smoother films compared to the DA-LbL deposition process. ,, Whereas in SP-LbL, the thickness and composition of PEM depend upon the amount of spray that impinges on the substrate.…”

“…Electrostatic interactions are predominantly responsible for the formation of PEM, which is achieved through alternate deposition of cationic PAH with anionic PAA with successive rinsing steps in between . SA-LbL-based devices were fabricated by alternatively spin coating the PAH and PAA solution by maintaining the spin time of 40 s and spin speed of 2000 rpm, accompanied by a mandatory DI water rinse for 40 s in between two depositions to remove loosely bound polyelectrolytes . DA-LbL-based devices were fabricated by dipping the substrates alternatively in PAH and PAA solutions, with 1 min being the dipping time, followed with a DI water rinse for 1 min .…”

Fast‐Dip Layer‐by‐Layer Self‐Assembly of Polyelectrolytes as a Low‐Cost Biosensing Platform

“…Woolam co. Inc, the detailed procedure was explained in the earlier work. [ 50 ] Tapping mode AFM scanning for thickness measurements and surface morphological studies were done using Bruker (Model: Innova). Scanning Electron Microscope (SEM) imaging was performed using a Zeiss microscope by keeping the working distance below 10 mm.…”

“…[64,65] Spin-LbL PEM devices were fabricated at a spin speed of 2000 RPM and a spinning time of 40 s for each layer deposition, followed by a mandatory DI water rinse of 40 s between every deposit, as detailed in our earlier work. [50] Figure 7a shows the thickness comparison of both spin and FDip-LbL. In addition to the experimental measurements, data is mapped with the standard power fit model, which is given in Equation ( 2), where a, and b are constants and t is the thickness, and n is the number of polyelectrolyte layers, the values of a and b are given in Table 2.…”