Investigating Zigzag Film Growth Behaviors in Layer-by-Layer Self-Assembly of Small Molecules through a High-Gravity Technique

Abstract

The zigzag film growth behavior in the layer-by-layer (LbL) assembly method is a ubiquitous phenomenon for which the growth mechanism was rarely investigated, especially for small molecules. To interpret the zigzag increasing manner, we hypothesized that the desorption kinetics of small molecules was dominant for the film growth behavior and demonstrated this hypotheis by introducing the high-gravity technique into the LbL assembly of a typical polyelectrolyte/small molecule system of polyethylenimine (PEI) and meso-tetra(4-carboxyphenyl)porphine (Por). The results showed that the high-gravity technique remarkably accelerated the desorption process of Por; the high-gravity LbL assembly provides a good platform to reveal the desorption kinetics of Por, which is tedious to study in conventional situation. We found that as much as 50 min is required for Por molecules to reach desorption equilibrium from the substrate to the bulk PEI solution for the conventional dipping method; however, the process could be accelerated and require only 100 s if a high-gravity field is used. Nonequilibrated desorption at 10 min for normal dipping and at 30 s for high-gravity-field-assisted assembly both exhibited a zigzag film growth, but after reaching desorption equilibrium at 100 s under a high-gravity field, film growth began to cycle between assembly and complete disassembly instead of LbL assembly. For the first time we have proven that the high-gravity technique can also accelerate the desorption process and demonstrated the desorption-dependent mechanism of small molecules for zigzag film growth behaviors.

Layer-by-Layer Nanoarchitectonics Using Protein–Polyelectrolyte Complexes toward a Generalizable Tool for Protein Surface Immobilization

“…In particular, we have shown that when a PE is adsorbed on a PPCs layer, it can complex the PE of the PPCs, which releases the protein and causes a decrease of the multilayer mass . Similar phenomena have been reported in PEMs, especially for systems containing small molecules, where typical stepwise curves in a sawtooth profile (adsorption–desorption steps) were observed . In a previous study, we suggested that this mechanism is a function of the PE–PE ion-pairing strength compared to the protein–PE pairing strength .…”

“…73 Similar phenomena have been reported in PEMs, especially for systems containing small molecules, where typical stepwise curves in a sawtooth profile (adsorption−desorption steps) were observed. 74 In a previous study, we suggested that this mechanism is a function of the PE−PE ion-pairing strength compared to the protein−PE pairing strength. 73 This hypothesis is in line with the difference in desorption observed for PAH compared to Chi, and for LL-37 compared to Ins and Gox.…”

Innovation in Layer-by-Layer Assembly

“…Some polymer combinations that grow exponentially using immersive LbL assembly grow linearly under high-gravity assembly . With long enough assembly times, complete desorption of polymers can be engineered with high gravity, rather than the partial desorption seen with many LbL techniques . An issue with high-gravity spin assembly is the requirement for the creation of a custom spinning machine, in comparison to standard spin assembly (with horizontal substrates) machines that are relatively common in research and industry settings.…”

Layer-by-Layer Assembly of Polyelectrolyte Multilayer onto PET Fabric for Highly Tunable Dyeing with Water Soluble Dyestuffs

“…Layer-by-layer (LbL) electrostatic self-assembly technique has received immense scientific and technological interest as a facile and powerful approach to preparing materials with tailored properties [18,19,20]. In the LbL assembly procedure, oppositely charged polyelectrolytes are alternately deposited on a pre-charged substrate to generate a nanometer-scale polyelectrolyte film on its surface.…”