lbl

Layer-by-Layer (LbL) assembly is a versatile technique for constructing ultrathin films via the successive adsorption of alternating species onto a substrate. The method relies on the electrostatic attraction between oppositely charged species, typically polyelectrolytes, though hydrogen bonding, hydrophobic interactions, and covalent bonding can also be used. The process commonly involves dipping or dipping-and-rinsing steps: a substrate is immersed in a solution containing a positively charged species, rinsed to remove weakly bound material, then alternately exposed to a negatively charged solution, with another rinse. Repeating the cycle builds up multilayered films whose thickness is approximately controlled by the number of bilayers and the identity of the materials. Each bilayer typically adds roughly 1–10 nanometers, depending on the chain length, conformation, and solvent.

LbL deposition was pioneered in the late 1990s by Gero Decher and colleagues, building on early work in layerwise ultrathin films. It enables precise control of film composition and thickness under mild aqueous conditions, and is compatible with various substrates, including polymers, ceramics, and surfaces with roughness.

Materials employed include polyelectrolytes (e.g., poly(allylamine hydrochloride), poly(styrene sulfonate)), nanoparticles, dyes, biomolecules, and enzymes, yielding polyelectrolyte multilayers (PEMs) and hybrid organic-inorganic films. Variants such as covalent LbL, hydrogen-bonded LbL, and LbL for biosensing and release applications exist.

Applications span surface modification for corrosion protection, anti-fouling coatings, drug delivery systems, sensors, catalysis, optics, and tissue engineering. Characterization techniques include ellipsometry, UV-Vis spectroscopy, FTIR, AFM, and XPS.