Exponential Growth of LBL Films with Incorporated Inorganic Sheets

Abstract

The fastest growth pattern of layer-by-layer (LBL) assembled films is exponential LBL (e-LBL), which has both fundamental and practical importance. It is associated with "in-and-out" diffusion of flexible polymers and thus was considered to be impossible for films containing clay sheets with strong barrier function, preventing diffusion. Here, we demonstrate that e-LBL for inorganic sheets is possible in a complex tricomponent film of poly(ethyleneimine) (PEI), poly(acrylic acid) (PAA), and Na(+)-montmorillonite (MTM). This system displayed clear e-LBL patterns in terms of both initial accumulation of materials and unusually thick individual bilayers later in the deposition process with film thicknesses reaching 200 microm for films composed of 200 pairs of layers. Successful incorporation of MTM layers was observed by scanning electron microscopy and thermo-gravimetric analysis. Surprisingly, the growth rate was found to be nearly identical in films with and without clay layers, which suggests fast permeation/reptation of polyelectrolytes between the nanosheets during the "in-and-out" diffusion of polymer. In considering these findings, e-LBL growth property is expected for a wide array of available inorganic nanoscale components and have a potential to greatly expand the e-LBL field and LBL field altogether. The large thickness and rapid growth of the films affords fast preparation of nanostructured materials which is essential for multiple practical applications ranging from optical devices to ultrastrong composites.

Porous Materials with Tunable Structure and Mechanical Properties via Templated Layer-by-Layer Assembly

“…These moduli are lower than reported for similar material systems (15.7 GPa and 15.4 GPa for PEI/PAA materials with and without nanoclay, respectively) 8,10 but are consistent with the much lower stiffness reported for PEI/PAA when produced under different LbL assembly conditions (approx. 0.225 GPa).…”

“…7 LbL assembly is capable of fabricating polymer nanocomposites with exceptionally high contents of welldispersed nano-reinforcement (approximately 50-70 volume %), and with correspondingly high stiffness (tensile moduli as high as 15.7 to 125 GPa). [6][7][8][9][10] The total thickness of an LbL assembled film is determined by the number of times an alternating deposition cycle of anionic and cationic species is repeated, 11,12 but the nano-to microscale thickness per deposition cycle typical for LbL assembly is a major limitation of the technique and an impediment to utilizing the resulting materials for macroscale applications. 13 LbL assembly of conformal coatings onto three-dimensional porous templates, such as foams, colloidal crystals, and hollow tubes has been implemented for a variety of applications, [14][15][16][17][18][19] but these studies have largely focused on modifying the surfaces of these materials rather than altering the porous structure and bulk mechanical behavior.…”

Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios

“…Solid-state 13 C CPMAS NMR experiments were performed on a Bruker AV700 NMR spectrometer under cross-polarization magicangle spinning (CPMAS) condition and spinning at 5 kHz. To improve the efficiency of 1 H-13 C cross-polarization under MAS a ramp (90/100) contact pulse was applied on the 1 H radio-frequency channel.…”

“…However, this is a major scientific and technological challenge as precise nanostructuration at such biomimetic compositions with high fractions of reinforcements is hard to combine with large-scale processing methods. Various efforts have been undertaken to mimic the layered hard/soft composite structure of nacre 9 via for example, several sequential approaches, such as LbL [10][11][12][13][14][15][16][17][18] and other multilayer deposition strategies 19,20 , ice-templating and sintering of ceramics [21][22][23] , spray coating 24,25 , glow discharge plasma deposition 26 , uncontrolled co-casting of polymer/clay mixtures 27,28 , or processes at interfaces 29,30 . Unfortunately, many of these approaches are limited to a very small scale, and remain technologically infeasible owing to energy-intensive and laborious multistep procedures.…”

Surface-enhanced Raman scattering biomedical applications of plasmonic colloidal particles

“…An additional advantage of using colloidal substrates is that they can be used as prepared or assembled into solid thin films or even in bulk materials, thereby providing more flexibility to the sensing process. In line with this trapping concept, other strategies have been reported involving the incorporation of colloidal silver nanoparticles inside exponentially grown layer-bylayer (LBL) films ( polyelectrolyte multilayer films with thickness exponentially increasing with the number of deposited layers; Podsiadlo et al 2008;Srivastava et al 2008), generating a high density of hot spots and allowing the direct, ultrasensitive analysis of molecules that could not be retained by other methods (Abalde-Cela et al 2009). These substrates were found to provide intense and uniform signals, even when excited with different laser lines (figure 3).…”