The Anomalous Influence of Polyelectrolyte Concentration on the Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers

Abstract

The deposition and nanostructure of polyelectrolyte (PEL) multilayers (PEMs) of branched poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA) onto silicon substrates was studied in terms of the dependence of pH and the PEL concentration (cPEL) in the individual adsorption steps z. Both a commercial automatic dipping device and a homebuilt automatic stream coating device (flow cell) were used. Gravimetry, SFM, transmission (TRANS) and in situ attenuated total reflection (ATR) FTIR spectroscopy were used for the quantitative determination of the adsorbed amount, thickness, chemical composition and morphology of deposited PEMs, respectively. Firstly, the combination of pH = 10 for PEI and pH = 4 for PAA, where both PEL were predominantly in the neutral state, resulted in an extraordinarily high PEM deposition, while pH combinations, where one PEL component was charged, resulted in a significantly lower PEM deposition. This was attributed to both PEL conformation effects and acid/base interactions between basic PEI and acidic PAA. Secondly, for that pH combination an exponential relationship between PEM thickness and adsorption step z was found. Thirdly, based on the results of three independent methods, the course of the deposited amount of a PEM-10 (z = 10) versus cPEL in the range 0.001 to 0.015 M at pH = 10/4 was non-monotonous showing a pronounced maximum at cPEL = 0.005 M. Analogously, for cPEL = 0.005 M a maximum of roughness and structure size was found. Fourthly, related to that finding, in situ ATR-FTIR measurements gave evidence for the release of outermost located PEI upon PAA immersion (even step) and of outermost PAA upon PEI immersion (odd step) under formation of PEL complexes in solution. These studies help us to prepare PEL-based films with a defined thickness and morphology for interaction with biofluids in the biomedical and food fields.

Anomalous Influence of Salt Concentration on Deposition of Poly(l-Lysine)/Cellulose Sulfate Multilayers Evidenced by In Situ ATR-FTIR

“…Nevertheless, there was a profound loss of PLL and CS only for c S = 1.0 M, as proven by the ex situ experiments on the respective CS and PLL adsorbing solutions which had been in contact with the PEM-1 to PEM-20 films. This finding was also observed for other systems, like the aforementioned PEI/PAA system [13], where besides diffusion, also escape from the PEM prevailed.…”

“…In these PEM spectra, the increasing overall intensity and the changes of both the Amide I and Amide II bands at around 1640 and 1550 cm −1 due to PLL and of ν(SO 2 ) band at 1248/1222 cm −1 (doublet), and of the ν(C-O) band at 1050 cm −1 due to CS in relation to z, are most significant. Furthermore, an increasing negative ν(OH) band at around 3400 cm −1 with increasing z shows up, which is not given herein but in the Figure S1 of the Supplementary Materials, and has been discussed previously for another PEM system [13]. The diagnostic IR bands are assigned in the following Table 1.…”

“…To further address this issue and check the findings from the in situ ATR-FTIR deposition data concerning the loss/uptake or depletion/enrichment in relation to salinity, we took ex situ ATR-FTIR measurements on 0.01 M PLL solutions and CS solutions after z = 20 consecutive adsorption steps for c NaCl = 0, 0.1 and 1.0 M. A similar experiment was reported recently for a PEM system composed of cationic poly(etyhleneimine) (PEI) and anionic poly(acrylic acid) (PAA) [13]. It was expected that in the FTIR spectra of the host PLL solution, traces of guest CS might be detected, while in those of the host CS solution, traces of guest PLL might be present, indicating either the complete loss of the outermost PEL or the depletion of internal PEL material.…”

Single-Step Application of Polyelectrolyte Complex Films as Oxygen Barrier Coatings

“… 37 In fact, the films are a mixture of PEI and PAA in both charged and uncharged forms so that the exact composition of the films cannot be determined from FT-IR spectra. 38 , 39 …”

Prediction of coating thickness for polyelectrolyte multilayers via machine learning

“…The growth function, describing changes in coating thickness d with the number of layers, N , has three coefficients, a 0 , a , and b , which vary depending on the coatings 16 , 17 . In this function parameter, b defines function curvature: for b ≥ 0.05, the growth is exponential, for b < 0.05, it is nearly linear.…”