Effect of Ionic Strength and Layer Number on Swelling of Polyelectrolyte Multilayers in Water Vapour

Abstract

The swelling behavior of polyelectrolyte multilayers (PEMs) of poly(sodium-4 styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) prepared from aqueous solution of 0.1 M and 0.5 M NaCl are investigated by ellipsometry and Atomic Force Microscopy (AFM). From 1 double-layer up to 4 double-layers of 0.1 M NaCl, the amount of swelling water in the PEMs decreases with increasing number of adsorbed double layers due to an increase in polyelectrolyte density as a result of the attraction between the positively charged outermost PDADMAC layer and the Si substrate. From 6 double layers to 30 double layers, the attraction is reduced due to a much larger distance between substrate and outermost layer leading to a much lower polyelectrolyte density and higher swelling water. In PEMs prepared from aqueous solution of 0.5 M NaCl, the amount of water constantly increases which is related to a monotonically decreasing polyelectrolyte density with increasing number of polyelectrolyte layers. Studies of the surface topology also indicate a transition from a more substrate affected interphase behavior to a continuum properties of the polyelectrolyte multilayers. The threshold for the transition from interphase to continuum behavior depends on the preparation conditions of the PEM.

Sorption/release of diclofenac sodium in/from free‐standing poly(acrylic acid)/poly(ethyleneimine) multilayer films

“…[12][13][14][15][16] Also, the properties of multilayer films are influenced by the assembly conditions, such as the concentration, pH, ionic strength and temperature of deposition solutions. [17][18][19][20][21][22][23][24] All these parameters allowed the design of a large variety of multilayer films, which have found applications as separation membranes, 25,26 anticorrosion, and flame-retardant coatings, 27,28 antimicrobial membranes, 29,30 drug delivery systems, [31][32][33][34][35] etc.…”

Polyelectrolytes

“…This high water content in the interior of the multilayers confers a gel-like character to the films that makes possible the diffusion of small molecules along the film. This latter plays a key role in applications such as the drug delivery [208,209]. In general, a decrease of the water content with the increase of N is observed by all the systems studied in literature [210].…”

“…The water content of the multilayers presents a great importance in the dynamic and stability of the formed structures [53,80,92,96,100,109,120,[202][203][204][205][206][207][208][209]. The role of the water in the polyelectrolyte multilayers is the control of the local molecular interactions, especially those related to the complexation between the polyelectrolytes [204].…”

“…The role of the water in the polyelectrolyte multilayers is the control of the local molecular interactions, especially those related to the complexation between the polyelectrolytes [204]. Different studies have pointed out that the water content of the multilayers is in general quite high, being in the 20-80 % range of the total weight of the PEMs [208,209]. The water content of the multilayers can be easily tuned changing the assembling conditions and/or the charge density of the polymers (see Fig.…”

Stick-Slip Mechanisms at the Nanoscale

“…For all substrates the root mean square (RMS) roughness was determined as published previously (8,22): For PTFE the roughness was 7.6 nm, for the SAM 3.3 nm, 0.2 nm for Mica, 0.3 nm for the diamond substrates, and 0.09 nm for Si and 2.2 nm for the PEMs. Although the roughness of the different surfaces varies between 0.09 nm and 7.6 nm, we showed in an earlier publication that this does not affect the behavior of single polymer adhesion (23) and is, therefore, not sufficient to explain the different friction motifs.…”