PDADMAC/PSS

FIG. 2 -potential as a function of layer number for PDADMAC/PSS multilayers on sulfate-stabilized polystyrene (PS) latices. The multilayers were assembled onto the negatively charged PS latices ( -potential of ca. -65 mV, layer number = 0) by the consecutive deposition of PDADMAC (odd layers) and PSS (even layers). Positive values are observed for PDADMAC deposition, and negative values for PSS adsorption. The alternating values are characteristic of stepwise growth of multilayer films on colloids. 

FIG. 3 Normalized SPLS intensity distributions of (from left to right) neat PS latices and PS lat-ices coated with one, five, and nine PDADMAC/PSS multilayers. (From Ref. 50.)... 

FIG. 4 Thickness of PDADMAC/PSS multilayers assembled on PS latices as a function of layer number. The layers were assembled by the consecutive adsorption of PDADMAC and PSS. The thicknesses were determined from SPLS data. 

Fig. 6 Temperature-controlled permeability of PDADMAC/PSS capsules. CLSM images of (a) capsules incubated with lOkDa FITC-dextran before heat treatment, and (b) after heat treatment. (c) Capsules heat treated in the presence of FITC-dextran and subsequently washed to remove unencapsulated dextran. (d) Schematic showing the encapsulation process for small and large molecules. Reprinted with permission from Advanced Functional Materials [49]...

Complexes made from polyelectrolytes with low and medium molar mass (such as PDADMAC, PSS, PEI, PAQ are studied very often and are used in different fields of application. 

Among them, Dautzenberg et al. reported early work on the influence of PEL concentration on the mass (M, not to be confused with the molecular weight of the PEL components) and size (herein Rq = 0 ) of PEC particles, based on SLS measurements of the PDADMAC/PSS system [27] (see Fig. 15). The plot of / G versus Cpel could be fltted by a simple power law of the type Rq Cpel ... 

Fig. 15 Dependence of PEL concentration on the Mw of PDADMAC/PSS PEC particles. (From [27] with kind permission of ACS)...

Fig. 17 Dependence of size parameters (Mw and Rq) of PEC particles of PDADMAC/PSS at X = 0.5 on ionic strength (I Cj) in the mixing PEL solutions. (From [68] with kind permission...

In comparable experiments using PDADMAC/poly(maleic acid-co-propylene) at CpEL = 0.001-0.004 M, Pergushov and Buchhammer found an increase in the hydro-dynamic radius/ Hftoml00nm withnoNaClto 300nmat0.23 MNaCl [71].In these experiments, the resolution of the salt concentrations was lower. Presumably, at CNaCi 0.005 M a minimum of for PDADMAC/PSS would also have been found. 

Dautzenberg studied the influence of the mixing ratio on the structural density p of PEC-PDADMAC/PSS [26]. A slight linear increase from around 0.4 g/cm at... 

Multilayer assemblies were furthermore investigated in dependence of the number of layers, , where an interesting influence of the outer layer potential on the multilayer system was found (see Fig. 26). Here, is displayed, which is a measure for the total IH immobilisation in the multilayer arrangement. In PDADMAC/PSS multilayers (squares) a monotonous increase of R2sp with layer number was observed and attributed to the additional water immobilised in each adsorbed layer. 

Fig. 2.4. -potential as function of layer number for coated polystyrene latex particles, diameter 640nm, PSS/PDADMAC, BSA/PDADMAC, PSS/PAH, a DNA/PDADMAC. 

It is worth mentioning that currently most of the works in the literature are devoted to the study of multilayers of synthetic poly electrolytes. Some iconic examples of these systems are multilayers of type (PDADMAC + PSS)n (PDADMAC poly(diallyl-dimethyl-ammonium chloride), and (PSS poly(4-sty-rene sulfonate of sodium)) where the subindex n indicates the number of bilayers in the multilayer [80-82] or (PAH - - PSS) (PAH poly(aIlylamine hydrochloride)) [83]. However, there is a growing interest in the last years on the fabrication of biocompatible systems, e.g. biomacromolecules [84, 85]. Some examples are multilayers of type (CHI - - HEP)n (being CHI Chitosan and HEP Heparin) [86] (PLL + HA)n (PLL is poly(L-lysine) and HA is hyaluronic acid) or (PLL + PGA)n (PGA is poly(glutamic acid)) [87, 88]. 

One of the most critical parameters in the control of the compensation mechanism is the ionic strength of the solutions. This is because the changes on the ionic equilibrium in the multilayers are associated to the modification of the charge density by ion condensation mechanism [111]. This fact has been pointed out for one of the classical model of PEMs, (PDADMAC PSS)n, by Schlenofl and... 

Fig. 1 Charge inversion for polyelectrolyte multilayers represented as the surface potential dependence on the number of adsorbed layer, N. a Charge inversion as it was obtained by the Kelvin probe for (PDADMAC + PSS) multilayers adsorbed from a NaCl solution of concentration 50 mM onto a flat surface. Adapted from Ref. [80] with permission from The Royal Society of Chemistry, b Zeta potential of (PSS + PAH)n multilayers deposited onto colloidal microparticles of methylformamide with a positive bare charge. Adapted with permission from Ref. [52]. Copyright (1998) American Chemical Society, c Zeta potential changes evaluated using Streaming potential for multilayers built with PSS and PAH, the results are represented as zeta potential against number of measurement. The number of measurements is related to the number of times that each single layer was measured and it shows as accumulative number with the increase of the layer number. Adapted with permission from Ref. [83]. Copyright (2000) American Chemical Society...

Fig. 3 Surface density of monomer, pmonomer, for polyanion and polycation layers in (PDADMAC + PSS) multilayers with different ionic strength. Notice that the different amount of adsorbed PDADMAC and PSS is a strong evidence of the existence of extrinsic compensation. Reproduced from Ref. [80] with permission from The Royal Society of Chemistry...

Fig. 4 a Re dependence on N for (PDADMAC + PSS)n films built at different ionic strengths, b Scheme of the distribution of extrinsic sites in (PDADMAC + PSS)n films terminated in PDADMAC and PSS. Re ninted with permission from Ref. [112]. Copyright (2012) American Chemical Society... 

Fig. 5 Changes on the UV-visible spectrum of (PDADMAC + PSS) multilayers adsorbed from pure water solutions with the number of bilayers. Note that only PSS layers show absorbance in this region. The inserted figure represents the dependence of the absorbance on the number of adsorbed bilayers. This latter is a representation of the adsorbed amount...

In general, two well separated kinetic processes are observed and were identified by Bertrand et al. [172] as a first fast nucleation of domains followed by a second slower reorganization of the polymer chains in the multilayer. A more detailed picture allows one to describe the first step as a diffusive process coupled to the adsorption through an electrostatic or steric barrier [166, 173], whereas the second step implies aU the reorganization steps that lead to the multilayer till the stationary state [167]. This latter step includes both in plane reorganization of the polymeric chains and the interdififusion of the polyelectrolyte chains along the whole multilayer structure [99]. Figure 13 shows the adsorption kinetics of a PDADMAC layer onto a (PDADMAC - - PSS)n film. 

Fig. 15 Kinetic times for (PDADMAC + PSS)n and (PAH + PSS) multilayers obtained using Eq. (3). a, b Times for the adsorption of PDADMAC open circle, filled square) and PAH layers, c, d Times for the adsorption of PSS in (PDADMAC + PSS) open triangle) and (PAH + PSS) (filled diamond) multilayers. Reprinted fiom Ref. [97], Copyright (2011), with permission from Elsevier...

Figure 15 shows as example of the time dependences on N the dependence of the adsorption times on N for the assembling of (PDADMAC + PSS)n and (PAH -I- PSS) adsorbed from NaCl solution of concentration 100 mM. The results point out the different phenomena involve in the adsorption for each specific pair of polymers. 

A last parameter involved in the control of the solvent quality is the temperature of the solutions, and its influence can be even stronger than that of I and pH. Despite its importance, low attention has been paid to this parameter in the literature. Salomaki et al. [102] pointed out that the modification of the temperature allows the modification of the growth trend of both (PDADMAC + PSS)n and (PAH + PSS)n multilayers. Special interest present the transition between linear and non-linear growth for (PAH + PSS)n multilayers mediated by the temperature since this system presents a linear growth trend in almost all the I and pH assembling conditions studied in the literature [83, 151]. 

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