Adsorption of poly(ethyleneimine) on silica surfaces: effect of pH on the reversibility of adsorption

The role of polymer charge density in the kinetics of the adsorption and desorption, on silica, of the polyelectrolyte poly(ethyleneimine) (PEI) was investigated by stagnation-point flow reflectometry. In the first series of experiments, PEI solutions were introduced at the same ionic strength and pH as the background solvent. It was found that the adsorbed amount of PEI increased by increasing pH. In the second series of investigations, several PEI solutions with ascending pH were introduced consecutively into the cell. In these cases, a stepwise buildup of the adsorbed amount was observed and the "final" adsorbed amounts were observed to be roughly equal with the adsorbed amounts of the first series of measurements at the same pH. Finally, adsorption/desorption experiments were performed where the preadsorption of PEI was followed by the introduction of PEI solutions of descending pH. No desorption was detected when the pH changed from pH = 9.7 to pH = 5.8. However, when there was a 9.7 --> 3.3 or 5.8 --> 3.3 decrease in the pH, the kinetic barriers of desorption seemed to completely disappear and roughly the same adsorbed amount as in the first series of experiments at pH = 3.3 was quickly attained by desorption of the PEI. This study reveals the high impact of pH, affecting parameters such as charge density of the surface and polyelectrolyte as well as the structure of the adsorbed macromolecules, on the desorption properties of weak polyelectrolytes. The observed interfacial behavior of PEI may have some important consequences for the stability of alternating polyelectrolyte multilayers containing weak polyelectrolytes.     

Influence of salt and rinsing protocol on the structure of PAH/PSS polyelectrolyte multilayers

A quartz crystal microbalance (QCM) and dual polarization interferometry (DPI) have been utilized to study how the structure of poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers is affected by the rinsing method (i.e., the termination of polyelectrolyte adsorption). The effect of the type of counterions used in the deposition solution was also investigated, and the polyelectrolyte multilayers were formed in a 0.5 M electrolyte solution (NaCl and KBr). From the measurements, it was observed that thicker layers were obtained when using KBr in the deposition solution than when using NaCl. Three different rinsing protocols have been studied: (i) the same electrolyte solution as used during multilayer formation, (ii) pure water, and (iii) first a salt solution (0.5 M) and then pure water. When the multilayer with PAH as the outermost layer was exposed to pure water, an interesting phenomenon was discovered: a large change in the energy dissipation was measured with the QCM. This could be attributed to the swelling of the layer, and from both QCM and DPI it is obvious that only the outermost PAH layer swells (to a thickness of 25-30 nm) because of a decrease in ionic strength and hence an increase in intra- and interchain repulsion, whereas the underlying layers retain a very rigid and compact structure with a low water content. Interestingly, the outermost PAH layer seems to obtain very similar thicknesses in water independent of the electrolyte used for the multilayer buildup. Another interesting aspect was that the measured thickness with the DPI evaluated by a single-layer model did not correlate with the estimated thickness from the model calculations performed on the QCM-D data. Thus, we applied a two-layer model to evaluate the DPI data and the results were in excellent agreement with the QCM-D results. To our knowledge, this evaluation of DPI data has not been done previously.     

In situ ATR-FTIR and SFM Studies on the Influence of Adsorption time on Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers

Summary: The deposition and the nanostructure of polyelectrolyte multilayers (PEM) of branched poly(ethyleneimine)/poly(acrylic acid) (PEI/PAC) was studied in dependence of the adsorption time (t_ADS) of the individual steps. PEM were reproducibly deposited applying up to z = 20 adsorption steps at the fixed pH combination of 10/4 and polyelectrolyte concentration c_PEL = 0.005 M in a flow cell using an automated valve system. in situ ATR-FTIR spectroscopy and SFM were used for quantitative determination of deposited amount and thickness, respectively. A linear relation between PEL band integrals and thickness of thin PEM films was found. Varying t_ADS from 0.5 to 5 min in each of the adsorption steps resulted in a steep rise of the deposited PEM amount. For t_ADS > 5 min the deposition did only marginally increase. Evidence for the release of outermost located PEI upon PAC immersion (even step) and of outermost PAC upon PEI immersion (odd step) was obtained. SFM images on consecutively deposited PEM-6 showed a slight increase in structure size and roughness for increasing t_ADS. These studies help to prepare polyelectrolyte based films with controlled thickness for the interaction with biofluids in the biomedical and food field.     

The impact of electrolyte on the adsorption of sodium dodecyl sulfate/polyethyleneimine complexes at the air-solution interface

The addition of electrolyte (0.1 M NaCl) is shown to have a significant impact upon the surfactant concentration and solution pH dependence of the adsorption of sodium dodecyl sulfate (SDS)/polyethyleneimine (PEI) complexes at the air-solution interface. Substantial adsorption is observed over a wide surfactant concentration range (from 10(-6) to 10(-)2 M), and over much of that range of concentrations the adsorption is characterized by the formation of surface multilayers. The surface multilayer formation is most pronounced at high pH and for PEI with a lower molecular weight of 2K, compared to the higher molecular weight of 25K. These results, obtained from a combination of neutron reflectivity and surface tension, highlight the substantial enhancement in surfactant adsorption achieved by the addition of a combination of the polyelectrolyte, PEI, and a simple electrolyte. Furthermore the effect of electrolyte on the pH dependence of the adsorption further highlights the importance of the hydrophobic interaction in surface surfactant/polyelectrolyte complex formation.     

Immobilization of enamel matrix derivate protein onto polypeptide multilayers. Comparative in situ measurements using ellipsometry, quartz crystal microbalance with dissipation, and dual-polarization interferometry

The buildup of biodegradable poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on silica and titanium surfaces and the immobilization of enamel matrix derivate (EMD) protein was followed by utilizing in situ ellipsometry, quartz crystal microbalance with dissipation, and dual-polarization interferometry (DPI). The use of the relatively new DPI technique validated earlier published ellipsometry measurements of the PLL-PGA polypeptide films. The hydrophobic aggregating EMD protein was successfully immobilized both on top of and within the multilayer structures at pH 5.0. DPI measurements further indicated that the immobilization of EMD is influenced by the flow pattern during adsorption. The formed polypeptide-EMD multilayer films are of interest since it is known that EMD is able to trigger cell response and induce biomineralization. The multilayer films thus have potential to be useful as bioactive and biodegradable coatings for future dental implants.     

Characteristics of polyelectrolyte multilayers: effect of PEI anchoring layer and posttreatment after deposition

The influence of a first (anchoring) layer and film treatment on the structure and properties of polyelectrolyte multilayer (PEM) films obtained from polyallylamine hydrochloride (PAH) and polysodium 4-styrenesulfonate (PSS) was studied. Branched polyethyleneimine (PEI) was used as an anchoring layer. The film thickness was measured by ellipsometry. Complementary X-ray reflectometry and AFM experiments were performed to study the change in the interfacial roughness. We found that the thickness of the PEM films increased linearly with the number of layers and depended on the presence of an anchoring PEI layer. Thicker films were obtained for multilayers having PEI as the first layer comparing to films having the same number of layers but consisting of PAH/PSS only. We investigated the wettability of PEM surfaces using direct image analysis of the shape of sessile water drops. Periodic oscillations in contact angle were observed. PAH-terminated films were more hydrophobic than films with PSS as the outermost layer. The effect of long time conditioning of PEM films in solutions of various pH's or salt (NaCl) concentrations was also examined. Salt or base solutions induced modification in wetting properties of the polyelectrolyte multilayers but had a negligible effect on the film thickness.     

Multilayers of weak polyelectrolytes of low and high molecular mass assembled on polypropylene and self-assembled hydrophobic surfaces

Hydrophobic self-assembled octadecyltrichlorosilane (ODTS), ultrathin films of polypropylene, and ODTS modified with cationic dioctadecyldimethylammonium bromide are employed as substrates for deposition of multilayers of poly(allylamine hydrochloride) and poly(acrylic acid) from aqueous solution. The assembly of highly dissipative polyelectrolyte multilayers (PEMs) is demonstrated by quartz crystal microgravimetry. The initial rate of adsorption is faster and the adsorbed amount larger on the cationic surface, while the detailed structure of the PEMs, as determined by atomic force microscopy imaging, is related primarily to the molecular weight of the adsorbing polymers. A more extensive PEM adsorption on the hydrophobic surfaces takes place with increasing ionic strength of the background electrolyte solution. The water contact angle depends on the type of polymer adsorbed as the outermost layer, indicating that, despite the expected interdiffusion for the different polymer chains, there is a net macromolecular segregation to the free surface. Surface modification with the high molecular weight PEMs produces a more marked reduction of the hydrophilicity of the substrate.     

Visco-elastic and adhesive properties of adsorbed polyelectrolyte multilayers determined in situ with QCM-D and AFM measurements

The build-up of multilayers constructed from polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) under different pH conditions was continuously monitored using the quartz crystal microbalance with dissipation. The adsorbed amount of polymer as well as the amount of coupled water was determined. Furthermore, from dissipation measurements, it was possible to determine the visco-elastic properties of the adsorbed multilayer. These properties were highly dependent on the polyelectrolyte present in the outermost layer. The multilayer was far more rigid and elastic with PAA as the outermost layer. Furthermore, a link has been established between the conformability or rigidity of a multilayer covered surface and the adhesion between such surfaces. Adhesion measurements using the atomic force microscope showed a greater pull-off force when the more viscous PAH was present in the outermost layer.     

Salt-regulated attraction and repulsion of spherical polyelectrolyte brushes towards polyelectrolyte multilayers

Adsorption of colloidal particles presents an interesting alternative to the modification of surfaces using covalent coupling or physisorption of molecules. However, to tailor the properties of these materials full control over the effective particle-substrate interactions is required. We present a systematic investigation of the adsorption of spherical polyelectrolyte brushes (SPB) onto polyelectrolyte multilayers (PEM). A brush layer grafted from colloidal particles allows the incorporation of various functional moieties as well as the precise adjustment of their adsorption behaviour. In the presence of oppositely charged surfaces the amount of adsorbed SPB monotonically increases with the ionic strength, whereas equally charged substrates efficiently prevent colloidal attachment below a threshold salt concentration. We found that the transition from the osmotic to the salted brush regime at approximately 100 mM coincided with a complete loss of substrate selectivity. In this regime of high ionic strength, attractive secondary interactions become dominant over electrosteric repulsion. Due to the soft polyelectrolyte corona a surface coverage exceeding the theoretical jamming limit could be realized. Both the adsorption kinetics and the resulting thin film morphologies are discussed. Our study opens avenues for the production of two-dimensional arrays and three-dimensional multilayered structures of SPB particles.     

Formation of polyelectrolyte multilayers on fibres: influence on wettability and fibre/fibre interaction

Polydimethyldiallylammonium chloride (PDADMAC) and polystyrene sulfonate (PSS) have been used to build-up polyelectrolyte multilayers (PEMs) on chemical soft wood fibres and on SiO2 at various electrolyte concentrations. Adsorption onto SiO2 was studied using a stagnation point adsorption reflectometer (SPAR), and the adsorbed amount of PDADMAC and PSS on the fibres was determined using nitrogen analysis and Sch?niger burning, respectively. The adsorption onto the two substrates was then compared. Paper testing showed that the tensile index (TI) increased by about 90% when 11 layers had been adsorbed, and that there was a correlation between the adsorbed amount and the increase in TI. It was also shown that the particular polymer present in the outermost layer significantly influenced the TI, and that PDADMAC produced a higher TI. A correlation between the adsorbed amount and the TI was also found. Individual fibres were partly treated with a PEM and analysed using a dynamic contact angle analyser (DCA) and environmental scanning electron microscopy (ESEM).     

DNA and polylysine adsorption and multilayer construction onto cationic lipid-coated microbubbles

We report on a novel application of the layer-by-layer (LbL) assembly technique to attach multiple layers of DNA and poly-l-lysine (PLL) onto preformed lipid-coated microbubbles to increase the DNA loading capacity. We first measured the effects of the cationic lipid fraction and salt concentration on the microbubble stability. Microbubble production and stability were robust up to a cationic lipid fraction of 40 mol % in 10 mM NaCl. DNA adsorption was heterogeneous over the microbubble shell and occurred primarily on the condensed phase domains. The amount of adsorbed DNA, and subsequently adsorbed PLL, increased linearly with the fraction of cationic lipid in the shell. DNA loading was further enhanced by the LbL assembly method to construct polyelectrolyte multilayers (PEMs) of DNA and PLL. PEM buildup was demonstrated by experimental results from zeta potential analysis, fluorescence microscopy, UV spectroscopy, and flow cytometry. The PEMs exhibited two growth stages and were heterogeneously distributed over the microbubble surface. The DNA loading capacity onto the microbubbles was enhanced by over 10-fold by using five paired layers. However, the PEM shell did not prevent oscillation or destruction during ultrasound insonification. These results suggest that the surface can be compartmentalized to make multifunctional, high-payload ultrasound contrast agents for targeted gene therapy.     

Preparation and adsorption of refined polyelectrolyte complex nanoparticles

We report on bulk and surface properties of centrifuged nonstoichiometric polyelectrolyte complex (PEC) dispersions. PECs were prepared by mixing poly(diallyldimethylammonium chloride) (PDADMAC) and sodium poly(maleic acid-co-alpha-methylstyrene) (PMA-MS) at the monomolar mixing ratio of 0.6 and polymer concentration >/=1 mmol/l. Centrifugation of initial PEC dispersions revealed three phases: supernatant (SUP), coacervate (COAC), and an insoluble precipitate. Mass, turbidity, particle hydrodynamic radii (R(h)), and the titratable charge amount were determined for those phases. The turbid COAC phase consisted of 200-nm nanoparticles and carried 60% of the polymer mass and 20% of the titratable charge amount of the initial PEC dispersion. The SUP phase showed no turbidity and no such nanoparticles, but carried 80% of the initial titratable charge amount, presumably caused by excess polycations. Furthermore, linear dependences of turbidity and R(h) on COAC concentration was observed. COAC adsorption was studied at polyelectrolyte multilayer (PEM) modified silicon surfaces in dependence on both adsorption time and concentration using attenuated total-reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The adsorption data were fitted by the simple Langmuir model. Comparison of COAC particles and polystyrene latices revealed similar adsorption features. SEM and AFM measurements resulted in hemispherically shaped adsorbed COAC particles with coverages >/=25%, whose calculated volumes correlated well with those in dispersion obtained by PCS.     

The Effect of a Cationic Polyelectrolyte on the Forces between Two Cellulose Surfaces and between One Cellulose and One Mineral Surface

The effect of a cationic polyelectrolyte, PCMA, on the forces between two cellulose surfaces and between one cellulose surface and one mica surface has been studied using the interferometric surface force apparatus (SFA). The cellulose surfaces were prepared by Langmuir-Blodgett deposition of trimethylsilyl cellulose onto hydrophobized mica. Prior to measurements the surfaces were desilylated to obtain pure cellulose. Introduction of a cationic polyelectrolyte into the solution drastically changed the interactions between the cellulose layers. It was found that the cationic polyelectrolyte does adsorb onto the cellulose surface, although the adsorbed amount is low. The adsorbed layer is very thin, as expected at a low electrolyte concentration. Before the adsorption has reached equilibrium, when only some polyelectrolyte had adsorbed, the adhesion between the surfaces was high, and it was noted that the cellulose layer was damaged on separation. After a longer adsorption time an electrostatic repulsion and no adhesion were observed between the polyelectrolyte-coated cellulose surfaces. An electrostatic repulsion was observed between cellulose and mica. When cationic polyelectrolyte was introduced to the system it overcompensated the charges on both surfaces, and the range and magnitude of the double-layer force was higher than without polyelectrolyte. The relevance of the results to flocculation mechanism and efficiency in cellulose systems is discussed. Copyright 2000 Academic Press.     

Combined effect of spin speed and ionic strength on polyelectrolyte spin assembly

Polyelectrolyte spin assembly (PSA) of multilayers is a sequential process featuring adsorption of oppositely charged polyelectrolytes from dilute solutions undergoing spin-coating flow. Here, we report on the dependence of PSA multilayer buildup of poly(sodium 4-styrenesulfonate) and poly(allylamine hydrochloride) on solution ionic strength and spin speed. We observed that at a given spin speed, the PSA coating growth rate (thickness/bilayer) and polymer surface coverage shows a nonmonotonic dependence on salt concentration, first increasing and then decreasing with increasing solution ionic strength. This is argued to be a manifestation of two competing mechanisms responsible for the layer formation. At low salt concentrations, the electrostatic interactions control the multilayer assembly process, while at high salt concentrations it is dominated by shear flow. We explain this nonmonotonic behavior in the framework of a Flory-like theory of multilayer formation from polyelectrolyte solution under shear flow. Additionally, the PSA process led to multilayer coatings with a radial dependence on thickness at lower spin speed in the shear-dominated regime. On increasing spin speed, such radial dependence subsided, eventually leading to uniform coatings by planarization. The surface topography of the multilayered coatings adsorbed at salt concentration less than 0.1 M was flat and featureless for all studied spin speeds. Unique morphological features in the films were formed at salt concentration higher than 0.1 M, the size of which depended on the spin speed and solution ionic strength.     

Adsorption of polyelectrolyte modified graphene to silica surfaces: monolayers and multilayers

Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI.     

Layer-by-layer electrostatic self-assembly of single-wall carbon nanotube polyelectrolytes

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness.     

Adsorption characteristics of stoichiometric and nonstoichiometric molecular polyelectrolyte complexes on silicon oxynitride surfaces

Adsorption properties of stoichiometric and nonstoichiometric polyelectrolyte complexes (PECs) have been investigated by means of dual polarization interferometry (DPI) and X-ray photoelectron spectroscopy (XPS). Poly(sodium styrenesulfonate) (NaPSS) of molecular weight 4300 g/mol was used as polyanion, and two bottle-brush copolymers possessing different molar ratios of the cationic segment methacryloxyethyltrimethylammonium chloride (METAC) and the nonionic segment poly(ethylene oxide) methyl ether methacrylate (PEO(45)MEMA) were used as polycations. They are referred to as PEO(45)MEMA:METAC-25 and PEO(45)MEMA:METAC-50, where the last digits denote the mol % of charged main-chain segments. The time evolution of the adsorbed amount, thickness, and refractive index of the PEC layers were determined in aqueous solution using DPI. We demonstrate that cationic, uncharged, and negatively charged complexes adsorb to negatively charged silicon oxynitride and that maximum adsorption is achieved when small amounts of PSS are present in the complexes. The surface composition of the adsorbed PEC layers was estimated from XPS measurements that demonstrated very low content of NaPSS. On the basis of these data, the PEC adsorption mechanism is discussed and the competition between PSS and negative surface sites for association with the cationic polyelectrolyte is identified as a key issue.     

The effect of support material and conditioning on wettability of PAH/PSS multilayer films

An efficient method for characterizing wetting properties of heterogeneous surfaces produced by sequential adsorption of polyelectrolytes was developed. Three types of polyelectrolytes were used: polyallylamine hydrochloride (PAH), polyethyleneimine (PEI), both of a cationic type, and polysodium 4-styrenesulfonate (PSS), of an anionic type. Multilayer films were prepared by 'layer-by-layer' (LbL) deposition technique. Natural ruby mica, glass, titanium foil and silicon wafers were used as the support material for PE films. Wetting of polyelectrolyte films was determined experimentally by contact angle measurements, using technique of direct image analysis of shape of sessile drops. Periodic oscillations in contact angle values were observed for multilayers terminated by polycation and polyanion, respectively, and the variations in contact angle values strongly depended on the conditions of adsorption and multilayer treatment after deposition. Therefore, the influence of ionic strength of polyelectrolyte solution used for deposition on wetting of multilayer films was considered and also the effect of conditioning in different environments was investigated. It is usually assumed that film properties and stability strongly depend on the first layer which is used to anchor a multilayer at the surface of support material. To investigate influence of the first layer, PAH/PSS films were compared with more complex ones having PEI as the first layer with a sequence of PSS/PAH deposited on top of it.     

Adsorption of cationic polyelectrolyte at the solid/liquid interface and dispersion of nanosized silica in water

Adsorption of cationic polyelectrolyte, a homopolymer of maleimide propyl trimethylammonium chloride (MPTMAC), on silica nanoparticles from aqueous solution was studied. The adsorbed amount of MPTMAC and the adsorption layer thickness from solutions of different pH, polyelectrolyte concentration, salt type, and salt concentration were measured. The adsorbed amount exhibited a maximum as a function of the electrolyte concentration. The onset of the decline in the adsorbed amount depended on the type of counterions. The thickness of the adsorption layer increased gradually with increased of electrolyte concentration and leveled off at high electrolyte concentration. The enhanced adsorption in the presence of Na2SO4 can be explained by the bivalent SO4(2-) causing a better shielding effect. With increasing pH the adsorbed amount of MPTMAC increased, whereas the thickness of an adsorbed layer of MPTMAC decreased. At low polyelectrolyte concentrations unstable silica suspensions were observed from a stability test. At high polyelectrolyte concentrations the higher particle coverage caused electrosteric stabilization of the dispersion. However, further increase in MPTMAC concentration after saturated adsorption would flocculate the dispersed system. At low pH, MPTMAC tending to create a loops or tails conformation stabilized the suspension.     

Dual-beam polarization interferometry resolves mechanistic aspects of polyelectrolyte adsorption

The electrostatically driven binding dynamics of a polyelectrolyte multilayer (PEMU) film was investigated in real-time using dual-beam polarization interferometry (DPI) and independently supported by quartz crystal microbalance with dissipation monitoring (QCM-D) studies. Multilayer assemblies of the polyanions poly[1-[4[(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl sodium salt] (PAZO) and poly(styrene sulfonate) (PSS) were respectively constructed with the polycation poly(ethylenimine) (PEI) on anionic functionalized substrates using the layer-by-layer electrostatic self-assembly method. DPI measurements indicate that polyelectrolyte adsorption occurs in three distinct stages. In the first stage, for approximately 5 s, coil-like segments of polyanion partially tether to the surface of the oppositely charged PEI. In the second stage, these coils unfurl over a period of approximately 10 s to cover the surface resulting in an increase in average density of the film. During the final adsorption step, the surface-bound polyelectrolyte diffuses into the multilayer assembly, exposing the surface to further deposition. This last step occurs over a much longer time period and results in a highly interpenetrated film containing a charge-overcompensated region at the film surface.