Characterization of the water-soluble comb–linear interpolyelectrolyte nanoaggregates by Monte Carlo simulations and fluorescence probe techniques

Insight into the microstructure of the aggregate formed by the Coulombic interaction between the cationic comb copolymer poly(acrylamide-co-[3-(methacryloylamino) propyl]trimethylammonium chloride)-graft-polyacrylamide, P(AM-co-MAPTAC)-g-PAM, and the anionic polyelectrolyte poly(sodium acrylate), NaPA, was provided by Monte Carlo simulations and the fluorescence probe technique. The computational outcome revealed a core–shell organization of the comb copolymer, with an indefinite boundary between the inner and outer region. The copolymer had a spherical shape, and its backbone moiety adopted an extended conformation. The spatial extension of the copolymer and the core region contracted when association with the oppositely charged polyelectrolyte occurred. The fluorescence probes 2-dimethylamino-6-propionylnaphthalene, PRODAN, and 1-anilinonaphthalene-8-sulfonic acid, ANS, exhibited a specific interaction with the complex. A lower polarity in the polyelectrolyte complex as compared with the water polarity was sensed by the fluorescence probes, a feature which was attributed to a certain compaction of the AM-co-MAPTAC part of comb copolymer.     

Influence of polyelectrolyte multilayer adsorption on the temperature sensitivity of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) (PNiPAM) microgels

The electrophoretic mobility and temperature-dependent particle size of poly(N-isopropylacrylamide) (PNiPAM) microgels after alternating adsorption of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) have been determined. First a PNiPAM-co-acrylic acid (AAc) shell was added to the PNiPAM microgel, then PDADMAC and PSS were adsorbed alternately. The studies of the electrophoretic mobility revealed charge reversal when a polyelectrolyte (PE) layer was adsorbed. Particle size measurements revealed a strong influence of polyelectrolyte adsorption on the temperature-dependent particle swelling. The strong influence of the adsorbed polyelectrolyte on the particle size is in contrast to polyelectrolyte multilayer adsorption on rigid particles.     

Preparation of monomodal polyelectrolyte complex nanoparticles of PDADMAC/poly(maleic acid-alt-alpha-methylstyrene) by consecutive centrifugation

We report on the refinement of anionic and cationic nanoparticles of nonstoichometric polyelectrolyte complexes (PEC) by consecutive centrifugation, which was studied by dynamic light scattering (DLS), atomic force microscopy (AFM), colloid titration and infrared spectroscopy (IR). PEC dispersions were prepared by mixing poly(diallyldimethylammonium chloride) (PDADMAC) and sodium poly(maleic acid-alt-alpha-methylstyrene) (PMA-MS) at the monomolar mixing ratio of n-/n+ = 1.50 (anionic PEC) and 0.66 (cationic PEC), respectively, and the polymer concentration of c(POL) = 0.002 M. The particle size (Rh), titrable charge amount, and IR spectra were determined for both dispersions in the original state, after the first centrifugation and after the second centrifugation. Freshly prepared PEC dispersions contained two different particle sizes: around 10-25 nm (small particles) and around 100 nm (large particles). Consecutive centrifugation of freshly prepared PEC dispersions resulted in the separation of highly charged excess polyelectrolyte (PEL) and small PEC particles from a low charged coacervate phase of the desired larger PEC particles. After the second centrifugation, the coacervate phase of both dispersions PEC-1.50 and PEC-0.66 consisted of monomodal particles sizing around 100 nm. These results were supported by AFM measurements on the respective dispersions deposited on glass plates. PEC-1.50 particles tended to adopt slightly smaller sizes ( approximately 90 nm) in comparison to PEC-0.66 ones (approximately 110 nm). No significant influence of the PDADMAC molecular weight on the particle size was found. IR spectroscopy showed changes in the environment of the carboxylate groups of PMA-MS by consecutive centrifugation. The centrifuged PEC-1.50 dispersions showed remarkable long-term stability over more than a year. The high macroscopic stability of the studied PEC dispersions is presumably due to repulsive electrostatic interparticle interactions and attractive hydrophobic intraparticle interaction. The introduced monomodal PEC particles might be projected as latex analogues or as nanocarriers for drugs and proteins.     

Effect of surface modification of bentonite nanoclay with polymers on its stability in an electrolyte solution

Recently surface modification of clay minerals has become increasingly important for improving the practical applications of clays and clay minerals. In this research work surface modifications of bentonite nanoclay particles were carried out by chemical grafting of different copolymers including poly(1-vinyl pyrrolidone-co-styrene) (PVP), poly(methyl methacrylate-co-methacrylic acid) (PMMA) and poly (acrylamide-co-diallyl dimethyl ammonium chloride) (PDADMAC). The efficiency of the grafting reactions was investigated using FTIR, TGA and XRD methods. It was shown that PVP as well as PDADMAC copolymers had been grafted successfully on the exterior of the nanoclay tactoids surfaces, while most of the PMMA molecules had entered the galleries and grafted on the inner surfaces of the nanoclay. Turbidimetry, zeta potentiometry and dynamic light scattering (DLS), were employed to analyze the dispersion stability of the unmodified and modified nanoclays in an electrolyte solution with high salinity. The turbidimetry results showed that stabilities of unmodified and modified nanoclay particles in the electrolyte solutions decreased as the time passed from their preparation, and after 24 h they settled completely in the solutions. However, rates of the settlement of unmodified and modified particles differed from each other, that of the modified ones being lower. This difference was attributed to the grafted copolymers on the modified particles surfaces. Also, the results of the zeta potentiometry and DLS were in harmony with the turbidimetry observations.     

Synthesis of Thermo‐ and pH‐Sensitive Polyion Complex Micelles for Fluorescent Imaging

Two thermo‐ and pH‐sensitive polypeptide‐based copolymers, poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)‐b‐poly(L ‐lysine) (P(NIPAAm‐co‐HMAAm)‐b‐PLL, P1 ) and poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)‐b‐poly(glutamic acid) (P(NIPAAm‐co‐HMAAm)‐b‐PGA, P2 ), have been designed and synthesized by the ring‐opening anionic polymerization of N‐carboxyanhydrides (NCA) with amino‐terminated P(NIPAAm‐co‐HMAAm). It was found that the block copolymers exhibit good biocompatibility and low toxicity. As a result of electrostatic interactions between the positively charged PLL and negatively charged PGA, P1 and P2 formed polyion complex (PIC) micelles consisting of polyelectrolyte complex cores and P(NIPAAm‐co‐HMAAm) shells in aqueous solution. The thermo‐ and pH‐sensitivity of the PIC micelles were studied by UV/Vis spectrophotometry, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Moreover, fluorescent PIC micelles were achieved by introducing two fluorescent molecules with different colors. Photographs and confocal laser scanning microscopy (CLSM) showed that the fluorescence‐labeled PIC micelles exhibit thermo‐ and pH‐dependent fluorescence, which may find wide applications in bioimaging in complicated microenvironments.     

Characterization of stimuli-sensitive polymers for biomedical applications

Stimuli-sensitive polymers were synthesized by copolymerizing varying ratios of N-isopropyl acrylamide(NIPAAm) and acrylic acid(AAc). The influence of polyelectrolytes on the lower critical solution temperatures(LCSTs) of these temperature/pH sensitive polymers was investigated in the pH range of 2-12. Polyelectrolyte complexes were prepared by mixing poly(NIPAAm-co-AAc) as anionic polyelectrolyte with poly(allyl amine)(PAA) or poly(L-lysine)(PLL) as cationic polyelectrolytes, respectively. Back titration was performed to determine the pK_a values of PAAc in poly(NIPAAm-co-AAc) and to study the effect of comonomer ionization on the cloud point temperature. The effect of polyelectrolyte complex formation on the conformation of PLL was studied as a function of temperature by means of circular dichroism(CD). The swelling ratio of poly(NIPAAm-co-AAc) hydrogels as a function of pH at various temperature was obtained by measuring the weight of the hydrogels in buffer solutions. The LCSTs of the poly(NIPAAm-co-AAc) were strongly affected by pH, polyelectrolyte solutes, AAc content, and charge density. The influence of more hydrophobic PLL as a polyelectrolyte on the cloud point of PNIPAAm/water in the copolymer was stronger than that of poly(allyl amine)(PAA). Indomethacin was loaded into these hydrogels, and controlled release of this molecule from the hydrogel was determined under various temperature and pH conditions using UV/Vis spectrophotometry.     

Potentiometric back titration as a robust and simple method for specific surface area estimation of lignocellulosic fibers

The specific surface area (SSA) of cellulosic or lignocellulosic fibers is seldom reported in the recent literature on papermaking, despite its close relation with the degree of refining and other key pulp properties. Amidst outdated assays (Pulmac permeability test) and methods that, while accurate, are of doubtful usefulness for papermaking purposes (N₂ adsorption–desorption), we suggest a methodology based on the cationic demand. A commonly used cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), became adsorbed onto thermomechanical pulp samples. Then, a potentiometric back titration with an anionic polyelectrolyte measured the cationic demand, expressed as microequivalents of PDADMAC per gram of pulp. Multiplying this value by the surface area of a microequivalent of polymer, considering rod-like conformation in the case of minimum ionic strength, yielded the SSA of the lignocellulosic pulp. Our system assumes that the quaternary ammonium groups were anchored through electrostatic and ion–dipole interactions. Measuring the carboxyl content allowed for discriminating between both kinds of forces. Finally, the model could be validated by plotting the estimated SSA values against the Schopper-Riegler degree, attaining high correlation coefficients (R²?~?0.98). Owing to the high molecular weight of the polyelectrolyte of choice (107 kDa), and more particularly in the case of fine-free pulps, SSA values estimated from the cationic demand were consistently lower than those from dye (Congo red) sorption. Instead of being a drawback, the limited diffusion of PDADMAC through fibers can enable papermakers to attain a more helpful quantification of the available surfaces in operations with low residence times.

     

Synthesis of anionic core-shell poly(styrene-<Emphasis Type="Italic">co-N</Emphasis>-isopropylacrylamide) colloids by a two-step surfactant-free emulsion polymerization

The aim of the performed work is to produce anionic core-shell poly(styrene-co-N-isopropylacrylamide) colloids with an N-isopropylacrylamide (NIPAM) content in the range from 5 to 30 mol %. Different batches of poly(styrene-co-NIPAM) colloids (poly(ST-co-NIPAM) colloids) are produced with varying NIPAM mol %, and the produced poly(ST-co-NIPAM) colloids are characterized by dynamic light scattering and scanning electron microscopy. Results show that the produced colloids have a core-shell morphology with a poly(styrene) core and a poly(NIPAM) shell. The swelling ratio of the produced poly(ST-co-NIPAM) colloids is similar to the swelling ratio found for similar poly(ST-co-NIPAM) colloids produced by the two-step seeded polymerization process. The text was submitted by the author in English.     

Swelling behavior of poly{N‐[3‐(dimethylaminopropyl)] methacrylamide‐co‐acrylamide} hydrogels in aqueous solutions of surfactants

Temperature sensitive poly{N‐[3‐(dimethylaminopropyl)]methacrylamide‐co‐acrylamide} [P(DMAPMA‐co‐AAm)] hydrogels were prepared by the free‐radical crosslinking copolymerization of corresponding monomers in water with N,N‐methylenebisacrylamide as the crosslinker, ammonium persulfate as the initiator, and N,N,N′,N′‐tetramethylethylenediamine as the activator. The swelling equilibrium of the P(DMAPMA‐co‐AAm) hydrogels was investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate and the cationic surfactant dodecyltrimethylammonium bromide. In pure water, regardless of the amount of N,N‐methylenebisacrylamide, the P(DMAPMA‐co‐AAm) hydrogels showed a discontinuous phase transition between 30 and 36 °C. However, the transition temperature changed from discontinuous to continuous with the addition of surfactants; this was ascribed to the conversion of nonionic P(DMAPMA‐co‐AAm) hydrogels into polyelectrolyte hydrogels due to the binding of surfactants through hydrophobic interactions. Additionally, the concentrations of free sodium dodecyl sulfate and dodecyltrimethylammonium bromide ions were measured at different temperatures by conductometry, and it was found that the electric conductivity of the P(DMAPMA‐co‐AAm)–surfactant systems depended strongly on the swelling ratio; most notably, it changed drastically near the phase‐transition temperature of the P(DMAPMA‐co‐AAm) hydrogel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1645–1652, 2006     

Photocatalytic efficiency of TiO2/poly[acrylamide-co-(acrylic acid)] composite for textile dye degradation

A novel photocatalytically degradable TiO₂/poly[acrylamide-co-(acrylic acid)] composite hydrogel (TiO₂/poly[AAm-co-AAc]) was synthesized by polymerization in an aqueous solution with N,N’-methylenebisacrylamide as the crosslinker and ammonium persulphate and TEMED as the initiator pair. The combined and separate effects of photodegradation and adsorption processes for dye removal were evaluated using methylene blue (MB) as the model dye for a photodegradation target, and compared with those of the neat poly[AAm-co-AAc], and a commercially available TiO₂ photocatalyst (Degussa P-25). Without photodegradation (i.e. in the dark), the TiO₂/poly[AAm-co-AAc] composite adsorbed up to 85% of the MB from a 5 mg L⁻¹ MB solution in 15 min compared to only 10% for the pristine TiO₂. The reproducibility in photodegradation of the reused poly[AAm-co-AAc] composite was also investigated, where poly[AAm-co-AAc] was found to be photocatalytically degraded under UV irradiation. Therefore, the TiO₂/poly[AAm-co-AAc] composite hydrogel is a good dye adsorber with self-photodegradability and it also can easily be separated from the reaction by simple filtration. With these properties, the TiO₂/poly[AAm-co-AAc] hydrogel can be called a green polymer for use in the photodegradation-adsorption process for the abatement of various pollutants.     

Polyelectrolyte complex formation between poly(diallyldimethyl-ammonium chloride) and copolymers of acrylamide and sodium-acrylate

 The interaction between oppositely charged polyelectrolytes, in this study poly(diallyldimethylammonium chloride) (PDADMAC) and copolymers of acrylamide and sodium-acrylate differing in their chain length and charge density parameter (ξ) was investigated in relation to the molar charge ratio of anionic to cationic charges (n ₋/n ₊). The molecular weights of the polyelectrolytes used were 2.9·10⁵g/mol for PDADMAC and for the polyacrylamide copolymers 14 ·10⁶g/mol as well as 5·10⁵g/mol obtained by ultrasonic degradation of the high molecular weight copolymers. The charge density parameters of the polyanions used (ξ ^PR ) varied between 0.14 and 0.64. Complexation between PDADMAC and high molecular weight polyanions leads mainly to macroscopic phase separation whereas the degraded polyanions and PDADMAC formed soluble complexes as well as stable dispersions, if charge excess was available. Precipitates and dispersions were characterized by several methods such as element analysis, thermogravimetry, pyrolysis-GC/MS, PEL titration, ζ-potential measurements, determination of turbidity, particle size measurements and determination of carbon content (TOC).  All precipitated complexes include about 20% water and are of 1:1 stoichiometry concerning ionic binding. Investigations of dispersions confirm 1:1 stoichiometry of complex particles stabilized by excess polyelectrolyte and soluble complexes. It was also found that the particle size can be varied via the charge density parameter of the polyanions used in the range of negative charge excess. Received: 21 June 2001 Accepted: 9 October 2001     

Adsorption of poly(vinyl formamide-co-vinyl amine) onto silica particle surfaces and stability of the formed hybrid materials

In order to produce silica/polyelectrolyte hybrid materials the adsorption of the polyelectrolyte poly(vinyl formamide-co-vinyl amine), P(VFA-co-VAm) was investigated. The adsorption of the P(VFA-co-VAm) from an aqueous solution onto silica surface is strongly influenced by the pH value and ionic strength of the aqueous solution, as well as the concentration of polyelectrolyte. The adsorption of the positively charged P(VFA-co-VAm) molecules on the negatively charged silica particles offers a way to control the surface charge properties of the formed hybrid material. Changes in surface charges during the polyelectrolyte adsorption were studied by potentiometric titration and electrokinetic measurements. X-ray photoelectron spectroscopy (XPS) was employed to obtain information about the amount of the adsorbed polyelectrolyte and its chemical structure. The stability of the adsorbed P(VFA-co-VAm) was investigated by extraction experiments and streaming potential measurements. It was shown, that polyelectrolyte layer is instable in an acidic environment. At a low pH value a high number of amino groups are protonated that increases the solubility of the polyelectrolyte chains. The solvatation process is able to overcompensate the attractive electrostatic forces fixing the polyelectrolyte molecules on the substrate material surface. Hence, the polyelectrolyte layer partially undergoes dissolving process.     

Colorimetric detection of Ni2+ based on an anionic triphenylmethane dye and a cationic polyelectrolyte in aqueous solution

The combination of xylenol orange (XO) and poly(diallyldimethylammonium chloride) (PDADMAC) has been utilized as a colorimetric sensor for selective recognition of Ni²⁺ in aqueous solution. Upon addition of Ni²⁺, the chemosensor exhibited the significant color change from red to purple with a bathochromic shift, whereas these change was not induced by other metal ions. XO alone did not recognize Ni²⁺ colorimetrically, indicating that PDADMAC was required for detecting Ni²⁺. This study can provide the facile method for the construction of new chemosensors by a simple mixture of an anionic water-soluble dye and cationic polyelectrolyte.     

Interaction of antigen and antibody on core-shell polymeric microspheres

Monodispersed microspheres with polystyrene as the core and poly(acrylamide-co-N-acryloxysuccinirnide) as the shell were synthesized by a two-step surfactant-free emulsion copolymerization.The core-shell morphology of the microspheres was shown by scanning electron microscopy and transmission electron microscopy.Rabbit immunoglobulin G (as antigen) was covalently coupled onto the microspheres by the reaction between succinimide-activated ester groups on the shell of the microspheres and amino groups of the antigen molecules.The size of particles was characterized by dynamic light scattering technique and was found to vary upon bioconjugation and interaction with proteins.The binding process was shown to be specific to goat anti-rabbit immunoglobulin G(as antibody) and reversible upon the addition of free antigen into the system.     

Thermosensitive and control release behavior of poly (N‐isopropylacrylamide‐co‐acrylic acid) latex particles

In this work, poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAAm‐AA)) copolymer latex particles (microgels) were synthesized by the method of soapless emulsion polymerization. Poly(NIPAAm‐AA) copolymer microgels have the property of being thermosensitive. The concentration of acrylic acid (AA) and crosslinking agent N,N′‐methylenebisacrylamide were important factors to influence the lower critical solution temperature (LCST) of poly(NIPAAm‐AA) microgels. The effects of AA and crosslinking agent on the swelling behavior of poly(NIPAAm‐AA) microgels were also studied. The poly(NIPAAm‐AA) copolymer microgels were then used as a thermosensitive drug carrier to load caffeine. The effects of concentration of AA and crosslinking agent on the control release of caffeine were investigated. How the AA content and crosslinking agent influenced the morphology and LCST of the microgels was discussed in detail. The relationship of morphology, swelling, and control release behavior of these thermosensitive microgels was established. A new scheme was proposed to interpret the control release of the microgels with different morphological structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5734–5741, 2008     

Thermal transitions in and structures of dried polyelectrolytes and polyelectrolyte complexes

Dynamic mechanical analysis (DMA) was used to explore the thermomechanical properties of dried polyelectrolytes and polyelectrolyte complexes (PECs) with different thermal and humidity histories. Although differences in the amount of water remaining in polyelectrolytes and PECs were small for ambient versus dessicator storage, the properties of polyelectrolyte‐based materials were drastically different for different humidity histories. Glass transition temperatures (T_gs) of poly(diallyldimethylammonium chloride) (PDADMAC) were shown to vary by 100 °C, depending on humidity and thermal histories. These parameters also change glassy storage modulus values by 100%. Furthermore, we observe that dried PDADMAC is highly lossy. DMA of dried poly(styrene sulfonate) (PSS) was more complex and did not exhibit a glass transition in the tested range. DMA of a PEC of PDADMAC and PSS revealed a humidity history‐dependent water melt in the first heating cycle, as well as storage modulus values of dried and annealed PECs that only varied by 17–26% over a 275 °C temperature range. Based on these results, we report for the first time humidity history as controlling structure and properties of polyelectrolyte‐based materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 684–691     

Controlled Stripping of Polyelectrolyte Multilayers by Quaternary Ammonium Surfactants

The quartz crystal microbalance with dissipation technique (QCM‐D) and atomic force microscopy (AFM) have been employed to study the interaction of N‐tetradecyl trimethyl ammonium bromide (TdTmAB) with polyelectrolyte multilayers containing poly(sodium 4‐styrene sulfonate) (PSS) as the polyanion and either poly(allylamine hydrochloride) (PAH) or poly(diallyl dimethyl ammonium chloride) (PDADMAC) as the polycations. The multilayers were exposed to aqueous solutions of TdTmAB. This resulted in a selective removal of PDADMAC PSS layers while layers with PAH as polycation remained stable. It is suggested that PDADMAC/PSS multilayers can be employed as strippable protecting layers.

     

PHOTOELECTRON SPECTROSCOPY STUDY OF AMMONIA-INDUCED CHANGES IN ELECTROSTATICALLY-ASSEMBLED CONJUGATED POLYMER FILMS

ABSTRACT

Exposure of electrostatically assembled polyelectrolyte films comprised of the anionic carboxylic conjugated polymer poly[2-(3-thienyl)-ethanolhydroxycarbonylmethyl-urethane], hereafter referred to as H-PURET, and polycations such as poly(diallyldimethylammonium) chloride, here after referred to as PDADMAC, to aqueous ammonia vapor leads to dra matic changes in the ultraviolet-visible absorption spectrum. In the case of H-PURET/PDADMAC, a shift from 442 to 494 nm is observed upon overnight ammonia exposure. X-ray photoelectron spectroscopy has been used to investigate the mechanism of the changes in optical properties. The C1s, O1s and S2p core levels exhibit negligible ammonia-induced changes. Two N1s peaks are observed in virgin H-PURET/PDADMAC assemblies, and ammonia exposure causes the nitrogen peak corresponding to the H-PURET side chain to become more intense relative to that of the PDADMAC layer. This selective change in the N1s feature suggests that ammonia interacts with the polythiophene side-chain, presumably by deprotonating the fraction of carboxylic acid groups that remain in the H-PURET layer. This deprotonation apparently leads to structural or single chain conformational changes in the conjugated polymer layers that alter the electronic absorption spectrum.     

Novel double hydrophilic block copolymers based on poly(p‐hydroxystyrene) derivatives and poly(ethylene oxide)

The synthesis of three series of double hydrophilic block copolymers (DHBCs), consisting of poly(ethylene oxide) as the neutral water soluble block and a second polyelectrolyte block of variable chemistry, is described. The synthetic scheme involves the anionic polymerization of poly(p‐tert‐butoxystyrene‐b‐ethylene oxide) (PtBOS‐PEO) amphiphilic block copolymer precursors followed by the acidic hydrolysis of the hydrophobic poly(p‐tert‐butoxystyrene) (PtBOS) block to an annealed anionic polyelectrolyte poly(p‐hydroxystyrene) (PHOS) block. The PHOS block was subsequently transformed into a high charge density annealed cationic polyelectrolyte namely poly[3,5‐bis(dimethylaminomethylene) hydroxystyrene] (NPHOS), via aminomethylation. Finally, the NPHOS block was transformed into a quenched polyelectrolyte, namely quaternized poly[3,5‐bis(dimethylaminomethylene) hydroxystyrene] (QNPHOS) block by reaction with CH₃I. The solution properties of the different series of the above block polyelectrolyte copolymers have been investigated using static, dynamic and electrophoretic light scattering, turbidimetry, and fluorescence spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5790–5799, 2007     

Layer‐by‐layer assembly of weak‐strong copolymer polyelectrolytes: A route to morphological control of thin films

Multilayer films were assembled from a strong polyelectrolyte (poly(diallyldimethylammonium chloride), PDADMAC) and a copolymer containing both strongly charged styrene sulfonate moieties and weakly charged maleic acid moieties (poly(4‐styrenesulfonic acid‐co‐maleic acid), PSSMA). Growth of PSSMA/PDADMAC multilayers was linear, as characterized by UV‐vis spectroscopy and quartz crystal microgravimetry. The influence of both the pH of the PSSMA adsorption solutions and the ratio of SS:MA in the PSSMA on multilayer properties was investigated. Fourier transform infrared spectroscopy results showed that the ionization of carboxylic acid groups in PSSMA/PDADMAC multilayers did not vary significantly with changes in the PSSMA assembly pH. However, the multilayers showed different thicknesses, surface morphologies, and stability to post‐assembly pH treatment. We also demonstrate that PSSMA/PDADMAC multilayers are significantly more stable than PSSMA/PAH multilayers after post‐assembly pH treatment (i.e. the films remain intact when exposed to pH extremes). In addition, the surface morphology of two films (PSSMA 1:1 assembled at pH 5.8, post‐treated at pH 2 and PSSMA 3:1 assembled at pH 5.8, post‐treated at pH 11) changed significantly when the films were exposed to solutions of different pH and, in the former case, this change in film morphology was reversible. The porous morphology after treatment at pH 2 could be reversed to give a significantly smoother film after subsequent exposure to water for 24 h. Our results demonstrate that by the rational choice of the assembly pH of PSSMA, stable and pH‐responsive films can be obtained via the sequential assembly of PSSMA and PDADMAC. These films have potential in controlled release applications where film stability and pH‐responsive behavior are essential. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4341‐4351, 2007