Assembly Of Polyelectrolyte Multilayers Research Articles

Bilayers as Basic Formation of Epimolecular Structure of Mostly Lyotropic (Hydrotropic) Structuralized Liquid Systems Being Influenced Predominantly by the Temperature

The bilayer’s formations of amphiphilic molecules or polyions of different ionogenity comprise the basic building units of most organic biological and non-biological systems. A theory has evolved to explain their behaviour during the creation of those organized structures, such as anisotropic liquid crystal (LC) in lyotropic (especially hydrotropic) systems and polyelectrolyte multilayer (PEM) assemblies. Particular attention has been paid to the temperature and the important role of water in the formation and behaviour of the bilayers. A novel insight into the formation of hydrotropic liquid LC systems and their thermotropic behaviour is presented. In this context, the systems PEM assemblies are also discussed. Essentially, a structuralised form of water fills out continuous and discontinuous, i.e., confined, nano-spaces among hydrophilic interfaces of bilayers, controlling their supramolecular structure through a system of attractive and repulsive hydration forces. The character of those sophisticated bonding hydration systems is predestined by the composition and type of these hydrophilic interface groups. The miscellaneous complexity of the bilayer’s aqueous systems suggests the need to study these examples in greater detail. Therefore, the bilayer’s processes connected with disruption as far as destruction of bilayers are mentioned, i.e., the processes with the highest potential to combat bacteria, fungi, and viruses, such as in a situation where a person exhales a breath of micro-droplets containing virus nanoparticles (e.g., the COVID-19 virus).

Chemoattractant releasing microneedles for enhanced DNA vaccination

Transcutaneous delivery of a DNA vaccine using microneedle (MN) has attracted much attention since there are a variety of immune cells underneath the skin. However, the clinical use of DNA vaccine is limited due to its poor cellular uptake of naked plasmid DNA (pDNA) and suboptimal presentation of an antigen by antigen presenting cells (APC). Herein, we designed a MN system for delivering polyplex-based DNA vaccine and recruiting APCs by a chemoattractant N-formyl-methionyl-leucyl-phenylalanine peptide (fMLP)-releasing microspheres (fMLP-MS) using MN coated with pH-responsive polyelectrolyte multilayer assembly (PMA). The PMA can be rapidly disrupted upon the application of MN to the skin, leading to the release of polyplex and fMLP-MS. The polyplex would be taken up by the epidermal cells and resident APCs to express and secrete the antigen (amyloid beta monomer, Aβ1-42) encoded in the DNA vaccine. fMLP released from fMLP-MS could recruit APCs to the site of MN administration by chemotactic effects. The MN-based vaccination system was able to induce robust antigen-specific antibody production.

Tunable Adhesion and Interfacial Structure of Layer‐by‐Layer Assembled Block co‐polymer Micelle and Polyelectrolyte Coatings

AbstractUnderstanding and tuning nanoscale structure is critical in developing new coatings and adhesives. In this work layer‐by‐layer assembly of block co‐polymer (BCP) micelles and oppositely charged polyelectrolytes produces structurally unique coatings with wet adhesion comparable to that of mussel adhesive proteins. Cationic (CAT) and anionic (ANI) BCPs, synthesized by atom transfer radical polymerization (ATRP), are used to create colloidally stable, self‐assembled, spherical BCP micelles. The assembly of BCP micelle and polyelectrolyte multilayers is monitored in situ where CAT‐ and ANI‐BCP micelles exhibit linear and super‐linear growth, respectively. Imaging of the surfaces reveals that CAT‐BCP micelles yield flat, uniform layers whereas ANI‐BCP micelle assemblies form islands that increase in surface area with each additional layer. The adhesion of these layers, measured by colloidal probe atomic force microscopy (CP‐AFM), shows that the distinct layers of CAT‐BCP micelle assemblies produce alternating high and low adhesion surfaces whereas ANI‐BCP micelle assemblies continually increase in adhesion with each additional bilayer. The unique behavior of each assembly demonstrates that both composition and structure play important roles in wet adhesion of submicron layers and that each can be tuned to target performance for different applications.

Highly penetrant organic solvent-resistant layer-by-layer assembled ultra-thin barrier coating for confined microchannel devices

Recently, there has been an increasing demand for developing high performance barrier films for effectively suppressing the penetration of organic solvent. Particularly, in microfluidic systems for lab-on-a-chip devices or inkjet printing, the predominantly faced challenges are swelling deformation and channel blockage by the penetrated solvents, which significantly deteriorates the device performance and lifetime. To address this issue, here we present a robust method for the deposition of barrier layers inside microchannels using a surface charge-regulated layer-by-layer assembly of polyelectrolyte multilayers (PEM). Owing to the highly negative surface charge and additionally employed crosslinking reaction using glutaraldehyde (GA), the Donnan repulsion at the barrier film surface and size-narrowing effect in internal pores can be simultaneously intensified, which rendered excellent barrier performance against highly penetrating organic solvents only with a 14-nm-thick coating layer. Further, we employed a wrinkling-based metrology for precisely evaluating the barrier property of the multilayered films. As a result, highly negatively charged PEM surface (−64.2 mV) with small inner pores (<0.5 nm) resulted in excellent barrier performance to the penetration of various conventional organic solvents used for microelectronic processing. Finally, the practical applicability of the PEM barrier films coated in complexly structured microchannels was demonstrated by fully securing the devices intact even under continuous exposure to organic solvent flowing for 4 h. As such, this study provides a general guideline for the internal deposition of barrier films regardless of the form factor of target surfaces toward next generation organic and wearable electronic devices, along with microfluidic chemical reactor systems.

Layer-by-Layer Deposited Hybrid Polymer Coatings Based on Polysaccharides and Zwitterionic Silanes with Marine Antifouling Properties.

Polyelectrolyte multilayer (PEM) assembly is a versatile tool to construct low-fouling coatings. For application in the marine environment, their structure needs to be stabilized by covalent linkage. Here, we introduce an approach for spin coating of silane-based sol-gel chemistries using layer-by-layer assembly of polysaccharide-based hybrid polymer coatings (LBLHPs). The silane sol-gel chemistry allows the films to be cross-linked under water-based and mild reaction conditions. Two different silanes were used for this purpose, a conventional triethoxymethyl silane and a de novo synthesized zwitterionic silane. The polysaccharide-silane hybrid polymer coatings were thoroughly characterized with spectroscopic ellipsometry, water contact angle (WCA) goniometry, attenuated total reflection-Fourier transform infrared spectroscopy, and atomic force microscopy. The coatings showed good stability in seawater, smooth surfaces, a high degree of hydration, and WCAs below or close to the Berg limit. LBLHPs showed low-fouling properties in biological assays against nonspecific protein adsorption, attachment of the diatom Navicula perminuta, and settlement of zoospores of the macroalga Ulva linza.

Methods for the Assembly and Characterization of Polyelectrolyte Multilayers as Microenvironments to Modulate Human Mesenchymal Stromal Cell Response.

Thin films are of interest in materials design because they allow for the modification of surface properties of materials while the bulk properties of the material are largely unaffected. In this work, we outline methods for the assembly of thin films using a technique known as layer-by-layer (LbL). Furthermore, their interactions with human mesenchymal stromal cells (hMSCs) are discussed. hMSCs are a subject of growing interest because of their potential to treat or cure diseases, given their immunosuppressive properties, multipotent differentiation capabilities, and tissue regeneration capabilities. Numerous improvements and modifications have been suggested for the harvesting, treatment, and culture of hMSCs prior to their administration in human subjects. Here, we discuss methods to assess the interactions of hMSCs with thin LbL-assembled films of heparin and collagen. Three different methods are discussed. The first details the preparation of heparin/collagen multilayers on different surfaces and the seeding of cells on these multilayers. The second method details the characterization of multilayers, including techniques to assess the thickness, roughness, and surface charge of the multilayers, as well as in situ deposition of multilayers. The third method details the analysis of cell interactions with the multilayers, including techniques to assess proliferation, viability, real-time monitoring of hMSC behavior, analysis of hMSC-adhesive proteins on the multilayers, immunomodulatory factor expression of hMSCs, and cytokine expression on heparin/collagen multilayers. We propose that the methods described in this work will assist in the design and characterization of LbL-assembled thin films and the analysis of hMSCs cultured on these thin films.

Design, development and characterization of polyelectrolyte multilayer membranes for potential filtration applications

Abstract The present work projects to modify the surface of commercially available microfiltration membranes using polyelectrolyte multilayer assembly. This polyelectrolytic modification changes the nature and properties of the membrane such as porosity, absorption capacity, charge etc. which can be used for potential environmental application such as herbicide removal from water. Chitosan (CHI) and polystyrene sulfonate (PSS) were incorporated into nanostructured polymeric films on polyamide membrane using layer-by-layer (LbL) technique. The developed polyelectrolyte multilayer assembly were characterized by using UV–vis spectroscopy, attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, thermo gravimetric analysis (TGA) and atomic force microscopy (AFM).

Cross-Plane and In-Plane Heat Conductions in Layer-by-Layer Membrane: Molecular Dynamics Study.

A material with anisotropic heat conduction characteristics, which is determined by molecular scale structure, provides a way of controlling heat flow in nanoscale spaces. As such, here, we consider layer-by-layer (LbL) membranes, which are an electrostatic assembly of polyelectrolyte multilayers and are expected to have different heat conduction characteristics between cross-plane and in-plane directions. We constructed models of a poly(acrylic acid)/polyethylenimine (PAA/PEI) LbL membrane sandwiched by charged solid walls and investigated their anisotropic heat conduction using molecular dynamics simulations. In the cross-plane direction, the thermal boundary resistance between the solid wall and the LbL membrane and that between the constituent PAA and PEI layers decrease with increasing degree of ionization (solid surface charge density and the number of electric charges per PAA/PEI molecule). When the degree of ionization is low, the cross-plane thermal conductivity of a constituent layer is higher than that of the bulk state. As the degree of ionization increases, however, the cross-plane thermal conductivity of PAA, a linear polymer, decreases because of the increase in the number of in-plane oriented polymer chains. In the in-plane direction, we investigated the heat conduction of each layer and found the enhancement of effective in-plane thermal conductivity again due to the in-plane oriented chain alignment. The heat conduction in the LbL membrane is three-dimensionally enhanced compared to those in the bulk states of the constituent polymers because of the electrostatic interactions in the cross-plane direction and the molecular alignment in the in-plane direction.

Catalytic Teflon AF-2400 membrane reactor with adsorbed ex situ synthesized Pd-based nanoparticles for nitrobenzene hydrogenation

Among the unconventional approaches of supporting catalyst nanoparticles, the layer-by-layer assembly of polyelectrolyte multilayers for nanoparticle adsorption represents an easy and convenient method. It enables the deposition of singularly adsorbed nanoparticles and prevents them from aggregating. In this work, polydopamine was grafted onto the internal surface of a Teflon AF-2400 tubular membrane, known for its excellent permeability to light gases and inertness to chemicals. Poly(acrylic acid) and poly(allylamine hydrochloride) were sequentially adsorbed onto the modified surface of the membrane. Ex situ synthesized spherical, cubical, truncated octahedral palladium or dendritic platinum-palladium nanoparticles were then incorporated. The catalytic membranes were assembled in a tube-in-tube configuration and tested over 6 h of continuous nitrobenzene hydrogenation with molecular hydrogen. Stable conversion was observed for the truncated octahedral and dendritic nanoparticles, while a progressive deactivation occurred for the other nanoparticles. Due to their small size, the 3.7 nm spherical nanoparticles exhibited the highest reaction rate, 629molreactant/(molcatalyst⋅h), while the cubical nanoparticles showed the highest turnover frequency, ∼3000 h−1. The reactor concept developed in this work demonstrates how such a design can serve as a platform for conducting continuous multiphase catalytic reactions in flow using singularly adsorbed and finely tuned nanoparticles. The small volume of pressurized gas present in the tube-in-tube reactor offers improved process safety compared to a batch process, while the Teflon AF-2400 membrane provides control over the gas permeation during reaction.

Study on self‐healing behavior of the layer‐by‐layer assembled polyethylenimine/poly(acrylic acid) film

AbstractMany studies have demonstrated that intrinsic self‐healing polyelectrolyte coatings can be fabricated by exponentially growing Layer‐by‐Layer (LbL) assembled polyelectrolyte multilayers. However, due to the lack of controlled self‐healing evaluation methods, the researches on self‐healing properties have remained at some simple qualitative characterization. In our study, a self‐healing branched polyethylenimine (bPEI)/poly(acrylic acid) (PAA) films is successfully prepared by LbL and a new systematical self‐healing evaluation method is developed. The cuts with controllable depth, width, and period can be easily fabricated on bPEI/PAA films through the colloidal lithography and photolithography. Colloidal lithography, as a facile, low‐cost, and versatile unconventional technique, can realize precise and repetitive fabrication of cuts at the same sample and in the same area, which will be beneficial to the systematic study and evaluate self‐healing behavior. The self‐healing behaviors on the different cuts are observed by scanning electron microscope (SEM). The SEM results reveal that bPEI/PAA film could realize damage/healing process for multiple times at the same sample and in the same area. In addition, the self‐healing abilities of the LbL films are related to the damage number, depth, and width of cuts. With the increase of damage number, depth, and width of cuts, the loss of polyelectrolyte was also increased, which lead to the flow of remaining polyelectrolytes were not enough to heal the cuts. This work provides a new route to systematically characterize the self‐healing ability of bPEI/PAA films as well as other polyelectrolyte films.

Stationary photocurrent generation from bacteriorhodopsin-loaded lipo-polymersomes in polyelectrolyte multilayer assembly on polyethersulfone membrane.

Vesicles constructed of either synthetic polymers alone (polymersomes) or a combination of polymers and lipids (lipo-polymersomes) demonstrate excellent long-term stability and ability to integrate membrane proteins. Applications using lipo-polymersomes with integrated membrane proteins require suitable supports to maintain protein functionality. Using lipo-polymersomes loaded with the light-driven proton pump bacteriorhodopsin (BR), we demonstrate here how the photocurrent is influenced by a chosen support. In our study, we deposited BR-loaded lipo-polymersomes in a cross-linked polyelectrolyte multilayer assembly either directly physisorbed on gold electrode microchips or cross-linked on an intermediary polyethersulfone (PES) membrane covalently grafted using a hydrogel cushion. In both cases, electrochemical impedance spectroscopic characterization demonstrated successful polyelectrolyte assembly with BR-loaded lipo-polymersomes. Light-induced proton pumping by BR-loaded lipo-polymersomes in the different support constructs was characterized by amperometric recording of the generated photocurrent. Application of the hydrogel/PES membrane support together with the polyelectrolyte assembly decreased the transient current response upon light activation of BR, while enhancing the generated stationary current to over 700nA/cm2. On the other hand, the current response from BR-loaded lipo-polymersomes in a polyelectrolyte assembly without the hydrogel/PES membrane support was primarily a transient peak combined with a low-nanoampere-level stationary photocurrent. Hence, the obtained results demonstrated that by using a hydrogel/PES support it was feasible to monitor continuously light-induced proton flux in biomimetic applications of lipo-polymersomes. Graphical abstract.

Impact of molecular weight on polyelectrolyte multilayer assembly and surface properties

Polyelectrolyte multilayers (PEMs) are a versatile category of materials due to their ability to modify surface properties for applications ranging from protective coatings to improved cell adhesion. Polyelectrolyte choice, including its structure and molecular weight (MW), is known to greatly influence PEM assembly and surface properties. In this work, poly(acrylic acid)/poly-l-lysine PEMs using three pairs of MWs (1.8k/15–30k, 100k/120k, and 250k/275k) were studied to determine the effects of their MWs on PEM assembly, topography and surface energy. PEMs assembly was monitored in a quartz crystal microbalance with dissipation, resulting in masses of 3.90 ± 0.87 µg/cm2, 10.80 ± 4.189 µg/cm2, and 30.04 ± 13.68 µg/cm2 for 10 bilayers of low, medium, and high MW pairs, respectively. The low MW PEM was more rigid. Low and high MW PEMs exhibited higher roughness than medium MW, caused by polyelectrolyte stripping. Surface energy remained constant with bilayer count in the low and high MW PEMs, but steadily increased in the medium MW PEM. Differences between medium MW PEMs from low and high MW systems indicate that, while PEM properties change with MW, they are not monotonically correlated and are instead related to changes in internal charge distributions and the resultant stripping that may occur.

Influence of cross-linking in loading/release applications of polyelectrolyte multilayer assemblies. A review.

Design of polymeric matrices for loading/release purposes is of great interest in various applications, such as drug delivery systems, antimicrobial surfaces, biosensors, water purification. Compared with other strategies to fabricate materials for such applications, the Layer-by-Layer (LbL) assembly remarked itself by the countless possibilities to tailor the organic architectures at nanoscale owing to the structural diversity of "nano-bricks" suitable for assembly and easiness to control the deposition features. LbL assembled systems have been extensively used as matrices to load/release low molecular compounds such as drugs and dyes, proteins and enzymes, or DNA (RNA). In many studies, cross-linking the layers was investigated as a mean to stabilize and to induce new functionalities in the obtained architectures, as well as to tune their loading/release properties. In this review we discuss recent progress in the use of LbL constructions in loading/release of bioactive species, with a main focus on the role of cross-linking on such features. Overviews of the LbL assembly strategy describing the parameters which influence the build-up process and of the main synthetic routes used to cross-link the obtained architectures are briefly presented. The use of LbL systems (either as thin films deposited on solid surfaces or as hollow capsules) to load/release low molecular compounds and proteins/enzymes, highlighting the role of cross-linking in such processes (construction of porous architectures capable to load high molecular compounds or decreasing the assemblies permeability to delay the release of encapsulated compounds) was thoroughly discussed.

Composite multilayer films based on polyelectrolytes and in situ‐formed carbon nanostructures with enhanced photoluminescence and conductivity properties

ABSTRACTWe report a facile route for the fabrication of thin composite films based on polyelectrolytes and carbon nanostructures. Composite films were made by layer‐by‐layer assembly of polyelectrolyte multilayers utilizing embedded dextran sulfate (Dex) solution as a carbon source. Raman measurements indicate the formation of carbon nanostructures from the Dex precursor over the whole film. Formation of these nanostructures results in enhanced photoluminescence and an increase in conductivity by two orders of magnitude to about 0.055 S cm−1. The latter corresponds to the level of wide‐gap semiconductors, in contrast to the initial insulating polyelectrolyte film. A distinct peak of photoluminescence of the films is found in the blue region at the wavelength of 450 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47718.

Encapsulation of Long Genomic DNA into a Confinement of a Polyelectrolyte Microcapsule: A Single-Molecule Insight.

Encapsulation of nucleic acids is an important technology in gene delivery, construction of “artificial cells”, genome protection, and other fields. However, although there have been a number of protocols reported for encapsulation of short or oligomeric DNAs, encapsulation of genome-sized DNA containing hundreds of kilobase pairs is challenging because the length of such DNA is much longer compared to the size of a typical microcapsule. Here, we report a protocol for encapsulation of a ca. 60 μm contour length DNA into several micrometer-sized polyelectrolyte capsules. The encapsulation was carried out by (1) compaction of T4 DNA with multivalent cations, (2) entrapment of DNA condensates into micrometer-sized CaCO3 beads, (3) assembly of polyelectrolyte multilayers on a bead surface, and (4) dissolution of beads resulting in DNA unfolding and release. Fluorescence microscopy was used to monitor the process of long DNA encapsulation at the level of single-DNA molecules. The differences between long and short DNA encapsulation processes and morphologies of products are discussed.

Fabrication of self-assembled polysaccharide multilayers on broke chemi-mechanical pulp fibers: Effective approach for paper strength enhancement

The present study was conducted to form polysaccharide-based multilayers of cationic starch (CS)/anionic starch (AS), and CS/carboxymethyl cellulose (CMC) on broke chemi-mechanical pulp (BCMP) fibers. It aimed to examine the buildup of CS/AS and CS/CMC polyelectrolyte multilayers (PEM) on the fibers surface, and explore the effects of PEM formation on the properties of the resulting papers. The assembly of PEM was analyzed by using zeta (ζ-) potential, water retention value (WRV), SEM micrographs, and paper properties such as thickness and strength. The results of ζ-potential inversions indicated successful constitution of PEM on the BCMP fiber surface by assembling CS/AS or CS/CMC multilayers. Further, larger ζ-potential variations occurred in depositing CS/CMC PEM, due to more charge of CMC, which presumably formed a layer with greater potential of absorption. Based on the SEM images, the surface of PEM-treated fibers was rougher, compared to the untreated fibers due to the coating with starch. Furthermore, the PEM fabrication resulted in creating fibers with higher degree of WRV, which was consistent with the significant improvement of the sheet strengths. Finally, the strength enhanced papers made from PEM-treated fibers with tensile index of about 37.33 ± 1.47 N m/g vs 22.24 ± 1.23 N m/g or 11.60 ± 0.57 N m/g for the papers made from original CMP and untreated BCMP fibers, respectively, may diminish the challenges related to web breaks in the paper machine conveying BCMP broke fibers.

Functionalization of halloysite nanotubes by enlargement and layer-by-layer assembly for controlled release of the fungicide iodopropynyl butylcarbamate.

Iodopropynyl butylcarbamate (IPBC) is currently one of the most important fungicides widely used for industrial coatings and bamboo treatment. In this work, a controlled release composite with IPBC for inhibition of mold and stain fungi was prepared using enlarged halloysite nanotubes (HNTs) with layer-by-layer (LbL) assembly of polyelectrolyte multilayers. The acid-treated HNTs retained their tubular structure with increased internal diameter, and IPBC loading efficiency was therefore increased to 24.4%, approximately three times the amount of raw HNTs (8.4%). In vitro drug release assay showed that IPBC could be released from HNTs in a sustainable manner with a total release amount of 33.8% over a period of 35 days. The release rate of IPBC could be further controlled by adjusting the number of LbL layers on the tubes and the released amount of IPBC could be limited to less than 10% in 100 days. An inhibition zone test indicated the as-prepared nanocomposites exhibited significant anti-fungal performance against three mold fungi (Aspergillus niger, Trichoderma viride, and Penicillium citrinum) and one stain fungus (Botryodiplodia theobromae). The results support the potential use of HNTs for a prolonged service life of bamboo products.

Novel magneto-responsive nanoplatforms based on MnFe2O4 nanoparticles layer-by-layer functionalized with chitosan and sodium alginate for magnetic controlled release of curcumin

Remotely assisted drug delivery by means of magnetic biopolymeric nanoplatforms has been utilized as an important tool to improve the delivery/release of hydrophobic drugs and to address their low cargo capacity. In this work, MnFe2O4 magnetic nanoparticles (MNPs) were synthesized by thermal decomposition, coated with citrate and then functionalized with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers, with chitosan as polycation and sodium alginate as polyanion. Simultaneous conductimetric and potentiometric titrations were employed to optimize the LbL deposition and to enhance the loading capacity of nanoplatforms for curcumin, a hydrophobic drug used in cancer treatment. ~200 nm sized biopolymer platforms with ~12 nm homogeneously embedded MNPs were obtained and characterized by means of XRD, HRTEM, DLS, TGA, FTIR, XPS and fluorescence spectroscopy techniques to access structural, morphological and surface properties, to probe biopolymer functionalization and to quantify drug-loading. Charge reversals (±30 mV) after each deposition confirmed polyelectrolyte adsorption and a stable LbL assembly. Magnetic interparticle interaction was reduced in the biopolymeric structure, hinting at an optimized performance in magnetic hyperthermia for magneto-assisted drug release applications. Curcumin was encapsulated, resulting in an enhanced payload (~100 μg/mg). Nanocytotoxicity assays showed that the biopolymer capping enhanced the biocompatibility of nanoplatforms, maintaining entrapped curcumin. Our results indicate the potential of synthesized nanoplatforms as an alternative way of remotely delivering/releasing curcumin for medical purposes, upon application of an alternating magnetic field, demonstrating improved efficiency and reduced toxicity.

Influence of polyelectrolyte chains on surface charge and magnetization of iron oxide nanostructures

The layer-by-layer (LbL) technique was employed to encapsulate maghemite (γ-Fe2O3) nanoparticles with natural and synthetic polyelectrolytes, with a view to producing magnetic nanoplatforms as a tool to improve remotely assisted delivery/release of hydrophobic drugs and to address their low cargo capacity. Magnetic nanoparticles (MNPs) were synthesized by coprecipitation and functionalized with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers. Simultaneous conductimetric and potentiometric titrations were utilized in order to find the optimal pH for the deposition of four intercalated layers of polystyrene sulfonate (PSS)/polyallylamine hydrochloride (PAH) or sodium carboxymethylcellulose (CMC)/chitosan (CHI) polyelectrolytes. XRD, TEM, DLS, TGA and FTIR techniques were utilized to access structural, morphological and surface properties. Charge reversals after each deposition confirmed a stable LbL assembly adsorbed on a multiparticulate nucleus (∼64 nm) of 8.8 nm-sized MNPs. Polymer layers of increasing thickness ranging from 4 to 15 nm (PSS/PAH) and from 21 to 48 nm (CMC/CHI) were estimated as MNPs were successively coated with polyelectrolytes. All the systems exhibited superparamagnetic-like behavior. Surprisingly, a stronger reduction was observed in the saturation magnetization of MNPs coated with synthetic polyelectrolytes (thinner shells) than in the system layered with natural polymers (thicker shells). Magnetization results suggest that synthetic polyelectrolytes adsorbed on the nanoparticle surface appear to have a stronger cooperativity than that of biopolymers, which could differently affect the interaction of spins located in the magnetically disordered regions in the nanoparticle surface.

Surfactants as mesogenic agents in layer-by-layer assembled polyelectrolyte/surfactant multilayers: nanoarchitectured "soft" thin films displaying a tailored mesostructure.

Interfacial supramolecular architectures displaying mesoscale organized components are of fundamental importance for developing materials with novel or optimized properties. Nevertheless, engineering the multilayer assembly of different building blocks onto a surface and exerting control over the internal mesostructure of the resulting film is still a challenging task in materials science. In the present work we demonstrate that the integration of surfactants (as mesogenic agents) into layer-by-layer (LbL) assembled polyelectrolyte multilayers offers a straightforward approach to control the internal film organization at the mesoscale level. The mesostructure of films constituted of hexadecyltrimethylammonium bromide, CTAB, and polyacrylic acid, PAA (of different molecular weights), was characterized as a function of the number of assembled layers. Structural characterization of the multilayered films by grazing-incidence small-angle X-ray scattering (GISAXS), showed the formation of mesostructured composite polyelectrolyte assemblies. Interestingly, the (PAA/CTA)n assemblies prepared with low PAA molecular weight presented different mesostructural regimes which were dependent on the number of assembled layers: a lamellar mesophase for the first bilayers, and a hexagonal circular mesophase for n ≥ 7. This interesting observation was explained in terms of the strong interaction between the substrate and the first layers leading to a particular mesophase. As the film increases its thickness, the prevalence of this strong interaction decreases and the supramolecular architecture exhibits a "bulk" mesophase. Finally, we demonstrated that the molecular weight of the polyelectrolyte has a considerable impact on the meso-organization for the (PAA/CTA)n assemblies. We consider that these studies open a path to new rational methodologies to construct "nanoarchitectured" polyelectrolyte multilayers.