Synthesis of a nanocomposite containing a water‐soluble polythiophene derivative and gold nanoparticles

This paper reports on a facile method for synthesizing gold nanoparticles (AuNps) with diameter around 5 nm encapsulated with water‐soluble polythiophene sulfonate poly[2‐(3‐thienyl)ethyloxy‐4‐butylsulfonate] sodium salt (PTS) and their physical–chemical characterization. The synthesis of hybrid materials of polythiophene derivatives and gold nanoparticles is a way to improve the polymer properties, mainly in application for chemical and optical sensing platforms. The AuNps were prepared by reducing gold salt with acid aqueous sodium citrate by the Turkvich method in the presence of PTS, and both PTS and citrate helped to stabilize the AuNps. The suspensions of AuNp:PTS presented good chemical and photostability for long period of storage. The nanoparticles encapsulated with the polymer presented smaller diameters than those obtained using only sodium citrate, according to scanning electron microscopy images. The AuNps obtained were used for fabrication LbL films with commercial chitosan, which were characterized by impedance spectroscopy measurements. The results showed that the charge transfer resistance values (R_ct) decrease as the average diameter of the AuNps decreases and the proportion of PTS increases in the nanocomposite. Such increase of the nanocomposite conductivity, given by the low values of R_ct, indicates that the novel film architecture developed is promising for chemical sensing applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1245–1254     

Influence of Side‐Chain Composition on Polythiophene Properties and Supramolecular Assembly of Anionic Polythiophene Derivatives

A series of 10 polythiophene derivatives is reported, in which each polymer has a different percentage of carboxylic acid‐bearing repeat units. The properties of these polymers are explored under acidic conditions, where the carboxylic acid moieties remain neutral, and under basic conditions, where the carboxylic acid units become anionic carboxylates. The properties that are examined for both solutions and films include UV–vis absorption spectroscopy, photoluminescence spectroscopy, and red‐edge optical band gaps. All the properties studied are strongly dependent both on protonation state and percentage of carboxylic acid/carboxylate side chains along the polymer backbone. The anionic form of each polythiophene derivative was also used in layer‐by‐layer film deposition with a cationic phosphonium polyelectrolyte. The film growth process was studied by spectroscopic techniques to assess the influence of side‐chain composition on the film growth and optical properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019     

Electropolymerization of layer‐by‐layer precursor polymer films

The layer‐by‐layer (LbL) self‐assembly has been used to fabricate polymer thin films on any solid substrates. The multilayer polymer thin films are constructed by alternating adsorption of anionic and cationic polymers. Polyelectrolyte multilayer ultrathin films containing anionic poly[2‐(thiophen‐3‐yl)ethyl methacrylate‐co‐methacrylic acid]; P(TEM‐co‐MA) and cationic poly[4‐(9H‐carbazol‐9‐yl)‐N‐butyl‐4‐vinyl pyridium bromide]; P4VPCBZ, were fabricated. The growth of multilayer ultrathin films was followed by UV–Vis absorption spectrophotometer and surface plasmon resonance spectroscopy (SPR). The deposition of P(TEM‐co‐MA)/P4VPCBZ as multilayer self‐assembled ultrathin films regularly grow which showed linear growth of absorbance and thickness with increasing the number of layer pair. Cross‐linking of the layers was verified by cyclic voltammetry (CV), UV–Vis spectrophotometry and electrochemical surface plasmon resonance (EC‐SPR) spectroscopy with good electro‐copolymerizability. This was verified by spectroelectrochemistry. The SPR angular‐reflectivity measurement resulted in shifts to a higher reflectivity according to the change in the dielectric constant of the electropolymerized film. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic Interrogation of Layer-by-layer Assembled Films of Conjugated Polyelectrolytes

Layer-by-layer fluorescent conjugated polyelectrolyte films have been studied. The photoluminescence of conjugate polyelectrolytes was observed to be highly tunable during this film assembly process. Efficient photoinduced electron transfer from thus prepared highly luminescent film to a natural electron-transfer protein cytochrome c has also been observed.     

Construction of albumin multilayer coating onto plasma treated poly(vinyl chloride) via electrostatic self‐assembly

Multilayer films consisting of polyethylenimine (PEI) and albumin were successffully prepared on plasma treated poly(vinyl chloride) (PVC) via electrostatic self‐assembly of the PEI and albumin. The layer‐by‐layer assembly of the PEI/albumin on plasma treated PVC was monitored by contact angle and ¹²⁵I radiolabeled method. The stability of the mutilayer coating was determined by ¹²⁵I radiolabeled method. The results revealed that less than 10% albumin was eluted by a phosphate buffered saline (PBS) solution in 45 days. The static platelet adhesion indicated that the PEI/albumin deposited PVC could resist the platelet adhesion effectively. Such an easy processing and shape‐independent method may have good potential for surface modification of cardiovascular device. Copyright © 2004 John Wiley & Sons, Ltd.     

Single Polyelectrolyte Microcapsules Fabricated By Glutaraldehyde‐Mediated Covalent Layer‐By‐Layer Assembly

Summary: Single polyelectrolyte component microcapsules and multilayers, exemplified by poly(allylamine hydrochloride) (PAH), have been prepared using a method of glutaraldehyde (GA)‐mediated covalent layer‐by‐layer (LbL) assembly. The GA cross‐linking of the adsorbed PAH results in surfaces covered by reactive aldehyde groups, which can then react with PAH to result in another layer of covalently linked PAH. The repeated assembly of single polyelectrolyte in an LbL manner can be thus achieved. The PAH multilayers can grow linearly along with the layer number, and their thickness can be controlled at the nanometer scale, as verified by UV‐vis absorption spectrometry and ellipsometry. Single polyelectrolyte microcapsules are obtained after removal of the template cores at low pH. The morphology and integrity are confirmed by scanning force microscopy and confocal laser scanning microscopy.

Schematic illustration of the preparation of a single polyelectrolyte component microcapsule by GA‐mediated covalent LbL assembly.     

Spin Self‐Assembled Clay Nanocomposite Passivation Layers Made from a Photocrosslinkable Poly(vinyl alcohol) and Na+‐Montmorillonite Enhance the Environmental Stability of Organic Thin‐Film Transistors

We investigated the effects of the multilayer polymer‐clay nanohybrid passivation films on the stability of pentacene organic thin‐film transistors (OTFTs) exposed to air and UV irradiation. Well‐ordered multilayer films were deposited by the spin‐assisted layer‐by‐layer assembly method using photocrosslinkable poly(vinyl alcohol) with the N‐methyl‐4(4′‐formylstyryl)pyridinium methosulfate acetal group (SbQ‐PVA) and Na⁺‐montmorillonite in a water‐based solution process. When photocrosslinked, these SbQ‐PVA/clay multilayers were found to serve as excellent barriers to O₂ and UV‐light. Moreover, when used as passivation layers, they enhanced the stability of pentacene OTFT devices exposed to air and UV radiation.     

Microfluidics as A Tool to Understand the Build‐Up Mechanism of Exponential‐Like Growing Films

Microfluidics is used here for the first time to efficiently tune the growth conditions for understanding the build‐up mechanism of exponentially growing polyelectrolyte (PE) films. The velocity of PE supply and time of interaction can be successfully altered during the layer‐by‐layer assembly. Another advantage of this method is that the deposition of poly‐L ‐lysine/hyaluronic acid (PLL/HA) films in microchannels can be monitored online by fluorescence microscopy. The study demonstrates that PE mass transport to the film surface and diffusion in the film are key parameters affecting PLL/HA film build‐up. Increase of PE supply rate results in a change in the “transition” (exponential‐to‐linear growth) towards higher number of deposition steps, thus indicating a mass transport‐mediated growth mechanism.     

Micelles‐Encapsulated Microcapsules for Sequential Loading of Hydrophobic and Water‐Soluble Drugs

Layer‐by‐layer (LbL) assembly was conducted on CaCO₃ microparticles pre‐doped with polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) micelles, and resulted in micelles encapsulation in the microcapsules after core removal. Distribution of the micelles in the templates and capsules was characterized by transmission electron microscopy and confocal laser scanning microscopy. The micelles inside the capsules connected with each other to form a chain and network‐like structure with a higher density near the capsule walls. The hydrophobic PS cores were then able to load small uncharged hydrophobic drugs while the negatively charged PAA corona could induce spontaneous deposition of water‐soluble positively charged drugs such as doxorubicin.

     

Nanoparticle Missiles from Exploding Polyelectrolyte Capsules

Out with a bang! Microcapsules have been prepared which, as a result of an explosion triggered by an external stimulus, distribute nanoparticles throughout the local environment both efficiently and rapidly (see picture). In this way a principle found in nature for the dispersal of seeds and defensive materials has now been realized in nanotechnology and might be utilized, for example, for the better distribution of drugs in organs.

     

Fabrication of a Stable Polyelectrolyte/Au Nanoparticles Multilayer Film

The fabrication of stable polyelectrolyte/Au nanoparticle multilayer films was achieved by the UV irradiation of layer‐by‐layer self‐assembled multilayers consisting of diazoresins and Au nanoparticles. The method promises to be a simple and efficient strategy to construct covalently attached organic/inorganic multilayer hybrids.     

Fast Self‐Healing of Polyelectrolyte Multilayer Nanocoating and Restoration of Super Oxygen Barrier

A self‐healable gas barrier nanocoating, which is fabricated by alternate deposition of polyethyleneimine (PEI) and polyacrylic acid (PAA) polyelectrolytes, is demonstrated in this study. This multilayer film, with high elastic modulus, high glass transition temperature, and small free volume, has been shown to be a super oxygen gas barrier. An 8‐bilayer PEI/PAA multilayer assembly (≈700 nm thick) exhibits an oxygen transmission rate (OTR) undetectable to commercial instrumentation (<0.005 cc (m⁻² d⁻¹ atm⁻¹)). The barrier property of PEI/PAA nanocoating is lost after a moderate amount of stretching due to its rigidity, which is then completely restored after high humidity exposure, therefore achieving a healing efficiency of 100%. The OTR of the multilayer nanocoating remains below the detection limit after ten stretching‐healing cycles, which proves this healing process to be highly robust. The high oxygen barrier and self‐healing behavior of this polymer multilayer nanocoating makes it ideal for packaging (food, electronics, and pharmaceutical) and gas separation applications.

     

Layer‐by‐Layer Assembled Nanotubes as Biomimetic Nanoreactors for Calcium Carbonate Deposition

Enzyme‐loaded magnetic polyelectrolyte multilayer nanotubes prepared by layer‐by‐layer assembly combined with the porous template could be used as biomimetic nanoreactors. It is demonstrated that calcium carbonate can be biomimetically synthesized inside the cavities of the polyelectrolyte nanotubes by the catalysis of urease, and the size of the calcium carbonate precipitates was controlled by the cavity dimensions. The metastable structure of the calcium carbonate precipitates inside the nanotubes was protected by the outer shell of the polyelectrolyte multilayers. These features may allow polyelectrolyte nanotubes to be applied in the fields of nanomaterials synthesis, controlled release, and drug delivery.

     

Stimuli‐Responsive Multilayered Hybrid Nanoparticle/Polyelectrolyte Capsules

Gold nanoparticles (Au_NP) with carboxyl groups on their surface were used in combination with PAH for the layer‐by‐layer coating of CaCO₃ microparticles, followed by the dissolution of the CaCO₃ core. SEM, TEM, and confocal microscopy are used to characterize the hybrid nanoparticles/polyelectrolyte capsules. As the Au_NP have carboxyl groups on their surface, their charge density is pH dependent; therefore, the capsules exhibit a pH‐dependent swelling and can be deconstructed both at low and high pH. By covalent cross‐linking of the carboxyl groups of the Au_NP and the amino groups of the PAH, it is possible to suppress the pH‐responsive behavior. Au_NP are used as activation centers using IR light and this ability is used to release encapsulated material from the nanoparticles/polyelectrolyte capsules as well as for the enhancement of detection and imaging of such capsules by Raman microspectrosopy.

     

Defined Picogram Dose Inclusion and Release of Macromolecules using Polyelectrolyte Microcapsules

Summary: Reversible pH‐induced swelling of (PAH/PSS) polyelectrolyte microcapsules is accompanied by increased porosity, making them permeable to poly(acrylic acid) (PAA) at pH values higher than 11.2. This pH‐switchable permeability was used to encapsulate the polyanion in alkaline conditions. Relationship between starting PAA concentration in solution and amount finally being encapsulated has been established and can be used further as calibration curve. A desired amount of encapsulated polymer in the picogram range per capsule can be achieved. The loaded capsules were then used as microreactors by forming a complex between the PAA and Ca²⁺ ions.

General scheme for pH‐induced encapsulation of (PAA) in alkali condition by switching their permeability.     

Crosslink effect and albumin adsorption onto chitosan/alginate multilayered systems: an in situ QCM-D study

The adsorption of HSA onto CHI/ALG multilayer assemblies was assessed in situ using QCM-D. It was found that the behavior of HSA on biomaterials surface can be tuned by adjusting parameters of the polyelectrolyte system such as pH, layer number, crosslinker and polymer terminal layer. Our results confirmed the key role of electrostatic interactions during HSA adsorption, since oppositely charged surfaces were more effective in promoting protein adhesion. QCM-D data revealed that crosslinking (CHI/ALG)(5) CHI films allows HSA to become adsorbed in physiological conditions. Our results suggested that the biological potential of biopolymers and the mild conditions of the LbL technique turn these natural nanoassemblies into a suitable choice to be used as pH-sensitive coatings.     

Reversible pH‐Dependent Properties of Multilayer Microcapsules Made of Weak Polyelectrolytes

Summary: We investigated microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) assembled on calcium carbonate cores. These capsules are stable in the pH range from 2.5 to 11.5, undergoing reversible swelling in the pH interval from 2.7 to 2.6. Capsule swelling occurs at a protonation degree above 90%. The pH‐dependent size variation of PAH/PMA capsules is blocked after crosslinking of the polyelectrolyte layers.

Schematic of the swelling and de‐swelling of the capsules with changing pH.