‘Bricks and mortar’ nanoparticle self‐assembly using polymers

Developments in self‐assembly methods allow access to hierarchical materials featuring a wide range of functionality and applications. Polymer‐based self‐assembly of nanoparticles opens up new avenues for the fabrication of highly structured nanocomposites that can serve as bridges between ‘bottom‐up’ and ‘top‐down’ methods. Of various interactions leading to self‐assembly of nanocomposites, hydrogen bonding and electrostatic interactions are commonly utilized. In this review, we illustrate the design and subsequent property tuning of various self‐assembled nanocomposite materials that were developed based on these interactions. Copyright © 2007 Society of Chemical Industry     

Layer‐by‐layer self‐assembled multilayer films of single‐walled carbon nanotubes and tin disulfide nanoparticles with chitosan for the fabrication of biosensors

In this study, multilayer films containing chitosan, tin disulfide (SnS₂) nanoparticles, and single‐walled carbon nanotubes were prepared on glassy carbon electrodes with the use of a layer‐by‐layer assembly technique. The resulting films were characterized with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy, and ultraviolet–visible absorption spectroscopy. The results of CV and EIS indicates that the peak currents and charge‐transfer resistance all had linear responses to the number of assembled layers. The multilayer‐film‐modified electrode showed excellent electrocatalytic properties for some species, such as dopamine hydrochloride (DA), ascorbic acid (AA), and uric acid (UA). The well‐separated voltammetric signals of DA, UA, and AA could be obtained on the assembled multilayer‐film‐modified electrode, and the peak‐to‐peak potential separations were 171, 136, and 307 mV for DA–UA, DA–AA, and UA–AA on CV, respectively. These facts showed that the multilayer‐film‐modified electrode could be used as a new sensor for the simultaneous detection of DA and UA in the presence of AA in a real sample. In addition, the multilayer films were stable, selective, and reproducible. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Controllable self‐assembly of polystyrene‐block‐poly(2‐vinylpyridine)

Block copolymers can form various ordered structures by self‐assembly, and their composites with inorganic materials may give surprising properties. This review summarizes recent developments in the preparation, mechanism and application of various types of self‐assembly of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP). The focus of the review is on how to control the self‐assembly of the dynamic and ordered structure of PS‐b‐P2VP based materials by applying effective factors such as thermal annealing, solvent annealing, block composition and blending. Moreover, the combination of the self‐assembly of PS‐b‐P2VP and various nanoparticles, with potentials in drug delivery, sensors and catalysis, is highlighted. © 2018 Society of Chemical Industry     

Influence of the phase state of self‐assembling redox mediators on their electrochemical activity

Self‐assembling redox mediators have the potential to be broadly useful in a range of interfacial electrochemical contexts because the oxidation state and state of assembly of the mediator are closely coupled. In this article, we report an investigation of the self‐assembly of single‐ and double‐tailed ferrocenyl amphiphiles [(11‐ferrocenylundecyl)trimethylammonium bromide (FTMA) and bis(11‐ferrocenylundecyl)dimethylammonium bromide (BFDMA), respectively] at the surfaces of Pt electrodes and the impact of the dynamic assembled state of the amphiphiles on their rate of oxidation. We conclude that frozen aggregates of BFDMA adsorb to the surfaces of the Pt electrodes, and that slow dynamics of reorganization of BFDMA within these aggregates limits the rate of electrooxidation of BFDMA. In contrast, FTMA, while forming assemblies on the surfaces of Pt electrodes, is characterized by fast reorganization dynamics and a corresponding rate of oxidation that is an order of magnitude greater than BFDMA. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1381–1392, 2014     

Comparison between the self‐assembling behaviors of PLLA‐PEO‐PLLA triblock copolymers and PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers

Poly(L ‐lactic acids) (PLLAs) were grafted to both ends of poly(ethylene oxide) (PEO) to produce biocompatible amphiphilic PLLA‐PEO‐PLLA triblock copolymers. The self‐assembling behaviors of two PLLA‐PEO‐PLLA copolymers in aqueous solutions were examined by Dynamic Light Scattering and Transmission Electron Microscopic techniques. PLLA‐PEO‐PLLA formed spherical micelles, whereas PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers were reported to produce vesicles. It is believed that the PPO segment within the PLLA‐PEO‐PPO‐PEO‐PLLA pentablock copolymers has a dominant role in the formation of vesicles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrospun self‐assembled nanofiber yarns

A technique for making self‐assembled electrospun (E‐spun) nanofiber yarns from poly(acrylonitrile) in a single step is described. The process involved formation of the nanofiber yarn directly within the electrospinning zone and its removal before it can reach the counter‐electrode. The yarn is presumably formed due to splitting of the main jet into numerous nanojets and their reassembly into a single entity midway between the two electrodes. The process was found to occur at a particular field strength, which varied considerably with the concentration of the polymer dope. The gross morphology of yarns and the alignment of nanofibers in the yarn were evaluated by scanning electron microscopy (SEM). The rationale behind the formation of the yarn like structure has been explained. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and self‐assembly of polyaniline nanorods and their application as electroactive actuators

To improve the performance of ion‐exchange polymer–metal composite (IPMC) actuators, an electrical pathway material for enhancing the surface adhesion between the membrane and the metal electrodes of the IPMC was studied. As an efficient electrical pathway material, polyaniline nanorods (PANI‐NRs) doped with p‐toluene sulfonic acid (TSA) were synthesized with a template‐free method. The factors affecting polyaniline morphology were studied with various dopant concentrations and oxidant feeding rates. Highly conductive PANI‐NRs were formed when they were synthesized with ammonium persulfate at a 5.0 mL/min oxidant feeding rate and doped with 0.125M TSA. The conductivity of the PANI‐NRs was 1.15 × 10^?1 S/cm, and their diameters and lengths were 120–180 nm and 0.6–2 μm, respectively. To apply the membrane as an actuator, perfluorosulfonated ionomer (Nafion)/PANI‐NR blends were prepared by solution blending and casting. The actuating ability of the three‐layered membrane consisting of Nafion/PANI‐NR blends was then examined and compared with that of Nafion only. The actuating ability of the IPMC was improved when Nafion/PANI‐NRs were used as electrical pathways. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on self‐assembly and characterization of polyelectrolytes and organic dyes

Four polyelectrolyte complexes were formed through the self‐assembly of poly‐N‐ethyl‐N,N‐ dimethylamino ethyl methacrylate (PEDEM) and poly‐ N‐ethyl‐4‐vinylpyridinium (PEVP) cations with methyl orange (MO) and metanil yellow (MY) anions in water. The FTIR spectra showed that the assembly was formed chiefly through electrostatic force and hydrophobic interaction between polyelectrolytes and organic dyes without new bonds emerging. The fluorescence spectra revealed that the emission waves of the complexes of PEDEM‐MY and PEDEM‐MO in alcohol were blue‐shift in comparison with those of dyes in alcohol, and the emission waves of the PEVP‐MY and PEVP‐MO complexes in alcohol were red‐shift in comparison with those of dyes in alcohol. The structure of the complexes in solid state were also investigated by differential thermal analysis (DTA) and X‐ray diffraction experiments. It was proved that the complexes were new materials formed through weak interactions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 638–644, 2002     

Poly(9‐vinylcarbazole)/silver composite nanotubes and networks formed at the air–water interface

Silver‐nanoparticle‐doped poly(9‐vinylcarbazole) (PVK) nanocomposites were prepared via the reduction of Ag⁺ ions and the self‐assembly of PVK on AgNO₃ aqueous solution surfaces. The formed composite nanostructures depended strongly on the experimental temperature. Thick round disks of PVK surrounded by discrete Ag nanoparticles and/or with irregular holes formed at room temperature; nanotubes and micronetworks doped with Ag nanoparticles formed at about 30–40°C, and networks formed at higher temperature. Further investigation revealed that the nanotubes were transformed from thin round disks. The length of the PVK/Ag composite nanotubes were longer than 10 μm, and the average size of the embedded Ag nanoparticles was found to be about 3.5 nm. The composite networks were composed of round pores with diameters of several hundred nanometers and fine silver nanoparticles embedded in the thin polymer films that covered the pores. The formation of the nanotubes was a very interesting self‐assembly phenomenon of the polymer at the air–water interface that has not been reported before. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Versatile synthesis of self‐assembling ABA triblock copolymers with polymethyloxazoline A‐blocks and a polysiloxane B‐block decorated with supramolecular receptors

BACKGROUND: Self‐assembling amphiphilic block copolymers with incorporated, biologically relevant functionalities have received limited attention, partly due to the fact that biomolecules are not robust enough to synthetic manipulation, do not lend themselves readily to systematic studies due to their complexity and leach rather quickly from a vesicle or membrane when physically incorporated. Synthetic supramolecules are used as biomolecule mimics in functional membranes. RESULTS: Reaction conditions were established for the synthesis of a tosyl‐terminated siloxane end‐blocker, which serves as molecular weight control in the synthesis of polydimethylsiloxane (PDMS) and poly(dimethylsiloxane‐co‐methylhydrosiloxane) [P(DMS‐co‐MHS)] copolymers. Hydrosilylation reactions were investigated for the covalent coupling of synthetic supramolecules (18‐crown‐6 ether, hydroxybenzoate) to the polymer backbone using the methylhydrosiloxane repeat units as the anchor moiety. Using P(DMS‐co‐MHS) or derivatized P(DMS‐co‐MHS) copolymers as macroinitiator for the ring‐opening polymerization of 2‐methyl‐4‐hydroxy‐oxazoline led to the formation of poly[(dimethylsiloxane‐co‐methylhydrosiloxane)‐block‐oxazoline] [P(DMS‐co‐MHS‐b‐Ox)] ABA triblock copolymers with defined PDMS to PMHS ratios and controlled molecular weights. CONCLUSION: Derivatized P(DMS‐co‐MHS‐b‐Ox) ABA triblock copolymers synthesized using a novel versatile procedure undergo vesicle formation upon electroformation with vesicle diameters ranging from 2 to 10 µm. The size of the vesicle depends on the overall polarity of the macromolecule. Copyright © 2008 Society of Chemical Industry     

Studies on self‐assembly and characterization of polyelectrolytes and organic dyes

Four polyelectrolyte complexes were formed through self‐assembly of poly‐N‐ethyl‐N,N‐(dimethylamino)ethyl methacrylate (PEDEM) and poly‐N‐ethyl‐4‐vinylpyridinium (PEVP) cations with methyl orange (MO) and metanil yellow (MY) anions in water. The FTIR spectra showed that the assembly was formed chiefly through electrostatic force and hydrophobic interaction between polyelectrolytes and organic dyes without new bonds emerging. The fluorescence spectra revealed that the emission waves of the complexes of PEDEM–MY and PEDEM–MO in alcohol were blue‐shifted in comparison with that of dyes in alcohol, and the emission waves of the PEVP–MY and PEVP–MO_ complexes in alcohol were red‐shifted in comparison with that of dyes in alcohol. The structure of the complexes in the solid state were also investigated by DTA and X‐ray diffraction experiments. It could be proved that the complexes were new materials formed through weak interactions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 369–374, 2003     

Directional self‐assembly by electrospun wet fibers

In this study, we examined directional self‐assembly by electrospun wet fibers. The landing point of the wet fibers was controllable as its trajectory was strictly limited by the adjustment of the parameters of electrospinning. The wet fibers would not stack on the grounded plate in an irregular pattern but in the direction of an electric field in sequence. The preliminary wet fibers deposited and erected on the ground plate to form a controllable circle. The subsequent wet fibers traveled to the top of the circle directionally to organize a mesh tube. The apical circle of the mesh tube was the precise landing point of the subsequent wet fibers. With the wet fibers landing continuously, the mesh tube grew longer and longer. Finally, the controllable circle grew to be the growing mesh tube step by step. We discovered that the mesh tube was assembled by fibers spontaneously in the electrostatic field. In this article, we also try to explain the mechanism of self‐assembly and the formation of wet fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43003.     

Emulsifier‐free synthesis and self‐assembly of an amphiphilic poly(styrene‐co‐acrylic acid) copolymer

A poly(styrene‐co‐acrylic acid) copolymer was synthesized by surfactant‐free polymerization with the assistance of power ultrasound in water. Fourier transform infrared, NMR, and differential scanning calorimetry measurements revealed that the copolymer was random. Atomic force microscopy and laser light scattering were used to investigate the self‐assembly of the copolymer, and it was found that the copolymer chains formed micelles or other self‐assemble structures in solution. Atomic force microscopy also indicated that the self‐assembled structures developed into nanospheres with a poly(acrylic acid)‐rich or polystyrene‐rich surface in a film, depending on the solvent used for the preparation of the film. In particular, a wheel‐like structure could resulted in a film when the copolymer film was prepared in a moist environment; it resulted from heterogeneous aggregates of poly(acrylic acid) at the rim of water bubbles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:3718–3726, 2006     

Studies on the self‐assembly of neat DBS and DBS/PPG organogels

The self‐assembly behavior of neat 1,3:2,4‐dibenzylidene‐D ‐sorbitol (DBS) and DBS/poly(propylene glycol) (PPG) organogels has been investigated by scanning electron microscopy, polarizing optical microscopy, and rheological measurements. DBS molecules are capable of self‐organizing into fibrils and exhibit the birefringent spherulitic textures during cooling from the melt. On the other hand, DBS can self‐assemble into a fibrillar network in PPG to produce organogels. DBS/PPG organogels also reveal a spherulite‐like morphology. When a small amount of DBS is dispersed into a PPG matrix, we find that the spherulite sizes are much smaller than those of neat DBS. This is because the dilution of DBS causes DBS to self‐assemble in PPG at a lower temperature. Therefore, more nucleation sites and smaller spherulite sizes are found in the DBS/PPG organogel system. The rheological measurements demonstrate that the elastic modulus (G′) in DBS/PPG organogels increases as the DBS concentration increases. However, the increase in G′ is less obvious, as the DBS content exceeds 3 wt %. suggesting that the DBS networks become saturated. Also, it is found that these organogels require a certain period of time to reach thermodynamic equilibrium, depending on DBS concentrations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Redox‐active LBL films via in situ template polymerization of hydroquinone

New redox‐active hydrogel thin films with poly(hydroquinone) (PHQ) as polymeric redox couple and chitosan hydrogel as matrix are synthesized. Single‐component layer‐by‐layer films of chitosan are first fabricated in a uniform and reproducible manner, which is proved by UV and AFM studies. The chitosan films are then treated in acidic hydroquinone (HQ) solution to introduce PHQ. In situ generation of PHQ in the films is proved by UV and FTIR spectroscopy. PHQ formation also results in an increased film roughness and thickness. We confirmed that oxygen acts as oxidant and chitosan acts as template in the polymerization of HQ. Cyclic voltammogram of the film presents two oxidation peaks at 0.21 and 0.75 V and one reduction peak at ?0.15 V(vs Ag/AgCl), indicating the film, which is originally not redox‐active, becomes redox‐active after the introduction of PHQ. The new redox‐active films may find applications in amperometric biosensors. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymer clay self‐assembly complexes on paper

Layer‐by‐layer (LBL) self‐assembly was used to form polymer/clay complexes on paper to enhance its wet strength properties. Initially, alternating layers of poly(allylamine hydrochloride) (PAH) and Kaolin clay were sequentially deposited on quartz substrate and characterized by UV/Vis/NIR spectroscopy as a model system. The same procedure was then applied to a paper test sheet to form multilayered coatings, which were examined with scanning electron microscopy. The wettability of the LBL coated paper test sheet was shown to change from hydrophilic to hydrophobic with increased number of multilayers and if the terminating layer was Kaolin clay. The wet strength of the coated test sheet was improved by more than 270% over the uncoated test sheet with 16 bilayers of PAH/kaolin complex on the surface. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Fabrication of Amino‐Terminated Multiwalled Carbon Nanotubes via Layer‐by‐Layer Self‐Assembly Approach

MWCNT‐based composites have been successfully synthesized via layer‐by‐layer self‐assembly of crosslinked polyphosphazene nanoparticles on the surface of MWCNTs. The amino‐terminated CNTs were characterized by XPS, FT‐IR spectroscopy, EDS, XRD and TEM. The degree of functionalization could be controlled by simply changing the mass of hexachlorocyclotriphosphazene with 4,4′‐diaminodiphenyl ether. The activity of the surface amino groups was confirmed by the reaction of these groups with HAuCl₄. In addition, the effects of the mass of HCCP and ODA ratios on the content of the surface amino groups was also investigated.

     

Electroless nickel deposition of a palladium‐activated self‐assembled monolayer on polyester fabric

In this study, an alternative Pd activation process was developed for electroless Ni plating on polyester fabric modified with a self‐assembled monolayer (SAM) of 3‐aminopropyltrimethoxysilane (APTMS). The presence of a highly oriented amino‐terminated SAM and the formation of Pd‐activated APTMS were demonstrated by X‐ray photoelectron spectroscopy analysis. After activation, electroless Ni plating was successfully initiated, and the Ni coating was deposited onto the surface of the polyester fibers. The resulting Ni coating was examined by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and X‐ray diffraction. The electromagnetic interference (EMI) shielding effectiveness (SE) and adhesive strength of the Ni‐plated polyester fabric were evaluated. On the basis of the experimental results, the Ni coating produced with a Pd‐activated SAM was uniform and dense. As the Ni weight on the treated fabric was 32 g/m², the EMI SE of the Ni‐plated polyester fabric modified with APTMS obtained was more than 30 dB at frequencies that ranged from 2 to 18 GHz. Compared with the conventional two‐step activation method, Ni coating on the Pd‐activated polyester fabric modified with APTMS improved the coating adherence stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Self‐assembling amphiphilic PEGylated block copolymers obtained through RAFT polymerization for drug‐delivery applications

In this work, ring‐opening polymerization and reversible addition‐fragmentation chain transfer polymerization (RAFT) have been employed for the production of block copolymers where the backbone is brushed with poly(ethylene glycol) (PEG) and polyester chains. Because of their amphiphilic properties, they are able to self‐assemble in water, forming micelles. Molecular dynamics simulations have been accomplished to study the behavior of the copolymer single chain in water, and the self‐assembly properties have been characterized and correlated to the copolymer structure in terms of critical micellar concentration and particle size. As a proof of their flexibility, these materials have been employed for the production of polymer–lipid hybrid nanoparticles with tunable dimensions (from 120 to 260 nm) adopted for the controlled release of anticancer compounds (paclitaxel and curcumin). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43084.     

Directed self‐assembly by photostimulation of an amorphous semiconductor surface

A method for nanoscale directed self‐assembly is demonstrated that employs an amorphous semiconductor containing subcritical nuclei for crystallization. This strategy combines attractive features of top‐down and bottom‐up approaches by exploiting the self‐organization capabilities latent in amorphous materials, but in a way that can be controlled by optical or electron beam exposure tools. The method was demonstrated with amorphous TiO₂ deposited on silicon, heated to 270°C, and exposed to low‐level ultraviolet light. © 2010 American Institute of Chemical Engineers AIChE J, 2010