Self-assembled Multilayer Films Research Articles

Surface functionalisation of contact lenses by CS/HA multilayer film to improve its properties and deliver drugs

Soft contact lenses are very popular for vision correction and cosmetic alterations since 1960. However, wearing soft contact lenses induced many healthy problems, which are often related to the surface properties of contact lenses such as low wettability and protein deposition. Chitosan (CS)/Hyaluronic acid (HA) multilayer was assembled on the surface of contact lenses by layer-by-layer (LbL) technique to improve the surface properties of low wettability and protein deposition in the research. Surface modification improved the hydrophilic, reduced protein adsorption, enhanced water retention and increased the surface roughness length. Since LbL self-assembled multilayer films were proved to deliver drug effectively, norfloxacin and timolol as model drugs were loaded into CS/HA multilayer during LbL process. The contact lens with CS/HA multilayer could control norfloxacin steadily release in 1 h, timolol steadily release in half an hour. The novel aspect of the research is the construction of CS/HA multilayer on the surface of contact lenses for improving their surface properties and drug delivery. The impact of the research concerns the applications of multilayer and LBL technique, which opens up a useful way to decrease the problem of wearing hydrogel contact lenses and increase the possibility of hydrogel contact lenses as drug carrier.

Stimuli-responsive self-assembled multilayer azo thin films: Photo-switchable absorbance and morphological characteristics

Light has been employed as a source of energy for surface modulation, tuning and control in photo-responsive azo-incorporating self-assembled polyelectrolyte multilayer thin films. A custom built setup for controlled exposure enabled successful photo-switching. Spectral changes were characterized through UV–vis spectroscopy, while scanning electron microscopy technique was employed to study structural properties and response of the films. The effects of chromophore aggregation and dispersion on thin film photo-responsiveness have been studied, with significant contributions made to a recently proposed model correlating structural and spectral properties of the azo thin films. Structural and optical photo-responses have been acquired for surface tuning and modulation, while photo-reversibility is also achieved to control surface properties cyclically.

Layer-by-layer self-assembly of ultrathin multilayer films composed of magnetite/reduced graphene oxide bilayers for supercapacitor application

This article describes electrochemical properties of layer-by-layer self-assembled multilayer films composed of magnetite nanoparticle (Fe3O4 NP) and chemically reduced graphene oxide (RGO) for supercapacitor application. The thickness of the Fe3O4/GO bilayer was determined by optical ellipsometry to be 6.53±0.17nm, which agreed well with the sum of the independently measured thickness for each Fe3O4 (5.61±0.14nm) and GO (0.91±0.1nm) layer component. Each layer was found to be deposited uniformly and regularly. Fe3O4/RGO multilayer film was obtained by reducing a Fe3O4/GO film using hydrazine. The multilayer film yielded a minimum resistance of 1.0×104Ω/sq (2.8S/cm) for a film with approximately 50 bilayers. The electrodes fabricated from 30 Fe3O4/RGO bilayers exhibited excellent capacitive performances with a maximum specific gravimetric capacitance (151F/g) at a current density of 0.9A/g.

Controlled Fabrication and Optoelectrical Properties of Metallosupramolecular Films Based on Ruthenium(II) Phthalocyanines and 4,4′-Bipyridine Covalently Anchored on Inorganic Substrates

Fully conjugated metallosupramolecular self-assembled multilayer films were controllably fabricated based on bibenzonitril-phthalocyaninato ruthenium(II) (BBPR) and 4,4'-bipyridine (BP) via axially coordination interaction between ruthenium ions and the pyridine groups on the modified substrates. The substrates were first functionalized by 4-(pyridine-4-ylethynyl)benzenic diazonium salt (PBD) through photodecomposition of diazonium group under UV irradiation. As a result, the pyridine-containing functional groups were vertically and covalently anchored onto the surface of substrate and got a stable monolayer. Soluble ruthenium phthalocyanine, axially coordinated by labile benzonitrile groups, was used to fabricate the layer-by-layer self-assembled films with BP through ligand-exchanging reaction between benzonitrile and pyridine in each self-assembled cycle. The UV-vis analysis results demonstrated the successful fabrication of bi(4,4'-bipyridine)phthalocyaninato ruthenium(II) (BPPR) metallosupramolecular ultrathin films with definite structures on PBD-modified substrate. Under illumination, the BPPR self-assembled multilayer films displayed a quick response to light. The maximum current density reached 120 nA/cm(2) at six bilayers. The Eg, HOMO, and LUMO of the six-bilayer were quantitatively measured to be 1.68, -5.29, and -3.61 eV, respectively. This strategy supplies a facile method to get full-conjugated metallosupramolecules and a platform for developing higher performance solar cell from the point of adjusting dye aggregate state structure.

Thickness and morphology of polyelectrolyte coatings on silica surfaces before and after protein exposure studied by atomic force microscopy

Analyte–wall interaction is a significant problem in capillary electrophoresis (CE) as it may compromise separation efficiencies and migration time repeatability. In CE, self-assembled polyelectrolyte multilayer films of Polybrene (PB) and dextran sulfate (DS) or poly(vinylsulfonic acid) (PVS) have been used to coat the capillary inner wall and thereby prevent analyte adsorption. In this study, atomic force microscopy (AFM) was employed to investigate the layer thickness and surface morphology of monolayer (PB), bilayer, (PB-DS and PB-PVS), and trilayer (PB-DS-PB and PB-PVS-PB) coatings on glass surfaces. AFM nanoshaving experiments providing height distributions demonstrated that the coating procedures led to average layer thicknesses between 1nm (PB) and 5nm (PB-DS-PB), suggesting the individual polyelectrolytes adhere flat on the silica surface. Investigation of the surface morphology of the different coatings by AFM revealed that the PB coating does not completely cover the silica surface, whereas full coverage was observed for the trilayer coatings. The DS-containing coatings appeared on average 1nm thicker than the corresponding PVS-containing coatings, which could be attributed to the molecular structure of the anionic polymers applied. Upon exposure to the basic protein cytochrome c, AFM measurements showed an increase of the layer thickness for bare (3.1nm) and PB-DS-coated (4.6nm) silica, indicating substantial protein adsorption. In contrast, a very small or no increase of the layer thickness was observed for the PB and PB-DS-PB coatings, demonstrating their effectiveness against protein adsorption. The AFM results are consistent with earlier obtained CE data obtained for proteins using the same polyelectrolyte coatings.

Photoelectrochemical properties of electrostatically self-assembled multilayer films formed by a cobalt complex and graphene oxide

The multilayer films consisting of graphene oxide and a cobalt complex were fabricated though electrostatic layer-by-layer self-assembly technique and characterized by UV–Vis absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and cyclic voltammetry. The results demonstrated that the hybrid films were successfully prepared and exhibited good electrochemical activity. The film was also subjected to photoelectrochemical studies and were found to exhibit large cathodic photocurrent density of 6.1μA/cm2 while irradiated with 100mW/cm2 polychromatic light (730nm>λ>325nm) at an applied potential of −0.4V versus saturated calomel electrode.

Nanoflake Patterning of Self-Assembled Multilayer Films

Nanopatterning has attracted much attention because of its growing use in designing nanoelectronic and optoelectronic devices. Development of a facile route to nanopatterning is a persistent goal in nanotechnology. Originating from positively charged polyethyleneimine (PEI) and negatively charged poly(4-styrenesulfonate) (PSS), we successfully designed separable nanoflake patterning using layer-by-layer self-assembly technique by sequential adsorption of PEI and PSS. The morphology and size of the nanopatterning can be controlled by adjusting the number of bilayers in the film. Electrochemical measurements reveal that the (PEI/PSS) nanoflakes have good electroactivity and permeability for the electrolytes undergoing redox reaction. By controlling the distribution of surface charges on substrates, nanopatterning can be facilely achieved by self-assembly method.

Detection of layer‐by‐layer self‐assembly multilayer films by low‐temperature plasma mass spectrometry

The detection of layer-by-layer self-assembly multilayer films was carried out using low-temperature plasma (LTP) mass spectrometry (MS) under ambient conditions. These multilayer films have been prepared on quartz plates through the alternate assembling of oppositely charged 4-aminothiophenol (4-ATP) capped Au particles and thioglycolic acid (TGA) capped Ag particles. An LTP probe was used for direct desorption and ionization of chemical components on the films. Without the complicated sample preparation, the structure information of 4-ATP and TGA on films was studied by LTP-MS. Characteristic ions of 4-ATP (M) and TGA (F), including [M](+•), [M-NH(2)](+), [M-HCN-H](+), and [F + H](+), [F-H](+), [F-OH](+), [F-COOH](+) were recorded by LTP-MS on the films. However, [M-CS-H](+) and [F-SH](+) could not be observed on the film, which were detected in the neat sample. In addition, the semi-quantitative analysis of chemical components on monolayer film was carried out, and the amounts of 4-ATP and TGA on monolayer surface were 45 ng/mm(2) and 54 ng/mm(2), respectively. This resulted the ionization efficiencies of 72% for 4-ATP and 54% for TGA. In order to evaluate the reliability of present LTP-MS, the correlations between this approach and some traditional methods, such as UV-vis spectroscopy, atomic force microscope and X-ray photoelectron spectroscopy were studied, which resulted the correlation coefficients of higher than 0.9776. The results indicated that this technique can be used for analyzing the films without any pretreatment, which possesses great potential in the studies of self-assembly multilayer films.

Layer-by-layer self-assembled hybrid multilayer films based on poly(sodium 4-styrenesulfonate) stabilized graphene with polyaniline and their electrochemical sensing properties

A new class of graphene/polyaniline multilayer film was constructed by layer-by-layer self-assembly, using poly(sodium 4-styrenesulfonate) stabilized graphene sheets (PSS-GS) and polyaniline (PANI) as building blocks. Poly(sodium 4-styrenesulfonate) (PSS) was used not only to stabilize the graphene sheets, but also facilitate the growth of the PSS-GS/PANI multilayer films via electrostatic interactions between PSS-GS and PANI. Furthermore, PSS can also act as a dopant for PANI during redox reactions. Ultraviolet-visible absorption spectrum (UV-vis), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM) results demonstrate the successful fabrication of the PSS-GS/PANI hybrid multilayer films. Electrochemical experiments show that PSS-GS inside the multilayer film can dope PANI effectively and the multilayer film still presents a redox activity at neutral pH. In addition, the obtained nanostructured PSS-GS/PANI multilayer film is very stable and shows high electrocatalytic ability toward H2O2, which makes it an ideal substrate for H2O2 detection and offers great promise for sensing.

Fabrication and thermal properties of self-assembled silver multilayer films on poly(ethylene terephthalate) substrate

This article uses the layer-by-layer self-assembly method to fabricate multilayer film on poly(ethylene terephthalate) substrate. The hydrolization of poly(ethylene terephthalate) film was primarily performed with sodium hydroxide aqueous solution to produce a carboxyl-enriched surface. The multilayer films were fabricated by the alternate adsorption of the oppositely charged poly(diallyldimethylammonium chloride) and silver nanoparticles on poly(ethylene terephthalate) substrate. The assembly process was monitored by UV–VIS spectroscopy and inductively coupled plasma. The surface topography and chemical composition of the self-assembly films was characterized by atomic force microscopy and X-ray photoelectron spectroscopy. The images indicated that the silver nanoparticles were successfully assembled and well distributed on the substrate. Furthermore, X-ray photoelectron spectroscopy confirmed the presence of metallic silver on the poly(ethylene terephthalate) substrate. The thermal properties of the multilayer films were investigated by thermogravimetric analysis and dynamic mechanical analyser. The results revealed that the storage modulus of ten-bilayer films decreases with temperature increasing and the glass transition temperature of ten-bilayer films have been found to be 99.3°C, whereas it is 94.8°C for the original poly(ethylene terephthalate) film.

Photoelectrochemical properties of electrostatically self-assembled multilayer films formed by three bipolar hemicyanines and H4SiW12O40

The electrostatically self-assembled multilayer films of three bipolar hemicyanines with varied alkyl chain lengths were prepared by alternating adsorption of H4SiW12O40 and these hemicyanines, and characterized by UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and cyclic voltammetry. The results showed that these inorganic–organic composite films were uniformly deposited with good electrochemical activity. Photoelectrochemical investigations showed that the films exhibited large cathodic photocurrent densities of 0.36–1.02μA/cm2 with the monochromatic incident photon-to-electron conversion efficiency of 0.75–0.98% while irradiated with 100mW/cm2 polychromatic light (730nm>λ>325nm) at an applied potential of −0.2V vs. saturated calomel electrode, being strongly dependent on the alkyl chain lengths.

Self-assembled Pd-dicyanobiphenyl multilayer films and their application in electrocatalytic oxidation of methanol in alkaline medium

Through the layer-by-layer technology, (Pd/dcbp)n (dcbp=4,4′-dicyanobiphenyl) multilayer films were prepared by alternately immersing quartz slide pre-coated with poly(ethylenimine) layer in PdCl2 and dcbp aqueous solutions. (Pd/dcbp)n multilayers were characterized by UV–vis spectra, atomic force image and X-ray photoelectron spectroscopy (XPS). UV–vis spectra showed that the fabrication of (Pd/dcbp)n multilayers depends on the coordination interaction between palladium ions and CN moieties. The results of XPS analysis show that mixed zero-valent and divalent Pd coexist in (Pd/dcbp)n multilayers. During the self-assembly process, Pd ions within the multilayers are in situ reduced by weak reducibility of the ligand bpcn. Transmission electron microscopy further demonstrated that Pd nanoparticles within multilayers were highly dispersed and uniform. The electrode modified with Pd/dcbp multilayer films showed electrocatalytic activity toward methanol oxidation in alkaline medium.

Layer-by-Layer Self-Assembled Multilayer Films Composed of Graphene/Polyaniline Bilayers: High-Energy Electrode Materials for Supercapacitors

Multilayer assemblies of uniform ultrathin film electrodes with good electrical conductivity and very large surface areas were prepared for use as electrochemical capacitors. A layer-by-layer self-assembly approach was employed in an effort to improve the processability of highly conducting polyaniline (PANi) and chemically modified graphene. The electrochemical properties of the multilayer film (MF-) electrodes, including the sheet resistance, volumetric capacitance, and charge/discharge ratio, were determined by the morphological modification and the method used to reduce the graphene oxide (GO) to reduced graphene oxide (RGO) in the multilayer films. The PANi and GO concentrations could be modulated to control the morphology of the GO monolayer film in the multilayer assemblies. Optical ellipsometry was used to determine the thickness of the GO film in a single layer (1.32 nm), which agreed well with the literature value (~1.3 nm). Hydroiodic acid (HI), hydrazine, or pyrolysis were tested for the reduction of GO to RGO. HI was found to be the most efficient technique for reducing the GO to RGO in the multilayer assemblies while minimizing damage to the virgin state of the acid-doped PANi. Ultimately, the MF-electrode, which could be optimized by fine-tuning the nanostructure and selecting a suitable reduction method, exhibited an excellent volumetric capacitance, good cycling stability, and a rapid charge/discharge rate, which are required for supercapacitors. A MF-electrode composed of 15 PANi/RGO bilayers yielded a volumetric capacitance of 584 F/cm(3) at a current density of 3.0 A/cm(3). Although this value decreased exponentially as the current density increased, approaching a value of 170 F/cm(3) at 100 A/cm(3), this volumetric capacitance is one of the best yet reported for the other carbon-based materials. The intriguing features of the MF-electrodes composed of PANi/RGO multilayer films offer a new microdimensional design for high energy storage devices for use in small portable electronic devices.

Biofunctionalization of titanium surface with multilayer films modified by heparin‐VEGF‐fibronectin complex to improve endothelial cell proliferation and blood compatibility

In-stent restenosis and subsequent thrombosis remain a significant complication following the implantation of coronary stents. Different approaches have been used in developing novel coronary stents to protect against thrombosis and minimize restenosis. In the present study, we designed a biomacromolecular layer-by-layer coating with heparin, vascular endothelial growth factor (VEGF), and fibronectin onto nickel-free titanium surface to improve blood compatibility and endothelial cell proliferation. The multilayer assembling process was monitored by water contact angle and surface plasmon resonance, respectively. With increasing the number of layers, the deposition of polyelectrolyte as self-assembled ultrathin multilayer films showed linear growth of absorbance. In vitro blood compatibility results revealed that the fabricated layers prolonged activated partial thrombin time and prothrombin time, reduced platelets activation and aggregation, and reduced blood hemolysis rate. Cell adhesion and growth results showed that the assembled multilayer films significantly promoted cell attachment and growth, and the endothelialization property of the multilayer films was preferable compared with the untreated titanium disk. In conclusion, these results suggest that titanium surface modification using biofunctional multilayer films composed of heparin, VEGF, and fibronectin may serve as a potential approach to inhibit thrombosis and promote re-endothelialization of cardiovascular stents.

In-situ synthesis of gold nanoparticles in nitrogen-doped titania nanosheets via layer-by-layer assembly method

Self-assembled multilayer films of nitrogen-doped exfoliated titania nanosheets and Au nanoparticles (NP) were fabricated via layer-by-layer assembly method followed by solar irradiation treatment. Au NP were found to form by in-situ reduction and thus disperse homogeneously between nitrogen-doped titania nanosheet galleries and the composite films of disordered structure, as confirmed by transmission electron microscope and X-ray diffractometer. Ultraviolet–visible absorption spectra in the multilayer buildup process indicated that plasmon resonance of the multilayer films was enhanced and red-shifted due to the changes of surrounding medium. It is found that nearly equal amounts of nanosheets were assembled and golds were reduced in each deposition cycle. X-ray photoelectron spectroscopy observation revealed that the interaction between the two components affects the distribution of electrons of Au, which causes the negative shift of the binding energy of Au NP. Compared with pure nitrogen-doped (N-doped) titania nanosheets, the higher hydroxyl density on the surface of such multilayer films was confirmed to be beneficial to efficiently separating the photogenerated electrons and holes, and as a result enhancing their photocatalytic activities.

Stimuli-responsive self-assembled multilayer azo thin films: Effect of aggregates and salt on significant spectral shifts

Layer-by-layer SAMU thin films of azo dye molecules and PEL exhibited two distinct absorbance maxima in visible and UV regions. This is attributed to the assumption that a fraction of the dye adsorbed as the monomeric form yields a visible peak, while the additional fraction of the oligomeric H-type aggregated form also appeared in the UV region. The UV peak, however, disappeared in films fabricated from salt solution to demonstrate suppression of aggregates and the stimuli-responsive effect.

Synthesis of a perylenediimide-viologen dyad (PDI-2V) and its electrochromism in a layer-by-layer self-assembled multilayer film with PEDOT:PSS

A new electrochromic molecule, perylenediimide-viologen dyad (PDI-2V), was synthesized and used in the fabrication of layer-by-layer (LBL) self-assembled multilayer films with poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS). Since PDI-2V is a tetracationic organic molecule with high molecular weight, it showed strong electrostatic adhesion to negatively charged PEDOT:PSS. When the electrochromic behaviour of the resulting LBL film was investigated with a single type electrochromic device, the PDI-2V showed a three-stage color change from red to blue to violet under the reduction potential range. A dual type electrochromic device was also fabricated with P3HT spin-coated ITO as a counter electrode. This device exhibited a sharp color change between deep red and dark blue when the applied potential was switched from +2.0 V to −2.0 V.

Self-assembled monolayer and multilayer films based onl-lysine functionalized perylene bisimide

Download options Please wait... Supplementary files Supplementary information PDF (492K) Article information DOI https://doi.org/10.1039/C1JM14521E Article type Paper Submitted 12 Sep 2011 Accepted 26 Oct 2011 First published 05 Dec 2011 Download Citation J. Mater. Chem., 2012,22, 4312-4318 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Self-assembled monolayer and multilayer films based on L-lysine functionalized perylene bisimide Y. Sun, Z. Li and Z. Wang, J. Mater. Chem., 2012, 22, 4312 DOI: 10.1039/C1JM14521E To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Yan Sun Zhibo Li Zhaohui Wang

Deposition Mechanism and Properties of Thin Polydopamine Films for High Added Value Applications in Surface Science at the Nanoscale

Polydopamine films have been introduced by Messersmith et al. as a possible “versatile” surface functionalization method allowing to coat the surface of almost all known materials even superhydrophobic surfaces. These new kinds of coatings also confer a plethora of functionalities to the coated materials owing to the complex chemistry of the catechol quinone moieties present on the surface of polydopamine. These coatings may hence become an interesting alternative to established surface coatings like self-assembled monolayers and polyelectrolyte multilayered films. In this review, we describe the knowledge acquired in the last 3 years about the deposition mechanisms of polydopamine films, their properties, and various applications in surface science at the nanoscale.

Influences of the thickness of self-assembled graphene multilayer films on the supercapacitive performance

In this study, graphene multilayer films with controlled thicknesses deposited on indium tin oxide glass substrates were fabricated using electrostatic layer-by-layer self-assembly of negatively charged graphene oxide followed by hydrazine hydrate reduction. X-ray diffraction spectroscopy, Raman spectroscopy, UV–vis spectroscopy, field emission scanning electron microscopy and atomic force microscopy were used to characterize the microstructures and morphologies of the as-fabricated multilayer films. The supercapacitive properties of the multilayer film electrodes were investigated via cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectrometry in a 0.5 M Na 2SO 4 electrolyte. The graphene multilayer films employed as the electrode materials not only exhibited nearly rectangular cyclic voltammetry curves at an exceedingly high scan rate of 2000 mV/s, but also exhibited highly linear and symmetrical charge/discharge curves, which indicated that they have ideal electric double-layer capacitive behavior. Furthermore, the supercapacitive performance of the as-prepared graphene multilayer films exhibited a strong dependence on the number of self-assembled layers. Moreover, the specific capacitance per surface area for each self-assembled graphene film exhibited almost no decay after 1500 cycles, implying excellent stability and reversibility. These electrochemical tests indicated that the as-prepared graphene films have great potential for supercapacitor applications.