Combining hydrogen-bonding complexation in solution and hydrogen-bonding-directed layer-by-layer assembly for the controlled loading of a small organic molecule into multilayer films

We have combined hydrogen-bonding complexation in solution and layer-by-layer assembly for the controlled loading of a water-insoluble small organic molecule, bis-triazine (DTA), an azobenzene derivative containing multiple hydrogen bond donors and acceptors, into layer-by-layer multilayer films of poly(acrylic acid) and diazo-resin. UV-visible spectroscopy indicates that DTA has been loaded into multilayer films, with the loading amount increasing linearly with the number of layers. The loading amount can be well tuned either by changing the concentration of DTA or the solvent composition at the complexation step. Fourier transform infrared spectroscopy has revealed that both the complexation and layer-by-layer assembly are driven by hydrogen bonding. After photo-cross-linking and immersion in dimethyl sulfoxide to release DTA, the film can serve as an absorbent for DTA. This study provides a new unconventional layer-by-layer assembly that combines hydrogen-bonding complexation in solution and hydrogen-bond-driven layer-by-layer assembly at the interface. This method provides a new route to load a variety of water-insoluble functional organic molecules into layer-by-layer films.     

Study of spin coated multilayer zirconia and silica films for non-quarterwavelength optical design based antireflection effect at 1,054 nm

A non-quarterwavelength optical design (design wavelength, λ_o = 1,054 nm) based antireflection (AR) coating was prepared by sol–gel spin coating technique. Two materials, zirconia and silica were chosen for the deposition of AR layers on borosilicate crown glass, refractive index (R. I. = 1.51). For this design, the bottom and middle layers were of zirconia with the R. I. range 1.941–1.958 while the top layer was of silica with R. I. 1.455. To understand the surface feature after each deposition, refractive index and physical thickness of the layers were measured ellipsometrically (λ = 632.8 nm) at different points over the area, 10 mm × 10 mm with an interval of 0.5 mm along the centre based perpendicular projection made on an imaginary chord. The surface feature was examined by plotting the measured values of the optical parameters against the displacement. The surface roughness decreased with increasing layers. This was verified by the study of AFM images of the layers. Specular reflection of the antireflection coated product at λ₀ was comparable to that of the theoretically simulated curve.     

Layer-by-layer fabrication of broad-band superhydrophobic antireflection coatings in near-infrared region

Broad-band superhydrophobic antireflective (AR) coatings in near infrared (NIR) region were readily fabricated on silicon or quartz substrates by a layer-by-layer (LbL) assembly technique. First, a porous poly(diallyldimethylammonium chloride) (PDDA)/SiO2 nanoparticle multilayer coating with AR property was prepared by LbL deposition of PDDA and 200 nm SiO2 nanoparticles. PDDA was then alternately assembled with sodium silicate on the PDDA/SiO2 nanoparticle coating to prepare a two-level hierarchical surface. Superhydrophobic AR coating with a water contact angle of 154 degrees was finally obtained after chemical vapor deposition of a layer of fluoroalkylsilane on the hierarchical surface. Quartz substrate with the as-fabricated superhydrophobic AR coating has a maximal transmittance above 98% of incidence light in the NIR region, which is increased by five percent compared with bare quartz substrate. Simultaneously, the superhydrophobic property endows the AR coating with water-repellent ability. Such superhydrophobic AR coatings can effectively avoid the disturbance of water vapor on their AR property and are expected to be applicable under humid environments.     

Cyto-mechanoresponsive polyelectrolyte multilayer films

Cell adhesion processes take place through mechanotransduction mechanisms where stretching of proteins results in biological responses. In this work, we present the first cyto-mechanoresponsive surface that mimics such behavior by becoming cell-adhesive through exhibition of arginine-glycine-aspartic acid (RGD) adhesion peptides under stretching. This mechanoresponsive surface is based on polyelectrolyte multilayer films built on a silicone sheet and where RGD-grafted polyelectrolytes are embedded under antifouling phosphorylcholine-grafted polyelectrolytes. The stretching of this film induces an increase in fibroblast cell viability and adhesion.     

Capillary electrochromatography using polyelectrolyte multilayer coatings

This review covers recent progress in polyelectrolyte multilayer (PEM) coatings applied to analytical separations using open-tubular capillary electrochromatography (OT-CEC). The simple preparation procedure involved in the PEM approach has provided some attractive features over other modes of capillary electrophoresis-based separations including packed column capillary electrochromatography (PC-CEC) and micellar electrokinetic chromatography (MEKC). PEM coatings have been used to alleviate the adsorption of basic analytes, to improve separations, and to improve the stability of the electroosmotic flow. Fundamental aspects of PEM coatings on surfaces and analytical separation platforms are briefly outlined in this review. In addition, applications of PEM coatings to fused-silica capillaries or microchip separation devices for the separation of small achiral or chiral analytes, as well as large biomolecules, are discussed.     

Photopatterning of multilayer n-alkylsilane films

Surface photopatterning of organosilane self-assembled monolayers (SAM) has received increasing attention since its introduction 20 years ago. Herein we report for the first time a cost-efficient soft photopatterning technique affording amplified 3D multilayer structures. The essential chemistry relies on a spatially controlled photoacid-catalyzed hydrolysis and polycondensation of n-alkyltrimethoxysilane precursors (n-C(12)H(25)Si(OCH(3))(3),). Amphiphilic siloxane species are photogenerated locally and are able to self-assemble spontaneously into a long-range-ordered lamellar mesostructure.     

Electrochromic properties of a metallo-supramolecular polymer derived from tetra(2-pyridyl-1,4-pyrazine) ligands integrated in thin multilayer films

The electrochromic behavior of iron complexes derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) and a hexacyanoferrate species in polyelectrolytic multilayer adsorbed films is described for the first time. This complex macromolecule was deposited onto indium-tin oxide (ITO) substrates via self-assembly, and the morphology of the modified electrodes was studied using atomic force microscopy (AFM), which indicated that the hybrid film containing the polyelectrolyte multilayer and the iron complex was highly homogeneous and was approximately 50 nm thick. The modified electrodes exhibited excellent electrochromic behavior with both intense and persistent coloration as well as a chromatic contrast of approximately 70%. In addition, this system achieved high electrochromic efficiency (over 70 cm(2) C(-1) at 630 nm) and a response time that could be measured in milliseconds. The electrode was cycled more than 10(3) times, indicating excellent stability.     

Self-organized TiO2 nanorod arrays on glass substrate for self-cleaning antireflection coatings

Herein we report the direct fabrication of TiO(2) subwavelength structures with 1-dimensional TiO(2) nanorods on glass substrate through solvothermal process to form self-cleaning antireflection coatings. TiO(2) precursor solutions with different solvent constituents create TiO(2) nanorods with much different morphologies grown on glass substrates. Apiculate TiO(2) nanorods with vertical orientation are grown on the glass substrate which is solvothermally treated in the precursor solution containing ethylene glycol. This glass substrate exhibit the highest transmittance of 70-85% in the range of 520-800 nm and negligible absorption in visible light region (400-800 nm). Furthermore, the TiO(2) nanorod arrays show high hydrophobicity and photocatalytic degradation ability which offer the glass substrate self-cleaning properties for both hydrophilic and oily contaminants.     

Characterisation of tribocorrosion behaviour of multilayer PVD coatings

The effect of repassivation on tribocorrosion behaviour of two multilayer coatings of different structures is studied experimentally by measuring the variation of instantaneous open-circuit potential during friction. One coating consists of alternating Cr and CrN layers, while another consists of alternated layers of CrN and ZrN. Analysis of the results showed that friction force, i.e. the rate of the mechanical energy supplied to the material in the contact zone, has no direct influence on the tribocorrosion behaviour; however, the wear rate does strongly influence the tribocorrosion. A simple phenomenological model of repassivation of the multilayer coating is developed assuming “surface coverage” approach. This model establishes the relationship between the rate of mechanical activation of material by friction and the behaviour of the open-circuit potential.     

Fibronectin adsorption onto polyelectrolyte multilayer films

The Layer-by-layer deposition of positively and negatively charged macromolecular species is an ideal method for constructing thin films incorporating biological molecules. We investigate the adsorption of fibronectin onto polyelectrolyte multilayer (PEM) films using optical waveguide lightmode spectroscopy (OWLS) and atomic force microscopy (AFM). PEM films are formed by adsorption onto Si(Ti)O2 from alternately introduced flowing solutions of anionic poly(sodium 4-styrenesulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH). Using OWLS, we find the initial rate and overall extent offibronectin adsorption to be greatest on PEM films terminated with a PAH layer. The polarizability density of the adsorbed protein layer, as measured by its refractive index, is virtually identical on both PAH- and PSS-terminated films; the higher adsorbed density on the PAH-terminated film is due to an adsorbed layer of roughly twice the thickness. The binding of monoclonal antibodies specific to the protein's cell binding site is considerably enhanced to fibronectin adsorbed to the PSS layer, indicating a more accessible adsorbed layer. With increased salt concentration, we find thicker PEM films but considerably thinner adsorbed fibronectin layers, owing to increased electrostatic screening. Using AFM, we find adsorbed fibronectin layers to contain clusters; these are more numerous and symmetric on the PSS-terminated film. By considering the electrostatic binding of a segmental model fibronectin molecule, we propose a picture of fibronectin adsorbed primarily in an end-on-oriented monolayer on a PAH-terminated film and as clusters plus side-on-oriented isolated molecules onto a PSS-terminated film.     

Photopatterned nanoporosity in polyelectrolyte multilayer films

We report on spatial control of nanoporosity in polyelectrolyte multilayer (PEM) films using photopatterning and its effects on film optical and adsorption properties. Multilayers assembled from poly(acrylic acid-ran-vinylbenzyl acrylate) (PAArVBA), a photo-cross-linking polymer, and poly(allylamine hydrochloric acid) (PAH) were patterned using ultraviolet light followed by immersion in low pH and then neutral pH solutions to induce nanoporosity in unexposed regions. Model charged small molecules rhodamine B, fluorescein, and propidium iodide and the model protein albumin exhibit increased adsorption to nanoporous regions of patterned PEM films as shown by fluorescence microscopy and radiolabeling experiments. Films assembled with alternating stacks of PAH/poly(sodium-4-styrene sulfonate) (SPS), which do not become nanoporous, and stacks of PAH/PAArVBA were patterned to create nanoporous capillary channels. Interdigitated channels demonstrated simultaneous, separate wicking of dimethyl sulfoxide-solvated fluorescein and rhodamine B. In addition, these heterostack structures exhibited patternable Bragg reflectivity of greater than 25% due to refractive index differences between the nanoporous and nonporous stacks. Finally, the PEM assembly process coupled with photo-cross-linking was used to create films with two separate stacked reflective patterns with a doubling in reflectivity where patterns overlapped. The combined adsorptive and reflective properties of these films hold promise for applications in diagnostic arrays and therapeutics delivery.     

Biomimetic click assembled multilayer coatings exhibiting responsive properties

Stimuli-responsive polymers are capable of changing their physico-chemical properties in a dynamic way, to respond to variations on the surrounding environment. These materials have gained increasingly importance for different areas, such as drug delivery, biosensors, microelectronic systems and also for the design and modification of biomaterials to apply on tissue engineering field. In the last years, different strategies have been envisaged for the development of stimuli-responsive biomaterials. Layer-by-layer (LbL) is a promising and versatile technique to modify biomaterials' surfaces, and has allowed tailoring interactions with cells. In this study, LbL is used to construct biomimetic stimuli-responsive coatings using elastin-like recombinamers (ELRs). The recombinant nature of ELRs provides the ability to introduce specific bioactive sequences and to tune their physicochemical properties, making them attractive for biomedical and biological applications. By using complementary clickable ELRs, we were able to construct multilayer coatings stabilized by covalent bonds, resulting from the Huisgen 1,3-dipolar cycloaddition of azides and alkynes. Herein, we exploited the switchable properties of the ELRs-based coatings which are dependent on lower critical solution temperature (LCST) transition. Above LCST, the polymers collapsed and nanostructured precipitates were observed on the surface's morphology, increasing the water contact angle. Also, the influence of pH on prompting reversible responses on coatings was evaluated. Finally, in vitro cell studies using a C2C12 myoblastic cell line were performed to perceive the importance of having bioactive domains within these coatings. The effect of RGD incorporation is clearly noted not only in terms of adhesion and proliferation but also in terms of myoblast differentiation.     

Interface and defects engineering for multilayer laser coatings

High-reflective multilayer laser coatings are widely used in advanced optical systems from high power laser facilities to high precision metrology systems. However, the real interface quality and defects will significantly affect absorption/scattering losses and laser induced damage thresholds of multilayer coatings. With the recent advances in the control of coating design and deposition processes, these coating properties can be significantly improved when properly engineered the interface and defects. This paper reviews the recent progress in the physics of laser damage, optical losses and environmental stability involved in multilayer reflective coatings for high power nanosecond near-infrared lasers. We first provide an overview of the layer growth mechanisms, ways to control the microstructures and reduce layer roughness, as well as the nature of defects which are critical to the optical loss and laser induced damage. Then an overview of interface engineering based on the design of coating structure and the regulation of deposition materials reveals their ability to improve the laser induced damage threshold, reduce the backscattering, and realize the desirable properties of environmental stability and exceptional multifunctionality. Moreover, we describe the recent progress in the laser damage and scattering mechanism of nodule defects and give the approaches to suppress the defect-induced damage and scattering of the multilayer laser coatings. Finally, the present challenges and limitations of high-performance multilayer laser coatings are highlighted, along with the comments on likely trends in future.     

Sum frequency generation from Langmuir-Blodgett multilayer films on metal and dielectric substrates

Sum frequency generation (SFG) vibrational spectra of cadmium arachidate multilayer films adsorbed on a substrate with high nonresonant susceptibility, i.e., gold, and on a low nonresonant susceptibility substrate, i.e., fused quartz, have been investigated in the C-H stretching region in air. The films were formed by Langmuir-Blodgett (LB) deposition and their spectra recorded using SFG spectrometers employing both 532-nm nanosecond and 800-nm femtosecond lasers, with counter-propagating and co-propagating beam geometries, respectively. Both kinds of substrate were rendered hydrophobic by coating them with per-deuterated octadecanethiol (gold) or per-deuterated cadmium arachidate (fused quartz) monolayers. Single per-protonated arachidate layers in otherwise per-deuterated 10-layer films were used to show that the SFG resonances arise only from the topmost and lowermost layers in a LB film comprised of an even number of per-protonated layers, although the SFG spectra from the two hydrophobic substrates are different from each other. The differences in the spectra from the same ten-layer per-protonated films deposited on the two types of hydrophobic substrate have been explained in terms of a simple model that accounts for resonant and nonresonant contributions.     

Alternating bioactivity of multilayer thin films assembled from charged derivatives of chitosan

Charged derivatives of chitosan, N-sulfofurfuryl chitosan (SFC) and N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC) were prepared by reductive alkylation of amino groups of chitosan (CHI) using 5-formyl-2-furansulfonic acid, sodium salt (FFSA) as a reagent and ring opening of glycidyltrimethylammonium chloride (GTMAC) by amino groups of chitosan, respectively. The chemical structures of the charged derivatives were verified by (1)H NMR and FTIR analyses. Multilayer assembly of SFC, HTACC, CHI and the selected oppositely charged polyelectrolytes was monitored by a quartz crystal microbalance (QCM). Stratification of the multilayer film fabricated on plasma-treated poly(ethylene terephthalate) (treated PET) substrate was demonstrated by water contact angle data. The coverage of the assembled films was characterized by AFM and ATR-FTIR analyses. The bioactivity of the deposited multilayer film on the treated PET substrate was tested against selected proteins having a distinctive size and charge. This research strongly suggests that both SFC and HTACC are potential candidates for altering the surface bioactivity of materials.