Internal reflection ellipsometry for real-time monitoring of polyelectrolyte multilayer growth onto tantalum pentoxide

Internal reflection ellipsometry was used for detection of the consecutive coating of two polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), onto a tantalum pentoxide (Ta₂O₅) substrate until the 10th bilayer. The UV patterned PAH-PAA-multilayer was characterized in air via ellipsometry and atomic force microscopy. Suited optical models enabled the determination of the layer thicknesses in wet and dry states. Linear multilayer formation could be proved by Attenuated Total Reflection — Fourier Transformed Infrared Spectroscopy measurements following the increase of the ν(C=O) band depending on the adsorption of the PAA. Streaming potential measurements after each layer deposition step indicated a change in surface charge after each layer deposition due to the consecutive coating of PAH and PAA. In this article the internal reflection ellipsometry is shown to be a convenient possibility to analyze the modification of a thin transparent Ta₂O₅ substrate.     

Preparation of nanoporous polyimide thin films via layer-by-layer self-assembly of cowpea mosaic virus and poly(amic acid)

Low dielectric (low-κ) materials are of key importance for the performance of microchips. In this study, we show that nanosized cowpea mosaic virus (CPMV) particles can be assembled with poly(amic acid) (PAA) in aqueous solutions via the layer-by-layer technique. Then, upon thermal treatment CPMV particles are removed and PAA is converted into polyimide in one step, resulting in a porous low-κ polyimide film. The multilayer self-assembly process was monitored by quartz crystal microbalance and UV-Vis spectroscopy. Imidization and the removal of the CPMV template was confirmed by Fourier transform infrared spectroscopy and atomic force microscopy respectively. The dielectric constant of the nanoporous polyimide film thus prepared was 2.32 compared to 3.40 for the corresponding neat polyimide. This work affords a facile approach to fabrication of low-κ polyimide ultrathin films with tunable thickness and dielectric constant.     

Synthesis and characterization of polycationic chitosan-graft-poly (l-lysine)

A type of polysaccharide/polypeptide hydride material, chitosan derivatives with polypeptide side chains, was prepared via ring-opening polymerization of N_ε-carbobenzyloxy-l-lysine NCA initiated by water-soluble chitosan and followed by removing the side-chain protective groups. The graft polymer was investigated through FTIR spectroscopy, proton nuclear magnetic resonance spectroscopy and X-ray diffraction to confirm the structure. Furthermore, the results of the atomic force microscopy (AFM) measurement indicated the chitosan-graft-poly (l-lysine) was a kind of extraordinary polycation.     

Luminescent guest–host composite films based on an azomethine dye in different matrix polymers

New hybrid guest/host composite films obtained by dispersing a light-emitting azomethine dimer into three different matrix polymers have been studied. Poly(methyl methacrylate) (PMMA), UDEL polysulfone (PSU) and chitosan were chosen as host matrix. Differential scanning calorimetry, polarized light microscopy, scanning electron microscopy and atomic force microscopy measurements revealed the composite morphology and their thermal properties. UV–vis and fluorescence spectroscopy indicated the influence of polymer matrix on the azomethine dye optical properties. The composite films exhibited strong photoluminescence emission when excited with maximum absorption wavelength. It was concluded that polysulfone is a good candidate in guest/host composite obtaining.     

Experimental investigations of semi-crystalline plasma polymerized poly(3-octyl thiophene)

Plasma polymerized thin film of conducting poly(3-octylthiophene) was deposited at room temperature by plasma enhanced chemical vapor deposition method using (3-octylthiophene) monomer as precursor. The radio frequency (RF: 13.56 MHz, power supply: 30 W) was applied at constant argon gas pressure for the formation of plasma. Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), X-ray diffractometry (XRD) and high resolution transmission electron microscopy (HRTEM) have been done for the as grown films. As reported in literature polythiophenes prepared by rf plasma polymerization are highly crosslinked and amorphous. However, in present investigations, well defined crystalline regions have been observed by HRTEM investigations and have been correlated with X-ray diffraction data. The observed crystallinity is attributed to controlling the parameters of the synthesis.     

Synthesis and layer-by-layer self-assembly of silver nanoparticles capped by mercaptosulfonic acid

Spherical silver nanoparticles capped by mercaptosulfonic acid with a diameter of about 8 nm were prepared by a simple chemical reaction. The resulting silver nanoparticles were characterized by UV–vis spectroscopy (UV–vis) and transmission electron microscopy (TEM). Using layer-by-layer (LBL) self-assembly technique, the multilayer films containing silver nanoparticles and polycation poly(dialyldimethylammonium chloride) (PDDA) were successfully fabricated. The fabrication process was monitored by UV–vis spectra and the morphology of the multilayer films was investigated by atomic force microscopy (AFM). The cyclic voltammogram (CV) measurements further confirmed that the silver nanoparticles had assembled into the multilayer films successfully. Surface-enhanced Raman spectroscopy (SERS) measurements showed that the multilayer films containing silver nanoparticles could serve as SERS-active substrate.     

Fabrication and characterization of nanostructured conducting polymer films containing magnetic nanoparticles

In this study, the layer-by-layer technique is used to deposit nanostructured films exhibiting electrical conductivity and magnetic behavior, from poly(o-ethoxyaniline) (POEA), sulfonated polystyrene (PSS) and positively-charged maghemite nanoparticles. In order to incorporate the nanoparticles into the films, maghemite nanoparticles, in the form of magnetic fluid, were added to POEA solutions, and the resulting suspensions were used for film deposition. UV-Vis spectroscopy and atomic force microscopy images reveal that POEA remains doped in the films, even in the presence of the maghemite nanoparticles, and its typical globular morphology is also present. Electrical measurements show that a POEA/PSS film prepared from POEA solution containing 800 µL of the magnetic fluid exhibits a similar conductivity to that of the control film and, additionally, magnetic measurements indicated that nanosized maghemite phase was incorporated within the polymeric film.     

Layered and interfacially blended polyelectrolyte multi-walled carbon nanotube composites for enhanced ionic conductivity

To enhance the ionic conductivity in solid phase polyelectrolyte systems for lithium ion battery applications demands effective control of the phase properties. Here, we report on a strategy involving a layer-by-layer methodology of two polyelectrolytes, poly(ethylene oxide) (PEO) and poly(acrylic) acid (PAA) and carboxylic acid functionalized multi-walled carbon nanotubes (MWNTs). Optimization of the assembly strategy revealed that undoped and lithium-ion doped stacking of four layers provides excellent film growth and improvement of the ionic conductivity of up to 10^− 5 S cm^− 1, which exceeds conventional assemblies of lithium-ion doped [PEO/PAA] by up to two orders of magnitude. Although ionic conductivity was most effectively enhanced for ultrathin films (< 100 nm), [PEO/PAA/PEO/(PAA + MWNT)] stacking still provides an ionic conductivity of > 10^− 6 S cm^− 1 for thick films (> 2 μm). The improvement of ionic conductivity was attributed to (i) interfacial phase mixing (blending) of the two polyelectrolytes, (ii) the MWNT contribution in the interfacial region, and (iii) the preferential adsorption of lithium-ions along the carbon nanotubes. This study involved a series of scanning probe methods including lateral force microscopy, and electrostatic force microscopy.     

Probing the stability of biocompatible sodium hyaluronate/chitosan nanocoatings against changes in salinity and pH

The stability of polyelectrolyte multilayer assemblies was investigated with emphasis on the effects of solution ionic strength, pH, and polymer molecular weight on the film thickness and surface topography. The multilayers consisting of two polysaccharides, the polyanion sodium hyaluronate (HA) and the polycation chitosan (CH) were studied using surface plasmon resonance (SPR) spectroscopy, impedance quartz crystal microbalance (QCM), and atomic force microscopy (AFM). SPR/QCM experiments show that coatings consisting of four HA/CH bilayers assembled at pH 4.5 in the presence of 0.15 M NaCl are stable in NaCl solutions of concentration less than 0.8 M. These multilayers are stable when placed in contact with aqueous solutions ranging in pH from 3.5 to 9. The molecular weight of the polysaccharides has only a marginal effect on the stability of the films in the range explored here (HA: Mn = 360,000 or 31,000 g/mol; CH: Mn = 160,000 or 30,000 g/mol). AFM imaging reveals that different mechanisms may account for the multilayers stability versus salt and pH treatments. While increasing the ionic strength induces reorganization of the surface topography from isolated spherical islets to elongated worm-like features, changes in pH have no appreciable effects on the coating topography prior to complete disintegration.     

Fabrication and elimination of PTAA/P4VP layer-by-layer films

Layer-by-layer (LBL) ultra-thin films have been assembled by alternate adsorption of poly(3-thiophene acetic acid) (PTAA) and poly(4-vinyl-pyridine) (P4VP) on planar quartz slides via hydrogen-bonding interaction. Subsequently, the multilayers can be controllably removed by changing the pH values of the aqueous solutions used for film immersion. Our present study is an attempt to reveal the mechanisms of the multilayer film with two-dimensional (2D) ultraviolet-visible (UV-vis) correlation spectroscopy. UV-vis spectroscopy is primarily employed here to monitor the buildup and removal of the ultra-thin films. 2D correlation analysis is performed on the basis of the corresponding spectra for further studies. The morphology of the multilayer film is characterized by atomic force microscopy (AFM). When eliminated in alkaline and acidic aqueous solutions, the polymers in the films show diverse phenomena mainly due to the different extents of dissociation of PTAA and protonation of P4VP at different pH values. In alkaline solution, the elimination of PTAA takes place before P4VP, while in acid solution, the removal of these two polymers adopts a reverse order.     

Ultraporous poly(3,4-ethylenedioxythiophene) for nanometric electrochemical supercapacitor

Ultrathin films of poly(3,4-ethylenedioxythiophene) (PEDOT) have been prepared by electropolymerization on steel and indium-tin oxide (ITO) substrates under identical experimental conditions. Scanning electron microscopy and atomic force microscopy indicate that the substrate affects dramatically both the morphology and topography of films when the polymerization times are very short. An ultraporous three-dimensional network involving ultrathin sticks with a fiber-like morphology was formed on ITO. Asymmetric and symmetric supercapacitors have been fabricated by assembling electrodes of PEDOT deposited on ITO and steel. The specific capacitance, electrochemical stability, supercapacitor behavior and Coulombic efficiency measured for devices with an ITO/steel configuration were similar to those reported for advanced PEDOT-inorganic hybrid composites. Furthermore, the performance of the ITO/steel assembly is higher than those determined for symmetric supercapacitors derived from two identical electrodes of PEDOT deposited on steel or on ITO. The unique properties of the asymmetric supercapacitors have been attributed to the ultraporous structure of the ultrathin films deposited on ITO, which is not significantly perturbed when the device is submitted to a very high number of consecutive oxidation-reduction processes, and the different electroactivities of the two electrodes.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

RAFT聚合合成聚丙烯酸-b-聚(N-异丙基丙烯酰胺)嵌段共聚物的自组装行为

采用可逆加成-断裂链转移自由基聚合方法制备了聚丙烯酸叔丁酯-b-聚(N-异丙基丙烯酰胺)(PtBA-b-PNIAAm)嵌段共聚物,用核磁共振谱和凝胶渗透色谱对其结构和组成进行了表征。通过水解反应脱去嵌段PtBA的叔丁基得到聚丙烯酸-b-聚(N-异丙基丙烯酰胺)(PAA-b-PNIAAm)嵌段共聚物,使用核磁共振谱确定了其水解率约为85.5%。使用动态光散射和原子力显微镜技术对其在水溶液中的温度和pH敏感性自组装行为做了初步研究。结果表明,PAA-b-PNIAAm胶束的临界聚集pH值约为5.3,最低临界溶解温度(LCST)约为34.0℃。     

Poly(3-hexylthiophene) based field-effect transistors with gate SiO2 dielectric modified by multi-layers of 3-aminopropyltrimethoxysilane

Top-contact organic field-effect transistors based on poly(3-hexylthiophene) (P3HT) active layer were fabricated using gate dielectric (SiO₂) modified with 3-aminopropyltrimethoxysilane (APTMS) multilayers. It has been demonstrated that the treatment of dielectric with APTMS enhances the field-effect mobility as well as the on/off ratio of the devices by nearly two orders of magnitude. This is attributed to conformational changes as well as to an improved uniformity of the spin coat P3HT films on the APTMS-modified substrate as revealed by atomic force microscopy, Fourier transform infrared spectroscopy and UV-Vis measurements.     

Mo/Si multilayers for EUV lithography by ion beam sputter deposition

Mo/Si multilayers for applications in extreme ultraviolet (EUV) lithography have been prepared on Si wafer substrates using ion beam deposition. The multilayers were characterised by transmission electron microscopy, secondary ion mass spectroscopy, atomic force microscopy, photoelectron spectroscopy, X-ray reflectometry at grazing incidence, and EUV-reflectivity measurements at nearly normal incidence. The surface and the interfaces of the multilayers are rather smooth with only small roughness. The material properties of the layers are characterised by some intermixing and silicide formation at the Mo-Si interfaces and a polycrystalline grain structure of the Mo layers, which is in agreement with prior studies. Appearance of multilayer diffraction spots, well-resolved Kiessig fringes and other diffraction evidence indicate very good coherence of the wave fields and in this manner a good reproducibility of the multilayer period of 6.7 nm. Normal incidence peak reflectivities of 64-65% in the EUV spectral range were routinely obtained at 13.4 nm wavelength. This reflectivity value and the formation of an EUV standing wave field are confirmed using photoelectron spectroscopy, and an application for defect particle analysis is proposed. The obtained results are discussed in comparison to literature data of multilayers prepared by other deposition techniques and considering new attempts of interface engineering.     

Ellipsometry study of poly(o-methoxyaniline) thin films

Spin-coated poly(o-methoxyaniline) (POMA) thin films on various substrates were investigated using spectroscopic ellipsometry (SE) in the 1.5–4.5 eV photon energy range. Spin-coating process parameters are reported (spin speed and concentration). Substrates with higher surface energy were found to increase polymer film thickness and decrease roughness. An optical model was developed using SE data along with complementary data from atomic force microscopy and UV–vis spectroscopy to obtain optical properties—refractive index n and extinction coefficient k for POMA. The model includes Lorentz oscillators for the POMA film and a Bruggeman effective medium approximation for roughness. In-plane film optical anisotropy was not observed, but a small out of plane anisotropy was detected for the polymer.     

Nonaqueous preparation of nanocomposite films containing both polyoxometalate and phthalocyanine with bifunctional electrocatalytic properties

New bifunctional nanocomposite films containing water-insolvable cobalt tetraaminophthalocyanine (CoTAPc) and 2:18 tungstophosphate anions (P₂W₁₈) were successfully fabricated using the electrostatic layer-by-layer (LbL) assembled method in nonaqueous (DMF) media. UV–vis spectroscopy, IR spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and electrochemical method were used to characterize the assembled multilayer films. UV–vis measurements revealed regular film growth with each four-layer {P₂W₁₈/CoTAPc/PSS/PAH} adsorption. AFM analysis provides the morphology of the multilayer films. The cyclic voltammetric curves indicate that the film shows electrocatalytic activity for chlorate anion.     

Surface modification of poly(dimethylsiloxane) for controlling biological cells’ adhesion using a scanning radical microjet

A scanning radical microjet (SRMJ) equipment using oxygen microplasma has been developed and successfully applied for controlling biological cells’ attachment on biocompatible polymer material, poly(dimethylsiloxane) (PDMS). The radical microjet has advantages in localized and high-rate surface treatment. Moreover, maskless hydrophilic patterning using SRMJ has been demonstrated to be applicable to patterned cell cultivation which is useful in emerging biotechnological field such as tissue engineering and cell-based biosensors. Since control of PDMS surface properties is an indispensable prerequisite for cells’ attachment, effects of oxygen flow rates and treatment time on localized hydrophilic patterning of PDMS surfaces were first investigated for controlling HeLa cells’ (human epitheloid carcinoma cell line) attachment. Relationships between surface conditions of treated PDMS films and attached cell density are also discussed based on surface properties analyzed using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).     

PEG交联有机硅/陶瓷杂化膜的制备及反渗透脱盐性能

采用聚乙二醇(PEG)和1,2-双(三乙氧基硅基)乙烷(BTESE)进行交联共聚, 以多孔α-Al₂O₃陶瓷膜为支撑体制备了一系列PEG交联的有机硅杂化膜。通过原子力显微镜(AFM)、场发射扫描电镜(FE-SEM)、傅里叶红外光谱(FT-IR)、热重分析(TGA)和水接触角测试(CA)对膜结构和物化性质进行了表征。将制备的BTESE/PEG杂化膜应用于反渗透脱盐, 考察了PEG含量、操作压力、进料浓度和操作温度等因素对改性杂化膜分离性能的影响。实验结果表明, 相比于未改性的BTESE膜, 10wt% PEG交联的有机硅杂化膜BTESE/PEG-10的水渗透率和盐离子表观截留率均有所提高。随着操作压力的升高和进料盐含量的下降, NaCl截留率上升而水渗透率基本恒定。在高达70℃的温度循环实验中, BTESE/PEG-10杂化膜表现出优异的水热稳定性, NaCl表观截留率始终保持在97%以上, 水渗透率高达1.2×10^-12 m³/(m²·s·Pa)。     

Patterning of hydrogen-bonded assembly film through ionization in vapor

The hydrogen-bonded films of poly(vinylpyrrolidone) (PVPON) and poly(acrylic acid) (PAA) were fabricated using layer-by-layer assembly technique. The films were incubated at three different vapor environments (acidic, neutral and basic). PAA would ionize in neutral or basic vapor environment, and then hydrogen bonds linking PVPON and PAA in the film would break and patterned topography would form gradually. Ionization degree of PAA in the film was characterized by Fourier transform infrared spectroscopy. Optical microscope and atomic force microscope were used to observe the film morphologies before and after incubation. Reflective spectroscopy and contact angle measurements were applied to further characterize the patterned surfaces.