In Situ Characterisation of Polymer Surfaces and Thin Organic Films in Plasma Processing

In situ sampling techniques are presented for investigation of plasma surface modification of polymers and plasma polymerisation. FTIR spectroscopy (infrared absorption reflection spectroscopy - IRRAS, and attenuated total reflection - ATR) are properly used for characterisation of the changes in the molecular structure of thin polymer films (polystyrene, polyethylene) due to low pressure plasma treatment. The thin films were prepared by dip or spin coating procedures. In the case of plasma polymerisation a novel fibre-ATR technique is applied to investigate the plasma polymerisation process in the plasma bulk. Results are exemplary shown for plasma polymerisation of styrene. Ellipsometric measurements allowed the characterisation of the thin plasma modified top polymer surface layer or thin deposited plasma polymer films by their refractive index and thickness. It was shown that the applied surface plasmon ellipsometry is very sensitive with respect to the usual ellipsometry for investigation of polymer surface modification. The in situ microgravimetry by means of electronic vacuum microbalance permitted to measure the change of the sample mass in the order of 1 μg during the plasma treatment. The first steps in plasma modification (concurrence between the incorporation of plasma particles and the material etching) were studied.     

EUV micropatterning for biocompatibility control of PET

We have investigated the influence of oriented microstructures at modified polyethylene terephthalate (PET) on the adhesion and alignment of Chinese hamster ovary (CHO) cells. For surface modification, the PET foils were exposed to the radiation of a laser-plasma extreme ultraviolet (EUV) source based on a double-stream gas-puff target. The emission of the plasma was focused onto the samples by means of a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated with the EUV pulses at a repetition rate of 10 Hz in a high vacuum. For control experiments, PET samples were also irradiated in air with the light of a 193 nm ArF-excimer laser. Different kinds of surface microstructures were obtained depending on the EUV or laser fluence and pulse number, including oriented wall- and ripple-type structures with lateral structure periods of a few μm. The surface morphology of polymer samples after the irradiation was investigated using a scanning electron microscope (SEM). Changes in chemical surface structure of the irradiated samples were investigated using X-ray photoelectron spectroscopy (XPS). We demonstrated that the cells show good adhesion and align along oriented wall- and ripple-type microstructures on PET surfaces produced by the EUV irradiation.     

Transformation of a hydrophilic membrane into semi-super-hydrophobic based on self-assembly of stearic acid monolayer over induced nanostructures on the membrane surface

Both the chemical and structural properties of a surface determine the contact angle. For the formation of super-hydrophobic surfaces, modification of surface chemistry must be always combined with surface roughness enhancement. The used methods to make a super-hydrophobic surface are expensive and need very complicated equipments and cannot be scale up easily. In this study a simple and less expensive method was developed to transform a hydrophilic membrane into a semi-super-hydrophobic. In order to modify the membrane surface geometrically, the required needle-like rugosities were created by boiling the membrane in the water. The chemical modification of the roughened surface was created by the chemical adsorption and controlling the reaction time of stearic acid (STA) on the polymer of the membrane surface. Finally, by controlling the surface roughness, the concentration of the STA solution and duration of reaction time, a semi-super-hydrophobic membrane with the contact angle of 120° was prepared.     

Protein adsorption resistant surface on polymer composite based on 2D- and 3D-controlled grafting of phospholipid moieties

To prepare the biocompatible surface, a phosphorylcholine (PC) group was introduced on this hydroxyl group generated by surface hydrolysis on the polymer composite composed of polyethylene (PE) and poly (vinyl acetate) (PVAc) prepared by supercritical carbon dioxide. Two different procedures such as two-dimensional (2D) modification and three-dimensional (3D) modification were applied to obtain the steady biocompatible surface. 2D modification was that PC groups were directly anchored on the surface of the polymer composite. 3D modification was that phospholipid polymer was grafted from the surface of the polymer composite by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC). The surfaces were characterized by X-ray photoelectron spectroscopy, dynamic water contact angle measurements, and atomic force microscope. The effects of the poly(MPC) chain length on the protein adsorption resistivity were investigated. The protein adsorption on the polymer composite surface with PC groups modified by 2D or 3D modification was significantly reduced as compared with that on the unmodified PE. Further, the amount of protein adsorbed on the 3D modified surface that is poly(MPC)-grafted surface decreased with an increase in the chain length of the poly(MPC). The surface with an arbitrary structure and the characteristic can be constructed by using 2D and 3D modification. We conclude that the polymer composites of PE/PVAc with PC groups on the surface are useful for fabricating biomedical devices due to their good mechanical and surface properties.     

等离子体结合六甲基二硅胺烷处理提升增透膜抗真空污染性能研究

本文采用溶胶-凝胶法制备了SiO₂增透膜,然后对其进行等离子体结合六甲基二硅胺烷（HMDS）表面改性处理。研究了后处理改性对增透膜表面形貌、微观结构、光学性能及激光损伤性能的影响规律,获得了抗真空有机污染的二氧化硅增透膜。结果表明,增透膜在采用等离子体结合HMDS表面改性处理后,膜层收缩、粗糙度下降、极性羟基等有机基团含量减少;两步后处理改善了增透膜膜层结构和光学性能,显著提高了膜层疏水能力和真空条件下的抗污染性能,并且对溶胶-凝胶二氧化硅增透膜的高损伤阈值属性不产生影响。     

Laser- and UV-assisted modification of polystyrene surfaces for control of protein adsorption and cell adhesion

An appropriate choice of laser and process parameters enables new approaches for the fabrication of polymeric lab-on-chip devices with integrated functionalities. We will present our current research results in laser-assisted modification of polystyrene (PS) with respect to the fabrication of polymer devices for cell culture applications. For this purpose laser micro-patterning of PS and subsequent surface functionalization was investigated as function of laser and process parameters. A high power ArF-excimer laser radiation source with a pulse length of 19 ns as well as a high repetition ArF-excimer laser source with a pulse length of 5 ns were used in order to study the influence of laser pulse length on laser-induced surface oxidation. The change in surface chemistry was characterized by X-ray photoelectron spectroscopy and contact angle measurements. The difference between laser-assisted modification versus UV-lamp assisted modification was investigated. A photolytic activation of specific areas of the polymer surface and subsequent oxidization in oxygen or ambient air leads to a chemically modified polymer surface bearing carboxylic acid groups well-suited for controlled competitive protein adsorption or protein immobilization. Finally, distinct areas for cell growth and adhesion are obtained.     

Fabrication of 3D metal/polymer microstructures by site-selective metal coating

Three-dimensional silver/polymer conjugated microstructures were fabricated by site-selective metal deposition on photopolymer structures in the sub-micrometer scale. Photopolymerizable resins with and without an amide group were independently prepared, and a three-dimensional polymer structure was fabricated with those resins by means of the two-photon-induced photopolymerization technique to confine the photopolymerization to a sub-micrometer volume. Silver was selectively deposited on the surface of the amide-containing polymer parts by electroless plating. This method can provide 3D arbitrary silver/polymer composite microstructures with sub-micrometer resolution. PACS 81.07-b; 81.16-c; 81.07.Pr     

Enhancing the performance of poly(3-hexylthiophene)/ZnO nanorod arrays based hybrid solar cells through incorporation of a third component

Sparse ZnO nanorod arrays(NRAs)are fabricated on transparent conducting oxide coated glass substrates by using a modified liquid phase epitaxial growth method.By adjusting the polymer concentrations and the spin-coating parameters,full infiltration of poly(3-hexylthiophene)(P3HT)into the as-prepared ZnO NRAs is achieved at 130°C in vacuum.A third component is incorporated into the P3HT/ZnO NRAs ordered bulk heterojunctions(BHJs)either through ZnO surface modification with N719dye or CdS shell layer or by inclusion of a fullerene derivative into the P3HT matrix.Experimental results indicate that performances of the hybrid solar cells are improved greatly with the incorporation of a third component.However,the working principles of these third components differ from one another,according to morphology,structure,optical property,charge transfer and interfacial properties of the composite structures.An ideal device architecture for hybrid solar cells based on P3HT/ZnO NRAs ordered BHJs is proposed,which can be used as a guidance to further increase the power conversion efficiency of such solar cells.     

Ultrahigh-density storage media prepared by artificially assisted self-assembling methods

Two types of recording media possessing nanodot structures were investigated. The media were prepared by an artificially assisted self-assembling (AASA) method, which includes simple nanopatterning using a nanoimprint and fine nanopatterning using self-assembling organic molecules. One type of recording media is circumferential magnetic patterned media prepared on a 2.5-in.-diam glass plate. A Ni master disk possessing spiral patterns with 60-250 nm width lands and a 400 nm width groove was pressed to a resist film on a CoCrPt film to transfer the spiral patterns. A diblock copolymer solution was cast into the obtained grooves, and then annealed to prepare self-assembling dot structures aligned along the grooves. According to the dot patterns, the lower magnetic films were patterned by ion milling to yield patterned media with 40 nm diameter. We have also prepared FePt dot media with high magnetic anisotropy for near-field and magnetic-field hybrid recording aiming at more than 1 Tbin.2 density. A Ni stamp disk with aligned dot structures was also prepared by the AASA method to produce patterned media at the lowest cost. The other type of media was organic patterned media for X-Y type near-field optical storage. Bulky dye molecules were evaporated in vacuum to produce self-assembling amorphous nanodots. The dots were arranged by the AASA method, i.e., according to the polymethylmethacrylate film hole arrays or chemically patterned surface.     

UV light induced surface modification of HDPE films with bioactive compounds

The development of different techniques for surface modification of polymers becomes popular in a last decade. These techniques preserve useful bulk polymer properties unchanged, while the activation of the polymer surface offers more possibilities for polymer applications.In this work, a new, one-step method for bio-activation of HDPE (high density polyethylene) surface by UV irradiation is presented. HDPE films coupled with selected active compound and a photoinitiator was treated by UV lamp, emitting light at 254 nm.For surface functionalization of HDPE films, the following compounds were employed: 2-aminopyridine (AP), N¹-(2-pyridylaminomethyl)-1,2,4-triazole (TA) and benzocaine (BC). The influence of irradiation time on the extent of surface changes was investigated. The modified polymer surfaces were investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy, scanning electron microscopy (SEM) and contact angle measurements, demonstrating successful functionalization of HDPE surface.     

Phase separated composite films of liquid crystals

Phase separation of liquid crystals from a solution with polymers has long been studied and used to prepare polymer stabilized and polymer dispersed structures. They are formed by spatially isotropic phase separation. A new mode, in which the phase separation proceeds anisotropically, has recently been discovered. Known as phase separated composite films (PSCOF), the resultant structures are made of adjacent parallel layers of liquid crystal and solidified polymer. PSCOFs have been made with nematic, ferroelectric (FLC), and antiferroelectric (AFLC) liquid crystals. Liquid crystals in PSCOFs exhibit electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer stabilization methods. Devices incorporating FLCs possess grey scale and switch 100 times faster at low fields than conventional surface stabilized devices. This method makes it possible to prepare very flexible devices and devices with liquid crystal film thickness comparable to optical wavelengths with great ease.     

The influence of UV-irradiation and support type on surface properties of poly(methyl methacrylate) thin films

Thin poly(methyl methacrylate) (PMMA) films were prepared by a solution casting on different supports (glass and aluminium plates with different gloss). UV-irradiation (λ = 254 nm) was used for polymer modification. Surface properties of PMMA were studied by contact angle measurements, attenuated total reflection infrared spectroscopy and optical microscopy. It was found that support type has no influence on surface properties of virgin PMMA, however, the changes in these properties were observed during UV modification of polymer film. The most efficient photochemical reactions appeared in sample placed on the rough Al, whereas the smallest effect was observed in polymer on the glass.     

ZnO micro-nano composite hydrophobic film prepared bythree-step method

<正>The hydrophobicity of the lotus leaf is mainly due to its surface micro—nano composite structure.In order to mimic the lotus structure,ZnO micro-nano composite hydrophobic films were prepared via the three-step method.On thin buffer films of SiO₂,which were first fabricated on glass substrates by the sol—gel dip-coating method,a ZnO seed layer was deposited via RF magnetron sputtering.Then two different ZnO films,micro-nano and micro-only flowerlike structures,were grown by the hydrothermal method.The prepared films have different hydrophobic properties after surface modification.The structures of the obtained ZnO films were characterized using x-ray diffraction and field-emission scanning electron microscopy.A conclusion that a micro-nano composite structure is more beneficial to hydrophobicity than a micro-only structure was obtained through research into the effect of structure on hydrophobic properties.     

MOCVD modification of the surface of multiwalled carbon nanotubes to impart to them necessary physicochemical properties

Multiwalled iron-containing carbon nanotubes were synthesized by the MOCVD method with pyrolysis of ferrocene and toluene mixtures in an argon flow at atmospheric pressure. Using the MOCVD method with vacuum pyrolysis of bis-arene-chromium compounds onto the surface of multiwalled carbon nanotubes (MWCNTs), pyrolytic chromium films were deposited and new composite materials MWCNT/pyrolytic chromium were obtained. The composite morphology depends on the conditions of pyrolytic chromium deposition. Regular bead-shaped structures were detected. The mechanism of their appearance due to the formation of bis-arene chromium compounds of the intermediate viscoplastic polymer phase and the onset of Plateau-Rayleigh instability during pyrolysis is discussed.     

Nano- and microstructured polymer LB layers: A combined AFM/SIMS study

Ultra thin structured polymer films have been prepared by horizontal precipitation Langmuir-Blodgett (HP-LB) method of polymer blends. In particular we used mixtures of two incompatible polymers, poly-2-vinylpyridine and polystyrene, the former giving the necessary surface activity for LB film formation. Upon spreading at the air-water interface, the blend forms different surface structures depending on the relative amount of the two components. By adjusting the experimental parameters it is possible to obtain relatively regular structures in the submicron size range, which can be transferred on a solid substrate. These systems have been investigated by means of SIMS and atomic force microscopy.     

Physical and chemical modifications of PET surface using a laser-plasma EUV source

Extreme ultraviolet (EUV) radiation is the electromagnetic radiation ranging from vacuum ultraviolet to soft X-rays. A single EUV photon carries enough energy to ionize any atom or molecule. The penetration depth of the radiation in any material is very short, ranging from tens to hundreds nanometers. Intense EUV pulses can remove material from the surface or modify its morphology or/and chemical structure. In this work, the radiation from a laser-plasma EUV source based on a double-stream gas-puff target was used for surface modification of polyethylene terephthalate (PET). The PET samples were irradiated with the EUV pulses emitted from krypton plasma and focused with a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated for 1 s–2 min at a 10-Hz repetition rate. Surface morphology of polymer samples after irradiation was investigated using a scanning electron microscope. Changes in chemical surface structure of the irradiated samples were investigated using an X-ray photoelectron spectroscopy. Different kinds of surface microstructures were obtained depending on the EUV fluence in a single pulse and the total EUV fluence. XPS measurements also revealed a modification of the chemical structure.     

Quality evaluation of rubber-to-metal bonded structures based on shearography

The quality of bonding is often a concern in rubber-to-metal bonded parts with regard to the integrity and stability of the structure. In this study, shearography has been used to detect the out-of-plane deformation of the defects caused by thermal and vacuum stresses. A sample of the vulcanized styrene-butadiene rubber bonded to steel with known artificial voids was prepared and during bonding process a region was glued with thick adhesives. The rubber surface of the sample was inspected in thermal radiation and vacuum modes respectively with a self-designed shearography device. Meanwhile, a numerical simulation was conducted to predict the out-of-plane deformation of the rubber surface in these two stress modes. Results from the numerical simulation and the experiments indicated that the debonding defects could be inspected in both loading modes. In the thermal radiation mode the region with thick adhesives could be identified successfully. This study provides a guideline for quality control of rubber-to-metal structures using an optical method.     

Laser-assisted modification of polystyrene surfaces for cell culture applications

Laser-assisted patterning and modification of polystyrene (PS) was investigated with respect to applications in micro-fluidics and cell culture. For this purpose the wettability, the adsorption of proteins and the adhesion of animal cells were investigated as function of laser- and processing parameters. The change of surface chemistry was characterized by X-ray photoelectron spectroscopy. The local formation of chemical structures suitable for improved cell adhesion was realized on PS surfaces by UV laser irradiation. Above and below the laser ablation threshold two different mechanisms affecting cell adhesion were detected. In the first case the debris deposited on and along laser irradiated areas was responsible for improved cell adhesion, while in the second case a photolytic activation of the polymer surface including a subsequent oxidization in oxygen or ambient air is leading to a highly localized alteration of protein adsorption from cell culture media and finally to increased cell adhesion. Laser modifications of PS using suitable exposure doses and an appropriate choice of the processing gas (helium or oxygen) enabled a highly localized control of wetting. The dynamic advancing contact angle could be adjusted between 2° and 150°. The hydrophilic and hydrophobic behaviour are caused by chemical and topographical surface changes.     

Polyaniline-Containing composites based on highly porous carbon cloth for flexible supercapacitor electrodes

Composites based on commercially available carbon cloth Busofit T-040 and conductive polymer polyaniline are fabricated using the electrochemical polymerization of aniline on the surface of carbon-cloth fibers. The sequence of technological operations for obtaining the composite is optimized; the procedure of preliminary modification of the carbon-cloth surface by electrochemical etching is worked out; and the capacitive characteristics of the obtained composites for use as flexible supercapacitor electrodes are studied. It is found that the introduction of polyaniline into the composition of composite electrode structures leads to an increase in the capacitance by 2–2.5 times compared to the initial carbon cloth due to the pseudocapacitance of polyaniline while maintaining a high electrical conductivity and efficiency. For a composite based on etched carbon cloth, the specific capacitance is 267 F/g (8.9 F/cm² per unit of the geometric surface of the electrode) with a charge efficiency of 97–99%. The specific surface area of the composite, determined by the BET method, is 548 m²/g.     

发射FTIR光谱技术在聚合物电解质导电机制研究中的应用

运用发射FTIR光谱技术,实时监测SBA-15掺杂制备的复合聚合物电解质随温度升高其结晶状态变化的规律,结合电化学和SEM研究结果分析了无机填料对离子电导率的影响,并初步提出离子导电增强的机制。文章将为发射FTIR光谱技术应用于锂电池研究进行了探索。