基于红外光谱聚类分析的纳滤膜污染动态发展行为研究

污水再生利用是解决水资源短缺问题的有效对策。纳滤技术由于能够生产高质量的再生水,成为污水深度处理、再生利用的有效方法之一。然而,在纳滤过程中存在复杂的、动态的膜污染现象,会导致产水通量、产水质量下降等问题。研究膜污染动态发展的行为,对于膜污染的分阶段针对性控制具有重要意义。有机物是污染层动态发展过程的重要指示性成分,红外光谱是表征污染层发展过程中表面有机物官能团变化情况的重要手段。但由于红外光谱中峰的数量多,系列样品之间峰强度的差别较小（尤其是当膜污染过程中的采样间隔较小时）,利用直观观察不易甄别不同样品间的谱图差异及其变化趋势,在此水平上难以对膜污染阶段进行准确识别、对各阶段特征进行有说服力的分类概括。为探索膜污染的动态发展过程,本研究将傅里叶变换红外光谱与统计学聚类分析相结合,对膜污染过程中不同时间点的膜样本进行红外光谱分析,再对红外光谱数据进行一系列预处理和系统聚类分析,从而客观解读膜污染动态发展过程中系列样品红外光谱分阶段变化规律。考虑到类别间距离度量方法、红外吸收峰强度标准化、峰之间自相关性、峰与样本之间交互作用等因素的影响,研究采用对应分析对红外数据进行预处理,提取各样本在主要维度上的得分,随后基于标准化欧式距离对各样本进行聚类。在为期一个月的城市污水深度处理纳滤试验过程中,由于污染物在膜表面累积,纳滤膜发生了较为严重的污染。通过对13个不同时间点的膜样本进行红外光谱聚类发现,膜污染可清晰划分为如下阶段：空白膜、阶段Ⅰ（3 h～8 d）、阶段Ⅱ（10～15 d）和阶段Ⅲ（20～30 d）。采用红外聚类,得到膜表面X射线光电子能谱（XPS）和三磷酸腺苷（ATP）含量分析等方法的交互验证。结果表明,随着膜污染的发展,膜表面有机物成分与共存微生物量发生协同变化,各阶段大致特征为：阶段Ⅰ各类有机污染物初步覆盖,微生物开始富集;阶段Ⅱ多糖类污染物比例上升,微生物的富集趋于稳定;阶段Ⅲ整体污染趋于成熟,有机污染物氢键特征更加明显。该研究通过对红外数据进行聚类分析,能够灵敏地探测各红外图谱之间的差别,有助于对红外光谱规律的深度挖掘,为膜污染阶段的识别和划分提供了一种客观、自动、可量化的辅助性方法,并且有助于归纳出不同阶段的污染层特征,可作为膜污染时序特征的侦查手段。此外,除了膜污染的研究,在材料、吸附等领域,只要有一系列变化的红外光谱,均可尝试采用红外光谱聚类分析方法,获取基于红外特征的定类信息或分阶段规律。     

Molecular mobility and transport in polymer membranes and polyelectrolyte multilayers

Polyelectrolyte multilayers prepared by the layer-by-layer technique provide an efficient way to generate planar structures of tailored surface charge and hydrophobicity, which are used as membranes for pervaporation. The use of polyelectrolyte multilayers to form the membrane permits tailoring the surface charge of the membrane and, thus, selectivity; at the same time, it reduces fouling of the membrane by adsorption of organic matter. Pulsed field gradient (PFG) nuclear magnetic resonance has been used to investigate the diffusion of probe molecules into polymer systems. Evaluation of the apparent diffusion coefficient in porous poly(amide) results in a pore size of 4 microm, as found in electron micrographs. For the pore size obtained for polyelectrolyte multilayers, no equivalent pores could be found in microscopy. Propagators for the diffusion of propanol and propanol-water mixture into multilayers reveal that there might be selective interaction of probe molecules with the polyelectrolyte system.     

Dielectric Analysis of Dynamic Fouling Behavior on Surface of Polyethersulfone Composite Ultrafiltration Membrane

基于界面极化与静电场理论建立了聚醚砜复合超滤膜表面污染层与溶液体系的介电解析模型. 应用参数敏感性分析和介电测量研究了体系中浓差极化层与滤饼层的厚度与电导率对超滤体系介电弛豫的影响机制. 结果表明超滤过程中浓差极化层能快速建立,而滤饼层的形成是一个增长与剥蚀的动态过程;并且浓差极化层与滤饼层的电学性质是影响超滤体系介电谱的关键因素. 比较介电测量与模拟结果证实了建立的超滤体系介电解析模型能够有效可靠地描述与解释超滤体系产生介电驰豫的机制.     

Biotoxicity of nanoparticles: effect of natural organic matter

Various natural organic matters (NOM) with different characteristics in aquatic environment may affect toxicity of leased nanoparticles, owing to interactions between NOM and nanoparticles. This study investigated the effect of NOM and physical characteristics of the effluent organic matter (EfOM) on the ecotoxicity of quantum dots (QD) using Daphnia magna. Organic matter samples were obtained from: Yeongsan River (YR-NOM), Dongbuk Lake (DL-NOM), Damyang wastewater treatment plant (EfOM), and Suwannee River NOM (SR-NOM). The QD was composed of a CdSe core, ZnS shell, and polyethylene glycol coating. The average size of the investigated QD was 4.8, 56.5, and 25.0 nm determined by transmission electron microscopy, dynamic light scattering, and asymmetric flow field-flow fractionation, respectively. The relative hydrophobicity of NOM was investigated using both specific UV absorbance at 254 nm and XAD-8/4 resins. The sorption of NOM on the QD was measured using a fluorescence quenching method. The highest hydrophobicity was exhibited by the SR-NOM, while the lowest was recorded for the DL-NOM. All tested NOMs significantly reduced the acute toxicity of D. magna when adsorbed to QD, and the order of effectiveness for each NOM was as follows: SR-NOM > EfOM > YS-NOM > DL-NOM. The sorption of NOM on the QD surface caused a decrease in the fluorescence intensity of QD at increasing NOM concentration. This suggests that the NOM coating influenced the physicochemical characteristics of QD in the internal organs of D. magna by inducing a reduced bioavailability. Results from this study revealed that NOM with relatively high hydrophobicity had a greater capability of inducing toxicity mitigation.     

Plasma surface modification of nanofiltration (NF) thin-film composite (TFC) membranes to improve anti organic fouling

Commercial nanofiltration (NF) thin-film composite (TFC) membranes were treated by low-pressure NH₃ plasma, and the effects of the plasma treatment were investigated in terms of the membrane hydrophilicity, pure water flux, salt rejection, protein adsorption, and humic acid fouling. Experimental results indicated that the membrane surface hydrophilicity was increased by the plasma treatment, and changes in the hydrophilicity as well as membrane performance including permeate flux and fouling varied with the original membrane characteristics (e.g., roughness and hydrophilicity). Water flux of plasma treated membranes was the highest with 10 min and 90 W of plasma treatment, and salt rejection was mainly affected by the intensity of the plasma power. Results of bovine serum albumin (BSA) adsorption demonstrated that the protein adsorption decreased with increasing plasma treatment time. The plasma treatment that resulted in more negatively charged surfaces could also better prevent Aldrich humic acid (AHA) attachment on the membrane surface.     

Role of surface ligands in nanoparticle permeation through a model membrane: a coarse-grained molecular dynamics simulations study

How nanoparticles interact with biological membranes is of significant importance in determining the toxicity of nanoparticles as well as their potential applications in phototherapy, imaging and gene/drug delivery. It has been shown that such interactions are often determined by nanoparticle physicochemical factors such as size, shape, hydrophobicity and surface charge density. Surface modification of the nanoparticle offers the possibility of creating site-specific carriers for both drug delivery and diagnostic purposes. In this work, we use coarse-grained molecular dynamic simulations to explore the permeation characteristics of ligand-coated nanoparticles through a model membrane. We compare permeation behaviors of ligand-coated nanoparticles with bare nanoparticles to provide insights into how the ligands affect the permeation process. A series of simulations is carried out to validate a coarse-grained model for nanoparticles and a lipid membrane system. The minimum driving force for nanoparticles to penetrate the membrane and the mechanism of nanoparticle–membrane interaction were investigated. The potential of the mean force profile, nanoparticle velocity profile, force profile and density profiles (planar and radial) were obtained to explore the nanoparticle permeation process. The structural properties of both nanoparticles and lipid membrane during the permeation, which are of considerable fundamental interest, are also studied in our work. The findings described in our work will lead to a better understanding of nanoparticle–lipid membrane interactions and cell cytotoxicity and help develop more efficient nanocarrier systems for intracellular delivery of therapeutics.     

Synthesis of Pt-Ni-Fe/CNT/CP nanocomposite as an electrocatalytic electrode for PEM fuel cell cathode

In order to use carbon nanotube (CNT)-supported catalyst as fuel cell electrodes, Pt-Ni-Fe/CNT/carbon paper (CP) electrode was prepared using an ethylene glycol reduction method. CNTs were directly synthesized on Ni-impregnated carbon paper, plain carbon cloth, and Teflonized carbon cloth using chemical vapor deposition. FESEM and TEM images and thermogravimetric analysis indicated that in situ CNT on carbon paper (ICNT/CP) possesses more appropriate structural quality and stronger adhesion to the substrate than other substrates. The contact angle analysis demonstrated that the degree of ICNT/CP surface hydrophobicity encountered a 24% increase in comparison to CP and promoted to superhydrophobicity from hydrophobicity. The polarization curves and electrochemical impedance spectroscopy results of the loaded Pt-Ni-Fe on in situ and ex situ CNT/CP illustrated that the power density increased and charge transfer resistance reduced compared to commercial Pt/C loaded on CP. The results can be attributed to the outstanding properties of CNTs and high catalytic activity of triple catalysts causing alloying of Pt with Ni and Fe, which makes them a proper candidate to be used as cathode electrodes in proton exchange membrane fuel cells.     

Improved aging performance of vapor phase deposited hydrophobic self-assembled monolayers

A hydrophobic self-assembled monolayer (SAM) of fluoro-octyl-trichloro-silane (FOTS) was deposited on silicon using a vapor phase technique. The aging of the hydrophobic layer was examined using water contact angle measurements. It has been found that while such monolayer films suffer from a loss of hydrophobicity with time, pre-immersion nitrogen annealing can significantly improve the aging characteristics of these monolayers. The effect of nitrogen annealing on the improved aging properties of SAM coatings has been investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The hydrolytic stability and the effect of nitrogen annealing were studied by morphological evolution during immersion. A spontaneous formation of silane mounds on the surface of the monolayers was found by AFM. These mounds have been irreversibly transformed from initially uniform hydrophobic surface layers. It is highly probable that the compliance of these mounds can reasonably allow hydrophilic sites to be located around the mounds. Interestingly, the density of these mounds formation is very less on the annealed samples. XPS reveals a higher level of coverage by the N₂-annealed film due to agglomeration. A relative abundance of CF₃ and CF₂ moieties in the annealed film may explain the enhancement of the hydrophobicity as revealed by higher level of water contact angle. This hydrophobicity was found to be significantly stable in water. This novel finding explains the improved hydrophobic stability of FOTS monolayers as primarily a morpho-chemical effect that originates from the densification of the monolayers upon annealing.     

Research on the icephobic properties of fluoropolymer-based materials

Fluoropolymer, because of the extremely low surface energy, could be non-stick to water and thus could be a good candidate as anti-icing materials. In this paper, the icephobic properties of a series of fluoropolymer materials including pristine PTFE plates (P-PTFE), sandblasted PTFE plates (SB-PTFE), two PTFE coatings (SNF-1 and SNF-CO1), a fluorinated room-temperature vulcanized silicone rubber coating (F-RTV) and a fluorinated polyurethane coating (F-PU) have been investigated by using SEM, XPS, ice adhesion strength (tensile and shear) tests, and static and dynamic water contact angle analysis. Results show that the fluoropolymer material with a smooth surface can significantly reduce ice adhesion strength but do not show obvious effect in reducing ice accretion at −8 °C. Fluoropolymers with sub-micron surface structures can improve the hydrophobicity at normal temperature. It leads to an efficient reduction in the ice accretion on the surface at −8 °C, due to the superhydrophobicity of the materials. But the hydrophobicity of this surface descends at a low temperature with high humidity. Consequently, once ice layer formed on the surface, the ice adhesion strength enhanced rapidly due to the existence of the sub-micron structures. Ice adhesion strength of fluoropolymers is highly correlated to CA reduction observed when the temperature was changed from 20 °C to −8 °C. This property is associated with the submicron structure on the surface, which allows water condensed in the interspace between the sub-micron protrudes at a low temperature, and leads to a reduced contact angle, as well as a significantly increased ice adhesion strength.     

Influence of photo-induced superhydrophilicity of titanium dioxide nanoparticles on the anti-fouling performance of ultrafiltration membranes

Fouling is one of the most present prominent problems in almost all membrane processes. An increase in the membrane hydrophilicity is one of the effective ways to improve the membrane resistance to fouling. In this research, TiO₂ nanoparticles were deposited on the surface of composite ultrafiltration (UF) membrane, and then irradiated by ultraviolet (UV) light. The coating of the membrane surface with TiO₂ nanoparticles and radiation with (UV) light led to the considerable increase of hydrophilicity on the membrane surface. The deposition of TiO₂ nanoparticles was carried out through coordinance bonds with OH functional groups of the polymer on the membrane surface. The flux through a coated and (UV) light radiated membrane was increased to a large extent compared to a virgin membrane. In this research, the effect of different concentrations of TiO₂ nanoparticles in the presence and absence of (UV) irradiation was investigated, and the role of increasing of hydrophilicity on the anti-fouling property of membranes was studied. In order to characterize the membranes FTIR, XRD, SEM, water contact angle and cross-flow filtration were employed. This procedure is a useful technique for improvement of hydrophilicity to decrease (increase) fouling (anti-fouling performance) and enhance the permeation of membranes.     

Strong correlation between membrane effective fixed charge and proton conductivity in the sulfonated polysulfone cation-exchange membranes

The effectiveness of fixed charge in sulfonated polysulfone membranes and its correlation with proton conductivity and physicochemical properties have been investigated in this work. The membranes were prepared with various concentrations of sulfonating agent (6% to 10% v/v) and followed by the characterizations that include membrane potential measurements, proton conductivity, and physicochemical properties (contact angle, water uptake, and ion-exchange capacity). Here, the effective fixed-charge concentrations of the membranes were obtained based on the data of membrane potential measurements using the Teorell–Meyer–Siever equation. The analysis results exhibit that a strong correlation between effective charge concentration and proton conductivity, which is expressed by the linear increase of proton conductivity with QX. This correlation is also supported by the membranes physicochemical data, such as water uptake, ionic exchange capacity, surface contact angle against water and functional analysis using FTIR. Finally, it was also developed an ionic conductivity equation that describes the correlation between proton conductivity and QX values.     

Influence of electronic structures of doped TiO2 on their photocatalysis

The modification of bandgap of TiO₂ was intensively studied for decades to improve its visible light absorbance efficiency. The practical application potential of TiO₂ as photocatalysts for water splitting and water purification has motivated enduring experimental and theoretical research of the doping effects in bulk and nanosized TiO₂ using transition metals, rear earths, p‐block metals and metalloids, and non‐metal elments as dopants to decrease the bandgap of TiO₂. This review summarized the typical theoretical results of the dopant induced variation in electronic structure, bandgap, and density of states of TiO₂. The codoping effects of metal/metal, metal/non‐metal combinations were also introduced briefly to display the modification of electronic structures. Some results were accompanied by experimental results to demonstrate the influence of improved light absorbance efficiency on the photocatalytic performance. The doping effects on the density of states of surface were also summarized briefly. The metal dopants show clear influences on the 3d electrons of titanium to elevate or depress the minimum of conduction band, while the non‐mental dopants mainly interact with the 2p electrons of oxygen to change the position of the maximum of the valence band. The review also noticed the theoretical development of the doping effect with the establishment of novel models, such as the water–TiO₂surface interaction. It should be noted that the theoretical models rarely consider the doping induced variation of defect types and concentration, Fermi level position, surface active sites, and charge transport due to the ground state simulation and shortcoming of density functional theory (DFT). The phenomenological explanations of the experimental results are arbitrary in most of the reports. A universal model is required to explain the complex dependence of the process of photocatalysis on the semiconducting properties, such as bandgap, Fermi level, charge transport, and surface states. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effects of high-intensity ultrasound on the structural,optical, mechanical and physicochemical properties of pea protein isolate-based edible film

Pea protein is a promising alternative to animal-based protein and the interest in its application in food industry has been rapidly growing. In this study, pea protein isolates (PPI) were used to form protein-based edible films and the effect of ultrasound treatment on the structure of PPI and the structural, optical, mechanical and physicochemical properties of PPI-films were investigated. Ultrasound induced unfolding of PPI and exposed interior hydrophobic groups to protein surface while both PPI dissociation and formation of large aggregates were observed, as confirmed by measuring intrinsic emission fluorescence, surface hydrophobicity, surface charge, and particle size distribution and polydispersity index, respectively. FE-SEM showed that ultrasound decreased the cracks and protein aggregates at the surface of PPI-film. The film structure was also investigated by FTIR, which showed peak shift in amide I and II region and noticeable difference of protein secondary structure as affected by ultrasound. As a result of such structural changes caused by ultrasound, the properties of PPI-films were improved. Results showed that ultrasound greatly improved the film transparency, significantly increased film tensile strength but not elongation at break, and decreased moisture content and water vapor permeability of the film. This study provided structural data as evidence for utilizing ultrasound technique to develop PPI-films with improved optical, mechanical and water barrier properties.     

Preparation and characterization of modified nano-porous PVDF membrane with high antifouling property using UV photo-grafting

In this study, the poly(vinylidene fluoride) (PVDF) membrane was prepared via immersion precipitation technique and modified by UV photo-grafting of hydrophilic monomers on the top membrane surface. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers and 2,4-phenylenediamine (PDA) and ethylene diamine (EDA) as amino monomers were used at different concentrations to modify the membrane and improve the hydrophilicity with less fouling tendency. Moreover the presence of benzophenon as photo-initiator for grafting the hydrophilic monomers onto PVDF membrane surface was elucidated. The virgin and modified PVDF membranes were characterized by contact angle, ATR-FTIR, SEM and cross-flow filtration. The contact angle measurements demonstrated that the hydrophilicities of the membranes were significantly enhanced by UV photo-grafting of hydrophilic monomers onto the membrane surface. The ATR-FTIR confirmed the occurrence of modification on PVDF membrane by UV photo-grafting. The pure water flux of membranes was declined by UV photo-grafting but the milk water permeation and protein rejection were slightly improved. Moreover the antifouling properties and flux recovery of PVDF membrane were improved by UV photo-grafting of hydrophilic monomers.     

Tuning the hydrophobicity of ZSM-5 zeolites by surface silanization using alkyltrichlorosilane

ZSM-5 zeolites were modified with alkyltrichlorosilanes of various chain lengths (octyltrichlorosilane, decyltrichlorosilane, dodecyltrichlorosilane and hexadecyltrichlorosilane) and characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Thermal gravimetric analysis (TGA) and contact angle measurements (CA). The results showed that a closely packed and hydrophobic layer was presented at the particles surface and the surface wetting property varied from hydrophilic to hydrophobic, even to superhydrophobic. It was interesting to notice that the hydrophobic properties of modified ZSM-5 particles could be tuned by varying the chain length of chlorosilane and changing the pretreatment temperature before silanization. With increasing the alkyl chain length of trichlorosilane, the hydrophobicity increased. However, with an increase in the pretreatment temperature, the hydrophobicity decreased. Moreover, the relationship between the wetting properties and thermal stability was also investigated, the results showed that the modified ZSM-5 particles possessed good hydrophobicity at a temperature below 250 °C in air. These modified ZSM-5 particles may be utilized for many potential applications, such as membrane fillers, selective adsorbents, catalysts, chromatographic supports and so on.     

High intensity ultrasound modified ovalbumin: Structure,interface and gelation properties

Influence of high intensity ultrasound (HIUS) on the structure and properties of ovalbumin (OVA) were investigated. It was found that the subunits and secondary structure of OVA did not change significantly with HIUS treatment from the electrophoretic patterns and circular dichroism (CD) spectrum. The amount of free sulfhydryl groups increased and intrinsic fluorescence spectra analysis indicated changes in the tertiary structure and partial unfold of OVA after sonication increased. Compared with the untreated OVA, HIUS treatment increased the emulsifying activity and foaming ability, and decreased interface tension (oil–water and air–water interface), which due to the increased surface hydrophobicity and decreased the surface net charge in OVA, while the emulsifying and foaming stability had no remarkable differences. The increased particle size may be attributed to formation of protein aggregates. Moreover, the gelation temperatures of HIUS-treated samples were higher than the untreated OVA according to the temperature sweep model rheology, and this effect was consistent with the increased in surface hydrophobicity for ultrasound treated OVA. These changes in functional properties of OVA would promote its application in food industry.     

Chronopotentiometry study of a cation-exchange membrane in the presence of cationic surfactant in membrane surface vicinity

In this study, the effect of cationic surfactant (benzalkonium chloride) on the transport of KCl through a sulfonated styrene-divinyl benzene cation-exchange membrane was investigated. The presence of benzalkonium chloride as the cationic surfactant, which interacts with the sulfonic groups on membrane surface, has to disturb the transport of K⁺ ions and directly gives responses in its chronopotentiogram. The electrodialysis of the cationic surfactant solution showed an irreversible monotonous increase of the total system potential due to the fouling phenomena. However, a small amount of cationic surfactant in the membrane surface vicinity was observed to give a fluctuating chronopotentiogram at the high current density. This fluctuation is started by a steep increase and followed by the decrease of potential, which finally relaxed to reach a steady state. This potential fluctuation is proposed to be the response of a structural transformation of surfactant micelles on the membrane surface under perturbation of the externally applied electric field, which is discussed and examined qualitatively in this report.     

Electrodynamics of spin currents in superconductors

In recent work we formulated a new set of electrodynamic equations for superconductors as an alternative to the conventional London equations, compatible with the prediction of the theory of hole superconductivity that superconductors expel negative charge from the interior towards the surface. Charge expulsion results in a macroscopically inhomogeneous charge distribution and an electric field in the interior, and because of this a spin current is expected to exist. Furthermore, we have recently shown that a dynamical explanation of the Meissner effect in superconductors leads to the prediction that a spontaneous spin current exists near the surface of superconductors (spin Meissner effect). In this paper we extend the electrodynamic equations proposed earlier for the charge density and charge current to describe also the space and time dependence of the spin density and spin current. This allows us to determine the magnitude of the expelled negative charge and interior electric field as well as of the spin current in terms of other measurable properties of superconductors. We also provide a `geometric' interpretation of the difference between type I and type II superconductors, discuss how superconductors manage to conserve angular momentum, discuss the relationship between our model and Slater's seminal work on superconductivity, and discuss the magnitude of the expected novel effects for elemental and other superconductors.     

表面增强拉曼光谱研究多糖和蛋白对PVDF膜的膜污染能力

膜在运行过程中形成的膜污染会引起严重的膜通量下降, 从而使得膜必须清洗甚至更换, 是膜技术的主要缺点。典型的膜污染物质包括蛋白和多糖。本文发展表面增强拉曼光谱作为一种新的工具研究蛋白和多糖对聚偏二氟乙烯(PVDF)膜的膜污染能力。通过比较三种不同蛋白和多糖在玻璃片上和经过膜过滤之后SERS相对强度的变化, 可迅速简便地判断出膜污染能力, 即多糖(海藻酸钠)>血红蛋白>卵蛋白>小牛血清蛋白。与基于荧光的技术相比, 拉曼谱峰窄、光谱分辨率高、尤其是使用相同的激发光和激光功率就可以获得多种物质的SERS信号, 使得SERS可以简便地判断不同物质的膜污染能力。     

XPS investigation of the PTFE induced hydrophobic properties of electrodes for low temperature fuel cells

In electrodes of low temperature fuel cells like polymer electrolyte membrane fuel cells (PEFC) or alkaline fuel cells (AFC) the reactants and the water must be transported. For this purpose the pore system in the electrodes needs a hydrophilic character for the transport of the water and a hydrophobic character for the transport of the gases. The degree of the hydrophobicity determines whether the pore system will be flooded by the reaction water. In the case of PEFC, this is also determined by the degree of the required humidification of the reaction gases. In AFC hydrophobicity determines the extension of the three-phase reaction zone. Caused by the strong influence of hydrophobicity on the transport processes, the electrochemical performance and the optimized operation conditions are also affected by hydrophobicity.Typically polytetrafluoro-ethylene (PTFE) is used to make the electrodes hydrophobic, because PTFE has a high chemical stability. Hydrophobicity depends on the concentration of PTFE on the electrode surface. The PTFE concentration, which is related to the hydrophobic character, can be determined by XPS. The changes in the PTFE content and structure of the electrode of a PEFC was investigated by cyclic voltammetry and XPS and correlated with the performance of the cell in long-term operation. With both methods an initial significant increase in free and electrochemically active surface platinum area is observed. This activation is associated with a degradation of the PTFE in the electrode which is responsible for the hydrophobic properties of the electrode. With further operation the performance of the cell decreases because the water management becomes more critical. Generally, it is shown that XPS can be used for the investigation of the hydrophobicity of electrodes prepared by various manufacturing techniques as well as of changes in their hydrophobicity induced by the electrochemical operation.