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Herein, we successfully fabricated porous nanocomposite membranes decorated with high loadings of nickel nanoparticles (25–45 wt %) by using chelating additives (sodium dodecyl sulfate (SDS) and Fumion) for the film casting cum phase separation approach. These additives decreased the nickel agglomeration and promoted the presentation of particles at the pore surface of the final membranes, leading to increased water permeances (450 to 1200–2400 L/m2 hbar) and porosities (56% to 70–78%) in comparison to a nanocomposite membrane made without additives. The hydrophobic ionomer Fumion, incorporated into the polyethersulfone matrix during solidification, further allowed us to tune the membrane hydrophobicity. We discovered that the same nickel nanoparticles exhibited a 5× increased H2 generation rate during the catalytic hydrogen formation from ammonia borane when presented in a membrane with a higher water contact angle (85° compared to 60°). We could attribute this improvement to the lower capillary pressure in more hydrophobic pores, which facilitates the release of H2 bubbles. The nanocomposite membranes were further employed as flow-through reactors for the catalytic hydrogenation of p-nitrophenol (p-NP) in the presence of ammonia borane. Membranes with an additive-directed nickel nanoparticle presentation at the pore surface demonstrated 6 to 7× higher p-NP turnover frequencies (TOFs). We also observed that the formation of hydrogen gas from ammonia borane results in a permeance decrease during the flow-through p-NP conversion. However, this effect was mitigated in more hydrophilic membranes with an anisotropic pore structure. [ABSTRACT FROM AUTHOR]

We compare the efficiency of grafting polyethylene glycol (PEG) and poly(sulfobetaine) hydrogel layer on poly(ether imide) (PEI) hollow-fiber ultrafiltration membrane surfaces in terms of filtration performance, fouling minimization and stability in cleaning solutions. Two previously established different methods toward the two different chemistries (and both had already proven to be suited to reduce fouling significantly) are applied to the same PEI membranes. The hydrophilicity of PEI membranes is improved by the modification, as indicated by the change of contact angle value from 89° to 68° for both methods, due to the hydration layer formed in the hydrogel layers. Their pure water flux declines because of the additional permeation barrier from the hydrogel layers. However, these barriers increase protein rejection. In the exposure at a static condition, grafting PEG or poly(sulfobetaine) reduces protein adsorption to 23% or 11%, respectively. In the dynamic filtration, the hydrogel layers minimizes the flux reduction and increases the reversibility of fouling. Compared to the pristine PEI membrane that can recover its flux to 42% after hydraulic cleaning, the PEG and poly(sulfobetaine) grafted membranes can recover their flux up to 63% and 94%, respectively. Stability tests show that the poly(sulfobetaine) hydrogel layer is stable in acid, base and chlorine solutions, whereas the PEG hydrogel layer suffers alkaline hydrolysis in base and oxidation in chlorine conditions. With its chemical stability and pronounced capability of minimizing fouling, especially irreversible fouling, protective poly(sulfobetaine) hydrogel layers have great potential for various membrane-based applications. [ABSTRACT FROM AUTHOR]

The present work evaluates the possibilities of processing cellulose with ionic liquids and functional nanoparticles like TiO2 toward a new generation of porous nanocomposites, shaped as films or spheres, which may find direct application in water purification, catalysis, and self-cleaning materials. The focus was set on the factors controlling the formation of the porous film structure during the nonsolvent induced phase separation process from polymer solutions in ionic liquids via immersion in water and during the porous film drying step. Temperature and cosolvent addition facilitate cellulose solubilization and help control the phase separation by improving the mass transfer. The complex relation between the catalytic activity of the porous TiO2-cellulose nanocomposite materials obtained under different processing conditions and their structure has been studied during the photodegradation of model organic dyes like rhodamine B and methylene blue. After drying, the catalytic activity of the nanocomposites decreases as a consequence of the reformation of the intra- and intermolecular hydrogen bonds in cellulose which diminish the flexibility and the mobility of the fine cellulose fibrils network. [ABSTRACT FROM AUTHOR]

In this work, a recently established,novel two-step imprintingstrategy combining surface imprinting and scaffold imprinting wasapplied successfully to prepare a molecularly imprinted polymer (MIP)adsorber for immunoglobulin G (IgG). Track-etched polyethylene terephthalate(PET) membranes with previously introduced aliphatic C–Br groupsas initiator on the pore surface were used to prepare first a functionalpolymer scaffold, grafted poly(methacrylic acid), via surface-initiatedatom transfer radical polymerization (SI-ATRP). After template protein(IgG) binding to the scaffold, UV-initiated cross-linking copolymerizationof acrylamide and methylenebisacrylamide (MBAA) as second step leadto a grafted MIP hydrogel layer. The influences of the three independentparameters, scaffold chain length by SI-ATRP time, degree of cross-linkingof the MIP layer by MBAA content, and grafted MIP layer thicknessby UV irradiation time, were studied to optimize protein binding capacityand selectivity. The results were also compared to previously obtaineddata for lysozyme imprinting using the same method, and significanteffects of protein size on imprinting efficiency could be identified.The best IgG MIP membrane adsorber was then used to separate IgG frommixtures with human serum albumin (HSA), demonstrating IgG bindingcapacities and eluted IgG purities, which were almost independentof the excess of HSA. The results of this study are a significantextension of the scope of molecular imprinting toward large targetbionanoparticles. The transfer of the approach from the model PETto other base membranes with higher specific surface area is straightforward,and the resulting affinity materials would, in principle, be suitedfor “capturing” of an antibody from a complex mixture. [ABSTRACT FROM AUTHOR]

The dispersibility of different lab-made and commercial TiO2 nanoparticles prepared by gas-phase processes in room temperature ionic liquids was for the first time studied by dynamic light scattering and advanced rheology. The characterization of the nanopowders has been done with transmission electron microscopy, X-ray diffraction analysis, nitrogen adsorption, and Brunauer–Emmett–Teller (BET) analysis and FT-IR spectroscopy. The colloidal stabilities of the resulting dispersions were strongly influenced by particle characteristics such as aggregation level, mean particle size, and surface functionality. The period of the ultrasound treatment, the powder concentration in the dispersion, and the hydrophilicity of the ionic liquid were also important influences. It was found that most types of powders disperse better in the hydrophilic ionic liquid because of the hydroxyl groups and adsorbed water present on the powders' surfaces. The best dispersions over a broader concentration range were obtained for a lab-made powder produced by chemical vapor synthesis (aerosol method) which had the smallest nonaggregated particles. [ABSTRACT FROM AUTHOR]

A simple scalable strategy is proposed to fabricate highly permeable antifouling nanofiltration membranes. Membranes with a selective thin polyamide layer were prepared via interfacial polymerization incorporating building blocks of zwitterionic copolymers. The zwitterionic copolymer, poly(aminopropyldimethylaminoethyl methacrylate)- co-poly(sulfobetaine methacrylate) with an average molecular weight of 6.1 kg mol -1 , was synthesized in three steps: (i) polymerization of dimethylaminoethyl methacrylate to yield the base polymer by atom transfer radical polymerization (ATRP), (ii) fractional sulfobetainization via quaternization, and (iii) amination via quaternization. The effect of the zwitterionic polymer content on the polyamide surface characteristics, fouling resistance, and permeance is demonstrated. The zwitterion-modified membrane becomes more hydrophilic with lower surface roughness, as the zwitterionic polymer fraction increases. The excellent fouling resistance of the zwitterion-modified membrane was confirmed by the negligible protein adsorption and low bacteria fouling compared to a pristine membrane without zwitterionic segments. In addition, the zwitterion-modified membranes achieve a water permeation around 135 L m -2 h -1 bar -1 , which is 27-fold higher than that of the pristine membrane, along with good selectivity in the nanofiltration range, confirmed by the rejection of organic dyes. This permeance is about 10 times higher than that of other reported loose nanofiltration membranes with comparable dye rejection. The newly designed membrane is promising as a highly permeable fouling resistant cross-linked polyamide network for various water treatment applications.

Thin-film composite (TFC) membranes still suffer from fouling and biofouling. In this work, by incorporating a graphene oxide (GO)-silver-based metal-organic framework (Ag-MOF) into the TFC selective layer, we synthesized a thin-film nanocomposite (TFN) membrane that has notably improved anti-biofouling and antifouling properties. The TFN membrane has a more negative surface charge, higher hydrophilicity, and higher water permeability compared with the TFC membrane. Fluorescence imaging revealed that the GO-Ag-MOF TFN membrane kills Escherichia (E.) coli more than the Ag-MOF TFN, GO TFN, and pristine TFC membranes by 16, 30, and 92%, respectively. Forward osmosis experiments with E. coli and sodium alginate suspensions showed that the GO-Ag-MOF TFN membrane by far has the lowest water flux reduction among the four membranes, proving the exceptional anti-biofouling and antifouling properties of the GO-Ag-MOF TFN membrane.

Stimuli-responsive membranes that can adjust mass transfer and interfacial properties "on demand" have drawn large interest over the last few decades. Here, we designed and prepared a novel magnetoresponsive separation membrane with remote switchable molecular sieving effect by simple one-step and scalable nonsolvent induced phase separation (NIPS) process. Specifically, poly(ether sulfone) (PES) as matrix for an anisotropic membrane, prefabricated poly(N-isopropylacrylamide) (PNIPAAm) nanogel (NG) particles as functional gates, and iron oxide magnetic nanoparticles (MNP) as localized heaters were combined in a synergistic way. Before membrane casting, the properties of the building blocks, including swelling property and size distribution for NG, and magnetic property and heating efficiency for MNP, were investigated. Further, to identify optimal film casting conditions for membrane preparation by NIPS, in-depth rheological study of the effects of composition and temperature on blend dope solutions was performed. At last, a composite membrane with 10% MNP and 10% NG blended in a porous PES matrix was obtained, which showed a large, reversible, and stable magneto-responsivity. It had 9 times higher water permeability at the "on" state of alternating magnetic field (AMF) than at the "off"-state. Moreover, the molecular weight cutoff of such membrane could be reversibly shifted from ∼70 to 1750 kDa by switching off or on the external AMF, as demonstrated in dextran ultrafiltration tests. Overall, it has been proved that the molecular sieving performance of the novel mixed matrix composite membrane can be controlled by the swollen/shrunken state of PNIPAAm NG embedded in the nanoporous barrier layer of a PES-based anisotropic porous matrix, via the heat generation of nearby MNP. And the structure of such membrane can be tailored by the NIPS process conditions. Such membrane has potential as enabling material for remote-controlled drug release systems or devices for tunable fractionations of biomacromolecule/-particle mixtures.

In this work, we explore the ability of utilizing hydrogels synthesized from a temperature-sensitive polymer and a polyelectrolyte to desalinate salt water by means of reversible thermally induced absorption and desorption. Thus, the influence of the macromolecular architecture on the swelling/deswelling behavior for such hydrogels was investigated by tailor-made network structures. To this end, a series of chemically cross-linked polymeric hydrogels were synthesized via free radical-initiated copolymerization of sodium acrylate (SA) with the thermoresponsive comonomer N-isopropylacrylamide (NIPAAm) by realizing different structural types. In particular, two different polyNIPAAm macromonomers, either with one acrylate function at the chain end or with additional acrylate functions as side groups were synthesized by controlled polymerization and subsequent polymer-analogous reaction and then used as building blocks. The rheological behaviors of hydrogels and their estimated mesh sizes are discussed. The performance of the hydrogels in terms of swelling and deswelling in both deionized water (DI) and brackish water (2 g/L NaCl) was measured as a function of cross-linking degree and particle size. The salt content could be reduced by 23% in one cycle by using the best performing material.

A strong polyelectrolyte hydrogel was graft copolymerized on a polyethersulfone (PES) ultrafiltration (UF) membrane using vinyl sulfonic acid (VSA) as the functional monomer, and N,N'-methylenbisacrylamide (MBAA) as the cross-linker monomer. This was carried out in one simple step using the UV photoirradiation method. The effect of the polymerization conditions on the degree of grafting (DG) was investigated using the gravimetric method which measures the total hydrogel grafted on the membrane, and with ATR-FTIR spectroscopy which indicates the functional monomer fraction in the hydrogel layer. The VSA could not graft polymerize without the cross-linker as comonomer. An increase in the cross-linker fraction from 0.25 to 2.5 mol % (relative to the functional monomer VSA) resulted in a higher DG. Although the surface morphology changed upon modification, the resulting surface roughness as measured by AFM was very low. From the monitoring of DG with UV time (4.5-30 min) at constant conditions, it was deduced that during the early stages of the polymerization mainly the cross-linker was grafted, thus inducing the graft copolymerization of the functional monomer. Polymerization using a higher monomer concentration (12.5-40% VSA) at constant monomer/cross-linker ratio resulted in a higher VSA fraction in the grafted hydrogel, although the gravimetric DG was similar. Ion exchange capacity and X-ray photoelectron spectroscopy measured after modification under the different conditions supported these findings. The new membranes were tested under nanofiltration (NF) conditions. A NF membrane could be obtained when the MBAA fraction was above 0.25%. The Na2SO4 rejection was 90-99% and the permeability 10-1 L m(-2) h(-1) bar(-1) when the MBAA fraction increased from 0.75 to 2.5%. The order of rejection of single salts solution was Na2SO4 > MgSO4 ≈ NaCl > CaCl2, as expected on the basis of Donnan exclusion for negatively charged NF membranes. An increase in the salts rejection with increasing degree of cross-linking and VSA fraction was attributed to an increase in the membrane charge density and to steric exclusion that also resulted in an increase of rejection for uncharged solutes such as sucrose or glucose. The new membrane presented a high, essentially unchanged Na2SO4 rejection (>97%) in the range of salt concentrations up to 4 g/L, and only slightly reduced rejection (>92%) at a concentration of 8 g/L; this can be related to its high barrier layer charge density measured by ion exchange capacity. In addition, because poly(vinyl sulfonic acid) (PVSA) is a strong polyelectrolyte the membrane separation performance was stable in the range of pH 1.5 to pH 10.

Because most "low fouling" polymers resisting bacterial attachment are hydrophilic, they are usually also significantly swollen. Swelling leads to purely physical dilution of interaction and weakens attachment; however, these nonspecific contributions are usually not separated from the specific effect of polymer chemistry. Taking advantage of the fact that chemistry and swelling of hydrogels may be independently varied through the fraction of a cross-linker, the roles of chemistry and physical dilution (swelling) in bacterial attachment are analyzed for selected hydrogels. Using as a quantitative indicator the rate of bacterial deposition in a parallel plate setup under defined flow conditions, the observed correlation of deposition rate with swelling provides a straightforward comparison of gels with different chemistries that can factor out the effect of swelling. In particular, it is found that chemistry appears to contribute similarly to bacterial deposition on hydrogels prepared from acrylamide and a zwitterioninic monomer 2-(methacryloyloxy)ethyl) dimethyl-(3-sulfopropyl) ammonium hydroxide so that the observed differences may be related to swelling only. In contrast, these gels were inferior to PEG-based hydrogels, even when swelling of the latter was lower, indicating a greater contribution of PEG chemistry to reduced bacterial deposition. This demonstrates that swelling must be accounted for when comparing different biofouling-resistant materials. Chemical and physical principles may be combined in hydrogel coatings to develop efficient antibiofouling surfaces.

Presented here is a radically novel approach to reduce concentration polarization and, potentially, also fouling by colloids present in aqueous feeds: magnetically responsive micromixing membranes. Hydrophilic polymer chains, poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted via controlled surface-initiated atom transfer radical polymerization (SI-ATRP) on the surface of polyamide composite nanofiltration (NF) membranes and then end-capped with superparamagnetic iron oxide magnetite (Fe(3)O(4)) nanoparticles. The results of all functionalization steps, that is, bromide ATRP initiator immobilization, SI-ATRP, conversion of PHEMA end groups from bromide to amine, and carboxyl-functional Fe(3)O(4) nanoparticle immobilization via peptide coupling, have been confirmed by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). These nanoparticles experience a magnetic force as well as a torque under an oscillating external magnetic field. It has been shown, using particle image velocimetry (PIV), that the resulting movement of the polymer brushes at certain magnetic field frequencies induces mixing directly above the membrane surface. Furthermore, it was demonstrated that with such membranes the NF performance could significantly be improved (increase of flux and salt rejection) by an oscillating magnetic field, which can be explained by a reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on polymer-nanoparticle conjugates has much broader implications.

A sugar-containing monomer (2-lactobionamidoethyl methacrylate, LAMA) was grafted on a polypropylene (PP) microfiltration membrane surface by UV-induced graft copolymerization. The degree of grafting can be controlled by variation of monomer concentration, UV irradiation time, and photoinitiator concentration. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the surface modification on the membranes. The water contact angle was used to evaluate the hydrophilicity change of the membrane surface before and after modification. Bacteria capture experiments showed that the membrane could selectively bind E. faecalis while adhesion of S. maltophilia was not influenced by the functionalization of PP with grafted poly(LAMA). The adhesion of E. faecalis onto poly(LAMA) grafted membrane could be inhibited by 200 mM galactose solution; however, glucose solution showed no inhibition effect. Moreover, occupying sugar residues on the membrane surface primarily by a galactose targeting lectin, peanut agglutinin, could significantly suppress the following adhesion of E. faecalis. All these results clearly demonstrate that this poly(LAMA) grafted PP membrane can selectively capture E. faecalis and that this selection is based on the interaction between galactose side groups on grafted flexible functional polymer chains on the membrane surface and galactose binding protein on the E. faecalis cell membrane.

In many cases, biomaterials surfaces are desired to be resistant to protein adsorption. A system fulfilling this task in nature is the so-called glycocalyx. The glycocalyx is an outer layer on the cell membrane with bound glycoproteins and glycolipids, exposing a pattern of carbohydrate groups. There is a growing interest to mimic this glycocalyx layer to have a tool to overcome the problems with uncontrolled protein adsorption on biomaterials. In this work a glycocalyx-like layer is artificially imitated by surface-initiated atom transfer radical polymerization (ATRP) of a glycomonomer, D-gluconamidoethyl methacrylate (GAMA), from a mixed self-assembled monolayer (SAM) of an ATRP initiator-immobilized hydroxyl-terminated thiol and a methyl-terminated thiol as diluent. Fourier transform infrared spectroscopy (FT/IR-ATR), contact angle, and ellipsometry measurements were employed to confirm the grafting of the glycopolymer. The anti-nonspecific protein binding properties of this glycopolymer layer were then investigated with surface plasmon resonance (SPR). Three proteins with different size, lysozyme, bovine serum albumin (BSA), and fibrinogen were used as model solutes to investigate the influence of protein size on the protein resistance behavior. The glycopolymer chain density was controlled during surface-initiated ATRP by varying the ratio of the components in the mixed SAM, and the chain length was adjusted by ATRP time. The effect of chain density in combination with the protein size was also evaluated. The most important results are that poly(GAMA) layers of higher grafting density show resistance to adsorption of the model proteins used in this work and that the amount of adsorbed protein depends on the length and density of the glycopolymer chains and also on the size of the proteins.

Nonlinear laser processing of silane-based monolayers is used to fabricate nanostructured chemical templates for the selective growth of polymer brushes in confined domains via surface-initiated polymerization (SIP). Upon varying the laser parameters, reactive domains with lateral dimensions from several micrometers down to the sub-100-nm range are fabricated. This provides a versatile means for studying the morphological scaling behavior of confined polymer brushes. Here, the surface-initiated growth of a stimuli-responsive polymer, poly(N-isopropylacrylamide) (PNiPAAm), via atom transfer radical polymerization (ATRP) is investigated. Polymer chains at the domain boundaries extend into the surrounding polymer-free areas. For this reason the width of confined polymer brushes is significantly larger than that of the underlying domains. Within experimental error, though, the excess width does not depend on the domain size. In contrast, the brush height decreases more and more when the domain size falls below a certain value. Simple considerations point to a geometrical scaling relation between height and width of the polymer brushes. These results are considered as essential for implementation of SIP routines in laser-assisted fabrication schemes targeting micro- and nanofluidic applications.

We report on the formation of self-supporting, double stimuli-responsive ultrafiltration membranes via the non-solvent-induced phase separation (NIPS) process. The polymers, polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA), were synthesized via living anionic polymerization in THF using sec-butyllithium as initiator. Two amphiphilic diblock copolymers were used, S(81)D(19)(75) and S(68)D(32)(100). The membranes were cast from mixtures of THF and DMF. The influence of the solvent composition, the "open-time" before immersion into the coagulation bath, and the casting film thickness onto the membrane morphology were thoroughly investigated, and flux values obtained for the different membrane systems were compared. The higher content in hydrophilic polymer for S(68)D(32)(100) resulted in a better compatibility with the nonsolvent bath consisting of water, leading to a slower precipitation and thus an improved control of the phase separation occurring. Under certain conditions, ordered microphase-separated porous morphologies were observed in parts of the membrane cross-section. Further, the "smart" properties of those novel materials are shown for two representative systems. It could be demonstrated that both stimuli for PDMAEMA, pH and temperature, can be reversibly and independently applied in order to significantly change the transmembrane water flux.

A new method for surface-initiated atom transfer radical polymerization (ATRP) on the technical polymer poly(ethylene terephthalate) (PET) has been developed which allows controlling and estimating the layer thickness of the grafted polymer in the isocylindrical pores of track-etched membranes. After PET surface treatment by oxidative hydrolysis, the bromoalkyl initiator was immobilized on the PET surface in a two-step solid-phase reaction; the isoporous membrane structure was preserved, and the pore diameter was increased from 760 to 790 nm. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted under ATRP conditions from a methanol/water mixture at room temperature. Both monomer concentration and reaction time could be used as parameters to adjust the degree of grafting. Effective grafted layer thickness and its response to temperature were estimated from pure water permeability. All data, especially the high polymer densities (0.37 g/cm3) in the swollen layers at 25 degrees C, indicate that grafted PNIPAAm with a "brush" structure has been achieved. For dry PNIPAAm layer thicknesses on the PET pore walls of up to 80 nm, a temperature-induced swelling/deswelling ratio of approximately 3 had been observed. Reduction of the brush grafting density, via composition of the reaction mixture used in solid-phase synthesis for initiator immobilization, led to an increase of that swelling/deswelling ratio. Further, density and temperature response of the grafted PNIPAAm layers synthesized via ATRP were compared with those obtained in the same membranes by less controlled photografting, leading to lower grafting density and larger gradients in grafted layer density and, consequently, much higher swelling/deswelling ratios (>15).

Highly fouling-resistant ultrafiltration (UF) membranes were synthesized by heterogeneous photograft copolymerization of two water-soluble monomers, poly(ethylene glycol) methacrylate (PEGMA) and N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPE), with and without cross-linker monomer N,N'-methylene bisacrylamide (MBAA), onto a polyethersulfone (PES) UF membrane. The characteristics, the stability, and the UF separation performance of the resulting composite membranes were evaluated in detail. The membranes were characterized with respect to membrane chemistry (by ATR-IR spectroscopy and elemental analysis), surface wettability (by contact angle), surface charge (by zeta potential), surface morphology (by scanning electron microscopy), and pure water permeability and rejection of macromolecular test substances (including the "cutoff" value). The surface chemistry and wettability of the composite membranes did not change after incubating in sodium hypochlorite solution (typically used for cleaning UF membranes) for a period of 8 days. Changes in water permeability after static contact with solutions of a model protein (myoglobin) were used as a measure of fouling resistance, and the results suggest that PEGMA- and SPE-based composite membranes at a sufficient degree of graft modification showed much higher adsorptive fouling resistance than unmodified PES membranes of similar or larger nominal cutoff. This was confirmed in UF experiments with myoglobin solutions. Similar results, namely, a very much improved fouling resistance due to the grafted thin polymer hydrogel layer, were also obtained in the UF evaluation using humic acid as another strong foulant. In some cases, the addition of the cross-linker during modification could improve both permeate flux and solute rejection during UF. Overall, composite membranes prepared with an "old generation" nonfouling material, PEGMA, showed better performance than composite membranes prepared with a "new generation" one, the zwitterionic SPE.

Poly(ethylene terephthalate) (PET) track-etched membranes with average pore diameters of 692 and 1629 nm were functionalized using the monomer N-isopropylacrylamide (NIPAAm) and a photoinitiated "grafting-from" approach in which a surface-selective reaction has been most efficiently achieved by combinations of the unmodified PET surface with benzophenone and, alternatively, of an aminated PET surface with benzophenone carboxylic acid. Consistent estimations of the pore diameters of the base PET membranes and of the effective grafted polyNIPAAm layer thicknesses on the PET pore walls were possible only on the basis of the permeabilities measured with aqueous solutions of higher ionic strength (e.g., 0.1 M NaCl). However, the permeabilities measured with ultrapure water indicated that the "electroviscous effect" was significant for both base membranes. The influences of membrane pore diameter, surface charge, and solution ionic strength could be interpreted in the framework of the space-charge model. Functionalized membranes with collapsed grafted polymer hydrogel layer thicknesses of a few nanometers exhibited almost zero values of the zeta potential estimated from the trans-membrane streaming potential measurements. This was caused by a "hydrodynamic screening" of surface charge by the neutral hydrogel. Very pronounced changes in permeability as a function of temperature were measured for PET membranes with grafted polyNIPAAm layers, and the effective layer thickness in the swollen state--here up to approximately 300 nm--correlated well with the degree of functionalization. The subtle additional effects of solution ionic strength on the hydrodynamic layer thickness at 25 degrees C were different from the effects for the base PET membranes and could be explained by a variation in the degree of swelling, resembling a "salting-out" effect. Overall, it had been demonstrated that the functionalized capillary pore membranes are well suited for a detailed and quantitative evaluation of the relationships between the synthesis, the structure, and the function of grafted stimuli-responsive polymer layers.

We report about the surface modification of polystyrene (PSt) with photoreactive alpha-4-azidobenzoyl-omega-methoxy poly(ethylene glycol)s (ABMPEG) of three different molecular weights (MWs of approximately 2, approximately 5, and approximately 10 kg/mol) and with two poly(ethylene glycol)/poly(propylene glycol) triblock copolymers (PEG-PPG-PEG) of about identical PEG/PPG ratio (80/20, w/w) and MW(PEG) of approximately 3 and approximately 6 kg/mol, all via adsorption from aqueous solutions. For ABMPEGs, an additional UV irradiation was used for photografting to the PSt. Contact angle (CA) and atomic force microscopy data revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surfaces as a function of PEG type and concentration used for the modification. In all cases, an incomplete coverage of the PSt was observed even after modification at the highest solution concentrations (10 g/L). However, clear differences were seen between PEG-PPG-PEGs and ABMPEGs; only for the latter was a nanoscale-ordered interphase structure with an influence of MW(PEG) on the PEG density observed; after modification at the same solution concentrations, the density was significantly higher for lower MW(PEG). The adsorption of three proteins, myoglobin (Mgb), bovine serum albumin (BSA), and fibrinogen to the various surfaces was analyzed by surface plasmon resonance. Pronounced differences between the two PEG types with respect to the reduction of protein adsorption were found. At high, but still incomplete, surface coverage and similar CA, the shielding of ABMPEG layers toward the adsorption of Mgb and BSA was much more efficient; e.g., the adsorbed Mgb mass relative to that of unmodified PSt was reduced to 10% for ABMPEG 2 kg/mol while for both PEG-PPG-PEGs the Mgb mass was still around 100%. In addition, for the ABMPEG layers an effect of MW(PEG) on adsorbed protein mass-decrease with decreasing MW-could be confirmed; and the highest Mgb/BSA selectivities were also observed. A "two-dimensional molecular sieving", based on PEG molecules having a nanoscale order at the hydrophobic substrate polymer surface has been proposed, and the main prerequisites were the use of PEG conjugates which are suitable for an "end-on" grafting (e.g., ABMPEGs), the use of suitable (not too high) concentrations for the surface modification via adsorption/self-assembly, optionally the photografting on the substrate (possible only for ABMPEG), and presumably, a washing step to remove the excess of unbound PEGs. The results of this study also strongly support the hypothesis that the biocompatibility of hydrophobic materials can be very much improved by PEG modifications at surface coverages that are incomplete but have an ordered layer structure controlled by the size and steric interactions of surface-bound PEGs.

Measurements of transient membrane potential after current switch-off have been used to study the electrochemical and other transport properties of nanoporous track-etched membranes (pore diameter of 24 nm) in KCl solutions of various concentrations. Due to their identical straight cylindrical pores within the nanorange, those membranes are a suitable object for the studies of fundamentals of nanofluidics. We have developed a theory, which enabled us to interpret the transients of membrane potential in terms of such properties as the ion transport numbers, the membrane diffusion permeability, and the specific chemical capacity. The fitted values have been further interpreted within the scope of the space-charge model and revealed good self-consistency. The dependence of fitted values of the surface charge density on salt concentration was in agreement with the mechanism of fixed charge formation due to the dissociation of weakly acidic groups, and the surface charge density corresponded well to the measurements by an independent method. Thus, our measurements have revealed a quantitative applicability of standard space-charge model to the description of electrochemical phenomena and electrolyte diffusion in straight cylindrical pores of tens of nanometers in diameter. Proceeding from our data, we could estimate the limiting current densities for our nanofluidic system. They have turned out to be more than 2 orders of magnitude lower than usually encountered in microfluidic systems with electro-osmotic fluid delivery. That finding may point to a considerable handicap in the application of such nanofluidic elements in microsystems.