Cover Picture

The cover picture shows nanometer‐thin elastomeric membranes made from polyisobutene star polymers with ionic head groups. Spreading of the polymers onto a water surface yields fluid monolayers. These can be transferred to cover openings in solid substrates. After transfer, the ionic head groups aggregate, cross‐link the membrane, and thus give rise to elastomeric properties. For example applying a small overpressure from one side gives rise to comparatively large, reversible deformations. These elastomeric membranes could be used in micromechanical devices such as membrane pumps and valves. More details on these membranes are reported by F. Mallwitz and W. Goedel on pages 2645 ff.     

Monolayers of a solvent-free polymer brush: Part 2. Crosslinking and transfer to form suspended films

Hydrophobic polymers with low glass transition temperature (polyisoprenes) and a single head group (sulfonate) bearing photoreactive side groups (anthracene) have been synthesised and characterised as insoluble monolayers on a water surface. The isotherms are similar to those of the parent polymers without anthracene side groups and the films can be transferred to solid substrates via the Langmuir-Blodgett technique with a transfer ratio of 0.85. The films on solid substrates as well as on the water surface can be crosslinked via irradiation with ultraviolet light. Films crosslinked on the water surface can be transferred to copper grids. The films span the openings of the grids and damaged parts of the suspended films have round borders. Irradiation of the monolayers through a mask followed by solvent treatment gives rise to laterally structured monolayers.     

Effectiveness of cell adhesive additives in different supramolecular polymers

Supramolecular motifs in elastomeric biomaterials facilitate the modular incorporation of additives with corresponding motifs. The influence of the elastomeric supramolecular base polymer on the presentation of additives has been sparsely examined, limiting the knowledge of transferability of effective functionalization between polymers. Here it was investigated if the polymer backbone and the additive influence biomaterial modification in two different types of hydrogen bonding supramolecular systems, that is, based on ureido-pyrimidinone or bis-urea units. Two different cell-adhesive additives, that is, catechol or cyclic RGD, were incorporated into different elastomeric polymers, that is, polycaprolactone, priplast or polycarbonate. The additive effectiveness was evaluated with three different cell types. AFM measurements showed modest alterations on nano-scale assembly in ureido-pyrimidinone materials modified with additives. On the contrary, additive addition was highly intrusive in bis-urea materials. Detailed cell adhesive studies revealed additive effectiveness varied between base polymers and the supramolecular platform, with bis-urea materials more potently affecting cell behavior. This research highlights that additive transposition might not always be as evident. Therefore, additive effectiveness requires re-evaluation in supramolecular biomaterials when altering the polymer backbone to suit the biomaterial application.     

Patterning molecularly thin films of polymers—new methods for photolithographic structuring of surfaces

Three novel photolithographic processes for patterning of molecularly thin polymer films are described. The polymer monolayers are prepared by immobilization of initiator molecules to surfaces of solid substrates followed by thermally or photochemically activated radical chain polymerization. Thus polymer chains which are covalently linked to the surfaces of the substrates are obtained. The films can be patterned using appropriate masks and deep or near UV irradiation before, during or after polymer formation. The procedures described in this paper allow the chemical tailoring of surfaces with high spatial resolution. Step-and-repeat procedures, which take advantage of the covalent linking of the polymers to the surfaces, permit the preparation of multifunctional polymer patterns.     

Photo-attaching functional polymers to cellulose fibers for the design of chemically modified paper

We introduce a novel approach for preparing polymer-modified and chemically microstructured paper substrates by a photo-chemical attachment of functional polymers to cellulose microfibers inside model filter papers. Poly(methyl methacrylate), PMMA copolymers, which carry a defined amount of photo-reactive benzophenone functional groups, are adsorbed to paper substrates from solution by a simple dip coating process, followed by covalent attachment of the physisorbed polymers through UV-light irradiation. Non-bound macromolecules can be removed from paper sheets by simple solvent extraction, and the resulting polymer-modified substrates were analysed with respect to chemical identity, attached polymer mass, and homogeneity of the polymer attachment. The amount of paper-attached polymers can be conveniently controlled in a wide range from a few mg/g cellulose fiber up to several tenth of mg/g cellulose fiber, by adjusting the polymer concentration in the coating solution. Polymers are being attached by photo-chemical means, and chemical micro patterns on paper can be designed by lithographical means. In first proof-of-concept studies, millimeter-scale channels were prepared that can be used to control fluid penetration by capillary actions. Because of the modularity in the design of photo-reactive polymers, a number of different chemically microstructured papers can be envisioned which may become potentially interesting in lab-on-paper devices.     

Perforated, freely suspended layer-by-layer nanoscale membranes

Ultrathin, perforated, and freely suspended membranes with uniform nanopores in the range of tens of nanometers have been fabricated using a fast, simple method of spin-assisted layer-by-layer assembly on hydrophobic substrates. Membranes with thicknesses down to 20 nm were robust enough to be released from the sacrificial substrates, transferred onto various surfaces, and suspended over microscopic openings. The nanopore size can be controlled by tuning the number of polyelectrolyte bilayers, spinning speed, and a proper selection of hydrophobic substrates. We demonstrate that the formation of nanopores is caused by the partial dewetting of polyelectrolyte layers in the course of their deposition on the underlying hydrophobic surfaces. The nanoscale thickness of perforated membranes with relatively uniform size and a high concentration of nanopores provides perspectives for higher rates of transport through freely suspended LbL membranes. The highly perforated LbL membranes introduced here can serve as a novel platform for ultrafine separation considering an intriguing combination of nanopores, nanoscale membrane thickness, and easy functionalization.     

Solid-supported biomimetic membranes with tailored lipopolymer tethers

Stable lipid membranes with controlled substrate-membrane spacing can be prepared using well-defined lipopolymers as a tether. Based on the living cationic ring-opening polymerization of 2-methyl- or 2-ethyl-2-oxazoline, lipopolymers can be synthesized bearing a lipid head group as well as a silanol reactive coupling end group. Using a “grafting onto” procedure these polymers can form dense, brush like monolayers, whose layered structures can be obtained by x-ray reflectivity measurements. By transfer of a pre-organized monolayer that is followed by vesicle fusion, stable polymer supported lipid membranes can be prepared. The substrate-membrane spacing can be controlled via the degree of polymerization, while the lateral diffusion of lipids within the membrane depends on the density of polymer tethers. Preliminary experiments implied that the membrane with long (N = 40) polymer tethers could reside trans-membrane receptors homogeneously, suggesting a large potential of this strategy.     

Reconstitution of the Torpedo californica nicotinic acetylcholine receptor into planar lipid bilayers

Detergent-solubilized acetylcholine receptor (nAcChR) proteins can be purified by affinity chromatography and reconstituted into lipid vesicles and afterwards into planar lipid bilayer membranes via, in principle, two methods: fusion or assembly from two vesicle-spread monolayers. In the presence of agonists (carbamoylcholine, suberoyldicholine) different kinds of channel openings are recorded: fast single channels, bursts and long openings with short closures in between. Similar results have been obtained with reconstituted membrane fragments rich in nAcChR. In addition, Torpedo californica nAcChR proteins give rise to fuzzy channels and less defined events of conductivity, which “reemerge” again all the time. Frequently the channel events have conductance levels of about 200 to 300 pS, obviously simultaneous openings of several aggregated receptors. Under these conditions 40 pS conductance events occur also. It appears that the conductance of the channels measured is a multiple of 6.3 pS. Often, with the same sample, no channel openings are seen. Contrary to patch-clamp investigations on whole cells, AcChR-channel openings in reconstituted systems occur only several minutes after agonist application and not immediately. It is not clear whether the “reconstituted channels” reflect rapid activation or whether they result from desensitized receptor states only. Although a clear-cut correlation of channel event and channel protein unit is only possible by reconstitution of the biochemically characterized protein, e.g. monomer, dimer or higher oligomers, the reconstitution technique is still in its infancy.     

Interfacial rheology of polyelectrolytes and polymer monolayers at the air–water interface

In this review, we describe interfacial rheology studies of polymer monolayers at the air–water interface. Since polyelectrolytes are usually soluble in water, the formation of surface monolayers requires the presence of a surfactant of opposite charge. The first part of the review is dedicated to these mixed monolayers. The second part is related to neutral monolayers that can be either adsorbed or deposited at the interface. Interfacial rheology studies of these systems are still scarce, despite a considerable interest: insoluble polymer monolayers in two dimensions are suitable model systems for the tests of polymer theories in two dimensions, such as and glass transition. The rheology of soluble polymer monolayers has important connections with the dynamic properties of dispersions stabilized with these polymers.     

Chemically resistant microfluidic valves from Viton® membranes bonded to COC and PMMA

We present a reliable technique for irreversibly bonding chemically inert Viton? membranes to PMMA and COC substrates to produce microfluidic devices with integrated elastomeric structures. Viton? is widely used in commercially available valves and has several advantages when compared to other elastomeric membranes currently utilised in microfluidic valves (e.g. PDMS), such as high solvent resistance, low porosity and high temperature tolerance. The bond strength was sufficient to withstand a fluid pressure of 400 kPa (PMMA/Viton?) and 310 kPa (COC/Viton?) before leakage or burst failure, which is sufficient for most microfluidic applications. We demonstrate and characterise on-chip pneumatic Viton? microvalves on PMMA and COC substrates. We also provide a detailed method for bonding fluorinated Viton? elastomer, a highly chemically compatible material, to PMMA and COC polymers. This allows the production of microfluidic devices able to handle a wide range of chemically harsh fluids and broadens the scope of the microfluidic platform concept.     

Fabrication and characterization of multilayer films from amphiphilic poly(p-phenylene)s

Over the past two decades, considerable efforts have been devoted to the development of conjugated polymeric materials for electronic applications due to the tunability of their properties through variation of their chemical structure. The LB technique is one of the most effective and precise methods for controlling the organization and thereby the properties of polymer films at the nanoscale for device fabrication. A detailed study was performed on the Langmuir-Schaefer (LS) monolayer and Langmuir-Blodgett-Kuhn (LBK) multilayer formation of newly designed conjugated poly(p-phenylene)s (C(n)PPPOH), incorporated with alkoxy groups with different chain lengths (C(6)H(13)O-, C(12)H(25)O-, and C(18)H(37)O-) and hydroxyl groups on the polymer backbone. The monolayer formed at the air-water interface was characterized using surface pressure-area isotherms, including hysteresis measurements. The films were then transferred to different hydrophilic solid substrates and analyzed using surface plasmon resonance spectroscopy, UV-vis spectroscopy, fluorescence spectroscopy, and AFM measurements. The results showed that the polymer with a short alkoxy chain (C(6)PPPOH) forms uniform monolayers at the air-water interface and can be transferred as multilayer films compared to C(12)PPPOH and C(18)PPPOH. The observed film thicknesses measured by SPR and AFM studies were similar to the theoretical value obtained in the case of C(6)PPPOH, whereas this was not the case with the other two polymers. The present study shows that the polymer C(n)PPPOH with short alkoxy chain can be transferred onto different solid substrates for device fabrication with molecular level control.     

Rigid Lipid Membranes and Nanometer Clefts: Motifs for the Creation of Molecular Landscapes

Amphiphilic lipids associate in water spontaneously to form micelles, vesicles, monolayers, or biological membranes. These aggregates are soft and their shape can be changed easily. They behave like complex fluids because they are merely held together by weak, nondirected forces. The most important characteristic of these monolayers is their ability to dissolve hydrophobic molecules in the form of freely movable monomers. The fluid molecular layers are not suitable to anchor the components of chain reactions. However, if the alkyl chains are replaced by rigid skeletons or if the head groups are connected through intermolecular interactions, the aggregates become rigid and their fluid solvent character is lost. The construction of chiral surfaces by synkinesis (synthesis of noncovalent compounds) and of enzyme‐type surface clefts of defined size can now be carried out by using rigid lipid membranes. Monolayers and nanometer pores on solid substrates attain sharp edges, and upright nanometer columns on smooth surfaces no longer dissipate. Five examples illustrate the advantages of using rigid molecular assemblies: 1) Cationic domains of rigid edge amphiphiles in fluid membranes act as manipulable ion channels. 2) Spherical micelles, micellar helical fibers, and vesicular tubes can be dried and stored as stable material. Molecular landscapes form on smooth surfaces. 3) α,ω‐Diamide bolaamphiphiles form rigid nanometer‐thick walls on smooth surfaces and these barriers cannot be penetrated by amines. Around steroids and porphyrins, they form rigid nanometer clefts whose walls and water‐filled centers can be functionalized. 4) The structure of rigid oligophenylene‐ and quinone monolayers on electrodes can be changed drastically and reversibly by changing the potential. 5) 10¹⁰ Porphyrin cones on a 1‐cm² gold electrode can be controlled individually by AFM‐ and STM‐tips and investigated by electrochemical, photochemical, and mechanical means. In summary, rigid monolayers and bilayers allow the formation of a great variety of membrane structures that cannot be obtained from classical fluid alkyl amphiphiles.     

Reversible activation of diblock copolymer monolayers at the interface by pH modulation, 2: Membrane interactions at the solid/liquid interface

A monolayer of the pH-responsive poly[2-(dimethylamino)ethyl methacrylate-block-methyl methacrylate] diblock copolymer [PDMAEMA-PMMA] was transferred from the air/water interface to a silicon substrate for evaluation as a tunable interlayer between biological material and solid substrates. Specular neutron reflectivity experiments revealed that the weak polyelectrolyte PDMAEMA chains at the solid/liquid interface can be reversibly activated by pH modulation. The thickness, scattering length density, and surface roughness of the polymer film can be systematically controlled by pH titration. As a simple model of plasma membranes, a lipid bilayer was deposited onto the polymer film. The membrane-substrate interaction was characterized by neutron reflectivity experiments, demonstrating that the membrane-substrate distance could be reversibly regulated by pH titration. These results confirm the potential of stimuli-responsive polymers for precise control of cell-surface interactions.     

Influence of molecular weight on stepwise collapse of Langmuir monolayers of cyclolinear polyorganosiloxanes

 The series of hexacyclo-linear polyorganosiloxanes containing methyl and phenyl side groups, which differ by molecular weight and tacticity, were analyzed for the dependence of surface pressure on surface area per monomer unit. The effects of temperature and the nature of substrate were also investigated. All the polymers investigated are capable of forming Langmuir monolayers on the surfaces of liquid substrates. Being under compression, the monolayers of these polymers are able to form discrete multilayers. This property is closely related to the existence of thermodynamically stable mesophase in cyclolinear polyorganosiloxanes. It has been established that formation of the multilayers in these polymers is quite sensitive to the molecular weight of the polymer. This effect is explained by a change in the value of the shear module of the polymer with molecular weight. Received: 2 March 1998 Accepted: 20 July 1998     

含杯芳烃聚合物的合成与应用

杯芳烃在主客体化学中是继冠醚和环糊精之后被广泛关注的第三代主体分子,能够选择性地与客体分子或离子形成络合物。近年来,含杯芳烃聚合物逐渐受到人们的重视。结合聚合物稳定性好,易于加工的特性,含杯芳烃聚合物将有望被开发成为新型功能高分子材料。本文详细介绍了含杯芳烃聚合物的合成及其应用。     

Flexible fabrication and applications of polymer nanochannels and nanoslits

Fluidic devices that employ nanoscale structures (<100 nm in one or two dimensions, slits or channels, respectively) are generating great interest due to the unique properties afforded by this size domain compared to their micro-scale counterparts. Examples of interesting nanoscale phenomena include the ability to preconcentrate ionic species at extremely high levels due to ion selective migration, unique molecular separation modalities, confined environments to allow biopolymer stretching and elongation and solid-phase bioreactions that are not constrained by mass transport artifacts. Indeed, many examples in the literature have demonstrated these unique opportunities, although predominately using glass, fused silica or silicon as the substrate material. Polymer microfluidics has established itself as an alternative to glass, fused silica, or silicon-based fluidic devices. The primary advantages arising from the use of polymers are the diverse fabrication protocols that can be used to produce the desired structures, the extensive array of physiochemical properties associated with different polymeric materials, and the simple and robust modification strategies that can be employed to alter the substrate's surface chemistry. However, while the strengths of polymer microfluidics is currently being realized, the evolution of polymer-based nanofluidics has only recently been reported. In this critical review, the opportunities afforded by polymer-based nanofluidics will be discussed using both elastomeric and thermoplastic materials. In particular, various fabrication modalities will be discussed along with the nanometre size domains that they can achieve for both elastomer and thermoplastic materials. Different polymer substrates that can be used for nanofluidics will be presented along with comparisons to inorganic nanodevices and the consequences of material differences on the fabrication and operation of nanofluidic devices (257 references).     

Multivalent host-guest interactions between beta-cyclodextrin self-assembled monolayers and poly(isobutene-alt-maleic acid)s modified with hydrophobic guest moieties

Poly(isobutene-alt-maleic acid)s modified with p-tert-butylphenyl or adamantyl groups interact with beta-cyclodextrin self-assembled monolayers (beta-CD SAMs) by inclusion of the hydrophobic substituents in the beta-cyclodextrin cavities. The adsorption was shown to be strong, specific, and irreversible. Even with a monovalent competitor in solution, adsorption to the beta-CD SAMs was observed, and desorption proved impossible. The adsorbed polymer layer was very thin as evidenced by surface plasmon resonance spectroscopy and AFM. Apparently, all or most hydrophobic groups of the polymers were employed efficiently in multivalent binding, as was further supported by the absence of specific binding of beta-CD-modified gold nanoparticles to the polymer surface assemblies. Supramolecular microcontact printing of the polymers onto the beta-CD SAMs led to assembly formation in the targeted areas of the substrates.     

Amphiphilic diacetylenes with pyridine and 2,2′-bipyridine headgroups — polymerization properties in the crystalline state,in LB-multilayers,and in complexes with transition metal salts. Morphology of polymerized multilayers

Synthesis, amphiphilic properties and polymerization behaviour of a variety of single and double chain esters of pyridine- and 2,2-bipyridine-carboxylic acids containing the diacetylene moiety are described. Conversion versus⁶⁰Co--ray dose curves indicate significant differences in solid-state reactivity of the individual compounds. The esters of isonicotinic acid form polymers that are soluble in chloroform. The monomers can be converted into salt derivatives and transition metal complexes, some of which are characterized concerning their solid state reactivity.Esters of isonicotinic acid form stable monolayers if spread onto neutral or acidified aqueous subphases at temperatures 15 °C. These monolayers can be deposited on substrates by the Langmuir-Blodgett technique and subsequently be UV-polymerized. In addition, attempts are reported to form polymeric mono- and multilayers by spreading the soluble polymeric amphiphiles at the air-water interface and subsequently transferring the films onto substrates.The two types of polymeric films exhibit morphologies that are significantly different. Polarizing micrographs indicate a domain structure of randomly shaped crystallites of only a few micrometers in diameter for LB-monolayers built up as monomers and polymerized on the substrate. On the other hand, polymer films built up as polymers are inhomogeneous and do not actually represent monomolecular films.     

Characterisation of LB multilayers of soluble phthalocyaninatopolysiloxane

Tetra(methoxy)tetra(octyloxy)phthalocyaninatopolysiloxane (PcPS), a soluble rigid-rod polymer, forms stable monolayers on water, which can be transferred onto solid substrates. The orientation of the polymer in the transferred layers is induced by the flow on the water subphase. If a convergent flow is induced, the molecules will be aligned parallel to the dipping direction. A DC-conductivity of 10⁻⁷ S · cm⁻¹ was measured for the undoped films. Measurements with an <HG/PcPS/ITO> sandwich structure show rectification and hysteresis characteristics. PcPS modified by terminal double bonds in the side chains can be crosslinked by UV irradiation. Patterns can be developed in these films using a negative photoresist technique.     

Some aspects of the control of physico-mechanical properties of polymer compositions with elastomeric inclusions

The paper reviews the author's works on the regulation of physico-mechanical properties of polymer compositions with elastomeric inclusions. The factors, determining the modification efficiency of elastomeric inclusions in epoxy matrices, are analyzed. The regularities of the phase separation in curing system and the control of the interface interaction and morphology of epoxy polymers with elastomeric inclusions are considered.