Deposited Polymer Layers Research Articles

Self-Sanitizing Polycaprolactone Electrospun Nanofiber Membrane with Ag Nanoparticles.

The objective of this research was to develop an environment-friendly and scalable method for the production of self-sanitizing electrospun nanofibers. This was achieved by immobilizing silver nanoparticles (Ag NPs) onto plasma-treated surfaces of biodegradable polycaprolactone (PCL) nanofibers. The plasma deposited polymer layer containing carboxyl groups played a critical role in providing a uniform distribution of Ag NPs on the nanofiber surface. Ag ions were absorbed by electrostatic interaction and then reduced under the action of UV-light. The concentration and release of Ag ions were analyzed using the EDXS/XPS and ICP AES methods, respectively. Although high levels of Ag ions were detected after 3 h of immersion in water, the material retained a sufficient amount of silver nanoparticles on the surface (~2.3 vs. 3.5 at.% as determined by XPS), and the release rate subsequently decreased over the next 69 h. The antipathogenic properties of PCL-Ag were tested against gram-negative and gram-positive bacteria, fungi, and biofilm formation. The results showed that the PCL-Ag nanofibers exhibit significant antimicrobial activity against a wide range of microorganisms, including those that cause human infections. The incorporation of Ag NPs into PCL nanofibers resulted in a self-sanitizing material that can be used in variety of applications, including wound dressings, water treatment, and air filtration. The development of a simple, scalable, and environmentally friendly method for the fabrication of these nanofibers is essential to ensure their widespread use in various industries. The ability to control the concentration and release rate of Ag ions in the PCL nanofibers will be critical to optimize their efficacy while minimizing their potential toxicity to human cells and the environment.

ИССЛЕДОВАНИЕ ПОЛИМЕР-ПОЛИМЕРНЫХ ИНТЕРФЕЙСОВ МЕТОДОМ АТОМНО-СИЛОВОЙ МИКРОСКОПИИ

The results of an experimental study of polymer-polymer interfaces in submicron films of polydiphenylene phthalide are presented. Using atomic force microscopy, it was found that polymer films have an internal structure, and the structural elements have the shape of spheroids. The properties of the polymer and the nature of the observed images made it possible to use a model of brittle polymer fracture to describe the results. A model of the formation of interface layers at the interface between the elements of the supramolecular structure and between sequentially deposited polymer layers is proposed. It was found that a transition layer with a thickness of about 10-20 nm formed by lateral fragments of polymer molecules is formed in the interface region.

Electropolymerization of thiazole derivatives bearing thiophene and selenophene and the potential application in capacitors

• Three thiazole derivatives bearing thiophene and selenophene were used as monomers for electropolymerization. • Pseudocapacitor performance of deposited polymer layers was investigated on macroelectrode and ultramicroelectrode. • Pseudocapacitor behavior is related to the anion intercalation/deintercalation processes by faradaic reactions of oligomer chains. • The approximate molecular weight of the solvated anion and the number of solvent molecules surrounding a solvated anion were analyzed. Three thiazole derivatives bearing thiophene and selenophene are synthesized and used as monomers for electropolymerization. The electropolymerization process is studied using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) techniques. Deep understanding is obtained regarding the pseudocapacitor performance of deposited polymer layers by subjecting the macroelectrode and ultramicroelectrode to CV and galvanostatic charging–discharging experiments in three kinds of electrolytes. Notably, the highest specific capacitance is observed in the derivative bearing selenopheno[3,4- d ]thiazole and selenophene in a solution of tetrabutylammonium tetrafluoroborate. Furthermore, the electropolymerization rate is influenced by the kind of chalcogenophene and the CV scan rate. A spectroelectrochemistry experiment reveals the optical and electrochromic behavior of the deposited polymer layers. From these results, the pseudocapacitor performance of the deposited polymer layers is related to anion intercalation/deintercalation processes by faradaic reactions of oligomer chains. The EQCM experiments also reveal these processes during electropolymerization and anion intercalation/deintercalation into the deposited polymer layers. Finally, the approximate molecular weight of the solvated anion and the number of solvent molecules surrounding a solvated anion are analyzed using the EQCM data.

PH-Responsive PEG/PAA Multilayer Assemblies for Reversible Adhesion of Micro-Objects

Manipulating micro-objects plays a crucial role in a wide range of fundamental and applied research works. Here, we propose an original strategy based on the chemical modification of a substrate by hydrogen-bonded films elaborated by layer-by-layer (LbL) assemblies of poly(ethylene glycol) (PEG) and poly(acrylic acid) (PAA). First, the influence of the polymer molecular weight on the growth of the PEG/PAA multilayer was evaluated. Optical reflectometry analysis used to follow in situ the film buildup revealed a strong dependence of the deposited amount of polymer on the ratio of monomer units of each polymer (nPAA/nPEG). Then, colloidal probe atomic force microscopy (AFM) microscopy was carried out in an aqueous medium to monitor the adhesion forces of multilayer surfaces composed of N polymer layers. Pull-off forces were converted using the Johnson–Kendall–Roberts (JKR) model to access the thermodynamic work of adhesion. Results indicated that PEG/PAA multilayer films exhibit weak adhesion forces that are sensitive to the number of deposited polymer layers at pH 2. In addition, a progressive increase of the solution pH reduced the adhesion due to the destruction of the hydrogen-bonded multilayer film. To simulate the capture and the release of a micro-object, borosilicate particles acting as spherical micro-objects were adsorbed onto a PEG/PAA film. Once again, an increase of the solution pH led to desorption of particles, as shown by optical microscopy. Finally, an AFM tip functionalized by a PEG/PAA multilayer was used to achieve successful micromanipulation operations (capture and release) of a 10 μm diameter borosilicate sphere in an aqueous solution.

Electropolymerization of thiazole derivative bearing thiophene and its application in capacitors and electrochromic devices

A thiazole derivative bearing thiophene as a monomer compound was synthesized and electropolymerized at carbon, gold, platinum, and fluorine doped tin oxide electrodes. From an in-depth analysis of cyclic voltammograms at several scan rates, deposited polymer layers, comprising thiophene functional groups, were shown to clearly exhibit capacitive behavior. This property is related to anion intercalation into these layers during charging and was demonstrated in this study using electrochemical quartz crystal microbalance experiments. It was also shown that in the case of both tetrafluoroborate and hexafluorophosphate anions, the molar ratio of monomers to anions was approximately 1:0.6, which is estimated as the ratio of anion intercalation into thiophene moiety of the polymer layers. This confirms that the capacitance properties of these deposited polymer layers have high stability against electrochemical perturbation. Furthermore, spectroelectrochemistry data obtained during this study indicate that these layers also have switchable electrochromic properties in the visible range.

Formation of Diode-Like Composite Membranes by Plasma Polymerization

A method for the preparation of polymer “diode-like” composite membranes with a conduction asymmetry in electrolyte solutions (rectification effect) exhibited under different orientations of the membranes in an electric field is examined. To produce such membranes with diode-like properties, thin polymer films formed by plasma polymerization of organic precursors were deposited onto one side of a track membranes made of poly(ethylene terephthalate) and polypropylene used as a porous substrate. It is established that the achievement of asymmetric conduction is mainly caused by change in the geometry of pores owing to a substantial decrease in their diameter in the deposited polymer layer, as well by an interface between the initial membrane and deposited polymer layer in the pores. It is shown that, in the case of a hydrophobic polymer layer, for the description of the electrochemical properties of the membranes, along with the consideration of electrostatic interaction between the electrolyte ions and the charge of pore walls, one should take into account the phenomenon of electrolyte slipping along the hydrophobic surface. The revealed effects indicate a possible way to create composite membranes with conduction asymmetry for their use in developing various feedback systems, as well as chemical and biochemical sensors.

Composite membranes with the hydrophobic and hydrophilic layers

The synthesis and characterization of polymer composite membranes with hydrophilic porous substrate and hydrophobic top layer were studied. To prepare the composite membranes a polytetrafluoroethylene thin film has been applied by the technique of electron- beam sputtering deposition in vacuum on one side of a poly(ethylene terephthalate) track-etched membrane used as a porous substrate. It was found that polymer deposition on the membrane surface results in the creation of composite membranes that possess asymmetric conductivity in electrolyte solutions – a rectification effect similar to that of a p-n junction in semiconductors. This effect is caused by decreasing the pore diameter in the deposited polymer layer that results in change of the pore geometry, as well as existence in the pores of an interface between two layers with different nature.

RESEARCH OF PROPERTIES OF THE POLYPROPYLENE TRACK MEMBRANES WITH A THIN POLYMER LAYER OBTAINED BY THE METHOD OF ELECTRON BEAM DISPERSION OF POLYTETRAFLUOROETHYLENE IN VACUUM

The surface, structure and electrochemical properties of a polypropylene track membranes with a polymer layer obtained by electron beam dispersion of polytetrafluoroethylene in vacuum has been studied. It has been found that the deposition of the polytetrafluoroethylene layer on the surface leads to the creation of composite membranes that exhibit in electrolyte solutions conductance asymmetry, the rectification effect similar to the p – n junction in semiconductors. It is shown that the observed effect of conductivity asymmetry is caused by a significant decrease in the diameter of pores in the deposited polymer layer and a change in the pore geometry, same as existence of an interface between the initial membrane and polytetrafluoroethylene layer.

Chemical diversity in electrochemically deposited conducting polymer-based sensor arrays

The mammalian olfactory system is highly complex, with more than 1000 non-specific binding receptors. The chemical diversity among these receptors yields differential responses resulting in a ‘fingerprint’ response pattern characteristic of a particular gas phase odorant or mixture. It is through these response-patterns that our brain perceives its chemical environment. While the concept of an electronic nose has been explored over the past several decades, the emergence of integrated circuits analogous to charge-coupled device (CCD) devices with this kind of chemical sensitivity have yet to emerge. One of the main stumbling blocks is the ability to deposit large numbers of chemically diverse sensing layers within large-scale integrated circuits. The use of electronically conducting polymers (ECP) as sensing layers are attractive since they can be electrodeposited on existing fabricated structures without the need for additional lithographic steps, however they are limited by the number of chemically different monomer units available. In this study, we demonstrate the ability to significantly increase the level of diversity through the control of the dopant and the oxidation level of the deposited polymer layers. By using two polymers, several dopants and different oxidation states determined by applied electrochemical potential, fifty-five chemically diverse sensing elements are produced. These results suggest that by using these orthogonal variables, a chemically diverse integrated sensor array chip can be generated through a combinatorial approach of deposition conditions.

Gas chemical sensitivity of a CMOS MEMS cantilever functionalized via evaporation driven assembly

This work demonstrates an electrostatically actuated resonant microcantilever fabricated in a complementary metal oxide semiconductor process and functionalized with a chemically sorbent polymer layer for the detection of volatile organic compounds. Deposition of the chemically sorbent layer is controlled through evaporation-driven assembly. Analytical and finite element analysis models of the deposited polymer layer on the microcantilever resonant frequency and mass sensitivity are presented. Fabrication of the chemical sensor, including a description of polymer deposition through evaporation-driven assembly within a capillary, is detailed. The completely functionalized resonator demonstrates a limit of detection of 1.6 ppm for toluene. An optimal polymer sensitive layer deposition of 42% of the total beam length is measured from frequency instability and sensitivity tests.

Surface modification of biaxially oriented polypropylene (BOPP) film using acrylic acid-corona treatment: Part II. Long term aging surface properties

In this work particular attention has been paid to the aging behavior of biaxially oriented polypropylene (BOPP) film surfaces modified with the acrylic acid (AAc) corona discharge treatment previously reported. Three different corona energies of 15.3, 38.2 and 76.4kJ/m2 were studied. The surface properties of treated films during 90days of aging were compared with those of normal air-corona treated films prepared with the same corona energies. The surface chemical compositions of aged films were analyzed by curve-fitting of the ATR-FTIR spectra. The wettabilities of all aged films were monitored by water contact angle and surface free energy measurements. The change of surface topology of air- and AAc-corona treated films was investigated at 1day, 7days and 90days of aging using the AFM technique. In addition, the surface adhesions of aged films were determined with the T-peeling test. The results showed that the amount of polar functional groups on the surface of aged films had changed. However, the aged films of the AAc-corona treated films still showed greater wettability than did the air-corona treated films and could retain high surface hydrophilicity for more than 90days of aging under ambient condition. The surface topology of both types of aged films changed after aging from a globular structure to a flatter surface, due to mobility of the deposited polymer layer. The AAc-corona treated films showed rougher surfaces due to the influence of poly(acrylic acid) deposition and they could retain the improved surface wettability despite the change in surface topography. The adhesion peel forces of aged films decreased slightly due to the topological changes. A mechanism for the change in surface topography and in chemical functionality of each type of aged film is proposed.

Electrospray ionization for deposition of ultra-thin polymer layers – principle, electrophoretic effect and applications

Nebulizing of polymer solutions, in a high-voltage field under atmospheric conditions by electrospray ionization (ESI), is a comfortable way to deposit ultra-thin layers of polar or ionic polymers onto any conductive substrate materials. The substrate is grounded and the polymer solution is sprayed through a powered capillary. The formed charged droplets shrink by solvent evaporation during their way to the grounded substrate, the charges close ranks and the droplets collapse consecutively by charge repulsion, thus forming finally charged single macromolecules. After their discharging at the grounded substrate, an ultra-thin ‘quasi-monomolecular’ polymer layer is formed. It could be shown by imaging of scratches through the polymer layer by atomic force microscopy that the deposited polymer layers are dense at a thickness of about 10 nm. Carbon fibre bundles were coated with poly(allylamine) (PAAm) or poly(acrylic acid) (PAA) as potential adhesion-promoting layers in fibre–polymer composites. The polymer deposition is self-inhibiting after formation of a continuous coverage of about 200 nm for PAAm and 30 nm for PAA as result of surface charging. Continuous deposition onto such isolating layers or polymers without charging can be achieved by using current of alternating polarity. The film formation is self-healing because of the electrophoretic effect, i.e. the ion discharging occurs preferentially at non-coated areas. This electrophoretic effect of ESI was demonstrated by completely enwrapping all the carbon fibres of the roving within a distance of about 100 μm far from its outside and also at the backside of the fibre bundle with about 80% of the topside coverage, as measured by X-ray photoelectron spectroscopy and visualized using scanning electron microscopy.

Swelling of a hemi-ellipsoidal ionic hydrogel for determination of material properties of deposited thin polymer films: an inverse finite element approach

Selective deposition of polymers at the surface of an ionic hydrogel is conventionally used to tailor properties of the composite material for application in for instance drug release and cell encapsulation. Here we describe a method for determination of the mechanical properties of a thin polymer film deposited on an ionic hydrogel core. The ionic strength-dependent hydrogel swelling is affected by the cross-link density and thickness of the deposited polymer layer. A hemi-ellipsoidal geometry of the hydrogel, corresponding to that employed in proof-of-concept experiments, is used to enforce biaxial deformation of the deposited layer when the ionic hydrogel core is equilibrated at various ionic strengths. The ionic strength dependent equilibrium swelling ratio of the hydrogel with the deposited polymer film is modeled using a finite element approach. The free energy of the hydrogel core includes contributions accounting for polymer mixing, elastic deformation of the network and the Donnan equilibrium. The latter type of contribution is not included in the neutral thin layer in the present study. Adding the polymer multilayer/shell at the surface reveals that the ionic strength-dependent swelling constraint is more pronounced the thicker and stiffer the film is. Combining thickness measurements of the polymer film with high resolution interferometric determination of reduction in swelling capacity of ionic hydrogels, an equivalent elastic property of the polymer layer is obtained using inverse finite element analysis. In the proof-of-concept experiments, analysis of data obtained for chitosan–alginate multilayers composed of four and eight polymer bilayers deposited on an anionic acrylamide-based hydrogel core suggests that these bilayers show an elastic stiffness one order of magnitude larger than that of the hydrogel core.

Morphology and structure of polymer layers protecting dental enamel against erosion

ObjectivesHuman dental erosion caused by acids is a major factor for tooth decay. Adding polymers to acidic soft drinks is one important approach to reduce human dental erosion caused by acids. The aim of this study was to investigate the thickness and the structure of polymer layers adsorbed in vitro on human dental enamel from polymer modified citric acid solutions. MethodsThe polymers propylene glycol alginate (PGA), highly esterified pectin (HP) and gum arabic (GA) were used to prepare polymer modified citric acids solutions (PMCAS, pH 3.3). With these PMCAS, enamel samples were treated for 30, 60 and 120s respectively to deposit polymer layers on the enamel surface. Profilometer scratches on the enamel surface were used to estimate the thickness of the polymer layers via atomic force microscopy (AFM). The composition of the deposited polymer layers was investigated with X-ray photoelectron spectroscopy (XPS). In addition the polymer–enamel interaction was investigated with zeta-potential measurements and scanning electron microscopy (SEM). ResultsIt has been shown that the profilometer scratch depth on the enamel with deposited polymers was in the range of 10nm (30s treatment time) up to 25nm (120s treatment time). Compared to this, the unmodified CAS-treated surface showed a greater scratch depth: from nearly 30nm (30s treatment time) up to 60nm (120s treatment time). Based on XPS measurements, scanning electron microscopy (SEM) and zeta-potential measurements, a model was hypothesized which describes the layer deposited on the enamel surface as consisting of two opposing gradients of polymer molecules and hydroxyapatite (HA) particles. SignificanceIn this study, the structure and composition of polymer layers deposited on in vitro dental enamel during treatment with polymer modified citric acid solutions were investigated. Observations are consistent with a layer consisting of two opposing gradients of hydroxyapatite particles and polymer molecules. This leads to reduced erosive effects of citric acid solutions on dental enamel surfaces.

Active surface modification for iron nanopowders produced by wire electrical explosion

The surface modification of metal iron nanopowders produced by wire electrical explosion (WEE) followed by immediate treatment with hexane, toluene, chloroform, and polymer solutions in hexane and toluene is investigated. It has been shown the nanopowders produced in the inert gas environment are shown to interact due to their active surface both with liquid media and with modifiers dissolved in them. X-ray diffraction and thermal analysis, including mass spectrometry, show that hexane is an inert liquid medium in respect to iron nanopowders, toluene treatment causes carbon deposition into the nanoparticle surface layers, and chloroform chemically interacts with iron nanoparticles with a high yield of FeCl2. Thermal analysis and transmission electron microscopy show that treating nanopowders with an oleic acid (OA) solution in hexane and isoprene rubber and polystyrene solutions in toluene results in the formation of a polymeric coating with a thickness of 3–6 nm at the nanoparticle surface. The polymer amount adsorbed at the surface reaches 0.4 mg/m2 depending on the polymer concentration in the solution. The deposited polymer layer has a loose structure formed by macromolecules adsorbed within the ball conformation.

Tuning the Permeability of Polymer Hydrogel Capsules: An Investigation of Cross-Linking Density, Membrane Thickness, and Cross-Linkers

Nanoengineered poly(methacrylic acid) hydrogel capsules (PMA HCs) are promising candidate carriers for biomedical applications, especially in the areas of drug delivery, encapsulated catalysis, and cell mimicry. The assembly, stability, and degradation of these carriers, as well as their use for the encapsulation of therapeutics, have received considerable attention. However, tailoring the permeability properties of PMA HCs to various types of cargo remains largely unexplored. Herein, we investigate fundamental parameters that govern the structural integrity and the capability of PMA HCs to encapsulate macromolecular cargo. The thiol content of the constituent polymers and the number of deposited polymer layers are shown to be key factors in controlling cargo retention within the PMA HCs. We further introduce a new strategy to achieve disulfide cross-linking for PMA HCs via a thiol-disulfide exchange in order to obtain capsules with superior cargo retention characteristics. Finally, we provide evidence for the semipermeable nature of PMA HCs based on the charge of the solutes and demonstrate that rational design of these systems can yield capsules with specific cargo retention properties. This work contributes toward the development of multilayered polymer capsules and PMA HCs and associated applications in biomedicine.

Interface roughness of plasma deposited polymer layers

The interface roughness of adjacent films which were made by plasma polymerization of hexamethyldisiloxane were investigated. Multilayered structures were made by using different plasma conditions in alteration resulting in different mechanical properties within each layer. Scanning force microscopy on the face side of fractured pieces of the multilayer structures revealed a significant phase contrast between the layers. The direct visualization of the interface using the mechanical contrast between layers allowed the estimation of the interfacial roughness. We found that the interfaces between hexamethyldisiloxane films deposited at a radio frequency (RF) input power of 90 W in the presence of oxygen on top of films made by 48 W without oxygen resulted in an interface roughness of ≈10 nm. In the reverse case, a significantly lower interface roughness of ≈3 nm was determined. We attribute the increase of the interfacial roughness compared to the surface roughness being <1 nm to partial etching of the films by the subsequent deposition process. A key role in the appearance of higher interface roughness plays the RF-input power that determines the cross linking density and the hydrocarbon content in layers.

Ultra-Thin Polymer Layer Deposition by Aerosol–Dielectric Barrier Discharge (DBD) and Electrospray Ionization (ESI) at Atmospheric Pressure

Polyolefins are chemically inert and do not adhere well to metals, polymers or inorganics. To overcome this problem, polyolefin surfaces were modified thermally, plasmachemically, or by flame treatment with different oxygen-containing groups, however, unfortunately, such treatments were accompanied by undesired, adhesion lowering polymer degradation. To solve this dilemma, solutions of synthetic polymers and copolymers were prepared, sprayed into the barrier discharge or electrosprayed without discharge and deposited as thin adhesion-promoting layers. The deposited polymer layers from poly(vinylamine), poly(ethylene glycol)–poly(vinyl alcohol) copolymers and poly(acrylic acid) were endowed with monotype functional groups. Using the aerosol — dielectric barrier discharge only a fraction of functional groups survived the deposition process in contrast to the electrospray in which all functional groups were retained.

Influence of polymer structure on electroosmotic flow and separation efficiency in successive multiple ionic layer coatings for microchip electrophoresis

The effect of successive multiple ionic layer (SMIL) coatings on the velocity and direction of EOF and the separation efficiency for PDMS electrophoresis microchips was studied using different polymer structures and deposition conditions. To date, the majority of SMIL studies have used traditional CE and fused-silica capillaries. EOF was measured as a function of polymer structure and number of layers, in one case using the same anionic polymer and varying the cationic polymer and in the second case using the same cationic polymer and varying the anionic polymer. In both situations, the EOF direction reversed with each additional deposited polymer layer. The absolute EOF magnitude, however, did not vary significantly with layer number or polymer structure. Next, different coatings were used to compare separation efficiencies on native and SMIL-coated PDMS microchips. For native PDMS microchips, the average separation efficiency was 4105 +/- 1540 theoretical plates. The addition of two layers of polymer increased the separation efficiency anywhere from two- to five-fold, depending on the polymer structure. A maximum separation efficiency of 12 880 +/- 1050 theoretical plates was achieved for SMIL coatings of polybrene (cationic) and dextran sulfate (anionic) polymers after deposition of six total layers. It was also noted that coating improved run-to-run consistency of the peaks as noted by a reduction of the RSD of the EOF and separation efficiency. This study shows that the use of polyelectrolyte coatings, irrespective of the polymer structure, generates a consistent EOF in the current experiments and dramatically improves the separation efficiency when compared to unmodified PDMS microchips.

Directed modification of the properties of vacuum deposited polymer layers by energy-stimulated processes

Vacuum deposited thin layers were investigated for obtaining nanocomposite films based on a polyimide matrix and copper phthalocyanine particles as ‘guests’. The paper presents a study related to energy-stimulated processes using microwave treatment as an alternative to the classical thermal processing. FTIR spectroscopy investigations demonstrated the possibility for a considerable shortening of the entire treatment process. The best results were obtained by combining the thermal and microwave treatments (15 min microwave + 15 min thermal treatment).