Adhesion and tack of polymers: Influence of mechanical properties and surface tensions

The adhesion of various polymers used as model adhesives, polyisobutylene, polyacrylates etc. has been investigated by means of an apparatus measuring the adhesive failure energyw in dependence on contact time, contact pressure, rate of separation, and temperature. The adhesive failure energy of adhesive joints formed with low contact pressure during a short contact time is called tack. After a sufficiently long contact time and with a high bonding pressure an adhesive joint exhibits its maximum energy of separationw _m .The viscoelastic properties of the model adhesives were characterized by creep experiments in dependence on time and temperature. The surface tension of the polymer adhesives and adherents could be determined by contact angle measurements. Adhesion measurements of polyisobutylene on a number of adherents were carried out in air and in various liquids in order to obtain information about the influence of surface tension on tack and maximum adhesive failure energy. w _m can be written as the product of two terms: the thermodynamic work of adhesionW _A which is related to the surface and interfacial tensions of adhesive and adherent and a dimensionless function dependent on temperature and rate of separation which describes the viscoeleastic properties of the adhesive and which obeys the rate-temperature superposition principle known from linear viscoelasticity. The tack is related to incomplete bond formation and cannot be described in the same manner. It is, however, strongly dependent on the viscoelastic properties of the adhesive showing a maximum at about 50 to 70 °C above the glass transition temperature. It is, moreover, influenced by the compliance in the plateau range above the glass transition which is determined by the entanglement network of the polymer. Wetting of the adherent by the adhesive is a further important condition for high tack values which is fulfilled if the adherent has a higher surface tension than the adhesive.     

Functionalized polynorbornene dielectric polymers: Adhesion and mechanical properties

Within the microelectronics industry, there is an ongoing trend toward miniaturization coupled with higher performance. High glass-transition temperature polynorbornenes exhibit many of the key performance criteria necessary for these demanding applications. However, homopolynorbornene exhibits poor adhesion to common substrate materials, including silicon, silicon dioxide, aluminum, gold, and copper. In addition, this homopolymer is extremely brittle, yielding less than 1% elongation-to-break values. To address these issues, the homopolymer was functionalized to improve adhesive and mechanical properties. Attaching triethoxysilyl groups to the polymer backbone substantially improved the adhesion, but at the cost of increasing the dielectric constant because of the polarity of the functional group. Alkyl groups were also added to the backbone, which decreased the rigidity of the system, and resulted in significantly higher elongation-to-break values and a decrease in residual stress. The addition of an alkyl group slightly decreased the dielectric constant of the polymer as a result of an increase in molar volume. The coefficient of thermal expansion and modulus are also reported for the polynorbornene functionalized with triethoxysilyl groups using a multiple substrate approach. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3003–3010, 1999     

New approaches to chromatographic determination of lipophilicity of xenobiotics

Liquid chromatography and capillary electrophoresis are unique tools for fast and efficient modeling of pharmacokinetic properties of drug candidates. Therefore numerous new separation methods and procedures have very recently been introduced to facilitate the high-throughput screening of biopartitioning features of xenobiotics. This report is a concise, up-to-date review of progress in the chromatographic assessments of data of importance for medicinal chemistry and molecular pharmacology.     

Synthetic approaches to new polymers

A plenary lecture should be an introduction into the main topic of the symposium and a review about the state of art. Therefore, in the first part of this presentation different possibilities for the preparation of new polymers are briefly discussed from a chemical point of view. Some selected examples from the literature show how methods of organic chemistry can be utilized for polymer science: new catalytic systems, new monomers, modification of polymers, new poly-reactions. In the second part, several polyelectrolytes are described: polymers with sec., tert. and quart. N-atoms in the main chain, block copolymers and block polyampholytes. The third part deals with the problems of rod-like macromolecules for instance oligo- and poly(p-phenylene)s, poly(p-phenyleneethynylene)s, aromatic polyimides and a new spiroionene.     

New β-linked pyrrole monomers: approaches to highly stable and conductive electrochromic polymers

An efficient synthetic route to β-linked dipyrrole monomers has been developed. Electrochemical polymerization of these monomers leads to the incorporation of polycyclic aromatic residues into a polymer backbone. The resulting conjugated polymer films are electroactive, robust electrochromic materials that are highly delocalized in their oxidized forms.     

Adhesion of polymers to fibers: Further elaboration of pull-out method

An interpretation of measurements of polymer adhesion to fibers obtained by the pull-out method is discussed. The study was performed using fibers of identical composition but different diameters. As was shown using the example of EDT-10 epoxide adhesive and glass fiber, all results were approximated satisfactorily by a single curve in coordinates τl/d.     

Nanocomposites of polymers and metals or semiconductors: Historical background and optical properties

Upon transmission of visible light through composites comprising of a transparent polymer matrix with embedded particles, the intensity loss by scattering is substantially reduced for particle diameters below 50–100 nm (nanoparticles, nanosized particles). As a consequence, related materials (nanocomposites) have found particular interest in optical studies. The first part of this article deals with a historical survey on nanoparticles and nanocomposites and the importance of small particle sizes on their optical properties. The second part focuses on results from our laboratory concerning nanocomposites with extremely high or low refractive indices and dichroic nanocomposites and their application in bicolored liquid crystal displays (LCD). The inorganic colloids required for these studies (lead sulfide, iron sulfides, gold, and silver) were prepared in situ in presence of a polymer or isolated as redispersable metal colloids modified at the surface with a self‐assembled monolayer (SAM) of an alkanethiol. The nanocomposites themselves were finally obtained by coprecipitation, spin coating, solvent casting or melt extrusion, with poly(ethylene oxide), gelatin, poly(vinyl alcohol) and polyethylene as matrix polymers.     

Analyzing the surface properties of acrylic-based water-soluble polymers

The surface properties of newly synthesized N-methoxy isopropyl acrylamide, N-methoxy isopropyl methacrylamide, cyclo propyl acrylamide, and cyclo propyl methacrylamide polymers were investigated using inverse gas chromatography. The highest dispersive component of the surface energy value was obtained for cyclo propyl methacrylamide at 30°C. The values obtained for all polymers were decreasing with the increasing temperature. The values obtained for the acidic and the basic parameters revealed strong basic characters for the surface of N-methoxy isopropyl methacrylamide and cyclo propyl methacrylamide polymers and weak basic characters for the surface of N-methoxy isopropyl acrylamide and cyclo propyl acrylamide polymers.     

Vinyl 2-hydroxyethyl sulfide polymers and their sorption properties with respect to transition metals

Vinyl 2-hydroxyethyl sulfide (VHES) homopolymer and the homopolymer and vinyl 2-hydroxyethyl sulfide-acryl amide copolymer cross-linked by bisacrylamide were prepared by radical polymerization. The sorption of Au(III), Ag(I), Pd(II), Pt(IV), Hg(II), Pb(II), Fe(III), Ni(II), Cu(II) on these polymers under the static conditions was studied in relation to the solution pH. The polymers are highly selective and efficient sorbents for Au(III), Ag(I) and Hg(II).     

Thermocapillary approaches to the deliberate patterning of polymers

The phenomenon of thermocapillarity, the response of fluids to thermal gradients due to thermal alteration of their surface tension, was first reported over a century ago. Since then, research has focused generally on either the fundamentals or mitigation of this effect during the processing of materials. Only in the past two decades has the deliberate use of thermocapillary forces for the patterning of polymers been actively pursued, either for the ordering of internal structure or the introduction of topographic features. This review seeks to highlight this work and to identify directions for further investigation. In particular, while thermocapillary forces are often inextricably bound to other mechanisms, there are emerging directions in the deliberate coupling of forces to improve the capabilities of each mechanism. Further, the applications of thermocapillary patterning to polymer-nanoparticle composites has recently provided another promising route to active architectures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1649–1668     

Adhesion of Yersinia ruckeri to fish farm materials: influence of cell and material surface properties

Two strains (an environmental strain and a reference one coming from a national culture collection) of Yersinia ruckeri, a fish pathogenic bacterium, are characterised according to the ability to adhere on wood, concrete, polyvinylchloride (PVC) and fibreglass, four materials commonly found in fish farms. The relationships between adherence, bacterial and support hydrophobicities and surface roughness are investigated. The results show that: (i) Y. ruckeri is strongly hydrophilic; (ii) the environmental strain exhibits a higher ability to adhere than the reference one; and (iii) for the two strains a strong correlation is observed between roughness amplitude (RA) of the support material and adhesion ability.     

Rapid determination of pharmacokinetic properties of new chemical entities: in vivo approaches

There is a continuing need for increased throughput in the evaluation of new chemical entities in terms of their pharmacokinetic (PK) parameters as part of new drug discovery. This review summarizes various approaches that have been used to increase throughput in this area. The article divides the approaches into two areas: assay enhancement and sample reduction.     

Durable bonding of silica nanoparticles to polymers by photoradiation for control of surface properties

Improvement of superhydrophobic surfaces durability is a critical key for potential commercial applications such as self‐cleaning and ice repellency. In this study, functionalization of silica nanoparticles by photoreactive benzophenone groups was made in order to covalently bond nanoparticles to polymer substrates to obtain durable coatings. Upon ultraviolet irradiation reactive excited triplet benzophenone species are formed enabling them to react with the polymer matrix through hydrogen abstraction. Two matrices were studied: radiation‐curable urethane acrylate and epoxy. The bonding of the particles to the surfaces was evaluated using atomic force microscope nanomanipulation and cross‐section analysis. The results have shown a greater stability of the photoreactive silica nanoparticles. Copyright © 2014 John Wiley & Sons, Ltd.     

Relaxation spectra of polymers and phenomena of electrical and hydrophobic recovery: Interplay between bulk and surface properties of polymers

Low‐density polyethylene, polypropylene, and polycarbonate were exposed to cold air plasma treatment. The decay of electret response, hydrophobic recovery, and mechanical relaxation of polymers were studied experimentally. The three‐exponential decay kinetic model was used for the treatment of mechanical and electret responses. The characteristic time scales of mechanical and electret responses turned out to be very close. The “longest” relaxation time, extracted from the experimental study of the hydrophobic recovery, was also close to the corresponding characteristic time spans of electret and mechanical responses. The kinetics of surface processes taking place in polymers is controlled by the mobility of their functional groups, represented by the bulk relaxation spectra. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 198–205     

Evaluation of the stress-strain properties of surface layers in plasma-treated polymers

The surface treatment of poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC) films in cold plasma over 1–15 min was carried out. It was found that the subsequent deformation of the films is accompanied by a special type of surface structuring that has been previously observed for polymer films with a thin hard coating. It was shown that unlike metal coatings, the thickness of the modified surface layer slightly depends on the time of treatment in plasma. The previously developed approach to analysis of the emerging patterns makes it possible to evaluate the stress-strain properties of the coatings. It was first revealed that the tensile strength of the modified layer produced in PET by plasma treatment is ∼12.3 MPa and its elongation at break varies from 20 to 90%. The differences in the properties between the plasma-modified surface layers of the polymer and the metal coatings studied earlier are discussed.     

Photooxidation of polymers: Relating material properties to chemical changes

This paper is devoted to a comprehensive study of the photo-oxidation of polymeric materials with the goal of correlating modifications of the polymer properties at the molecular and macroscopic levels. Several techniques were used to characterise the modifications of the chemical properties and mechanical behaviour over time under UV light. The methodology was developed on materials used as organic coatings; initially, a well-characterised phenoxy resin (PKHJ^®) was chosen as a model and then the approach was applied to an acrylate-melamine thermoset currently used as a topcoat in the automotive industry. Analysis of degraded samples by IR spectroscopy allowed us to propose a photo-oxidation mechanism. This mechanism suggested that chain scission occurred under photo-oxidation. To entirely understand the degradation of the polymers, gel fraction, thermoporosimetry, DMA, AFM nanoindentation and micro-hardness determinations were performed. The results showed that crosslinking reactions occurred in competition with chain scission and explained for the first time why crosslinking reactions were quite prevalent. Based on the obtained results, quantitative correlations were made between the various criteria of degradation, thus relating the chemical structure changes to the mechanical property modifications.     

New approach to filled polymers

Mechanopolymerization of pentabromobenzyl (mono)acrylate (PBB-MA) on the surface of inorganic fillers Mg(OH)₂ and CaCO₃ was studied. The role of activated surface of fillers was investigated using DSC and FTIR. The influence of milling time and of the filler chemical content on polymerization starting temperature and polymerization enthalpy was studied using DSC. It was shown that an increase of the filler concentration leads to a higher maximum conversion degree. The correlation between conversion kinetics and polymerization enthalpy of the material notpolymerized during milling was shown. This paper was presented on the Second Conference of The Israel Group of Mechanochemistry.