1,721,086 research outputs found
Biomimetic adhesive interlayers for technological applications with intrinsic stress-sensitive respons
No full textImpressive adhesive mechanisms are encountered in nature, such as the sticking properties of mussels onto various surfaces mediated by a series of mussel-foot proteins containing dihydroxyphenylalanine (DOPA). In order to better exploit the bio-based adhesive functions in technical applications such as microsystem components, sensor devices and biopolymer composites, a synthetic route has been developed for coupling of a specific adhesive peptide with a lipid diacetylenic tail and self-organization into nanoscale vesicles that were stabilized by UV-induced polymerization. Adhesive micro-arrays were made onto patterned substrates by means of a lithographic methods and subsequent confinement of the aqueous vesicle solution onto hydrophilic spots. Alternatively, the vesicles may be adsorbed onto cellulosic fibers in order to control the interface properties after incorporation into polymer composites. The colorimetric and fluorescent responses of the interfaces are probed as a function of interfacial stress
Biomimetic adhesive interlayers for technological applications with intrinsic stress-sensitive respons
No full textImpressive adhesive mechanisms are encountered in nature, such as the sticking properties of mussels onto various surfaces mediated by a series of mussel-foot proteins containing dihydroxyphenylalanine (DOPA). In order to better exploit the bio-based adhesive functions in technical applications such as microsystem components, sensor devices and biopolymer composites, a synthetic route has been developed for coupling of a specific adhesive peptide with a lipid diacetylenic tail and self-organization into nanoscale vesicles that were stabilized by UV-induced polymerization. Adhesive micro-arrays were made onto patterned substrates by means of a lithographic methods and subsequent confinement of the aqueous vesicle solution onto hydrophilic spots. Alternatively, the vesicles may be adsorbed onto cellulosic fibers in order to control the interface properties after incorporation into polymer composites. The colorimetric and fluorescent responses of the interfaces are probed as a function of interfacial stress
Superhydrophobic surfaces fabricated from nano- and microstructured cellulose stearoyl esters
No full textRobust, superhydrophobic and self-cleaning films were fabricated using nano- or microstructured cellulose fatty acid esters, which were prepared via nanoprecipitation. The superhydrophobic films could be coated on diverse surfaces with non-uniform shapes by distinct coating techniques
Confining acrylate-benzophenone copolymers into adhesive micropads by photochemical crosslinking
No full textThe creation of micrometer adhesive pads by dewetting and subsequent crosslinking of a benzophenone-acrylatecopolymer onto a substrate that is lithographically patterned with a benzophenone-fluoropolymer, has beeninvestigated in relation to the adhesive performance of either continuous or patterned adhesive interlayers. First,the intrinsic adhesive properties of a n-butyl acrylate methacryloyl-4-oxy-benzophenone copolymer were in-vestigated as a function of composition (4, 10, 20 mol-% benzophenone), concentration (1–5 mg/ml) andphotochemical cross-linking conditions (1–120 min). Under optimized conditions, the benzophenone-acrylateprovides a good balance of adhesive strength and ductility at low concentrations of photo-reactive groups andperforms better than reference adhesives. The latter can be understood by the formation of a dense polymernetwork with different degree of crosslinking resulting in high stiffness. Second, the benzophenone-acrylate wassuccessfully confined into adhesive pads through spontaneousflow and pinning of the contact line of the liquidadhesive at the hydrophobic/hydrophilic interface of chemically patterned substrates, followed by dimensionalstabilization of the droplet shape through partial crosslinking. The adhesive strength of interfaces with discreteadhesive pads (diameter 2000 to 500μm) is significantly higher than continuous adhesive interlayers and isconfirmed by cohesive failure of the adhesive
Thermo-responsive superhydrophobic paper using nanostructured cellulose stearoyl ester
No full textHydrophilic paper was rendered with hydrophobic and superhydrophobic property after the treatment with solutions and nanoparticles of cellulose stearoyl ester (CSE), respectively. Cellulose stearoyl ester with a degree of substitution of 2.99 was synthesized from cellulose using stearoyl chloride. By dip-coating paper in CSE solution of at least 3 mg/ml in toluene, paper became hydrophobic with stable water contact angles of more than 120°. After further spray-coating using CSE nanoparticles that were prepared from CSE solution via nanoprecipitation, paper surface became superhydrophobic with water contact angles of larger than 150°. These superhydrophobic surfaces also exhibited self-cleaning character. Furthermore, the superhydrophobic paper surfaces showed a temperature-responsive character and could be turned hydrophobic after a heat-treatment at 70 °C for 5 min
Formation of nanostructured cellulose stearoyl esters via nanoprecipitation
No full textNanoparticles (NPs) from derivatives of native polysaccharides have not been as intensively studied yet as those from synthetic polymers. In this report, NPs in aqueous suspensions were fabricated using cellulose stearoyl esters (CSEs) with different molecular weights via nanoprecipitation using dropping and dialysis techniques. The average diameters of NPs depended strongly on the concentrations of CSE solutions, molecular weights of CSE and also the nanoprecipitation technique. Both nanoprecipitation techniques are based on different mechanisms and NPs from dialysis are generally larger than NPs from dropping. The mechanism for dropping nanoprecipitation was further analyzed based on the properties of NPs which contain crystallized stearoyl groups in CSE chains. The average diameters of freshly-prepared CSE nanoparticles decreased with rising temperature, which is accompanied by the release of THF from the interior of NPs. The intensity of the size reduction of up to 35% depended on the one hand on the concentration of CSE solutions, and on the other hand on the molecular weights of CSEs. Finally, it was shown that these NPs can be used for the fabrication of temperature-responsive superhydrophobic surfaces
Dewetting and photochemical crosslinking of adhesive pads onto lithographically patterned surfaces
No full textThe design of structured adhesive interfaces can be realized by dewetting of a liquid adhesive onto substrates with hydrophilic and hydrophobic domains followed by photochemical crosslinking. The latter allows the creation of well-defined arrays of confined adhesive pads with a controlled geometry. In a first step, the surfaces are covered by a hydrophobic film and lithographically patterned through a mask with an array of spots with diameter of 2 mm. The adhesive can consequently be locally deposited by a dosing syringe and remains confined within the hydrophilic spots. By defining the volume of the adhesive droplets, the contact angle and height of the adhesive pads are controlled through pinning at the hydrophilic/hydrophobic interface, which prevents further spreading. Alternatively, the dip coating and spontaneous dewetting of liquid adhesive over the patterned surface provide a continuous fabrication method for adhesive pad arrays. In a second step, the geometry of the deposited adhesive pads is stabilized by partial crosslinking during different times under UV light. Finally, an adhesive joint is created by applying the counterface followed by full cross-linking. The adhesive strength and mechanical performance are further optimized by considering different crosslinking times and pattern designs
Superhydrophobic Hybrid Paper Sheets with Janus-Type Wettability
No full textTrosien, Simon/0000-0001-5081-5265; Biesalski, Markus/0000-0001-6662-0673WOS:000449239600098PubMed: 30360125We introduce the design of Janus-type paper sheets where one side of the paper exhibits superhydrophobic properties, whereas the other side of the sheet remains hydrophilic and therefore can take up aqueous solutions by capillary wicking. Such papers are being prepared by chemically immobilizing a thin hybrid coating on paper sheets that consists of cross-linked poly(dimethylsiloxane) (PDMS) and inorganic particles of various sizes ranging from nanometers to several tens of micrometers. Both commercially available Whatman No. 1 filter paper and lab-engineered cotton linters-based paper substrates were treated with this approach. The hybrid paper sheets have high chemical durability, mechanical stability, and flexibility because of a covalent attachment of the particles to paper fibers and the inherent elasticity of PDMS chains. In spite of the superhydrophobicity of the coating, the untreated side of the paper substrates preserved its hydrophilicity, resulting in Janus type wetting and wicking properties, respectively. The functionalized paper samples remained porous and permeable to gases, while possessing a gradual change in chemistry between the two sides exhibiting a dramatic wetting contrast. Such two-sided properties open up new applications for such hybrid paper materials, such as in wound dressings and/or bandages with a liquid directing and confinement ability.German Academic Exchange Service (DAAD)Deutscher Akademischer Austausch Dienst (DAAD)This research was financially supported by German Academic Exchange Service (DAAD)
Janus Interface Materials: A Critical Review and Comparative Study
No full textBiesalski, Markus/0000-0001-6662-0673; Trosien, Simon/0000-0001-5081-5265WOS:000526398200007In recent years, Janus interface materials with wettability contrast have attracted remarkable attention because of their beneficial properties and versatile potential applications in materials science including transport, purification/separation, analytical testing, and medical applications. Regarding the wide range of highly promising possible application areas, these materials will have a major impact on the next generation of smart systems. In this Review, our aim is to highlight the current status of the research on Janus interface materials with special emphasis on wettability contrast. In the first section, a brief history of the literature on Janus-type materials and interfaces, materials possessing different chemistries or topographies on opposing sites, is introduced. In the second section, theories behind wetting, including "wettability integration", are summarized, which can be regarded as the combination of opposing wetting properties within the same material. Afterwards, natural examples of Janus interfaces, a branch of superwettability integration, are discussed, which inspired the researchers to mimic the nature and develop artificial analogues. In the next section, the current status on artificial Janus interfaces with wettability contrast are reviewed, subcategories for which are implemented according to the (possible) application areas and also the origin of their base substrates. Then, the inorganic and organic based artificial Janus interfaces were compared in terms of advantages and disadvantages. Finally, a conclusion and outlook are given
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