Oktay Yarimaga

Inkjet printing of conjugated polymer precursors on paper substrates for colorimetric sensing and flexible electrothermochromic display.

Inkjet-printable aqueous suspensions of conjugated polymer precursors are developed for fabrication of patterned color images on paper substrates. Printing of a diacetylene (DA)-surfactant composite ink on unmodified paper and photopaper, as well as on a banknote, enables generation of latent images that are transformed to blue-colored polydiacetylene (PDA) structures by UV irradiation. Both irreversible and reversible thermochromism with the PDA printed images are demonstrated and applied to flexible and disposable sensors and to displays.

A cauliflower-like gold structure for superhydrophobicity

We present a two-step route to produce a hierarchical cauliflower-like gold structure that involves the adsorption of gold nanoparticles described by the random sequential adsorption (RSA) model, followed by the electrochemical growth on the surfaces of the primary gold nanoparicles. The structure was confirmed using scanning electron microscopy (SEM), energy dispersive spectrometer analysis (EDS), and X-ray diffraction (XRD). After fluoroalkylsilane modification, the cauliflower-like structured surface exhibits a high contact angle and a low sliding angle.

An inkjet-printable microemulsion system for colorimetric polydiacetylene supramolecules on paper substrates

Owing to their flexible, light-weight and disposable properties, paper-based electronic and sensor systems have gained much attention. Efficient immobilization and patterning of functional materials on paper substrates are critical to device performance. Herein, we report an inkjet printable and photopolymerizable diacetylene (DA) containing microemulsion system that can be readily transferred to paper substrates using a common office inkjet printer. UV-induced polymerization afforded clean formation of polydiacetylene (PDA) supramolecules on paper and the polymer displayed a typical thermochromism. The resolution of the printed PDA images was found to be equivalent to that of conventional black ink. The randomly oriented DA in the oil phase was found to be transformed to self-assembled layered structures upon printing. The printed PDA supramolecules derived from 5,7-dodecadiyne-1,12-diol bis[((butoxycarbonyl)methyl)urethane] (4BCMU) displayed a blue-to-red-to-yellow color transition upon heating. Thus, the blue colored 4BCMU-derived polymer was converted to a red colored PDA at 100 °C and further heating to 180 °C resulted in the generation of a yellow colored PDA. Upon cooling to room temperature, the yellow colored PDA became red and a complete colorimetric reversibility was observed between red (30 °C) and yellow (180 °C). The thermally promoted reversible PDA phase transition was successfully applied to a banknote to demonstrate an application to a potential counterfeit prevention method.

Substrate surface roughness-dependent 3-D complex nanoarchitectures of gold particles from directed electrodeposition

The effects of substrate surface roughness on the directed electrodeposition of gold 3-D complex nanoarchitectures with hedgehog-shaped, cauliflower-shaped, or bunch-of-grapes-shaped surface features are revealed. The surface morphology of the synthesized particles was observed using a scanning electron microscope (SEM). Their chemical composition was confirmed using X-ray diffraction (XRD) patterns. The surfaces of ITO/glass substrate with different roughness were checked using atomic force microscopy (AFM) and contact angle measurements. Effects of variation of the deposition potential on the growth of Au nanocomplex structure have provided valuable information to clarify the substrate surface roughness-dependent 3-D nanocomplex synthesis. Pt/Au bimetallic particles with different surface features were produced under the same experimental conditions using mentioned different rough ITO/glass substrates. The growth follows a diffusion controlled mechanism. Electrochemical experimental results demonstrated that such hedgehog-shaped Au particles exhibit enhanced voltammetric responses. These findings offer insight into the electrosynthesis of complex micro/nano-structures. Interesting 3-D nanostructures can be realized by controlling the surface roughness of the substrate.

Fabrication of Patterned Polydiacetylene Composite Films Using a Replica-Molding (REM) Technique

Functional three-dimensional (3D) micropatterns of diacetylene supramolecules embedded in a host polymer have been successfully fabricated by a replica-molding (REM) technique. Dimensional reduction as a result of liquid evaporation during the curing process does not affect the conformational features of the transferred patterns. Polymerization of the diacetylene vesicles using 254 nm UV-light irradiation from the back-side of the transparent substrate induces blue colored polydiacetylene (PDA) micro-images. Interestingly, the polymerization selectively occurs in the molded areas because of the sub-300 nm light blocking property of SU-8. 3D fluorescence patterns are readily obtained by heat treatment of the blue images on the film.

Electrophoretic deposition of amphiphilic diacetylene supramolecules: polymerization, selective immobilization, pattern transfer and sensor applications

We describe the results of electrophoretic deposition characteristics of a conjugated polymer, polydiacetylene (PDA), that reveal film forming behavior, polymerization effects, pattern transfer capabilities, and fluorescence based thermo/mechano-responsive features of the deposited layer. The electric field applied in a two electrode system promotes the oriented motion of diacetylene (DA) supramolecules in aqueous solution in a direction that is determined by the charge polarities of tailorable pendant groups on the DA monomers. Through this mechanism, electrophoretic deposition of DA supramolecules on a conductive layer takes place to yield vesicular clustered aggregates with continuous leaf-like morphologies. In addition, unusual conformational changes of the DA monomers during the deposition result in the formation of polymerized blue colored PDAs on the working electrode. Based on these properties, selective deposition of the supramolecules on pre-patterned templates and consequent pattern transfer to a flexible substrate can be utilized to fabricate PDA-based microarray sensors. The chromatic change of the vesicles induced by an applied mechanical stress during pattern transfer is found to be dependent on the side groups of the DA monomers. Owing to inherent non-fluorescence to fluorescence transition features of PDA supramolecules occurring as a response to thermal perturbations, electrophoretically deposited PDA vesicles are employed to monitor the temperature of a heat dispensing micro-heater device.

A thermally actuated organic display device using thermo-chromatic polymer composite film with self-aligned patterns

A thermally actuated organic display device using UV-sensitive polydiacetylene (PDA)-polyvinyl alcohol (PVA) composite film with self aligned patterns is presented. A novel technique that patterns UV-sensitive organic films on a transparent substrate using a chip-embedded photomask is demonstrated. In contrast to related works regarding PDA and its composites, the current investigation represents the first attempt to realize a PDA derivative film for a thermal-display. Micro-pixels ranging from 200 mum to 700 mum size were fabricated on a glass substrate. The transition tones of the blue, red and yellow micro-pixels were successfully tuned with embedded micro-heaters under the PDA-PVA layer using both low-temperature (75degC) and high-temperature (180degC) activation processes. The retention time was measured and found to be less than a few hundred milliseconds.

Detection of a Nanoscale Hot Spot by Hot Carriers in a Poly-Si TFT Using Polydiacetylene-Based Thermoresponsive Fluorometry

The thermal distribution of polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) with sizes close to the nanoregime is analyzed by means of a fluorescent nanothermographic imaging technique based on the heat-induced fluorescence feature of polydiacetylene (PDA) supramolecules. The direct detection of nanoscale hot spots generated by hot carriers in poly-Si TFTs is demonstrated with sufficient spatial resolution. The thermal information of poly-Si TFTs under operation is recorded in a PDA-embedded polyvinyl alcohol film in the fluorescence state. The proposed thermal analysis method for poly-Si TFTs overcomes the fundamental spatial resolution limitation of conventional infrared detection systems and guarantees nanoscale spatial resolution. This approach, which offers cost effectiveness, nontoxicity, and simplicity of calibration steps, can be useful for further analysis of the degradation mechanism and reliability issues of submicrometer poly-Si TFTs.