Inkjet Printing Based Mono-layered Photonic Crystal Patterning for Anti-counterfeiting Structural Colors

Photonic crystal structures can be created to manipulate electromagnetic waves so that many studies have focused on designing photonic band-gaps for various applications including sensors, LEDs, lasers, and optical fibers. Here, we show that mono-layered, self-assembled photonic crystals (SAPCs) fabricated by using an inkjet printer exhibit extremely weak structural colors and multiple colorful holograms so that they can be utilized in anti-counterfeit measures. We demonstrate that SAPC patterns on a white background are covert under daylight, such that pattern detection can be avoided, but they become overt in a simple manner under strong illumination with smartphone flash light and/or on a black background, showing remarkable potential for anti-counterfeit techniques. Besides, we demonstrate that SAPCs yield different RGB histograms that depend on viewing angles and pattern densities, thus enhancing their cryptographic capabilities. Hence, the structural colorations designed by inkjet printers would not only produce optical holograms for the simple authentication of many items and products but also enable a high-secure anti-counterfeit techniqueope

Fabrication and Actuation of Hierarchically-Patterned Polymer Substrates for Dynamic Surface and Optical Properties

Switchable optical materials, which possess reversible color and transparency change in response to external stimuli, are of wide interest for potential applications such as windows and skylights in architectural and vehicular settings or optical sensors for environmental monitoring. This thesis considers the tuning of optical properties by tailoring and actuating responsive materials. Specifically, we demonstrate the design and fabrication of tilted pillar arrays on wrinkled elastomeric polydimethylsiloxane (PDMS) as a reversibly switchable optical window. While the original PDMS film exhibits angle-dependent colorful reflection due to Bragg diffraction of light from the periodic pillar array, the tilted pillar film appears opaque due to random scattering. Upon re-stretching the film to the original pre-strain, the grating color is restored due to the straightened pillars and transmittance is recovered. Then, we develop a composite film, consisting of a thin layer of quasi-amorphous array of silica nanoparticles (NPs) embedded in bulk elastomeric PDMS, with initial high transparency and angle-independent coloring upon mechanical stretching. The color can be tuned by the silica NP size. The switch between transparency and colored states could be reversibly cycled at least 1000 times without losing the film’s structural and optical integrity. We then consider the micropatterning of nematic liquid crystal elastomers (NLCEs) as micro-actuator materials. Planar surface anchoring of liquid crystal (LC) monomers is achieved with a poly(2-hydroxyethyl methacrylate)-coated PDMS mold, leading to monodomains of vertically aligned LC monomers within the mold. After cross-linking, the resulting NLCE micropillars show a relatively large radial strain when heated above nematic to isotropic transition temperature, which can be recovered upon cooling. Finally, the understanding of liquid crystal surface anchoring under confined boundary conditions is applied to the self-assembly of gold nanorods (AuNRs) driven by LC defect structures and to dynamically tune the surface plasmon resonance (SPR) properties. By exploiting the confinement of the smectic liquid crystal, 4-octyl-4’-cyanobiphenyl (8CB), to patterned pillars treated with homeotropic surface anchoring, topological defects are formed at precise locations around each pillar and can be tuned by varying the aspect ratio of the pillars and the temperature of the system. As a result, the AuNR assemblies and SPR properties can be altered reversibly by heating and cooling between smectic, nematic and isotropic phases

Information-Directed Hybridization of Abiotic, Sequence-Defined Oligomers

The capacity for sequence-specific polymer strands to selectively assemble into intricate, folded structures and multimeric complexes relies upon the information borne by their residue sequences. Particularly suitable for the formation of multi-dimensional structures, nucleic acids have emerged as sophisticated nanoconstruction media where encoded sequences self-assemble in a designed manner through the gradual cooling of denatured and dissociated strands from raised temperatures. Unfortunately, the weakness of the hydrogen bonds holding the strands together affords nanoconstructs with thermal and mechanical instabilities. In contrast, molecular self-assembly employing dynamic covalent interactions has contributed to the improved mechanical and chemical stabilities of resultant structures. Nevertheless, compared with supramolecular chemistries, dynamic covalent interactions suffer from low dissociation rates, impeding rearrangement amongst the assembled components and often result in the kinetic trapping of non-equilibrium species. To overcome this limitation, molecular architectures are generally restricted to homo-functionalized constituents bearing few reactive sites or utilize harsh self-assembly conditions. This dissertation examines the deliberate equilibrium shifting of dynamic covalent interactions to fabricate sequence-selective molecular architectures with high degrees of functionalization. First, we explored the use of a Lewis acidic catalyst, scandium triflate, Sc(OTf)3, to affect the equilibrium of imine formation, a well-characterized dynamic covalent interaction. Here, high concentrations of scandium triflate, dissociated oligomeric-strands encoded with amine- and aldehyde-pendant group species. Upon removal of excess scandium triflate with a liquid-liquid extraction, the equilibrium was shifted as to promote imine-formation between complementary strands. Subsequent annealing of the self-assembly solutions at 70°C, enabling rearrangement and error-correction of out-of-registry or non-complementary sequences, afforded the simultaneous formation of three distinct information-bearing ladder species and a mechanism for information storage and retrieval of data by abiotic polymers. The information-directed self-assembly of encoded molecular ladders was further developed by incorporating an orthogonal reaction into the oligomeric strands to mimic the information dense, sequence-selective hybridization of DNA. Thus, the base-4 information-directed assembly of molecular ladders and grids bearing covalent bond-based rungs was demonstrated from encoded precursor strands using dual concurrent, orthogonal dynamic covalent interactions (i.e., amine/aldehyde and boronic acid/catechol condensation reactions). Additionally, the self-assembly of well-characterized ladder species employing the thermally-reversible Diels-Alder cycloaddition reaction was explored to establish a self-assembly mechanism requiring an external stimulus to alleviate or eliminate kinetic trapping. By utilizing furan-protected maleimide and furfurylamine residues, sequence-defined strands were synthesized simultaneously bearing both furan and maleimide species while precluding premature hybridization and self-assembled in an information-directed manner to form distinct ladder species using a temperature-mediated process. Finally, given the large-scale efforts underway to develop rapid SARS-CoV-2 (Severe Acute Respiratory Syndrome - coronavirus – 2) diagnostic tests, the fundamental principles of sequence-selective hybridization were applied to transform blood-typing tests into SARS-CoV-2 serology tests using robust gel card agglutination reactions in combination with easily prepared antibody-peptide bioconjugates.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162941/1/sleguiz_1.pd

3D/4D printing of cellulose nanocrystals-based biomaterials: Additives for sustainable applications

Cellulose nanocrystals (CNCs) have gained significant attraction from both industrial and academic sectors, thanks to their biodegradability, non-toxicity, and renewability with remarkable mechanical characteristics. Desirable mechanical characteristics of CNCs include high stiffness, high strength, excellent flexibility, and large surface-to-volume ratio. Additionally, the mechanical properties of CNCs can be tailored through chemical modifications for high-end applications including tissue engineering, actuating, and biomedical. Modern manufacturing methods including 3D/4D printing are highly advantageous for developing sophisticated and intricate geometries. This review highlights the major developments of additive manufactured CNCs, which promote sustainable solutions across a wide range of applications. Additionally, this contribution also presents current challenges and future research directions of CNC-based composites developed through 3D/4D printing techniques for myriad engineering sectors including tissue engineering, wound healing, wearable electronics, robotics, and anti-counterfeiting applications. Overall, this review will greatly help research scientists from chemistry, materials, biomedicine, and other disciplines to comprehend the underlying principles, mechanical properties, and applications of additively manufactured CNC-based structures

Gradient metasurfaces: a review of fundamentals and applications

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic

Bioinspired stimuli-responsive color-changing systems

Stimuli-responsive colors are a unique characteristic of certain animals, evolved as either a method to hide from enemies and prey or to communicate their presence to rivals or mates. From a material science perspective, the solutions developed by Mother Nature to achieve these effects are a source of inspiration to scientists for decades. Here, an updated overview of the literature on bioinspired stimuli-responsive color-changing systems is provided. Starting from natural systems, which are the source of inspiration, a classification of the different solutions proposed is given, based on the stimuli used to trigger the color-changing effect

La realidad virtual como entorno fortalecedor para el cambio personal: la contribución del laboratorio de tecnología aplicada a la neuropsicología

When we exercise real choice, we gain increased control over our lives and are able to change ourselves. However for many subjects it is not easy to exercise effective choices: patients often don’t have the knowledge, skills, assertiveness, or self esteem needed. In this situation Virtual Reality (VR), an artificial reality that projects the user into a 3D space generated by the computer, may offer a critical advantage to the therapist. The enriched experience and the total level of control on its features, transform VR in an “empowering environment”, where patients can start to explore and act without feeling actually threatened. The attempt of defining, developing and testing VR tools supporting personal empowerment is the main goal of the Applied Technology for Neuro-Psychology Laboratory –ATN-P Lab– at the Istituto Auxologico Italiano. The paper describes the actual work done by the ATN-P Lab. in this area. Specifically, the open source "NeuroVR" system and its potential clinical applications –anxiety disorders, obesity and eating disorders– are presented and discussed.La capacidad de elección nos proporciona control sobre nuestras vidas y nos ofrece posibilidades de cambio. Sin embargo, para muchas personas no es fácil realizar elecciones efectivas; por ejemplo, los pacientes carecen muchas veces del conocimiento, la habilidad, la asertividad o autoestima necesarias. En esas situaciones, la realidad virtual (RV), una realidad artificial que coloca al sujeto en un espacio generado por el ordenador, puede ser para el terapeuta un recurso decisivo. La experiencia enriquecida y el control total sobre todos sus aspectos transforman la RV en un “entorno fortalecedor”, en el que los pacientes pueden comenzar a explorar y actuar sin sentirse amenazados. El principal objetivo del “Applied Technology for Neuro-Psychology Laboratory” (ATN-P Lab), perteneciente al Instituto Auxologico Italiano, es intentar definir, desarrollar y probar aplicaciones basadas en RV que faciliten el fortalecimiento personal. En este artículo se describe el trabajo que se viene realizando sobre este tema en ese laboratorio. Se presenta y discute, específicamente, el sistema de código abierto denominado “NeuroVR”, así como sus aplicaciones clínicas potenciales sobre los trastornos de ansiedad, la obesidad y los trastornos alimentarios