Nanoparticle Induced Morphology Modulation in Spin Coated PS/PMMA Blend Thin Films

Biomimetic Fingerprint-like Unclonable Optical Anticounterfeiting System with Selectively In Situ-Synthesized Perovskite Quantum Dots Embedded in Spontaneous-Phase-Separated Polymers

Anticounterfeiting technologies meet challenges in the Internet of Things era due to the rapidly growing volume of objects, their frequent connection with humans, and the accelerated advance of counterfeiting/cracking techniques. Here, we, inspired by biological fingerprints, present a simple anticounterfeiting system based on perovskite quantum dot (PQD) fingerprint physical unclonable function (FPUF) by cooperatively utilizing the spontaneous-phase separation of polymers and selective in situ synthesis PQDs as an entropy source. The FPUFs offer red, green, and blue full-color fingerprint identifiers and random three-dimensional (3D) morphology, which extends binary to multivalued encoding by tuning the perovskite and polymer components, enabling a high encoding capacity (about 108570000, far surpassing that of biometric fingerprints). The strategy is compatible with mainstream production techniques that are widely used in traditional low-cost printed anticounterfeiting labels including spray printing, stamping, writing, and laser printing, avoiding complicated fabrication. Macrographical patterns and micro/nanofingerprint patterns with multiscale-tailorable inter-ridge sizes can be fused into a single FPUF label, satisfying different levels of anticounterfeiting requirements. Furthermore, a smart fused scheme of enhanced deep learning and fingerprint characteristic comparison is leveraged, by which high-efficiency, high-accuracy authentication of our FPUFs is achieved even for the increasingly huge FPUF databases and imperfectly captured images from users.

High temperature QDs organization and re-crystallization in glass supported MgO QDs doped PMMA film

We have blended MgO QDs with poly (methylmethacrylate) (PMMA) thin films using solution-casting method. MgO QDs were doped at 5 wt %, 10 wt %, and 15 wt % in PMMA film and annealed for 02, 04, 06, 08, 10, 12, 14, 20, 24, and 28 h at 130 degree Celsius. We have comprehensively investigated the molecular-scale restructuring and morphological evolution of the composite films and have accounted for the reasons based on the observations made on chemical bonding, crystallinity, bandgap, Urbach energy, and fluorescence and Raman spectra. We observe that the film loses its overall crystallinity in the initial stages of annealing, which improves slightly owing to the temperature-induced limited diffusion of MgO QDs (sizes in the range of 7.0603-9.5647 nm). MgO QDs undergo coarsening at temperatures as low as 130 0C. The limited diffusion of MgO QDs allows for the formation of larger clusters, which in turn affects the local crystallinity of the composite films. We report local-scale re-crystallization driven by dispersion forces acting globally. As far as the quantum nature of forces is concerned, this work clearly demonstrates some unique energy dissipation mechanism of charge carriers in QDs via overlapping with long-range dispersion forces. The morphological evolution of the films is the outcome of the reconciliation of forces. We discuss the role of competing forces. The evolution of nano-micro scale structures inside films is governed by the reconciliation between inter- and intra-molecular forces. The temperature of the film plays an important role in facilitating the entire process. To obtain molecular-scale insights, we have estimated the crystallinity, bandgap, and Urbach energy of the pure and hybrid films. MgO QDs diffuse locally and coalesced to form larger spherical clusters. The anchoring of MgO QDs on the PMMA surface and vice-versa appears to provide thermal stability and mechanical strength to the nanocomposite films, as the MgO QDS-doped PMMA film form nanometer-sized particulates of PMMA. In contrast, the overall crystallinity of the hybrid film drastically decreases as the formation of boundaries, interfaces, and voids overwhelmed the entire process. The formation of larger nanoaggregates at later stages of annealing slightly improves the crystallinity of the films. The estimation of the bandgap and Urbach energy calculations confirm the same. The micro-level phenomenological understanding of the diffusion process of nanodots in a nearly solid film is technically important for ensuring the sustainability of such nanocomposites that undergo a heating process.

Simulation of Polymer Fractal Formation Using a Triangular Network Growth Model

Fractal formation in spin-coated thin-film polymers is of experimental and theoretical interest. Modeling the determinants and dynamics of this process will deepen our understanding of polymer aggregation and the predictability of thin-film structures. This is especially true if the model used has readily interpretable parameters and has been demonstrated to yield a close match to experimental processes under a variety of conditions. In this work, we adapted and applied a relatively new model of fractal growth comprised of a spreading and contracting triangular network, to model spin-coated, thin-film polymers made of poly(vinyl alcohol) on polydimethylsiloxane substrates. We drew clear connections between model parameters and the process of polymer aggregation and we demonstrated the ability of the model to simulate fractal formation under a wide variety of conditions including varying the degree of hydrolysis of the polymer, changing the spin-coating process, and solvent annealing and reforming of polymer fractals under different drying conditions. We also showed how the model is able to replicate idiosyncratic experimental settings yielding novel fractal patterns.

Multifunctional Acrylic Polymers with Enhanced Adhesive Property Serving as Excellent Edge Encapsulant for Stable Optoelectronic Devices

Pendant groups in acrylic adhesive polymers (Ads) have a profound influence on adhesive and cohesive properties and additionally on encapsulant application. However, a systematic investigation to assess the impact of the pendant groups' length and bulkiness is rare, and there is not even a single report on applying Ads as interfacial adhesion promotors and encapsulation materials simultaneously. Herein, we have developed a series of multifunctional methacrylic polymers, namely, R-co-Ads, with varying pendant length and bulkiness (R = methyl (C1), ethyl (C2), propyl (C3), butyl (C4), pentyl (C5), hexyl (C6), isobutyl (iC4), and 2-ethylhexyl (2EH)). The adhesion-related experimental results reveal that R-co-Ads have high transparency, strong adhesion strength to the various contact surfaces, and a fast cure speed. In particular, C1-co-Ad shows a superior adhesion performance with an improved cross-cut index of 4B and a shear bonding strength of 1.56 MPa. We also have adopted C1-co-Ad for encapsulation of various emerging optoelectronic applications (e.g., perovskite solar cell-, charge transport-, and conductivity-related characteristics), demonstrating its excellent edge encapsulant served to improve the device stability against ambient air conditions. Our study establishes the structure-adhesion-surface relationships, advancing the better design of adhesives and encapsulants for various research fields.

Designing Multicomponent Polymer Colloids for Self-Stratifying Films

Aqueous polymer colloids known as latexes are widely used in coating applications. Multicomponent latexes comprised of two incompatible polymeric species organized into a core-shell particle morphology are a promising system for self-stratifying coatings that spontaneously partition into multiple layers, thereby yielding complex structured coatings requiring only a single application step. Developing new materials for self-stratifying coatings requires a clear understanding of the thermodynamic and kinetic properties governing phase separation and polymeric species transport. In this work, we study phase separation and self-stratification in polymer films based on multicomponent acrylic (shell) and acrylic-silicone (core) latex particles. Our results show that the molecular weight of the shell polymer and heat aging conditions of the film critically determine the underlying transport phenomena, which ultimately controls phase separation in the film. Unentangled shell polymers result in efficient phase separation within hours with heat aging at reasonable temperatures, whereas entangled shell polymers effectively inhibit phase separation even under extensive heat aging conditions over a period of months due to kinetic limitations. Transmission electron microscopy is used to track morphological changes as a function of thermal aging. Interestingly, our results show that the rheological properties of the latex films are highly sensitive to morphology, and linear shear rheology is used to understand morphological changes. Overall, these results highlight the importance of bulk rheology as a simple and effective tool for understanding changes in morphology in multicomponent latex films.

Visualizing Surface Phase Separation in PS-PMMA Polymer Blends at the Nanoscale

Phase-separated polymer blend films are an important class of functional materials with numerous technological applications in solar cells, catalysis, and biotechnology. These technologies are underpinned by the precise control of phase separation at the nanometer length-scales, which is highly challenging to visualize using conventional analytical tools. Herein, we introduce tip-enhanced Raman spectroscopy (TERS), in combination with atomic force microscopy (AFM), confocal Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), as a sensitive nanoanalytical method to determine lateral and vertical phase-separation in polystyrene (PS)-poly(methyl methacrylate) (PMMA) polymer blend films. Correlative topographical, molecular, and elemental information reveals a vertical phase separation of the polymers within the top ca. 20 nm of the blend surface in addition to the lateral phase separation in the bulk. Furthermore, complementary TERS and XPS measurements reveal the presence of PMMA within 9.2 nm of the surface and PS at the subsurface of the polymer blend. This fundamental work establishes TERS as a powerful analytical tool for surface characterization of this important class of polymers at nanometer length scales.

Perpendicular alignment of the phase-separated boundary in adhered polymer droplets

We investigated the effect of the adhered interface on the phase separation pattern using two or three adhered droplets containing a binary solution of poly(ethylene glycol) and gelatin. Under the experimental conditions, single domains of the gelatin-rich phase exhibited partial wetting to the droplet adhered interface (DAI) and nonadhered droplet surface. In the case of isolated spherical droplets, the location of the phase separation interface (PSI) of the domains was completely random owing to spatial symmetry. In the adhered droplets, the random orientation of the PSI was observed when the PSI did not contact the DAI. On the other hand, when the PSI contacted the DAI, the PSI was aligned perpendicular to the DAI. Frequency analysis showed that whether the PSI contacts the DAI is purely stochastic. However, the PSI alignment perpendicular to the DAI increases significantly with three adhered droplets, suggesting that the probability increases with increasing DAI area ratio. We explain this perpendicular pattern by the minimization of the interfacial energy and kinetics with a change in the wetting contact angle. These findings will facilitate the research on the phase separation of polymer solutions inside nonspherical micrometric spaces.

Energy dependent XPS measurements on thin films of a poly(vinyl methyl ether)/polystyrene blend concentration profile on a nanometer resolution to understand the behavior of nanofilms

The composition of the surface layer in dependence from the distance of the polymer/air interface in thin films with thicknesses below 100 nm of miscible polymer blends in a spatial region of a few nanometers is not investigated completely. Here, thin films of the blend poly(vinyl methyl ether) (PVME)/polystyrene (PS) with a composition of 25/75 wt% are investigated by Energy Resolved X-ray Photoelectron Spectroscopy (ER-XPS) at a synchrotron storage ring using excitation energies lower than 1 keV. By changing the energy of the photons the information depth is varied in the range from ca. 1 nm to 10 nm. Therefore, the PVME concentration could be estimated in dependence from the distance of the polymer/air interface for film thicknesses below 100 nm. Firstly, as expected for increasing information depth the PVME concentration decreases. Secondly, it was found that the PVME concentration at the surface has a complicated dependence on the film thickness. It increases with decreasing film thickness until 30 nm where a maximum is reached. For smaller film thicknesses the PVME concentration decreases. A simplified layer model is used to calculate the effective PVME concentration in the different spatial regions of the surface layer.