Optical metasurfaces are starting to find their way into integrated devices, where they can enhance and control the emission, modulation, dynamic shaping, and detection of light waves. In this study, we show that the architecture of organic light-emitting diode (OLED) displays can be completely reenvisioned through the introduction of nanopatterned metasurface mirrors. In the resulting meta-OLED displays, different metasurface patterns define red, green, and blue pixels and ensure optimized extraction of these colors from organic, white light emitters. This new architecture facilitates the creation of devices at the ultrahigh pixel densities (>10,000 pixels per inch) required in emerging display applications (for instance, augmented reality) that use scalable nanoimprint lithography. The fabricated pixels also offer twice the luminescence efficiency and superior color purity relative to standard color-filtered white OLEDs.

Three polystyrene-block-poly(2-vinylpyridine) (S2VP diblock) and three polystyrene-block-poly-(4-vinylpyridine) (S4VP diblock) copolymers with varying molecular weights and block compositions were synthesized via anionic polymerization, and their order-disorder transition temperatures (T ODT s) were determined using oscillatory shear rheometry and small-angle X-ray scattering (SAXS). It has been found that for comparable molecular weight and block composition the T ODT of S4VP diblock copolymer is exceedingly high compared with that of S2VP diblock copolymer. The experimental observation has been confirmed by theoretical predictions from currently held mean-field theory. For the theoretical predictions, temperature-dependent interaction parameters for the polystyrene (PS)/poly(2-vinylpyridine) (P2VP) pair and the PS/poly(4-vinylpyridine) (P4VP) pair were determined from SAXS profiles obtained at varying temperatures ranging from 125 to 185 °C for a low-molecularweight (LMW) S2VP diblock copolymer and ranging from 160 to 195 °C for an LMW S4VP diblock copolymer and curve fitting to the Leibler theory. The molecular weights of LMW S2VP and LMW S4VP diblock copolymers employed were 10 200 and 2720, respectively, enabling us to obtain SAXS profiles in the disordered state of the respective block copolymers. The temperature-dependent specific volumes of PS, P2VP, and P4VP were determined at temperatures ranging from 25 to 200 °C using spectroscopic ellipsometry. To find the origin of the experimentally observed difference in T ODT between S2VP and S4VP diblock copolymers, the thermally stimulated current method and dielectric relaxation spectroscopy were employed to investigate differences in polarizability between S2VP and S4VP diblock copolymers. It is concluded that much higher T ODT of S4VP diblock copolymers as compared with the T ODT of S2VP diblock copolymers is attributable to the stronger polarizability of P4VP in S4VP diblock copolymer compared with the polarizability of P2VP in S2VP diblock copolymer.

Highly asymmetric lamellar microdomains, such as those required for many lithographic line patterns, cannot be straightforwardly achieved by conventional block copolymer self-assembly. We present a conceptually new and versatile approach to produce highly asymmetric lamellar morphologies by the use of binary blends of block copolymers whose components are capable of hydrogen bonding. We first demonstrate our strategy in bulk systems and complement the experimental results observed by transmission electron microscopy and small-angle X-ray scattering with theoretical calculations based on strong stretching theory to suggest the generality of the strategy. To illustrate the impact on potential lithographic applications, we demonstrate that our strategy can be transferred to thin film morphologies. For this purpose, we used solvent vapor annealing to prepare thin films with vertically oriented asymmetric lamellar patterns that preserve the bulk morphological characteristics. Due to the highly asymmetric lamellar microdomains, the line width is reduced to sub-10 nm scale, while its periodicity is precisely tuned.

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We present a strong stretching theory model for microphase segregation of AB + AC block copolymer blends in which the B and C segments possess strongly attractive (hydrogen bonding) interactions. In microphase separated morphologies, we demonstrate that the attraction between the B and the C segments causes a bending force toward the A layers. Such bending forces may induce transitions from lamellar and A-majority cylindrical morphologies in the pure component systems to "inverted" cylindrical and spherical morphologies in blends in which the B and C segments constitute the matrix phase. Similar driving forces may also drive transitions from A-majority spherical phases in pure component systems to highly asymmetric lamellar morphologies in blends. The predictions of our model are in excellent agreement with the trends observed in recent experimental results.

The effect of cadmium chloride (CdCl 2 ) on the phase behavior of polystyrene-block-poly(4vinylpyridine) copolymer (S4VP) was investigated by using rheometry, small-angle X-ray scattering, and transmission electron microscopy. For this purpose, symmetric S4VPs with various molecular weights were prepared by anionic polymerization. We found that with the addition of CdCl 2 the order-to-disorder transition of S4VP was significantly increased because of the intermolecular coordination connecting different P4VP block chains. We also studied the change of the domain spacing (D) upon addition of CdCl 2 as well as gelation behavior. At a relatively low content of CdCl 2 (γ < 6, where γ is the number of coordinated CdCl 2 per chain), D remains unchanged. However, when the amount of CdCl 2 increases further, D begins to decrease due to many coordinations of CdCl 2 that strongly perturb block copolymer conformation, including many ring closures. Furthermore, it is found that the scaled gelation point increases with increasing molecular weights of S4VP.

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