Tailored growth of graphene oxide liquid crystals with controlled polymer crystallization in GO-polymer composites

Graphene Oxides (GOs) have been frequently employed as fillers in polymer-based applications. While GO is known to nucleate polymer crystallization in GO-polymer composites reinforcing the mechanical properties of semicrystalline polymers, its counter effect on how polymer crystallization can alter the microstructure of GO has rarely been systematically studied yet. In this work, we study the GO nematic liquid crystal (LC) phase during polymer crystallization focusing on their hierarchical structures by employing in situ small/wide-angle X-ray scattering/diffraction (SAXS/WAXD) techniques. We found that GO LC and polymer crystals co-exist in the GO/polymer complex, where the overall liquid crystallinity is influenced by polymer crystallization. While polymer crystallizes in bulk or at the interface depending on the cooling rate, the interfacial crystallization of poly(ethylene glycol) (PEG) on GO improves both GO alignment and orientation of PEG crystal. This work provides an opportunity to develop a hierarchical structure of GO-based crystalline polymer nanocomposites, whose directionality can be controlled by polymer crystallization under proper cooling rates

Optical Transmittance Improvements of Al2O3/TiO2 Multilayer OLED Encapsulation Films Processed by Atomic Layer Deposition

Encapsulation of organic light-emitting diodes (OLEDs) is the only way to prevent degradation due to the penetration of moisture and oxygen. However, the upper encapsulation layer, located in the path through which light from the OLED passes, adversely affects light transmission. In this study, we calculated the optical transmittance by using admittance trajectory simulation and compared the data with actual Al2O3/TiO2 multilayer film processed by atomic layer deposition (ALD). By applying the simulated data on to actual encapsulation layer, we can observe the optical transmittance increase of up to 8% compared to the film of Al2O3/TiO2/Al2O3 structure. Over 90% of optical transmittance was achieved for all the visible wavelength ranges while maintaining water vapor transmission rate (WVTR) of the processed multilayer thin film as low as of 5 ?? 10???5 g/m2/day, which was measured using MOCON Aquatran 2

Wide concentration liquid crystallinity of graphene oxide aqueous suspensions with interacting polymers

Graphene oxides (GOs), an oxygenated derivative of graphene, spontaneously undergo monolayer exfoliation in water, and thus, form liquid crystalline (LC) suspensions. Unfortunately, the resultant suspensions vitrify at around a 1 wt% composition, which commonly acts as an obstacle for GO-based material fabrication, while degrading the molecular ordering and relevant material properties. Here, we systematically investigate the phase behaviour and structural evolution of GO LC suspensions under various experimental conditions and disclose how the glass transition of GO dispersions is affected particularly in the presence of strongly interacting polymers. The supplementary polymer additives can effectively retard the ???glass transition??? of a GO suspension, broaden the concentration range for a nematic LC phase toward lower and higher concentration ranges and dramatically decrease the viscosity of the suspension down to the 1/100-1/1000 level. Extensive small-angle X-ray scattering and rheological measurements are employed to characterize the molecular level GO structures in LC suspensions

Assessment of stroke drivers' performance in a driving simulator: A pilot study results

About 795,000 people experience a new or recurrent stroke in the United States each year and it is known that between 30% and 43% of the stroke survivors in the US resume driving within one year of the stroke incidence. In Korea, the stroke is the second leading cause of death and the incidence of stroke onset increases steadily. However, there are no guidelines for assessing driving performance for stroke patients yet. In this study, we developed an assessment environment using a driving simulator to evaluate driving performancce of stroke patients. The driving scenario consists of 3.5km urban traffic conditions (3 minutes), 10km divided 4-lane straight highway (6 minutes), and 7km 2-lane curved or hilly rural roads (6 minutes). Performance parameters during the simulated drive were automatically generated by the simulator software. The parameters included number of road edge excursions, centerline crossings, collisions, reaction time, and runtime. The stroke drivers’ performace was compared with healthy young drivers.1

Tailored Colloidal Stability and Rheological Properties of Graphene Oxide Liquid Crystals with Polymer-Induced Depletion Attractions

Graphene oxide liquid crystallinity (GO LC) has been widely exploited for high-performance graphene-based applications. In this regard, colloidal stability of GO LC suspension is a crucial requirement, particularly while polymers are often added to the GO LC. Unfortunately, current level of knowledge on how polymers influence the structure and properties of GO LC is not sufficient to systematically guide the development of applications. Here, we investigate the microstructure and rheological properties of GO LC suspensions in the presence of polymer additives with varying molecular weights and concentrations. Similar to conventional colloidal systems, non-negligible polymer-induced interactions are found in GO LC suspensions, which can effectively modulate the interaction among GO platelets and the relevant physical properties. On the basis of extensive small-angle X-ray scattering and rheological measurements, we demonstrate that, contrary to the general perception, polymer-induced depletion attraction can increase the colloidal stability of GO, while also preventing the vitrification of GO LC. In addition, a proper level of polymer additive can reduce the viscosity of GO LC suspensions by orders of magnitude, providing an effective route to GO LC-based solution processing. After all, the colloidal stability and rheological properties of GO can significantly impact the quality of GO. Therefore, we believe that our finding will be of great interest in the field of graphene-based applications, as it presents effective strategies for improving properties

Nonvolatile Memory Device with Designed Geometric Nanocrystal and its Analytical Modeling

Nonvolatile memory (NVM) characteristics are presented using well-ordered geometric Cr nanocrystal (NC) through the assistance of the block copolymer template. An analytical model for a cone shaped NC was developed and it was well-matched with the measured data. Program efficiency depending on different NC shapes: hemisphere, circular cone, and sphere was comprehensively investigated by the proposed model Nonvolatile Memory Device with Designed Geometric Nanocrystal and its Analytical Modeling. Available from: http://www.researchgate.net/publication/266471802_Nonvolatile_Memory_Device_with_Designed_Geometric_Nanocrystal_and_its_Analytical_Modeling [accessed Oct 12, 2015]

Geometric Effects of Nanocrystals in Nonvolatile Memory Using Block Copolymer Nanotemplate

This study describes geometric characteristics of a nonvolatile memory (NVM) device with a designed chromium (Cr) nanocrystal (NC) floating gate. By using a block copolymer (BCP) nanotemplate as a mask layer, cone-shaped NCs and disc-shaped NCs were formed. It Was found that the NVM device using the cone-shaped NC had a better program efficiency than that of the device using the disc-shaped one. This trend was verified by a theoretical model, which considered an effect of the capacitive-coupling ratio between a control gate and a NC floating gate. (C) 2009 Elsevier Ltd. All rights reserved.close2

Wrinkle-Directed Self-Assembly of Block Copolymers for Aligning of Nanowire Arrays

Highly aligned metal nanowire arrays with feature sizes approaching 10 nm are fabricated. This is made possible by the self-assembly of block copolymers (BCPs) on graphene-wrinkle arrays. Thickness-modulated BCP films confined on the wrinkled reduced graphene oxide (rGO) surface promote the strict alignment of the self-assembled BCP lamellae in the direction of the film thickness gradient.118171sciescopu

Hybrid perovskites: Effective crystal growth for optoelectronic applications

Outstanding material properties of organic-inorganic hybrid perovskites have triggered a new insight into the next-generation solar cells. Beyond solar cells, a wide range of controllable properties of hybrid perovskites, particularly depending on crystal growth conditions, enables versatile high-performance optoelectronic devices such as light-emitting diodes, photodetectors, and lasers. This article highlights recent progress in the crystallization strategies of organicinorganic hybrid perovskites for use as effective light harvesters or light emitters. Fundamental background on perovskite crystalline structures and relevant optoelectronic properties such as optical band-gap, electron-hole behavior, and energy band alignment are given. A detailed overview of the effective crystallization methods for perovskites, including thermal treatment, additives, solvent mediator, laser irradiation, nanostructure, and crystal dimensionalityis reported offering a comprehensive correlation among perovskite processing conditions, crystalline morphology, and relevant device performance. Finally, future research directions to overcome current practical bottlenecks and move towards reliable high performance perovskite optoelectronic applications are proposed.

Negative-Tone Block Copolymer Lithography by In Situ Surface Chemical Modification

Negative-tone block copolymer (BCP) lithography based on in situ surface chemical modifi cation is introduced as a highly effi cient, versatile self-assembled nanopatterning. BCP blends fi lms consisting of end-functionalized low molecular weight poly(styrene- ran -methyl methacrylate) and polystyrene- block -Poly(methyl methacylate) can produce surface vertical BCP nanodomains on various substrates without prior surface chemical treatment. Simple oxygen plasma treatment is employed to activate surface functional group formation at various substrates, where the end-functionalized polymers can be covalently bonded during the thermal annealing of BCP thin fi lms. The covalently bonded brush layer mediates neutral interfacial condition for vertical BCP nanodomain alignment. This straightforward approach for high aspect ratio, vertical self-assembled nanodomain formation facilitates single step, site-specifi c BCP nanopatterning widely useful for various substrates. Moreover, this approach is compatible with directed self-assembly approaches to produce device oriented laterally ordered nanopatterns.1221sciescopu