Molecular Dynamics Modeling of Methylene Blue−DOPC Lipid Bilayer Interactions

We present a coarse-grained MARTINI model for methylene blue (MB) and investigate the interactions of MB with dioleylphosphatidylcholine (DOPC) lipid bilayers by molecular dynamics simulations. Our results show that the charge state of MB and the oxidation degree of the DOPC bilayer play critical roles on membrane properties. Oxidation of the DOPC bilayer significantly increases permeability of water and MB molecules, irrespective of the charge state of MB. The most significant changes in membrane properties are obtained for peroxidized lipid bilayers in the presence of cationic MB, with ∼11% increase in the membrane area per lipid head group and ∼7 and 44% reduction in membrane thickness and lateral diffusivity, respectively

Photoinduced Demulsification of Emulsions Using a Photoresponsive Gemini Surfactant

This Article reports on the influence of light irradiation on the stability of emulsions prepared using a photoresponsive gemini surfactant (C₇-azo-C₇) having an azobenzene skeleton as a spacer. When mixtures of <i>trans</i> C₇-azo-C₇ aqueous solution and <i>n-</i>octane are homogenized, stable emulsions are obtained in a specific region of weight fraction and surfactant concentration. Fluorescence microscopy observations using a small amount of fluorescent probes show that the stable emulsions are oil-in-water (O/W)-type. UV irradiation of stable O/W emulsions promotes the <i>cis</i> isomerization of <i>trans</i> C₇-azo-C₇ and leads to the coalescence of the oil (octane) droplets in the emulsions, that is, demulsification. While the equilibrated interfacial tension (IFT) between aqueous <i>trans</i> C₇-azo-C₇ solution and octane is almost the same as that between aqueous <i>cis</i> C₇-azo-C₇ and octane, the occupied area per molecule for C₇-azo-C₇ at octane/water interface decreases with the <i>cis</i> photoisomerization of <i>trans</i> isomer. Dynamic IFT measurement shows that UV irradiation to the interface between aqueous <i>trans</i> C₇-azo-C₇ solution and octane brings about an increase in the interfacial tension, indicating that the Gibbs free energy at the interface increases. From these results, the <i>cis</i> isomerization of <i>trans</i> C₇-azo-C₇ molecules at the O/W interface due to UV irradiation leads to direct contact between the water and octane phases, because of the reduction of molecular area at the interface, and subsequently makes the emulsions demulsified

Photoinduced Demulsification of Emulsions Using a Photoresponsive Gemini Surfactant

This Article reports on the influence of light irradiation on the stability of emulsions prepared using a photoresponsive gemini surfactant (C₇-azo-C₇) having an azobenzene skeleton as a spacer. When mixtures of <i>trans</i> C₇-azo-C₇ aqueous solution and <i>n-</i>octane are homogenized, stable emulsions are obtained in a specific region of weight fraction and surfactant concentration. Fluorescence microscopy observations using a small amount of fluorescent probes show that the stable emulsions are oil-in-water (O/W)-type. UV irradiation of stable O/W emulsions promotes the <i>cis</i> isomerization of <i>trans</i> C₇-azo-C₇ and leads to the coalescence of the oil (octane) droplets in the emulsions, that is, demulsification. While the equilibrated interfacial tension (IFT) between aqueous <i>trans</i> C₇-azo-C₇ solution and octane is almost the same as that between aqueous <i>cis</i> C₇-azo-C₇ and octane, the occupied area per molecule for C₇-azo-C₇ at octane/water interface decreases with the <i>cis</i> photoisomerization of <i>trans</i> isomer. Dynamic IFT measurement shows that UV irradiation to the interface between aqueous <i>trans</i> C₇-azo-C₇ solution and octane brings about an increase in the interfacial tension, indicating that the Gibbs free energy at the interface increases. From these results, the <i>cis</i> isomerization of <i>trans</i> C₇-azo-C₇ molecules at the O/W interface due to UV irradiation leads to direct contact between the water and octane phases, because of the reduction of molecular area at the interface, and subsequently makes the emulsions demulsified

Effects of Magnetite Nanoparticles on Soybean Chlorophyll

Nanoparticles (NPs) have emerged as one of the most innovative and promising application in agriculture. Since plants are recognized as essential component of all ecosystems, the effects of NPs on plants may pave a new insight to the ecosystems. Here, uptake and translocation of superparamagnetic iron oxide NPs (SPIONs), with various surface charges, on soybean has been probed; in addition, the effects of SPIONs on variations of chlorophyll, in hydroponic condition, together with their ability for reduction of iron deficiency chlorosis were explored. We find that SPIONs, which were entered and translocated in the soybean, increased chlorophyll levels, with no trace of toxicity. Furthermore, it was found that physicochemical characteristics of the SPIONs had a crucial role on the enhancement of chlorophyll content in subapical leaves of soybean. The equivalent ratio of chlorophyll a to b, in all treatments with conventional growth medium iron chelate and SPIONs (as iron source), indicated no significant difference on the photosynthesis efficiency. Finally, it was observed that the effect of SPIONs on the soybean chlorophyll content may have influence on both biochemical and enzymatic efficiency in different stages of the photosynthesis reactions

Delivery Modulation in Silica Mesoporous Supports via Alkyl Chain Pore Outlet Decoration

This article focuses on the study of the release rate in a family of modified silica mesoporous supports. A collection of solids containing ethyl, butyl, hexyl, octyl, decyl, octadecyl, docosyl, and triacontyl groups anchored on the pore outlets of mesoporous MCM-41 has been prepared and characterized. Controlled release from pore voids has been studied through the delivery of the dye complex tris­(2,2′-bipyridyl)­ruthenium­(II). Delivery rates were found to be dependent on the alkyl chain length anchored on the pore outlets of the mesoporous scaffolding. Moreover, release rates follow a Higuchi diffusion model, and Higuchi constants for the different hybrid solids have been calculated. A decrease of the Higuchi constants was observed as the alkyl chain used to tune the release profile is longer, confirming the effect that the different alkyl chains anchored into the pore mouths exerted on the delivery of the cargo. Furthermore, to better understand the relation between pore outlets decoration and release rate, studies using molecular dynamics simulations employing force-field methods have been carried out. A good agreement between the calculations and the experimental observations was observed

Measurement of Small Molecular Dopant F4TCNQ and C₆₀F₃₆ Diffusion in Organic Bilayer Architectures

The diffusion of molecules through and between organic layers is a serious stability concern in organic electronic devices. In this work, the temperature-dependent diffusion of molecular dopants through small molecule hole transport layers is observed. Specifically we investigate bilayer stacks of small molecules used for hole transport (MeO-TPD) and p-type dopants (F4TCNQ and C₆₀F₃₆) used in hole injection layers for organic light emitting diodes and hole collection electrodes for organic photovoltaics. With the use of absorbance spectroscopy, photoluminescence spectroscopy, neutron reflectometry, and near-edge X-ray absorption fine structure spectroscopy, we are able to obtain a comprehensive picture of the diffusion of fluorinated small molecules through MeO-TPD layers. F4TCNQ spontaneously diffuses into the MeO-TPD material even at room temperature, while C₆₀F₃₆, a much bulkier molecule, is shown to have a substantially higher morphological stability. This study highlights that the differences in size/geometry and thermal properties of small molecular dopants can have a significant impact on their diffusion in organic device architectures

Transition and Stability of Copolymer Adsorption Morphologies on the Surface of Carbon Nanotubes and Implications on Their Dispersion

In this study, the adsorption morphologies as well as stability and transitions of a commercial dispersant copolymer (BYK 9076) on the surface of multiwalled carbon nanotubes (MWCNTs) were studied using Fourier transform infrared and UV–vis spectroscopy, dynamic light scattering, and electron microscopy techniques. The results show that the dispersion of carbon nanotubes in ethanol does not increase continuously with increasing copolymer/CNT ratio, which is correlated with the adsorption morphologies of the copolymer on the CNT surface. At a ratio of copolymer/CNT below 0.5, the morphology is random, shifting to a hemimicelle structure at a ratio from 0.5 to 1.0 while at ratios above 1.0, a cylindrical pattern is seen. The hemimicelle morphology is able to prevent the agglomeration of CNTs when the CNT concentration increases to 8.7 mg/mL, while cylindrical morphology is more efficient and stable to provide dispersion of CNTs at higher concentrations of CNTs

Response to Extreme Temperatures of Mesoporous Silica MCM-41: Porous Structure Transformation Simulation and Modification of Gas Adsorption Properties

Molecular dynamics (MD) and Monte Carlo (MC) simulations were applied together for the first time to reveal the porous structure transformation mechanisms of mesoporous silica MCM-41 subjected to temperatures up to 2885 K. Silica was experimentally characterized to inform the models and enable prediction of changes in gas adsorption/separation properties. MD simulations suggest that the pore closure process is activated by a collective diffusion of matrix atoms into the porous region, accompanied by bond reformation at the surface. Degradation is kinetically limited, such that complete pore closure is postponed at high heating rates. We experimentally observe decreased gas adsorption with increasing temperature in mesoporous silica heated at fixed rates, due to pore closure and structural degradation consistent with simulation predictions. Applying the Kissinger equation, we find a strong correlation between the simulated pore collapse temperatures and the experimental values which implies an activation energy of 416 ± 17 kJ/mol for pore closure. MC simulations give the adsorption and selectivity for thermally treated MCM-41, for N₂, Ar, Kr, and Xe at room temperature within the 1–10 000 kPa pressure range. Relative to pristine MCM-41, we observe that increased surface roughness due to decreasing pore size amplifies the difference of the absolute adsorption amount differently for different adsorbate molecules. In particular, we find that adsorption of strongly interacting molecules can be enhanced in the low-pressure region while adsorption of weakly interacting molecules is inhibited. This then results in higher selectivity in binary mixture adsorption in mesoporous silica

Introducing Solubility Control for Improved Organic P‑Type Dopants

To overcome the poor solubility of the widely used p-type dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), we have synthesized a series of structure-modified, organic p-type dopants to include alkyl ester groups designed to enable solubility and miscibility control. UV–vis–NIR and cyclic voltammetry measurements show increased solubility of mono- and diester substituted dopants with only modest changes to acceptor strength. Using absorption spectroscopy, photoluminescence, and in-plane conductivity measurements, we demonstrate that the new dopants can successfully p-type dope poly­(3-hexylthiophene-2,5-diyl) (P3HT). Monoester substituted dopants are characterized by only slightly reduced electron affinity relative to F4TCNQ, but greater doping effectiveness due to increased miscibility with P3HT. Diester substituted dopants undergo a dimerization reaction before assuming their doped states, which may help anchor dopants into position post deposition, thus decreasing the negative effect of dopant drift and diffusion. We conclude that increased dopant solubility/miscibility increases the overall effectiveness of doping in solution-cast polymer films and that ester modification is a practical approach to achieving solubility/miscibility control in TCNQ-type dopants

Reversible Optical Control of Conjugated Polymer Solubility with Sub-micrometer Resolution

Organic electronics promise to provide flexible, large-area circuitry such as photovoltaics, displays, and light emitting diodes that can be fabricated inexpensively from solutions. A major obstacle to this vision is that most conjugated organic materials are miscible, making solution-based fabrication of multilayer or micro- to nanoscale patterned films problematic. Here we demonstrate that the solubility of prototypical conductive polymer poly(3-hexylthiophene) (P3HT) can be reversibly “switched off” using high electron affinity molecular dopants, then later recovered with light or a suitable dedoping solution. Using this technique, we are able to stack mutually soluble materials and laterally pattern polymer films by evaporation or with light, achieving sub-micrometer, optically limited feature sizes. After forming these structures, the films can be dedoped without disrupting the patterned features; dedoped films have identical optical characteristics, charge carrier mobilities, and NMR spectra as as-cast P3HT films. This method greatly simplifies solution-based device fabrication, is easily adaptable to current manufacturing workflows, and is potentially generalizable to other classes of materials