Interfacially compatibilized PI/PDMS blends with reduced octadecylamine-functionalized graphene oxide: morphological and rheological properties.

We investigate the interfacial compatibilization effect of reduced octadecylamine-functionalized graphene oxide (ODA-GO) on the morphological and rheological properties of immiscible homopolymer blends of polydimethylsiloxane (PDMS) and polyisoprene (PI). We prepared droplet-matrix blends with a PI : PDMS ratio of 30 : 70 or 70 : 30 and interfacially localized ODA-GO stabilizer loadings from 0.1% to 1%. Blends were examined by optical microscopy and rheometry. Both blends show typical droplet-matrix morphology with stabilized round drops that do not stick together. With the addition of ODA-GO, smaller drops were observed in PI-continuous blends as compared to the PDMS-continuous blends suggesting that the effects of particles are not symmetric in the two cases. At sufficiently high ODA-GO loadings, flow-induced coalescence is suppressed almost completely. Dynamic oscillatory rheology broadly confirms the morphological observations. Specifically, all the blends show an interfacial relaxation process that is distinct from the bulk viscoelasticity, and the dependence of this process on GO content and flow conditions confirms the compatibilizing effect of the ODA-GO. This work provides a strategy for interfacially-compatibilizated polymer blends with specific properties for practical applications.

Hybrids of Bowl-like and Crumpled Hollow Carbon Particles Synthesized through Encapsulation Templating.

The one-pot synthesis of hybrid hollow nanoparticles of symmetric and asymmetric shapes is a challenging task and has rarely been reported. This work proposes a method for a high-yield synthesis of hybrid hollow carbon particles. In the first step, hexadecane/styrene (HD/St) is encapsulated in a silica shell. Then, by the polymerization of St, a silica/polystyrene double shell is formed. Finally, hollow carbon particles with bowl-like and crumpled shapes are obtained by carbonization. The results show that the ratio of diameter to thickness (D/H) for obtaining crumpled particles is ∼4-12, whereas this ratio is ∼7-18 for bowl-like particles. We study the effects of HD and St concentrations on the D/H ratio and the composition of hybrid particles. In contrast to suspensions of hollow carbon spheres, the suspensions of hybrid nanoparticles show shear-thinning behavior over the examined range of shear rates, which is attributed to their enhanced packing. The shape effect of hybrid particles also increases their adsorption on human mesenchymal stem cells (hMSCs) compared to the hollow carbon spheres.

Interplay between phase separation and dewetting in PS/PVME thin films: effect of temperature.

We studied the effects of temperature on the interplay between dewetting and phase separation at shallow and deep depths at two-phase temperatures in PS/PVME polymer blend thin films. Optical microscopy, AFM measurements, and ellipsometry analysis were performed to investigate the dewetting behavior of the films. At the deep quench depth (phase separation temperature of 115 °C), a two-layer film formed, consisting of a thin PVME layer directly on the surface of a silicon wafer (as the wetting layer) and a bulk layer which was the upper layer. In the bulk layer, the phase separation mechanism was controlled by an apparent nucleation and growth mechanism, which was driven by entropic and anisotropic limitations rather than thermodynamic preferences. After about 106 min of annealing, liquid-liquid dewetting occurred in the interface of the formed layers, triggered by Laplace pressure differences. However, at the shallow quench depth (phase separation temperature of 95 °C), a tri-layered structure formed in the thin films and concentration fluctuations at the interfaces of the formed layers triggered surface fluctuations and instabilities (dewetting phenomenon).

Effect of drug amlodipine on the charged lipid bilayer cell membranes DMPS and DMPS + DMPC: a molecular dynamics simulation study.

In this work, the effects of the anti-hypertensive drug amlodipine in native and PEGylated forms on the malfunctioning of negatively charged lipid bilayer cell membranes constructed from DMPS or DMPS + DMPC were studied by molecular dynamics simulation. The obtained results indicate that amlodipine alone aggregates and as a result its diffusion into the membrane is retarded. In addition, due to their large size aggregates of the drug can damage the cell, rupturing the cell membrane. It is shown that PEGylation of amlodipine prevents this aggregation and facilitates its diffusion into the lipid membrane. The interaction of the drug with negatively charged membranes in the presence of an aqueous solution of NaCl, as the medium, is investigated and its effects on the membrane are considered by evaluating the structural properties of the membrane such as area per lipid, thickness, lipid chain order and electrostatic potential difference between bulk solution and lipid bilayer surface. The effect of these parameters on the diffusion of the drug into the cell is critically examined and discussed.

Interaction of drugs amlodipine and paroxetine with the metabolizing enzyme CYP2B4: a molecular dynamics simulation study.

The interactions of the drugs amlodipine and paroxetine, which are prescribed respectively for treatment of hypertension and depression, with the metabolizing enzyme cytochrome CYP2B4 as the drug target, have been studied by molecular dynamics (MD) simulation. Poly ethylene glycol was used to control the drugs' interactions with each other and with the target CYP2B4. Thirteen simulation systems were carefully designed, and the results obtained from MD simulations indicated that amlodipine in the PEGylated form prescribed with paroxetine in the nonPEGylated form promotes higher cytochrome stability and causes fewer fluctuations as the drugs approach the target CYP2B4 and interact with it. The simulation results led us to hypothesize that the combination of the drugs with a specific drug ratio, as proposed in this work, manifests more effective diffusivity and less instability while metabolizing with enzyme CYP2B4. Also, the active residues in the CYP2B4 enzyme that interact with the drugs were determined by MD simulation, which were consistent with the reported experimental results. Graphical Abstract Efficient drug-enzyme interactions, as a result of PEGylation.

Combination of anti-hypertensive drugs: a molecular dynamics simulation study.

The anti-hypertensive drugs amlodipine, atenolol and lisinopril, in ordinary and PEGylated forms, with different combined-ratios, were studied by molecular dynamics simulations using GROMACS software. Twenty simulation systems were designed to evaluate the interactions of drug mixtures with a dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane, in the presence of water molecules. In the course of simulations, various properties of the systems were investigated, including drug location, diffusion and mass distribution in the membrane; drug orientation; the lipid chain disorder as a result of drug penetration into the DMPC membrane; the number of hydrogen bonds; and drug surface area. According to the results obtained, combined drugs penetrate deeper into the DMPC lipid bilayer membrane, and the lipid chains remain ordered. Also, the combined PEGylated drugs, at a combination ratio of 1:1:1, enhance drug penetration into the DMPC membrane, reduce drug agglomeration, orient the drug in a proper angle for easy penetration into the membrane, and decrease undesirable lipotoxicity due to distorted membrane self-assembly and thickness. Graphical abstract ᅟ.

Interaction of PEGylated anti-hypertensive drugs, amlodipine, atenolol and lisinopril with lipid bilayer membrane: A molecular dynamics simulation study.

The interaction of PEGylated anti-hypertensive drugs, amlodipine, atenolol and lisinopril with lipid bilayer membrane dimyristoylphosphatidylcholine (DMPC) has been studied in nine different simulation systems consisting of 128 lipid molecules and appropriate number of water molecules by molecular dynamics method and by utilizing GROMACS software. The influences of PEGylation on the mentioned drugs and the differences in application of two types of spacer molecules on the performance of drugs and DMPC membrane have been evaluated and mass density of the components in the simulation box, mean square displacement (MSD), electrostatic potential, hydrogen bonding, radial distribution function (RDF), area per lipid, order parameter, and angle distribution of the component molecules including drug, DMPC and PEG has been investigated. Furthermore, umbrella sampling analysis indicated that, PEGylation of the drugs made amlodipine to behave more hydrophilic, whereas in case of lisinopril and atenolol, PEGylation made these drugs to behave more hydrophobic. In almost all of the simulated systems, PEGylation increased the diffusion coefficient of the drugs.

Controlling the kinetics of viscoelastic phase separation through self-assembly of spherical nanoparticles or block copolymers.

Viscoelastic phase separation (VPS) can produce a network structure of the minor phase, which needs to be stabilized for designing a heterogeneous structure with desired mechanical and electrical functions. In this work, we investigate the stabilization of the VPS-induced network structure in a dynamically asymmetric PS/PVME blend by incorporation of a SEBS-g-MA block copolymer or dimethyldichlorosilane modified nanosilica. The addition of SEBS-g-MA retards the volume shrinking process and slows down the kinetics of phase separation due to its localization at the PS/PVME interfaces. Consequently, in the later stage of VPS, phase inversion occurs at longer times with respect to the neat blend due to the decreased interfacial tension. In contrast, hydrophobic nanoparticles self-assemble in the bulk of PS-rich phase and restrain the dynamics of polymer chains enhancing the dynamic asymmetry of the system. The efficiency of nanoparticles in controlling the kinetics of phase separation is found to be superior compared to block copolymer-based compatibilizers indicating the significance of chain dynamics. Moreover, beyond a critical nanoparticle volume fraction, phase separation is pinned due to particle percolation within the PS-rich phase, yielding a kinetically trapped VPS-induced network structure.