Study on thermooxidative degradation of poly(vinyl alcohol)/silica nanocomposite prepared with SAM technique

The thermooxidative degradation of poly (vinyl alcohol)/silica (PVA/SiO2) nanocomposite prepared with self-assembly monolayer (SAM) technique is investigated by using a thermogravimetry (TG) and Fourier transform infrared spectroscopy coupled thermogravimetry (FTIR/TG). The results show that although the thermooxidative degradation process of prepared nanocomposite is similar to that of the pure PVA, its thermooxidative stability has been greatly improved.

Poly (vinyl alcohol) / silica nanocomposites: morphology and thermal degradation kinetics

The morphology of self-assembled poly(vinyl alcohol)/silica (PVA/SiO₂) nanocomposites is investigated with atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the SiO₂ nanoparticles are homogenously distributed throughout the PVA matrix in a form of spherical nano-cluster. The average size of the SiO₂ clusters is below 50 nm at the low contents (SiO₂ ≤ 5 wt%), while particle aggregations are clearly observed and their average size markedly increases to 110 nm when 10 wt% SiO₂ is loaded. The thermogravimetric analysis (TGA) shows that the nanocomposite significantly outperforms the pure PVA in the thermal resistance. By using a multi-heating-rate method, the thermal degradation kinetics of the nanocomposite with a SiO₂ content of 5 wt% is compared to the PVA host. The reaction activation energy (E) of the nanocomposite, similar to the pure PVA, is divided into two main stages corresponding to two degradation steps. However, at a given degradation temperature, the nanocomposite presents much lower reaction velocity constants (k), while its E is 20 kJ/mol higher than that of the PVA host.

Crystal structure of a ceIII/feIII heterobimetallic complex

A central μ₃—O moiety linking two Fe^III and one Ce^III sites supported by two distinct heterometallic carboxylate bridging modes features in self-assembled [CeFe₂(bpy)₂(μ₃—O)(μ—L)₂(μ—LH)₂(LH)(H₂O)₂]·0.5(bpy)·7H₂O (1) (LH₂ = glycolic acid), and the structure models potential bonding modes of the Rare Earth corrosion inhibitor Ce(glycolate)₃ to iron or iron oxide.

Single molecule conductance through rigid norbornylogous bridges with zero average curvature

A new homologous series of norbornylogous (NB) bridges has been synthesized in which the average curvature of the bridges is very small. The molecules are rigid and have two thiol moieties at each end to allow them to form self-assembled monolayers (SAMs) and to connect to two gold electrodes to form a molecular junction. The SAMs formed were characterized using electrochemistry to determine the surface coverage of molecules on gold surface and to provide an indication of the packing of the NB bridges while ellipsometry and X-ray photoelectron spectroscopy (XPS) were used to provide an indication of the SAM thickness and orientation. Single molecule conductance of NB bridges was measured as a function of the molecular length. The conductance was found to decrease exponentially with the length with a decay constant that is exactly correlated with photoelectron transfer and other studies at the multiple molecule level. The molecule−electrode contact resistance was determined and compared with that of related alkanedithiol molecular junctions.

The boundary lubrication of chemically grafted and cross-linked hyaluronic acid in phosphate buffered saline and lipid solutions measured by the surface forces apparatus

High molecular weight hyaluronic acid (HA) is present in articular joints and synovial fluid at high concentrations; yet despite numerous studies, the role of HA in joint lubrication is still not clear. Free HA in solution does not appear to be a good lubricant, being negatively charged and therefore repelled from most biological, including cartilage, surfaces. Recent enzymatic experiments suggested that mechanically or physically (rather than chemically) trapped HA could function as an “adaptive” or “emergency” boundary lubricant to eliminate wear damage in shearing cartilage surfaces. In this work, HA was chemically grafted to a layer of self-assembled amino-propyl-triethoxy-silane (APTES) on mica and then cross-linked. The boundary lubrication behavior of APTES and of chemically grafted and cross-linked HA in both electrolyte and lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) solutions was tested with a surface forces apparatus (SFA). Despite the high coefficient of friction (COF) of μ ≈ 0.50, the chemically grafted HA gel significantly improved the lubrication behavior of HA, particularly the wear resistance, in comparison to free HA. Adding more DOPC lipid to the solution did not improve the lubrication of the chemically grafted and cross-linked HA layer. Damage of the underlying mica surface became visible at higher loads (pressure >2 MPa) after prolonged sliding times. It has generally been assumed that damage caused by or during sliding, also known as “abrasive friction”, which is the main biomedical/clinical/morphological manifestation of arthritis, is due to a high friction force and, therefore, a large COF, and that to prevent surface damage or wear (abrasion) one should therefore aim to reduce the COF, which has been the traditional focus of basic research in biolubrication, particularly in cartilage and joint lubrication. Here we combine our results with previous ones on grafted and cross-linked HA on lipid bilayers, and lubricin-mediated lubrication, and conclude that for cartilage surfaces, a high COF can be associated with good wear protection, while a low COF can have poor wear resistance. Both of these properties depend on how the lubricating molecules are attached to and organized at the surfaces, as well as the structure and mechanical, viscoelastic, elastic, and physical properties of the surfaces, but the two phenomena are not directly or simply related. We also conclude that to provide both the low COF and good wear protection of joints under physiological conditions, some or all of the four major components of joints—HA, lubricin, lipids, and the cartilage fibrils—must act synergistically in ways (physisorbed, chemisorbed, grafted and/or cross-linked) that are still to be determined.

Influence of ionic liquids on the electrical conductivity and morphology of PEDOT:PSS films

Small-molecule nonvolatile additives based on ionic liquids (IL) as electrical conductivity enhancer in Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) was studied. Ionic liquids were investigated in the synthesis of self-assembled, highly organized hybrid nanostructures due to their ability as supramolecular solvents. Different percentage of five ionic liquids, such as 1-butyl-3-methylimidazolium tetrafluoroborate (bmim) F 4 and 1-butyl-3-methylimidazolium bromide (bmim)Br were added to a PEDOT:PSScommercial dispersion. Films of pure PEDOT:PSS showed an average conductivity of 14 S cm-1, which corresponded to the value range given by the supplier. AFM images showed that IL induced the formation of a three-dimensional conducting network with smaller PEDOT domains. The ionic character of the films was significantly increased because of the presence of ionic liquids, which can be used effectively in optoelectronic devices.

Microphase separation induced by competitive hydrogen bonding interactions in semicrystalline triblock copolymer/homopolymer complexes

Microphase separation through competitive hydrogen bonding interactions in ABC/D triblock copolymer/ homopolymer complexes is studied for the first time. This study investigated self-assembled nanostructures that are obtained in the bulk, by the complexation of a semicrystalline polystyrene-block-poly(4-vinylpyridine)-block-poly(ethylene oxide) (SVPEO) triblock copolymer with a poly(4-vinyl phenol) (PVPh) homopolymer in tetrahydrofuran (THF). In these complexes, microphase separation takes place due to the disparity in intermolecular interactions among PVPh/P4VP and PVPh/PEO pairs. At low PVPh concentrations, PEO interacts relatively weakly with PVPh, whereas in the complexes containing more than 30 wt% PVPh, the PEO block interacts considerably with PVPh, leading to the formation of composition-dependent nanostructures. SAXS and TEM results indicate that the cylindrical morphology of a neat SVPEO triblock copolymer changes into lamellae structures at 20 wt% of PVPh then to disordered lamellae with 40 wt% PVPh. Wormlike structures are obtained in the complex with 50 wt%PVPh, followed by disordered spherical microdomains with size in the order of 40–50 nm in the complexes with 60–80 wt% PVPh. Moreover, when the content of PVPh increases to 80 wt%, the complexes show a completely homogenous phase of PVPh/P4VP and PVPh/PEO with phase separated spherical PS domains. The fractional crystallization behavior in SVPEO and complexes at lower PVPh content was also examined. A structural model was proposed to explain the microphase separation and self-assembled morphologies of these complexes based on the experimental results obtained. The formation of nanostructures and changes in morphologies depend on the relative strength of hydrogen bonding interactions between each component block of the copolymer and the homopolymer.

Polystyrene-b-poly(oligo(ethylene oxide) monomethyl ether methacrylate)-bpolystyrene triblock copolymers as potential carriers for hydrophobic drugs

A simple and effective method is introduced to synthesize a series of polystyrene-b-poly(oligo(ethylene oxide) monomethyl ether methacrylate)-b- polystyrene (PSt-b-POEOMA-b-PSt) triblock copolymers. The structures of PSt-b-POEOMA-b-PSt copolymers were characterized by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopy. The molecular weight and molecular weight distribution of the copolymer were measured by gel permeation chromatography (GPC). Furthermore£ the self-assembling and drug-loaded behaviours of three different ratios of PSt-b-POEOMA-b-PSt were studied. These copolymers could readily self-assemble into micelles in aqueous solution. The vitamin E-loaded copolymer micelles were produced by the dialysis method. The micelle size and core-shell structure of the block copolymer micelles and the drug-loaded micelles were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The thermal properties of the copolymer micelles before and after drug-loaded were investigated by different scanning calorimetry (DSC). The results show that the micelle size is slightly increased with increasing the content of hydrophobic segments and the micelles are still core-shell spherical structures after drug-loaded. Moreover, the glass transition temperature (Tg) of polystyrene is reduced after the drug loaded. The drug loading content (DLC) of the copolymer micelles is 70%-80% by ultraviolet (UV) photolithography analysis. These properties indicate the micelles self-assembled from PSt-b- POEOMA-b- PSt copolymers would have potential as carriers for the encapsulation of hydrophobic drugs.

Phase behaviour and properties of microemulsions and lyotropic liquid crystals

This research study has developed new ways to control bulk properties of self-assembled microemulsions and lyotropic liquid crystals (LLCs) by manipulations of their corresponding precursor phase behaviour. Investigation into relating phase behaviour with the morphology, porosity, thermal stability, rheological property, and photoresponse of these assemblies has been carried out.

Effect of magnetic treatment on microstructure and cycle performance of LiFePO4/C cathode material

LiFePO4/C composite was prepared by hydrothermal synthesis along with a magnetic treatment method. The LiFePO4/C composite synthesized without magnetic treatment is an integrated rhombic shape crystal, whereas the LiFePO4/C material synthesized with magnetic treatment presents a rhombus shape which is self-assembled by a number of small crystal particles with an average size of about 100 nms. The capacity retention for the LiFePO4/C cathode material synthesized without magnetic treatment is only 77% after 30 charge-discharge cycles at 0.2 C, but the LiFePO4/C composite synthesized with magnetic treatment has a capacity retention of 100% after 100 charge-discharge cycles at 1 C and 5 C. It suggests that magnetic treatment can remove Fe3+ cations effectively during the preparation process and enhance the cycle performance of the LiFePO4/C material.

Theoretical modeling and experimental validation of surface stress in thrombin aptasensor

Adsorption of target molecules on the immobilized microcantilever surface produced beam displacement due to the differential surface stress generated between the immobilized and non-immobilized surface. Surface stress is caused by the intermolecular forces between the molecules. Van der Waals, electrostatic forces, hydrogen bonding, hydrophobic effect and steric hindrance are some of the intermolecular forces involved. A theoretical framework describing the adsorption-induced microcantilever displacement is derived in this paper. Experimental displacement of thrombin aptamer-thrombin interactions was carried out. The relation between the electrostatic interactions involved between adsorbates (thrombin) as well as adsorbates and substrates (thrombin aptamer) and the microcantilever beam displacement utilizing the proposed mathematical model was quantified and compared to the experimental value. This exercise is important to aid the designers in microcantilever sensing performance optimization.

Lubricin: a versatile, biological anti-adhesive with properties comparable to polyethylene glycol

Lubricin is a glycoprotein found in articular joints which has been recognized as being an important biological boundary lubricant molecule. Besides providing lubrication, we demonstrate, using a quartz crystal microbalance, that lubricin also exhibits anti-adhesive properties and is highly effective at preventing the non-specific adsorption of representative globular proteins and constituents of blood plasma. This impressive anti-adhesive property, combined with lubricin's ability to readily self-assemble to form dense, highly stable telechelic polymer brush layers on virtually any substrates, and its innate biocompatibility, makes it an attractive candidate for anti-adhesive and anti-fouling coatings. We show that coatings of lubricin protein are as effective as, or better than, self-assembled monolayers of polyethylene glycol over a wide range of pH and that this provides a simple, versatile, highly stable, and highly effective method of controlling unwanted adhesion to surfaces.

Morphology and mechanical properties of nanostructured thermoset/block copolymer blends with carbon nanoparticles

Here we report the effect of multi-walled carbon nanotubes (MWCNTs) and thermally reduced graphene (TRG) on the miscibility, morphology and final properties of nanostructured epoxy resin with an amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The addition of nanoparticles did not have any influence on the miscibility of PEO-PPO-PEO copolymer in the resin. However, MWCNTs and TRG reduced the degree of crystallinity of the PEO-rich microphases in the blends above 10 wt.% of copolymer while they did not change the phase morphology at the nanoscale, where PPO spherical domains of 20-30 nm were found in all the samples studied. A synergic effect between the self-assembled nanostructure and the nanoparticles on the toughness of the cured resin was observed. In addition, the nanoparticles minimized the negative effect of the copolymer on the elastic modulus and glass transition temperature in the resin.

Synergistic effects of sodium lauroyl sarcosinate and glutamic acid in inhibition assembly against copper corrosion in acidic solution

© 2015 Elsevier B.V. All rights reserved. A self-assembled multilayer (SAM) from sodium lauroyl sarcosinate (SLS) and glutamic acid (GLU) is formed on copper surface. Its inhibition ability against copper corrosion is examined by electrochemical analysis and weight loss test. In comparison to SAM formed by just SLS or GLU, a synergistic effect is observed when the coexistence of SLS and GLU in SAM. The SLS/GLU SAM has an acicular multilayer structure, and SAM prepared under the condition of 5 mM SLS and 1 mM GLU shows the best protection efficiency. PM6 calculation reveals that the synergistic effect stems from interactions between SLS, GLU and cupric ions.

Tunnelling current recognition through core-satellite gold nanoparticles for ultrasensitive detection of copper ions

We report a new method for ultrasensitive detection of Cu(2+), which is based on changes in the tunnelling recognition current across self-assembled core-satellite gold nanoparticles (GNPs) networks functionalised with amino acids (l-cysteine). The addition of copper ions induces the formation of GNP/l-cysteine/Cu(2+)/l-cysteine/GNP molecular junctions and generates a significant decrease in the resistance through the networks. The networks are ultrasensitive to over ten orders range of copper ion concentrations.