Non-isothermal crystallisation kinetics of self-assembled polyvinylalcohol/silica nano-composite

A novel polyvinylalcohol/silica (PVA/SiO₂) nano-composite is prepared with the self-assembly monolayer (SAM) technique. The SiO₂ nano-particles are homogenously distributed throughout the PVA matrixes as nano-clusters with an average diameter ranged from 15 to 240 nm depending on the SiO₂ contents. Using differential scanning calorimetry (DSC), the non-isothermal crystallisation behaviour and kinetics of the PVA/SiO₂ nano-composites are investigated and compared to those of the pure PVA. There are strong dependences of the degree of crystallinity (X_c), peak crystallisation temperature (T_p), half time of crystallisation (t_1/2), and Ozawa exponent (m) on the SiO₂ content and cooling rate. The crystallisation activation energy (E) calculated with the Kissinger model is markedly lower when a small amount of SiO₂ is added, then gradually increases and finally becomes higher than that of the pure PVA when there is more than 10% SiO₂ in the composite.

Self-assembled complexes of poly(4-vinylphenol) and poly(ε-caprolactone)-block-poly(2-vinylpyridine) via competitive hydrogen bonding

Nanostructured complexes were prepared from poly(ε-caprolactone)-block-poly(2-vinylpyridine) (PCL-b-P2VP) and poly(4-vinylphenol) (PVPh) in tetrahydrofuran (THF). The phase behavior, specific interactions, and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). In this A-b-B/C type block copolymer/homopolymer system, both blocks of the PCL-b-P2VP block copolymer have favorable intermolecular interaction toward PVPh via hydrogen bonding, but the interaction between P2VP block and PVPh is significantly stronger than that between PCL block and PVPh. It was found that the disparity in competitive intermolecular interactions, specifically PVPh and P2VP block interact strongly whereas PVPh and PCL block interact weakly, leads to the formation of a variety of nanostructures depending on PVPh concentration. Spherical micelles of 30−40 nm in diameter were obtained in the complex with 10 wt % PVPh, followed by wormlike micelles with size in the order of 40−50 nm in the complexes with 30−60 wt % PVPh. At low PVPh concentrations, PCL interacts weakly with PVPh, whereas in the complexes containing more than 20 wt % PVPh, the PCL block began to interact considerably with PVPh, leading to the formation of composition-dependent nanostructures. The complex becomes homogeneous with PVPh content beyond 60 wt %, since a sufficient amount of PVPh is available to form hydrogen bonds with both PCL and P2VP. Finally, a model was proposed to explain the self-assembly and microphase morphology of these complexes based on the experimental results obtained. The competitive hydrogen-bonding interactions cause the self-assembly and formation of different microphase morphologies.

Superhydrophobic modification of polyimide films based on gold-coated porous silver nanostructures and self-assembled monolayers

We present a facile and effective method for controlling the surface hydrophobicity of polyimide films from sticky to superhydrophobic properties by tailoring their topographies. Nanostructured silver layers were produced on polyimide films by treatment with aqueous KOH and AgNO3, followed by thermal treatment at 200 degrees C or higher temperatures. Further modification of the gold-coated silver layers with n-dodecanethiol led to hydrophobic surfaces. Different morphologies of the silver layers at the micro- and nano-meter scales, which result in the variety of hydrophobicity, can be tailored by controlling the thermal treatment temperature. Surfaces prepared at 320 degrees C showed a sticky property that water drops did not slide off even when the sample was held upside down. Superhydrophobic surfaces were obtained when the temperature was above 340 degrees C. A remarkable superhydrophobicity, as evidenced by a very large water contact angle of 162 degrees and a very small sliding angle of 7 degrees, was achieved by heating the modified polyimide films at 360 degrees C. This is also the first example for superhydrophobic modification of polyimide films.

Self-assembled natural rubber/silica nanocomposites : its preparation and characterization

A novel natural rubber/silica (NR/SiO2) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO2 nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO2 loading is less than 6.5 wt%. At low SiO2 contents (less-than-or-equals, slant4.0 wt%), the NR latex (NRL) and SiO2 particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO2 are observed. When more SiO2 is loaded, secondary aggregations of SiO2 nanoparticles are gradually generated, and the size of SiO2 cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO2 nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO2 nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO2 has great potential to manufacture medical protective products with high performances.

Self-assembled natural rubber/multi-walled carbon nanotube composites using latex compounding techniques

Functionalization of multi-walled carbon nanotubes (MWCNTs) plays an important role in eliminating nanotube aggregation for reinforcing polymeric materials. We prepared a new class of natural rubber (NR)/MWCNT composites by using latex compounding and self-assembly technique. The MWCNTs were functionalized with mixed acids (H2SO₄/HNO₃ = 3:1, volume ratio) and then assembled with poly (diallyldimethylammonium chloride) and latex particles. The Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy were used to investigate the assembling mechanism between latex particles and MWCNTs. It is found that MWCNTs are homogenously dispersed in the natural rubber (NR) latex as individual nanotubes since strong self-aggregation of MWCNTs has been greatly depressed with their surface functionalization. The well-dispersed MWCNTs produce a remarkable increase in the tensile strength of NR even when the amount of MWCNTs is only 1 wt.%. Dynamic mechanical analysis shows that the glass transition temperature of composites is higher and the inner-thermogenesis and thermal stability of NR/MWCNT composites are better, when compared to those of the pure NR. The marked improvement in these properties is largely due to the strong interfacial adhesion between the NR phase and MWCNTs. Functionalization of MWCNTs represents a potentially powerful technology for significant reinforcement of natural rubber materials.

Self-assembled diblock copolymer complexes via competitive hydrogen bonding

This thesis investigates self-assembly and microphase separation induced by competitive hydrogen bonding in A-b-BC diblock copolymer/homopolymer systems. A series of ordered and disordered morphologies including lamellae, hexagonal cylinders, wormlike microdomains and hierarchical structures were observed. The morphological transitions are correlated with hydrogen bonding interactions in terms of the association constants.

Analysis of self-assembled monolayer interfaces by electrospray mass spectrometry : a gentle approach

A general mass spectrometry technique for the characterization of alkanethiol-modified surfaces is presented. Alkanethiol self-assembled onto a gold surface (in this case, peptides were attached to the gold surface via a thiolate bond) was reductively desorbed in 0.05 M KOH in the presence of octadecyl-derivatized silica gel. The peptide adsorbed onto the silica gel, whereupon it could be filtered, washed to remove any salts, and then eluted using a mixture of 4:1 v/v methanol/water. The eluant containing the peptide was injected into a Fourier transform ion-cyclotron resonance mass spectrometer (FTICR/MS) via electrospray ionization. The spectrum showed no fragmentation of the peptide, demonstrating the gentleness of the technique. This simple procedure is not limited to FTICR/MS and could be adapted to other mass spectrometers.

Stepwise synthesis of Gly−Gly−His on gold surfaces modified with mixed self-assembled monolayers

Peptide-modified electrode surfaces have been shown to have excellent recognition properties for metal ions. An efficient method of screening a potential peptide for its selectivity for a given metal would involve the synthesis of the peptide directly on the electrode surface. This paper outlines a procedure in which the tripeptide Gly−Gly−His was synthesized one amino acid at a time on a gold surface modified with a self-assembled monolayer of the mixed alkanethiolates 3-mercaptopropionic acid (MPA) and 3-mercaptopropane (MP). Electrochemistry and high-resolution mass spectrometry were used to elucidate the structure of the adsorbed species and follow the synthesis. The amino acids can be attached only to MPA, but the presence of a diluting unreactive molecule of MP reduces steric crowding about the reaction center. The maximum coverage of synthesized tripeptide occurs at a ratio of MPA/MP of 1:1.

Characterisation of gold electrodes modified with self-assembled monolayers of l-cysteine for the adsorptive stripping analysis of copper

Electrochemical sensors for copper ions in environmental samples were prepared by modifying gold electrodes with l-cysteine by self-assembly. The adsorption of l-cysteine on gold electrodes was studied by electrochemical reductive desorption in 0.5 M KOH, and the interaction of l-cysteine with copper ions was investigated by cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy. At low concentrations the ratio of l-cysteine to bound Cu(II) is 2:1. At higher concentrations (0.1 M) copper reacts with adsorbed cysteine forming copper sulfide on the electrode surface. On a modified l-cysteine gold electrode, Osteryoung square wave voltammetric determination of Cu(II) with a detection limit below 5 ppb has been demonstrated.

The self-assembled monolayer modification of electrodes - some recent advances in biological application

The modification of an electrode surface at the molecular level using the technique of depositing self-assembled monolayers (SAM) is a typical example of the techniques used in nanotechnology, from the process "bottom up", which is to create a nanostructure by successive additions of molecular or atomic entities on a surface. This article presents some recent advances in the field, with examples: the development of systems Sat hybridized with biomolecules, nanoparticles or nanotubes in bioelectronics, the use of switchable electrodes to study the adhesion and migration of biological cells , and the integration of molecular son in the SAM to recognize and allow the transduction of a biological response allowing the practice of electrochemistry in a complex biological environment.