Pulsed plasma polymerization of hexamethyldisiloxane onto wool : control of moisture vapor transmission rate and surface adhesion

A new fabric with potential in medical textiles has been developed by application of a surface coating on wool using pulsed plasma polymerization of HMDSO. This coating enabled a controllable MVTR and surface adhesion. MVTR in the range recommended for optimum wound healing was obtained by varying frequency, monomer pressure and deposition time. Lower surface adhesion was achieved. Peeling tests, contact angle measurements, SPM force curves and ATR FT-IR were used to characterize the surfaces for both wool and a PE model substrate. All these results were consistent with a decrease in surface energy after PP-HMDSO treatment. ATR FT-IR results showed a siloxane film with less organic Si(CH₃)_n groups and more SiOSi cross-links.

Transparent uv-shielding films from organic small molecule-intercalated layered double hydroxide nanoplatelets/polymer composite

In this study, layered double hydroxide (LDH) with nitrate as the interlayer anion has been partially exfoliated in dimethyl sulfoxide (DMSO). Atomic force microscopy (AFM) images showed that both the lateral size and the thickness of the LDH nanoplatelets were decreased after DMSO treatment. Formation of transparent LDH suspension in DMSO was observed. Taking this advantage, we have prepared transparent LDH/ethylene-vinyl alcohol copolymer (EVOH) nanocomposite films using DMSO as the processing solvent. Organic small molecules, UV absorbers, were intercalated into the LDH interlayers to incorporate the UV-shielding property into the transparent composite films. The thermal stability of UV absorbers was considerably improved after intercalation, which was attributed to the electrostatic interaction between the guest UV absorbers and the host LDH layers. The prepared composite films were flexible and exhibited excellent UV-shielding capability, but had transmittance as high as 90% in the visible region. The effect of LDH filler on thermal and mechanical properties of the composite films was also examined.

Adhesion performance of polymer nanofibres under shear loading

Geckos have extraordinary wall-climbing ability because of the millions of hairs with micro/nano fibrillar structures on their feet. Mimicking gecko's feet is of scientific and engineering importance for development of physical adhesion materials and devices. The design of gecko-inspired physical adhesives seems to be geometry dominated. In this study, Finite Element Method (FEM) has been used to analyse the vertical peel-off force of polyporpylene (PP) nanofibres having different fibre dimensions, inclining angels and contact areas on a flat glass substrate. It has been found that the main parameters affecting the frictional adhesion are fibre diameter and fibre aspect ratio, the inclining angle between the fibre and the substrate surface, and the intimate contact areas. Our analysis has shown that PP nanofibres with a diameter of less than 200nm can generate less peel-off force than fibres of larger diameters, indicating more stable adhesion with the glass substrate for thinner fibres. A bent fibre with more intimate contact area can bear more shear force than a straight fibre with less contact area. Also, under the same shear loading, fibres with an inclining angle of less than 30° provide a low peel off force.

Exploring molecular changes at the surface of polypropylene after accelerated thermomolecular adhesion treatments

A central composite rotatable design (CCRD) method was used to investigate the performance of the accelerated thermomolecular adhesion process (ATmaP), at different operating conditions. ATmaP is a modified flame-treatment process that features the injection of a coupling agent into the flame to impart a tailored molecular surface chemistry on the work piece. In this study, the surface properties of treated polypropylene were evaluated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). All samples showed a significant increase in the relative concentration of oxygen (up to 12.2%) and nitrogen (up to 2.4%) at the surface in comparison with the untreated sample (0.7% oxygen and no detectable nitrogen) as measured by XPS. ToF-SIMS and principal components analysis (PCA) showed that ATmaP induced multiple reactions at the polypropylene surface such as chain scission, oxidation, nitration, condensation, and molecular loss, as indicated by changes in the relative intensities of the hydrocarbon (C₃H₇⁺ , C₃H₅⁺ , C₄H₇⁺, and C₅H₉⁺), nitrogen and oxygen-containing secondary ions (C₂H₃O⁺, C₃H₈N⁺, C₂H₅NO⁺, C₃H₆NO⁺, and C₃H₇NO⁺). The increase in relative intensity of the nitrogen oxide ions (C₂H₅NO⁺ and C₃H₇NO⁺) correlates with the process of incorporating oxides of nitrogen into the surface as a result of the injection of the ATmaP coupling agent.

Tailoring the surface chemistry of carbon fiber and E-glass composites for improved adhesion

The main challenges in the manufacture of composite materials are low surface energy and the presence of silicon-containing contaminants, both of which greatly reduce surface adhesive strength. In this study, carbon fiber (CF) and E-glass epoxy resin composites were surface treated with the Accelerated Thermo-molecular adhesion Process (ATmaP). ATmaP is a multiaction surface treatment process where tailored nitrogen and oxygen functionalities are generated on the surface of the sample through the vaporization and atomization of n-methylpyrrolidone solution, injected via specially designed flame-treatment equipment. The treated surfaces of the polymer composites were analyzed using XPS, time of flight secondary ion mass spectrometry (ToF-SIMS), contact angle (CA) analysis and direct adhesion measurements. ATmaP treatment increased the surface concentration of polar functional groups while reducing surface contamination, resulting in increased adhesion strength. XPS and ToF-SIMS showed a significant decrease in silicon-containing species on the surface after ATmaP treatment. E-glass composite showed higher adhesion strength than CF composite, correlating with higher surface energy, higher concentrations of nitrogen and CO functional groups (from XPS) and higher concentrations of oxygen and nitrogen-containing functional groups (particularly C₂H₃O⁺ and C₂H₅NO⁺ molecular ions, from ToF-SIMS).

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.

Bovine lactoferrin : potential antioxidant effector molecule in colon carcinoma

This research generated important insight into the antioxidant capacity and effector molecule capability of bovine lactoferrin in both its Apo- (iron free) and metal saturated forms within the gastrointestinal system, giving rise to bovine lactoferrin's potential at regulating oxidative stress associated signalling molecules within colon carcinoma.

Interfacial chemistry and adhesion between titanium dioxide nanotube layers and titanium substrates

Interfacial chemistry and adhesion between titanium dioxide (TiO₂) nanotube layers and titanium (Ti) substrates were studied in this Article. TiO₂ nanotube layers were produced on pure Ti by anodization and annealed in air for different time durations. The adhesion of the TiO₂ nanotube layers was then investigated by Rockwell C indentation test. Results show that adhesion of TiO₂ nanotube layers improved with the extension of annealing time. This improvement in adhesion of TiO₂ nanotube layers was analyzed from the viewpoint of interfacial chemistry using energy dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). It suggests that more Ti-O bonds formed in the interface after annealing, and this led to the improved adhesion of the TiO₂ nanoube layers.

Measurement of the deformation and adhesion of solids in contact

Two curved surfaces of molecularly smooth mica are brought into contact under a controlled load, and their deformed shape is measured using optical interference fringes of equal chromatic order. This technique allows exceptionally accurate measurements of surface profiles at separations down to a molecular scale. Contact between the surfaces can be made either adhesive or nonadhesive by suitable choice of the medium between them. Results have been obtained in both cases and compared with the theories of Hertz (nonadhesive contact) and Johnson, Kendall, and Roberts (adhesive contact).

Contact electrification and adhesion between dissimilar materials

Simultaneous measurements of surface force and surface charge demonstrate strong attraction due to the spontaneous transfer of electrical charge from one smooth insulator (mica) to another (silica) as a result of simple, nonsliding contact in dry nitrogen. The measured surface charge densities are 5 to 20 millicoulombs per square meter after contact. The work required to separate the charged surfaces is typically 6 to 9 joules per square meter, comparable to the fracture energies of ionic-covalent materials. Observation of partial gas discharges when the surfaces are approximately 1 micrometer apart gives valuable insight into the charge separation processes underlying static electrical phenomena in general.

Measuring the adhesion force on natural fibre surface using scanning probe microscopy

This work has focused on measuring the adhesion forces on both untreated and atmospheric helium plasma treated single jute fibre surfaces using scanning probe microscopy (SPM). The measurements were conducted on three differently aged surfaces for one week, three weeks and six weeks using a standard silicon nitride tip in force-volume (f-v) mode. Up to 256 adhesion data points were collected from various locations on the surface of the studied fibres using in-house developed software and the resulting data were statistically analysed by the histogram method. Results obtained from this analysis method were found to be very consistent with a small statistical variation. The work of adhesion, Wa, was calculated from measured adhesion force using the Johnson–Kendall–Roberts (JKR) and Derjaguin–Muller–Toporov (DMT) models. Increases in both adhesion force and work of adhesion were observed on jute fibre with certain levels of atmospheric plasma treatment and ageing time.