Ordering in thin films of block copolymers: fundamentals to potential applications

The ordering of block copolymers in thin films is reviewed, starting, from the fundamental principles and extending to recent promising developments as templates for nanolithography which may find important applications in the semiconductor industry. Ordering in supported thin films of symmetric and asymmetric AB diblock and ABA triblock copolymers is discussed, along with that of more complex materials such as ABC triblocks and liquid crystalline block copolymers Techniques to prepare thin films, and to characterise ordering within them, are summarized. Several methods to align Hock copolymer nanostructures, important in several applications are outlined A number of potential applications in nanolithography, production of porous materials, templating. and patterning of organic and inorganic materials are then presented. The influence of crystallization on the morphology of a block copolymer film is briefly discussed, as are structures in grafted block copolymer films. (C) 2009 Elsevier Ltd All rights reserved.

Non-invasive imaging of roots with high resolution X-ray micro-tomography

ray micro-tomography is a well-established technique for non-invasive imaging and evaluation of heterogeneous materials. An inexpensive X-ray micro-tomography system has been designed and built for the specific purposes of examining root growth and root/soil interactions. The system uses a silver target X-ray source with a focal spot diameter of 80 mum, an X-ray image intensifier with a sampling aperture of about 100 mum, and a sample with a diameter of 25 mm. Pre-germinated wheat and rape seeds were grown for up to 8-10 days in plastic containers in a sandy loam soil sieved to < 250 μm, and imaged with the X-ray system at regular intervals. The quality of 3 D image obtained was good allowing the development and growth of both root axes and some first-order laterals to be observed. The satisfactory discrimination between soil and roots enabled measurements of root diameter (wheat values were 0.48-1.22 mm) in individual tomographic slices and, by tracking from slice to slice, root lengths were also measured. The measurements obtained were generally within 10% of those obtained from destructive samples measured manually and with a flat-bed scanner. Further developments of the system will allow more detailed examination of the root: soil interface.

Degradation of atrazine and isoproturon in surface and sub-surface soil materials undergoing different moisture and aeration conditions

The influence of different moisture and aeration conditions on the degradation of atrazine and isoproturon was investigated in environmental samples aseptically collected from surface and sub-surface zones of agricultural land. The materials were maintained at two moisture contents corresponding to just above field capacity or 90% of field capacity. Another two groups of samples were adjusted with water to above field capacity, and, at zero time, exposed to drying-rewetting cycles. Atrazine was more persistent (t(1/2) = 22-3S days) than isoproturon (t(1/2) = 5-17 days) in samples maintained at constant moisture conditions. The rate of degradation for both herbicides was higher in samples maintained at a moisture content of 90% of field capacity than in samples with higher moisture contents. The reduction in moisture content in samples undergoing desiccation from above field capacity to much lower than field capacity enhanced the degradation of isoproturon (t(1/2) = 9-12 days) but reduced the rate of atrazine degradation (t(1/2) = 23-35-days). This demonstrates the variability between different micro-organisms in their susceptibility to desiccation. Under anaerobic conditions generated in anaerobic jars, atrazine degraded much more rapidly than isoproturon in materials taken from three soil profiles (0-250 cm depth). It is suggested that some specific micro-organisms are able to survive and degrade herbicide under severe conditions of desiccation. (C) 2004 Society of Chemical Industry.

A narrow band pulsed eddy current instrument for materials testing

The principles of operation of an experimental prototype instrument known as J-SCAN are described along with the derivation of formulae for the rapid calculation of normalized impedances; the structure of the instrument; relevant probe design parameters; digital quantization errors; and approaches for the optimization of single frequency operation. An eddy current probe is used As the inductance element of a passive tuned-circuit which is repeatedly excited with short impulses. Each impulse excites an oscillation which is subject to decay dependent upon the values of the tuned-circuit components: resistance, inductance and capacitance. Changing conditions under the probe that affect the resistance and inductance of this circuit will thus be detected through changes in the transient response. These changes in transient response, oscillation frequency and rate of decay, are digitized, and then normalized values for probe resistance and inductance changes are calculated immediately in a micro processor. This approach coupled with a minimum analogue processing and maximum of digital processing has advantages compared with the conventional approaches to eddy current instruments. In particular there are: the absence of an out of balance condition and the flexibility and stability of digital data processing.

Synthesis of well-dispersed nanoparticles within porous solid structures using surface-tethered surfactants in supercritical CO2

We have developed a new method for the synthesis of Pd nanoparticles with controllable sizes within a silica matrix using solid-supported surfactants in supercritical CO2. XRD, HRTEM and CO chemisorption data show that unformly sized Pd nanoparticles are evenly distributed within the porous silica and are chemically tethered by surfactant molecules [poly(oxyethylene stearyl ether) and fluorinated poly(oxyethylene)]. It is postulated that tiny solid-supported surfactant assemblies act as nano-reactors for the template synthesis of nanoparticles or clusters from the soluble precursors therein.

Comparative study of Barium Fluoride thin films produced by ion-beam sputtering and thermal evaporation

Coatings and filters for spaceflight far-infrared components require a robust, non-absorptive low-index thin film material to contrast with the typically higher refractive index infrared materials. Barium fluoride is one such material for the 10 to 20µm wavelength infrared region, however its optical and mechanical properties vary depending on the process used to deposit it in thin film form. Thin films of dielectric produced by thermal evaporation are well documented as having a lower packing density and refractive index than bulk material. The porous and columnar micro structure of these films causes possible deterioration of their performance in varied environmental conditions, primarily because of the moisture absorption. Dielectric thin films produced by the more novel technique of ion-beam sputtering are denser with no columnar micro structure and have a packing density and refractive index similar to the bulk material. A comparative study of Barium Fluoride (BaF2) thin films made by conventional thermal evaporation and ion-beam sputtering is reported. Films of similar thicknesses are deposited on Cadmium Telluride and Germanium substrates. The optical and mechanical properties of these films are then examined. The refractive index n of the films is obtained from applying the modified Manifacier's evvelope method to the spectral measurements made on a Perkin Elmer 580 spectrophotometer. An estimate is also made of the value of the extinction coefficient k in the infrared wavelength transparent region of the thin film. In order to study the mechanical properties of the BaF2 films, and evaluate their usefulness in spaceflight infrared filters and coatings, the thin film samples are subjected to MIL-F-48616 environmental tests. Comparisons are made of their performance under these tests.

Amphoteric nano-, micro-, and macrogels, membranes, and thin films

This review describes the state-of the-art of nano-, micro- and macrogels, membranes, micro- and nanocapsules, as well as multilayered thin films exhibiting amphoteric character. The synthetic strategies and physicochemical properties of amphoteric materials are outlined in light of the stimuli-responsive behavior and their potential application in nanotechnology, biotechnology and medicine.