A series of surfactants were designed and synthesized for use as clay modification reagents to investigate the impact of their chemical structure on the nanocomposites morphology obtained following polymerization. The behavior of the surfactant-modified clays at three different stages were investigated: after ion exchange, following dispersion in styrene monomer, and once polymerization was complete. The propensity of the styrene monomer to swell the surfactant-modified clay was observed to be a useful indicator of compatibility and predictor of the resultant polystyrene nanocomposite morphology which was directly observed using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (TEM). It was found that the key components of surfactant design driving exfoliated morphologies were (1) the position of the ammonium group, (2) the inclusion of a polymerizable group, (3) the solubility of the surfactant in the monomer, (4) the length of the alkyl chain, and (5) sufficient concentration of surfactant used to exchange the clay. This understanding should lead to better design of clay modifications for use in polymer nanocomposites.

The introduction of mini-multi-leaf collimators (MMLC) into radiotherapy has seen the use of smaller field sizes become increasingly important. Small field sizes that tightly conform to precise target regions are sought in radiotherapy to deliver doses with a high therapeutic ratio. MMLCs have made it possible to shrink field sizes in radiotherapy to below half a centimetre. The dosimetry of such fields with conventional dosimeters such as gas-ionisation chambers is not feasible due to limitations caused by the chambers relatively large size compared to the size of the collimated beam. In this work, the dose distribution of radiotherapy beams collimated to such small sizes were examined using polyacrylamide gels dosimeters, Gafchromic films and micro-thermoluminescence dosimeters (micro-TLDs). Dose penumbra widths obtained with gel dosimeters, Gafchormic film and micro-TLDs were generally in agreement with each other, although a wider FWHM of the field was measured with gel in comparison to film. An asymmetric dose distribution between the two axis profiles of a 3×3mm collimated field was observed and can be attributed to an inherent asymmetry of the MMLC.

A study has been conducted to clarify the relationship between polymer structure, annealing temperature, and the extent of plasticization by high-pressure CO2 for two typical polyimide membranes; BTDA-DAPI (poly(3,3'-4,4'-benzophenone tetracarboxylic-dianhydride diaminophenylindane) and 6FDA-TMPDA (poly(2,2'bis-(3,4'-dicasrboxyphenyl) hexafluoropropane dianhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine). Both membrane materials are exposed to varying levels of thermal annealing at 200 and 250 degrees C. The effect of this heat treatment on free volume is examined using positron annihilation lifetime spectroscopy (PALS), whereas fluorescence spectroscopy is used to monitor changes in electronic structure. Results show that thermal annealing causes a reduction in both the size and number of free volume elements. A strong relationship is found between the fluorescence peak intensity for 6FDA-TMPDA and both the membrane gas permeability and plasticization pressure. This correlation is most likely the result of the formation of charge transfer complexes, particularly at 250 degrees C. However, the formation of covalent crosslinks at these temperatures cannot be discounted. No fluorescence is observed for BTDI-DAPI. Although thermal annealing has a significant effect on the extent of plasticization in both polymers, it is found that the rate of plasticization is unaffected by the annealing temperature. (C) 2008 Wiley Periodicals, Inc.

Some radiotherapy patients are treated with titanium surgical aneurysm clips in the radiation field. This is of particular importance for stereotactic radiosurgery brain treatments, where the length of the blade of the clip may be comparable to the size of the radiation field. This study seeks to determine the extent of the dosimetric effects caused by surgical clips in stereotactic radiosurgery, using polyacrylamide gel phantoms and EBT type Gafchromic films. Using gel phantoms scanned with magnetic resonance imaging scanner, dose enhancement of around 20% was noted at distances less than 2 mm away from the clip surface. Gafchromic films showed about 6% variations in the dose up to few millimeters from the clip. These experimental results confirmed results predicted by Monte Carlo simulation techniques for higher density material surgical clips such as lead and platinum. Moreover, these experimental measurements clearly indicate dose reduction due to radiation attenuation behind the clip of about 4%.

This paper considers the blending of epoxide and diamine components into a glassy polyimide structure (2,2'-bis(3,4'-dicarboxyphenyl) hexafluoropropane dianhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TMPDA) intended for use as a gas separation membrane. It is shown that the diamine component can react both with the epoxide component to form an epoxy network and with the polyimide backbone itself, leading to a complex grafted structure. Bulk density and X-ray diffraction results show that this leads to a denser, more amorphous membrane structure. This effect appears to be independent of the diamine structure. Gas permeability is reduced and selectivity increases, consistent with established free volume theory. Importantly, however, plasticization resistance also increases. This implies that membrane performance will be more robust when exposed to condensable gases such as carbon dioxide. In this particular case, the increase in plasticization resistance is possibly insufficient to warrant the loss in permeability, particularly when compared to the relatively high permeability measured for diamine-cross-linked polyimide.

Electron or x-ray energies above the threshold for photonuclear activation of certain elements (such as oxygen and copper) can be achieved in some of the high energy beams used today in radiotherapy. Neutrons and gamma radiations are produced in such reactions. These secondary radiations, beside their implications on the treatment, they have potential to be used for quality testing of the radiation beam and can also be imaged with a PET scanner and hence employed for testing such imaging modalities. In this work applications and implications of such secondary radiations in radiotherapy is investigated through oxygen that is in the water molecules inside gel dosimeters and copper in its solid and solution format.

The complexes trans-[Pt(CCC6H4-4-CCPh)Cl(PMe2Ph)2] (1), 1,3,5-C6H3{CCC6H4-4-CC-trans-[PtCl(PMe2Ph)2]}3 (2) and 1,3,5-C6H3(CCC6H4-4-CC-trans-[Pt(PMe2Ph)2]CC-4-C6H4CC-3,5-C6H3-{CC-trans-[Ru(CCPh)(dppe)2]}2)3 (3) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. The optical limiting merit of 1 and 2 has been assessed at 523nm employing 40ns pulses; the effective absorption cross-section for 1 is low, while that of 2 is larger, but the complex is susceptible to photo-damage. The third-order nonlinearity of the Ru6Pt3 dendrimer 3 has been examined at 800nm using 150 fs pulses; it is larger than that of a related Ru6 dendrimer, but smaller than that of a Ru9 dendrimer under the same conditions, suggesting that increasing metal content and electron richness is correlated to increased nonlinearity in these complexes.

Dose measurements at small fields (around 1×1 cm) in radiotherapy is increasingly becoming important by the introduction of new technologies such as IMRT and it is a challenging task at the same time. Most if not all of the known dosimeters fail to measure the dose reliably at such small fields. Gel dosimeters are tissue equivalent and they are used as phantom and dosimeters at the same time. Their dose resolution is limited by the pixel sizes of the imaging modality used for their scanning, in this case an MRI scanner. Therefore reducing the pixel size increases the dose resolution since the contrast is very high in MRI images. In using normal scanners pixel sizes of around one millimeter at reasonable scanning times is usually obtained. In this work a small core and strong magnetic field scanners are employed which produces pixels of the order of 30 micrometers rendering them as micro-dosimeters.

Purpose: Microdosimetry (measurement of radiation dose on the μm scale) suitable for micro‐beam radiotherapy is a challenging task with known dosimeters such as ionization chambers and others dosimeters. The purpose of this work was to use gel dosimeters for dose determination across micro‐beam radiotherapy fields. Method and Materials: A gel dosimeter that was highly resistant to radiation was developed by using a free radical scavenger in the gel to reduce the rate of polymerisation. The samples were irradiated using the x‐ray collimated micro‐beam from a synchrotron in order to measure the synchrotron's high‐dose. Gel scanning was performed using special type MRI scanner, Raman spectroscopy and also attempted using phase contrast imaging. Results: It was found that using current equipment and techniques, that MRI with resolution down to 20 μm is possible, but given the size of the beam (30 μm), is unable to adequately describe the dose distribution across the beam. Raman spectroscopy measurements of gel have been shown to be possible, and work in this area is involved in gaining accurate measurements in this method. Comparative measurements made using CCD camera on the beams show similar results. Conclusions: This work shows the dose measurement in gel down to the μm range is possible and could be applied in many fields such as microbeam radiotherapy.

Membrane plasticization is the process whereby penetrant dissolution causes membrane swelling or dilation, which in turn, can increase membrane diffusivity and solubility and lead to long time frame polymer relaxation processes. In this work, the effect of temperature upon the plasticization of a rigid polyimide, poly(4,4′-hexafluoroisopropylidene diphthalic anhydride–2,3,5,6-tetramethyl-1,4-phenylenediamine) (6FDA-TMPDA), by carbon dioxide is investigated. It is found that across the full range of temperatures studied, plasticization has little effect on carbon dioxide solubility as all results can be characterized by a standard dual mode sorption model. However, the effect upon diffusivity is significant and this can be described by both an exponential relationship with penetrant concentration and an Arrhenius relationship with temperature. The polymer relaxation processes induced by plasticization are also temperature dependent. However, the total proportion of penetrant sorption associated with such relaxation processes is relatively unaffected by temperature. This paper shows that plasticization effects are dominated by Henry's law dissolution. Conversely, while Henry's law species contribute most to diffusion at high temperatures, at lower temperatures the movement of Langmuir component species also contributes to the total diffusion coefficient.

Steric control of the extent of reaction has been developed to rapidly synthesize ligated metal-containing dendrons that have been employed in arylalkynyl complex dendrimer synthesis. Reaction of 1,3,5-triethynylbenzene with excess cis-[RuCl(2)(dppe)(2)] affords 1,3-{trans-[(dppe)(2)ClRuCC]}(2)-5-HCCC(6)H(3) (1). Reaction of 1 with 4-RC(6)H(4)CCH affords 1,3-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)-5-HCCC(6)H(3) [R = H (2a), NO(2) (2b), NH(2) (2c)]. 2a-care coupled with 4-Me(3)SiCCC(6)H(4)I under Sonogashira conditions to give 1,3-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)-5-(Me(3)SiCCC(6)H(4)-4-CC)C(6)H(3) [R = H (3a), NO(2) (3b), NH(2) (3c)], which can be desilylated to afford 1,3-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)-5-(HCCC(6)H(4)-4-CC)C(6)H(3) [R = H (4a), NO(2) (4b), NH(2) (4c)]. Sonogashira coupling of 4a-c with 1,3,5-triiodobenzene gives the systematically varied peripherally metalated arylalkynyl dendrimers 1,3,5-(3,5-{trans-[(dppe)(2)(RC(6)H(4)-4-CC)RuCC]}(2)C(6)H(3)-1-CCC(6)H(4)-4-CC)(3)C(6)H(3) [R = H (5a), NO(2) (5b), NH(2) (5c)]. All complexes show two reversible oxidation processes by cyclic voltammetry. Cubic nonlinearities determined using the Z-scan technique and low-repetition femtosecond pulses at 660 and 800 nm increase on pi-system lengthening and progression from dendron to dendrimer. In contrast to all other complexes in this study, 5b is a saturable absorber at 800 nm. Dispersion of both the refractive and the absorptive nonlinearities of 5b has been determined, and the behavior has been modeled for the first time with an inorganic complex.

The reversible chemical cross-linking of polyimide membranes with diamines has been investigated. This investigation has been carried out on model compounds, polymers and flat sheet polymeric membranes. Reaction between an imide containing model compound and an amine causes each imide ring to be converted into two amide functional groups. Upon heating under vacuum, this reaction can be reversed. The reaction between an amine and the polyimide 6FDA–durene and the subsequent thermal reversal has been investigated. Upon thermal reconversion of the amide linkages back to imide rings, the molecular weight of the polymer is significantly reduced. It is proposed that the polymer undergoes backbone scission with incorporation of the amine as an end group. Polymeric gas separation membranes were formed incorporating the cross-linker in the casting process. The process in which these membranes were constructed ensured that there was a low degree of cross-linking. While significant changes in the physical properties of these membranes are observed upon cross-linking, no insoluble gels are formed. These membranes show a decrease in carbon dioxide permeability and an increase in plasticization resistance and selectivity upon reaction with a diamine. Compared with some literature examples of diamine cross-linked membranes, the reduction in permeability in the membranes presented here is considerably lower but the plasticization resistance is less extensive.

Small field sizes are increasingly becoming important in radiotherapy particularly since the introduction of intensity-modulated radiation therapy (IMRT) techniques. It is normally a challenging task to reliably measure the delivered dose and to determine its distribution in a medium for such small fields using conventional-type dosimeters such as gas ionisation chambers. Recently, attempts have been made to use films, but they are not tissue equivalent, they measure the dose only in two dimensions and they are not as responsive to radiations. In the present work, polyacrylamide gel (PAG) dosimeters are employed to measure the dose and its distribution in three dimensions for very small field sizes, such as those typically used in stereotactic radiosurgery. Field sizes of 6 x 6 and 18 x 18 mm in width are investigated. The results show an agreement with radiochromic film and ionisation diode measurements, with some variation in measured doses near the edge of the field, where the gel data decreases more rapidly than the other methods.

Global warming has been identified as one of the world's major environmental issues. While it is impossible to completely stop the effects of anthropological global warming, it is possible to mitigate these effects via a variety of options. One such option is the reduction of greenhouse gas emissions by the capture of carbon dioxide from flue gases followed by underground sequestration. For this technology to become widespread, new methods of capturing carbon dioxide must be devised. While capture of carbon dioxide with amine solvents is the most mature technology, another possible contender is gas separation membranes. This review will focus on novel materials for gas separation. In particular, polymeric gas separation membranes are examined. Possible design strategies, synthesis, fabrication and role of novel materials are discussed.

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.

The title compound, [Ru(C8H5)(C2H3N)(C26H24P2)(2)]PF6 center dot-0.5C(2)H(5)OH, comprises a pseudo-octahedral ruthenium complex cation with two bidentate diphosphine ligands and trans-disposed acetonitrile and phenylethynyl ligands, together with a disordered hexafluorophosphate anion and a disordered ethanol solvent molecule.

Low-generation alkynylruthenium dendrimers with arylethynyl branching and spacer units have been synthesized. A "steric control" methodology to rapidly afford the necessary organometallic dendrons has been developed. The dendrimer complexes possess interesting nonlinear optical properties, including very large two-photon absorption cross-sections, the wavelength dependence of which has been examined in one case. They also undergo reversible oxidation in solution, which results in both linear and nonlinear electrochromism.

The title compound, [Ru(C 8 H 5 )(C 2 H 3 N)(C 26 H 24 P 2 ) 2 ]PF 6 ·0.5C 2 H 5 OH, comprises a pseudo-octa­hedral ruthenium complex cation with two bidentate diphosphine ligands and trans -disposed acetonitrile and phenyl­ethynyl ligands, together with a disordered hexa­fluoro­phosphate anion and a disordered ethanol solvent mol­ecule.