Minimal understanding of the formation mechanism and structure of polydopamine (pDA) and its natural analogue, eumelanin, impedes the practical application of these versatile polymers and limits our knowledge of the origin of melanoma. The lack of conclusive structural evidence stems from the insolubility of these materials, which has spawned significantly diverse suggestions of pDA's structure in the literature. We discovered that pDA is soluble in certain ionic liquids. Using these ionic liquids (ILs) as solvents, we present an experimental methodology to solvate pDA, enabling us to identify pDA's chemical structure. The resolved pDA structure consists of self-assembled supramolecular aggregates that contribute to the increasing complexity of the polymer. The underlying molecular energetics of pDA solvation and a macroscopic picture of the disruption of the aggregates using IL solvents have been investigated, along with studies of the aggregation mechanism in water.

The design, capability and construction of a novel, experimental apparatus for the study of low temperature regeneration CO2 capture agents is presented. The decisions and challenges in developing a new experimental capability are discussed, as well as how it addresses the experimental intermediate between bench scale experiments and large, application specific projects. To demonstrate the utility and capability of the apparatus, a low temperature regenerating CO2 capture protic ionic liquid (PIL) solution - dimethylpropylenediamine acetate + 50% H2O - was used to remove CO(2 )from an incoming gas stream consisting of 10% (v/v) CO2 in air. SuperPhobic (R) 2.5 x 8 hollow fibre membrane contactors were used for both the absorption and regeneration processes. The loading-only experiment achieved pseudo steady state in approximately 12 min, achieving a pseudo steady-state mass transfer rate (K-overall) of (3.66 +/- 0.2) x 10(-5) m s(-1), and a CO(2 )removal rate of 5.15 x 10(-3) g M-2 s(-1). This value is comparable to other ionic liquid CO2 capture agents such as 1-ethyl-3-methylimidazolium ethylsulfate that have also been measured under pseudo-steady state conditions. In continuous operation, where CO2 is absorbed and stripped in series, steady-state was achieved in approximately 15 h. Due to the higher concentration of CO(2 )in the liquid under steady-state conditions, the value of K overall decreased to (1.80 +/- 0.1) x 10(-5) m s(-1), with a CO2 removal rate of 2.89 x 10(-3) g m(-2) s(-1). The effects of several parameters on the steady-state CO(2 )capture rate, namely vacuum pressure of regeneration and liquid flow through the contactor were studied. Several factors were found to affect the stability of the overall CO(2 )removal rate, including H2O loss from the aqueous solution. With the utility and flexibility of the designed system, we have demonstrated that PILs are certainly worthy of further investigation as CO2 capture agents for a range of applications.

The Materials Genome is in action: the molecular codes for millions of materials have been sequenced, predictive models have been developed, and now the challenge of hydrogen storage is targeted. Renewably generated hydrogen is an attractive transportation fuel with zero carbon emissions, but its storage remains a significant challenge. Nanoporous adsorbents have shown promising physical adsorption of hydrogen approaching targeted capacities, but the scope of studies has remained limited. Here the Nanoporous Materials Genome, containing over 850 000 materials, is analyzed with a variety of computational tools to explore the limits of hydrogen storage. Optimal features that maximize net capacity at room temperature include pore sizes of around 6 Å and void fractions of 0.1, while at cryogenic temperatures pore sizes of 10 Å and void fractions of 0.5 are optimal. Our top candidates are found to be commercially attractive as “cryo-adsorbents”, with promising storage capacities at 77 K and 100 bar with 30% enhancement to 40 g/L, a promising alternative to liquefaction at 20 K and compression at 700 bar.

The physical absorption of CO2 by protic and aprotic ionic liquids such as 1-ethyl-3-methyl-imidazolium tetrafluoroborate was examined at the molecular level using symmetry adapted perturbation theory (SAPT) and density functional techniques through comparison of interaction energies of noncovalently bound complexes between the CO2 molecule and a series of ionic liquid ions and ion pairs. These energies were contrasted with those for complexes with model amines such as methylamine, dimethylamine, and trimethylamine. Detailed analysis of the five fundamental forces that are responsible for stabilization of the complexes is discussed. It was confirmed that the nature of the anion had a greater effect upon the physical interaction energy in non functionalized ionic liquids, with dispersion forces playing an important role in CO2 solubility. Hydrogen bonding with protic cations was shown to impart additional stability to the noncovalently bound CO2···IL complex through inductive forces. Two solvation models, the conductor-like polarizable continuum model (CPCM) and the universal solvation model (SMD), were used to estimate the impact of solvent effects on the CO2 binding. Both solvent models reduced interaction energies for all types of ions. These interaction energies appeared to favor imidazolium cations and carboxylic and sulfonic groups as well as bulky groups (e.g., NTf2) in anions for the physical absorption of CO2. The structure-reactivity relationships determined in this study may help in the optimization of the physical absorption process by means of ionic liquids.

The electrochemical behavior and deposition morphology of Pb2+ was investigated in the Room Temperature Ionic Liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([C(2)mim] [NTf2]) containing the salt Pb(NTf2)(2). Cyclic Voltammetry (CV) experiments were found to result in a range of electrochemical responses depending on the working electrode material being used, with both Pt and Pb based electrodes showing the highest current and lowest overpotential for deposition, respectively. Pb was found to undergo a single diffusion controlled reduction process at a coulombic efficiency of 95 % on a Pt working electrode. The deposition of Pb was found to follow a 3 dimensional progressive nucleation mechanism, regardless of the substrate material or the temperature during the experiment. During the deposition, the diffusion coefficient of Pb2+ was found to be 1.3 x 10(-7) cm(2).s(-1) by chronoamperometric analysis. Finally, the resulting morphologies of the Pb metal deposits were found to be heavily dependent on the deposition substrate, ranging from pyramids of 3 mu m in diameter on Pt, to fine sub-micron interwoven needles on glassy carbon. Interestingly, the potential of deposition appeared to make little difference to the resulting morphology on Cu substrates. Finally, to demonstrate the cycling ability of the Pb metal surfaces, Pb was cycled on Pb electrodes 200 times, showing that the resulting Pb films were compact and non-dendritic in nature. It is concluded that [C(2)mim][NTf2] containing Pb(NTf2)2 shows many favourable cycling characteristics. (C) 2015 Elsevier Ltd. All rights reserved.

Carbon dioxide (CO2) chemical absorption and regeneration was investigated in two diamino carboxylate protic ionic liquids (PILs), dimethylethylenediamine formate (DMEDAH formate) and dimethylpropylenediamine acetate (DMPDAH acetate), using novel calorimetric techniques. The PILs under study have previously been shown to possess a CO2 absorption capacity similar to the industrial standard, 30% aqueous MEA, while requiring much lower temperatures to release the captured CO2. We show that this is in part due to the fact that the PILs exhibit enthalpies of CO2 desorption as low as 40 kJ mol(-1), significantly lower than the 85 kJ mol(-1) required for 30% aqueous MEA. Computational and spectroscopic analyses were used to probe the mechanism of CO2 capture, which was found to proceed via the formation of carbamate moieties on the primary amine of both DMEDAH and DMPDAH. Evidence was also found that weakly acidic counter-ions such as formate and acetate provide, unexpectedly, an additional proton acceptor site in the traditional carbamate mechanism, revealing opportunities to increase CO2 uptake capacity in the future through careful design of the anion and cation used in the PIL capture agent.

A protic ionic ethylenediamine liquid N,N-dimethyl-aminoethylammonium formate (DMEDAH formate) was evaluated for the removal of carbon dioxide from carbon dioxide and nitrogen mixed gas streams. This evaluation was conducted via a series of vapour liquid equilibrium (VLE) experiments, wetted wall measurements and solvent contactor trials with the results compared to the performance of the industrial standard 30 wt% monoethanolamine (MEA). The VLE of the ionic liquid indicated that the sorption process included a chemical reaction component and is comparable to MEA. The mass transfer coefficient, calculated via the wetted wall column apparatus is an order of magnitude lower than MEA, which is likely due to the higher viscosity of the ionic liquid and its impact on carbon dioxide diffusivity. The solvent contactor trials indicated the solvent may be used in such an arrangement with good performance at low CO2 loadings, but would benefit from the use of alternative membrane materials. (C) 2014 Elsevier Ltd. All rights reserved.

A series of multifunctional protic ionic liquids (PILs), some of which are based on a combination of primary and tertiary amines in the same moiety coupled with a carboxylic acid, have been synthesised and employed for CO2 capture, yielding absorption capacities comparable to standard absorbents. In contrast to traditional amine absorbers, CO2 was found to desorb at lower temperatures and hence could result in a significant reduction in both the energy required to strip the absorber of CO2 and the thermally activated degradation mechanisms, which in traditional absorbers result in the loss of absorber and the production of toxic compounds. The lower basicity of the amine sites resultant from PIL formation decreases the binding energy of the CO2 to the absorber. The weaker basicity is also evidenced by lower pH of the PIL CO2 absorbers, which reduces common corrosion problems associated with traditional amine absorbers.

Pyrene fluorescence spectra have been recorded in five poly(alkyl methacrylate)s (where alkyl is ethyl butyl, isobutyl, cyclohexyl and hexadecyl) over a 20-400 K temperature range. The changes in the position and the full width at half maximum (FWHM) of the 0-0 emission band (peak I) have been correlated with the structural characteristics of the alkyl groups in the different relaxation regimes of the polymers to assess the degree of coupling of the excited singlet states with the polymer cybotactic regions. Data treatment of the peak I positions using an electron-phonon model indicates that longitudinal optical modes are involved, and that the magnitude of coupling depends on the polymer structure and follows the same trend as the glass transition temperatures. The same spectral parameters have been correlated also with "hole" free volumes from positron annihilation spectroscopy over temperature ranges which span the glass or melting transitions of the polymers. Reasons why free volume and FWHM measurements follow the same trends, and other aspects of the systems, are discussed.

A study was undertaken on a Ti–25Nb–3Mo–3Zr–2Sn alloy using differential scanning calorimetry (DSC) in order to improve understanding of the precipitation reactions occurring during aging heat treatments. The investigation showed that isothermal ω phase can be formed in the cast and solution treated alloy at low aging temperatures. An exothermic peak in the temperature range of 300 to 400°C was detected for precipitation of the ω phase, with approximate activation energy of 176 kJ/mol. The ω phase begins to dissolve at temperatures around 400°C and precipitation of the α phase is favoured at higher temperatures between 400°C and 600°C. An exothermic peak with activation energy of 197 kJ/mol was measured for precipitation of the α phase. Deformation resulting in the formation of the stress induced α″ phase altered the DSC heating profile for the solution treated alloy. The exothermic peak associated with precipitation of the ω phase was not detected during heating of the deformed material and increased endothermic heating associated with recovery and recrystallisation was observed.

Formation of homo-interpenetrating polymer networks (homo-IPNs) of poly(2-hydroxyethyl methacrylate) (PHEMA) and their capacity for calcification are investigated. A sequential method is established to generate IPNs of rank I and II, containing two or three crosslinked networks. Although the networks are chemically identical, thermo-mechanical analysis (DSC, DMA) suggests some phase separation. Calcification of PHEMA hydrogels, thought to be controlled by the free volume pathways accessible to calcium ions, is investigated by positron annihilation lifetime spectroscopy (PALS) and experimental calcium deposition. While calcium uptake is reduced in IPNs, the size of the free volume elements estimated by PALS remain constant at radii of 2.6 angstrom (dry) and 2.9 angstrom (hydrated), both in PHEMA and IPNs. The reduction of calcium uptake cannot be therefore associated with the size reduction of the angstrom-size free volume elements detectable by PALS, and is attributed to the effect of chain packing on pores too large to be detected by PALS. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Depth profiling experiments by positron annihilation spectroscopy have been used to investigate the free volume element size and concentration in films assembled using the layer-by-layer (LbL) adsorption method. Films prepared from strong polyelectrolytes, weak polyelectrolytes, hydrogen-bonding polymers, and blended polyelectrolyte multilayers have different chain packing that is reflected in the free volume characteristics. The influence of various parameters on free volume, such as number of bilayers, salt concentration, solution pH, and molecular weight, has been systematically studied. The free volume cavity diameters vary from 4 to 6 Å, and the free volume concentrations vary from (1.1-4.3) × 10(20) cm(-3), depending on the choice of assembly polymers and conditions. Films assembled from strong polyelectrolytes have fewer free volume cavities with a larger average size than films prepared from weak polyelectrolytes. Blending the weak polyanion poly(acrylic acid), PAA, with the strong polyanion poly(styrene sulfonate), PSS, to layer alternately with the polycation poly(allyamine hydrochloride), PAH, is shown to be a viable method to achieve intermediate free volume characteristics in these LbL films. An increase in salt concentration of the adsorption solutions for films prepared from strong polyelectrolytes makes these films tend toward weaker polyelectrolyte free volume characteristics. Hydrogen-bonded layered films show larger free volume element size and concentration than do their electrostatically bonded counterparts, while reducing the molecular weight of these hydrogen-bonded polymers results in slightly reduced free volume size and concentration. A study of the effect of solution pH on films prepared from weak polyelectrolytes shows that when both polyelectrolytes are substantially charged in solution (assembly pH = 7.5), the chains pack similarly to strong polyelectrolytes (i.e., lower free volume concentration), but with smaller average cavity sizes. These results give, for the first time, a clear indication of how the free volume profile develops in LbL thin films, offering numerous methods to tailor the Ångström-scale free volume properties by judicious selection of the assembly polymers and conditions. These findings can be potentially exploited to tailor the properties of thin polymer films for applications spanning membranes, sensing, and drug delivery.

The properties of ionic liquids give rise to applications in diverse technology areas including mechanical engineering, mining, aerospace and defence. The arbitrary physical property that defines an ionic liquid is a melting point below 100 °C, and as such, an understanding of crystallisation phenomena is extremely important. This is the first report dealing with the mechanism of crystallisation in ionic liquids. Assuming crystallisation of the ionic liquids is a thermal or mass diffusion-controlled process, the values of the isothermal Avrami exponent obtained from three different ionic liquids with three different anions and cations all indicate that growth occurs with a decreasing nucleation rate (n=1.8-2.2). For one of the ionic liquids it was possible to avoid crystallisation by fast cooling and then observe a devitrification upon heating through the glass transition. The isothermal Avrami exponent of devitrification suggested growth with an increasing nucleating rate (n=4.1), compared to a decreasing nucleation rate when crystallisation occurs on cooling from the melt (n=2.0). Two non-isothermal methods were employed to determine the Avrami exponent of devitrification. Both non-isothermal Avrami exponents were in agreement with the isothermal case (n=4.0-4.15). The applicability of JMAK theory suggests that the nucleation event in the ionic liquids selected is a random stochastic process in the volume of the material. Agreement between the isothermal and non-isothermal techniques for determining the Avrami exponent of devitrification suggests that the pre-exponential factor and the activation energy are independent of thermal history. The heating rate dependence of the glass transition enabled the calculation of the fragility index, which suggests that the ionic liquid is a "strong" glass former. This suggests that the temperature dependence of the rate constant could be close to Arrhenius, as assumed by JMAK theory. More generally, therefore, it can be concluded that there is nothing unusual about the crystallisation mechanism of the ionic liquids studied here.

Addition of silica nanoparticles functionalised with lithium propane sulfonate to the organic ionic plastic crystal N-ethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([C2mpyr][NTf2]) results in a significant increase in ionic conductivity. Analysis of these nanocomposites by impedance spectroscopy, NMR, positron annihilation lifetime spectroscopy (PALS) and Raman spectroscopy suggests that this is the result of higher matrix mobility due to an increase in defect size and concentration. The effect of these functionalised nanoparticles is compared to that previously observed for unfunctionalised nanoparticles in the lithium-doped and pure plastic crystal.

The most common way to analyse PALS spectra involves fitting a parameter-dependent model to the experimental data. Traditionally, this fit involves local non-linear optimisation routines that depend on a reasonable initial guess for the searched parameters. This, together with the fact that very different sets of parameters may yield indistinguishably good fits for a given experimental spectrum, gives rise to ambiguities in the data analysis in most but the simplest cases. In order to alleviate these difficulties, a computer program named PAScual was developed that incorporates 2 advanced algorithms to provide a robust fitting tool: on the one hand, it incorporates a global non-linear optimisation routine based on the Simulated Annealing algorithm and, on the other hand, it yields information on the reliability of the results by means of a Markov Chain Monte-Carlo Bayesian Inference method. In this work the methods used in PAScual are described and tested against both simulated and experimental spectra, comparing the results with those from the well-established program LTv9. The examples focus on the type of complex data that results from the study of self-assembled amphiphile materials containing co-existing aqueous and hydrocarbon regions.

Many biodegradable polymer materials have not been found to be suitable replacements for more traditional non-biodegradable polymers owing to their insufficient gas and vapor barrier properties. The use of a series of novel organically modified synthetic fluorohectorites (FHTs) has been explored to produce biodegradable polybutylene succinate adipate (PBSA)-clay nanocomposites with improved barrier. Highly oriented nanoclay structures (clearly showing a tortuous path required to reduce gas and vapor transmission) were observed using transmission electron microscopy (TEM), resulting in a significant reduction in oxygen permeability (up to a 53% decrease). In particular, these oriented structures were observed in the FHTs modified with di poly(oxyethylene) alkyl methyl ammonium and the longer chain dimethyl dialkyl ammonium. Orientation and dispersion were found to be a result of chemical functionality, chain length, and unique aspect ratios of these FHTs. It was concluded that this reduction in permeability was predominantly due to the tortuous path created by oriented platelets and not from any nucleating effects the platelets may have had. Interestingly, the FHTs were shown to disrupt crystallinity and no change in free volume (as measured using positron annihilation life-time spectroscopy) was observed. The excellent clay dispersion and orientation also led to significant increases in other properties.

Doping lithium bis(trifluoromethanesulfonyl) amide (Li[NTf(2)]) into the N-ethyl,N'-methylpyrrolidinium bis(trifluoromethanesulfonyl) amide ([C(2)mpyr][NTf(2)]) plastic crystal material has previously indicated order of magnitude enhancements in ion transport and conductivity over pure [C(2)mpyr][NTf(2)]. Recently, conductivity enhancements in this ionic plastic crystal induced by SiO(2) nanoparticles have also been reported. In this work the inclusion of SiO(2) nanoparticles in Li ion doped [C(2)mpyr][NTf(2)] has been investigated over a wide temperature range by differential scanning calorimetry (DSC), impedance spectroscopy, positron annihilation lifetime spectroscopy (PALS), Raman spectroscopy, NMR spectroscopy and scanning electron microscopy (SEM). Solid state (1)H NMR indicates that the addition of the nanoparticles increases the mobility of the [C(2)mpyr] cation and positron lifetime spectroscopy (PALS) measurements indicate an increase in mean defect size and defect concentration as a result of nanoparticle inclusion, especially with 10 wt% SiO(2). Thus, the substantial drop in ion conductivity observed for this doped nanocomposite material was surprising. This decrease is most likely due to the decrease in mobility of the [NTf(2)] anion, possibly by its adsorption at the SiO(2)/grain boundary interface and concomitant decrease in mobility of the Li ion.

Positron annihilation lifetime spectroscopy (PALS) has potential as a novel rapid characterization method for self-assembly amphiphile systems; however, a lack of systematic correlation of PALS parameters with structural attributes has limited its more widespread application. In this study, using the well-characterized phytantriol/water and the phytantriol/vitamin E acetate/water self-assembly amphiphile systems, the impact of systematic structural changes controlled by changes in composition and temperature on PALS parameters has been studied. The PALS parameters (orthopositronium (oPs) lifetime and intensity signatures) were shown to be sensitive to the molecular packing and mobility of the self-assembled lipid molecules in various lyotropic liquid crystalline phases, enabling differentiation between liquid crystalline structures. The oPs lifetime, related to the molecular packing and mobility, is correlated with rheological properties of the individual mesophases. The oPs lifetime links the lipid chain packing and mobility in the various mesophases to resultant macroscopic properties, such as permeability, which is critical for the use of these mesophase structures as diffusion-controlled release matrices for active liposoluble compounds.