Thermal studies of L, D and β-alanine

α-Amino acids are generally studied by spectroscopic techniques, to determine their structure and distinguish between L and D forms (Caroline et al., 2009). Their study via thermal analysis is usually combined with other analytical techniques such as FT-IR, MS, HPLC, GC or NMR to identify the products of thermal decomposition (Kumar et al., 2006, Rodante and Marrosu, 1990). It is intriguing to ascertain whether thermal analytical techniques alone can provide useful information about amino acids, in terms of their physicochemical properties, and their techniques ability to distinguish between L and D forms

Phase behaviour of dehydrated phosphatidylcholines

Dehydrated DLPC, DMPC, DPPC and DSPC have been characterised at temperatures below the diacyl carbon chain-melting transition (Tm), using DSC. For the first time, the existence of pre-Tm transition processes, which are, usually, only observed in the colloidal/liposomal state of saturated phospholipids have been detected for the dehydrated phosphatidylcholines. Temperature modulated differential scanning calorimetry (TMDSC) was used to characterize the several complex, overlapping pre-Tm transition processes. Kinetic studies of the chain-melting (Tm) transition show the activation energy dependence on α (conversion rate) i.e. activation energy decreases as the transition progresses, pointing to the importance of initial cooperative (intra- and inter-molecular) mobility. Furthermore the activation energy increases with increase in diacyl chain length of the phosphatidylcholines which supports the finding that greater molecular interactions of the polymer chain and its head groups in the dehydrated solid state lead to enhanced stability of dehydrated phosphatidylcholines

Wettability changes in trichloroethylene-contaminated sandstone

It is usually assumed that chlorinated solvent nonaqueous-phase liquids (NAPLs) are nonwetting with respect to water-saturated porous media. The focus of this work was to examine whether this supposition is appropriate for used trichloroethylene (TCE) samples. In this work, the term "used" indicates that the sample has been employed industrially and therefore contains solutes and breakdown products related to its previous use. The data obtained in this study indicate that exposure of initially water wet quartz slides to industrially used solvents can cause a contact angle change, measured through the aqueous phase, of 100 degrees with a maximum stable contact angle of 170 degrees (indicative of strong NAPL wetting characteristics) being recorded. The work on quartz slides was complemented by the use of sandstone cores. Wettability was measured using the Amott lest. Used TCE again proved able to alter the wetting properties of sandstone to neutral wetting. The complexity of the industrially used samples precluded any realistic attempt to examine the agents causing these wetting changes. The data captured in these experiments were compared with laboratory grade TCE, and some attempts were made to synthesize known mixtures in order to replicate wetting changes. These experiments resulted in contact angle changes but did not alter the overall wettability of the quartz slides or sandstone cores. Finally the work reported here also demonstrates that increasing the duration of exposure to solvent has an important impact upon measured contact angle

Investigations of naphthalene solubilization in aqueous solutions of ethylene oxide-b-propylene oxide-b-ethylene oxide copolymers

The enhanced apparent solubility of naphthalene in aqueous solutions of several ABA block copolymeric surfactants has been measured using HPLC. The surfactants investigated combine, within their structure, a block of propylene oxide (PO) (the hydrophobic B block) sandwiched between two blocks of ethylene oxide (EO) (the hydrophilic A blocks). This commercially produced family of surfactants encompass a variety of materials which differ from each other in terms of block sizes and thus in terms of the balance of hydrophobic and hydrophilic forces. It is this balance which controls the ability of the surfactants to effect particular solubility enhancements. Substantial increases in solubility arise from the incorporation of naphthalene into block copolymer micelles. However the experimental data also point to solubility enhancements arising from naphthalene-surfactant interactions at surfactant concentrations below the critical micelle concentration (cmc). The apparent equilibrium constant-describing the solute distribution between the aqueous phase and the surfactant-that characterizes this interaction correlates well with the surfactant cmc. It is concluded that the more hydrophobic EO-PO-EO copolymers produce micellar environments that are more favorable for naphthalene incorporation compared to the hydrophilic members of the family and that surfactant-naphthalene interactions below the cmc can substantially increase apparent aqueous solubilities. Experimental determinations of cmc values were measured by reductions in surface tension and by high-sensitivity differential scanning calorimetry and compared with the values estimated by naphthalene solubilization. The values obtained by the three methods are comparable. The data clearly demonstrate that cmc values are strongly dependent upon molecular composition and molecular size and that the cmc values are largest for small molecules with large hydrophilic blocks

An investigation of adsorption at the air–water and soil–water interfaces for non-micellizing ethylene oxide–propylene oxide surfactants

Adsorption at the air-water interface and soil sorption from aqueous solution have been investigated for a group of ethylene oxide (EO)-propylene oxide (PO) block copolymeric surfactants. The group which have a common structural formula of EOm POn EOm is distinguished by the fact that they have large critical micelle concentration (CMC) values and therefore do not readily form micelles at common environmental concentrations and temperatures. Adsorption at the air-water interface is readily shown to be driven by the size of the hydrophobic PO block. The size of the reduction in surface tension produced by a common concentration of 10(-5) mol dm(-3) linearly increases with the size of the PO block as does the efficiency of adsorption at the air-water interface as measured by pC(20) - the negative logarithm of the surfactant concentration that produces a reduction in surface tension of 20 mN m(-1). Soil sorption data have also been captured for these compounds and the data are readily fitted to the Freundlich adsorption isotherm. However soil sorption is shown to be inversely related to the molecular mass of the molecules and appears to be related to the size of the hydrophilic EO blocks in the molecule

Polycyclic aromatic hydrocarbon extraction from a coal tar-contaminated soil using aqueous solutions of nonionic surfactants

The efficiency and kinetics of surfactant facilitated extraction of phenanthrene and anthracence - two exemplar PAH compounds - from a coal tar-contaminated soil, using five surfactants have been investigated. Three of the surfactants used were ethylene oxide/propylene oxide block copolymers in which the propylene oxide (PO) block was of constant length but the ethylene oxide (EO) block lengths were varied. Steady state extraction values - for PAH removal - were obtained after 50 hours for four of the five surfactants. The extraction efficiency - calculated as the fraction of PAH removed in one washing - is shown to be related to the EO/PO ratio for the block copolymers. Apparent soil/aqueous surfactant solution distribution coefficients (K-d) were also obtained and suggest that the surfactants can reduce K-d by several orders of magnitude. Finally the kinetic data is readily fitted to the Elovich equation an essentially empirical equation which has been used, previously, to fit phosphate adsorption data

Slow elastic modulus changes in plasticised poly (vinyl chloride)

The Young's Modulus of PVC plasticised with various dialkylphthalates at concentrations from 40–120 phr that has been subject to a short heat treatment at 100°C, increases linearly with the logarithm of the time of storing at temperatures from 20–100°C. Both the Young's Modulus and its rats of increase with time is found to increase with increasing size of plasticiser to increase with decreasing concentration of plasticiser and to pass through a maximum with changing temperature of storage at a temperature of about 38°C. These effects can be explained if it is assumed that the elasticity results from a network linked by crystallites that can be melted on heating and reformed on storing at a lower temperature. The density of the plasticiser compositions is found to increase with time and this together with the development of endothermic DSC peaks support the hypothesis that changes in rigidity result from changes in crystallinity. The endothermic peak occurs at an almost constant temperature independent of plasticiser concentration or the size of the plasticiser molecule. It is suggested that the effect of these variables on the the melting point is nullified by the changes they also produce in crystallite size

Predicting surfactant modified soil/water distribution coefficients using micellar HPLC

Soil water/distribution coefficients (K-d) have been measured for the partitioning of naphthalene, phenanthrene and pyrene between aqueous surfactant solutions and a clean soil. The surfactants used are ABA block copolymers constructed from ethylene oxide (the monomer used to synthesise the hydrophilic A blocks) and propylene oxide (used for the manufacture of the hydrophobic B block). Three of these surfactants comprising the same size propylene oxide block but different ethylene oxide/propylene oxide ratios were investigated. Increasing amounts of surfactant in the system result in a progressive decrease in the K-d values signifying an increasing tendency for the hydrophobic solutes to be dispersed in aqueous solution due to the action of the surfactant. More significantly for equal surfactant doses the most hydrophobic surfactant possessing the lowest ethylene oxide/propylene oxide ratio reduces K-d by the greatest amount whereas the most hydrophilic surfactant reduces K-d the least. Finally micellar HPLC using the above surfactants and hydrophobic solutes was undertaken. Interpolated capacity factors evaluated for particular surfactant doses correlated well with K-d values calculated for the same surfactant doses. The relationship between K-d and capacity was found to be log-linear and the correlation line could be fitted to the data obtained for all three surfactants. It is therefore concluded that micellar HPLC may be used for preliminary evaluations of the effectiveness of particular surfactants proposed for contaminated soils restoration schemes