Temperature and concentration effects on decyltrimethylammonium micelles in water

Wide-angle neutron scattering experiments combined with Empirical Potential Structural Refinement modelling have been used to study the detailed structure of decyltrimethylammonium bromide (C 10TAB) micelles at two different temperatures; 25°C and 50°C and two concentrations; 0.4 and 0.8 M in water. At higher temperature, the micelles become smaller, and fewer counterions bind to the micelle surfaces, however, the headgroup positions are more ordered, possibly due to crowding in the smaller micelles. At higher concentration, the models suggest the micelles become elongated, although the aggregations numbers are smaller than those at the lower concentration. The smaller micelles found in 0.8 M solutions have more hydrated headgroups and lower counterion binding than the ellipsoidal micelles found in 0.4 M C 10TAB solutions. </p

Neutron Scattering Analysis of Water’s Glass Transition and Micropore Collapse in Amorphous Solid Water

The question of the nature of water’s glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4 K min−1) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at 121 K, in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water’s glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K—in contrast to all earlier experiments in the field

Atomic and vibrational origins of mechanical toughness in bioactive cement during setting

Bioactive glass ionomer cements (GICs) have been in widespread use for ~40 years in dentistry and medicine. However, these composites fall short of the toughness needed for permanent implants. Significant impediment to improvement has been the requisite use of conventional destructive mechanical testing, which is necessarily retrospective. Here we show quantitatively, through the novel use of calorimetry, terahertz (THz) spectroscopy and neutron scattering, how GIC’s developing fracture toughness during setting is related to interfacial THz dynamics, changing atomic cohesion and fluctuating interfacial configurations. Contrary to convention, we find setting is non-monotonic, characterized by abrupt features not previously detected, including a glass–polymer coupling point, an early setting point, where decreasing toughness unexpectedly recovers, followed by stress-induced weakening of interfaces. Subsequently, toughness declines asymptotically to long-term fracture test values. We expect the insight afforded by these in situ non-destructive techniques will assist in raising understanding of the setting mechanisms and associated dynamics of cementitious materials

Bulk and Confined Benzene-Cyclohexane Mixtures Studied by an Integrated Total Neutron Scattering and NMR Method

From Springer Nature via Jisc Publications RouterHistory: accepted 2021-04-10, registration 2021-04-10, pub-electronic 2021-04-23, online 2021-04-23, pub-print 2021-08Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000266; Grant(s): N008995, N009304Abstract: Herein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement

Temperature and concentration effects on decyltrimethylammonium micelles in water

Wide-angle neutron scattering experiments combined with Empirical Potential Structural Refinement modelling have been used to study the detailed structure of decyltrimethylammonium bromide (C 10TAB) micelles at two different temperatures; 25°C and 50°C and two concentrations; 0.4 and 0.8 M in water. At higher temperature, the micelles become smaller, and fewer counterions bind to the micelle surfaces, however, the headgroup positions are more ordered, possibly due to crowding in the smaller micelles. At higher concentration, the models suggest the micelles become elongated, although the aggregations numbers are smaller than those at the lower concentration. The smaller micelles found in 0.8 M solutions have more hydrated headgroups and lower counterion binding than the ellipsoidal micelles found in 0.4 M C 10TAB solutions. </p

Structure and interactions in simple solutions

Neutron scattering with hydrogen/deuterium isotopic substitution techniques has been used to investigate the full range of structural interactions in a dilute 0.02 mol fraction solution of tertiary butanol in water, both in the absence and in the presence of a small amount of sodium chloride. Emphasis is given to the detailed pictures of the intermolecular interactions that have been derived using the empirical potential structure refinement technique. Analysis has been performed to the level of the spatial density distribution functions that illustrate the orientational dependence of the intermolecular interactions between all combinations of molecular and ionic components. The results show the key structural motifs involved in the interactions between the various components in a complex aqueous system. They underline the structural versatility of the water molecule in accommodating a range of different kinds of interactions while retaining its characteristic first-neighbour interaction geometry. Within this framework, the results highlight the complex interplay between the polar, non-polar and charged molecular interactions that exist in the system