title: A neutron scattering and modelling study of aqueous solutions of tetramethylammonium and tetrapropylammonium bromide.
abstract: We have investigated the properties in water of two tetraalkylammonium bromides (tetramethylammonium, TMA(+), and tetrapropylammonium, TPA(+)), at 0.4 M, using neutron scattering coupled with empirical potential structure refinement to arrive at an atomistic description. Having both a polar and an apolar moiety, it is of interest to determine the strength of each moiety as a function of the alkyl chain length. TMA(+) and TPA(+), having different impact as structure directors in zeolite synthesis, were chosen for this study. Water arranges tetrahedrally around TMA(+) and in an almost featureless manner around TPA(+). TMA(+) and TPA(+) show an apolar hydration with TPA(+) being slightly more apolar. TPA(+) has a tendency to form small clusters of 2-4 molecules and to fold into a compact configuration. Both molecules correlate similarly with the bromide ion but do not dissociate completely at this concentration.
authors.affiliation: Physical Chemistry, KILU, Lund University, P.O. Box 124, SE-22100 Lund, Sweden.
authors.forename: Emelie J
authors.initials: EJ
authors.lastname: Nilsson
authors.affiliation: Physical Chemistry, KILU, Lund University, P.O. Box 124, SE-22100 Lund, Sweden.
authors.forename: Viveka
authors.initials: V
authors.lastname: Alfredsson
authors.affiliation: ISIS, Science and Technology Facilities Council Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, UK.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Bowron
authors.affiliation: Physical Chemistry, KILU, Lund University, P.O. Box 124, SE-22100 Lund, Sweden and Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK. k.edler@bath.ac.uk.
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Edler