Small-angle neutron scattering of multiwalled carbon nanotubes in aqueous suspensions in presence of laponite platelets or cetyltrimethylammonium bromide

The results of small angle neutron scattering (SANS) study of semidiluted 0.1 and 0.3 % wt aqueous suspensions of multiwalled carbon nanotubes (MWCNTs) are reported. The additives of Laponite platelets or cationic surfactant cetyltrimethylammonium bromide (CTAB) were used for enhancing the dispersion ability of MWCNTs. At high values of wave vector q, (1 nm-1 < q < 3.5 nm-1) all samples exhibited behavior characteristic for rigid rods (i.e., q-1 variation of neutron scattering intensity was observed). At low values of q (0.1 nm-1 < q < 0.5 nm-1), the neutron scattering intensity followed the power law q- with exponent the in the range of 1.2 - 2, depending on concentration of the Laponite platelets or CTAB. Addition of Laponite platelets or CTAB allowed improvement of dispersion ability of MWCNTs. The effects were optimal at the certain value of Laponite/MWCNTs ratio X 0.5 or CTAB concentration (0.2 %wt). SANS also revealed existence of a mesh structure in MWCNT aggregates with characteristic mesh size of 7.4 nm and 6.3 nm in suspensions with concentration of 0.1 and 0.3 % wt of MWCNTs, respectively

Lyotropic model membrane structures of hydrated DPPC: DSC and small-angle X-ray scattering studies of phase transitions in the presence of membranotropic agents

Multibilayer structures of hydrated phospholipids, often considered as model biological membranes, are, from the physical viewpoint, lyotropic liquid crystalline systems undergoing temperature-induced mesomorphic phase transitions. Effects of silver nitrate and urocanic acid on lyotropic phase states of hydrated L-α-dipalmitoylphosphatidylcholine (DPPC) have been studied by small-angle X-ray scattering and differential scanning calorimetry (DSC). Both methods show increase of the main phase-transition temperature (Tm) of hydrated DPPC upon introduction of AgNO3 or urocanic acid, decrease of pre-transition temperature (Tp) in the presence of urocanic acid and its increase in the presence of AgNO3. Thus, urocanic acid widened the ripple-phase temperature region. Silver nitrate caused the appearance of an additional high-temperature peak on DSC thermograms, evidencing phase separation in the system. Both agents caused minor effects on DPPC lipid bilayer repeat distance (D) in gel phase, but resulted in noticeable increase of D in the liquid crystal phase with temperature as compared to undoped DPPC structures

Neutron scattering investigations of the lipid bilayer structure pressure dependence

Lipid bilayer structure investigation results obtained with small angle neutron scattering method at the Joint Institute for Nuclear Research IBR-2M nuclear reactor (Dubna, Russia) are presented. Experiment has been per-formed with small angle neutron scattering spectrometer YuMO, upgraded with the apparatus for performing P-V-T measurements on the substance under investigation. D2O-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liquid system, presenting the model of natural live membrane, has been taken as the sample for investiga-tions. The lipid bilayer spatial period was measured in experiment along with isothermal compressibility simulta-neously at different pressures. It has been shown, that the bilayer structural transition from ripple (wavelike gel-phase) phase to liquid-crystal phase is accompanied with anomalous rise of isothermal compressibility, indicat-ing occurrence of the phase transition