| Surfactant has special molecular structure containing both hydrophobic groups (at their tails) and hydrophilic groups (at their heads), and can self-assembly to form a variety of orderly aggregates, which achieve the effective control on the material microstructure. It also can adsorb on the surface of nanoparticles to reduce the interfacial tension between nanomaterials and medium, where through the competition among electrostatic repulsion, space steric effect and Van der Waals interactions to avoid agglomeration of nanoparticles. What's more, modifying the surface of the nanomaterials using different surfactant molecules can help to get some new nanomaterials. Basing on modifying and controling the surface of the nanomaterials by surfactants, if Graphene oxide (GO), as a nonstoichiometric layer materials, including rich oxygen-containing functional groups and extremely easily combining with other polar molecules, is used as materials providing limited two-dimensional space to research the complex dynamics behavior of surfactants, it will provide important theoretical guidance for the design and improvement of new nanomaterials, which bring new opportunities and challenges for the field of nanomaterials. Meanwhile, the study on the dynamics of solid surfactant molecules under the restricted condition of the surface also helps to understand the basic issue on dynamics and structural problems of surfactants, which has important scientific significance.Therefore, in this paper, a modified Hummers method was used to prepare two batches of Graphite oxide, and then it was used as host material to prepare a series of nanocomposites for surfactant molecules intercalated in GO, to study the dielectric relaxation behavior of different kinds of solid surfactnat and intercalating into the GO layer. And, the effect of concentration on the surfactant molecules intercalated into the GO layer on the dielectric properties is also analyzed. Specific details are as follows:(1) For the first time, dielectric spectroscopy was used to study the dielectric relaxation of solid surfactants and intercalating into the GO layer below the room temperature. Cn-GO (n=12,14,16,18) nanocomposites with surfactants intercalates different in alkyl chain length were obtained by adding surfactants CnH2n+1N(CH3)3X (CnNX; X=C1, Br; n=12,14,16,18) to GO dispersed in NaOH solution. X-ray diffraction (XRD) results imply that the stack of the confined alkyl chains located as flat monolayer for Cn-GO (n=12,14,16) or bilayer for C18-GO with their long axis parallel to the GO layer. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) results imply that alkylammonium cations CnN+ has been connected to C-O- functional groups through electrostatic interaction. All samples'temperature-dependent impedance spectra exhibited an obvious relaxation process below the room temperature, no matter what in the pure solid surfactants or in Cn-GO nanocomposites, and the apparent activation energy of this relaxation increases with the increase of the alkyl chains length. As the loss peak deviates from ideal Debye characteristic, the Ngai's correlated-states model was used. From the best fitting Ngai curves, the actual activation energy?110 meV was obtained, which is consistent well with the internal rotation barrier of alkyl macromolecule. So the relaxational process is attributed to wobbling motion of distinctive alkylammonium cations, but not to C3 reorientation of the common CH3 at headgroup. It is the intrinsic thermal motion of alkyl chains.(2) The effect of different concentrations of hexadecyltrimethylammonium ions (C16N+) confined in GO layer on dielectric behavior is studied by impedance spectroscopy. GO nanocomposites containing various concentrations of intercalated C16N+ have been sucessfully synthesized through the above similar experimental method. XRD results exhibit that the confined alkyl chains may lie parallel to the GO plane one or two layers thick, or they form two columns inclined at an angle?37° to the plane depending on their concentration. XPS and FTIR results exhibit that C16N+ has been successfully inserted into GO layer through electrostatic attraction between C16N+ and C-O- functional groups. Dielectric spectroscopy still reveals a relaxation process far below the room temperature. After the loss peaks fitted by the Ngai's correlated-states model, the actual activation energy (?110 meV) is consistent well with the internal rotation barrier of alkyl macromolecule. The apparent activation energy of this relaxation increases as intercalates changes from one to two layers, and to dual columns, due to the increasing coupling with increasing interactions among the intercalated molecules. An additional small peak occurs in composites with high concentrations of intercalate at about 316 K where do not change with the change of frequency, which is consistant well with the result of differential scanning calorimetry. After being analyzed through introducing the order parameter fluctuation for the dynamics behavior, the small peak exists as a result of an ordered phase to a disordered phase for the confined alkyl chains... |
PDF Full Text Request