Effect of differently terminal groups of poly(amido-amine) dendrimers on dispersion stability of nano-silica and ab initio calculations

Abstract

To investigate the effect of differently terminal groups of the lowest-order generation poly(amido-amine) dendrimers on dispersion stability of nano-silica, the four types of G0-CH 2 CH 3 (G0E), G0-CH 2 CH 2 CH 2 CH 3 (G0B), G0-NH 2 (G0N), and G0-COOH (G0C) dendrimer molecules are used to modify the silica based on the dry modification. The zeta potential, the surface charge density, and the storage stability of kinds of modified SiO 2 dispersion systems have been studied. The results show that the effect of carboxyl groups on dispersion stability is stronger than that of the other groups such as the amine and alkyl groups. Mulliken charge distributions of the main active sites are analyzed through the conductor-like polarizable calculation model (CPCM) on basis of the density functional theory (DFT) method, indicating the formation of chemical bonding between the modifiers and SiO 2 particles. The most stable SiO 2 dispersion system modified by G0-COOH dendrimer molecule is obtained due to the combined effect including the hydrogen bonding, electrostatic repulsive force, and the steric hindrance of the terminal groups.

Corrosion resistance of itaconic acid doped polyaniline /nanographene oxide composite coating

“…All calculations were performed with the Gaussian 09 program in the Vienna Ab initio Simulation Package. The projector augmented wave method was used to describe the core electrons [26][27][28] and the Perdew-Burke-Ernzerh exchangecorrelation functional [29]. To further simplify the calculation, one structural unit of PANI represents the doped process in scheme 1(A), reaction route 1.…”

Triethylenetetramine/hydroxyethyl cellulose-functionalized graphene oxide monoliths for the removal of copper and arsenate ions

“…the generated Cu(I) is in the form of CuBr (2θ = 25.5°, 45°) and CuCl (2θ = 27.5°) [54][55][56][57][58]. Arsenate ions can precipitate in the form of a double salt with other ions including copper and hydroxyl because of the electrostatic interaction from these charged groups [59][60][61]. Moreover, for NaCu 3 H(AsO 4 ) 2 (OH) 2 the intensity of XRD peak (2θ = 14°) is stronger.…”

The electronic and optical properties of amorphous silica with hydrogen defects by ab initio calculations

“…According to the theoretical [4,17,18] and experimental [19] findings, the bond lengths of Si-O (1.61 Å) Si-H (1.54 Å), O-H (1.11 Å) and bond angles of O-Si-O (109.47°), Si-O-Si (145°-150°) are employed in the models. The outermost shell electron distribution Si 3s 2 p 2 forms sp 3 hybridized orbits and Si-O covalent bonds [20] . As SiO 2 is a tetrahedral network structure, silicon locates in the center, while four oxygen ions array around a central silicon.…”

“…2(b) for the negative charged state, the H atom is bound to Si forming a Si-H bond to give a fivefold coordinated Si(V). After geometry optimization, around fivefold coordinated Si(V), the distances between Si and O are 1.67, 1.68, 1.69, 1.68 Å, corresponding to SOA standing for ≡SiO - [20][21][22] , meanwhile Si-H bond length is 1.45 Å smaller than experimental values of 1.54 Å [19] . Therefore, an electrostatic force attraction can be formed between the hydrogen atomic nucleus and electron cloud of neighboring elect- 042002-2 ronegative atoms [20] .…”

“…After optimization, around threefold coordinated O(III), the distances between Si and O are 1.61, 1.62 Å, corresponding to SOR standing for ≡SiO + [20][21][22] , meanwhile O-H bond length is 1.16 Å larger than experimental values of 1.11 Å [19] . Therefore, a weak electrostatic force attraction may be formed between the hydrogen atomic nucleus and electron cloud of neighboring electronegative atoms [20] . During the calculation, all the dangling bonds were saturated by hydrogen in order to eliminate the effects of dangling bonds as defects, which can significantly influence both the electronic and optical properties.…”