Relationship between the continually expanded interlayer distance of layered silicates and excess intercalation of cationic surfactants

Excess intercalation of cationic surfactants into Na-montmorillonites (MMTs) was investigated in organically modified silicates (OMSs), synthesized with MMTs and octadecylammonium chloride (OAC) by systematically varying the surfactant loading level from 0.625 to 1, 1.25, 1.56, 2, and 2.5 with respect to the cation exchange capacity (CEC) of MMTs. Wide-angle X-ray diffraction and thermogravimetric analysis results indicated that the continuous increase of interlayer distances came from the entering of surfactants into the interlayer of MMTs. Excess surfactants were extracted with a Soxhlet apparatus, which showed two kinds of intercalation states of surfactants in the interlayer when the surfactant loading level was beyond the CEC. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to explore the microstructures of OMSs. It was found that the surfactants arranged more orderly as the loading level increased and the excess surfactants piled up in the interlayer together with counterions, forming a sandwiched surfactant layer. On the basis of the results, the layer structures of OMSs and the mechanism by which the surfactants entered the interlayer were expounded: surfactant cations entered the interlayer through cation exchange reactions and were tightly attracted to the silicate platelet surfaces when the surfactant loading level was below the CEC;

Brittle-tough transition in PP/EPDM blends: effects of interparticle distance and tensile deformation speed

The toughness of polypropylene (PP)/ethylene-propylene-diene monomer rubber (EPDM) blends containing various EPDM contents as a function of the tensile speed was studied. The toughness of the blends was determined from the tensile fracture energy of the side-edge notched samples. A sharp brittle-tough transition was observed in the fracture energy versus interparticle distance (ID) curves when the crosshead speed < 102.4 mm/min. It was observed that the brittle-ductile transition of PP/EPDM blend occurred either by reducing ID or by decreasing the tensile speed. The correlation between the critical interparticle distance and tensile deformation rate was compared with that between the critical interparticle distance and temperature for PP/EPDM blends. (C) 2000 Elsevier Science Ltd. All rights reserved.

Brittle-ductile transition in high-density polyethylene/glass-bead blends: Effects of interparticle distance and temperature

The toughness of high-density polyethylene (HDPE)/glass-bead blends containing various glass-bead contents as a function of temperature was studied. The toughness of the blends was determined from the notch Izod impact test. A sharp brittle-ductile transition was observed in impact strength-interparticle distance (ID) curves at various temperatures. The brittle-ductile transition of HDPE/glass-bead blends occurred either with reduced ID or with increased temperature. The results indicated that the brittle-ductile-transition temperature dropped markedly with increasing glass-bead content. Moreover, the correlation between the critical interparticle distance (ID.) and temperature was obtained. Similar to the ID, of polymer blends with elastomers, the ID, nonlinearly increased with increasing temperature. However, this was the first observation of the variation of the ID, with temperature for polymer blends with rigid particles. (C) 2001 John Wiley & Sons, Inc. J Polym. Sci Part B: Polym. Phys 39: 1855-1859, 2001.

Atom space distance and computing of molecular similarity

A mathematical model on computation of molecular similarity was suggested, The algorithmic techniques for measuring the degree of similarity between pairs of three-dimensional chemical molecules was represented by modified interatomic distance matrices. Current work was carried out on Indigo 2 work station with Sybyl software. Four groups of molecules were used to compute the molecules similarity to testing the mathematical model with satisfactory results.

Effect of polymer chain structure and chain distance on luminescent efficiency

Three kinds of PPV-based copolymers were synthesized and characterized. Their luminescent properties were investigated and discussed by PL spectrum, and time-dependence luminescent spectrum in film and solution stare. The results show that in the range of our study, the PL intensity and lifetime of luminescent decay increase with the increasing length of flexible segments and the solution diluting, indicating the tendency of the increase of luminescent efficiency.

Interparticle distance-temperature-strain rate equivalence for the brittle-tough transition in polymer blends

From the angle of energy transformation an equation was obtained for the brittle transition in polymer blends. The effects of interparticle distance, temperature and strain rate on the brittle-tough transition in polymer blends were characterized by this equation. The calculations show that, for this transition: (1) increasing temperature and decreasing interparticle distance are equivalent and the shift factor increases with increasing temperature; (2) decreasing strain rate and decreasing interparticle distance have equivalent effects on the transition; (3) the strain rate must be optimum in order to find the brittle-tough transition phenomena for a given temperature region. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.