Percolation Of Aggregates Research Articles

CHANGES IN THE MECHANICAL, MICRO-, AND NANO-STRUCTURAL PROPERTIES OF REINFORCED VULCANIZED NATURAL RUBBER COMPOUNDS: THEIR DEPENDENCE ON THE SiO2/CB RATIO

ABSTRACT A systematic study on the influence of fillers on the structural properties at micro and nanoscale of vulcanized compounds based on a natural rubber matrix reinforced with silica and/or carbon black is presented. Several compounds with different SiO2/CB ratios (1.5/1, 2.25/1, and 3/1) and total filler contents (55, 60, and 65 phr) were prepared and vulcanized at 150 °C. The experimental techniques used were rheometric, swelling and dynamic mechanical tests, and positron lifetime spectroscopy. From these techniques, cure reaction parameters, the fraction at the maximum degree of swelling, storage modulus, loss tangent, and fractional free volume were measured. Using a recent model based on a hydrodynamic description and the percolation of aggregates in a rubber matrix, it was found that regardless of the filler combinations, the dynamic storage modulus is well represented as a function of the filler volume fraction. Besides, beyond a critical SiO2/CB ratio (2.25/1) in the formulations of the compounds, the loss tangent does not depend on the SiO2/CB ratio. The results obtained show a direct correlation among mechanical properties, swelling and fractional free volume, and the type and amount of fillers in the reinforced compounds.

Mechanism of heat-induced gelation for ovalbumin and its N-terminus cleaved form

Heat-induced gelation mechanism of ovalbumin (OVA) in neutral, salt-free aqueous solution was investigated by dynamic light scattering and small-angle neutron scattering. The scattering profiles obtained from OVA solutions/gels showed a correlation peak. It is clarified that the position of the peaks was independent of the concentration after heating. From this fact, we described the gelation mechanism as a percolation of aggregates. In addition to this, the gelation mechanism of pOVA was also investigated and compared with that of OVA, where pOVA is a large OVA fragment lacking in N-terminal short peptide region. Although the primary structures of OVA and pOVA are almost the same, the scattering profiles obtained from pOVA were totally different from that of OVA. This difference can be explained by the difference of their dispersion states in the solution, which is originated from small difference of their primary structures.