Influence of pendant chains on the loss modulus of model networks

Abstract

The progress of the loss component of the shear modulus, G ", of a model silicone network has been studied during the cross-linking reaction. It has been observed that G " increases steadily after the gel point until a maximum value is reached. Then G" decreases up to a final definite value when the reaction is completed. By a recursive technique, the evolution of the molecular structure of the network with the extent of the reaction was calculated and associated with G", leading to the conclusion that pendant chains contribute significantly to the loss modulus of an amorphous rubbery material.

Nano and macro tribology of elastomers

“…PDMS B exhibits a lower friction resistance, despite a higher adhesion as shown in a previous study focussing on PDMS tack properties [4,5]. PDMS B contains a larger number of free and pendant chains (which are also longer) [6]. We can then suppose that these numerous and longer chains favour a sliding behaviour, due notably to chain alignment along the friction direction, as shown recently by FTIR spectroscopy using a reflection mode with polarisation modulation [7].…”

Physical Gelation of Biopolymers

“…G" sometimes passes through a parabolic maximum, and then decreases to zero, and sometimes plateaus off. According to Valles and co-workers, in covalent networks the former effect is associated with the relaxation of "dangling chain ends" (12). We have observed and noted a qualitative correlation, with biopolymer gels formed from more flexible chains (e.g., gelatin) giving such a G" parabola, whereas those from stiffer chains (e.g., agarose) give a slight maximum followed by a plateau (13).…”

Dependence of viscoelastic spectrum width on the structure of model imperfect networks prepared by endlinking

“…Much less attention has been devoted to the problem of the relation between the detailed chain structure and the viscoelastic behaviour of the networks, especially since the relation between them has been given much less theoretical treatment than in the case of equilibrium properties. For model networks obtained from endvinyl-substituted poly(dimethylsiloxane) crosslinked with three-functional silane, it was found [16] that at constant temperature, the value of the loss component of the shear modulus G" correlates with the content of dangling chains. Also, it was found [17,18] that the experimental long-term viscoelastic behaviour of natural rubber networks is in agreement with a theory based on the reptation model of branched molecules in the presence of topological constraints.…”