INVESTIGADORES
VILLAR Marcelo Armando
congresos y reuniones científicas
Título:
Rheological properties of model networks with known amount of defects
Autor/es:
M.A. VILLAR
Lugar:
Porto de Galinhas, RE
Reunión:
Simposio; XIV Latin American Simposium on Polymers, SLAP14 and XII Ibero American Congress on Polymers, CIP14; 2014
Institución organizadora:
Associação Brasileira de Polímeros
Resumen:
We studied the dynamic response of end-linked poly(dimethylsiloxane) networks containing entangled linear pendant or unattached freechains. Viscoelastic properties of the networks were found to be a function of both the concentration and molar mass of either free or pendant chains. An increase in the concentration of either free or pendant chains decreases the elastic modulus due, fundamentally, to the reduction in the concentration of elastically active chains in the resulting networks. On the other hand, an increase in loss properties is observed. At low frequencies loss modulus of networks containing pendant chains is at least one order of magnitude higher than values obtained for networks with free chains with the some molecular weight. All these experimental results are in good agreement with the theoretical predictions of the tube model.Upon increasing the content of unattached guest polymer chainsthere is an increasing dissipation and a reduction in network elasticity.It was found that the width of the relaxation spectrum is nearly insensitive to the content of guest chains, indicating that network structure is not affected by the presence of these defects and that the effective number of entanglements associated to guest chains is independent of the equilibrium elastic modulus of the networks.The inhibition of the constraints release mechanism for molecules trapped in polymer networks have enormous consequences on the dynamic response, producing a dramatic slowing down in the relaxational dynamics of defects. The presence of different kind of defects in polymer networks is physically unavoidable, even under optimum reaction conditions. It was found that slow dynamics of soluble branched structures or dangling molecules can easily hide the contribution of linear unattached molecules.