Structure of Polymer Chains Confined in Vycor

Jyotsana Lal , Sunil Sinha , Loïc Auvray

We observe by Small Angle Neutron Scattering the structure of polystyrene chains in semi-dilute solutions confined in a model porous medium, Vycor. The size of the free chains in solution is always larger than the pore diameter, 70 Å. The use of a suitable mixture of hydrogenated and deuterated solvents and polymers enables us to measure directly the form factor of one single chain among the others. The penetration of the chains in the porous medium is almost complete for the concentration (Φ = 20%) and the range of molecular weight (35000 < Mw < 800000) used. The radius of gyration of the confined chains is always smaller than the radius of gyration of the free chains in the equivalent bulk solution. Our measurements are in agreement with the theoretical predictions established by Daoud and de Gennes for chains confined in a cylindrical pore when the chains are entangled and laterally squeezed but remain ideal at large scale along the cylinder axis because of the screening of the excluded volume interactions (so-called regime of “semi-dilute cigars”). The values of the partition coefficient of the chains between the porous medium and the free solution and the asymptotic behavior of the structure factors indicate that polystyrene adsorbs onto the bare surface of Vycor. We show that silanizing Vycor suppresses this adsorption.

Domaines: Articles anciens

Jyotsana Lal, Sunil Sinha, Loïc Auvray. Structure of Polymer Chains Confined in Vycor. Journal de Physique II, 1997, 7 (11), pp.1597-1615. ⟨10.1051/jp2:1997205⟩. ⟨jpa-00248538⟩