PORE SIZE, SURFACE INTERACTIONS AND EVAPORATION KINETICS IN SWOLLEN POROUS POLYMER NETWORKS DETERMINED BY NMR RELAXATION.

SILLETTA, EMILIA V.; VELASCO, MANUEL I.; GOMEZ, CESAR G.; STRUMIA, MIRIAM C.; MONTI, GUSTAVO; ACOSTA, RODOLFO H.

La Plata

Congreso; V Encuentro Argentino de Materia Blanda; 2014

INIFTA

Polymer porous matrices are widely used in several areas such as catalysis, enzyme immobilization, HPLC, adsorbents or drug controlled release. These polymers have pores in its structure both in the dry and swollen state. Although it is well known that the structures and properties greatly differ between these two states, only few analytical methods provide information about the swollen state, even though most of the applications involve the matrices in this situation and in nearly every case its performance is a sensitive function of the distribution of internal pore size. Nuclear Magnetic Resonance is a suitable tool for the study of the molecular dynamics of different liquids spatially confined in macro, meso and nanopores through changes in relaxation times. In this work, we describe the study of the pore structure of the macroporous polymer of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co- HEMA)] in the dry and in the swollen state by measuring relaxation times of liquids contained in the polymer network [1, 2]. This information allows the characterization of the matrices in terms of pore distribution, water uptake, and swelling. The behaviour of polar liquids during evaporation and deswelling dynamics is monitored and described. An internal migration of water from the swollen polymer mesh into expanding pores takes place. With this procedure, it is possible to obtain information about the microscopic morphology behaviour of the matrix during evaporation and deswelling. Additionally, the pore diameter can be determined by measuring diffusion which is encoded though magnetic field distortions that arise due to heterogeneities in the magnetic field, which are produced by changes in magnetic susceptibilities in going from the pore wall to the pore void (DDIF - Decay due to Diffusion in Internal Field) [3]. Comparison of the relaxation times present in different pore sizes provides information on surface interaction [4], in particular the influence of hydrogen bond between water and hydroxyl groups as a function of the amount of crosslinker is determined.