Poly (N-Isopropylacrylamide) Hydrogel Networks and Sieving Characteristics

Abstract

The three-dimensional of hydrogel networks within nm range can microscopically be considered as “porous”mesh. This feature may imply that hydrogel networks possess sieving characteristics; i.e. exclusion of solutes or molecules based on size. In this study the network and sieving characteristics of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were investigated. PNIPAAm hydrogels were prepared via free radical using N-isopropylacrylamide (NIPAAm) as main monomers and N,N‘-methylenebisacrylamide (MBAAm) as crosslinkers. As the composition of the hydrogels was varied, the mesh sizes of the resulting hydrogels were in the range of 4.0 to 11.0 nm. These data were obtained from swelling experiments. Dextrans as test solutes with molecular weight in the range of 4 to 2000 kg/mol were used in partitioning experiments to investigate the sieving of the hydrogel networks. The partitioning data indicated that of hydrogel networks excluded the solutes which were bigger than its mesh sizes. The experimental results not only show a good correlation of sieving coefficient on the size basis but also nicely fitted to the partition data estimated from the Ogston model. Undoubtedly, PNIPAAm hydrogel networks possessed sieving characteristics to separate molecules exclusively and selectively as a function of size.

Novel hydrogel pore-filled composite membranes with tunable and temperature-responsive size-selectivity

“…In general, the DOF increased with reaction time and showed a tendency to level off (the difference between 15 and 20 min for BM_1000 is within the error range); this is an indication that full conversion of PNIPAAm into a hydrogel network was achieved. 28 For BM_400, DOF was already at a relatively high level after 5 min but further increased with irradiation time. For BM_200, DOF was significantly smaller for 5 and 10 min of irradiation compared to 15 min.…”

“…ref. 28 obtaining size-selectivity under convective transport conditions. Analogously, a molecular weight within the 20 to 50 kg mol À1 range with a systematic trend from BM_200 to BM_1000 had only been seen for a limited base pore size range (Fig.…”

“…28,31 The hydrogels possess rubber-like elasticity and mesh properties due to crosslinking, either chemical or physical. Thus, a polymer chain in a crosslinked network can be envisioned as an entropic spring.…”

“…28 The fabrication of HPFCM was done with 15 wt% of NIPAAm as functional monomer, and 5 wt% of MBAAm as crosslinker monomer relative to NIPAAm. It should be noted that the synthesis of a hydrogel in a limited volume leads typically to a non-equilibrated structure; only upon immersion into an excess of water the free swelling equilibrium will be reached.…”

“…Pore-filling functionalization via photoinitiated in situ crosslinking copolymerization. An aqueous reaction mixture of the same composition as used in the previous experiments for the bulk gel preparation (NIPAAm/MBAAm/Irgacure 2959; 15/ 0.75/0.3 wt%) 28 was prepared and used for pore-filling (Fig. 2).…”