Network parameters and volume phase transition behavior of poly(N‐isopropylacrylamide) hydrogels

Abstract

Thermosensitive hydrogels were prepared by free radical polymerization in aqueous solution from N-isopropylacrylamide (NIPA) monomer and N,N-methylenebis(acrylamide) (MBAAm) crosslinker. The swelling equilibrium of the hydrogels in deionized water was investigated as a function of temperature and MBAAm content. The results indicated that the swelling behavior and temperature sensitivity of the hydrogels were affected by the amount of MBAAm content. The average molecular mass between crosslinks (M c ) and polymer-solvent interaction parameter () of the hydrogels were determined from equilibrium swelling values. The swelling variations were explained according to swelling theory based on the hydrogel chemical structure. The swelling equilibrium of the hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In deionized water, the hydrogels showed a discontinuous volume phase transition at 32°C. In SDS and DTAB solutions, the equilibrium swelling ratio and the volume phase transition temperature (lower critical solution temperature) of the hydrogels increased, which is ascribed to the conversion of nonionic PNIPA hydrogel into polyelectrolyte hydrogels because of binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method; it was found that the electric conductivity of the PNIPA-surfactant systems depended strongly on both the type and concentration of surfactant solutions.

Smart Nanohydrogels for Controlled Release of Food Preservatives

“…Therefore, nanoparticles' rigidity is expected to increase as the CL-percentage is increased. In accordance with the theory [138,90,30] and previous reports [217, 114,109], 3% CL gels resulted more elastic than 5% CL gels for all the conditions studied. In addition, both for 3% and 5% CL nanoparticles, the higher the AA content, the higher the Z-average (i.e., higher elasticity), which could be due to the increase in repulsive interactions between moieties with charges of the same sign.…”

“…Elasticity is, in turn, strongly influenced by the cross-linking degree of the gel matrix. According to Otake et al [138], Inomata et al [90], Çaykara et al [30], the increasing of cross-linking points in the gel matrix will arrest the formation of any hydration structure near the cosslinking points, which drecreases the volume changes assotiated with thermal transitions in PNIPA gels. Therefore, nanoparticles' rigidity is expected to increase as the CL-percentage is increased.…”

Spherically Symmetric Solvent is Sufficient to Explain the LCST Mechanism in Polymer Solutions

“…The results of our model are applicable to cross‐linked thermoresponsive polymers as the lengths of the segments between successive cross‐links are usually very long. Also, it is known that the degree of cross linking only affects the extent of swelling and does not change the LCST . Another interesting feature of our model is that the variation in behavior with temperature for different values (see Figure a) is analogous to different polymers in the family of poly( N , N ‐alkyl alkyl acrylamide).…”

Insights into Thin, Thermally Responsive Polymer Layers Through Quartz Crystal Microbalance with Dissipation

“…33,34 Ellipsometry measurements in a swelling cell gave a swelling ratio of 3.0 ( 0.3, 8 from which an average mesh size of 6.0 ( 0.2 nm was estimated. This value is significantly larger than the hydrodynamic radius of BSA (r H = 3.36 nm), 35 confirming that BSA could penetrate the mesh, as indicated by the QCM-D data.…”