Abstract
Smart hydrogels (SH) were prepared by thermal free radical polymerization of N-isopropyl acrylamide (NIPAAm), acrylamide (AAm) with acrylic acid (A) or maleic acid (M), and N,N′-methylene bisacrylamide. Spectroscopic and thermal characterizations of SHs were performed using FTIR, TGA, and DSC. To determine the effects of SHs on swelling characteristics, swelling studies were performed in different solvents, solutions, temperatures, pHs, and ionic strengths. In addition, cycle equilibrium swelling studies were carried out at different temperatures and pHs. The temperature and pH transition points of SHs are calculated using a sigmoidal equation. The pH transition points were calculated as 5.2 and 4.2 for SH-M and SH-A, respectively. The NIPAAm/AAm hydrogel exhibits a critical solution temperature (LCST) of 28.35 °C, while the SH-A and SH-M hydrogels exhibit the LCST of 34.215 °C and 28.798 °C, respectively, and the LCST of SH-A is close to the body. temperature. Commercial (CHSA) and blood human serum albumin (BHSA) were used to find the adsorption properties of biopolymers on SHs. SH-M was the most efficient SH, adsorbing 49% of CHSA while absorbing 16% of BHSA. In conclusion, the sigmoidal equation or Gaussian approach can be a useful tool for chemists, chemical engineers, polymer and plastics scientists to find the transition points of smart hydrogels.
Highlights
Temperature responsivity of smart hydrogels can be achieved with hydrophobic monomers ((such as N-isopropyl acrylamide, vinyl methylether, N-methyl acrylamide, N,N-dimethyl acrylamide, N-tert-butyl acrylamide), and pH and ionic responsivity can be achieved with ionizable organic acidic or basic monomers [4,5,6,7,8,9,10]
Despite the mention of LSCT in 812 of these publications, there are no studies on the determination of the transition points and the magnitude of the stimuli-responsivity, which are very important in the use of smart hydrogels as biomaterials, with appropriate equations
In line with our research interest in AAm based materials, [17,18,19,20,21,22] in this article we report the copolymerization of N-isopropyl acrylamide (NIPAAm) with AAm
Summary
Three-dimensional cross-linked polymeric structures that love water are called hydrogels [1,2,3], and those that respond to external stimuli (such as pH, temperature, ionic strength, electric field, light, magnetic field, and so forth) as volume changes are called smart or intelligent or stimuli-responsive hydrogels [4,5,6,7,8,9,10,11,12,13,14,15]. The resulting positive charges repel each other, water diffusion is achieved, and swelling is observed in the gel. This swelling shrinkage transition pH is called the inflection point (IP) [4,5,6,7,8,9,10,11,12,13,14,15]. Despite the mention of LSCT in 812 of these publications, there are no studies on the determination of the transition points (i.e., such as LCST, IP) and the magnitude of the stimuli-responsivity, which are very important in the use of smart hydrogels as biomaterials, with appropriate equations. A detailed understanding of the physical properties of these new ionizable hydrogels concerning molecular heterogeneity is an important criterion in targeted applications such as temperature-, pH-, ionic strength-, and solvent-responsive sorbent systems
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