Multi-faced investigation for pH-sensitivity and solvent polarity in highly charged thermo-responsive hydro- and cryogels with strongly dissociated groups: A comparative evaluation of physico-chemical properties. (January 2018)

• Record Type: Journal Article
• Authors: Boyaci, Talin; Orakdogen, Nermin
• Is Part Of: European polymer journal. Volume 98(2018)
• Page Start: 137
• Page End: 153
• Publication Date: 2018-01
• Subjects: N-isopropylacrylamide -- Charge density -- Diffusion -- Thermosensitivity -- Elasticity -- Swelling; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2017.11.015
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: The change in the specific properties of multi-responsive gels consisting of NIPA and NaA has been interpreted based on the different physico-chemical characteristics and interactions. Highlights: Poly( N -isopropylacrylamide-co-sodium acrylate) hydrogels and cryogels were prepared. Elasticity and swelling were combined by Flory-Rehner theory and Rubber elasticity. Results revealed increased elastic modulus for hydrogels having higher content of NaA. Existence of reentrant swelling transition in solvent-water mixtures was explained. Weakening strength of PNIPA-water interaction and hydrophobic hydration of solvent. Abstract: Different series of strong polyelectrolyte poly( N -isopropylacrylamide- co -sodium acrylate) P(NIPA- co -NaA) hydrogels and cryogels were prepared in aqueous solution. With changing the ionic comonomer NaA ratio in reaction mixture, the resulting physico-chemical and swelling properties varied significantly. The findings elucidated that ionic P(NIPA- co -NaA) gels exhibited multi-stimuli performances with pH-, temperature-, solvent-, surfactant- and salt-responsivity, showing more sensitivity than non-ionic PNIPA. Their swollen/collapsed behaviors were strongly dependent on various synthesis/external parameters, including the content of ionic comonomer, temperature and solvent polarity. The effects produced by non-solvents were qualitatively compared considering the aspects related to co-nonsolvency phenomenon and re-entrant swelling transition on the basis of weakening of PNIPA-water interactions. Measurements of the elastic properties and swelling degree of samples having different NaA content were treated by combining Flory-Rehner theory and rubber elasticity to interpret the experimental observations. The polymer-solvent interaction parameter χ of hydrogels was calculated from the swelling studies in water at different temperatures and was related to the composition and temperature. The ionic strength-reversibility and on-off switching kinetics of hydrogels and cryogels were studied in 10 −5 M and 1.0 M of NaBr solutions. Diffusion kinetics showed that the swelling of ionic hydrogels is of non-Fickian-type transportation, however, non-ionic PNIPA hydrogels and P(NIPA- co -NaA) cryogels showed pseudo-Fickian diffusion. The resulting hydrogels and cryogels containing both temperature and pH-sensitive units are able to interact with oppositely charged groups via hydrophobic and electrostatic interactions.