Mechano-optical behavior of loosely crosslinked double-network hydrogels: Modeling and real-time birefringence measurement during uniaxial extension

Abstract

Real-time uniaxial strain-induced birefringence in loosely crosslinked double-network (DN) hydrogels synthesized from acrylamide (AAm) and N,N-dimethyl(acrylamide) (DMA) was measured. Tensile tests were performed at different extension rates from quasi-static conditions to very rapid tests followed by a holding for relaxation. Both DN hydrogels exhibit negative birefringence whose absolute value increased with extension and remained constant during relaxation. DN hydrogel synthesized from AAm displayed a linear stress optical (birefringencetrue stress) behavior, however, a nonlinear trend was observed for the DN gel synthesized from DMA. A simple photoelastic model was developed based on the mechanical behavior of the gels using Fung elastic potential and Brewster's stress-optical law, and the model was compared with the experimental data.

Molecular anisotropy and rearrangement as mechanisms of toughness and extensibility in entangled physical gels

“…6(b) and 13(a)], indicating macroscopic alignment in the direction of loading [97]. At both deformation rates, initial increases in birefringence matched initial increases in stress, as expected for small deformations governed by linear stressoptical relationships [64][65][66][67]69]. During slow deformations, unentangled hydrogels exhibited a maximum birefringent intensity I PF of 5 ± 1% near 30% engineering strain, followed by a decay corresponding to high extensibility of the gel.…”

“…Entangled physical gels exhibited rate-dependent, nonmonotonic birefringence [ Fig. 13(b)], in contrast to monotonic birefringence typically observed in tough, chemically crosslinked gels with fixed network junctions [64][65][66]. Nonmonotonic birefringence requires structural rearrangement during uniaxial extension and rarely emerges from stretched polymer networks, with notable exceptions including composite polymer-nanoparticle gels [62,63] hydrogels comprising both physical and chemical crosslinks [59].…”

“…In situ POM measures birefringence to provide a relative measure of polymer chain orientation and alignment, which complements detailed nanostructural information from in situ SAXS. Emergent birefringence is commonly observed in polymers with liquid-crystalline domains [59,60], hydrogels with flow-induced alignment [61], and polymer networks during extensional deformation [62][63][64][65][66][67].…”

Çift Ağlı Hidrojellerin Basma Yükü Altında Gerilme Gevşemesi Davranışı

“…Alginates have a wide variety of properties depend on the type and parts of algae that they are cultivated form. Typically, alginates are used for their viscosifying properties for which they are used in the textile food and biotechnological industries [23]. AAM is the one of the common materials that are used in variety of tissue engineering areas, but the pure AAM have extremely poor mechanical properties and biocompatibility [24].…”

“…Aljinatlar, yetiştirildikleri alglerin türüne ve kısımlarına bağlı olarak çok çeşitli özelliklere sahiptir. Aljinatlar, genel olarak tekstil, gıda ve biyoteknoloji endüstrilerinde viskozite ayarlayıcı özelliklerinden dolayı kullanılır [23]. AAM, çeşitli doku mühendisliği alanlarında yaygın kullanılan malzemelerdendir, ancak saf AAM, son derece zayıf mekanik özelliklere ve biyouyumluluğa sahiptir [24].…”