Length Effects of Short Alkyl Side Chains on Phase-Separated Structure and Dynamics of Hydrophobic Association Hydrogels

Abstract

Phase separation plays a crucial role in toughening hydrogels. Thus, regulating the phase-separation structure is vital to understanding the toughening mechanism in phase-separated hydrogels. Current synthesis strategies often provide limited control on phase-separated structures. In this work, a library of short-alkyl-side-chain-modified hydrogels is fabricated as model phase-separated hydrogels to investigate the length effects of short alkyl side chains on the phase-separated structure, apparent mechanics, and dynamics. Short-alkyl-chain-modified polymers undergo vapor-induced phase separation from highly concentrated solutions and coalesce into a well-connected polymer-rich phase. With increasing length of the side chains, the polymer-rich domain thickens due to enhanced hydrophobic interaction. Rheology suggests that longer alkyl side chains result in higher “glass”-transition temperatures and slower dynamics. However, by correlating the stretch rate and temperature dependence of both the small deformation properties (linear rheology) and the large deformation properties (tensile behavior), we find that regardless of the length of the side chain, hydrogels become tough and strong when the tensile test temperature approaches the glass-transition temperature or the stretch rate matches the relaxation time in the intermediate frequency regime. The strength and toughness of the gels obtained in this work are the combined effect of phase separation and glass transition. This work sheds light on the design principles for the mechanical elements in phase-separated hydrogels.

A Repeatable Dual‐Encryption Platform from Recyclable Thermosets with Self‐Healing Ability and Shape Memory Effect

“…Since the increase of C 18 segments enhances the hydrophobic interactions and facilitates phase separation, more hydrophobic segments are aggregated in water to form thicker and denser white domains more quickly, hampering the transmission of light (Figure 5b). [ 25 ]…”

“…Since the increase of C 18 segments enhances the hydrophobic interactions and facilitates phase separation, more hydrophobic segments are aggregated in water to form thicker and denser white domains more quickly, hampering the transmission of light (Figure 5b). [25] The asynchronous hydrophobicity of the thermosets can be innovatively applied in encryption. As shown in Figure 5c, a "T"-shaped A 3 O 1 P 6 and an "F"-shaped A 2 O 1 P 6 were embedded within a rectangular A 1 O 1 P 6 panel with a hollowed-out "TF" pattern (all assembled films with a thickness of 0.5 mm, Figure S16, Supporting Information).…”

Rationally Tuning Phase Separation in Polymeric Membranes toward Optimized All-day Passive Radiative Coolers

“…Such rarity can be attributed to the fact that the precedents of NIPS are constrained to the “hard” polymers with glass-transition temperatures ( T g ) much higher than room temperatures . A high T g means that the phase separation would be instantly arrested in a shallow depth, with constrained tunability . In the following context, these two factors were adjusted to obtain a series of membranes with tunable porosity, and porosity was correlated to optimize the solar “whiteness” .…”

Advances in Cellulose-Based Hydrogels for Biomedical Engineering: A Review Summary

“…Physical cross-linking methods have the following four mechanisms: (1) interaction between ions: the physical cross-linking network based on PVA and chitosan (CS) was mainly constructed by immersing the Na 3 Cit solution as the dynamic bond, and the N-glucosamine unit of the CS chain in the tridentate coordination of the Cit 3− anion [ 94 ]; (2) crystal cross-linking: Koichi proposed a non-damage enhancement strategy for hydrogels using strain-induced crystallization [ 34 ]. For the highly oriented slip-ring hydrogels with polyethylene glycol chains exposed to each other under large deformation, crystallization formed and melted with elongation and contraction, resulting in almost 100% rapid recovery of tensile energy and excellent toughness of 6.6 to 22 megajoules each square meter; (3) hydrogen bond cross-linking: there is a new strategy to dynamically adjust the hydrogen bond cross-linking between PVA and tannic acid (TA) by ethanol, which can be simply coated on the surface of porous substrates by different methods [ 95 ]; and (4) hydrophobic association: Sun made the short alkyl side chain modified hydrogel library into a model phase separation hydrogel [ 96 ]. With the increase of side chain length, stronger hydrophobic interaction was generated.…”