How to Force Polymer Gels to Show Volume Phase Transitions

Dušková‐Smrčková, Miroslava; Dušek, Karel

doi:10.1021/acsmacrolett.8b00987

Cited by 12 publications

(15 citation statements)

References 68 publications

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“…It would also be interesting to extend our model to other geometries, in particular, to look at the core-shell structure that forms in spherical beads, and the impact of expansive stresses on the core [15]. In two-and three-dimensional situations involving a gel that is thin compared to its length h L 0 , we expect additional instabilities to affect, for example, the transition fronts induced by the forced influx of solvent.…”

Section: Discussionmentioning

confidence: 99%

“…A composition-dependent quadratic form of χ for PHEMA-water gels is given in Ref. [15] and varies between 0.4 and 1.3. The temperature and concentration dependence of χ for PNIPAM-water has been measured in Ref.…”

Section: Numerical Solutionsmentioning

confidence: 99%

“…The volume phase transition was theoretically predicted [13] and then identified in polyacrylamide gels upon temperature and fluid compositional changes [14], and explored in a host of situations and potential applications. Recently, it was shown that external stimuli such as stretching or compression of the gel can also greatly affect the transition [15]. Sudden quenching of a swollen polymer bead leads to a cloudy appearance, indicating the onset of phase separation via spinodal decomposition, followed by growth and expulsion of the solvent-rich domains from the gel [16].…”

Section: Introductionmentioning

confidence: 99%

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Phase separation in swelling and deswelling hydrogels with a free boundary

2020

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We present a full kinetic model of a hydrogel that undergoes phase separation during swelling and deswelling. The model accounts for the interfacial energy of coexisting phases, finite strain of the polymer network, and solvent transport across free boundaries. For the geometry of an initially dry layer bonded to a rigid substrate, the model predicts that forcing solvent into the gel at a fixed rate can induce a volume phase transition, which gives rise to coexisting phases with different degrees of swelling, in systems where this cannot occur in the freeswelling case. While a nonzero shear modulus assists in the propagation of the transition front separating these phases in the driven-swelling case, increasing it beyond a critical threshold suppresses its formation. Quenching a swollen hydrogel induces spinodal decomposition, which produces several highly localized, highly swollen phases which coarsen and are then ejected from free boundary. The wealth of dynamic scenarios of this system is discussed using phase-plane analysis and numerical solutions in a one-dimensional setting.

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Section: Discussionmentioning

confidence: 99%

Section: Numerical Solutionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Phase separation in swelling and deswelling hydrogels with a free boundary

2020

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“…For cross-linked systems, it has been suggested that the combinatorial part of

refers to the loss of entropy due to coupling of segments into clusters of functionality f [ 41 , 42 , 43 ] because there is no logical reason to reduce

for networks to solutions of linear polymers of infinite molecular weight. Within this concept, the extensive form of

for Flory–Huggins lattice model reads

where subscript n denotes a network,

is number of moles of solvent,

and

are volume fractions of solvent and polymer, respectively,

is the cycle rank of elastically active network chains, EANCs; it holds

where f e is the number–average number of EANCs issuing from an elastically active crosslink,

is the number of elastically active chains;

is the interaction function.…”

Section: The Mixing Contributionmentioning

confidence: 99%

“…One of such equations was used for the analysis of the effect of strain in ref. [ 43 ] and a choice of them can be found in ref. [ 41 ].…”

Section: The Elastic Contribution and Swelling Change Of The Chemimentioning

confidence: 99%

Volume Phase Transition in Gels: Its Discovery and Development

Dušek

Dušková‐Smrčková

2020

Gels

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The history of volume phase transition of responsive gels from its theoretical prediction to experimental discovery was described and the major role of mixing Gibbs energy function in theoretical models was stressed. For detailed analysis and fine tuning of the volume phase transition, the generalized Flory–Huggins model with concentration and temperature dependent interaction function coupled with Maxwell construction as a tool is very suitable. Application of expansive stresses can uncover the potential of various swelling gels for volume phase transition. Experimentally, the abrupt, equilibrium-controlled phase transition is often hard to achieve due to passage of gel through states of mechanical instability and slow relaxation processes in macroscopic objects.

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Thermally Responsive Fibers for Versatile Thermoactivated Protective Fabrics

Sun

Luo

Yan

et al. 2022

Adv Funct Materials

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Smart textiles with good mechanical adaptability play an important role in personal protection, health monitoring, and aerospace applications. However, most of the reported thermally responsive polymers has long response time and poor processability, comfort, and wearability. Skin-core structures of thermally responsive fibers with multiple commercial fiber cores and temperature-responsive hydrogel skins are designed and fabricated, which exhibit rapid mechanical adaptability, good thermohardening, and thermal insulation. This universal method enables tight bonding between various commercial fiber cores and hydrogel skins via specific covalently anchored networks. At room temperature, prepared fibers show softness, flexibility, and skin compatibility similar to those of ordinary fibers. As temperature rises, smart fibers become hard, rigid, and self-supporting. The modulus of hydrogel skin increases from 304% to 30883%, showing good mechanoadaptability and impact resistance owing to the synergy between hydrophobic interactions and ionic bonding. Moreover, this synergistic effect leads to an increase in heat absorption, and fibers exhibit good thermal insulation, which reduces the contact temperature of the body surface by ≈25 °C under the external temperature of 95 °C, effectively preventing thermal burns. Notably, the active mechanoadaptability of these smart fibers using conductive fibers as cores is demonstrated. This study provides feasibility for fabricating environmentally adaptive intelligent textiles.

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How to Force Polymer Gels to Show Volume Phase Transitions

Cited by 12 publications

References 68 publications

Phase separation in swelling and deswelling hydrogels with a free boundary

Phase separation in swelling and deswelling hydrogels with a free boundary

Volume Phase Transition in Gels: Its Discovery and Development

Thermally Responsive Fibers for Versatile Thermoactivated Protective Fabrics

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