Theory of one-dimensional swelling dynamics of polymer gels under mechanical constraint

Continuum mechanical model is proposed for dynamical processes in gels that involve coupling between the elastic deformation and solvent permeation. Basic equations are derived by two methods, by a physical argument, and by a variational principle. The model is then applied to discuss the swelling of gels, in which solvent permeation causes deformation, and the squeezing of gels, in which mechanical force induce solvent permeation. The model is also applied to the dynamics of the volume transition of gels. It is shown that the elasticity of gels creates various unusual features in the phase transition dynamics.

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“…An experiment for such a system was first performed by Suzuki et al, 36) and theoretical analysis was carried out in ref. 37.…”

Section: Gel Confined By Rigid Platementioning

confidence: 99%

Gel Dynamics

2009

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“…The static strain induces a finite further swelling. The stress-induced swelling [6][7][8] becomes more clearly recognizable as the strain increases. In the case of 50% strain, the diameter levels off at about 150 s. The results of the static strain experiments confirm that the stress-induced swelling occurs even in the collapsed state although the magnitude is smaller than that in the swollen state.…”

Section: Static Propertiesmentioning

confidence: 96%

“…This phenomenon is called ''stress-induced swelling'' and has become of much interest. [6][7][8] By contrast, there are few corresponding measurements on the PNIPA gels in the collapsed state above T t and thus the details of the deformation behavior of the collapsed gels are still unclear. [9][10][11] In the present paper, we report the creep behavior of the collapsed PNIPA gels under static and dynamic stresses (or strains) revealed by the same method in the previous papers.…”

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confidence: 99%

Creep Behavior of Poly(N-isopropylacrylamide) Gels in the Collapsed State

Nosaka

Urayama

Takigawa

2006

Polym J

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ABSTRACT:Creep behavior of cylindrical poly(N-isopropylacrylamide) hydrogels in the collapsed state has been investigated. When an elongational stress is applied to the collapsed gels in water, the length of the gels increases and the diameter decreases toward the new equilibrium values. When the stress is removed, the gel recovers the original state through the reverse process. The creep behavior of the collapsed gels is in contrast to the prominent further swelling behavior (i.e., increase in both length and diameter) of the same gels in the swollen state under a constant stress. The similar measurements under constant strains reveal that the collapsed gels undergo a small but definite stressinduced increase in volume. Under sinusoidal stress, the amplitude of the displacement decreases and the phase lag increases as angular frequency increases. A polymer gel consists of a polymer network swollen by a large amount of solvent and has been paid much attention as a unique soft material. The volume of polymer gels varies in response to the change in the environmental factors such as temperature, pH, composition of the solvent.1-4 By using these properties or functions, polymer gels have been expected as smart devices in various fields: for example, drug delivery systems and actuators. Poly(N-isopropylacrylamide) (PNIPA) hydrogels undergo the volume phase transition in response to an infinitesimal change in temperature, and the transition temperature (T t ) has been reported to be T t % 32 C: A slight increase in temperature causes a drastic decrease in volume around 32 C. Below T t the gels are highly swollen by water and this state is called ''swollen state''. Above T t the gels consist of polymer network and a very small amount of water, which is called ''collapsed gels'', or ''gels in the collapsed state''. In the previous papers 5, 6 we reported the swelling behavior of the PNIPA hydrogels in the swollen state below T t under static or dynamic stress. Elongational stress applied to the fully swollen gels induces a further swelling as a result of the shift to another equilibrium state under deformation. This phenomenon is called ''stress-induced swelling'' and has become of much interest.6-8 By contrast, there are few corresponding measurements on the PNIPA gels in the collapsed state above T t and thus the details of the deformation behavior of the collapsed gels are still unclear. [9][10][11] In the present paper, we report the creep behavior of the collapsed PNIPA gels under static and dynamic stresses (or strains) revealed by the same method in the previous papers. 5,6 EXPERIMENTAL Preparation of Gel SamplesPoly(N-isopropylacrylamide) (PNIPA) hydrogels were synthesized by radical copolymerization of Nisopropylacrylamide (NIPA) and N,N 0 -methylenebis-(acrylamide) (BIS). First, N-isopropylacrylamide and BIS (as a closslinker) were dissolved in distilled water under nitrogen atmosphere. The total monomer concentration of NIPA and BIS was fixed to be 6 wt %, and the molar ratio [NIPA]/[BIS] was also fixed to b...

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“…In their theory, however, the flow of a surrounding fluid is not considered. Doi and coworkers [3][4][5][6] have presented equations for the gel deformation that include the effects of the friction force between gel and solvent. They analyzed the swelling of gels under mechanical constraints or external forces using their model.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Swelling Behavior of a Droplet of Polymer Solution Immersed in a Solvent

Masaoka

Yamamoto

2012

J. Soc. Rheol., Jpn

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A formulation for simulating the kinematics of a droplet of polymer solution in solvent is proposed. In this formulation both polymer solution and solvent are characterized by Newtonian viscous fluids, the viscosity of polymer solution is much higher than that of solvent. Furthermore the effects of both osmotic pressure and friction force between polymers and solvent are considered. The deformation of a droplet is described by the convection equation of the volume fraction of polymer solution. Numerical simulations for a swelling and de-swelling problem of a polymer droplet in solvent are performed. The numerical results indicate that both the osmotic pressure and the friction force significantly affect the behavior of polymer droplet.

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Theory of one-dimensional swelling dynamics of polymer gels under mechanical constraint

Cited by 52 publications

References 5 publications

Gel Dynamics

Gel Dynamics

Creep Behavior of Poly(N-isopropylacrylamide) Gels in the Collapsed State

Numerical Simulation of Swelling Behavior of a Droplet of Polymer Solution Immersed in a Solvent

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