Modeling of photo-thermo-sensitive hydrogels by applying the temperature expansion analogy

Abstract

Hydrogels are an outstanding material for sensor and actuator applications, for example, chemosensors and microfluidics, and have been extensively studied in both, experiments as well as in modeling within the last years. The theoretical investigations of hydrogels are key factors for the development of new hydrogel-based concepts in research and engineering. The recent approaches in modeling of the light-sensitive behavior of hydrogels are often complicated and very detailed. Commonly, they are based on the Helmholtz free energy function within a continuum-mechanical framework. In contrast, the Stimulus Expansion Model (SEM) is a simple and very effective approach to embed the swelling properties of a hydrogel into a continuum mechanical framework. Originally, the SEM was applied to chemical stimulation processes based on available experimental swelling curves. The current work provides an extension of the SEM for photo-thermo-sensitive hydrogels. The present approach considers (i) the attenuation of light by applying Lambert-Beer’s law as well as (ii) the energy transfer of light into heat. In this study, PNIPAm hydrogels with incorporated light-absorbing particles of copper-chlorophyllin are investigated. To demonstrate the capabilities of the presented approach, the effect of the variation of (i) light power, (ii) particle volume fraction, and (iii) ambient temperatures on the swelling behavior is analyzed. The obtained results show an excellent correlation with experimental results from literature. Concluding, the extended Stimulus Expansion Model provides further opportunities to design and simulate photo-thermo-sensitive hydrogels for engineering applications.

Active Layered Composites: A Variable Kinematics Approach With Stimulus Expansion Model

“…where The stimulus distribution can be derived by solving the stimulus field equation ( 2) with Ψ being the temperature and ψ = 0. This is the stationary form of Fourier's heat transfer equation without heat sources/sinks, as shown in our previous works [17,18]. For chemical stimuli, it is Fick's law of diffusion; sources and sinks are chemical reactions there.…”

Surface Softness Tuning with Arch‐Forming Active Hydrogel Elements

“…Extensions of this modeling approach were presented in our previous works, including multisensitivity and the coupling with the thermal field equations. [83] Also, nonlinear constitutive equations, like the neo-Hookean material model, can be applied. [84] Figure 3.…”