We propose a simple approach, based onthe minimization of the total (entropic plus unfolding) energyofatwo-state system, todescribe the unfolding of multidomain macromolecules (proteins, silks, polysaccharides, nanopolymers). The model is fully analytical and enlightens the role of the different energetic components regulating the unfolding evolution. As an explicit example, we compare the analytical results with a titin atomic force microscopy stretch-induced unfolding experiment showing the ability of the model to quantitatively reproduce the experimental behaviour. In the thermodynamic limit, the sawtooth force-elongation unfolding curve degenerates to a constant force unfolding plateau.

The onset of compression induces wrinkling in actuation devices based on electroactive polymer thin films, which leads to a sudden decrease in performances and, eventually, to failure. Inspired by the classical tension field theory for thin membranes, we provide a general framework for the analysis of the insurgence of in-plane compressions. Our main result is the analytical deduction of a voltage-dependent domain of tensile configurations in the principal stretches plane.

Based on the choice of two physically meaningful strain measures, we study necessary and sufficient conditions for strong ellipticity of the equilibrium equations for twodimensional isotropic hyperelastic bodies. Specifically, we show, depending on the values of the derivatives of the energy function, that strong ellipticity is equivalent to a single condition with a clear physical interpretation.

Based on an energetic approach, we analytically determine inhomogeneous equilibrium configurations of thin electroactive polymeric films of under assigned voltage. We show that our results are useful in the analysis of well known failure phenomena taking place in this type of devices. Moreover, we demonstrate that neglecting inhomogeneity effects may lead to a drastic overestimate of the activation performances.

Based on an energy minimization approach, we analyse the elastic deformations of a thin electroactive polymer (EAP) film sandwiched by two elastic electrodes with non-negligible stiffness. We analytically show the existence of a critical value of the electrode voltage for which non-homogeneous solutions bifurcate from the homogeneous equilibrium state, leading to the pull-in phenomenon. This threshold strongly decreases the limit value proposed in the literature considering only homogeneous deformations. We explicitly discuss the influence of geometric and material parameters together with boundary conditions in the attainment of the different failure modes observed in EAP devices. In particular, we obtain the optimum values of these parameters leading to the maximum activation performances of the device

In this paper we present a model for the description of rate-independent hysteresis in Electroactive Polymers (EAPs). Our analysis is based on a model proposed by the authors for the description of damage and healing effects in polymeric materials and on a variational formulation for the resulting electromechanical equilibrium problem. The analysis of the class of equibiaxial strain, relevant for many actuation and energy harvesting devices, evidences that the model is effective and computationally efficient. The model shows a significant agreement with important experimental phonemena observed in EAP devices.

Actuation devices based on dielectric elastomers, typically exhibit various kinds of instability which may determine a decrease of performances and,eventually, the device failure. In this work we focus on wrinkling instabilities for polymer films subjected to an electric field. The main result is the definition of a domain of taut states in the plane of principal stretches strongly dependent on the applied voltage and on the constitutive properties of the polymer film. We discuss these features, crucial in the perspective of electroactive materials design, through simple boundary value problems for Neo-Hookean and Ogden materials.

Based on physically meaningful choice of the strainmeasures,we study the equilibrium and stability of an inflated spherical membrane. First, we obtain general results deduced by global geometric properties and then we analyze the possibility of inhomogeneous configurations. The stability analysis shows that under special constitutive assumptions the global energy minimum can be attained by inhomogeneous spherical configurations that we analytically describe. We argue that these deformations can reproduce well-known experimental results.

By means of a bifurcation analysis we show the onset of inhomogeneous equilibrium configurations in thin electroelastic polymeric films under assigned voltage. The resulting activation threshold decreases the diffusely adopted value obtained under the assumption of homogeneous deformations. We argue that the bifurcated inhomogeneous solution describes experimentally observed localization effects.

Thickness non-uniformities in electrostatic capacitors and in electroactive polymers arising from manufacturing processes or electromechanical induced inhomogeneous deformations may lead todrastic charge and electric field localizations and, ultimately, to an anticipated device failure. Based on ageometric interpretation of the Gauss equation enlightening the effect of the electrode curvature, weobtain an analytic expression of the electric field and of the surface charge density localization for nonperfectly planar capacitors with symmetric thickness non-uniformities. The efficiency of the model isexploited by analyzing specific boundary value problems of technological interest.

Lizards and insects can strongly attach to walls and then detach applying negligible additional forces. We propose a simple mechanical model of this phenomenon which implies active muscle control. We show that the detachment force may depend not only on the properties of the adhesive units, but also on the elastic interaction among these units. By regulating the scale of such cooperative interaction, the organism can actively switch between two modes of adhesion: delocalized (pull off) and localized (peeling).