Consisting of alternating swelling and nonswelling polymeric layers (SLs and NLs), lamellar gels are 1D photonic crystals with tunable optical properties.  The lamellar structure induces a constraint between the SLs and the NLs, resulting in an anisotropic swelling behavior coupled with deformation.  The coupling gives rise to the mechano-chromatic effect, and quantitative understanding of it is the key to many applications.  This letter formulates a nonlinear continuum model for lamellar gels by considering the constrained swelling of SLs and the anisotropic deformation in both types of layers.  A finite-element method is further developed to simulate the response to non-uniform deformation.

The Department of Aerospace Engineering at Iowa State University (www.aere.iastate.edu) invites applicants for faculty positions in each of the broad areas of Computational Propulsion, Thermal Management & Heat Transfer, and Experimental Robotics & Autonomous Aerospace Systems. Applications are sought for tenured and tenuretrack appointments at the level of Assistant or Associate Professor, and exceptional candidates who qualify for the rank of Full Professor may also be considered for the Dennis and Rebecca Muilenburg Chair in Aerospace Engineering.

TENURE-TRACK FACULTY POSITION: The Department of Aerospace Engineering at Iowa State University invites applicants for a faculty position in the area of autonomous space systems. The appointment will start in August 2011. The search is focused at the Assistant and Associate Professor level, but exceptional candidates who qualify for the rank of Full Professor will also be considered. The primary research interests include robotic and human space exploration, on-board autonomy, and space systems analysis, with background in the disciplines of adaptive guidance and control, navigation, and space flight mechanics. A balanced research program with a strong experimental interest is desirable. An earned Ph.D.

Dielectric elastomer, as an important category of electroactive polymers, is known to have viscoelastic properties that strongly affect its dynamic performance and limit its application. Very few models accounting for the effects of both electrostatics and viscoelasticity exist in the literature, and even fewer are capable of making reliable predictions under general loads and constraints. Based on the principals of nonequilibrium thermodynamics, this paper develops a field theory that fully couples the large inelastic deformations and electric fields in deformable dielectrics. Our theory recovers existing models of elastic dielectrics in the equilibrium limit.

Ionic polymer-metal composite (IPMC) is a polyelectrolyte (usually Nafion or Femion swollen by simple salt solution) strip or membrane with both sides plated with metal electrodes. It is a particular design of electroactive-polymer device rather than a new class of material. When a voltage is applied between its electrodes, it will bend toward either electrode depending on the polarity (anode for a negatively charged gel), and the magnitude of deformation could be controlled by the electric signal.  Reversely, the deformation of an IPMC can generate electric signal or even energy output [1-4].  Therefore IPMC has recently becomes a hot topic in actuation, sensor and energy harvesting applications, especially when integrated with the characteristics of certain gels that are responsive to other environmental stimuli such as pH value or temperature.

The Society of the Engineering Science is sponsoring the 47th Annual Technical Meeting (SES2010) on October 4-6, 2010 at Iowa State University in Ames, IA. The meeting is held on biannual basis as a standalone meeting to foster and promote the exchange of ideas and information among the various disciplines of engineering and the fields of physics, chemistry, mathematics, bioengineering and related scientific and engineering fields.

Now the conference is open to abstract submission.  Please visit the conference website and submit your abstract online.  The deadline for submitting your abstract is Friday, May 7, at 5pm (CST).

AWARDS SYMPOSIA

Dear Colleague:

The Society of the Engineering Science is sponsoring the 47th Annual Technical Meeting (SES2010) on October 4-6, 2010 at Iowa State University in Ames, IA. The meeting is held on biannual basis as a standalone meeting to foster and promote the exchange of ideas and information among the various disciplines of engineering and the fields of physics, chemistry, mathematics, bioengineering and related scientific and engineering fields.

The overarching theme of the conference is multi-scale multi-physics phenomena. The conference will have the following general topical tracks:

Due to the migration of mobile molecules and ions, a thin diffusive layer of distributed charge - the electric double layer - forms at the interface between a polyelectrolyte gel and a liquid ionic solution.  When two polyelectrolyte gels are brought closely together, the electric double layers overlap and interact with each other, resulting in an effective repulsion.  The multiphysics coupling nature of soft gels makes their surface interactions significantly different from the interactions between rigid solids.

The electric-field-induced phase transition was investigated under mechanical confinements in bulk samples of an antiferroelectric perovskite oxide at room temperature. Profound impacts of mechanical confinements on the phase transition are observed due to the interplay of ferroelasticity and the volume expansion at the transition. The uniaxial compressive prestress delays while the radial compressive prestress suppresses it. The difference is rationalized with a phenomenological model of the phase transition accounting for the mechanical confinement.

When a block of an elastomer is bent, the compressed surface may form a crease. This paper analyzes the critical condition for creasing by comparing the elastic energy in a creased body and that in a smooth body. This difference in energy is expressed by a scaling relation. Critical conditions for creasing are determined for elastomers subject to general loads and gels swelling under constraint. The theoretical results are compared with existing experimental observations.

Immersed in an ionic solution, a network of polyelectrolyte polymers imbibes the solution and swells, resulting in a polyelectrolyte gel. The swelling is reversible, and is regulated by ionic concentrations, mechanical forces, and electric potentials. This paper develops a field theory to couple large deformation and electrochemistry. A specific material model is described, including the effects of stretching the network, mixing the polymers with the solvent and ions, and polarizing the gel. We show that the notion of osmotic pressure in a gel has no experimental significance in general, but acquires a physical interpretation within the specific material model.

The Department of Aerospace Engineering at Iowa State University invites applications for multiple tenure-track faculty positions at the assistant, associate, or full professor ranks to begin August 2009. Applicants are sought in all areas of aerospace engineering and engineering mechanics but preference will be given to those with interest and expertise in aerospace structures/mechanics of materials, multidisciplinary design and analysis, experimental thermal-fluids, propulsion, wind energy, and wind engineering.

There are currently 5 openings for perspective graduate students (preferably applying for a PhD program) in the area of experimental, theoretical or computational solid mechanics (or combined), starting from Fall, 2009.  Recruited students are expected to work with Ashraf Bastawros or Wei Hong.  Possible research topics include: Smart materials/structures, Reliability of micro-electronic devices, Layered structures, Mechanics of soft active materals, etc.

A network of polymers can imbibe a large quantity of a solvent and swell, resulting in a gel.  The swelling process can be markedly influenced by a mechanical load and geometric constraint.  When the network, solvent, and mechanical load equilibrate, the gel usually swells by a field of inhomogeneous and anisotropic deformation.  We show that this field in the swollen gel is equivalent to that in a hyperelastic solid.  We implement this theory in the finite-element package, ABAQUS, and analyze examples of swelling-induced deformation, contact, and bifurcation.  Because commercial software like ABAQUS is widely available, this work may provide a powerful tool to study complex phenomena in gels.

Prof. Zhigang Suo and Prof. Frans Spaepen, of the Harvard School of Engineering and Applied Sciences, have just been elected to the National Academy of Engineering.  They are among 65 new members elected to the NAE in 2008.  Update:  Also elected this year is another mechanician, Robert Dodds, of the University of Illinois.

Hydrogels have enormous potential for making adaptive structures in response to diverse stimuli.  In a structure demonstrated recently, for example, nanoscale rods of silicon were embedded vertically in a swollen hydrogel, and the rods tilted by a large angle in response to a drying environment (Sidorenko, et al., Science 315, 487, 2007).  Here we describe a model to show that this behavior corresponds to a bifurcation at a critical humidity, analogous to a phase transition of the second kind.

   A large quantity of small molecules may migrate into a network of long polymers, causing the network to swell, forming an aggregate known as a polymeric gel.  This paper formulates a theory of the coupled mass transport and large deformation.

A (001) surface of silicon consists of terraces of two variants, which have an identical atomic structure, except for a 90° rotation. We formulate a model to evolve the terraces under the combined action of electric current and applied strain. The electric current motivates adatoms to diffuse by a wind force, while the applied strain motivates adatoms to diffuse by changing the concentration of adatoms in equilibrium with each step. To promote one variant of terraces over the other, the wind force acts on the anisotropy in diffusivity, and the applied strain acts on the anisotropy in surface stress. Our model reproduces experimental observations of stationary states, in which the relative width of the two variants becomes independent of time. Our model also predicts a new instability, in which a small change in experimental variables (e.g., the applied strain and the electric current) may cause a large change in the relative width of the two variants.

MECHANICAL AND AEROSPACE ENGINEERING

POSITION: The Department of Mechanical and Aerospace Engineering invites applications for one or more TENURE-TRACK or TENURED FACULTY POSITIONS at the Assistant, Associate or Full Professor levels. Successful candidates will be expected to teach undergraduate and graduate courses in Mechanical and Aerospace Engineering and to establish a vigorous extramurally funded research program.

QUALIFICATIONS: Ph.D. or equivalent degree.

RANK AND SALARY: Level of appointment commensurate with qualifications; salary based on published UC pay scales.

CLOSING DATE FOR APPLICATIONS: November 30, 2006.

Send detailed resume, personal statement summarizing teaching experience and research interests, leadership efforts and contributions to diversity, and names/addresses of 5 professional references to:

The Engineering Science and Mechanics Department at The Pennsylvania State University invites applications for a tenure-track faculty position in computational mechanics at the assistant professor level. Exceptional candidates at the associate or full professor level will also be considered. Candidates are sought with a foundation and research interests in mechanics across all scales from the molecular to the macroscopic, including expertise in: efficient massive and nonlinear computations; molecular and multiscale simulations; innovative and efficient approaches to nonlinear FEM for large deformations, inhomogeneities, and/or inclusions; problems with evolving microstructure such as phase transitions and damage evolution; massively parallel simulations of large systems of equations; novel numerical/empirical approaches to modeling multiscale constitutive behavior of composite, biological or otherwise novel material systems.

We propose a model of persistent step flow, emphasizing dominant kinetic processes and strain effects. Within this model, we construct a morphological phase diagram, delineating a regime of step flow from regimes of step bunching and island formation. In particular, we predict the existence of concurrent step bunching and island formation, a new growth mode that competes with step flow for phase space, and show that the deposition flux and temperature must be chosen within a window in order to achieve persistent step flow. The model rationalizes the diverse growth modes observed in pulsed laser deposition of SrRuO3 on SrTiO3

 Physical Review Letters 95, 095501 (2005)

A vicinal Si (001) surface may form stripes of terraces, separated by monatomic-layer-high steps of two kinds, SA and SB . As adatoms diffuse on the terraces and attach to or detach from the steps, the steps move. In equilibrium, the steps are equally spaced due to elastic interaction. During deposition, however, SA is less mobile than SB . We model the interplay between the elastic and kinetic effects that drives step motion, and show that during homoepitaxy all the steps may move in a steady state, such that alternating terraces have time-independent, but unequal, widths. The ratio between the widths of neighboring terraces is tunable by the deposition flux and substrate temperature. We study the stability of the steady state mode of growth using both linear perturbation analysis and numerical simulations. We elucidate the delicate roles played by the standard Ehrlich-Schwoebel (ES) barriers and inverse ES barriers in influencing growth stability in the complex system containing (SA+SB) step pairs.

Preprint available in the attachment.