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1. A Hybrid Syntactic Foam-Based Open-Cell Foam with Reversible Actuation

   https://doi.org/10.1021/acsami.2c16168  

   Sarrafan, Siavash; Li, Guoqiang (November 2022, ACS Applied Materials & Interfaces)
2. Contact Nonlinearity in Indenter–Foam Dampers

   https://doi.org/10.1115/1.4054054  

   Liu, Lejie; Yerrapragada, Karthik; Henak, Corinne R.; Eriten, Melih (October 2022, Journal of Vibration and Acoustics)

   Abstract In this paper, the nonlinear response of indenter–foam dampers is characterized. Those dampers consist of indenters pressed on open-cell foams swollen with wetting liquids. Recently, the authors identified the dominant mechanism of damping in those dampers as poro-viscoelastic (PVE) relaxations as in articular cartilage, one of nature’s best solutions to vibration attenuation. Those previous works by the authors included dynamic mechanical analyses of the indenter–foam dampers under small vibrations, i.e., linear regime. The current study features the dynamic response of similar dampers under larger strains to investigate the nonlinear regime. In particular, the indenter–foam dampers tested in this paper consist of an open-cell polyurethane foam swollen with castor oil. Harmonic displacements are applied on the swollen and pre-compressed foam using a flat-ended cylindrical indenter. Measured forces and corresponding hysteresis (force–displacement) loops are then analyzed to quantify damping performance (via specific damping capacity) and nonlinearities (via harmonic ratio). The effects of strain and strain rates on the damping capacity and harmonic ratio are investigated experimentally. The dominant source of the nonlinearity is identified as peeling at the indenter–foam interface (and quantified via peeling index). A representative model consisting of a linear viscoelastic foam and rate-dependent adhesive interface (slider element with limiting adhesive strength) explains the observed trends in peeling and thus nonlinear dynamic response. Possible remedies to suppress those nonlinearities in future designs of indenter–foam dampers are also discussed. 

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3. An Expanding Foam‐Fabric Orthopedic Cast

   https://doi.org/10.1002/admt.202101563  

   Root, Samuel E.; Sanchez, Vanessa; Tracz, Jovanna A.; Preston, Daniel J.; Zvi, Yoav S.; Wang, Kemble; Walsh, Conor J.; Homer‐Vanniasinkam, Shervanthi; Whitesides, George M. (September 2022, Advanced Materials Technologies)

   Abstract Traditional orthopedic casting strategies used in the treatment of fractured limbs, such as fiberglass and plaster‐based tapes, suffer from several drawbacks, including technically challenging molding for application, occurrence of skin complications, and the requirement of a potentially hazardous oscillatory saw for removal, which is frightening for pediatric patients. This work presents the design and evaluation of a foam‐fabric cast (FFC) to overcome these drawbacks by integrating strategies from soft materials engineering and functional apparel design. A fabric sleeve is designed to enable the reactive injection molding of a polymer foam and provide a form‐fitting orthopedic cast for the human forearm—with sufficient mechanical reinforcement to stabilize a fractured limb. Through testing with a replica limb and human subjects with a range of forearm volumes, the FFC application process is demonstrated and characterized. The thermal, pressural, chemical, and hygienic safety are comparable to or safer than existing clinical technologies. The FFC weighs only ≈150 g, is water resistant, and represents a robust alternative to traditional casts that can be i) manufactured at a large scale for a low cost; ii) applied to patients simply, rapidly (≈5 min), and reliably; and iii) removed easily with a pair of scissors. 

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4. Foam evaluation and Kronheimer–Mrowka theories

   https://doi.org/10.1016/j.aim.2020.107433  

   Khovanov, Mikhail; Robert, Louis-Hadrien (January 2021, Advances in Mathematics)

   null (Ed.)
5. Spinodal stratification in ultrathin micellar foam films

   https://doi.org/10.1039/C8ME00102B  

   Yilixiati, Subinuer; Wojcik, Ewelina; Zhang, Yiran; Sharma, Vivek (June 2019, Molecular Systems Design & Engineering)

   null (Ed.)

   We report the discovery of a hitherto unreported mechanism of drainage and rupture of micellar foam films that presents unexplored opportunities for understanding and controlling the stability, lifetime and properties of ubiquitous foams. It is well-known that ultrathin micellar foam films exhibit stratification, manifested as stepwise thinning and coexistence of thin–thick flat regions that differ in thickness by a nanoscopic step size equal to the intermicellar distance. Stratification typically involves the spontaneous formation and growth of thinner, darker, circular domains or thicker, brighter mesas. Mechanistically, domain expansion appears similar to hole growth in polymer films undergoing dewetting by nucleation and growth mechanism that can be described by considering metastable states resulting from a thickness-dependent oscillatory free energy. Dewetting polymer films occasionally phase separate into thick and thin regions forming an interconnected, network-like morphology by undergoing spinodal dewetting. However, the formation of thick–thin spinodal patterns has never been reported for freestanding films. In this contribution, we show that the thickness-dependent oscillatory contribution to free energy that arises due to confinement-induced layering of micelles can drive the formation of such thick-thin regions by undergoing a process we term as spinodal stratification. We visualize and characterize the nanoscopic thickness variations and transitions by using IDIOM (interferometry digital imaging optical microscopy) protocols to obtain exquisite thickness maps of freestanding films. We find that evaporation and enhanced drainage in vertical films play a critical role in driving the process, and spinodal stratification can occur in both single foam films and in bulk foam. 

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