We report the use of a novel extrusion tip that allows for the omnidirectional printing of eutectic gallium-indium (eGaIn) alloy onto the surface of hydrogel materials into complex 2-dimensional patterns. The use of these printed soft “wires” as an electrothermal heating element for soft robotics purposes was explored. Heating of the eGaIn structures encapsulated in an alginate/acrylamide ionic-covalent entanglement hydrogel was measured by a thermal imaging camera. It was determined that eGaIn is a suitable material for use in future soft robotics applications as an electrothermal heating element to actuate thermally responsive N-isoproylacrylamide hydrogels.

In this work, we propose a multi-sensor platform where sensors are stacked over one another (3D stacked) each offering a unique functionality. The technique involves the use of Polyurethane (PU) sponge and PVDF/graphene (Gr) /ZnO composites for various sensing applications. The sponge was made conductive by dipping it in different weight percentages of pencil lead dispersed in ethanol through ultrasonication. Large area Gr/PVDF films were fabricated by simple solution mixing and casting method which also served as a substrate for the 3D stacked sensor. ZnO was grown hydrothermally over Gr/PVDF film by masking a portion of Gr/PVDF film to form a p-n junction. Silver paste and copper tape were used as contact pads. All the three fabricated devices were stacked with PU sponge sandwiched between Gr/PVDF/ZnO (top) and large area Gr/PVDF (bottom) as substrate. Performance of individual sensors and 3D stacked sensor was compared and no notable change was observed. The 3D stacked sensor array platform with its multifunctionality would be a step ahead in wearable electronics which can be integrated on human and can function as an e-skin for burn and acid victims, robotics and human-machine interactions.

S-layer proteins of various lattice-forming types are the most abundant protein by mass on earth. They form the outermost cell crystalline component in a broad range of bacteria and archaea. They are porous monomolecular layer with unit cell size in tens of nanometers. These monomer proteins are capable of forming self-assembled mono- or double layers. Isolated from cell surfaces or through recombinant protein production, they are able to form ordered 2D crystal lattice on a variety of non-cellular surfaces. We study S-layer SbpA protein, which is found in mesophilic organism Lysinibacillus sphaericus with square lattice crystallinity. The recombinant SbpA (rSbpA) can be genetically modified and expressed in E. coli in different truncated forms. Using both the wtSpbA and truncated rSbpA, we reproduced the unique two-dimensional self-assembly pattern on several solid or flexible surfaces of interests towards electronic devices. By surface modification we can promote the self-assembly of SbpA on low affinity substrates. This enables a potential mean of creating complex functional bio-nanostructure. Delicate control of the self-assembly processes of S-layer on surfaces also serves the prerequisite of building the supramolecular structure as bio-electronic platform through protein fusing. Understanding of the electrical response from s-layer proteins provides a bridge between biological systems and electronic devices. Scale-up production and understanding the detailed interaction of the S-layer interface will likely be useful for nanobiotechnology and synthetic biology.

The high field electric breakdown of polyethylene/montmorillonite nanocomposites was studied in detail, and compared to the unfilled respective films. The electric breakdown strength (EBD) of ‘aligned’ composite films (i.e., films with fillers oriented parallel to the film surface) is much higher than the EBD of the respective ‘isotropic’ composites (i.e., films with fillers of random orientation) and of the unfilled polymer films. This behavior suggests a barrier mechanism as the origin of electric strength improvement, a supposition that was investigated in detail here and is supported by: (a) EBD is not related to filler-induced or strain-induced polymer crystallinity changes; (b) EBD decreases with modulus, but improves with toughness for these films; (c) there is no change in the polymer EBD for a small temperature jump (ΔT from 25 °C to 70 °C), but there is a definitive change in the composite EBD for the same ΔT. All these, support the postulation that the electrical breakdown of these systems is predominately through thermal degradation mechanisms, which can be affected by the existence of oriented inorganic nanofillers (and of oriented polymer crystallites). Thus, the controlled orientation of nanofillers is shown to be an effective approach to substantially improve the electric breakdown strength of PE dielectric/insulating films.

In previous work we have shown that aligned high aspect-ratio (pseudo-2D) nanofillers can yield large dielectric breakdown strength (EBD) improvements for a nanocomposite with a low-crystallinity polyethylene matrix. Here, we report a systematic study which delineates the contributions of the aligned inorganic fillers and of the aligned polymer crystallites in the overall EBD improvement achieved in the nanocomposites. Specifically, extrusion blown-molded polyethylene/montmorillonite nanocomposite films were cold-stretched to various strains, to further align the nanoparticles parallel to the film surface; this filler alignment is accompanied by a commensurate alignment of the polymer crystallites, especially those heterogeneously nucleated by the fillers. A systematic series of films are studied, with increased extent of alignment of the fillers and of the crystalline lamellae (quantified through Hermans orientation order parameters from 2D X-ray diffraction studies) and the aligned structure is correlated to the electric field breakdown strength (quantified through Weibull failure studies). It is shown that aligned pseudo-2D inorganic nanofillers provide additional strong improvements in EBD, improvements that are beyond, and added in excess of, any EBD increases due to polymer-crystal orientation.

Traditional solar power applications largely avoid using the infrared spectrum. Nevertheless, this region makes up about 45% of the solar power spectrum and therefore represents an untapped resource. Temperature control of buildings represents a significant cost for both businesses and private consumers. We are interested in developing thermochromic materials for building coatings to help moderate solar infrared absorption and thereby offset temperature control costs for buildings. Our initial effort in this study has been to characterize materials which might represent starting points for our research. We previously designed and 3D-printed an optical test platform to perform reflectance measurements with an ultraviolet-visible-near infrared spectrometer over a spectral range from 200-1000nm. The test platform temperature can be adjusted in real time using Peltier modules. In this study, a sample of microencapsulated 7-anilino-3-diethylamino-6-methyl fluoran was studied by diffuse reflectance spectroscopy from 15-40 degrees Celsius. Scanning electron microscopy was used to characterize the dye particles. Temperature and spectral data were monitored while the sample temperature was adjusted. The visible diffuse reflectance from the sample increased from around 15% below the transition to more than 40% above the transition. A modification of this fluoran which extends the switching behavior into the infrared may be viable for passive thermo-optical switching in building coatings.

We perform molecular dynamics (MD) simulations to understand thermally triggered shape memory behavior of a thermoplastic polyurethane (TPU) elastomer with an enhanced coarse-grained (CG) model. Hard and soft phases of shape memory polymers (SMPs) are known as fixed and reversible phase, respectively. Fixity depends on the content of hard segments due to their restricted mobility. On the contrary, recovery depends on the dynamic motion of the soft segments as well the degree of cross-linking, which is also affected by the quantity of hard segment. Several CG models of the TPU are constructed varying the weight percentage of soft segments to observe their effects on shape recovery and fixity. All of the models are equilibrated at 300K (above glass transition, Tg: 200-250 K) and deformed under uniaxial loading with NPT (isothermal-isobaric) ensembles. The deformed state is cooled to 100K (below Tg) and further equilibrated to estimate the shape fixity. Shape recovery is predicted by heating and equilibrating the structures back to 300K. By the end of this study, we may answer how much the shape fixities and recoveries are changed for varying concentration of hard segments from thermomechanical cycles with CGMD simulations.