1,721,002 research outputs found
Hydrogel Composite Adhesives Inspired by Algae and Mussels
Full text linkThe ocean is a vast source of a multitude of materials used in daily life, but has also provided numerous sources of inspiration for creating novel bio-inspired materials. Marine mussels are one of the best-known marine organisms that have inspired numerous underwater adhesives. These materials have found applications in a broad variety of fields; their usage in biomedical applications is the most prevalent, due to the abundance of wet environments within the body. However, many organisms that adhere to rocks and the sea floor have their own unique strategies for achieving adhesion in wet conditions. Many synthetic bio-inspired adhesives look purely to the chemistry of mussel adhesion for inspiration, while other facets of mussel adhesive strategies (such as process control) offer their own improvements. The objective of this dissertation is to develop and fabricate underwater adhesives that take inspiration from the adhesive chemistry and processes of both marine mussels and benthic algae.
Algae and mussel systems were firstly combined by covalently modifying alginate polymer chains (extracted from brown algae) with catechol functionality (inspired by mussel chemistry). After ionic crosslinking, the resulting hydrogels were adhesive to soft and organic materials, showing promise adhesion to animal tissue samples. The effects of catechol functionalization on the mechanical properties of the gels were also investigated, and differences in adhesion between soft and rigid substrates was observed. Secondly, alginate and dopamine were combined together through noncovalent interactions; the ionic crosslinking of alginate and coordinate bonding of dopamine were exploited by using ferric ions to link the adhesive and cohesive components. By mimicking the processes of mussel and algae adhesion, a sequential application method was developed to improve adhesion of the algae-mussel-inspired glue, leading to adhesive strengths over 100 times that of pure alginate and over 5 times that of a non-sequential method. Finally, the stability and workability of the algae-mussel glue was improved by controlling dissolution and dispersion of the components. This was used to formulate both one-part and two-part adhesives that could be used hours or days after preparation, respectively, with the ability to be applied directly to objects underwater to bond them together
Water Based Polyurethane Multi-Functional Composites
Full text linkPolyurethanes (PUs) are a class of versatile polymers that exhibit various mechanical, physical, chemical and biological properties depending on their structure and morphology. Polyurethanes (PUs) have been employed in a variety of industrial applications including foams, coatings, textiles, machinery, sporting, transportation, vehicles and construction. However, the potentials of PUs in the emerging technology fields such as soft and wearable electronics, energy storage devices, biosensors, actuators, photovoltaic devices and stimuli-responsive materials are largely unexplored. The major objective of the thesis research is to develop PU composites for such emerging applications as e-textiles, self-healing electronics, and smart windows. In this project, we select water-based polyurethane (WPU) as the main polymer matrix to develop a variety of ink systems for multiple applications.
Firstly, to investigate the application of WPU in flexible and stretchable electronics, we develop a WPU-silver and WPU-polypyrrole (PPy) conductive ink for textile. The effective penetration of obtained ink makes the textile conductive and mechanically robust. The electrical conductivity of the PU-silver textile is high but drops significantly under stretching due to the intrinsically rigid property of metal. In contrast, the WPU-PPy textile shows a stable conductive performance under large elongation, however the electrical conductivity is four orders of magnitude lower than that of WPU-silver textile.
Secondly, taking advantage of the ionic properties of WPU, we develop a self-healing elastomer through WPU/polyethylenimine (PEI) latex polyelectrolyte coacervation system, which contains opposite charges but is stable in water solution. Self-healing is achieved via water through two types of non-covalent bonds: ionic interaction between WPU and PEI, and polymer entanglement of WPU itself. This WPU-PEI dispersion can be combined with conductive filler such as silver flakes for printable self-healing soft antenna, indicating the potential applications in soft electronics industries.
Finally, we replace the positively charged PEI with negatively charged poly methacrylic acid sodium salt (PMANa) to functionalize the WPU dispersion. The WPU-PMANa film shows a sharp change in transparency under mechanical strain, which can be used as robust mechanoresponsive smart windows. Additionally, the polyurethane smart window is multi-functional, its potential applications in the field of camouflage and dynamic optical gratings have been explored.
A study of cellulose nanocrystal reinforcing effect in polyurethane and vitrimer system
Full text linkNanocellulose-based composites and materials have received remarkable attention due to their high mechanical performance, low weight, and environmental friendliness. However, the compatibility between CNCs and polymer may vary significantly according to the polarity and hydrophobicity of polymer. The dispersity of CNCs in the polymer matrix is also critical to the physical and chemical performance of final nanocomposites. These limitations challenge the reinforcing effect of nanocellulose in nanocomposite materials in practical applications. In this study, we used both solvent casting and in situ polymerization methods to add CNCs into polymer matrices to achieve an improved performance of CNC-reinforced nanocomposites.
In the first part, CNC suspension was directly mixed with waterborne polyurethane (WPU), and then a film was obtained after evaporation at room temperature. Further tensile tests confirmed the excellent reinforcing effect of CNCs, with improved values for stress of 27.8 MPa and Young’s modulus of 100.46 MPa compared to 19.6 MPa and 16.73 MPa for neat WPU. The results of scratch and friction tests exhibited better scratch resistance and increased coefficient of friction, making it a potential material for coating and packing applications. The thermal stability of CNC-reinforced nanocomposites was not influenced by the addition of CNC particles, and the 5% weight loss and maximum weight loss temperatures also remained the same. The water contact angle did change with the addition of CNCs, due to their hydrophilic features, reducing from 89° to 31°.
In the second part, CNCs were incorporated into vitrimer by in situ polymerization method. CNCs were initially grafted with polycaprolactone (PCL) to allow CNCs to be directly incorporated into the synthesis of vitrimer material. The addition of PCL-grafted-CNCs (PCL) increased the tensile strength and storage modulus of the vitrimer both at room temperature and above the glass transition temperature (Tg). The CNC-vitrimer composites were all insoluble in toluene even at high temperatures, suggesting a three-dimensional network was formed. Furthermore, after several reprocessing cycles, the CNC-vitrimer still displayed good mechanical properties. The effect of PCL-CNCs on the vitrimer system was also evaluated by dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, and swelling tests. It was found that the addition of polycaprolactone-grafted-CNCs (PCL-CNCs) increased the temperature values for the melting point, crystallization, and glass transition. Also, the gradual decrease in activation energy with the increased amount of PCL-CNCs reflect that the stress relaxation behavior is less sensitive to the temperature. The thermo-dynamic properties are controlled by the concentration of PCL-CNCs. When PCL-CNCs were at lower amounts, the hydroxyl and ester groups dominate the covalent adaptable networks (CANs) dynamic, leading to a faster stress relaxation behavior. However, when the amount of PCL-CNC increased, the crystals and aggregation started to constrain the mobility of polymer chain, resulting a longer stress relaxation time
Liquid Crystal Networks for Smart Biomimetic Micro/nano Structured Adhesives
No full textAs modern technology demands for miniaturized structures with higher surface area to the volume ratio, the design and synthesis of materials with tailored surfaces is becoming more important. Moreover, some emerging technologies require materials with smart surface properties that can be controlled remotely, and work adaptively in “on” and “off” states when stimulated externally. Fascinating surface structures and adaptive functionalities that can be found in biological systems have provided great inspirations to researchers for fabrication of synthetic biomimetic assemblies. While the fabrication of materials with non-smart bio-inspired surface structures has been greatly accomplished, the mimicking of adaptive functionalities of the living systems is less investigated. Thus, there is a great zeal in developing materials with smart and adaptive biomimetic structured surfaces. The objective of this dissertation is to design and develop materials with smart biomimetic micro/nanostructured surfaces that can show desirable responses when remotely stimulated.
First, an experimental study on the integration of a dissipative material (resembling the dissipative and wet nature of the tree frog toe pads) to an elastic fibrillar interface (resembling the dry and fibrillar nature of the gecko foot pads) is carried out. Accordingly, a new type of functionally graded adhesive is developed, which is composed of an array of elastic micropillars at the base, a thin elastic intermediate layer and a viscoelastic top layer. The results showed that the new proposed graded structure has remarkable adhesive properties in terms of pull-off force, work of adhesion, and structural integrity (i.e., inhibited cohesive failure). Second, muscle-driven actuation of biomimetic microfibrillar structures is achieved using integrative soft-lithography on a backing splayed liquid crystal elastomer or networks (LCEs/LCNs). Variation in the backing LCE layer thickness yields different modes of thermal deformation from a pure bend to a twist-bend. The muscular motion and dynamic self-cleaning of gecko toe pads are mimicked via this mechanism. Finally, the self-peeling of gecko toes is mimicked by the integration of film-terminated fibrillar adhesives to hybrid nematic LCN cantilevers. A soft gripper is developed based on the gecko-inspired attachment/detachment mechanism. Performance of the fabricated gripper for transportation of thin delicate objects is evaluated by the optimum mechanical strength of the LCN and the maximum size of the adhesive patch
Evaluation of Bio/pMDI Wood Adhesives
Full text linkWith the increasing concerns about formaldehyde emissions from wood-based panels and the demands of the sustainable products, the potential of synthetic wood resins derived from biomass resources has sparked enormous interest. To date, extensive efforts have been devoted to investigating the mechanism, the properties, and the modification approach of the bio-adhesives. To overcome the limitations of pure bio-adhesives (low reactivity, low moisture resistance, and biodegradation), many approaches have been developed to partially replace the bio-polymer with synthetic thermosetting adhesives. In this project, a functional experimental grade binder, made from the reactive extrusion modification process of biopolymers with other reagents, is used as a co-binder in combination with polymeric methylene diphenyl diisocyanate (pMDI) resin, to study the resulting performance of the system for wood adhesive applications.
To evaluate the influence of the experimental grade biopolymer binder on the performance of the pMDI adhesive, a pMDI adhesive blended with water was first investigated. The effect of water content on emulsion morphology and viscosity was characterized. For bonded samples, formulations obtaining the highest bonding strength of the water/pMDI adhesives was determined by comparing the pull-off stress and the lap-shear stress. To further improve the bonding performance, the wood substrate was modified by the silane coupling agent, (3-aminopropyl) triethoxysilane (APTES). The penetration depth of pMDI in the different wood substrates (neat wood, 1wt% APTES-treated wood, 3wt% APTES-treated wood) was accurately determined. These studies indicate that both strong interactions between the adhesives and wood substrate, and a certain level of penetration of the adhesives, are required for the good bonding performance of the water/pMDI adhesives.
The biopolymer/pMDI adhesives were prepared and investigated based on the protocols from the industry partner Ecosynthetix. By comparing the biopolymer/pMDI adhesives with the water/pMDI adhesives, the effect of the biopolymer to the pMDI was determined. The biopolymer can work as a thickener, emulsifier of the system to reduce the dosage of pMDI. In terms of bonding performance, the bonding strength of the biopolymer/pMDI adhesive is comparable with the highest stress achieved by water/pMDI resin, indicating the experimental grade biopolymer can be applied as an effective wood adhesive binder to partially replace pMDI without reducing the overall bonding performance
Fabrication and characterization of biomimetic dry adhesives supported by foam backing material
Full text linkUsing sacrificial templates to create 3D structures is commonly employed in various fields such as tissue engineering and water remediation to create complex and high surface area scaffolds. Herein, several sacrificial templating techniques are tried, tested, and evaluated and several methods for creating 3D porous material are discussed, including: solvent casting particulate leaching (SCPL) and simple sugar and salt leaching. The porous material is then integrated with polymer soft lithography patterning to create a single functionally graded adhesive (FGA) material to use in dry adhesive applications. The use of a soft foam backing layer helps to improve the compliance and flexibility of the adhesive pad, thus enhancing peel tolerance, buckling, and deflection and vibration resistance.
A dry FGA based on film-terminated silicone foam is developed utilizing the polymer foam's capacity to absorb large amounts of energy and so deliver high adhesion and peel resistance. The fabrication technique is based on simple sugar cube templating of common elastomers, followed by film termination of the polymer cubes using the same material. Dependencies of the pull-off adhesive force and energy release rate on preload and foam thickness are systematically investigated through a series of axisymmetric indentation/de-bonding tests. The contribution of the foam backing layer to the overall compliance and adhesion is analysed and discussed. The developed elastic film-terminated structure strongly enhances the pull-off force and work of adhesion, and can be employed in the transport of delicate objects, as demonstrated in the pick and place of a silicon wafer. Furthermore, the proposed foam-based FGAs can be readily detached from the adherent surface by applying shear deformation between the pad and the surface. This research clarifies the role of mechanical graded properties in adhesion and can have technical implications in the development of a simple but effective dry adhesive material for mounting and transporting objects using automated robotic devices.
The film terminated dry adhesive pads were further developed to investigate the feasibility of using a foam backing material as a universal platform to improve the adhesive properties of other terminal surface morphologies. Integrating other fast prototyping technologies as an alternative to lithographic templating techniques, scaled acrylonitrile butadiene styrene (ABS) 3D printed mushroom capped terminal structures are determined to be comparable to polyacrylate microstructure templated moulds. The effect of the foam is systematically evaluated using a similar axisymmetric indentation/de-bonding test with a probe of a large radius of curvature. Contact splitting through the control of terminal structures in both micro and millimetre scales shows improved contact properties with the addition of foam backing material. The mushroom capped adhesive pads are employed to demonstrate shear peel tolerance and cold temperature surface tolerance demonstrations.
Lastly, various sugar and salt templating techniques are explored and optimized for consistency and repeatability to select the material most suitable for current research. Statistical analysis is used in the selection process. A linearly approximated model to determine the pull-off force from foam porosity and stiffness parameters are reported as sample candidates. Model estimates find that the density of sugar granules and the applied preload force are the mostly significant contributors to increasing pull-off force
Evaluation of Hybrid Electrically Conductive Adhesives
No full textAn electrically conductive adhesive (ECA) is a composite material acting as a conductive paste, which consists of a thermoset loaded with conductive fillers (typically silver (Ag)). Many works that focus on this line of research were successful at making strides to improve its main weakness of low electrical conductivity. Most research focused on developing better silver fillers and co-fillers, or utilizing conductive polymers to improve its electrical conductivity, however, most of these works are carried out on small scale. In this work, we aim to produce larger quantities of hybrid ECA to successfully test its properties.
Industry is interested in materials with superior physical properties. As such, rheological behavior and mechanical strength were explored as it has been theoretically hinted that incorporation of exfoliated graphene within the composite could impact those factors listed in a positive manner.
In the first step of this project, pre-treated sodium dodecyl sulfate (SDS)-decorated graphene’s rheological properties were examined. An epoxy resin diglycidylether of bisphenol-A (DGEBA) was the main polymer used for this study: a well-known material that can behave either as a shear-thinning or shear-thickening material depending on the supplier. We showed how composites that contain graphene (Gr) had higher viscosities than ones that contained SDS decorated graphene Gr(s). Not only did we confirm that surfactant was a key factor in the decrease of viscosity, but we also report how Gr and Gr(s) had a special effect that suppresses the intrinsic shear thickening behavior of epoxy resin at weight concentrations (wt%) higher than 0.5 wt%. The results showed that Gr(s) is not only beneficial in terms of improving the conductivity of conventional ECAs, but it also acts as a solid lubricant that decreases the viscosity of the composite paste at higher weight concentrations.
In the second step of the project, pre-treated SDS decorated graphene’s mechanical properties were examined. In specific, its lap-shear strength (LSS) as well as the effect of residual solvent when present in our hybrid ECA system were studied in order to follow up on the thermal results obtained from a previous study. We showed that our initial suspicion was correct as the LSS did decrease for all of the solvent-assisted formulations that contained Gr(s) ranging from 66 to 84%, however, we were not able to tell whether or not that decrease was caused by lower crosslinking density. Instead, we uncovered another reason for this decrease: bubble formation during the curing step. This suspicion was confirmed qualitatively through light microscopy and quantitatively through optical profilometry, where we present an increase in surface roughness for the solvent-assisted samples. Furthermore, by using SEM, we also confirmed that this bubble formation extends throughout the entire bulk material rather than just at the interface. Lastly, we investigated whether the use of solvent to assist in the mixing process significantly improves the electrical conductivity at a lower weight loading of Ag, and compared the electrical conductivity with that of the products prepared under the same higher weight loading of Ag using a solvent-free mixing method from previous work.
Thirdly, we investigated another mechanical property of our hybrid ECAs through indentation tests, where we use Hertizan equations to characterize elastic modulus. Since we learned that the addition of Ag flakes is detrimental to the mechanical strength, we focused on the difference between the elastic moduli for Gr and Gr(s) in a solvent-free environment.
In the last step of this project, we explored the use of a liquid-suspended co-filler (instead of carbon filler-based materials) in Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS): a conductive polymer that is frequently in conductive thin-films. We report that by using PEDOT:PSS as a conductive co-filler into the conventional ECA with 60 wt% of Ag, we observed higher conductivity equivalent to adding an extra 20 wt% of Ag into the system. Furthermore, we report that an increase of PEDOT:PSS in the composite appears to decrease the LSS of the material by 20%.
Photopolymerization based 3D printing of thermoresponsive hydrogel precursors
No full textThermoresponsive hydrogels, which alter their shape in response to temperature changes, have crucial applications in wound dressings, sensors, and other biomedical contexts due to their responsive collapse behavior, high water content, and biocompatibility. Recent advancements in 3D printing have significantly improved the complexity and precision of hydrogel fabrication beyond traditional casting methods. Bioprinting is the most prevalent method for 3D printing hydrogels but is generally expensive, low-resolution, and restricted to academic settings. One alternative photopolymerization-based 3D printing offers greater accessibility and compatibility with synthetic hydrogel systems, capable of creating micrometer-sized features. However, the mechanical limitations of the printed objects and the temperature fluctuations during polymerization pose challenges for printing thermoresponsive hydrogels.
This thesis aims to develop 3D printing methods for thermoresponsive hydrogels using a printed organo-gel precursor, which allows for enhanced mechanical properties without triggering thermoresponsive behaviors during printing. This research targets applications in wound dressings and digital health, facilitating point-of-care fabrication. Mask stereolithography was investigated for creating thermoresponsive hydrogels from poly(N-isopropyl acrylamide) (PNIPAm) and poly(oligoethylene glycol) acrylate, incorporating bio-based polysaccharides as strengthening additives and ionic crosslinkers. The first experimental system used PNIPAm with poloxamers and a double network of sodium alginate, yielding a resin capable of printing precise structures and forming patient-specific wound dressings. This system displayed superior mechanical properties at room temperature and temperature-dependent drug release and adhesion. However, the use of dimethyl sulfoxide (DMSO) and NIPAm’s neurotoxicity prompted a shift to poly(oligoethylene glycol) acrylate-based resins. In the second system, quaternized chitosan/3-sulfopropyl acrylate (QCh:SPA) salts and 2-hydroxyethyl acrylate (HEA) was investigated for producing supramolecular hydrogels along with the use of a cellulose-derived solvent Cyrene to replace DMSO making the process greener. These hydrogels exhibited enhanced elasticity and feature resolution compared to other systems, also showing conductive properties due to ionic interactions. In the third system, the studies were conducted to investigate the incorporation ethylene glycol methyl ether acrylate with HEA and the use of octylamine-grafted cellulose nanofibrils (OA-CNF) and sodium alginate to develop core-shell microparticles. This enhanced the hydrogel's mechanical properties and exhibited broad LCST behavior, offering improved stability and laying the groundwork for future enhancements aimed at refining printability and tuning LCST responses
Interface dynamics of soft solids with liquids, solids, and gels
Full text linkSoft solids are commonly composed of polymeric networks suspended in liquids while maintaining their physical form. They have intermediate properties between viscous liquids and elastic solids, which are easily deformed even by small stresses (e.g., the interfacial tension with liquid droplets) but also resist deformation. Their distinctive softness has attracted many researchers and engineers to fruitfully apply soft solids in modern technologies such as 3D printing, in-vitro studies, soft robots, diagnostic chips, and artificial organs. In addition, many biological materials are soft solids, such as living tissues capable of conforming to the surface shape of the culture substrate and easily adapting to the surrounding environment.
The intermediate properties of soft solids create distinctive and unpredictable behaviors at interfaces beyond the scope of classical physics for pure liquids and solids. For example, soft solids show a time lag between the applied stress and the resultant strain. In addition, under certain extreme stress, soft solids might experience phase-separation between liquid and solid phases. Also, the polymeric chains might cause stick-slip motions of spreading liquid or sliding solid in contact with the soft polymeric surfaces. Understanding and controlling the different interfacial properties (e.g., lubrication, adhesion, and wetting) of soft solids are crucial to developing advanced technologies for using soft solids and better understanding the wisdom of nature. However, the physical principles behind numerous phenomena at soft interfaces are not yet clearly understood. Thus, the objective of this dissertation was to reveal the root causes of the salient features of different soft contact systems: soft solids in contact with sliding solids, flowing fluids, and stationary solids and gels.
The sliding tribosystem is one of the most prevalent contact systems. In this thesis, the role of viscoelasticity was first investigated on the sliding tribological behavior with and without lubricants. The lateral friction force of purely soft tribopairs (soft-on-soft) was examined. Through a regression analysis, a correlation was found among key parameters (e.g., sliding speed, preload, and viscoelasticity), showing the significant role of the loss tangent in the friction coefficient. On the one hand, above a certain level of free liquids in the elastic network of tribopairs (~ 30 wt.%), the liquid phase predominantly reduced the friction coefficient, potentially working as a lubricant at the interface.
Inspired by the findings on the role of the free liquids in the sliding tribosystem, a more detailed study on the surface deformation of soft solids with a larger fraction of liquids (~ 62 wt.%) (i.e., gel) was further investigated in contact with a stationary glass sphere. The soft surface evolved significantly longer (~ 85 hr) than its typical time scale (milliseconds) while the resultant strain was still within the elastic limit. The reasons behind this were the predominant finite-size and preload effects, minimized or neglected in most conventional and modified contact theories. The scope of research in this thesis was further expanded by engaging flowing Newtonian fluids (e.g., water and glycerol) in contact with soft solids.
The role of viscoelastic solids was researched on the flowing fluids by measuring the pressure drop of flowing fluids. To focus on the interface dynamics between soft solids and flowing fluids, the deflection of soft walls (i.e., bulging effect) was prevented by fabricating soft walls inside a rigid backing layer (i.e., rigid tube). Nonetheless, soft wall channels presented a reduced pressure drop compared to the calculated value of the Hagen-Poiseuille equation for rigid channels. As the free liquids fraction of the soft walls increased, the lower pressure drop was measured, implying that less energy was consumed. The cause of this reduced pressure drop was found to be the lubricating effect of free liquids on the soft surfaces, which was confirmed through dynamic contact angle measurements.
Lastly, via gels, the static contact signatures of two extreme physical states, pure liquids and solids, were bridged. A broad range of the effective elasticity of contact pairs was investigated from as low as near zero Pa to a few GPa. A scaling law was provided, connecting the wetting and adhesive contact regimes based on the measured contact radius and wetting foot. In addition, the experimental findings were validated through comparison with the experimental data presented in representative previous studies
Bio-inspired Oleophobic/Conductive Micro/nano Structures and Their Applications in Frozen Oil Adhesion Reduction
No full textInspired by the excellent superhydrophobicity and self-cleaning properties of the lotus leaf, numerous superhydro-oleophobic micro/nanostructures have been developed which mimicked biological systems. These structures have broad applications in industrial processes, especially oil transportation, oil/water separation and anti-fouling applications where oil adhesion is a critical factor. Although the adhesion properties of oils have been well explored on a variety of surfaces at ambient environment, low temperature behaviors were rarely reported especially when the oil is frozen under a frigid environment. For instance, there are cases in which oils are stuck or frozen onto the walls of engines or pipelines resulting in a large drag force thus leading to excess energy consumption and potential instrument malfunction. In this research project, the initial stage was mainly focused on developing an effective approach to construct well-defined superhydro-oleophobic microstructures and investigating the effects of structures and surface chemistry on superoleophobicity. In this stage, two different chemical modification approaches were applied to both flat and micropillared PDMS: 1) vapour deposition of trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane (FDTS) on cured polydimethylsiloxane (PDMS) elastomer surface (FDTS coated PDMS); 2) blending FDTS with the liquid PDMS precursor before curing (FDTS blended PDMS). Surfaces with varied oleophobicity were fabricated to investigate the effects of superhydro-oleophobicity on the reduction of frozen oil adhesion as characterized by knock-off tests. The relationship between the oleophobicity, which ranged from oleophilic flat surfaces to superoleophobic micropillars, and the reduction of oil adhesion at low temperatures was examined. It was observed that reduced contact angle hysteresis (CAH) led to reduced adhesion strength. By blending FDTS into PDMS micropillars, 60% adhesion strength reduction compared with flat surfaces was achieved. In order to eliminate the frozen oil effectively, electrical de-freezing was proposed by passing electrical current through the top surface layer to induce joule heating effect. To achieve this, epoxy-silver flakes composite micropillars were developed, demonstrating electrical conductivity and superoleophobicity. The effects of resistivity and superoleophobicity on the reduction and elimination of frozen-oil adhesion have been systematically studied, showing that the larger the resistivity and the oleophobicity, the less force was needed to remove frozen-oil droplet. After developing the electrically conductive polymer composite micropillars for eliminating frozen oil adhesion, we have extended this work, aiming to reduce the amount of conductive Ag flakes in the composite and make stretchable multifunctional composite elastomers. Electrically conductive and superoleophobic PDMS has been fabricated by embedding Ag flakes (SFs) & Ag nanowires (SNWs) into microstructures of the FDTS-blended PDMS elastomer achieved in the first stage of this project. A series of surface analyses and characterizations showed that highly conductive and superoleophobic surfaces were indeed obtained with a relatively low surface coverage of conductive fillers. A significant improvement to the conductivity was further achieved by using SNWs to partially replace the SFs. The stretchability and conductivity were examined under external strain, which showed that the as-prepared samples are highly stretchable and reversible. The electrical resistance of the SFs/SNWs embedded surface was less dependent on the strain due to the presence of the SNWs, creating a bridging effect and allowing current to flow consistently even as the silver particles were stretched apart from each other. This research demonstrates a simple approach to transform insulating elastomers into functional composites with a desired surface oleophobicity and electrical conductivity, which is of great help for the development multifunctional superoleophobic structures and their applications in oil adhesion reduction at low temperatures
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