An official website of the United States government
Abstract Programmable mechanically active materials (MAMs) are defined as materials that can sense and transduce external stimuli into mechanical outputs or conversely that can detect mechanical stimuli and respond through an optical change or other change in the appearance of the material. Programmable MAMs are a subset of responsive materials and offer potential in next generation robotics and smart systems. This review specifically focuses on hydrogel‐based MAMs because of their mechanical compliance, programmability, biocompatibility, and cost‐efficiency. First, the composition of hydrogel MAMs along with the top‐down and bottom‐up approaches used for programming these materials are discussed. Next, the fundamental principles for engineering responsivity in MAMS, which includes optical, thermal, magnetic, electrical, chemical, and mechanical stimuli, are considered. Some advantages and disadvantages of different responsivities are compared. Then, to conclude, the emerging applications of hydrogel‐based MAMs from recently published literature, as well as the future outlook of MAM studies, are summarized.
more »
« less
Thermoresponsive Conductivity of Graphene‐Based Fibers
Abstract Smart materials are versatile material systems which exhibit a measurable response to external stimuli. Recently, smart material systems have been developed which incorporate graphene in order to share on its various advantageous properties, such as mechanical strength, electrical conductivity, and thermal conductivity as well as to achieve unique stimuli‐dependent responses. Here, a graphene fiber‐based smart material that exhibits reversible electrical conductivity switching at a relatively low temperature (60 °C), is reported. Using molecular dynamics (MD) simulation and density functional theory‐based non‐equilibrium Green's function (DFT‐NEGF) approach, it is revealed that this thermo‐response behavior is due to the change in configuration of amphiphilic triblock dispersant molecules occurring in the graphene fiber during heating or cooling. These conformational changes alter the total number of graphene‐graphene contacts within the composite material system, and thus the electrical conductivity as well. Additionally, this graphene fiber fabrication approach uses a scalable, facile, water‐based method, that makes it easy to modify material composition ratios. In all, this work represents an important step forward to enable complete functional tuning of graphene‐based smart materials at the nanoscale while increasing commercialization viability.
more »
« less
- Award ID(s):
- 1719875
- PAR ID:
- 10398806
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 19
- Issue:
- 20
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Stimuli-responsive hydrogel strain sensors that synergize the advantages of both soft-wet hydrogels and smart functional materials have attracted rapidly increasing interest for exploring the opportunities from material design principles to emerging applications in electronic skins, health monitors, and human–machine interfaces. Stimuli-responsive hydrogel strain sensors possess smart and on-demand ability to specifically recognize various external stimuli and convert them into strain-induced mechanical, thermal, optical, and electrical signals. This review presents an up-to-date summary over the past five years on hydrogel strain sensors from different aspects, including material designs, gelation/fabrication methods, stimuli-responsive principles, and sensing performance. Hydrogel strain sensors are classified into five major categories based on the nature of the stimuli, and representative examples from each category are carefully selected and discussed in terms of structures, response mechanisms, and potential medical applications. Finally, current challenges and future perspectives of hydrogel strain sensors are tentatively proposed to stimulate more and better research in this emerging field.more » « less
-
Smart emulsions are both versatile additives to smart materials and functional smart materials themselves, acting as active components and structural elements driving innovative development. Emulsions offer versatility, ease of manipulation, and stability to smart materials. This review explores the multifaceted roles of emulsions, examining their formulation methods, applications, and role as building blocks in smart materials. The significance of emulsions in smart materials is discussed for applications such as drug delivery and adaptive coatings, as well as their role in stimuli‐responsive colloidal systems and nanocomposites. The smart emulsions reviewed encompass all manner of material types, including fluid and solid/polymerized smart materials. These include both emulsions with dynamic properties and emulsions used in the process of synthesizing other materials. Smart emulsions are categorized by application into shape memory, self‐healing, biological, and stimuli‐responsive, with analysis of formulation methods, metrics, and methods of final incorporation. Smart emulsions can be found initially as fluid systems and some react into solid polymers, tailored to meet functional needs. A comparative analysis reveals emerging trends such as coupling coating self‐healing/corrosion inhibition and use of waterborne polyurethanes. The discussion of smart emulsions concludes by outlining challenges and future directions for leveraging smart emulsions.more » « less
-
Abstract The cost‐effective and scalable synthesis and patterning of soft nanomaterial composites with improved electrical conductivity and mechanical stretchability remains challenging in wearable devices. This work reports a scalable, low‐cost fabrication approach to directly create and pattern crumpled porous graphene/NiS2nanocomposites with high mechanical stretchability and electrical conductivity through laser irradiation combined with electrodeposition and a pre‐strain strategy. With modulated mechanical stretchability and electrical conductivity, the crumpled graphene/NiS2nanocomposite can be readily patterned into target geometries for application in a standalone stretchable sensing platform. By leveraging the electrical energy harvested from the kinetic motion from wearable triboelectric nanogenerator (TENG) and stored in micro‐supercapacitor arrays (MSCAs) to drive biophysical sensors, the system is demonstrated to monitor human motions, body temperature, and toxic gas in the exposed environment. The material selections, design strategies, and fabrication approaches from this study provide functional nanomaterial composites with tunable properties for future high‐performance bio‐integrated electronics.more » « less
-
Recently, graphene fibers derived from wet-spinning of graphene oxide (GO) dispersions have emerged as viable electrodes for fiber-shaped supercapacitors (FSCs) and/or batteries, wherein large surface area, high electrical conductivity, and sufficient mechanical strength/toughness are desired. However, for most fiber electrodes reported so far, compromises have to be made between energy-storage capacity and mechanical/electrical performance, whereas a graphene fiber with high capacity and sufficient toughness for direct machine weaving or knitting is yet to be developed. Inspired by the alum mordant used for natural dyes in the traditional textile dyeing industry, our research group has synthesized wet-spun GO fibers and coagulated them with different multivalent cations ( e.g. Ca 2+ , Fe 3+ , and Al 3+ ), where dramatically different fiber morphologies and properties have been observed. The first principles density functional theory has been further employed to explain the observed disparities via cation–GO binding energy calculation. When assembled into solid-state FSCs, Al 3+ -based reduced GO (rGO) fibers offer excellent stability against bending, and a specific capacitance of 148.5 mF cm −2 at 40 mV s −1 , 1.4, 4.8, and 6.8 times higher than that of the rGO fibers based on other three coagulation systems (Fe 3+ , Ca 2+ and acetic acid), respectively. The volumetric energy density of the Al 3+ -based FSC is up to 13.26 mW h cm −3 , while a high power density of 250.87 mW cm −3 is maintained.more » « less
