The authors are grateful for the support from City University of Hong Kong Strategic Research Grant with the Project No. 7005547, the support from the Research Grants Council (RGC) of the Hong Kong Special Administrative Region, China, with the&#160;Project No. R5007-18, and the support from Shenzhen Science and Technology Innovation Committee under the grant JCYJ20170818103206501.

1. Build the atomistic models
<ol>
	<li>Open the Materials Studio software to create five 3D atomistic documents and rename these documents as graphene, asphaltene, polar aromatics, naphthene aromatics, and saturates, respectively.</li>
	<li>Build the graphene model by creating the unit cell of graphene sheet in the 3D atomistic document using the Sketch Atom option.</li>
	<li>Construct the final structure using the Supercell option in the Build &#62; Symmetry menu. Define the size of the graphene sheet as 40 &#197; x 40 &#197;, which is larger than the asphalt chains and the crack width.</li>
	<li>Build and pack the four types of asphalt molecules.
	<ol>
		<li>Use the Sketch Atom option to draw the molecular structures of asphaltene, polar aromatics, naphthene aromatics, and saturates separately.</li>
		<li>Pack the four kinds of asphalt molecules into the simulation box using the Calculation option in the Modules &#62; Amorphous Cell menu.</li>
	</ol>
	</li>
	<li>Build the asphalt structure with the crack.
	<ol>
		<li>Set the height of the crack zone in the x dimension the same as the height of the box of 70 &#197; and the depth of the crack zone in the y dimension is half of the height of the box as 35 &#197;.</li>
		<li>Set two cases of the crack widths in the z dimension of 15 &#197; and 35 &#197;. Delete the redundant molecules in the crack zones of the middle-down area of asphalt bulk using the Delete option and keep the asphalt matrix in the middle-up area unchanged.</li>
	</ol>
	</li>
	<li>Build the graphene-modified asphalt structure with the crack. Incorporate the graphene sheet into the top area of the crack tip and the left crack surface separately before the packing step using the Copy + Paste command.</li>
	<li>Pack the asphalt molecules into the simulation box based on the final compositions listed in Table 1 to construct the graphene-modified asphalt structure.</li>
	<li>Convert the structure file to a data file. Save the structure files as the molecule files with structure information (*.car and *.mdf) from Materials Studio. Convert the molecule files (*.car and *.mdf) to data files using the msi2lmp tool in large-scale atomic/molecular massively parallel simulator (LAMMPS)55 package. Read the data file by the read_data command in LAMMPS.</li>
</ol>
2. Perform the simulations
<ol>
	<li>Define the parameters of the simulations.
	<ol>
		<li>Set the timestep as 1 fs in the input file considering the balance of accuracy and efficiency of the carried simulations.</li>
		<li>Set the cutoff distance of non-bonded interactions as 12 &#197;, which is less than half the length of the simulation box in consideration of the periodic boundary condition and the calculational efficiency.</li>
		<li>Employ the particle-particle particle-mesh (PPPM) algorithm to describe the long-range Coulombic interactions and set the relative error in per-atom forces calculated by the long-range solver as 10-5 for high accuracy.</li>
	</ol>
	</li>
	<li>Fix the profile of crack. Select the asphalt molecules on the profile by the Group Molecules command in LAMMPS. Apply the constraints on the asphalt molecules using the Fix Spring/Self command in LAMMPS to avoid the movements of asphalt molecules.</li>
	<li>Achieve the equilibrium
	<ol>
		<li>Keep the whole simulation box fully relaxed after 500 ps under the isothermal-isobaric (NPT) ensemble with a temperature of 300 K and pressure of 1 atm.</li>
		<li>Make the asphalt bulk equilibrated to the desired density value of the experimental measurements41 of 0.95-1.05 g/cm3&#160;by continuously examining the temperature, pressure, density, and energy values using the Thermal command.</li>
		<li>Check the convergence of potential energy and the mean-squared displacement (MSD) in the whole system for achieving the fully relaxed state.</li>
	</ol>
	</li>
	<li>Perform the self-healing process.
	<ol>
		<li>Set the whole simulation box under the NPT ensemble with a temperature of 300 K and pressure of 1 atm.</li>
		<li>Remove the constraint of the asphalt molecules on the contour of the crack zone.</li>
		<li>Track and record the size of the simulation box and the coordinates of atoms and use the Dump command for postprocessing.</li>
		<li>Average the simulation results during the self-healing process over three independent configurations with three different initial velocity seeds in order to decrease the random errors.</li>
	</ol>
	</li>
</ol>
3. Postprocessing
<ol>
	<li>Visualize the self-healing behaviors. Open the Open Visualization Tool OVITO56 to visualize the simulation progress, and then open the trajectory files in the lammpstrj format generated by LAMMPS55. Record the snapshots of the self-healing process and track the paths of asphalt molecules using the Render command.</li>
	<li>Analyze the contour of the atom number. Export the coordinates of the atoms to data analysis and graphing software from the trajectory files outputted from LAMMPS. Project the coordinates of atoms in the whole system onto the yz plane. Record atom numbers at different areas of the yz plane and plot the contour with different colors.</li>
	<li>Analyze the atom mobility and relative position.
	<ol>
		<li>Analyze the atom mobility of different asphalt components by the mean-squared displacement (MSD) using the Compute msd command.</li>
		<li>Calculate the relative positions between graphene and asphalt molecules by the radial distribution functions (RDF) curves for the system of graphene-modified asphalt systems with the 15 &#197; and 35 &#197; crack widths using the Compute rdf command in LAMMPS.</li>
		<li>Draw the RDF curves to check how the density of asphalt varies as a function of distance from the graphene sheet.</li>
	</ol>
	</li>
</ol>

The authors have no conflicts of interest to declare.

The critical steps within the Protocol part are as follows: step 1.4 - Build and pack the four types of asphalt molecules; step 1.5 - Build the asphalt structure with the crack; step 2.3 - Achieve the equilibrium; step 2.4 - Perform the self-healing process. These steps indicate the most cohesive and important contents of the protocol. To create the desired shapes of the inserted crack, the packing process is modified compared to the normal packing in Materials Studio. The crack shape is created and filled inside the sim...

Deterioration under daily vehicle loadings and variant environmental conditions, and the aging of asphalt during service result in degradation or even structural failures, i.e., cracking and raveling, which can further weaken the durability of asphalt pavements. The inherent response of asphalt to repair micro-cracks and voids automatically helps it recover from damages and restore strength1. This self-healing capability can considerably extend the service life of asphalt, save costs on maintenance, and reduce the emission of greenhouse gases2,3. The self-healing behavior of asphalt generally depends on several influencing factors, including its chemical composition, the degree of damage, and environmental conditions4. The improved self-healing capability of asphalt that can fully heal damage within a short period is desired; this has attracted extensive research interest in better mechanical performance and durability for asphalt pavements within civil engineering.
Novel methods to improve the self-healing capability of asphalt mainly include three approaches - inducing heating, encapsulation healing, and incorporating nanomaterials - which can be applied individually or simultaneously5,6. Inducing heating can significantly improve the mobility of asphalt and activate its self-healing for recovery7. The self-healing technology of asphalt by inducing heating can be ascribed to the assisted self-healing technique, which indicates that the self-healing properties of asphalt are improved by external stimuli. The objective of adding the steel wool fibers is to enhance the electrical conductivity so as to increase the healing capacity of the asphalt binder8. The approach to induce heat is to expose these electrically conductive fibers to the high-frequency alternating electromagnetic field, which can induce eddy currents, and the heat energy can diffuse into the asphalt binder by the conductive fibers9. The steel wool fibers enhance not just the&#160;electrical conductivity&#160;but also the thermal conductivity, both of which can positively affect the self-healing properties of asphalt. However, it is challenging to select the proper mixing time for fibers10. The length of fibers decreases with increased mixing time and influences thermal conductivity, while the decreased mixing time leads to clusters of fibers and impedes the mechanical properties of asphalt9. The encapsulation method can supply light components of aged asphalt such as aromatics and saturates and refresh the self-healing capability of asphalt11,12. However, this is a once-only treatment, and the healing materials cannot be replenished after the release. With the development of nanotechnology, nanomaterials have become promising modifiers for enhancing asphalt-based materials. Asphalt binders incorporated with nanomaterials present better thermal conductivity and mechanical properties13. Graphene with excellent mechanical performance and high thermal performance is regarded as an excellent candidate to improve the self-healing ability of asphalt14,15,16,17. The increased healing properties of graphene-modified asphalt can be attributed to the fact that graphene increases the capacity of the asphalt binder to be heated and produce heat transfer inside the asphalt binder, which means that graphene-modified asphalt can be heated more rapidly and reach up to higher temperature than pure asphalt18. The generated heat can be transferred throughout the graphene-modified asphalt at a faster speed than that through pure asphalt. The crack region of the asphalt binder can be influenced easily and healed faster by the heat flow with higher temperature and higher heating capacity. The self-healing reaction will begin if the energy that is equal to or larger than the healing activation energy exists at the crack surface of the asphalt19. Graphene can improve the thermal activation healing performance and accelerate the healing rate of asphalt19,20. Besides, graphene can save heating energy&#160;up to 50% during the healing process, which can benefit energy efficiency and reduce maintenance costs21.&#160;As a microwave-absorbent material, graphene is reported to improve the healing ability of asphalt during the rest period of microwave heating22. It is expected that the addition of graphene into asphalt will improve not only the mechanical performance but also the self-healing and energy-saving capacity, which requires in-depth knowledge of the self-healing mechanism.
Self-healing at the nanoscale is mainly due to the wetting and diffusion of asphalt molecules at the fractured faces23. As asphalt consists of various polar and non-polar molecules, its self-healing capability is strongly related to molecular interactions and movements of&#160;asphalt molecules of different components1. However, current research mainly relies on experimental techniques to quantify macroscopic mechanical properties, which causes missing information in the change of microstructures and the interactions among asphalt molecules when trying to understand the healing mechanism. The reinforcing mechanism of graphene in the self-healing capability of asphalt is also unclear at this stage. Molecular dynamics (MD) simulations play an influential role in investigating molecular interactions and motions of nanocomposite systems, and link microstructural deformation with molecular interactions and movements24,25,26,27,28,29,30,31. MD simulations have become more and more popular for analyzing material behaviors that cannot be accessed easily by experiments32,33. Existing studies have shown the feasibility and availability of MD simulations in asphalt systems; the cohesion, adhesion, aging, and thermomechanical properties of asphalt and asphalt composites can be explored by MD simulations34,35,36,37. The self-healing behaviors of asphalt can also be predicted by MD simulations38,39,40. Therefore, it is believed that the investigation using MD simulations is an effective way to understand both the self-healing and reinforcing mechanisms.
The objectives of this study are to investigate the self-healing behaviors of pure asphalt and graphene-modified asphalt nanocomposites and to understand the role of graphene in improving the healing capacity of asphalt through MD simulations. The self-healing simulations of pure asphalt and graphene-modified asphalt composites are carried out by introducing cracks into the initial structures. The self-healing capabilities are characterized by the contour of atom numbers, the reorientation and entanglement&#160;of molecules at the fractured face, and the mobility of asphalt components during the self-healing processes. By investigating the healing efficiency of graphene at different sites, the reinforcing mechanism of graphene contributing to the self-healing abilities of asphalt is unveiled, which can help with the monitoring of nanofillers in an optimal way and thus enable the life extension of asphalt pavements. An investigation of the self-healing capacity at the atomistic scale can provide an efficient way to develop advanced asphalt-based materials for future research.
According to asphalt chemistry, asphalt consists of various types of hydrocarbons and non-hydrocarbons with different polarity and shapes, which can mainly be divided into the four components of asphaltene, polar aromatics, naphthene aromatics, and saturates41,42. Asphaltene molecules are relatively larger and heavier than other molecules in asphalt, with a mean atomic mass of roughly 750 g/mol and a molecular diameter in the range of 10-20 &#197;. It has been widely accepted that asphaltene is composed of large aromatic cores that contain heteroatoms and are surrounded by different lengths of alkyl groups43. A modified asphaltene molecule is constructed, as shown in Figure 1a. The molecules of polar aromatics and naphthene aromatics are constructed based on the polarity and the element ratio of asphalt molecules, with benzobisbenzothiophene (C18H10S2) representing the polar aromatic molecule and 1,7-dimethylnaphthalene (C12H12) chosen as the representative naphthene aromatic molecule, as shown in Figure 1b-c. N-docosane (n-C22H46) is constructed as shown in Figure 1d. The parameters listed in Table 1 for asphalt molecules are selected and used to meet the desired criteria, including the elemental mass fraction, the atom ratio, and the aromatic/aliphatic ratio, of real asphalt from experiments41. The same mass ratio has been defined in our previous studies, and the other thermomechanical properties like density, glass transition temperature, and viscosity are in good agreement with experimental data of real asphalt36. The molecular structure of graphene applied in this study is shown in Figure 1e. The adopted graphene sheet in this study has no defect and no fold compared to that of the real case, while the real graphene sheet usually has several defects such as&#160;atomic vacancies and Stone-Wales defects44, and some of the graphene sheets can be folded during the mixing process in the asphalt matrix45. These imperfect situations are not considered in this study, since we focus on the effect of the site of the graphene sheet on the self-healing properties and choose it as the only variable. The variables of graphene sheets in terms of the defects and folded cases will be the focus of our future studies. The mass ratio of graphene to asphalt in this study is 4.75%, which is the normal situation (&#60;5%) for graphene modified asphalt in the experiment46,47.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63303/63303fig01.jpg" /> 
Figure 1: Chemical structure. The atomistic models of (a) asphaltene molecule (C53H55NOS), (b) naphthene aromatic molecule (C12H12), (c) polar aromatic molecule (C18H10S2), (d) saturate molecule (C22H46), (e) graphene, and (f) pure asphalt. For the atomistic asphalt model, the carbon, oxygen, nitrogen, sulfur, and hydrogen atoms are shown in gray, red, blue, yellow, and white, respectively. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/63303/63303fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Asphalt model</td>
			<td>Mass (g/mol)</td>
			<td>Chemical formula</td>
			<td>Numbers of molecules</td>
			<td>Total mass (g/mol)</td>
			<td>Mass fraction (%)</td>
		</tr>
		<tr>
			<td>Asphaltene</td>
			<td>754.04</td>
			<td>C53H55NOS</td>
			<td>43</td>
			<td>32423.72</td>
			<td>26</td>
		</tr>
		<tr>
			<td>Naphthene aromatic</td>
			<td>156.22</td>
			<td>C12H12</td>
			<td>65</td>
			<td>10154.3</td>
			<td>8</td>
		</tr>
		<tr>
			<td>Polar aromatic</td>
			<td>290.38</td>
			<td>C18H10S2</td>
			<td>74</td>
			<td>21485.16</td>
			<td>17</td>
		</tr>
		<tr>
			<td>Saturate</td>
			<td>310.59</td>
			<td>C22H46</td>
			<td>205</td>
			<td>63670.95</td>
			<td>49</td>
		</tr>
		<tr>
			<td>Asphalt binder</td>
			<td></td>
			<td></td>
			<td>387</td>
			<td>127734.13</td>
			<td>100</td>
		</tr>
		<tr>
			<td>Graphene</td>
			<td>6369.28</td>
			<td>C525H63</td>
			<td>1</td>
			<td>6369.28</td>
			<td></td>
		</tr>
	</tbody>
</table>
Table 1: Overall components of pure asphalt model and graphene-modified asphalt model.
With respect to the protocol described below, two types of wedge-like cracks with different sizes are inserted into the middle of the asphalt model with a blunt crack tip and two parallel crack surfaces, while the middle-top area of the asphalt bulk remains intact. Two crack widths are chosen as 15 &#197; and 35 &#197;, as shown in Figure 2a-b. The reason for selecting 15 &#197; is that the crack width should be wider than the cutoff of 12 &#197; to avoid the early self-healing of asphalt molecules during the equilibrium process while investigating an extreme case for a small crack. The reason for selecting 35 &#197; is that the crack width should be wider than the length of the saturate molecules of 34 &#197; in order to prevent the bridging effect. The height of the crack is 35 &#197;, the same as the box width, and the depth of the crack is 70 &#197;, the same as the box length. In the real situation, the observed micro-crack sizes can be varied in the range from several micrometers to several millimeters, which is far larger than the length scale we are modeling here. Normally, the length scale in MD simulation is limited to the scale of 100 nm, which is still several orders of magnitude smaller than the real crack size. However, the cracks initiate at the nanoscale and grow into macroscale cracks with continuous deformation48. The understanding of the self-healing mechanism at the nanoscale can help to prevent the growth and further propagation of the crack at the macroscale. Even though the selected crack sizes are in the range of nanometer, the results can still be influential and applicable to explore the self-healing behaviors of asphalt molecules. There are two locations for the graphene sheets in the crack areas: one is on top of the crack tip and the other is perpendicular to the left crack surface. It has been found that these are the most common positions for graphene in graphene-modified nanocomposites with cracks49.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/63303/63303fig02.jpg" /> 
Figure 2: The self-healing schemes for pure asphalt and graphene-modified asphalt. The self-healing model of pure asphalt with a crack width of (a) 15&#160;&#197; and (b) 35 &#197;. The self-healing model of graphene-modified asphalt with the graphene sheet is located (c) at the top of the crack tip and (d) perpendicular to the crack surface. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/63303/63303fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In MD simulations, the intramolecular and intermolecular interactions in the asphalt nanocomposites are described by the Consistent Valence Forcefield (CVFF)50, which works well with asphalt and graphene-based materials. The functional form of CVFF is expressed as&#160;the following expression:
<img alt="Equation 1" src="/files/ftp_upload/63303/63303eq01v2.jpg" /> 1
Here, the total energy Etotal is composed of the bonded energy terms and the non-bonded energy terms. The bonded interactions consist of the covalent bond stretching, the bond angle bending energy, the torsion angle rotation, and the improper energies as expressed in the first four terms. The non-bonded energy includes an LJ-12-6 function for the van der Waals (vdW) term and a Coulombic function for the electrostatic interactions. CVFF has been widely employed in simulating asphalt materials51,52. The simulated physical and mechanical properties such as density, viscosity, and bulk modulus are in good agreement with the experimental data, which demonstrates the reliability of CVFF51. CVFF is not only suitable for inorganic materials, but it has also been successfully employed in structures consisting of organic and inorganic phases such as asphalt-silica52 and the system of epoxy-graphene53. In addition, the interfacial interactions between graphene and asphalt can be characterized by CVFF36,54. Since the major part in selecting forcefield is to determine the asphalt-graphene interface, the non-bonded interactions described by CVFF are more reliable, which is also considered in our previous study36. Overall, the forcefield CVFF is adopted in this study.&#160;The partial charges for different kinds of atoms are calculated by the forcefield-assigned method.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Atomistic models of asphalt and graphene/Materials Studio</td>
			<td>BIOVIA</td>
			<td>Materials Studio 8.0</td>
			<td>The atomistic models are built for molecular dynamics simulations.</td>
		</tr>
		<tr>
			<td>Large-scale Atomic/Molecular Massively Parallel Simulator Package</td>
			<td>Sandia National Laboratories</td>
			<td>lammps-stable20</td>
			<td>The equilibrium is achieved under NPT ensemble, and the atomistic models get self-healed.</td>
		</tr>
		<tr>
			<td>OVITO</td>
			<td>Materials Science Department of Technische Universit&#228;t Darmstadt, Germany</td>
			<td>ovito-basic-3.1.0-win64</td>
			<td>The self-healing behaviors of the atomistic models are visualized.</td>
		</tr>
		<tr>
			<td>Origin</td>
			<td>OriginLab</td>
			<td>Origin 2018 64Bit</td>
			<td>The contours of the atom numbers of the trajectory are drawn and analyzed.</td>
		</tr>
	</tbody>
</table>

advanced self-healing asphalt reinforced by graphene structures: an atomistic insight

Graphene can improve the self-healing properties of asphalt with high durability. However, the self-healing behaviors of graphene-modified asphalt nanocomposite and the role of incorporated graphene are still unclear at this stage. In this study, the self-healing properties of pure asphalt and graphene-modified asphalt are investigated through molecular dynamics simulations. Asphalt bulks with two crack widths and locations for graphene are introduced, and the molecular interactions among asphalt components and the graphene sheet are analyzed. The results show that the location of graphene significantly affects the self-healing behaviors of asphalt. Graphene near the crack surface can greatly accelerate the self-healing process by interacting with the aromatic molecules through &#960;-&#960; stacking, while graphene at the top area of the crack tip has a minor impact on the process. The self-healing process of asphalt goes through the reorientation of asphaltene, polar aromatic, and naphthene aromatic molecules, and the bridging of saturate molecules between crack surfaces. This in-depth understanding of the self-healing mechanism contributes to the knowledge of the enhancement for self-healing properties, which will help to develop durable asphalt pavements.

The contour of atom number 
The contours of the atom number of pure asphalt and graphene-modified asphalt models in the yz plane are shown in Figure 3, where the color bar from blue to red exhibits atom numbers varying from 0 to 28. Figure 3a-c illustrates the contour of the atom number of the structures with 15 &#197; crack width in pure asphalt and asphalt nanocomposites modified by graphene at the crack ...

Watch this Scientific Journal Video about Advanced Self-Healing Asphalt Reinforced by Graphene Structures: An Atomistic Insight at JoVE.com

Advanced Self-Healing Asphalt Reinforced by Graphene Structures: An Atomistic Insight

Graphene-modified asphalt nanocomposite has shown an advanced self-healing ability compared to pure asphalt. In this protocol, molecular dynamics simulations have been applied in order to understand the role of graphene in the self-healing process and to explore the self-healing mechanism of asphalt components from the atomistic level.

Graphene can improve the self-healing properties of asphalt with high durability. However, the self-healing behaviors of graphene-modified asphalt ...

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4.4K Views.  City University of Hong Kong. Graphene-modified asphalt nanocomposite has shown an advanced self-healing ability compared to pure asphalt. In this protocol, molecular dynamics simulations have been applied in order to understand the role of graphene in the self-healing process and to explore the self-healing mechanism of asphalt components from the atomistic level.

Video: Advanced Self-Healing Asphalt Reinforced by Graphene Structures: An Atomistic Insight

Development of a 3D Graphene Electrode Dielectrophoretic Device

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The protocol details the procedures to construct a versatile, reusable, multiple layer, laminated dielectrophoresis chamber. Specifically, six layers of 50 &#181;m x&#160;0.7 cm x&#160;2 cm graphene paper and five layers of double sided tape were alternately stacked together, then clamped to a glass slide. Then a 700 &#956;m diameter micro-well was drilled through the laminated structure using a computer-controlled micro drilling machine. Insulating properties of the tape layer between adjacent graphene layers were assured by resistance tests. Silver conductive epoxy connected alternate layers of graphene paper and formed stable connections between the graphene paper and external copper wire electrodes. The finished device was then clamped and sealed to a glass slide. The electric field gradient was modeled within the multi-layer device. Dielectrophoretic behaviors of 6 &#956;m polystyrene beads were demonstrated in the 1 mm deep micro-well, with medium conductivities ranging from 0.0001 S/m to 1.3 S/m, and applied signal frequencies from 100 Hz to 10 MHz. Negative dielectrophoretic responses were observed in three dimensions over most of the conductivity-frequency space and cross-over frequency values are consistent with previously reported literature values. The device did not prevent AC electroosmosis and electrothermal flows, which occurred in the low and high frequency regions, respectively. The graphene paper utilized in this device is versatile and could subsequently function as a biosensor after dielectrophoretic characterizations are complete.

A microdevice with high throughput potential is used to demonstrate three-dimensional (3D) dielectrophoresis (DEP) with novel materials. Graphene nanoplatelet paper and double sided tape were alternately stacked; a 700 &#956;m micro-well was drilled transverse to the layers. DEP behavior of polystyrene beads was demonstrated in the micro-well.

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

One-step fabrication method for obtaining freestanding epitaxial double heterostructure is presented. This approach could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure, leading to a piezoelectric nanogenerator with an increased output electrical performance.

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we ...

Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are proposed to create the electrical network in this work: (a) the incorporation of the nanoplatelets into the epoxy matrix and (b) the coating of the glass fabric with a sizing filled with the same nanoplatelets. Both types of multiscale composite materials, with an in-plane electrical conductivity of ~10-3 S/m, showed an exponential growth of the electrical resistance as the strain increases due to distancing between adjacent functionalized graphene nanoplatelets and contact loss between overlying ones. The sensitivity of the materials analyzed during this research, using the described procedures, has been shown to be higher than commercially available strain gauges. The proposed procedures for self-sensing of the structural composite material would facilitate the structural health monitoring of components in difficult to access emplacements such as offshore wind power farms. Although the sensitivity of the multiscale composite materials was considerably higher than the sensitivity of metallic foils used as strain gauges, the value reached with NH2 functionalized graphene nanoplatelets coated fabrics was nearly an order of magnitude superior. This result elucidated their potential to be used as smart fabrics to monitor human movements such as bending of fingers or knees. By using the proposed method, the smart fabric could immediately detect the bending and recover instantly. This fact permits precise monitoring of the time of bending as well as the degree of bending.

The integration of conductive nanoparticles, such as graphene nanoplatelets, into glass fiber composite materials creates an intrinsic electrical network susceptible to strain. Here, different methods to obtain strain sensors based on the addition of graphene nanoplatelets into the epoxy matrix or as a coating on glass fabrics are proposed.

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are ...

Scanning SQUID Study of Vortex Manipulation by Local Contact

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the lattice, and with other magnetic objects. Here, we present a protocol for vortex manipulation in thin superconducting films by local contact, without applying current or magnetic field. Vortices are imaged using a scanning superconducting quantum interference device (SQUID), and vertical stress is applied to the sample by pushing the tip of a silicon chip into the sample, using a piezoelectric element. Vortices are moved by tapping the sample or sweeping it with the silicon tip. Our method allows for effective manipulation of individual vortices, without damaging the film or affecting its topography. We demonstrate how vortices were relocated to distances of up to 0.8 mm. The vortices remained stable at their new location up to five days. With this method, we can control vortices and move them to form complex configurations. This technique for vortex manipulation could also be implemented in applications such as vortex based logic devices.

We present a protocol for manipulation of individual vortices in thin superconducting films, using local mechanical contact. The method does not include applying current, magnetic field or additional fabrication steps.

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual ...

Experimental Protocol to Determine the Chloride Threshold Value for Corrosion in Samples Taken from Reinforced Concrete Structures

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these structures. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation. While it is well known that the ability of a structure to withstand corrosion depends strongly on factors such as the materials used or the age, it is common practice to rely on threshold values stipulated in standards or textbooks. These threshold values for corrosion initiation (Ccrit) are independent of the actual properties of a certain structure, which clearly limits the accuracy of condition assessments and service life predictions. The practice of using tabulated values can be traced to the lack of reliable methods to determine Ccrit on-site and in the laboratory.
Here, an experimental protocol to determine Ccrit for individual engineering structures or structural members is presented. A number of reinforced concrete samples are taken from structures and laboratory corrosion testing is performed. The main advantage of this method is that it ensures real conditions concerning parameters that are well known to greatly influence Ccrit, such as the steel-concrete interface, which cannot be representatively mimicked in laboratory-produced samples. At the same time, the accelerated corrosion test in the laboratory permits the reliable determination of Ccrit prior to corrosion initiation on the tested structure; this is a major advantage over all common condition assessment methods that only permit estimating the conditions for corrosion after initiation, i.e., when the structure is already damaged.
The protocol yields the statistical distribution of Ccrit for the tested structure. This serves as a basis for probabilistic prediction models for the remaining time to corrosion, which is needed for maintenance planning. This method can potentially be used in material testing of civil infrastructures, similar to established methods used for mechanical testing.

We propose a method to measure a parameter that is highly relevant for corrosion assessments or predictions of reinforced concrete structures, with the main advantage of permitting testing of samples from engineering structures. This ensures real conditions at the steel-concrete interface, which are crucial to avoid artifacts of laboratory-made samples.

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these ...

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism. 
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.

This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they ...

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for applications in two-dimensional nanoelectronics devices. Although many methods to synthesize SnSe nanocrystals have been developed, a simple way to fabricate large-sized single-layer SnSe flakes remains a great challenge. Herein, we show the experimental method to directly grow large-sized single-layer rectangular SnSe flakes on commonly used SiO2/Si insulating substrates using a straightforward two-step fabrication method in an atmospheric pressure quartz tube furnace system. The single-layer rectangular SnSe flakes with an average thickness of ~6.8 &#197; and lateral dimensions of about 30 &#181;m &#215; 50 &#181;m were fabricated by a combination of vapor transport deposition technique and nitrogen etching route. We characterized the morphology, microstructure, and electrical properties of the rectangular SnSe flakes and obtained excellent crystallinity and good electronic properties. This article about the two-step fabrication method can help researchers grow other similar two-dimensional, large-sized, single-layer materials using an atmospheric pressure system.

A protocol is presented demonstrating a two-step fabrication technique to grow large-sized single-layer rectangular shaped SnSe flakes on low-cost SiO2/Si dielectrics wafers in an atmospheric pressure quartz tube furnace system.

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for ...

An Efficient Method for Selective Desalination of Radioactive Iodine Anions by Using Gold Nanoparticles-Embedded Membrane Filter

Here, we demonstrate a detail protocol for the preparation of nanomaterials-embedded composite membranes and its application to the efficient and ion-selective removal of radioactive iodines. By using citrate-stabilized gold nanoparticles (mean diameter: 13 nm) and cellulose acetate membranes, gold nanoparticle-embedded cellulose acetate membranes (Au-CAM) have easily been fabricated. The nano-adsorbents on Au-CAM were highly stable in the presence of high concentration of inorganic salts and organic molecules. The iodide ions in aqueous solutions could rapidly be captured by this engineered membrane. Through a filtration process using an Au-CAM containing filter unit, excellent removal efficiency (&gt;99%) as well as ion-selective desalination result was achieved in a short time. Moreover, Au-CAM provided good reusability without significant decrease of its performances. These results suggested that the present technology using the engineered hybrid membrane will be a promising process for the large-scale decontamination of radioactive iodine from liquid wastes.

An efficient method for the rapid and ion-selective desalination of radioactive iodine in several aqueous solutions is described by using gold nanoparticles-immobilized cellulose acetate membrane filters.