Functional graphene materials for use as adhesives and sealants

Abstract

The present invention provides certain chemical compounds or materials with adhesive properties or functionality that act as adhesives or sealants in a variety of applications. Specifically, the present invention, including its various embodiments, relates to certain functional graphene materials having adhesive moieties attached thereto that impart adhesive properties or functionality to the resulting compound, allowing it to be used in a variety of applications, for example, as an adhesive or sealant in the in-situ repair of leaks or defects in fluid-carrying pipes such as condenser pipes in power plants.

Description

Technical Field

[0001] Background of the Invention Field of the Invention The present invention relates to certain chemical substances having adhesive properties or functionality that act as adhesives or sealants in various applications, including its various embodiments. Specifically, the present invention relates to certain functional graphene materials having bonded adhesive portions, including its various embodiments, which have adhesive properties or functionality and can be used as adhesives or sealants in on-site repairs of leaks or defects in pipes carrying fluids, such as condenser tubes in power plants.

Background Art

[0002] Description of Related Art In power plants such as Rankine cycle power plants, undesirable leaks in condenser tubes frequently occur, resulting in a decrease in power output, an increase in the burden on downstream systems, and significant revenue losses. More permanent repair measures require complete replacement of the damaged tubes and significant time and cost, so generally observed leaks can only be addressed by temporary repair measures. Currently, physically plugging with particles such as wood powder is the industry standard for non-self-repairing (self-healing) condenser tubes. However, wood powder has limitations due to its strong aggregation properties and lack of adhesive portions. Furthermore, due to the crystallinity and uniformity of the types of functional groups present, wood powder has limited potential for chemical modification to impart and regulate aggregation and adhesion. Therefore, wood powder is unsuitable as a solution for leaks in condenser tubes because it has undesirable high aggregation properties and lacks adhesive properties to form a durable seal.

[0003] Therefore, an improved sealant for leaks in condenser tubes is needed. Specifically, there is a need for an improved in-situ sealant that can be used to provide long-term defect repair or long-term sealing of condenser tubes to avoid or minimize other more costly repairs.

Summary of the Invention

Means for Solving the Problems

[0004] Brief Summary of the Invention Generally, the present invention relates to specific chemical compounds or materials having adhesive properties or functionality that act as adhesives or sealants in various applications. Specifically, the present invention, including its various embodiments, is a specific functional graphene material having a bonded adhesive portion, which imparts adhesive properties or functionality to the resulting compound and can be used as an adhesive or sealant in on-site repairs of leaks or defects in pipes carrying fluids, such as condenser tubes in power plants.

[0005] The chemical composition of the FGM of the present invention is a graphene scaffold functionalized with a covalently bonded low-molecule such as a catechol derivative adhesive that acts as an adhesive or imparts an adhesive function to the scaffold, and is a graphene scaffold that results in one class of functional graphene materials or FGM. The FGM can be derived from various graphene scaffolds. For example, graphene oxide (GO), which is a micron-sized sheet with atomic-level thinness of bonded and integrated oxidized carbon atoms, can be used as the graphene scaffold. Derivatives of GO known as Claisen graphene (CG) can also be used as the graphene scaffold.

[0006] In one embodiment, the FGM includes a graphene scaffold and a molecule covalently bonded to the graphene scaffold having a portion including 1,2-dihydroxybenzene that can adhere to a metal surface. In one embodiment, the graphene scaffold includes graphene oxide or Claisen graphene. In one embodiment, the molecule covalently bonded to the graphene scaffold includes a nucleophile that covalently bonds the molecule to the graphene scaffold and a primary amine. In some embodiments, the molecule is a catechol derivative, such as 3,4-dihydroxybenzylamine.

[0007] FGM can be used as an adhesive or a sealant in various applications. For example, FGM can be used to provide on-site repair of leaks in tubes or pipes. In one embodiment, the present invention is a method for reducing leaks in a pipe, which comprises adding a sealant to a fluid passing through the pipe, wherein the sealant comprises a graphene scaffold having covalently bonded molecules having a moiety containing 1,2-dihydroxybenzene, the pipe comprises a leak through which the fluid passes, adding, adhering the sealant to the pipe adjacent to the leak, and forming a seal containing the sealant, thereby covering the leak.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0028] Detailed Description of the Invention Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. The present invention is described in relation to specific embodiments, but such embodiments should be regarded as examples and should not be seen as limiting or describing the only embodiments of the present invention. Rather, the present invention includes various embodiments or forms and various related aspects or features and uses, as well as alternatives, modifications, and equivalents thereof, whether or not explicitly described herein, all of which are within the spirit and scope and claims of the present invention. Further, the use of the terms "invention", "the present invention", "embodiment" and similar terms throughout this specification is used in a broad sense, and does not mean that the present invention requires or is limited to any particular embodiment or aspect described, or that such description is the only way in which the present invention can be made or used.

[0029] Generally, the present invention relates to certain chemical compounds or materials having adhesive properties or functionality that act as adhesives or sealants in various applications. Specifically, the present invention, including its various embodiments, is a specific functional graphene material having a bonded adhesive moiety that imparts adhesive properties or functionality to the resulting compound and can be used as an adhesive or sealant in the in-situ repair of leaks or defects in pipes carrying fluids, such as condenser tubes in power plants. These materials are referred to as functional graphene materials (“FGMs”) or functional graphene material sealants and have the ability to effectively repair or seal adhesive or sealant functions and defects in surfaces such as metal surfaces. In particular, the FGMs of the present invention provide the ability to repair or seal defects or leaks in the metal surfaces of pipes, such as condenser tubes in power plants, thereby effectively minimizing or reducing or eliminating leaks in the pipes. Further, the FGMs of the present invention provide the ability to repair or seal such defects or leaks in-situ. Thus, the FGMs can be added to fluids being transported through pipes or tubes having defects or leaks, such as leaking condenser tubes, during the use or operation of the pipes. The FGMs adhere to the inner surface of the pipe at the location of the defect or leak, thereby repairing the defect or leak in-situ without the need to stop the use of the pipe. Further, the seal provided by the FGMs is a relatively long-term seal that minimizes the maintenance required to repair the leak in the absence of such a seal.

[0030] The chemical composition of the FGM of the present invention is a graphene scaffold functionalized with a covalently bonded small molecule, such as a catechol derivative adhesive, that acts as an adhesive or imparts an adhesive function to a scaffold, and is a graphene scaffold that results in a class of functional graphene materials or FGMs. The FGM can be derived from various graphene scaffolds. For example, graphene oxide (GO), which is a micron-sized sheet having atomic-level thinness of bonded and integrated oxidized carbon atoms, can be used as a graphene scaffold. Derivatives of GO known as Kleisen graphene (CG) can also be used as graphene scaffolds. It should be understood that the ability to chemically modify GO and CG to impart adhesive properties makes these materials particularly useful. In particular, the carboxylic acid content of GO and CG is utilized to enhance in-situ sealant performance. The carboxylic acids on GO and CG are used as chemical handles for covalently installing small molecules that act as adhesives (e.g., adhesive catechols), thereby producing FGMs for use as sealants or adhesives in various applications. It should be understood that it is the small molecule, i.e., the molecule bonded to the scaffold, that imparts the adhesive function throughout the FGM. The adhesive function enables bonding to a given surface to be repaired, such as a metal pipe having surface defects or leaks.

[0031] The following description, in conjunction with the drawings, provides further details regarding FGMs, including the synthesis, resulting properties, and use of FGMs. Some examples of research and analysis conducted regarding the synthesis and properties of FGMs are also described throughout.

[0032] Figure 1 shows a consideration of the material design for maximizing the sealant ability of a functional graphene material (FGM) sealant according to an embodiment of the present invention. As shown, there are two components used to form the FGM, namely a graphene scaffold and a small molecule adhesive. Generally, the graphene scaffold is synthesized and then the small molecule adhesive is covalently bonded to produce an FGM having appropriate or desired adhesion and aggregation, providing a sealant such as a sealant that can be applied in situ to a surface.

[0033] The degree of oxidation (amount of oxygen functional groups), the position of the oxygen groups (including carboxylic acids) used to tether the adhesion molecules, and the steric hindrance of the carboxylic acid tethers on a given graphene scaffold are all factors that affect the performance of the sealant and should be considered in designing the FGM. Regarding the graphene scaffold, as shown in the illustration, the amount of oxidation of the graphene scaffold (shown as number 1), the position of the oxygen groups containing carboxylic acid groups (shown as number 2), and the steric hindrance of the carboxylic acid tethers (shown as number 3) are all properties that can be used to select an appropriate graphene material. It should be understood that adhesion and aggregation are competing properties for the purpose of fabricating in-situ sealants. The sealant should be able to, for example, adhere (adhere) to the metal surface in a damaged condenser tube and form a robust mass that fuses together to seal defects or leaks (aggregate). However, the aggregation property cannot be too strong, or the material may aggregate in the undamaged areas of the surface to be treated, causing unwanted blockages. Therefore, the above factors can be used in considering the selection of materials for use as scaffolds, including graphene materials.

[0034] In some embodiments, the graphene scaffold can be graphene oxide (GO), which is a micron-sized sheet of atomically thin, oxidized carbon atoms that are bonded and integrated, or a derivative of GO known as Krisen graphene (CG). As shown in the corresponding columns, GO and CG have different levels of oxidation, different positions of the corresponding oxygen groups on the graphene scaffold, and different steric aspects. However, both can be used in the FGM.

[0035] Regarding GO, it is important to understand that the degree of oxidation of GO can be controlled during synthesis to address the adjustability of adhesion and aggregation. By generating a series of GO with increasing degrees of oxidation, both the carboxylic acid content and basal plane oxidation also increase. The higher the carboxylic acid content, the more chemical handles are created for installing adhesives, increasing the adhesion properties. More basal plane oxidation increases the water dispersibility and decreases the aggregation properties. The degree of oxidation can be used to adjust both the adhesion and aggregation properties of the FGM material.

[0036] Regarding CG, the graphene skeleton of CG is less prone to oxidation and has a different distribution of functional groups that cannot be approached solely by oxidizing graphite to GO. Due to the large surface area of the basal plane, CG has a higher carboxylic acid content than GO, and a large number of tertiary alcohols can be converted to carboxylic acids.

[0037] The contrast in the positions of carboxylic acids on GO and CG can affect the adhesion properties. On GO, the carboxylic acids are localized at the sheet edges, while tertiary alcohols and epoxides are predominant on the basal plane. On the other hand, the carboxylic acids on CG are present throughout the basal plane without being confined over a larger surface area, and if these carboxylic acids are used to tether adhesion molecules by covalent bonds, the adhesion can be amplified.

[0038] The steric hindrance of carboxylic acids on GO and CG can affect the functionalization efficiency and thus the adhesion properties. GO has carboxylic acids directly bonded to the skeleton at the sheet edges, and the skeleton can sterically hinder the electrophilic carbon that is the target of functionalization. However, the carboxylic acids on CG are separated from the skeleton by a two-carbon spacer. The spacer on CG reduces the steric hindrance of the electrophilic carbon and can promote better functionalization efficiency to enhance the adhesion properties.

[0039] Furthermore, as noted above, the ability to chemically modify GO and CG to impart adhesion properties makes these materials particularly useful. In particular, the carboxylic acid content of GO and CG is utilized to enhance in-situ sealant performance. Thus, the binding of low molecular weight adhesives to the graphene scaffolds imparts this functionality. Accordingly, the selection of appropriate GO or CG and corresponding low molecular weight adhesives can be used to control adhesion and aggregation to enhance the sealant performance of the FGM or to control the adhesion and aggregation of the FGM. For example, the adhesion properties of the graphene scaffolds can be controlled by the spatial location and amount of the low molecular weight adhesives bound to the graphene sheets, while the aggregation properties were affected by the degree of oxidation on the basal plane.

[0040] Low molecular weight adhesives can be selected based on molecules that form strong adhesions to various substrates in a wet environment, and can be derived from molecules produced by various organisms or contain specific low molecules based on molecules produced by various organisms. For example, mussels form polymers containing catechol moieties that form such adhesions. Therefore, it has been recognized that catechol derivatives can be used as low molecular weight adhesives. For example, as shown in the illustration, the adhesive is a catechol derivative adhesive. Catechol molecules contain a diol that is extremely important for adhesion on the benzyl backbone. This diol functionality can be preserved by selecting a catechol derivative having additional pendant groups that can be used for covalent bonding, such as 3,4-dihydroxybenzylamine (DHBA), which contains a nucleophilic primary amine pendant that can react with the electrophilic carbon on the graphene substrate and the central catechol moiety. The nucleophilic primary amine on DHBA involved in amidation to form the FGM sealant and the electrophilic carboxylic acid on the graphene scaffold are indicated by a circle and an asterisk (*), respectively. In some embodiments, it should be understood that the adhesive molecule is characterized by 1,2-dihydroxybenzene that can coordinate to a metal and adhere, and a nucleophile (e.g., a primary amine) that can covalently bond to the graphene scaffold. To make the FGM sealant, any low molecule that meets these two criteria (containing a 1,2-dihydroxybenzene moiety and a nucleophile) can be used. In some embodiments, any catecholamine can function. For example, tyrosine, DOPA, dopamine, norepinephrine, epinephrine. In some embodiments, 5-hydroxydopamine and 6-hydroxydopamine can be used as FGM sealant molecules.

[0041] Based on the above, it was found that GO and CG are ideal scaffolds that can be used in combination with bonded molecules that impart adhesive properties for forming FGM. GO and CG provide an ideal scaffold for in-situ sealants due to their moderate aggregation properties, water dispersibility, high specific surface area, and oxygen groups that can be utilized as chemical handles for imparting adhesion. By modifying the chemical handles on GO or CG with wetting adhesive molecules, the resulting FGM is water-dispersible and actively fuses and adheres to defects in the substrate. The FGM imparts increased aggregation properties that are up to three times higher than those of non-functionalized materials, providing a more stable seal. When applied to leaks in metal condenser tubes, the FGM material essentially creates a plug for sealing the leak in-situ. In contrast, non-functionalized scaffolds completely lack sealing ability. Furthermore, as described further below, the FGM sealant also imparts improved antibacterial ability (up to a 55% reduction in E. coli) for reducing or preventing biofouling.

[0042] Turning to the synthesis of FGM, first GO or CG is prepared, and then the adhesive is covalently bonded to the graphene scaffold. The following is a detailed description of the synthesis steps used to produce FGM prepared from GO and FGM prepared from CG.

[0043] Figure 2 shows the synthesis of GO according to an embodiment of the present invention. As shown, GO can be prepared using a modified Hummers' method by oxidizing graphite with potassium permanganate (KMnO4). Hummers, W.S.; Offeman, R.E., Preparation of Graphitic Oxide, J. Am. Chem. Soc. 1958, 80(6), 1339-1339, https: / / doi.org / 10.1021 / ja01539a017 and Holt, B.D.; Arnold, A.M.; Sydlik, S.A., In It for the Long Haul: The Cytocompatibility of Aged Graphene Oxide and Its Degradation Products, Adv. Healthcare Mater, 2016, 5(23), 3056-3066 https: / / doi.org / 10.1002 / adhm.201600745 are hereby incorporated by reference.

[0044] As an example, four different GOs with various KMnO4 to graphite ratios (1:1, 2:1, 3:1, and 4:1) were synthesized. Specifically, four different batches of GO were prepared by varying the weight ratio of potassium permanganate (KMnO4) to graphite at w / w ratios of 1:1, 2:1, 3:1, and 4:1. Each reaction was carried out by dispersing 5 g of graphite flakes (graphite flakes, natural, -325 mesh, 99.8% metal based; Alfa Aesar, Ward Hill, MA, USA) in 125 mL of concentrated sulfuric acid (Fisher Scientific, Pittsburg, PA, USA) in a 1 L Erlenmeyer flask. The mixture was stirred and cooled with ice. Then, KMnO4 (Sigma-Aldrich, St. Louis, MO, USA) was added slowly over 20 - 30 minutes. The mass of KMnO4 added to each reaction was either 5 g, 10 g, 15 g, or 20 g to produce GO 1:1, GO 2:1, GO 3:1, and GO 4:1, respectively. The ice bath was removed, the reactants were warmed to room temperature and stirred for 2 hours. Then, the reactants were gently heated to 35 °C and stirred for an additional 2 hours. The heat was removed and the GO reaction was quenched by slowly adding 700 mL of deionized (DI) water, 10 mL of 30% H2O2 (Fisher Scientific), and then 225 mL of DI water. Finally, the reactants were stirred overnight.

[0045] To purify the GO reactant, the GO reactant was vacuum filtered through a Buchner funnel. The pack was carefully removed from the funnel without rubbing the filter paper and filled into a 3500 molecular weight cut-off dialysis tube (SNAKESKIN dialysis tube, Thermo Scientific, Waltham, MA, USA). The reactant was dialyzed against DI water for 3 - 7 days. The DI water was changed twice on the first day and then once a day until it became clear. Then, the GO batch was frozen at -80 °C and freeze-dried for 3 - 5 days until dry.

[0046] Figure 3 shows the synthesis of CG according to an embodiment of the present invention. As shown, the CG is converted from GO by a Johnson-Claisen rearrangement that hydrolytically installs a stable C-C moiety on the basal plane using a tertiary alcohol while simultaneously reducing the graphene backbone. The basal plane tertiary alcohol on graphene oxide (GO) is converted to an ester separated from the scaffold by a 2-carbon linker through a [3,3] sigmatropic rearrangement. By saponification, these ester groups can be converted to carboxylic acids. See Sydlik, S.A.; Swager, T.M., Functional Graphenic Materials Via a Johnson-Claisen Rearrangement, Advanced Functional Materials 2013, 23(15), 1873-1882, https: / / doi.org / 10.1002 / adfm.201201954 and Holt, B.D.; Arnold, A.M.; Sydlik, S.A., Peptide-Functionalized Reduced Graphene Oxide as a Bioactive Mechanically Robust Tissue Regeneration Scaffold, Polym Int 2017, 66(8), 1190-1198, https: / / doi.org / 10.1002 / pi.5375, which are incorporated herein by reference.

[0047] As an example, CG was synthesized according to the Johnson–Claisen rearrangement and saponification. 1.23 g of GO (2:1 ratio) and 250 mL of triethyl orthoacetate (Alfa Aesar, Haverhill, MA, USA) were added to a round-bottom flask under flame-dried nitrogen. The reaction mixture was sonicated for 10 min (240 W, 42 kHz ultrasonic cleaner, Kendal). Then, 21 mg of p-toluenesulfonic acid was added and the reaction mixture was refluxed under nitrogen for 36 h (142 °C). Heat was removed and 50 mL of 1.0 M NaOH (in ethanol) was added during the cooling process at 85 °C with rapid stirring. Once the reaction reached room temperature, it was stirred for an additional 3 h. CG was centrifuged at 3600×g for 5 min and the supernatant was discarded. The pellet was redispersed in DI water, centrifuged at 3600×g for 5 min, and the supernatant was discarded. The pellet was washed with DI water three more times and with acetone twice. Then, CG was dried under vacuum for 24–48 h until dry.

[0048] Figure 4 shows the synthesis of FGM from GO and CG according to an embodiment of the present invention. As described above, carboxylic acids on GO and CG were used as chemical handles to install catechol-derived adhesives. In one embodiment, the catechol molecule has a nucleophilic amine that is used to covalently bond to GO or CG using thionyl chloride amidation. In other words, thionyl chloride amidation is used to covalently conjugate an amine-containing low molecular weight adhesive, such as a catechol derivative adhesive, to the GO or CG backbone to form FGM. In this embodiment, the catechol molecule contains a diol on the benzyl backbone that is extremely important for adhesion, and thus the diol functional group is preserved by selecting a catechol derivative having additional pendant groups that can be used for covalent bonding. Thus, 3,4-dihydroxybenzylamine (DHBA) contains a pendant primary amine that is a strong nucleophile capable of reacting with the core catechol moiety and the electrophilic carbon on the graphene substrate, and can therefore be used as a catechol adhesive. As shown, the amine nucleophile and diol functional group on the low molecular weight adhesive (DHBA) are highlighted by a circle and a square, respectively, and the graphene sheet is represented as a simplified pyrene structure for clarity.

[0049] As an example, five different formulations of the FGM sealant were produced using GO 1:1, GO 2:1, GO 3:1, GO 4:1 and CG as starting graphene materials to produce catechol GO (CGO) and catechol CG (CCG). CGO and CCG were prepared via an acyl chloride intermediate. See Functional Graphenic Materials Via a Johnson-Claisen Rearrangement cited above. 100 mg of graphene material, 50 mL of anhydrous dioxane and 5 drops of dimethylformamide were charged into a round bottom flask under flame-dried nitrogen. The mixture was sonicated for 10 minutes and then 0.7 mL of thionyl chloride (Sigma-Aldrich, St. Louis, MO, USA) was slowly added dropwise. The reaction was stirred overnight at room temperature. Then 250 mg of 3,4-dihydroxybenzylamine (DHBA) (Sigma-Aldrich, St. Louis, MO, USA) was added. The reaction was heated to 100 °C and stirred overnight under nitrogen. The reaction was cooled to room temperature and centrifuged at 3600×g for 5 minutes and the supernatant was discarded. The pellet was redispersed in dichloromethane, centrifuged at 3600×g for 5 minutes and the supernatant was discarded. This was repeated once more with dichloromethane, twice with DI water and twice with acetone. Then CGO and CCG were dried under vacuum for 24 - 48 hours until dry.

[0050] Figure 5 shows the results of thermogravimetric analysis of GO, CG, and FGM generated according to an embodiment of the present invention. Thermogravimetric analysis (TGA) was performed on a PerkinElmer TGA 4000 under nitrogen (flow rate of 20 mL / min) at a heating rate of 10 °C / min from 50 to 800 °C. The derivative of the thermogram was smoothed by a simple moving average (step size 50). The data was then analyzed with TRIOS software (TA Instruments) to determine the onset temperature (To), endset temperature (Te), peak temperature of the first derivative (Tp), percent weight loss (%D), and char weight percent. To and Te were determined from the thermogram using the onset and endset functions of Trios, respectively, using the average of three measurements. Tp was determined from the signal minimum of the first derivative of the thermogram. %D was calculated as the area under the first derivative curve from the start to the end of the decomposition event. Finally, the char weight percent was determined from the remaining weight percent of the material via the thermogram at 800 °C.

[0051] Thermograms (A) of GO, CG, and FGM sealants in two graphs, and thermogravimetric analysis data obtained from the thermograms and the first derivative of the thermograms, including the onset temperature (To) in graph B, the peak temperature of the first derivative (Tp) in graph C, the functional group weight loss of the decomposition event (%D) in graph D, and the char weight percent at 800 °C in graph E, shown in Figure 5. It should be understood that the graphs A - E on the left side of Figure 5 are for GO and CG, and the graphs A - E on the right side of Figure 5 are for the corresponding FGM. It should be understood that the bars in graphs B - E represent the average of n = 3 separate TGA runs for each material, and the error bars are the standard deviation.

[0052] Figure 6 shows the results of X-ray photoelectron spectroscopy (XPS) analysis of GO, CG, and FGM generated according to an embodiment of the present invention. The XPS spectra were collected on a Thermo Fisher ESCALAB 250 Xi instrument equipped with an Al K-Alpha source gun. Powdered samples were prepared by adhering them onto double-sided copper tape for analysis. All spectra were collected using a 200 μm spot size. Survey scans (5 cumulative scans per spectrum) were performed on three separate spot positions of the sample. Elemental quantification was performed using CasaXPS software (CasaXPS) with a smart baseline. C1s, O1s, N1s, Br3d, S2p, and Cl2p emission peaks were used for the quantification of carbon, oxygen, nitrogen, bromine, sulfur, and chlorine, respectively.

[0053] The C / O ratios of GO and CG were calculated using the quantification of the C1s and O1s emission peaks. The C / O ratios of CGO and CCG were more complex due to the presence and incorporation of DHBA catechol (which contributes to both the carbon atom percentage and the oxygen atom percentage) and thionyl chloride impurities (which contribute to the oxygen atom percentage). Therefore, the atomic percentages of carbon and oxygen require correction factors to remove the contributions from catechol derivatives and thionyl chloride such that the carbon and oxygen atomic percentages solely reflect the graphene backbone, thereby enabling direct comparison of the C / O ratios of CGO and CCG with the non-functionalized starting materials.

[0054] Since there are seven carbon atoms for every nitrogen atom in DHBA, the nitrogen atom percent can be subtracted from the total carbon atom percent in the material, multiplied by a factor of seven (total carbon atom% - 7(nitrogen atom%)). The oxygen atom percent required three corrections: 1) DHBA molecules not bound to the GO scaffold introduce two oxygen atoms per molecule of DHBA. The atomic percent of unbound DHBA was approximated using the bromine atom percent. 2) DHBA bound to the GO scaffold adds one oxygen atom per molecule of DHBA. Bound DHBA was approximated by subtracting bromine (an indicator of unbound DHBA) from the total nitrogen atom percent. 3) Sulfur and chlorine impurities were assumed to be due to unreacted thionyl chloride. Thionyl chloride impurities introduce one oxygen atom per molecule of thionyl chloride, and the sulfur atom percent was used to determine the amount of thionyl chloride impurities. (total oxygen atom% - 2(bromine atom%) - (nitrogen atom% - bromine atom%) - (sulfur atom%)).

[0055] The resulting atomic compositions and C / O ratios, including XPS of the non-functionalized scaffold and FGM sealant, are shown in FIG. 6. The elemental compositions obtained from the survey scans of GO and CG are shown in graph A, and the elemental compositions obtained from the survey scan of the FGM sealant are shown in graph B. The carbon-to-oxygen (C / O) ratios obtained from elemental analysis of GO and CG are shown in graph C, and the carbon-to-oxygen (C / O) ratios obtained from elemental analysis of CGO and CCG are shown in graph D. Note that the values for CGO and CCG were obtained through the above carbon and oxygen corrections to isolate the carbon and oxygen content present on the scaffold backbone. It should be understood that the bars in the graph are the average of n = 3 and the error bars are the standard deviation.

[0056] The oxidation degrees of GO, CG, and FGM sealants were evaluated using TGA and XPS. As shown respectively by the increase in the weight loss of functional groups during decomposition (%D) and the increase in the carbon-to-oxygen (C / O) ratio, the results shown in Figures 5 and 6 indicate that the oxidation of GO increases as the ratio of KMnO4 to graphite increases. Due to the high-temperature synthesis conditions, CG is the material with the lowest degree of oxidation, having a C / O ratio of 4.5. XPS also confirmed that the oxidation degree of the FGM sealant decreases gently after thionyl chloride amidation.

[0057] More specifically, TGA reveals the effective catechol (3,4-dihydroxybenzylamine, DHBA) conjugation and the preservation of oxygen groups after the synthesis of the adhesive FGM. Referring to Figure 5, the primary derivative peak temperature (Tp) increases by 70 - 83 °C, suggesting the presence of stronger bonds such as amides (excluding CG which already contains strong C-C bonds). The percentage of weight loss of functional groups during decomposition (%D) increases to 13 wt% after synthesis. The increases in Tp and %D differentiate that DHBA was loaded onto the FGM sealant. Furthermore, there is no significant increase in the onset temperature (To) of the FGM sealant after conjugation, and the oxygen groups on the graphene scaffold begin to decompose at 159 - 214 °C. This suggests that oxygen still exists on the backbone of the FGM sealant, and thus, our synthesis approach does not fully reduce the scaffold.

[0058] Referring to FIG. 6, the XPS elemental composition reveals the presence of catechol and impurities resulting from the synthesis conditions. The incorporation of DHBA into the product is evident from the presence of nitrogen, which is unique to DHBA, after synthesis. The elemental scan also shows bromine, sulfur, and chlorine impurities. Bromine is a result of unreacted DHBA occluded in the material. However, nitrogen and bromine have a 1:1 molar ratio in DHBA, and when catechol is covalently tethered to the graphene backbone, bromine is substituted. Since the atomic percentage of nitrogen > the atomic percentage of bromine, this suggests that some of the nitrogen is covalently bonded to the FGM sealant. Additionally, sulfur and chlorine impurities may result from the occlusion of thionyl chloride or side reactions.

[0059] Figure 7 shows the chemical characterization of non-functionalized GO and CG scaffolds and FGM sealants using XPS according to one embodiment of the present invention. Figure 8 shows high-resolution XPS of non-functionalized and catechol (3,4-dihydroxybenzylamine, DHBA)-functionalized materials. Figure 9 shows the XPS of 3,4-dihydroxybenzylamine (DHBA) according to one embodiment of the present invention.

[0060] High-resolution scans (10 cumulative scans per spectrum) of the C1s spectrum were performed at three separate spot positions on the sample. The raw C1s spectrum was smoothed in OriginPro (OriginLab) using the Savitzky-Golay method with a second-order polynomial with a 15-point step width. Next, a charge correction for adventitious carbon (284.8 eV) was applied to the C1s spectrum, and the data was truncated to 292 - 280 eV. Next, Shirley baseline subtraction of the C1s spectrum was performed using Fityk software (version 0.9.8), and deconvolution was performed using Gaussian peak fitting. The peak position and full width at half maximum of all peaks were limited to ±0.2 eV and 1.4 eV, respectively, for all graphene materials.

[0061] High-resolution N1s scans (25 cumulative scans per spectrum) were also performed at three separate spot positions. The raw N1s spectra were smoothed in OriginPro using the Savitzky-Golay method (second-degree polynomial) with a 25-point step width. The data were then truncated to 405 - 395 eV and processed in Fityk. Shirley background was removed, and deconvolution of the N1s spectra was performed using Gaussian peak fitting. The peak position (400.1 eV) and full width at half maximum (1.64 eV) of the amine were determined using DHBA as a standard (see Figure 9 showing the XPS of 3,4-dihydroxybenzylamine (DHBA) including the XPS survey scan in Graph A and the XPS high-resolution N1s spectrum in Graph B. Note that the bars in Graph A are the average of n = 3, and the error bars are the standard deviation.). A new peak appears in the N1s spectrum of the FGM sealant, indicating an amide with a peak position of 398.8 eV and a full width at half maximum of 2.30 eV.

[0062] Representative carbon functional groups on the non-functionalized backbone identified using the high-resolution carbon (C1s) spectrum shown in Graph A and representative nitrogen bonds present in the FGM sealant identified using the high-resolution nitrogen (N1s) spectrum shown in Graph B are shown in Figure 7. The nitrogen content is a unique element introduced by the presence of DHBA and is not present on the non-functionalized scaffold. Therefore, deconvolution of the nitrogen spectrum provides insight into the types of DHBA nitrogen bonds in the FGM sealant. That is, the amounts of DHBA that contribute (amide-bonded DHBA) and do not contribute (free + ester-bonded DHBA) to the adhesion properties of the FGM sealant can be quantified. It should be understood that the bars represent the average of n = 3 XPS measurements at different spot positions for each material, and the error bars are the standard deviation.

[0063] High-resolution X-ray photoelectron spectroscopy (XPS) of non-functionalized and catechol (3,4-dihydroxybenzylamine, DHBA)-functionalized materials, including C1s spectra and N1s spectra, are shown in Graphs A - F of Figure 8, respectively. The high-resolution C1s spectra of GO and CG, where the functional groups present in the spectra are represented by a simplified pyrene structure, are shown in Graph A. The peak deconvolution of the C1s spectrum is shown in Graph B, and the quantification of the area under the curve from the deconvolved C1s spectrum is shown in Graph C. The high-resolution N1s spectrum of the catechol-functionalized scaffold, where the structures of free, ester-bonded, and amide-bonded catechol (DHBA) on the graphene backbone of the FGM sealant are represented in Graph D. The peak deconvolution of the N1s spectrum is shown in Graph E, and the quantification of the area under the curve of the deconvolved N1s spectrum is shown in Graph F.

[0064] Further results are shown in Tables 1 and 2 below:

Table 1

Table 2

[0065] The deconvolution of the high-resolution XPS carbon (C1s) spectrum indicates that the increased oxidation of GO increases carboxylic acids and basal plane oxygen groups. This method reveals that the carboxylic acid content on GO can be controlled by oxidation conditions until saturation is reached. The observation of carboxylic acid saturation rather than saturation of other functional groups is likely due to the fact that carboxylic acids are only located at the edges of GO and the oxidation of graphite to GO occurs from the edges to the center. Therefore, at a low KMnO4 to graphite ratio, KMnO4 is consumed before reaching the center of the sheet, so oxidation is completed at the edges and remains minimal in the inward direction. In the case of CG, since carboxylic acid functionalization occurs on the basal plane, CG is not subject to the same limitations as GO, so CG had the highest carboxylic acid content. In the case of GO, basal plane functionalization by tertiary alcohols and epoxides contributes to higher oxidation after carboxylic acid saturation is reached. Therefore, oxidation can be used to control the carboxylic acid content (which affects adhesion) and the basal plane oxygen content of GO (which affects aggregation).

[0066] Deconvolution of the high-resolution XPS nitrogen (N1s) spectrum confirmed that CCG had the most DHBA bound to the backbone in the desired orientation for adhesion, probably due to the reduced steric hindrance of carboxylic acids on CG. As described above, the amine peak of DHBA was identified at 400.1 eV.

[0067] In the CGO and CCG materials, there was the appearance of a new peak at 398.8 eV corresponding to amide bonds. Quantification of the nitrogen spectrum enabled the quantitative determination of DBHA amide-bonded to the FGM scaffold, where amide-bonded DHBA is a desirable covalent bond for promoting adhesion. CGO 1:1 had the least amount of amide-bonded DBHA. The remaining CGO had more amounts of amide-bonded DHBA, but all were similar. CCG had the largest amount of amide-bonded DHBA, indicating that CG provided the most efficient functionalization.

[0068] Figure 10 shows the Fourier transform infrared (FTIR) spectroscopy of GO, CG), and FGM sealants according to an embodiment of the present invention. The FTIR spectrum of the powdered graphene material was collected using a PerkinElmer Frontier FT-IR Spectrometer equipped with an attenuated total reflection (ATR) attachment containing a germanium crystal. 4 cm -1 The raw spectrum was recorded at a resolution of and from 4000 to 700 cm -1 All spectra were ATR, and the baseline was corrected using Spectrum software (PerkinElmer). The spectrum was then converted from percent transmittance to absorbance, and the hydroxyl stretch (3400 - 3200 cm -1 ) was normalized to an absorbance of 0.1. For clarity, the spectrum was converted back to percent transmittance and offset. The resulting spectra are shown in graphs A and B of Figure 10. Note that each vertical bar in graphs A and B represents a carboxylic acid and an amide stretch, respectively.

[0069] To evaluate the covalent bonding of DHBA to the GO and CG scaffolds, FTIR spectroscopy and TGA were used as qualitative tools (see also Figure 5). FTIR spectroscopy demonstrates the loading of covalent DHBA and the utilization of all carboxylic acids. The carboxylic acid peak at 1710 - 1680 cm -1 completely disappears, while in the FGM sealant, a new peak corresponding to the amide bond at 1680 - 1630 cm -1 appears, and the FGM sealant is specifically represented as CGO and CCG. Furthermore, the complete disappearance of the carboxylic acid band suggests that all reaction sites were utilized for tethering. TGA was combined with FTIR spectroscopy. The increase in the peak temperature of the first derivative (Tp) and the weight loss of the functional groups during decomposition (%D) suggest effective DHBA conjugation in the FGM sealant.

[0070] Figure 11 shows the antibacterial ability of an unfunctionalized scaffold and an FGM sealant using E. coli in a buffered medium. Specifically, the standard fluorescence emission prepared using the LIVE / DEAD® BACLIGHT™ assay is shown in Graph A. The calibration curve created from the ratio of the green (530 nm) and red (630 nm) fluorescence peak intensities is shown in Graph B. The fluorescence microscope images of the calibration curve are shown in the images in C. The percentage of live bacteria determined in the experimental samples is shown in Graph D, where the negative control was not treated with any material and the positive control was treated with penicillin / streptomycin.

[0071] To prevent contamination, all reagents and samples were handled using aseptic techniques. A buffered medium was prepared by dissolving 12.5 g of LB Miller Broth (Fisher BIOREAGENTS™, USA) and 0.75 g of Tris HCl (Promega, Madison, WI, USA) in 500 mL of deionized water, reaching a final broth component concentration of 10 g / L tryptone, 10 g / L NaCl, and 5 g / L yeast extract. The medium was autoclaved at 121 °C for 1 hour and cooled to room temperature before use. Escherichia coli (E. coli) K12 strain was purchased from ATCC (ATCC® 25404™). Cultures were maintained in 5 mL of medium in 15 mL centrifuge tubes with loose caps on a rotary shaker (MINIMIXER™, Benchmark Scientific, Sayreville, NJ, USA) at 37 °C (MyTemp Mini Digital Incubator, Benchmark Scientific) and incubated for 16 hours. Bacteria were then pelleted by centrifugation at 10,000×g for 15 minutes, the supernatant was aspirated, and the pellet was resuspended in 5 mL of fresh medium. The cultures were then used for the experiment at a 1:4 split ratio with fresh medium (1 mL of cell suspension stock in 4 mL of fresh medium). The graphene raw material was weighed into a 20 mL glass scintillation vial and irradiated with ultraviolet light at 254 nm for 5 minutes for sterilization. The powder was dispersed in medium (sterilized and buffered LB Miller Broth) to a final concentration of 5 mg / mL. The graphene stock dispersion was then sonicated briefly to break up aggregants.

[0072] Negative controls, positive controls, and graphene samples were prepared and added to the inner wells of a 96-well cell culture plate. All samples contained 4% v / v Escherichia coli from the cell stock solution. The negative control was untreated (containing only Escherichia coli and medium), and the positive control was given penicillin / streptomycin (ThermoFisher Scientific) diluted to 100 U / mL. The graphene samples were prepared by giving the Escherichia coli a graphene stock dispersion (5 mg / mL) to a final concentration of 1 mg / mL. Finally, each sample was diluted with medium to a final concentration of 250 μL per well. The 96-well cell culture plate (with cell culture plate lid) was then incubated at 37 °C for 16 h on a rotary shaker, and cell analysis was performed by the LIVE / DEAD® BACLIGHT™ assay according to the manufacturer's protocol. All samples were run in triplicate. Additional negative controls were run to generate a calibration curve using the LIVE / DEAD® BACLIGHT™ Bacterial Viability Kit (ThermoFisher Scientific, Waltham, MA, USA).

[0073] After performing the LIVE / DEAD® BacLight™ assay, fluorescence data of experimental samples (calibration curves, negative controls, positive controls, and graphene samples) in a 96-well cell culture plate were acquired on a SPARK® plate reader (Tecan) using SPARKCONTROL® v2.2 software. Fluorescence was measured at an excitation wavelength of 470 nm and a bandwidth of 10 nm. The fluorescence emission spectrum from 500 to 700 nm was collected with a bandwidth of 10 nm and a step size of 5 nm. Fluorescence microscopy samples were prepared by depositing 10 μL of the stained bacterial sample onto a #1.5 coverslip spanning across the objective lens of the microscope using a stage insert. Fluorescence microscopy images were rapidly acquired using an EVOS® FL Auto Cell Imaging System (ThermoFisher Scientific) equipped with a 100x, 1.40 numerical aperture oil immersion objective lens before any evaporation occurred.

[0074] Antibacterial ability can be an important aspect of in-situ sealants, such as those used to reduce further damage to condenser tube defect sites caused by microbial colonization and biofilm formation. As shown, all graphene materials containing conjugated catechol (FGM sealants) were antibacterial. CGO and CCG reduced the proportion of live E. coli cells by up to 55%. Unfunctionalized GO 3:1, GO 4:1, and CG were ineffective, while GO 1:1 and GO 2:1 had moderate effects. The catechol moiety and impurities in the sealant formulation can contribute to enhanced bactericidal properties. Chlorine, identified as an impurity in the XPS spectrum (see Figure 6), is also an excellent antibacterial agent.

[0075] Figure 12 shows the dynamic mechanical analysis of the hydrated graphene pack measured in the compressed and twisted states according to an embodiment of the present invention. Figure 13 also shows the dynamic mechanical analysis of the hydrated graphene pack measured in the compressed and twisted states according to an embodiment of the present invention. These results were obtained by various tests. The dynamic mechanical analysis (DMA) was performed using a Discovery Hybrid Rheometer HR-2 (TA Instruments, New Castel, DE). A force of 1 N was applied (and maintained) in advance throughout all mechanical tests. All tests were performed using a 25 mm aluminum plate polished as the bottom shape and an 8 mm steel upper shape (abraded by sandblasting). A 3 mL polypropylene syringe barrel was cut into a 2-inch long cylinder and fixed to the center of the bottom shape using an epoxy adhesive. The epoxy adhesive was applied to the outside and bottom shape of the polypropylene syringe. To prevent the material from coating the inside bottom shape of the polypropylene syringe tube and thereby creating a non-uniform test surface that could introduce artificial phenomena, the application of the epoxy adhesive was done carefully. The epoxy was dried for 15 minutes, and then the syringe was completely sealed to the bottom shape using high vacuum silicone grease (DOW CORNING (registered trademark)) (in this case, by applying silicone grease to the outside of the polypropylene syringe tube in the same manner as the epoxy adhesive). Then, after adding approximately 30 mg of graphene powder to the syringe, 1 mL of DI water was added. After 15 minutes, the graphene material settled on the bottom of the syringe device as a pack-like mass for mechanical testing, and the pack had a thickness of 0.6 - 1.2 mm.

[0076] Amplitude sweeps in torsional shear were performed at 1 Hz up to a strain of 0.01 - 50%. The linear viscoelastic region (LVR) and critical strain (γ c ) were determined from the amplitude sweeps according to ASTM D7175.6. That is, the LVR and γ c were calculated using a ±10% deviation of the storage modulus (G’) at a strain of 0.01%. The apparent yield stress (σ y ) was approximated from the following equation: σ y =γc ×G*, where G* is the complex elastic modulus at 0.01% strain. The raw amplitude sweep data was converted to the complex elastic modulus using TRIOS software. The cohesion energy (CE) was determined by the following equation: CE = 1 / 2 × γ c 2 × G, where G’ is measured at 0.01% strain. All amplitude sweeps were performed in triplicate for each material.

[0077] Turning to the results obtained from the above tests, Figure 12 shows, in Image A, an image of the empty test apparatus. A representative amplitude sweep is shown in Graph B. The critical strain (γ c ), cohesion energy and apparent yield stress (σ y ) obtained from the amplitude sweep are shown in Graphs C, D and E respectively, with n = 3 and error bars being the standard deviation. Figure 13 shows, in Graph A, a representative amplitude sweep collected at 1 Hz. The storage modulus (E’), loss modulus (E’’) and tan δ (all data were acquired at 1 Hz and 0.01% strain) are shown in Graphs B - D respectively. Note that the bars in the graph are the average for n = 3 and the error bars are the standard deviation.

[0078] Figure 14 shows an image of an aqueous dispersion of graphene according to an embodiment of the present invention. Figure 15 shows the adsorption spectroscopy of an aqueous dispersion of a graphene material according to an embodiment of the present invention. Figure 16 shows the sealing ability of a graphene dispersion in a defective polypropylene syringe according to an embodiment of the present invention. Figure 17 also shows the sealing ability of a non-functionalized graphene dispersion in a defective polypropylene syringe according to an embodiment of the present invention. Figure 18 shows an AFM image of a defect sealed with FGM extracted from a syringe according to an embodiment of the present invention. Figure 19 shows an atomic force microscope (AFM) image of an FGM-sealed defect according to an embodiment of the present invention.

[0079] The results shown in FIGS. 14 to 19 were generated using various procedures. The adhesion properties were characterized using an aqueous dispersion of graphene (1 mg / mL) that was sonicated for a short time to break up large aggregates. The dispersion was stirred at 120 revolutions per minute and images were acquired with a 16 megapixel camera. Absorption spectroscopy was used on powder samples that were diluted in DI water to 100 μg / mL, vortexed, and sonicated for less than 1 minute (240 W, 42 kHz ultrasonic cleaner, Kendal). Samples were placed in quartz cuvettes with a path length of 1 cm. Ultraviolet-visible absorption spectroscopy was performed using a Varian Cary 5000 spectrophotometer over a wavelength range of 200:1:800 nm.

[0080] To test the sealing ability of the FGM, small defects were created in a 20 mL polypropylene syringe by puncturing with the tip of an 18-gauge hypodermic needle. The defects were tested with DI water to confirm complete penetration of the syringe wall. That is, the syringe was filled with 24 mL of DI water, and then the syringe nozzle was sealed and the plunger was compressed to force the DI water through the syringe defect. After confirming the defect that penetrated the entire wall of the syringe, bright-field, monochrome imaging of the defect was performed with an EVOS® FL Auto Cell Imaging System equipped with a 10x, 0.30 numerical aperture objective lens. An image of the entire syringe was also taken using a 16-megapixel camera. A graphene aqueous dispersion was prepared at a concentration of 350 μg / mL and then sonicated for 20 minutes to ensure complete dispersion of large aggregants. Next, 24 mL of GO 2:1, CGO 2:1, CG, and CCG dispersions were filled into the syringe. The sealing ability of the formulation was tested by forcing the graphene dispersion through the syringe defect until the syringe defect was sealed or completely emptied. This was achieved by applying force to the syringe plunger while simultaneously covering the syringe nozzle to prevent liquid loss. After the experiment, the defects were imaged again using a microscope and photographs. All data processing of the acquired microscope images was performed with ImageJ (National Institutes of Health, Bethesda, Maryland).

[0081] After the syringe defect was successfully sealed with CGO 2:1 or CCG, the syringe was emptied and the section of the syringe immediately surrounding the sealed defect was carefully excised. Next, atomic force microscopy (AFM) was performed. The excised sample was placed on the AFM stage. Using a tip (#MPP-11200-10; Bruker AFM Probes, Camarillo, CA, USA) with a spring constant of 40 N / m and a resonance frequency of 300 kHz, AFM imaging of the graphene seal was performed on an NT-MDT SOLVER Nano atomic force microscope in semi-contact mode. Images were acquired and processed using Nova Px 3.2.5 software. The acquired height images were subjected to a fourth-order fitting line 1D flattening correction.

[0082] Particle imaging was also performed. An aqueous dispersion of graphene (100 μg / mL) was sonicated for a short time (20 minutes) to disperse large aggregants. Then, 20 μL aliquots were dropped onto microscope slides and air-dried. The microscope slides were covered with a #1.5 microscope cover slip and fixed with tape to prevent the introduction of artifacts (such as adhesives). Brightfield color imaging was performed on an EVOS® FL Auto Cell Imaging System using a 40x, 0.65 numerical aperture, long working distance objective lens. To identify particles, the images were converted to 8-bit grayscale images in ImageJ. The images were then intensity thresholded, converted to binary, and all open structures were closed using the "binary closing" function, manually checked and adjusted as necessary, and then all objects less than 4 pixels 2 were excluded and quantified using the "particle analysis" function. The mean area and standard error of the mean were calculated from all detected particles with n > 100 particles per sample. The pixel area was converted to microns through the known image pixel size conversion of our imaging system. The diameter was calculated from the area using the formula for the area of a circle. The histogram of the particle size distribution was created using the "hist" function in MATLAB® (The MathWorks, Inc.).

[0083] As described above, the data collected from these procedures are shown in FIGS. 14 to 19. FIG. 14 shows an image of an aqueous dispersion of graphene at a concentration of 1 mg / mL that is gently stirred. FIG. 15 shows the absorption spectroscopy of an aqueous dispersion of a graphene material. Specifically, it shows the spectrum of the ultraviolet-visible spectrum in Graph A and an enlarged view of the n-π* and π-plasmon features in Graph B. FIG. 16 shows the sealing ability of a graphene dispersion or an FGM sealant (350 μg / mL) in a polypropylene syringe containing defects of about 250 μm in Images A, B, D, and C. Optical microscope images of the inside and outside of the syringe defects before and after the addition of the FGM sealant (CGO 2:1 and CCG), together with the amount of the volume of the liquid lost after the addition of the FGM sealant and the repair of the defects, are shown in Images C and F, including images of the syringe and the defects before and after the addition of the FGM sealant. In some embodiments where the defects were successfully sealed, the defects in the syringe were about 0.07 mm 2 in size, and the concentration of the FGM material was about 25 mg / L.

[0084] For comparison, FIG. 17 shows the sealing ability of a 350 μg / mL dispersion of an unfunctionalized graphene material in a syringe containing defects of about 250 μm in Images A, B, D, and E. Optical microscope images of the syringe defects (external and internal) before and after the addition of GO 2:1 and CG, together with the amount of the volume of the liquid lost after the addition of the FGM sealant and the repair of the defects, are shown in Images C and F.

[0085] Figure 18 shows an AFM image of a defect sealed with FGM extracted from a syringe. Figure 19 shows the characterization of particles and aggregants of FGM and non-functionalized graphene materials. A representative optical image of an aqueous suspension of non-functionalized scaffolds is shown in Image A, and a representative optical image of the FGM sealant is shown in Image B. Images C and E show the average particle sizes determined by high-resolution optical microscopy of the corresponding optical images in A and B. The bars are the sample averages and the error bars are the standard errors. Note that the distributions of the particle sizes determined by the images are shown in Graphs D and F and the data have been offset for clarity.

[0086] Based on the above analysis, the FGM sealant, which is a catechol-graphene conjugate, can aggregate in water into a solid structure that is more stable than GO and CG and resembles a stopper. The linear viscoelastic region and the aggregation energy were significantly increased in the FGM sealant compared to the non-functionalized materials. This suggests that the FGM sealant forms a more stable structure in water due to stronger aggregation interactions between the graphene sheets. Furthermore, the aggregation characteristics of all the FGM sealants were similar to each other. It should be understood that the basal plane oxidation in the FGM sealant is shielded by the presence of DHBA. DHBA can participate in π-π aromatic interactions that form strong hydrogen bonds and result in intersheet stacking between the graphene skeletons in the FGM sealant. The above analysis can be used to evaluate whether other scaffold materials, including other graphene materials, and conjugated small molecules with adhesive properties can impart the desired properties to be used as adhesives or sealants.

[0087] Based on the above tests, it should be understood that a wide ratio of adhesive molecules to the graphene material can be used to produce an FGM that functions as an adhesive or a sealant. However, it should be understood that a smaller ratio may be more efficient in that the excess adhesive molecules used are not wasted. In other words, as the amount of adhesive molecules increases relative to the graphene material, a saturation point may be reached that limits the further ability to covalently bond the adhesive molecules to the graphene scaffold due to the lack of available carboxylic acids on the graphene material. The unbound adhesive molecules are not simply washed away during the purification of the FGM. Nevertheless, the FGM still functions as an adhesive or a sealant despite the excess adhesive molecules. Thus, in some embodiments, a weight ratio of adhesive molecules to graphene material in the range of about 1:1 to 10:1 can be used. In some embodiments, a weight ratio of adhesive molecules to graphene material in the range of about 1:1 to 5:1 can be used. In some embodiments, a weight ratio of adhesive molecules to graphene material in the range of about 1:1 to 2.5:1 can be used. In some embodiments, a weight ratio of adhesive molecules to graphene material in the range of about 1:1, 2.5:1 or 5:1 can be used.

[0088] In use, the FGM of the present invention, which is identified and synthesized as described above and has the above-described properties, can be used in various applications. Generally, the FGM of the present invention can be used as a sealant or an adhesive. In some embodiments, the FGM of the present invention can be used as a sealant for repairing leaks or defects in pipes or tubes carrying fluids. In some embodiments, the FGM of the present invention can be used in situ to repair leaks or defects in pipes or tubes carrying fluids. In some embodiments, the FGM of the present invention can be used in situ to repair leaks or defects in condenser tubes used in power plants such as Rankine cycle power plants. In such embodiments, the FGM can simply be added to the fluid being carried in the pipe or tube during normal use of the pipe or tube, and the FGM adheres to the location of the defect or leak, such as an opening or leak in the wall of the pipe or tube, and provides a seal that reduces or eliminates the leak or repairs a defect that could otherwise become a leak if the FGM did not adhere to the location of the leak. It should be understood that the pressure drop across the defect or leak acts to direct the FGM towards the site of the defect or leak.

[0089] Qualitatively, the FGM sealant can adhere to metal surfaces. This was observed during rheology tests using steel and aluminum shapes. After the mechanical tests were completed, the FGM sealant adhered to the upper steel shape and the lower aluminum shape. The non-functionalized GO and CG scaffolds did not exhibit the same metal adhesion properties. Thus, the adhesion and stability of the FGM sealant to metal condenser tubes will be stronger than the non-polar polypropylene syringe used above to evaluate the sealing ability of the FGM. Thus, when directed to the site of a defect or leak in a metal surface based on the existing pressure drop, the FGM is attracted to that region of the metal surface and adheres in place, thereby constructing a seal and effectively reducing or eliminating the leak.

[0090] Figure 20 shows a process for using FGM according to one embodiment of the present invention. As shown, condenser tube 2002 is shown with an unsealed defect or leak 2004 that illustrates fluid loss from the condenser tube. Also shown is a repaired leak 2006 that includes a plug or seal made from FGM 2008. To repair an existing leak 2004, an FGM such as catechol oxidized graphene (CGO) 2010 or catechol claisen graphene (CCG) 2012 can be added to fluid 2014 such that the FGM is dispersed within the fluid to form a dispersed FGM sealant in the fluid. The fluid can be, for example, a working fluid transported by a pipe, in this case water that normally flows through the condenser tube during normal use. In this case, the repair can be done in place and the FGM can be added to the water without the need to stop the use of the condenser tube. Alternatively, the FGM material can be added to a fluid such as water that is simply passing through a tube having a leak or defect while the tube is not in use. In either case, the repair can be done in place without the need to remove the leaking tube for repair. The amount of FGM required and the contact time required between the FGM and the defect or leak vary. For example, larger defects require more material. Since the water is circulating, larger defects may take longer to seal as the size of the FGM plug increases. It should be understood that the magnitude of the pressure drop at the site of the defect or leak also affects the amount of FGM drawn to that location, which in turn affects the amount of FGM that needs to be added to the fluid. Nevertheless, the amount of FGM required to provide a seal against a defect or leak can be determined based on the adequacy of the repair or the reduction in the size of the leak.

[0091] Various embodiments of the present invention have been described above. However, it should be understood that alternative embodiments are possible and that the present invention is not limited to the specific embodiments described above. For example, other materials may be used as the scaffold and the adhesive molecule. In these examples, the above analysis can be used to determine whether such a scaffold or adhesive or various combinations thereof function well as an adhesive or a sealant and whether they provide in-situ repair of surface defects or leaks. The present invention provides, for example, the following items. (Item 1) A compound having adhesion properties, a graphene scaffold, and a molecule covalently bonded to the graphene scaffold having a portion containing 1,2-dihydroxybenzene capable of adhering to a metal surface, a compound containing the same. (Item 2) The compound according to Item 1, wherein the graphene scaffold contains graphene oxide. (Item 3) The compound according to Item 1, wherein the graphene scaffold contains Kleisen graphene. (Item 4) The compound according to Item 1, wherein the molecule contains a nucleophile that covalently bonds the molecule to the graphene scaffold. (Item 5) The compound according to Item 1, wherein the nucleophile contains a primary amine. (Item 6) The compound according to Item 1, wherein the molecule contains a catechol derivative. (Item 7) The compound according to Item 1, wherein the molecule contains 3,4-dihydroxybenzylamine. (Item 8) Sealing of an opening in a tube wall, the opening in the tube wall, and a seal including a graphene scaffold having a covalently bonded molecule having a portion containing 1,2-dihydroxybenzene, the seal being adhered to a part of the tube wall thereby covering the opening, a seal of an opening in a tube wall including the same. (Item 9) The compound according to Item 8, wherein the graphene scaffold contains graphene oxide. (Item 10) The compound according to Item 8, wherein the graphene scaffold contains Kleisen graphene. (Item 11) The compound according to Item 8, wherein the molecule contains a catechol derivative. (Item 12) The compound according to Item 8, wherein the molecule contains 3,4-dihydroxybenzylamine. (Item 13) A method for reducing a leak in a tube, adding a sealant to a fluid passing through the tube, the sealant including a graphene scaffold having a covalently bonded molecule having a portion containing 1,2-dihydroxybenzene, the tube including a leak through which the fluid passes, adding, adhering the sealant to the tube adjacent to the leak, forming a seal including the sealant thereby covering the leak, a method including the same. (Item 14) The method according to Item 13, wherein the graphene scaffold contains graphene oxide. (Item 15) The method according to item 13, wherein the graphene scaffold contains Claisen graphene. (Item 16) The method according to item 13, wherein the molecule contains a catechol derivative. (Item 17) The method according to item 13, wherein the molecule contains 3,4-dihydroxybenzylamine. (Item 18) The method according to item 13, wherein the forming includes preventing the fluid from passing through the leak opening.

Claims

1. A compound having an adhesion property, a graphene scaffold, and a molecule covalently bonded to the graphene scaffold having a portion containing 3,4-dihydroxybenzylamine capable of adhering to a metal surface, A compound comprising.

2. The compound according to claim 1, wherein the graphene scaffold contains graphene oxide.

3. The compound according to claim 1, wherein the graphene scaffold contains Krisen graphene.

4. The compound according to claim 1, wherein the molecule contains a nucleophile that covalently bonds the molecule to the graphene scaffold.

5. A sealant for an opening in a pipe wall, A sealant comprising a graphene scaffold having a covalently bonded molecule containing a catechol derivative, the sealant being adhered to a part of the pipe wall, thereby covering the opening, a sealant for an opening in a pipe wall.

6. The sealant according to claim 5, wherein the graphene scaffold contains graphene oxide.

7. The sealant according to claim 5, wherein the graphene scaffold contains Krisen graphene.

8. The sealant according to claim 5, wherein the molecule contains 3,4-dihydroxybenzylamine.

9. A method for reducing a leak in a pipe, a step of adding a sealant to a fluid passing through the pipe, the sealant comprising a graphene scaffold having a covalently bonded molecule containing a catechol derivative, the pipe comprising a leak through which the fluid passes, the step; a step of adhering the sealant to the pipe adjacent to the leak; a step of forming a seal including the sealant, thereby covering the leak; A method including

10. The method according to claim 9, wherein the graphene scaffold contains graphene oxide.

11. The method according to claim 9, wherein the graphene scaffold contains Claisen graphene.

12. The method according to claim 9, wherein the molecule contains 3,4-dihydroxybenzylamine.

13. The method according to claim 9, wherein forming includes preventing the fluid from passing through the leak opening.

14. The sealant according to claim 5, wherein the catechol derivative contains 1,2-dihydroxybenzene.

15. The method according to claim 9, wherein the catechol derivative contains 1,2-dihydroxybenzene.

16. A tube including a tube wall, an opening in the tube wall, and a sealant for the opening, wherein the sealant includes a graphene scaffold having covalently bonded molecules containing a catechol derivative, and the sealant is adhered to a part of the tube wall, thereby covering the opening.

17. The tube according to claim 16, wherein the graphene scaffold contains graphene oxide.

18. The tube according to claim 16, wherein the graphene scaffold contains Claisen graphene.

19. The tube according to claim 16, wherein the molecule contains 3,4-dihydroxybenzylamine.

Images