Strong Interfacial Adhesion Research Articles

Interface Coupling in Rubber/Carbon Black Composites toward Superior Energy-Saving Capability Enabled by Amino-Functionalized Polysulfide

Natural rubber/carbon black (NR/CB) composites have found indispensable application in aircraft tires. Interfacial modification of NR/CB composites for acquiring uniform CB dispersion and strong interfacial adhesion is a persistent and challenging theme, as it is a prerequisite to improve comprehensive mechanical properties and decrease energy loss of the composites under dynamic deformations. In this work, we reported the use of an amino-functionalized polysulfide (PDAS) synthesized by inverse vulcanization of sulfur and m-phenylenediamine as a novel interfacial modifier in NR/CB composites. Specifically, the amino of PDAS can react with the carboxyl groups on the CB surface, meanwhile the polysulfide chains of PDAS can react with rubber chains, enabling the crosslinking of NR and establishment of a molecular bridge between NR and CB. The influences of PDAS dosages on CB dispersion and interfacial adhesion are revealed, and their correlations with composite properties are discussed. Compared with the unmodified counterpart, CB dispersion is greatly improved and interfacial adhesion is significantly enhanced in the PDAS-modified composite having an identical crosslink density, leading to remarkably decreased hysteresis loss. In addition, PDAS can significantly resist thermal-oxidative aging of the composites due to its radical scavenging activity.

Compression and thermophysical properties of carbon fiber-reinforced high textured pyrocarbon and SiC dual matrix composites

C/C–SiC composites with high textured pyrocarbon (HT PyC) were fabricated by isothermal chemical vapor infiltration and reactive melt infiltration. The evolution of HT PyC before and after heat treatment at 2100 °C as well as the internal defects of the composites, such as pores and cracks, were characterized. The compression and thermophysical properties of the C/C–SiC composites with 2100 °C heat-treated HT PyC (C–S-21) and C/C composites with 2100 °C heat-treated HT PyC (C–C-21) were studied. The results showed that the compression strength and modulus of C–S-21 were 323.19 ± 11.52 MPa and 4.49 ± 0.13 GPa, which were increased by 58.94% and 125.63%, respectively, compared with those of C–C-21 owing to the smaller number of pores and the higher modulus of SiC and Si, respectively. However, fewer pores and strong interfacial adhesion resulted in the brittle fracture of C–S-21. The thermal conductivity of C–S-21 was 73.56 W/(m·K) and 44.94 W/(m·K) in the XY and Z directions, respectively, which was attributed to the fewer defects and better orientation of the graphitized layer in HT PyC as well as the smaller number of pores.

Strong Anchoring of Hydrogels through Superwetting‐Assisted High‐Density Interfacial Grafting

AbstractStrong adhesion of hydrogels on solids plays an important role in stable working for various practical applications. However, current hydrogel adhesion suffers from poor interfacial bonding with solid surfaces. Here, we propose a general superwetting‐assisted interfacial polymerization (SAIP) strategy to robustly anchor hydrogels onto solids by forming high‐density interfacial covalent bonds. The key of our strategy is to make the initiator fully contact solid surfaces via a superwetting way for enhancing the interfacial grafting efficiency. The designed anchored hydrogels show strong bulk failure with a high breaking strength of ≈1.37 MPa, different from weak interfacial failure that occurs in traditional strategies. The strong interfacial adhesion greatly enhances the stability of hydrogels against swelling destruction. This work opens up new inspirations for designing strongly anchored hydrogels from an interfacial chemistry perspective.

Strong Anchoring of Hydrogels through Superwetting-Assisted High-Density Interfacial Grafting.

Strong adhesion of hydrogels on solids plays an important role in stable working for various practical applications. However, current hydrogel adhesion suffers from poor interfacial bonding with solid surfaces. Here, we propose a general superwetting-assisted interfacial polymerization (SAIP) strategy to robustly anchor hydrogels onto solids by forming high-density interfacial covalent bonds. The key of our strategy is to make the initiator fully contact solid surfaces via a superwetting way for enhancing the interfacial grafting efficiency. The designed anchored hydrogels show strong bulk failure with a high breaking strength of ≈1.37 MPa, different from weak interfacial failure that occurs in traditional strategies. The strong interfacial adhesion greatly enhances the stability of hydrogels against swelling destruction. This work opens up new inspirations for designing strongly anchored hydrogels from an interfacial chemistry perspective.

Segregation-modified interfacial strength and deformation mechanism at SiCp/2009Al composite interface

The reinforcement/matrix interface is a crucial factor affecting the mechanical performance of metal matrix composites (MMCs). However, it is difficult to quantitatively characterize the correlation between interfacial microstructure and mechanical properties, especially between interfacial segregation and interfacial strength. In this study, composite micro-pillars containing a single slanted interface with Mg segregation were fabricated in engineering SiCp/2009Al composites produced by the powder metallurgy technique (PMT). Upon uniaxial compression, changes in interfacial deformation behavior depended on the Mg segregation amount. Specifically, as the segregation amount increased, the interfacial shear strength increased from 174.5 MPa to 230 MPa, and the misorientation angles of the interfacial micro-region increased from 1.2 ± 0.5° to 8.8 ± 5.6°. It was demonstrated that the Mg segregation in the SiC/Al interface can considerably enhance interfacial adhesion by improving interfacial wettability, and the interfacial micro-region with stronger interfacial adhesion can endure more external strain through grain fragmentation. Characterization the correlation of “a single interface - mechanical properties” in engineering 15 vol.% SiCp/2009Al composites. • The fabrication method of composite micro-pillar with a single and slanted interface containing interfacial segregation in engineering PRMMCs. • The impact of interfacial segregation on the interfacial shear strength and the deformation mechanisms of the interfacial micro-region.

High sensitivity and excellent durability of wearable microenvironmental humidity sensors inspired by the spider-web

In this study, we report a high-performance microenvironmental humidity sensor inspired by a spider-web structure, where a carbon nanotube network with cellulose nodes is constructed on the surface of cotton fabric by micro-dissolution technology. The obtained MWCNTs/cotton fabrics, as wearable humidity sensors, show excellent sensitivity when compared to other cotton fabric-based humidity sensors (maximum response of 99.6 %). In addition, the cellulose interlocking structure between the spider-web humidity-sensitive layer and the cotton substrate, provides the sensor with a strong interfacial adhesion. The sensor exhibits excellent durability (50 times cycling, 500 times folding, 20 times friction and stability over 3 months). As a theoretical validation, we simulated baby nappy moisture detection. The sensor shows significantly higher sensitivity and accuracy than commercial hygrometers and nappy discoloration strips, indicating that our sensor has great potential for humidity detection and early warning in body-worn microenvironments.

Electrochemical Bonding of Hydrogels at Rigid Surfaces.

Flexible hydrogels can be chemically/physically bonded on soft surfaces. However, there is a lack of a facile method to build strong interfacial adhesion between hydrogel and various rigid surfaces. Herein, an electrochemical bonding protocol, which improves the interfacial adhesion energy of hydrogel from initial 8 to 3480 J m-2 , ≈435 times enhancement at rigid glass surface, superior to the most of traditional methods, is proposed. A series of electrochemical bonding models to analyze the bonding mechanism, is demonstrated. The results indicate that the electrode reactions generate Fe3+ ions at the anode and OH- ions at the cathode, which migrate and react to form nanoparticles of Fe(OH)3 . These nanoparticles form hump-like physical structures at the interface and work as mechanical-bonding sites, enabling the strong interfacial adhesion. Upon applying acidic solution to decompose the nanoparticles, the strong adhesion can be weakened to easily remove hydrogel from the bonded surface. The electrochemically-bonded hydrogel can maintain its adhesion in water, which enables the electrochemical bonding of hydrogels for repairing various damaged surfaces such as plastic water tubes/bags, indicating promising potential for adhesive engineering applications.

Characterizations of Hybrid Composites of Linen /Glass Fibers for Automotive and Transportation Applications

Recently, the sustainability issue has become crucial to operation, which motivates researchers to search for naturally generated, sustainable materials, especially in automotive applications outside of reduced prices and enhanced performance. Glass-linen/Polyvinyl Butyral hybrid composites' mechanical characteristics were examined in relation to the effect of linen fiber loading. The composite and hybrid composite samples of linen/glass fiber reinforced PVB film were created using a hot press with various layering patterns. The results were high impact values with increased both tensile and flexural strength values. Compared to other hybrid composites, the mechanical behaviors of the H1 (Glass / Linen) hybrid have a greater tensile strength measuring 401.30 MPa, while, H2 (Glass / Linen/ Glass) hybrids are found to have the highest flexural strength, measuring 160.80 MPa. An optical and scanning electron microscope morphological analysis on linen hybrid composites revealed good results. This indicated decreased rates of delamination between the fibers and matrix layers. The loading of the fibers was shown to have varying effects on the composite's mechanical behaviors. The linen/glass composites also demonstrated strong interfacial adhesion, which enabled the PVB-phenolic resin to penetrate the fiber bundles and produce a matrix with the good interlocking of the fibers

Ultrathin diamond blades for dicing single crystal SiC developed using a novel bonding method

Dicing is an important process in the making of semiconductor chips. In recent years, high performance dicing technologies are badly needed for the new-generation wafers such as silicon carbide (SiC) and sapphire as those hard-to-machine brittle materials have posed great challenges for dicing. In this work, a novel bond metal, i.e., Ti-15/75Al binary alloy, was used to fabricate ultrathin diamond blades. The performance of the developed blades was assessed in the dicing of single crystal SiC. The blade using Ti-rich Ti15Al alloy (T-type) as bonding agent was found to produce lower dicing force, smaller chipping size, and higher removal ratio, in comparison to the blades using Al-rich Ti75Al (A-type) and conventional Cu-rich Cu20Sn alloys (C-type) as bond metals. The ground surface produced using the T-type blade was found to be smoother than those generated using the A- and C-type blades. The superior performance of the Ti-rich Ti15Al blade was attributed to the strong interfacial adhesion of diamond grits with the bond alloy. Such adhesion was established through forming titanium carbides at the interface, which helped retention of diamond grits during dicing. The strong adhesion also enabled the blade to possess a relatively high hardness and a sufficiently large porosity in bond matrix, both favored the material removal in the dicing of SiC.

Inverse Vulcanization of Vinyltriethoxysilane: A Novel Interfacial Coupling Agent for Silica-Filled Rubber Composites

Sulfur-containing silane coupling agents (SSCAs) are widely incorporated into silica-filled rubber composites to improve silica dispersion and enhance interfacial adhesion, maximizing the potential of silica. However, SSCA synthesis involves multistep procedures and requires organic solvents. In addition, modifying rubber composites with SSCAs has persistent issues, such as low coupling efficiency and uncontrollable structure. Herein, we report the facile synthesis of alkoxysilyl-functionalized polysulfides (SPVs) with a tunable molecular structure (sulfur rank and alkoxysilyl fraction) via inverse vulcanization of vinyltriethoxysilane (VTES) with a copolymer of sulfur and styrene. SPVs serve as interfacial modifiers in silica-filled rubber composites by separately reacting with the silica and rubber chains. In particular, the multiple alkoxysilyl sites in the SPV chain increase the probability of silanization, yielding high coupling efficiency in the rubber composite. Although the molar content of alkoxysilyl groups in SPV1 (the mass feed ratio of VTES and copolymer is 1) is half of that in the most widely used small-molecules SSCAs of bis(3-triethoxysilylpropyl)tetrasulfide, stronger interfacial adhesion and better silica dispersion are achieved in SPV1-modified composites, which consequently lead to more improvements on the composite properties. In addition, the advantages of SPV1 as an interfacial modifier in improving the “magic triangle” properties of a practical tread composite have been demonstrated. More importantly, the effects of the SPV molecular structure on silica dispersion and interfacial adhesion have been investigated, providing the fundamentals for unraveling the coupling mechanism and guiding composite property regulation.

Preparation of Biocomposites with Natural Reinforcements: The Effect of Native Starch and Sugarcane Bagasse Fibers.

Biocomposites were prepared from poly(lactic acid) and two natural reinforcements, a native starch and sugarcane bagasse fibers. The strength of interfacial adhesion was estimated by model calculations, and local deformation processes were followed by acoustic emission testing. The results showed that the two additives influence properties differently. The strength of interfacial adhesion and thus the extent of reinforcement are similar because of similarities in chemical structure, the large number of OH groups in both reinforcements. Relatively strong interfacial adhesion develops between the components, which renders coupling inefficient. Dissimilar particle characteristics influence local deformation processes considerably. The smaller particle size of starch results in larger debonding stress and thus larger composite strength. The fracture of the bagasse fibers leads to larger energy consumption and to increased impact resistance. Although the environmental benefit of the prepared biocomposites is similar, the overall performance of the bagasse fiber reinforced PLA composites is better than that offered by the PLA/starch composites.

Respiratory mucosa-inspired “sticky-slippery coating” with transparency and structure adaptation based on comb-polymer nanogel

Liquid-repellent coatings with a combined competence of strong interfacial adhesion, excellent structural stability, and environmental friendliness are substantially demanded in daily life and industry. However, it is still extremely challenging to create such materials. Here, we present a respiratory mucosa-inspired robust sticky-slippery liquid-like coating by the assembly of comb-polymer nanogel, in which hexafluorobutyl methacrylate (HF) served as a mediator to improve the compatibility between adhesive and lubricant monomers, generating homogenous nanogel with covalently attached comb-type lubricant brushes. By virtue of nanoscale size and viscous flow nature, our nanogel enables a universal tool to tightly wrap desirable coatings with a unique multilayer structure on various structured substrates (e.g., plane, curved surface, and porous net) while maintaining their pristine morphologies. The lubricant brushes enriched at the coating surface form a uniform liquid-like lubricant layer with ultralow liquids sliding angle (<5°), while adhesive segments adhere to the substrate with high adhesion strength (>9.0 MPa). Meanwhile, the resultant coating exhibited excellent flexibility, fascinating transparency, good antifouling performance, and long-term structure stability under harsh conditions. The synthesis of such fascinating sticky-slippery liquid-like coating may offer new insights into the design and development of environmentally friendly slippery coatings for numerous applications.

Material and Environmental Properties of Natural Polymers and Their Composites for Packaging Applications-A Review.

The current trend of using plastic material in the manufacturing of packaging products raises serious environmental concerns due to waste disposal on land and in oceans and other environmental pollution. Natural polymers such as cellulose, starch, chitosan, and protein extracted from renewable resources are extensively explored as alternatives to plastics due to their biodegradability, biocompatibility, nontoxic properties, and abundant availability. The tensile and water vapor barrier properties and the environmental impacts of natural polymers played key roles in determining the eligibility of these materials for packaging applications. The brittle behavior and hydrophilic nature of natural polymers reduced the tensile and water vapor barrier properties. However, the addition of plasticizer, crosslinker, and reinforcement agents substantially improved the mechanical and water vapor resistance properties. The dispersion abilities and strong interfacial adhesion of nanocellulose with natural polymers improved the tensile strength and water vapor barrier properties of natural polymer-based packaging films. The maximum tensile stress of these composite films was about 38 to 200% more than that of films without reinforcement. The water vapor barrier properties of composite films also reduced up to 60% with nanocellulose reinforcement. The strong hydrogen bonding between natural polymer and nanocellulose reduced the polymer chain movement and decreased the percent elongation at break up to 100%. This review aims to present an overview of the mechanical and water vapor barrier properties of natural polymers and their composites along with the life cycle environmental impacts to elucidate their potential for packaging applications.

Synthesis and Effect of Nanocellulose Obtained from East Java Kenaf Fiber on Mechanical Properties of Polyurethane Foam Composites as Strong and Lightweight Materials

Cellulose is a fascinating biopolymer and sustainable raw material. Cellulose particles with at least one dimension in the nanoscale are referred to as nanocellulose. Kenaf fiber is a natural fiber used in this study because it has high mechanical properties and strong interface adhesion with polymers so it provides superior properties to other natural fibers. Polyurethane (PU) foam is widely used as a core layer in sandwich composite construction to produce a lightweight material. This study presents a synthesis of cellulose nano-fibrils (CNF) extracted from East Java, Indonesia based kenaf fibers, an analysis of the effect of adding CNF as a filler and a reinforcement in PU foam composites, and a formulation of PU-CNF foam composite that provided the best mechanical properties as strong and lightweight materials in structural applications. The CNF extraction from kenaf fiber started by fiber pre-treatment including alkalization and bleaching, then mechanical treatment with an Ultra Fine Grinder to produce CNF suspension. The weight variations of CNF in PU foam were 0, 3, 5, 7, and 10 wt%. PU-CNF composite fabrication using the in-situ polymerization method. CNF characterization included TEM, XRD, and FT-IR. TEM results on CNF show that the CNF diameter is in the range of 40-70 nm. The functional group from the FT-IR results showed that the pre-treatment process on kenaf fiber was successful in reducing the lignin and hemicellulose content. XRD results showed that the CNF crystallinity was 75.22%. The PU-CNF foam composite characterization included a compressive test, 3-point bending test, and SEM. The PU foam composite with 3 wt% CNF reinforcement is the best composite which has the optimum value from the results of the compression test and the 3-point bending test. The compressive strength value increased by 20.01%, from 236.997 kPa to 284.434 kPa, the compressive modulus value increased by 29.21% from 5.67 MPa to 7.32 MPa, and the 3-point bending strength value increased 28.29% from 572.24 to 734.15 kPa. All the results expected to support that CNF was a potential reinforcement material with a high surface area for a wide variety of applications.

Preparation and properties of glass fiber reinforced nylon56 composites

AbstractGlass fiber (GF) reinforced nylon56 composites (nylon56/GF) were prepared by melting and blending through twin‐screw extruder with continuous fiber feeding. The structure and properties of the composites were characterized by electron density tester, polarizing microscope, scanning electron microscope, electro‐mechanical universal testing machine and thermal analyzer. The results showed that the density of the prepared composites is less than 1.37 g/cm3. There is strong interface adhesion between glass fiber and nylon56 matrix in the composite system, and the glass fiber length in the system is 0.47–0.61 mm. With the increase in the content of high‐performance glass fiber, the mechanical properties of the composite are significantly improved. When four bundles of GF are added, the properties of the nylon56/GF composite are the best. The tensile strength of nylon56/GF composite reaches 160 MPa, 86.9% higher than that of nylon56. The bending strength is 180 MPa and increases by 98.7% more than that of nylon56. The flexural modulus is 7100 MPa and rises by 125.6% compared with nylon56, and the impact strength is 11 kJ/mm2, which is 307.4% higher than that of nylon56. The nylon56/GF composite has a low density and excellent performance and can be widely used in locomotive and wind power.

Environment-friendly AgNWs/Ti3C2Tx transparent conductive film based on natural fish gelatin for degradable electronics.

Recently, the electronic waste (E-waste) has become the most serious environmental trouble because of the iteration of electronic products. Transparent conductive films (TCFs) are the key component of flexible electronic devices, so the development of devices based on degradable TCFs has become an important way to alleviate the problem of E-waste. Gelatin, one of the most prevalent natural biomacromolecules, has drawn increasing attention due to its good film-forming ability, superior biocompatibility, excellent degradability, and commercial availability at a relatively low cost, but has few applications in flexible electronics. Here, we report a method for preparing flexible TCF based on naturally degradable material-fish gelatin, in which silver nanowires and Ti3C2Tx flakes were used as conductive fillers. The obtained TCF has low roughness (RMS roughness = 5.62 nm), good photoelectric properties (Rs = 25.2 Ω/sq., T = ca.85% at 550 nm), strong interfacial adhesion and good degradability. Moreover, the film showed excellent application in the field of EMI shielding and green light OLED device. We believe that these TCFs will shine in the smart wearable field in the future.

Polyhydric SiO2 coating assistant to graft organophosphorus onto glass fabric for simultaneously improving flame retardancy and mechanical properties of epoxy resin composites

It is still a great challenge to develop epoxy resin/glass fabric (EP/GF) composites with well-balanced enhancements on flame retardancy and mechanical properties. Herein, a novel strategy that polyhydric SiO2 coating assistant to graft organophosphorus (DOPO) onto GF was developed for simultaneously improving flame retardancy and mechanical properties of EP composites. The grafting amount of DOPO could reach to 43.64 wt% via the helpful bridging of polyhydric SiO2, so that EP composites displayed excellent flame retardancy with the LOI of 37.2%, the V0 rating on UL-94 and a 63.3% decrease on PHRR in cone calorimeter test. According to the analysis of char morphology and structure, the flame retarded mechanism was mainly ascribed to the enhanced barrier effect of a continuous and intergrow char layer, which was composed of GF@SiO2 as framework and P-containing condensed carbon as stuffing. Meanwhile, EP composites exhibited outstanding mechanical performances with 35% and 60% increases on tensile strength and impact strength respectively, which resulted from the special molecular structure of GF@SiO2-g-DOPO with strong interfacial adhesion with EP chains via hydrogen bond and chemical bond. In summary, this work will be favorable to design multifunctional polymer composites with well-balanced comprehensive performances, and expand their widespread applications in high-end fields.

Rollable Ultraviolet Photodetector Based on ZnAl‐Layered Double Hydroxide/Polyvinylidene Fluoride Membrane

AbstractHigh‐performance, reliable, and rollable ultraviolet (UV) photodetectors have attracted considerable attention for wireless sensor network technology. Despite the improved responsivity of UV photodetectors, high‐performance rollable UV photodetectors have not been reported. This paper reports a rollable UV photodetector based on ZnAl‐layered double hydroxide (LDH) nanosheets on a porous polyvinylidene fluoride (PVDF) membrane. Vertically aligned ZnAl‐LDH nanosheets are grown on a porosity‐controlled PVDF membrane. The UV photodetector exhibits an excellent photoresponse at wavelengths below 420 nm, even in curvature with a 0.6 mm radius. The rollable UV photodetector also shows reliable, responsive performance even after 5 000 rolling cycles, indicating the reasonable durability of the ZnAl‐LDH nanosheet. The reliable photodetector performance is attributed to the elasticity of the PVDF and the strong interfacial adhesion force between the porous PVDF and ZnAl‐LDH nanosheets.

Rapid ultraviolet curing of epoxy acrylate films with low refractive index and strong interfacial adhesion

The low refractive index of coatings for optical fiber helps to reduce the information loss in optical transmission. However, previous studies focused on decreasing refractive index by adding fluorine-containing monomers into the curing system, ignoring the effect of the functional monomer on the adhesion of the coating onto the optical fiber. To address this limitation, this paper established a rapid light-curing system that reduced the refractive index of the cured film while enhancing the interfacial adhesion between optical fiber and coatings. Based on the Lorentz equation, the low molar refractive index of fluorine atoms was utilized to reduce the refractive index of the light-cured films. Simultaneously, the bisphenol A epoxy acrylate, as an oligomeric main resin, was highly active in cationic photoreaction and can effectively enhance interfacial adhesion. Moreover, the methyl methacrylate was applied to increase the compatibility of epoxy resins and fluorine-containing monomers. The experimental data indicated that the refractive indices of the cured films with fluorine-containing monomers were adjustable from 1.4930 to 1.5576, and the light transmittance was greater than 90%. The curing rate of the sample containing 11.3 wt% of fluorine (F-11.3%) was 26.26 J∙cm−2, which was 28.6% higher compared to that without fluorine. Intriguingly, in terms of molecular dynamics simulations, the interfacial interaction between fluorine-containing monomers and SiO2 crystalline surfaces was modeled. As a result, the interfacial energy between the curing system F-11.3% and SiO2 was −1879.91 kcal/mol, which was 1.16 times higher compared with the cured system without trifluoromethyl methacrylate, proving that increasing the fluorine content is profitable to promote the adhesion force in this system. This paper provided a design method of optical fiber coatings with strong interfacial adhesion, low refractive index and rapid light curing.

Graphene-Promoted Adhesion-Reduced Expansion of Discontinuous Palladium Nanowires upon Hydrogenation.

Monitoring conductivity changes of discontinuous palladium (Pd) nanostructures upon hydrogenation is becoming one of the most promising approaches toward hydrogen sensing. Development of sensors in this type has long been impeded due to strong ubiquitous interfacial adhesion which could distinctly restrict Pd expansion so as to hinder the closing of a nanogap. Herein, graphene underlayers were applied in the fabrication of nanogap-based hydrogen sensors to promote the lateral expansion of a Pd nanowire upon hydrogenation by reducing the adhesion between the metal and the substrate. In order to clarify details as well as mechanisms underlaid of graphene-enhanced Pd expansion, nanowire samples with serial lengths (6-48 μm) and gaps (0-260 nm in width) were controllably prepared on single-layer graphene (SLG), double-layer graphene (DLG), and quadruple-layer graphene (QLG, DLG × 2) via the combination of electron beam lithography (EBL) and electron beam deposition (EBD) technology. Response features and intrinsic analysis in physical sense of the graphene-based discontinuous Pd circuits upon hydrogen were established, in light of which the effects of underlayers on Pd expansion and on nanogap closing process were investigated. Such graphene-promoted expansion was demonstrated through the achievement of the closure of a large gap threshold (Gt) up to 260 nm as well as the systematical investigation of its influence on the sensing performance.