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Here we demonstrate the imbibition-induced, spontaneous and selective wetting properties of gallium-based liquid metal alloys on metalized surfaces with microscale topographical features. Gallium-based liquid metal alloys are amazing materials with enormous surface tension. Therefore, it is difficult to form them into thin films. Complete wetting of the eutectic alloy of gallium and indium was achieved on the microstructured copper surface in the presence of HCl vapors, which removed the natural oxide from the liquid metal alloy. This wetting is numerically explained based on the Wenzel model and the osmosis process, showing that microstructure size is critical for efficient osmosis-induced wetting of liquid metals. In addition, we demonstrate that spontaneous wetting of liquid metals can be selectively directed along microstructured regions on a metal surface to create patterns. This simple process evenly coats and shapes liquid metal over large areas without external force or complex handling. We have demonstrated that liquid metal patterned substrates retain electrical connections even when stretched and after repeated cycles of stretching.
Gallium based liquid metal alloys (GaLM) have attracted much attention due to their attractive properties such as low melting point, high electrical conductivity, low viscosity and flow, low toxicity and high deformability1,2. Pure gallium has a melting point of about 30 °C, and when fused in eutectic compositions with some metals such as In and Sn, the melting point is below room temperature. The two important GaLMs are gallium indium eutectic alloy (EGaIn, 75% Ga and 25% In by weight, melting point: 15.5 °C) and gallium indium tin eutectic alloy (GaInSn or galinstan, 68.5% Ga, 21.5% In, and 10% tin, melting point: ~11 °C)1.2. Because of their electrical conductivity in the liquid phase, GaLMs are being actively investigated as tensile or deformable electronic pathways for a variety of applications, including electronic3,4,5,6,7,8,9 strained or curved sensors 10, 11, 12, 13, 14 and leads 15, 16, 17. The fabrication of such devices by deposition, printing, and patterning from GaLM requires knowledge and control of the interfacial properties of GaLM and its underlying substrate. GaLMs have high surface tension (624 mNm-1 for EGaIn18,19 and 534 mNm-1 for Galinstan20,21) which can make them difficult to handle or manipulate. The formation of a hard crust of native gallium oxide on the GaLM surface under ambient conditions provides a shell that stabilizes the GaLM in a non-spherical shape. This property allows GaLM to be printed, implanted into microchannels, and patterned with the interfacial stability achieved by oxides19,22,23,24,25,26,27. The hard oxide shell also allows GaLM to adhere to most smooth surfaces, but prevents low viscosity metals from flowing freely. Propagation of GaLM on most surfaces requires force to break the oxide shell28,29.
Oxide shells can be removed with, for example, strong acids or bases. In the absence of oxides, GaLM forms drops on almost all surfaces due to their huge surface tension, but there are exceptions: GaLM wets metal substrates. Ga forms metallic bonds with other metals through a process known as “reactive wetting”30,31,32. This reactive wetting is often examined in the absence of surface oxides to facilitate metal-to-metal contact. However, even with native oxides in GaLM, it has been reported that metal-to-metal contacts form when oxides break at contacts with smooth metal surfaces29. Reactive wetting results in low contact angles and good wetting of most metal substrates33,34,35.
To date, many studies have been carried out on the use of the favorable properties of reactive wetting of GaLM with metals to form a GaLM pattern. For example, GaLM has been applied to patterned solid metal tracks by smearing, rolling, spraying, or shadow masking34, 35, 36, 37, 38. Selective wetting of GaLM on hard metals allows GaLM to form stable and well-defined patterns. However, the high surface tension of GaLM hinders the formation of highly uniform thin films even on metal substrates. To address this issue, Lacour et al. reported a method for producing smooth, flat GaLM thin films over large areas by evaporating pure gallium onto gold-coated microstructured substrates37,39. This method requires vacuum deposition, which is very slow. In addition, GaLM is generally not allowed for such devices due to possible embrittlement40. Evaporation also deposits the material on the substrate, so a pattern is required to create the pattern. We are looking for a way to create smooth GaLM films and patterns by designing topographic metal features that GaLM wets spontaneously and selectively in the absence of natural oxides. Here we report the spontaneous selective wetting of oxide-free EGaIn (typical GaLM) using the unique wetting behavior on photolithographically structured metal substrates. We create photolithographically defined surface structures at the micro level to study imbibition, thereby controlling the wetting of oxide-free liquid metals. The improved wetting properties of EGaIn on microstructured metal surfaces are explained by numerical analysis based on the Wenzel model and the impregnation process. Finally, we demonstrate large area deposition and patterning of EGaIn through self-absorption, spontaneous and selective wetting on microstructured metal deposition surfaces. Tensile electrodes and strain gauges incorporating EGaIn structures are presented as potential applications.
Absorption is capillary transport in which the liquid invades the textured surface 41, which facilitates the spreading of the liquid. We investigated the wetting behavior of EGaIn on metal microstructured surfaces deposited in HCl vapor (Fig. 1). Copper was chosen as the metal for the underlying surface. On flat copper surfaces, EGaIn showed a low contact angle of <20° in the presence of HCl vapor, due to reactive wetting31 (Supplementary Fig. 1). On flat copper surfaces, EGaIn showed a low contact angle of <20° in the presence of HCl vapor, due to reactive wetting31 (Supplementary Fig. 1). На плоских медных поверхностях EGaIn показал низкий краевой угол <20 ° в присутствии паров HCl из-за реактивного смачивания31 (дополнительный рисунок 1). On flat copper surfaces, EGaIn showed a low <20° contact angle in the presence of HCl vapor due to reactive wetting31 (Supplementary Figure 1).在平坦的铜表面上，由于反应润湿，EGaIn 在存在HCl 蒸气的情况下显示出<20° 的低接触角31（补充图1）。在平坦的铜表面上，由于反应润湿，EGaIn在存在HCl На плоских медных поверхностях EGaIn демонстрирует низкие краевые углы <20 ° в присутствии паров HCl из-за реактивного смачивания (дополнительный рисунок 1). On flat copper surfaces, EGaIn exhibits low <20° contact angles in the presence of HCl vapor due to reactive wetting (Supplementary Figure 1). We measured the close contact angles of EGaIn on bulk copper and on copper films deposited on polydimethylsiloxane (PDMS).
a Columnar (D (diameter) = l (distance) = 25 µm, d (distance between columns) = 50 µm, H (height) = 25 µm) and pyramidal (width = 25 µm, height = 18 µm) microstructures on Cu/PDMS substrates. b Time-dependent changes in the contact angle on flat substrates (without microstructures) and arrays of pillars and pyramids containing copper-coated PDMS. c, d Interval recording of (c) side view and (d) top view of EGaIn wetting on the surface with pillars in the presence of HCl vapor.
To assess the effect of topography on wetting, PDMS substrates with a columnar and pyramidal pattern were prepared, on which copper was deposited with a titanium adhesive layer (Fig. 1a). It was demonstrated that the microstructured surface of the PDMS substrate was conformally coated with copper (Supplementary Fig. 2). The time-dependent contact angles of EGaIn on patterned and planar copper-sputtered PDMS (Cu/PDMS) are shown in Figs. 1b. The contact angle of EGaIn on patterned copper/PDMS drops to 0° within ~1 min. The improved wetting of EGaIn microstructures can be exploited by the Wenzel equation\({{{{\rm{cos}}}}}}\,{\theta}_{{rough}}=r\,{{ { {{ \rm{ cos}}}}}}\,{\theta}_{0}\), where \({\theta}_{{rough}}\) represents the contact angle of the rough surface, \ (r\) Surface Roughness (= actual area/apparent area) and contact angle on the plane \({\theta}_{0}\). The results of enhanced wetting of EGaIn on the patterned surfaces are in good agreement with the Wenzel model, since the r values ​​for the back and pyramidal patterned surfaces are 1.78 and 1.73, respectively. This also means that an EGaIn drop located on a patterned surface will penetrate into the grooves of the underlying relief. It is important to note that very uniform flat films are formed in this case, in contrast to the case with EGaIn on unstructured surfaces (Supplementary Fig. 1).
From fig. 1c,d (Supplementary Movie 1) it can be seen that after 30 s, as the apparent contact angle approaches 0°, EGaIn starts to diffuse further away from the edge of the drop, which is caused by absorption (Supplementary Movie 2 and Supplementary Fig. 3). Previous studies of flat surfaces have associated the time scale of reactive wetting with the transition from inertial to viscous wetting. The size of the terrain is one of the key factors in determining whether self-priming occurs. By comparing the surface energy before and after imbibition from a thermodynamic point of view, the critical contact angle \({\theta}_{c}\)of imbibition was derived (see Supplementary Discussion for details). The result \({\theta}_{c}\) is defined as \({{{({\rm{cos))))))\,{\theta}_{c}=(1-{\ phi } _{S})/(r-{\phi}_{S})\) where \({\phi}_{s}\) represents the fractional area at the top of the post and \(r\) represents surface roughness. Imbibition can occur when \({\theta }_{c}\) > \({\theta }_{0}\), ie, the contact angle on a flat surface. Imbibition can occur when \({\theta }_{c}\) > \({\theta }_{0}\), ie, the contact angle on a flat surface. Впитывание может происходить, когда \ ({\ theta } _ {c} \) > \ ({\ theta } _ {0} \), т. е. контактный угол на плоской поверхности. Absorption can occur when \({\theta }_{c}\) > \({\theta }_{0}\), i.e. the contact angle on a flat surface.当\({\theta }_{c}\) > \({\theta }_{0}\)，即平面上的接触角时，会发生吸吸。当\({\theta }_{c}\) > \({\theta }_{0}\)，即平面上的接触角时，会发生吸吸。 Всасывание происходит, когда \ ({\ theta} _ {c} \) > \ ({\ theta} _ {0} \), контактный угол на плоскости. Suction occurs when \({\theta }_{c}\) > \({\theta }_{0}\), contact angle on the plane. For post-patterned surfaces, \(r\) and \({\phi}_{s}\) are calculated as \(1+\{(2\pi {RH})/{d}^{2} \ } \ ) and \(\pi {R}^{2}/{d}^{2}\), where \(R\) represents the column radius, \(H\) represents the column height, and \ (d\) is the distance between the centers of two pillars (Fig. 1a). For the post-structured surface in fig. 1a, the angle \({\theta}_{c}\) is 60°, which is larger than the \({\theta}_{0}\) plane (~25° ) in HCl vapor Oxide-free EGaIn on Cu/PDMS. Therefore, EGaIn droplets can easily invade the structured copper deposition surface in Fig. 1a due to absorption.
To investigate the effect of the topographic size of the pattern on the wetting and absorption of EGaIn, we varied the size of the copper-coated pillars. On fig. 2 shows the contact angles and absorption of EGaIn on these substrates. The distance l between the columns is equal to the diameter of the columns D and ranges from 25 to 200 μm. The height of 25 µm is constant for all columns. \({\theta}_{c}\) decreases with increasing column size (Table 1), which means that absorption is less likely on substrates with larger columns. For all sizes tested, \({\theta}_{c}\) is greater than \({\theta}_{0}\) and wicking is expected. However, absorption is rarely observed for post-patterned surfaces with l and D 200 µm (Fig. 2e).
a Time-dependent contact angle of EGaIn on a Cu/PDMS surface with columns of different sizes after exposure to HCl vapor. b–e Top and side views of EGaIn wetting. b D = l = 25 µm, r = 1.78. in D = l = 50 μm, r = 1.39. dD = l = 100 µm, r = 1.20. eD = l = 200 µm, r = 1.10. All posts have a height of 25 µm. These images were taken at least 15 minutes after exposure to HCl vapor. The droplets on EGaIn are water resulting from the reaction between gallium oxide and HCl vapor. All scale bars in (b – e) are 2 mm.
Another criterion for determining the likelihood of liquid absorption is the fixation of the liquid on the surface after the pattern has been applied. Kurbin et al. It has been reported that when (1) the posts are high enough, droplets will be absorbed by the patterned surface; (2) the distance between the columns is rather small; and (3) the contact angle of the liquid on the surface is sufficiently small42. Numerically \({\theta}_{0}\) of the fluid on a plane containing the same substrate material must be less than the critical contact angle for pinning, \({\theta}_{c,{pin)) } \ ), for absorption without pinning between posts, where \({\theta}_{c,{pin}}={{{{{\rm{arctan}}}}}}(H/\big \{ ( \sqrt {2}-1)l\big\})\) (see additional discussion for details). The value of \({\theta}_{c,{pin}}\) depends on the pin size (Table 1). Determine the dimensionless parameter L = l/H to judge whether the absorption occurs. For absorption, L must be less than the threshold standard, \({L}_{c}\) = 1/\(\big\{\big(\sqrt{2}-1\big){{\tan} } { \ theta}_{{0}}\large\}\). For EGaIn \(({\theta}_{0}={25}^{\circ})\) on a copper substrate \({L}_{c}\) is 5.2. Since the L column of 200 μm is 8, which is greater than the value of \({L}_{c}\), EGaIn absorption does not occur. To further test the effect of geometry, we observed self-priming of various H and l (Supplementary Fig. 5 and Supplementary Table 1). The results agree well with our calculations. Thus, L turns out to be an effective predictor of absorption; liquid metal stops absorbing due to pinning when the distance between the pillars is relatively large compared to the height of the pillars.
Wettability can be determined based on the surface composition of the substrate. We investigated the effect of surface composition on the wetting and absorption of EGaIn by co-depositing Si and Cu on pillars and planes (Supplementary Fig. 6). The EGaIn contact angle decreases from ~160° to ~80° as the Si/Cu binary surface increases from 0 to 75% at a flat copper content. For a 75% Cu/25% Si surface, \({\theta}_{0}\) is ~80°, which corresponds to \({L}_{c}\) equal to 0.43 according to the above definition . Because the columns l = H = 25 μm with L equal to 1 greater than the threshold \({L}_{c}\), the 75% Cu/25% Si surface after patterning does not absorb due to immobilization. Since the contact angle of EGaIn increases with the addition of Si, higher H or lower l is required to overcome pinning and impregnation. Therefore, since the contact angle (i.e. \({\theta}_{0}\)) depends on the chemical composition of the surface, it can also determine whether imbibition occurs in the microstructure.
EGaIn absorption on patterned copper/PDMS can wet the liquid metal into useful patterns. In order to evaluate the minimum number of column lines causing imbibition, the wetting properties of EGaIn were observed on Cu/PDMS with post-pattern lines containing different column line numbers from 1 to 101 (Fig. 3). Wetting mainly occurs in the post-patterning region. The EGaIn wicking was reliably observed and the wicking length increased with the number of rows of columns. Absorption almost never occurs when there are posts with two or less lines. This may be due to increased capillary pressure. For absorption to occur in a columnar pattern, the capillary pressure caused by the curvature of the EGaIn head must be overcome (Supplementary Fig. 7). Assuming a radius of curvature of 12.5 µm for a single row EGaIn head with a columnar pattern, the capillary pressure is ~0.98 atm (~740 Torr). This high Laplace pressure can prevent wetting caused by absorption of EGaIn. Also, fewer rows of columns can reduce the absorption force that is due to capillary action between EGaIn and columns.
a Drops of EGaIn on structured Cu/PDMS with patterns of different widths (w) in air (before exposure to HCl vapor). Rows of racks starting from the top: 101 (w = 5025 µm), 51 (w = 2525 µm), 21 (w = 1025 µm), and 11 (w = 525 µm). b Directional wetting of EGaIn on (a) after exposure to HCl vapor for 10 min. c, d Wetting of EGaIn on Cu/PDMS with columnar structures (c) two rows (w = 75 µm) and (d) one row (w = 25 µm). These images were taken 10 minutes after exposure to HCl vapor. Scale bars on (a, b) and (c, d) are 5 mm and 200 µm, respectively. The arrows in (c) indicate the curvature of the EGaIn head due to absorption.
The absorption of EGaIn in post-patterned Cu/PDMS allows EGaIn to be formed by selective wetting (Fig. 4). When a drop of EGaIn is placed on a patterned area and exposed to HCl vapor, the EGaIn drop collapses first, forming a small contact angle as the acid removes scale. Subsequently, absorption begins from the edge of the drop. Large-area patterning can be achieved from centimeter-scale EGaIn (Fig. 4a, c). Since absorption occurs only on the topographic surface, EGaIn only wets the pattern area and almost stops wetting when it reaches a flat surface. Consequently, sharp boundaries of the EGaIn patterns are observed (Fig. 4d, e). On fig. 4b shows how EGaIn invades the unstructured region, especially around the place where the EGaIn droplet was originally placed. This was because the smallest diameter of the EGaIn droplets used in this study exceeded the width of the patterned letters. Drops of EGaIn were placed on the pattern site by manual injection through a 27-G needle and syringe, resulting in drops with a minimum size of 1 mm. This problem can be solved by using smaller EGaIn droplets. Overall, Figure 4 demonstrates that spontaneous wetting of EGaIn can be induced and directed to microstructured surfaces. Compared to previous work, this wetting process is relatively fast and no external force is required to achieve complete wetting (Supplementary Table 2).
emblem of the university, the letter b, c in the form of a lightning bolt. The absorbing region is covered with an array of columns with D = l = 25 µm. d, enlarged images of ribs in e (c). Scale bars on (a–c) and (d, e) are 5 mm and 500 µm, respectively. On (c–e), small droplets on the surface after adsorption turn into water as a result of the reaction between gallium oxide and HCl vapor. No significant effect of water formation on wetting was observed. Water is easily removed through a simple drying process.
Due to the liquid nature of EGaIn, EGaIn coated Cu/PDMS (EGaIn/Cu/PDMS) can be used for flexible and stretchable electrodes. Figure 5a compares the resistance changes of original Cu/PDMS and EGaIn/Cu/PDMS under different loads. The resistance of Cu/PDMS rises sharply in tension, while the resistance of EGaIn/Cu/PDMS remains low in tension. On fig. 5b and d show SEM images and corresponding EMF data of raw Cu/PDMS and EGaIn/Cu/PDMS before and after voltage application. For intact Cu/PDMS, deformation can cause cracks in the hard Cu film deposited on PDMS due to elasticity mismatch. In contrast, for EGaIn/Cu/PDMS, EGaIn still well coats the Cu/PDMS substrate and maintains electrical continuity without any cracks or significant deformation even after strain is applied. The EDS data confirmed that gallium and indium from EGaIn were evenly distributed on the Cu/PDMS substrate. It is noteworthy that the thickness of the EGaIn film is the same and comparable with the height of the pillars. This is also confirmed by further topographical analysis, where the relative difference between the thickness of the EGaIn film and the height of the post is <10% (Supplementary Fig. 8 and Table 3). This is also confirmed by further topographical analysis, where the relative difference between the thickness of the EGaIn film and the height of the post is <10% (Supplementary Fig. 8 and Table 3). Это также подтверждается дальнейшим топографическим анализом, где относительная разница между толщиной пленки EGaIn и высотой столба составляет <10% (дополнительный рис. 8 и таблица 3). This is also confirmed by further topographical analysis, where the relative difference between EGaIn film thickness and column height is <10% (Supplementary Fig. 8 and Table 3).进一步的形貌分析也证实了这一点，其中EGaIn 薄膜厚度与柱子高度之间的相对差异<10%（补充图8 和表3）。 <10% Это также было подтверждено дальнейшим топографическим анализом, где относительная разница между толщиной пленки EGaIn и высотой столба составляла <10% (дополнительный рис. 8 и таблица 3). This was also confirmed by further topographical analysis, where the relative difference between EGaIn film thickness and column height was <10% (Supplementary Fig. 8 and Table 3). This imbibition-based wetting allows the thickness of EGaIn coatings to be well controlled and kept stable over large areas, which is otherwise challenging due to its liquid nature. Figures 5c and e compare the conductivity and resistance to deformation of the original Cu/PDMS and EGaIn/Cu/PDMS. In the demo, the LED turned on when connected to untouched Cu/PDMS or EGaIn/Cu/PDMS electrodes. When intact Cu/PDMS is stretched, the LED turns off. However, the EGaIn/Cu/PDMS electrodes remained electrically connected even under load, and the LED light only dimmed slightly due to the increased electrode resistance.
a Normalized resistance changes with increasing load on Cu/PDMS and EGaIn/Cu/PDMS. b, d SEM images and energy dispersive X-ray spectroscopy (EDS) analysis before (top) and after (bottom) polydiplexes loaded in (b) Cu/PDMS and (d) EGaIn/Cu/methylsiloxane. c, e LEDs attached to (c) Cu/PDMS and (e) EGaIn/Cu/PDMS before (top) and after (bottom) stretching (~30% stress). The scale bar in (b) and (d) is 50 µm.
On fig. 6a shows the resistance of EGaIn/Cu/PDMS as a function of strain from 0% to 70%. The increase and recovery of resistance is proportional to deformation, which is in good agreement with Pouillet’s law for incompressible materials (R/R0 = (1 + ε)2), where R is resistance, R0 is initial resistance, ε is strain 43. Other studies have shown that when When stretched, solid particles in a liquid medium can rearrange themselves and become more evenly distributed with better cohesion, thereby reducing the increase in drag 43, 44 . In this work, however, the conductor is >99% liquid metal by volume since the Cu films are only 100 nm thick. In this work, however, the conductor is >99% liquid metal by volume since the Cu films are only 100 nm thick. Однако в этой работе проводник состоит из >99% жидкого металла по объему, так как пленки Cu имеют толщину всего 100 нм. However, in this work, the conductor consists of >99% liquid metal by volume, since the Cu films are only 100 nm thick.然而，在这项工作中，由于Cu 薄膜只有100 nm 厚，因此导体是>99% 的液态金属（按体积计）。然而，在这项工作中，由于Cu 薄膜只有100 nm 厚，因此导体是>99% However, in this work, since the Cu film is only 100 nm thick, the conductor consists of more than 99% liquid metal (by volume). Therefore, we do not expect Cu to make a significant contribution to the electromechanical properties of conductors.
a Normalized change in EGaIn/Cu/PDMS resistance versus strain in the range 0–70%. The maximum stress reached before failure of the PDMS was 70% (Supplementary Fig. 9). Red dots are theoretical values ​​predicted by Puet’s law. b EGaIn/Cu/PDMS conductivity stability test during repeated stretch-stretch cycles. A 30% strain was used in the cyclic test. The scale bar on the inset is 0.5 cm. L is the initial length of EGaIn/Cu/PDMS before stretching.
The measurement factor (GF) expresses the sensitivity of the sensor and is defined as the ratio of change in resistance to change in strain45. GF increased from 1.7 at 10% strain to 2.6 at 70% strain due to the geometric change of the metal. Compared to other strain gauges, the GF EGaIn/Cu/PDMS value is moderate. As a sensor, although its GF may not be particularly high, the EGaIn/Cu/PDMS exhibits robust resistance change in response to a low signal to noise ratio load. To evaluate the conductivity stability of EGaIn/Cu/PDMS, the electrical resistance was monitored during repeated stretch-stretch cycles at 30% strain. As shown in fig. 6b, after 4000 stretching cycles, the resistance value remained within 10%, which may be due to the continuous formation of scale during repeated stretching cycles46. Thus, the long-term electrical stability of EGaIn/Cu/PDMS as a stretchable electrode and the reliability of the signal as a strain gauge were confirmed.
In this article, we discuss the improved wetting properties of GaLM on microstructured metal surfaces caused by infiltration. Spontaneous complete wetting of EGaIn was achieved on columnar and pyramidal metal surfaces in the presence of HCl vapor. This can be explained numerically based on the Wenzel model and the wicking process, which shows the size of the post-microstructure required for wicking-induced wetting. Spontaneous and selective wetting of EGaIn, guided by a microstructured metal surface, makes it possible to apply uniform coatings over large areas and form liquid metal patterns. EGaIn-coated Cu/PDMS substrates retain electrical connections even when stretched and after repeated stretching cycles, as confirmed by SEM, EDS, and electrical resistance measurements. In addition, the electrical resistance of Cu/PDMS coated with EGaIn changes reversibly and reliably in proportion to the applied strain, indicating its potential application as a strain sensor. Possible advantages provided by the liquid metal wetting principle caused by imbibition are as follows: (1) GaLM coating and patterning can be achieved without external force; (2) GaLM wetting on the copper-coated microstructure surface is thermodynamic. the resulting GaLM film is stable even under deformation; (3) changing the height of the copper-coated column can form a GaLM film with controlled thickness. In addition, this approach reduces the amount of GaLM needed to form the film, as the pillars occupy part of the film. For example, when an array of pillars with a diameter of 200 μm (with a distance between the pillars of 25 μm) is introduced, the volume of GaLM required for film formation (~9 μm3/μm2) is comparable to the film volume without pillars. (25 µm3/µm2). However, in this case, it must be taken into account that the theoretical resistance, estimated according to Puet’s law, also increases nine times. Overall, the unique wetting properties of liquid metals discussed in this article offer an efficient way to deposit liquid metals on a variety of substrates for stretchable electronics and other emerging applications.
PDMS substrates were prepared by mixing Sylgard 184 matrix (Dow Corning, USA) and hardener in ratios of 10:1 and 15:1 for tensile tests, followed by curing in an oven at 60°C. Copper or silicon was deposited on silicon wafers (Silicon Wafer, Namkang High Technology Co., Ltd., Republic of Korea) and PDMS substrates with a 10 nm thick titanium adhesive layer using a custom sputtering system. Columnar and pyramidal structures are deposited on a PDMS substrate using a silicon wafer photolithographic process. The width and height of the pyramidal pattern are 25 and 18 µm, respectively. The height of the bar pattern was fixed at 25 µm, 10 µm, and 1 µm, and its diameter and pitch varied from 25 to 200 µm.
The contact angle of EGaIn (gallium 75.5%/indium 24.5%, >99.99%, Sigma Aldrich, Republic of Korea) was measured using a drop-shape analyzer (DSA100S, KRUSS, Germany). The contact angle of EGaIn (gallium 75.5%/indium 24.5%, >99.99%, Sigma Aldrich, Republic of Korea) was measured using a drop-shape analyzer (DSA100S, KRUSS, Germany). Краевой угол EGaIn (галлий 75,5 %/индий 24,5 %, >99,99 %, Sigma Aldrich, Республика Корея) измеряли с помощью каплевидного анализатора (DSA100S, KRUSS, Германия). The edge angle of EGaIn (gallium 75.5%/indium 24.5%, >99.99%, Sigma Aldrich, Republic of Korea) was measured using a droplet analyzer (DSA100S, KRUSS, Germany). EGaIn（镓75.5%/铟24.5%，>99.99%，Sigma Aldrich，大韩民国）的接触角使用滴形分析仪（DSA100S，KRUSS，德国）测量。 EGaIn (gallium75.5%/indium24.5%, >99.99%, Sigma Aldrich, 大韩民国) was measured using a contact analyzer (DSA100S, KRUSS, Germany). Краевой угол EGaIn (галлий 75,5%/индий 24,5%, >99,99%, Sigma Aldrich, Республика Корея) измеряли с помощью анализатора формы капли (DSA100S, KRUSS, Германия). The edge angle of EGaIn (gallium 75.5%/indium 24.5%, >99.99%, Sigma Aldrich, Republic of Korea) was measured using a shape cap analyzer (DSA100S, KRUSS, Germany). Place the substrate in a 5 cm × 5 cm × 5 cm glass chamber and place a 4–5 μl drop of EGaIn onto the substrate using a 0.5 mm diameter syringe. To create an HCl vapor medium, 20 μL of HCl solution (37 wt.%, Samchun Chemicals, Republic of Korea) was placed next to the substrate, which was evaporated enough to fill the chamber within 10 s.
The surface was imaged using SEM (Tescan Vega 3, Tescan Korea, Republic of Korea). EDS (Tescan Vega 3, Tescan Korea, Republic of Korea) was used to study elemental qualitative analysis and distribution. The EGaIn/Cu/PDMS surface topography was analyzed using an optical profilometer (The Profilm3D, Filmetrics, USA).
To investigate the change in electrical conductivity during stretching cycles, the samples with and without EGaIn were clamped on the stretching equipment (Bending & Stretchable Machine System, SnM, Republic of Korea) and were electrically connected to a Keithley 2400 source meter. To investigate the change in electrical conductivity during stretching cycles, the samples with and without EGaIn were clamped on the stretching equipment (Bending & Stretchable Machine System, SnM, Republic of Korea) and were electrically connected to a Keithley 2400 source meter. Для исследования изменения электропроводности во время циклов растяжения образцы с EGaIn и без него закрепляли на оборудовании для растяжения (Bending & Stretchable Machine System, SnM, Республика Корея) и электрически подключали к измерителю источника Keithley 2400. To study the change in electrical conductivity during stretching cycles, samples with and without EGaIn were mounted on a stretching equipment (Bending & Stretchable Machine System, SnM, Republic of Korea) and electrically connected to a Keithley 2400 source meter. To study the change in electrical conductivity during stretching cycles, samples with and without EGaIn were mounted on a stretching device (Bending and Stretching Machine Systems, SnM, Republic of Korea) and electrically connected to a Keithley 2400 SourceMeter. Measures the change in resistance in the range from 0% to 70% of sample strain. For the stability test, the change in resistance was measured over 4000 30% strain cycles.
For more information on study design, see the Nature study abstract linked to this article.
Data supporting the results of this study are presented in the Supplementary Information and Raw Data files. This article provides the original data.
Daeneke, T. et al. Liquid Metals: Chemical Basis and Applications. Chemical. society. 47, 4073–4111 (2018).
Lin, Y., Genzer, J. & Dickey, MD Attributes, fabrication, and applications of gallium‐based liquid metal particles. Lin, Y., Genzer, J. & Dickey, MD Attributes, fabrication, and applications of gallium-based liquid metal particles. Lin, Y., Genzer, J. and Dickey, M.D. Properties, fabrication and application of gallium-based liquid metal particles. Lin, Y., Genzer, J. & Dickey, MD 镓基液态金属颗粒的属性、制造和应用。 Lin, Y., Genzer, J. & Dickey, MD Lin, Y., Genzer, J. and Dickey, M.D. Properties, fabrication and application of gallium-based liquid metal particles. Advanced science. 7, 2000–192 (2020).
Koo, HJ, So, JH, Dickey, MD & Velev, OD Towards all‐soft matter circuits: prototypes of quasi‐liquid devices with memristor characteristics. Koo, HJ, So, JH, Dickey, MD & Velev, OD Towards all-soft matter circuits: prototypes of quasi-liquid devices with memristor characteristics. Koo, H. J., So, J. H., Dickey, M. D., and Velev, O. D. To circuits composed entirely of soft matter: Prototypes of quasi-liquid devices with memristor characteristics. Koo, HJ, So, JH, Dickey, MD & Velev, OD 走向全软物质电路：具有忆阻器特性的准液体设备原型。 Koo, HJ, So, JH, Dickey, MD & Velev, OD Koo, H. J., So, J. H., Dickey, M. D., and Velev, O. D. Towards Circuits All Soft Matter: Prototypes of Quasi-Fluid Devices with Memristor Properties. Advanced alma mater. 23, 3559–3564 (2011).
Bilodeau, RA, Zemlyanov, DY & Kramer, RK Liquid metal switches for environmentally responsive electronics. Bilodeau, RA, Zemlyanov, DY & Kramer, RK Liquid metal switches for environmentally responsive electronics. Bilodo R.A., Zemlyanov D.Yu., Kramer R.K. Liquid metal switches for environmentally friendly electronics. Bilodeau, RA, Zemlyanov, DY & Kramer, RK 用于环境响应电子产品的液态金属开关。 Bilodeau, RA, Zemlyanov, DY & Kramer, RK Bilodo R.A., Zemlyanov D.Yu., Kramer R.K. Liquid metal switches for environmentally friendly electronics. Advanced alma mater. Interface 4, 1600913 (2017).
So, JH, Koo, HJ, Dickey, MD & Velev, OD Ionic current rectification in soft‐matter diodes with liquid‐metal electrodes. So, JH, Koo, HJ, Dickey, MD & Velev, OD Ionic current rectification in soft-matter diodes with liquid-metal electrodes. Так, JH, Koo, HJ, Dickey, MD & Velev, OD Ионное выпрямление тока в диодах из мягкого материала с электродами из жидкого металла. Thus, JH, Koo, HJ, Dickey, MD & Velev, OD Ionic current rectification in soft material diodes with liquid metal electrodes. So, JH, Koo, HJ, Dickey, MD & Velev, OD 带液态金属电极的软物质二极管中的离子电流整流。 So, JH, Koo, HJ, Dickey, MD & Velev, OD Так, JH, Koo, HJ, Dickey, MD & Velev, OD Ионное выпрямление тока в диодах из мягкого материала с жидкометаллическими электродами. Thus, JH, Koo, HJ, Dickey, MD & Velev, OD Ionic current rectification in soft material diodes with liquid metal electrodes. Extended capabilities. alma mater. 22, 625–631 (2012).
Kim, M.-G., Brown, DK & Brand, O. Nanofabrication for all-soft and high-density electronic devices based on liquid metal. Kim, M.-G., Brown, DK & Brand, O. Nanofabrication for all-soft and high-density electronic devices based on liquid metal. Kim, M.-G., Brown, D.K. and Brand, O. Nanofabrication for all-soft and high-density liquid metal-based electronic devices. Kim, M.-G., Brown, D.K., and Brand, O. Nanofabrication of high-density, all-soft electronics based on liquid metal. National commune. 11, 1–11 (2020).
Guo, R. et al. Cu-EGaIn is an extensible electron shell for interactive electronics and CT localization. alma mater. Level. 7. 1845–1853 (2020).
Lopes, PA, Paisana, H., De Almeida, AT, Majidi, C. & Tavakoli, M. Hydroprinted electronics: ultrathin stretchable Ag–In–Ga E-skin for bioelectronics and human–machine interaction. Lopes, PA, Paisana, H., De Almeida, AT, Majidi, C. & Tavakoli, M. Hydroprinted electronics: ultrathin stretchable Ag–In–Ga E-skin for bioelectronics and human–machine interaction. Lopez, P.A., Paysana, H., De Almeida, A.T., Majidi, K., and Tawakoli, M. Hydroprinting Electronics: Ag-In-Ga Ultrathin Stretchable Electronic Skin for Bioelectronics and Human-Machine Interaction. Lopes, PA, Paisana, H., De Almeida, AT, Majidi, C. & Tavakoli, M. Hydroprinted electronics: ultrathin stretchable Ag-In-Ga E-skin for bioelectronics and human-machine interaction. Lopes, PA, Paisana, H., De Almeida, AT, Majidi, C. & Tavakoli, M. Hydroprinted electronics: ultrathin stretchable Ag-In-Ga E-skin for bioelectronics and human-machine interaction. Lopez, P.A., Paysana, H., De Almeida, A.T., Majidi, K., and Tawakoli, M. Hydroprinting Electronics: Ag-In-Ga Ultrathin Stretchable Electronic Skin for Bioelectronics and Human-Machine Interaction. ACS
Yang, Y. et al. Ultra-tensile and engineered triboelectric nanogenerators based on liquid metals for wearable electronics. SAU Nano 12, 2027–2034 (2018).
Gao, K. et al. Development of microchannel structures for overstretch sensors based on liquid metals at room temperature. the science. Report 9, 1–8 (2019).
Chen, G. et al. EGaIn superelastic composite fibers can withstand 500% tensile strain and have excellent electrical conductivity for wearable electronics. ACS refers to alma mater. Interface 12, 6112–6118 (2020).
Kim, S., Oh, J., Jeong, D. & Bae, J. Direct wiring of eutectic gallium–indium to a metal electrode for soft sensor systems. Kim, S., Oh, J., Jeong, D. & Bae, J. Direct wiring of eutectic gallium–indium to a metal electrode for soft sensor systems. Kim, S., Oh, J., Jeon, D. and Bae, J. Direct bonding of eutectic gallium-indium to metal electrodes for soft sensing systems. Kim, S., Oh, J., Jeong, D. & Bae, J. 将共晶镓-铟直接连接到软传感器系统的金属电极。 Kim, S., Oh, J., Jeong, D. & Bae, J. 就共晶gallium-indium metal electrode directly attached to soft sensor system. Kim, S., Oh, J., Jeon, D. and Bae, J. Direct bonding of eutectic gallium-indium to metal electrodes for soft sensor systems. ACS refers to alma mater. Interfaces 11, 20557–20565 (2019).
Yun, G. et al. Liquid metal-filled magnetorheological elastomers with positive piezoelectricity. National commune. 10, 1–9 (2019).
Kim, K.K. Highly sensitive and stretchable multidimensional strain gauges with percolation grids of prestressed anisotropic metal nanowires. Nanolet. 15, 5240–5247 (2015).
Guo, H., Han, Y., Zhao, W., Yang, J. & Zhang, L. Universally autonomous self-healing elastomer with high stretchability. Guo, H., Han, Y., Zhao, W., Yang, J. & Zhang, L. Universally autonomous self-healing elastomer with high stretchability. Guo, H., Han, Yu., Zhao, W., Yang, J., and Zhang, L. Versatile self-healing elastomer with high elasticity. Guo, H., Han, Y., Zhao, W., Yang, J. & Zhang, L. 具有高拉伸性的通用自主自愈弹性体。 Guo, H., Han, Y., Zhao, W., Yang, J. & Zhang, L. Guo H., Han Yu, Zhao W., Yang J. and Zhang L. Versatile offline self-healing high tensile elastomers. National commune. 11, 1–9 (2020).
Zhu X. et al. Ultradrawn metallic conductive fibers using liquid metal alloy cores. Extended capabilities. alma mater. 23, 2308–2314 (2013).
Khan, J. et al. Study of electrochemical pressing of liquid metal wire. ACS refers to alma mater. Interface 12, 31010–31020 (2020).
Lee H. et al. Evaporation-induced sintering of liquid metal droplets with bionanofibers for flexible electrical conductivity and responsive actuation. National commune. 10, 1–9 (2019).
Dickey, M.D. et al. Eutectic gallium-indium (EGaIn): liquid metal alloy used to form stable structures in microchannels at room temperature. Extended capabilities. alma mater. 18, 1097–1104 (2008).
Wang, X., Guo, R. & Liu, J. Liquid metal based soft robotics: materials, designs, and applications. Wang, X., Guo, R. & Liu, J. Liquid metal based soft robotics: materials, designs, and applications. Wang, X., Guo, R. and Liu, J. Soft robotics based on liquid metal: materials, construction and applications. Wang, X., Guo, R. & Liu, J. 基于液态金属的软机器人：材料、设计和应用。 Wang, X., Guo, R. & Liu, J. Liquid metal-based soft robots: materials, design and applications. Wang, X., Guo, R. and Liu, J. Soft robots based on liquid metal: materials, construction and applications. Advanced alma mater. technology 4, 1800549 (2019).