Polydimethylsiloxane Surface Research Articles

Design and Fabrication of Metallic-Conductive Polymer-Based Hybrid Film Interconnections for Stretchable Electronic Devices

Stretchable circuit is a technological innovation that has transformed the microelectronic landscape due to its enormous applications in the field of medicine. The consistency or durability of health monitoring devices can increase the dependability with which non-invasive clinical measures are collected. Metal–conductive polymer (CP) hybrid interconnects and metal–polyimide dual-layered interconnects were all produced as stretchable interconnections. Stretchable substrate for all of the interconnects was selected as soft elastomer polydimethylsiloxane (PDMS). However, the PDMS substrate presents challenges because it is temperature sensitive, limiting the process temperature. The extreme hydrophobic nature of the PDMS surface makes it difficult to deposit components that contain water and results in poor adhesion with different metals. Following the development of processes for fabricating materials on the PDMS substrate, methods for resolving these issues were investigated.

Biofilm Formation of Two Different Marine Bacteria on Modified PDMS Surfaces is Affected by Surface Roughness and Topography.

Different strategies were tested to reduce biofilm formation of the model marine bacteria Cobetia marina and Marinobacter hydrocarbonoclasticus on cross-linked polydimethylsiloxane (PDMS) coated aluminum and cellulose acetate surfaces modified by addition of multi-walled carbon nanotubes (MWCNT) or exposure of the surfaces to bromine vapors in the presence and absence of UV irradiation. The three surface modifications explored led to important reductions in biofilm formation for the two marine bacteria, up to 30% in the case of exposure to Br2(g). Biofouling reduction could be correlated to surface properties in all cases through the introduction of a quantitative theoretical model based on an effective roughness parameter, Raeff, that accounted for the different morphological changes observed. The model considers the possibility of bacterial inclusion into large surface wells, as observed by AFM in the case of Br2(g) + UV light treatment. In addition, a linear relationship was observed between biofouling reduction and the Raeff effective roughness parameter.

Spatio-temporal programming of lyotropic phase transition in nanoporous microfluidic confinements

HypothesisThe nanoporous polydimethylsiloxane (PDMS) surfaces of a rectangular microfluidic channel, selectively uptakes water molecules, concentrating the solute molecules in an aqueous phase, that could drive phase transitions. Factors such as surface wettability, channel geometry, the surface-to-volume ratio, and surface topography of the confinements could play a key role in tuning the phase transitions spatio-temporally. ExperimentsUsing a lyotropic chromonic liquid crystal as model biological material, confined within nanoporous microfluidic environments, we study molecular assembly driven by nanoporous substrates. By combining timelapse polarized imaging, quantitative image processing, and a simple mathematical model, we analyze the phase transitions and construct a master diagram capturing the role of surface wettability, channel geometry and embedded topography on programmable lyotropic phase transitions. FindingsIntrinsic PDMS nanoporosity and confinement cross-section, together with the imposed wettability regulate the rate of the N-M phase transition; whereas the microfluidic geometry and embedded topography enable phase transition at targeted locations. We harness the emergent long-range order during N-M transition to actuate elasto-advective transport of embedded micro-cargo, demonstrating particle manipulation concepts governed by tunable phase transitions. Our results present a programmable physical route to material assembly in microfluidic environment, and offer a new paradigm for assembling genetic components, biological cargo, and minimal synthetic cells.

Triboelectric active pressure sensor with ultrabroad linearity range by femtosecond laser shaping based on electrons dynamics control

Pressure sensor plays an extremely important role for the pulse monitoring, which has greatly demands of sensitivity and ultrabroad linearity sensing range. Here, we propose a active triboelectric pressure sensor with ultrabroad linearity range by femtosecond laser shaping gradient height microstructures for triboelectric layers. We fabricate microcolumn arrays with gradient height on polydimethylsiloxane (PDMS) surfaces using femtosecond laser spatial-temporal shaping technology to shape Gaussian beam into double-pulse Bessel beams, and supplementing it with wet etching and imprinting technology. Based on these fabricated PDMS layers, the effects of the microcolumns with different gradients on the linearity range of the sensor are systematically characterized. When the height difference of the microcolumns is 2 µm, the sensor can maintain a high linearity (R2 ≈ 0.99996) with a sensitivity of 0.304 V·kPa-1 even when the detection pressure range reaches 0–330 kPa, which increase the linearity range of the pressure measurements by 66 times than that with uniform height microcolumns. As practical applications of the proposed sensor, it is shown to sense weak airflow, generate high-stability Morse code signals, and enable the detection of pathological heart rates. These results highlight the potential applications of self-powered triboelectric pressure sensors for health monitoring and human machine interaction.

Highly Durable Bidirectional Rotary Triboelectric Nanogenerator with a Self-Lubricating Texture and Self-Adapting Contact Synergy for Wearable Applications.

Sliding-freestanding triboelectric nanogenerators (SF-TENGs) are desirable for application in wearable power sources; however, improving their durability is the primary challenge. Meanwhile, few studies focus on enhancing the service life of tribo-materials, especially from an anti-friction perspective during dry operation. Herein, for the first time, a surface-textured film with self-lubricating property is introduced into the SF-TENG as a tribo-material, which is obtained by the self-assembly of hollow SiO2 microspheres (HSMs) close to a polydimethylsiloxane (PDMS) surface under vacuum conditions. The PDMS/HSMs film with micro-bump topography simultaneously reduces the dynamic coefficient of friction from 1.403 to 0.195 and increases the electrical output of SF-TENG by an order of magnitude. Subsequently, a textured film and self-adapting contact synergized bidirectional rotary TENG (TAB-TENG) is developed, and the superiorities of the soft flat rotator with bidirectional reciprocating rotation are systematically investigated. The obtained TAB-TENG exhibits a remarkable output stability and an outstanding mechanical durability over 350 000 cycles. Furthermore, a smart foot system for stepping energy harvesting and wireless walking states monitoring is realized. This study proposes a pioneering strategy for extending the lifetime of SF-TENGs and advances it toward practical wearable applications.

Ink-based transparent compliant electrode for direct coating on untreated hydrophobic PDMS surface

Polydimethylsiloxane (PDMS) is widely used as the substrate for wearable sensors and elastomeric actuators because of its good dielectric property, stretchability, thermal/chemical resistance, biocompatibility, and transparency. PDMS-based stretchable sensors and electroactive actuators need a coating of thin compliant electrodes. However, PDMS is hydrophobic with water contact angle above 120°. Such low surface energy of PDMS creates issues for uniform coating of ink-based electrodes and/or their adhesion. Similarly, metal thin-film or nanowire-based materials coated on PDMS easily peels off. Surface treatments like UV/plasma exposure can temporarily increase PDMS's surface energy. However, these surfaces return to its original state within hours leaving behind a brittle surface layer that cracks upon stretching. To address these issues, we formulated a viscous composite ink with PEDOT:PSS and PDMS that can easily be coated on untreated PDMS by blade casting, screen printing, and so on. These coatings are highly transparent, stretchable, electrically conductive and work as compliant electrodes. We fabricated transparent dielectric elastomer actuators by coating PEDOT:PSS/PDMS composite ink on Elastosil (PDMS) substrates. The actuation strain and breakdown-fields were slightly lower compared to DEA with conventional graphite electrodes. However, the additional self-clearing capability of PEDOT:PSS/PDMS electrodes enhanced robustness of the DEA in events of localized dielectric breakdown.

Why does SLIPS inhibit P.aeruginosa initial adhesion in static condition?

Slippery liquid-infused porous surfaces (SLIPSs) have distinguished themselves in inhibiting bacteria attachment and biofilm development in static conditions. However, underlying antifouling mechanisms, especially from gene level in bioinformatics, is still lacking. In this work, we investigated the initial attachment difference of Pseudomonas aeruginosa PAO1 on polydimethylsiloxane (PDMS) surface and the infused silicone slippery surface (i-PDMS). RNA sequencing (RNA-seq) was used to investigate the differences in the expression of PAO1 gene on elastomer surface during initial adhesion before and after oil injection. Compared with PDMS, bacterial attachment on i-PDMS was remarkably decreased 98.0 ± 0.7 % within 10 mins. And the antifouling ability of i-PDMS significantly outperformed PDMS throughout the entire culture period of PAO1 (14 days) in static conditions. RNA-seq reveals that the down-regulated PA1382 of PAO1 in bulk near the i-PDMS surfaces may inhibit bacterial initial adhesion. PA1382 gene encodes type II secretion outer membranes (OM) secretin, also known as type II secretion system (T2SS) protein GspD, which is involved in regulating the opening or closing of exoprotein channels, influencing bacterial adhesion and biofilm formation by controlling the secretion of toxins or effectors. Our findings provide a deeper understanding of the mechanism by which SLIPS inhibits initial bacterial adhesion.

One Droplet toward Efficient Alcohol Detection Using Femtosecond Laser Textured Micro/Nanostructured Surface with Superwettability.

Alcohol with different concentrations is commonly used in food, industry, and medicine fields all over the world. However, current methods for detecting alcohol concentration are restricted to large sample consumption, additional senergy consuming, or complex operations. Here, inspired by superwettability of lotus leaves, a superhydrophobic and superorganophilic surface is designed on the polydimethylsiloxane (PDMS) for one droplet efficient alcohol detection, which is prepared via femtosecond laser direct writing technology. Meanwhile, the contact angles of droplets with various alcohol concentrations on the laser-treated PDMS (LTP) surface are different. Based on the above characteristic, alcohol concentration through contact angle measurement without any external energy is directly detected, which is simple and efficient. Furthermore, it is worth noting that the LTP surface remains stable wettability after 1000 water-ethanol cycles and 300 days tests in air, indicating strong surface repeatability and stability. Significantly, the LTP surface has a broad potential application in one droplet detecting alcohol concentration, fake or genuine wine, and alcohol molecules. This work provides a new strategy to fabricate a superwetting surface for efficient one droplet alcohol detection.

The influence of ions on the lubricative abilities of mucin and the role of sialic acids

Mucus reduces friction between epithelial surfaces by providing lubrication in the boundary and mixed regime. Mucins, the main macromolecule, are heavily glycosylated proteins that polymerise and retain water molecules, resulting in a hydrated biogel. It is assumed that positively charged ions can influence mucin film structure by screening the electrostatic repulsions between the negatively charged glycans on mucin moieties and draw in water molecules via hydration shells. The ionic concentration can vary significantly in different mucus systems and here we show that increasing the ionic concentration in mucin films leads to an increase in lubrication between two polydimethylsiloxane surfaces at sliding contact in a compliant oral mimic. Mucins were found to bind sodium ions in a concentration-dependent manner and increased ionic concentration appears to cause mucin films to swell when assessed by Quartz Crystal hiMicrobalance with Dissipation (QCM-D) analysis. Furthermore, we determined that the removal of negatively charged sialic acid moieties by sialidase digestion resulted in reduced adsorption to hydrophilic surfaces but did not affect the swelling of mucin films with increasing ionic concentrations. Moreover, the coefficient of friction was increased with sialic acid removal, but lubrication was still increased with increasing ionic concentrations. Taken together this suggests that sialic acids are important for lubrication and may exert this through the sacrificial layer mechanism. Ionic concentration appears to influence mucin films and their lubrication, and sialic acids, at least partly, may be important for ion binding.

Surface-modified polydimethylsiloxane with soft-plasma as dielectric layer for flexible artificial synaptic transistors

The conductance of field-effect transistors (FETs) can be effectively stimulated by electrical or optical pulses, which could be potentially applied as artificial synapses. The combination of solution processable elastomers with polymer semiconductors has attracted extensive interest in all-polymer flexible synaptic electronics, due to the flexible and light weight property. In this work, a glow-discharge soft-plasma is utilized to treat the widely-used elastomer polydimethylsiloxane (PDMS) layer. Subsequently, the surface energy of PDMS is increased, from the contact angle of 100° to fully spread state and induce high charge trapping density (Δn, about 1.9 × 1012 cm−2 under 525 nm green light irradiation and positive gate-bias stress) on the surface. The PDMS surface are homogenously etched by soft plasma without damaging underneath materials, which can be used as dielectric layer in organic FETs. Thus, prepared organic FETs warrant quick charge transfer dynamics between PDMS surface and semiconductor layer. Upon which, flexible synaptic FETs are demonstrated, corresponding synaptic functions like excitatory postsynaptic current (EPSC), paired pulse facilitation (PPF), short-term plasticity (STP) are all realized. Furthermore, the handwritten digits with an accuracy of 86.2% are realized utilizing prepared synaptic devices.

Stiffening of polydimethylsiloxane surface as result of exposure to low‐pressure argon discharge plasma

AbstractPolydimethylsiloxane (PDMS) surface has been exposed to negative glow discharge plasma of a low‐pressure discharge in pure argon for a duration varying from 10 s to 2 min. Shallow atomic force microscopy indentation experiments were performed to investigate the effect of plasma treatment on PDMS surface stiffness and adhesion energy to the silicon nitride indenter surface. The results showed an important increase in Young's modulus and a slight increase of work of adhesion. X‐ray photoelectron spectroscopy investigation of plasma‐treated PDMS surface showed a decrease of atomic content of carbon accompanied by an increase of oxygen content and suggests that the stiffening of PDMS surface can be attributed to generation of new cross‐linking Si–O–Si and Si–CH2–CH2–Si bonds between PDMS molecules.

Friction measurement of modified Polydimethylsiloxane(PDMS) surfaces inspired by Malayopython Reticulatus

The lack of limbs on snakes enables its ventral scales to be in almost constant contact with the substrate. Their skin is presumably adapted to generate high and low friction to slither. This frictional characteristics in snakes were hypothesized to be contributed by the be tooth-shaped or denticle-like microstructures found on the snake ventral scales. The frictional properties of the microstructures found on snake ventral scales was studied and its feasibility as an inspiration for surface modifications was observed. This study was carried out to analyze the frictional anisotropy exhibit by the snake ventral scale microstructures and also how it changes the frictional properties of the PDMS surface when the microstructures are replicated on to it. The PDMS embedded-elastomeric stamping method was used in this experiment to replicate the snake ventral scales onto the PDMS. Based on the data collected the microstructures on the snake ventral scales does exhibit frictional anisotropy. The PDMS with replicated snakeskin microstructures displays higher COF compared to PDMS with smooth surface. When sliding on most types of surfaces, the COF of real snakeskin and replicated snakeskin is higher if the surface is semi wet. Whereas for smooth PDMS the COF is lower when the surfaces are semi wet. Generally, from both experiments, when the replicated snakeskin is sliding on the surface in the lateral direction, it is observed that the COF is the lowest followed by the caudal then the rostral direction.

Deposition of polypyrrole on wrinkled polydimethylsiloxane to fabricate stretchable conductive membranes for multifunctional bioreactor applications

Physical cues are critical for regulating the differentiation of myoblasts in vitro, and mechanical and electrical stimulations are the most effective ones. Therefore, we developed a multifunctional bioreactor to simultaneously perform these two stimulations. Conductive polypyrrole (PPy) was prepared on a flexible polydimethylsiloxane (PDMS) substrate to form a highly stretchable conductive PPy/PDMS membrane. To promote PPy deposition, surfaces of PDMS were etched by NaOH to increase roughness and functionality. These PPy/PDMS membranes maintained electrical resistance lower than 20 kΩ when the tensile strain was lower than 35 % and was reliable for repeated cyclic stretching at 10 % of tensile strain. These PPy/PDMS membranes were dark but transparent and thus were feasible to directly monitor cells on their surfaces. Therefore, we applied PPy/PDMS membranes to build a bioreactor for the application of electrical and mechanical stimulations. Cyclic stretching effectively promoted myotube formation. Furthermore, C2C12 cells under cyclic stretching were aligned perpendicular to the stretching direction, so the formed myotubes were parallel to each other. The combination of cyclic stretching and electrical stimulation demonstrated synergistic effects and myotube alignment can be preserved. Overall, this bioreactor constructed by PPy/PDMS membranes can perform two diverse stimulations and is potential for muscle tissue engineering applications.

Competitive Adsorption of a Monoclonal Antibody and Nonionic Surfactant at the PDMS/Water Interface.

Interfacial adsorption of monoclonal antibodies (mAbs) can cause structural deformation and induce undesired aggregation and precipitation. Nonionic surfactants are often added to reduce interfacial adsorption of mAbs which may occur during manufacturing, storage, and/or administration. As mAbs are commonly manufactured into ready-to-use syringes coated with silicone oil to improve lubrication, it is important to understand how an mAb, nonionic surfactant, and silicone oil interact at the oil/water interface. In this work, we have coated a polydimethylsiloxane (PDMS) nanofilm onto an optically flat silicon substrate to facilitate the measurements of adsorption of a model mAb, COE-3, and a commercial nonionic surfactant, polysorbate 80 (PS-80), at the siliconized PDMS/water interface using spectroscopic ellipsometry and neutron reflection. Compared to the uncoated SiO2 surface (mimicking glass), COE-3 adsorption to the PDMS surface was substantially reduced, and the adsorbed layer was characterized by the dense but thin inner layer of 16 Å and an outer diffuse layer of 20 Å, indicating structural deformation. When PS-80 was exposed to the pre-adsorbed COE-3 surface, it removed 60 wt % of COE-3 and formed a co-adsorbed layer with a similar total thickness of 36 Å. When PS-80 was injected first or as a mixture with COE-3, it completely prevented COE-3 adsorption. These findings reveal the hydrophobic nature of the PDMS surface and confirm the inhibitory role of the nonionic surfactant in preventing COE-3 adsorption at the PDMS/water interface.

Highly flexible, stretchable, durable conductive electrode for human-body-attachable wearable sensor application

Flexible/stretchable electrodes based on conductive polymers are used in various fields, including wearable devices and human body sensors. However, the durability of flexible/stretchable electrodes is insufficient. In this study, a carbon nanotube (CNT) electrode layer was formed on a polydimethylsiloxane (PDMS) surface with a controlled precuring time using a simple spray-coating method. The electrical properties and durability of the CNT-based conductive polymers were evaluated. To evaluate the durability of the electrodes, bending, stretching, tribo, and scratch tests were performed. The degree of embedding of the CNT electrode layer on the PDMS surface differed according to the PDMS precuring time, which showed a difference in durability. The case in which the CNTs were coated at a precuring time of approximately 8–12 h had the best durability. It was verified that CNT-embedded PDMS electrodes fabricated under optimal conditions can be attached to the skin of human joints and used as human-body-attachable wearable sensors that measure changes in electrical resistance according to joint movement, resulting in excellent elasticity, durability, and performance.

Surface properties of [formula omitted]m and sub-[formula omitted]m polydimethylsiloxane thin films after oxygen plasma treatment

Polydimethylsiloxane (PDMS) is widely used in many areas of science due to its outstanding properties. The continuous expansion of its applications is evidenced by a large number of research studies dedicated to modifying this soft material, ultimately leading to tailored properties. These studies highlighted the important role of film thickness (in the range of a few micrometers to millimeters) on surface properties, including mechanical properties, wettability, and surface topography. In this work, we investigated these surface properties of pristine as well as oxygen plasma-treated PDMS, in a thickness range of submicrometer and micrometer. We explored the effects of film thickness, dilution ratio, and plasma treatment time on effective Young’s modulus, surface topography (buckling structures), and wettability (hydrophobicity recovery) of the PDMS surfaces by conducting force–distance measurements, atomic force microscopy (AFM) and contact angle (CA) measurements, respectively, over a period of more than one month after the plasma treatment. The results of effective Young’s modulus on pristine PDMS show a high correlation with the dilution ratio and no dependency on the thickness. The characterized waviness (λ) and amplitude (A) of the resulting buckling structures forming on the plasma-treated surfaces reveal a correlation with film thickness, which is not included in the theoretical predictions. The results of CAs show a faster recovery process for the advancing than for the receding condition, and uncover a high correlation with both film thickness and dilution ratio for short-time plasma treatment. Furthermore, the buckling structures as well as the hydrophobicity recovery process in this work revealed a significantly different domain in comparison to the studies in literature, where these properties of PDMS membranes with a thickness ranging from a few micrometers to a few millimeters have been investigated.

Tracking and Erosion of Polydimethlysiloxane With Different Molecular Weight for Outdoor Insulation

In this paper, the degradation mechanisms of unfilled polydimethylsiloxane with different molecular weights is investigated under dry-band arcing using the inclined plane tracking and erosion test and material characterization techniques. Tracks of carbonaceous residue formed as byproducts of radical-based crosslinking are prevalent over erosion as the molecular weight increases. Erosion becomes dominant with polydimethylsiloxane that undergoes mainly depolymerization during degradation at lower molecular weights. Accordingly, tracking due to a progressive carbonaceous residue formed on the surface is the degradation pattern observed under the dry-band arcing for the polydimethylsiloxane with higher molecular weights (45000 and 28000 g/mol) during the inclined plane test, whereas erosion due to depolymerization is more evident on the polydimethylsiloxane surfaces with lower molecular weights (17200 and 9400 g/mol). This study highlights the possibility to tune the tracking and erosion tendency of silicone rubber outdoor insulation by controlling the molecular weight of the organosiloxane base, without the sole reliance on fillers as commonly perceived.

Simulation and Experimental Analysis of Microalgae and Membrane Surface Interaction

The microalgae-induced membrane system applied in wastewater treatment has attracted attention due to microalgae’s outstanding nutrient fixation capacity and biomass harvesting. However, the fundamental understanding of the interaction of microalgae and membrane surfaces is still limited. This study presents experimental and numerical methods to analyze the attachment of microalgae to the membrane. An atomic force microscope (AFM) analysis confirmed that a polydimethylsiloxane (PDMS) sensor, as a simulated membrane surface, exhibited a rougher surface morphology than a polyurethane (PU) sensor did. The contact angle and adsorption analysis using a quartz crystal microbalance confirmed that the PDMS surface, representing the membrane surface, provided a better attachment affinity than the PU surface for microalgae because of the lower surface tension and stronger hydrophobicity of PDMS. The simulation studies of this work involved the construction of roughly circular-shaped particles to represent microalgae, rough flat surfaces to represent membrane surfaces, and the interaction energy between particles and surfaces based on XDLVO theory. The modeling results of the microalgae adsorption trend are consistent and verified with the experimental results. It was observed that the interfacial energy increased with increasing the size of particles and asperity width of the membrane surface. Contrarily, the predicted interaction energy dropped with elevating the number of asperities and asperity height of the microalgae and membrane. The most influential parameter for controlling interfacial interaction between the simulated microalgae and membrane surface was the asperity height of the membrane; changing the height from 50 nm to 250 nm led to alteration in the primary minimum from −18 kT to −3 kT. Overall, this study predicted that the microalgae attachment depends on the size of the asperities to a great extent and on the number of asperities to a lesser extent. These results provide an insight into the interaction of microalgae and membrane surface, which would provide information on how the performance of microalgae-based membrane systems can be improved.

PDMS Micropatterns Coated with PDA and RGD Induce a Regulatory Macrophage-like Phenotype

Regulatory macrophages (Mreg) are a special cell type that present a potential therapeutic strategy for various inflammatory diseases. In vitro, Mreg generation mainly takes 7-10 days of treatment with chemicals, including cytokines. In the present study, we established a new approach for Mreg generation using a three-dimensional (3D) micropatterned polydimethylsiloxane (PDMS) surface coated with a natural biopolymer adhesive polydopamine (PDA) and the common cell adhesion peptide motif arginylglycylaspartic acid (RGD). The 3D PDMS surfaces were fabricated by photolithography and soft lithography techniques and were subsequently coated with an RGD+PDA mixture to form a surface that facilitates cell adhesion. Human monocytes (THP-1 cells) were cultured on different types of 2D or 3D micropatterns for four days, and the cell morphology, elongation, and Mreg marker expression were assessed using microscopic and flow cytometric analyses. The cells grown on the PDA+RGD-coated 3D micropatterns (20-µm width/20-µm space) exhibited the most elongated morphology and strongest expression levels of Mreg markers, such as CD163, CD206, CD209, CD274, MER-TK, TREM2, and DHRS9. The present study demonstrated that PDA+RGD-coated 3D PDMS micropatterns successfully induced Mreg-like cells from THP-1 cells within four days without the use of cytokines, suggesting a time- and cost-effective method to generate Mreg-like cells in vitro.

Deformation- and rupture-controlled friction between PDMS and a nanometer-scale SiOx single-asperity

This work investigates the friction between polydimethylsiloxane (PDMS) and silicon oxide (SiOx) in single asperity sliding contact by atomic force microscopy (AFM). Two friction dependences on the normal force are identified: a tensile regime and a compressive regime of normal forces. In the compressive regime, friction is governed by the shear deformation and rupture of junctions between PDMS and SiOx. In this case, the shear strength τ ≈ 10 MPa is comparable with the cohesive strength of PDMS under compressive loading. In contrast, friction in the tensile regime is also affected by the elongation of the junctions. The single SiOx-asperity follows a stick-slip motion on PDMS in both normal force regimes. Statistical analysis of stick-slip as a function of the normal force allows determining the necessary amount of energy to break a SiOx/PDMS junction. Friction between a SiOx-asperity and a PDMS surface can be rationalized based on an energy criterion for the deformation and slippage of nanometer-scale junctions.