Abstract: The exciting functionalities of natural superhydrophilic and superhydrophobic surfaces served as inspiration for a variety of biomimetic designs. In particular, the combination of both extreme wetting states to micropatterns opens up interesting applications, as the example of the fog-collecting Namib Desert beetle shows. In this paper, the beetle’s elytra were mimicked by a novel three-step fabrication method to increase the fog-collection efficiency of glasses. In the first step, a double-hierarchical surface structure was generated on Pyrex wafers using femtosecond laser structuring, which amplified the intrinsic wetting property of the surface and made it superhydrophilic (water contact angle 150°). In the last step, the Teflon-like coating was selectively removed by fs-laser ablation to uncover superhydrophilic spots below the supe...

Abstract: The role of nanoparticles in cancer medicine is vast with debate still surrounding the distinction between therapeutic efficacy of actively targeted nanoparticles versus passively targeted systems for drug delivery. While it is commonly accepted that methodologies that result in homing a high concentration of drug loaded nanoparticles to the tumor is beneficial, the role of intracellular trafficking of these nanoparticles in dictating the overall therapeutic outcome remains unresolved. Herein we demonstrate that the therapeutic outcome of drug loaded nanoparticles is governed beyond simply enabling nanoparticle internalization in cells. Using two model polymeric nanoparticles, one decorated with the GE11 peptide for active targeting of the epidermal growth factor receptor (EGFR) and the other without, we demonstrate that EGFR mediated intracellular internalization results in an enhanced therapeutic effect compared to the nontargeted formulation. Our findings demonstrate that the intracellular destination of nanoparticles beyond its ability to internalize is an important parameter that has to be accounted for in the design of targeted drug delivery systems.

Abstract: Nanostructured copper sulfide synthesized with the assistance of surfactant with nanoscale particle size and high Brunauer–Emmett–Teller surface area was for the first time applied for the capture of elemental mercury (Hg0) from coal combustion flue gas The optimal operation temperature of nano-CuS for Hg0 adsorption is 75 °C, which indicates that injection of the sorbent between the wet flue gas desulfurization and the wet electrostatic precipitator systems is feasible This assures that the sorbent is free of the adverse influence of nitrogen oxides Oxygen (O2) and sulfur dioxide exerted a slight influence on Hg0 adsorption over the nano-CuS Water vapor was shown to moderately suppress Hg0 capture efficiency via competitive adsorption The simulated adsorption capacities of nano-CuS for Hg0 under pure nitrogen (N2), N2 + 4% O2, and simulated flue gas reached 12240, 11206, and 8943 mgHg0/g nano-CuS, respectively Compared to those of traditional commercial activated carbons and metal sulfides, the

Abstract: A series of four cellulose nanocrystal (CNC) suspensions were prepared from bleached softwood kraft pulp using different conditions of sulfuric acid hydrolysis. The CNCs were identical in size (95 nm in length × 5 nm in width) but had different surface charges corresponding to the harshness of the hydrolysis conditions. Consequently, it was possible to isolate the effects of surface charge on the self-assembly and viscosity of the CNC suspensions across surface charges ranging from 0.27%S to 0.89%S. The four suspensions (never-dried, free of added electrolyte) all underwent liquid crystalline phase separation, but the concentration onset for the emergence of the chiral nematic phase shifted to higher values with increasing surface charge. Similarly, suspension viscosity was also influenced by surface charge, with suspensions of lower surface charge CNCs more viscous and tending to gel at lower concentrations. The properties of the suspensions were interpreted in terms of the increase in effective diameter...

Abstract: Ice formation and accretion on surfaces is a serious economic issue in energy supply and transportation. Recent strategies for developing icephobic surfaces are intimately associated with superwettability. Commonly, the superwettability of icephobic materials depends on their surface roughness and chemical composition. This article critically categorizes the possible strategies to mitigate icing problems from daily life. The wettability and classical nucleation theories are used to characterize the icephobic surfaces. Thermodynamically, the advantages/disadvantages of superhydrophobic surfaces are discussed to explain icephobic behavior. The importance of elasticity, slippery liquid-infused porous surfaces (SLIPSs), amphiphilicity, antifreezing protein, organogels, and stimuli-responsive materials has been highlighted to induce icephobic performance. In addition, the design principles and mechanism to fabricate icephobic surfaces with superwettability are explored and summarized.

Abstract: Polydopamine-based chemistry has been employed for various surface modifications attributed to the advantages of universality, versatility, and simplicity. Co-deposition of polydopamine (PDA) with polyethyleneimine (PEI) has then been proposed to realize one-step fabrication of functional coatings with improved morphology uniformity, surface hydrophilicity, and chemical stability. Herein, we report the co-deposition kinetics related to the solution composition with different dopamine/PEI ratios, PEI molecular weights, dopamine/PEI concentrations, and the substrate surface with varying chemistry and wettability. The addition of PEI to dopamine solution suppresses the precipitation of PDA aggregates, resulting in an expanded time window of steady co-deposition compared with that of PDA deposition. Low-molecular-weight PEI at low concentration accelerates the co-deposition process, while high-molecular-weight PEI and high concentration of either PEI or dopamine/PEI are detrimental to the co-deposition effici...

Abstract: Laser ablation in liquid was used to prepare homogeneous copper–zinc alloy catalysts that exhibited excellent selectivity for C2H4 in CO2 electroreduction, with faradaic efficiency values as high as 33.3% at a potential of −1.1 V (vs reversible hydrogen electrode). The high proximity of Cu and Zn atoms on the surface of the catalyst was found to facilitate both stabilization of the CO* intermediate and its transfer from Zn atoms to their Cu neighbors, where further dimerization and protonation occur to give rise to a large amount of ethylene product. The new homogeneous nanocatalyst, along with the mechanism proposed for its performance, may be very helpful for in-depth understanding of processes related to carbon dioxide electroreduction and conversion.

Abstract: A facile synthesis strategy was adopted to prepare resilient graphene aerogel (GA) with properties of high emulsified oil adsorption capacities, excellent rebounding performance, oil–water selectivity, and recycling abilities. The maximum adsorption capacity of GA for emulsified diesel oil was 2.5 × 104 mg g–1. The microscopic kinetic and thermodynamic mutual reaction models of diesel oil emulsion adsorption onto GA were investigated to describe the adsorption mechanism. The emulsified diesel oil was able to be separated efficiently from the oil–water emulsion by GA because of their high oil selectivity. Interestingly, both kinetics and thermodynamic experiments show that emulsified oil adsorption on GA is a physical adsorption and spontaneous process. Besides, GA can be reused with prominent repeatability for at least 10 cycles, demonstrating feasibility in practical applications of GA-based oily water treatment.

Abstract: Sulfated cellulose nanocrystals (CNC) with high surface charge density are inadequate for stabilizing oil–water emulsions, which limits their applications as interfacial stabilizers. We performed end-group modification by introducing hydrophobic chains (polystyrene) to CNC. Results showed that the modified CNC are more effective in emulsifying toluene and hexadecane than pristine CNC. Various parameters were investigated, such as concentration of particles, electrolytes, and polarity of solvents on the characteristics of the emulsions. This study provides strategies for the modification of cellulose nanocrystals to yield amphiphilic nanoparticles that enhance the stability of emulsions. Such systems, bearing biocompatible and environmentally friendly characteristics, are attractive for use in a wide range of industries spanning food, biomedicine, pharmaceuticals, cosmetics, and petrochemicals.

Abstract: We reported an example of metal–organic framework (MOF)-based porous liquid by dispersing ZIF-8 ({Zn(mim)2}, mim = 2-methylimidazole) nanocrystallites in ionic liquid (IL) of [Bpy][NTf2] (N-butyl pyridinium bis(trifluoromethyl sulfonyl)imide). Two essential challenges, stable colloid formation and porosity retention, have been overcome to prepare MOF-based porous liquid. Preventing ZIF-8 nanocrystals from aggregation before dispersing is vital to form a stable ZIF-8 colloid in IL via enhancing the interaction between ZIF-8 and IL. The resultant ZIF-8–[Bpy][NTf2] colloid is able to be stable over months without precipitating. [Bpy][NTf2] with larger ion sizes cannot occupy pores in ZIF-8, leaving the ZIF-8 cage empty for enabling access by guest molecules. The porosity of this porous liquid system was verified by positron (e+) annihilation lifetime spectroscopy and I2 adsorption in ZIF-8 in the colloid. MOF-based porous liquids could provide a new material platform for liquid-bed-based gas separations.

Abstract: Two-dimensional (2D) nanomaterials have attracted considerable attention in biomedical and environmental applications due to their antimicrobial activity. In the interest of investigating the primary antimicrobial mode-of-action of 2D nanomaterials, we studied the antimicrobial properties of MnO2 and MoS2, toward Gram-positive and Gram-negative bacteria. Bacillus subtilis and Escherichia coli bacteria were treated individually with 100 μg/mL of randomly oriented and vertically aligned nanomaterials for ∼3 h in the dark. The vertically aligned 2D MnO2 and MoS2 were grown on 2D sheets of graphene oxide, reduced graphene oxide, and Ti3C2 MXene. Measurements to determine the viability of bacteria in the presence of the 2D nanomaterials performed by using two complementary techniques, flow cytometry, and fluorescence imaging showed that, while MnO2 and MoS2 nanosheets show different antibacterial activities, in both cases, Gram-positive bacteria show a higher loss in membrane integrity. Scanning electron micro...

Abstract: Superlubricity based on hydration lubrication provides a near-frictionless lubrication state for the extreme reduction of friction in aqueous conditions. Nevertheless, how to obtain the hydration superlubricity under macroscale conditions with higher load-carrying capacity still remains a challenge and the mechanisms governing macroscale superlubricity with hydrated ions are still not well comprehended. Here, we demonstrate that macroscale superlubricity based on hydrated alkali metal ions (Li+, Na+, K+) can be realized under high contact pressure between the Si3N4 ball and sapphire disk. The ultralow friction coefficients of 0.005 are obtained under average contact pressure up to 0.25 GPa by a universal micro-tribometer after a running-in period with acid solutions. The results reveal that running-in stage with acid solutions can not only make the worn region smoother but also generate a silica layer that is easy to shear, which provides excellent boundary lubrication. The hydration superlubricity occurs because hydration shells surrounding the alkali metal ions could generate the hydration repulsive force to sustain a large normal load and have a fluid response to shear simultaneously. These findings pave the way to the scale-up of hydration superlubricity and thus to the wide application of new water-based lubricants.

Abstract: In recent years, there has been a resurgence of interest in Pickering emulsions because of the recognition of the unique high steric stabilization provided by particles at interfaces. This interest is particularly keen for water-in-oil (W/O) emulsions because of the limited range of suitable Pickering stabilizers available. We demonstrate for the first time that W/O emulsions can be stabilized by using crystals from naturally occurring polyphenols (curcumin and quercetin particles). These particles were assessed based on their size, microstructure, contact angle, interfacial tension, and ζ-potential measurements in an attempt to predict the way that they act as Pickering stabilizers. Static light-scattering results and microstructural analysis at various length scales [optical microscopy, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM)] confirmed that the quercetin particles has a nearly perfect crystalline rod shape with a high aspect ratio; that is, the ratio of length ...

Abstract: Micromotors are an emerging class of micromachines that could find potential applications in biomedicine, environmental remediation, and microscale self-assembly Understanding their propulsion mechanisms holds the key to their future development This is especially true for a popular category of micromotors that are driven by asymmetric surface photochemical reactions Many of these micromotors release ionic species and are propelled via a mechanism termed “ionic self-diffusiophoresis” However, exactly how it operates remains vague To address this fundamental yet important issue, we have developed a dielectric-AgCl Janus micromotor that clearly moves away from the AgCl side when exposed to UV or strong visible light Taking advantage of numerical simulations and acoustic levitation techniques, we have provided tentative explanations for its speed decay over time as well as its directionality In addition, photoactive AgCl micromotors demonstrate interesting gravitactic behaviors that hint at three-dime

Abstract: Although metallic biomaterials find numerous biomedical applications, their inherent low bioactivity and poor osteointegration had been a great challenge for decades. Surface modification via silanization can serve as an attractive method for improving the aforementioned properties of such substrates. However, its effect on protein adsorption/conformation and subsequent cell adhesion and spreading has rarely been investigated. This work reports the in-depth study of the effect of Ti6Al4V surface functionalization on protein adsorption and cell behavior. We prepared self-assembled monolayers (SAMs) of five different surfaces (amine, octyl, mixed [1:1 ratio of amine:octyl], hybrid, and COOH). Synthesized surfaces were characterized by Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, contact angle goniometry, profilometry, and field emission scanning electron microscopy (FESEM). Quantification of adsorbed mass of bovine serum albumin (BSA) and fibronectin (FN) was determined on...

Abstract: Lightweight and compatible metal-organic framework (MOF)-derived carbon-based composites are widely used in electromagnetic (EM) absorption. Their combination with laminated TiO2-C (derived from Ti3C2T x) is expected to further strengthen the EM attenuation ability. Herein, novel laminated Co/TiO2-C hybrids were derived from Ti3C2T x/Co-MOF using heat treatment. Compared with pristine MOF-derived carbon-based composites, the EM absorption ability of Co/TiO2-C was improved by multiple reflections between multilayered microstructures and the improved polarization loss (due to the heterogeneous interfaces, residual defects, and dipole polarization) and the strengthened conductivity loss caused by the carbon layers. Specifically, for the Co/TiO2-C hybrids at thicknesses of 3.0 and 2.0 mm, the optimal reflection loss (RL) was -41.1 dB at 9.0 GHz and -31.0 dB at 13.9 GHz, with effective bandwidths (RL ≤ -10 dB) of 3.04 and 4.04 GHz, respectively. This study will underline the preparation of carbon-based absorbing materials starting from MXene/MOF hybrids.

Abstract: Synthetic hectorite clay Laponite RD/XLG is composed of disk-shaped nanoparticles that acquire dissimilar charges when suspended in an aqueous medium. Owing to their property to spontaneously self-assemble, Laponite is used as a rheology modifier in a variety of commercial water-based products. In particular, an aqueous dispersion of Laponite undergoes a liquid-to-solid transition at about 1 vol % concentration. The evolution of the physical properties as the dispersion transforms to the solid state is reminiscent of physical aging in molecular as well as colloidal glasses. The corresponding soft glassy dynamics of an aqueous Laponite dispersion, including the rheological behavior, has been extensively studied in the literature. In this feature article, we take an overview of recent advances in understanding soft glassy dynamics and various efforts taken to understand the peculiar rheological behavior. Furthermore, the continuously developing microstructure that is responsible for the eventual formation o...

Abstract: A pH- and ultrasound dual-responsive drug release pattern was successfully achieved using mesoporous silica nanoparticles (MSNs) coated with polydopamine (PDA). In this paper, the PDA shell on the MSN surface was obtained through oxidative self-polymerization under the alkaline condition. The morphology and structure of this composite nanoparticle were fully characterized by a series of analyses, such as infrared (IR), transmission electron microscopy, and thermogravimetric analysis. Doxorubicin hydrochloride (DOX)-loaded composite nanoparticles were used to study the performances of responsive drug storage/release behavior, and this kind of hybrid material displayed an apparent pH response in DOX releasing under the acidic condition. Beyond that, upon high-intensity focused ultrasound exposure, loaded DOX in composite nanoparticles was successfully triggered to release from pores because of the ultrasonic cavitation effect, and the DOX-releasing pattern could be optimized into a unique pulsatile fashion by switching the on/off status. From the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, it was observed that our blank nanoparticles showed no toxicity to HeLa cells, but DOX-loaded nanoparticles could inhibit the growth of tumor cells. Furthermore, these composite nanoparticles displayed an effective near-IR photothermal conversion capability with a relatively high conversion efficiency (∼37%). These as-desired drug delivery carriers might have a great potential for future cancer treatment that combine the chemotherapy and photothermal therapy.

Abstract: The structural memory effect of layered double hydroxides (LDHs) is one of the important reasons for their extensive use in environmental remediation. In this study, humic acid (HA) was extracted from black soil and sediments and characterized to determine their structures. The regeneration mechanisms of calcinated LDHs (CLDHs) including different divalent metals (Mg-CLDH and Zn-CLDH) in deionized water and different HA solutions were carefully elucidated, and the reasons for the behavior differences in the two materials were explained. The presence of the HAs significantly increased the dissolution rate of Mg2+ ions from Mg-CLDHs and subsequent regeneration of Mg-LDH. Because of the diverse functional groups in the HAs, these groups were complexed with metallic ions such as Mg2+ on the surface of Mg-CLDH in the beginning. During the process, the HAs adsorbed the regenerated LDHs on the surfaces. Therefore, the crystallinity, morphology, and specific surface area of the regenerated Mg-LDH significantly ch...

Abstract: High durability, low cost, and superior anti-icing and active deicing multifunctional surface coatings, especially in the extreme environment, are highly desired to inhibit and/or eliminate the detriment of icing in many fields, such as automobile, aerospace, and power transmission. Herein, we first report a facile and versatile strategy to prepare novel slippery polyols-infused porous surfaces (SPIPS’s) with the inexpensive polyols as the lubricant liquids. These SPIPS’s are fabricated by a spray-coating approach based on amino-modified magnetic Fe3O4 nanoparticles (MNP@NH2) and amphiphilic P(poly(ethylene glycol) methyl ether methacrylate-co-glycidyl methacrylate) copolymer covalent cross-linked hybrids, followed by infusion with various polyols. The as-prepared surface exhibits excellent antifrosting property, that is, it can greatly postpone frost formation as long as 2700 s at −18 °C. Meanwhile, differential scanning calorimetry results clearly demonstrate that SPIPS’s show a remarkable freezing poin...

Abstract: Some polyzwitterionic brushes exhibit a strong “anti-polyelectrolyte effect” and ionic specificity that make them versatile platforms to build smart surfaces for many applications. However, the structure–property relationship of zwitterionic polymer brushes still remains to be elucidated. Herein, we aim to study the structure-dependent relationship between different zwitterionic polymers and the anti-polyelectrolyte effect. To this end, a series of polyzwitterionic brushes with different cationic moieties (e.g., imidazolium, ammonium, and pyridinium) in their monomeric units and with different carbon spacer lengths (e.g., CSL = 1, 3, and 4) between the cation and anion were designed and synthesized to form polymer brushes via the surface-initiated atom transfer radical polymerization. All zwitterionic brushes were carefully characterized for their surface morphologies, compositions, wettability, and film thicknesses by atomic force microscopy, contact angle measurement, and ellipsometry, respectively. The...

Abstract: Many surfaces reversibly change their structure and interfacial energy upon being in contact with a liquid. Such surfaces adapt to a specific liquid. We propose the first order kinetic model to describe dynamic contact angles of such adaptive surfaces. The model is general and does not refer to a particular adaptation process. The aim of the proposed model is to provide a quantitative description of adaptive wetting and to link changes in contact angles to microscopic adaptation processes. By introducing exponentially relaxing interfacial energies and applying Young’s equation locally, we predict a change of advancing and receding contact angles depending on the velocity of the contact line. Even for perfectly homogeneous and smooth surfaces, a dynamic contact angle hysteresis is obtained. As possible adaptations, we discuss changes and reconstruction of polymer surfaces or monolayers, diffusion and swelling, adsorption of surfactants, replacement of contaminants, reorientation of liquid molecules, or for...

Abstract: A methodology for determining the micropore, mesopore, and external surface areas of hierarchical microporous/mesoporous materials from N2 adsorption isotherms at 77 K is described. For FAU-Y zeolites, the microporous surface area calculated using the Rouquerol criterion and the Brunauer–Emmett–Teller (BET) equation is in accord with the geometrical surface determined by the chord length distribution method. Therefore, BET surface area (SBET) is the well representative of micropore surface areas of microporous materials and of total surface area of microporous/mesoporous materials. Mechanical mixtures of mesoporous MCM-41 and microporous FAU-Y powders of known surface areas were used to calculate the respective surface areas by weighted linear combination and the results were compared to the values obtained by the t-plot method. The first slope of the t-plot determined the mesopore and external surface areas (Smes+ext). The linear fit of the first slope is in general in the range 0.01 < p/p0 < 0.17 and co...

Abstract: The spreading and rebound patterns of low-viscous droplets upon impacting spherical solid surfaces are investigated numerically. The studied cases consider a droplet impinging onto hydrophobic and superhydrophobic surfaces with various parameters varied throughout the study, and their effects on the postimpingement behavior are discussed. These parameters include impact Weber number (through varying the surface tension and impingement velocity), the size ratio of the droplet to the solid surface, and the surface contact angle. According to the findings, the maximum spreading diameter increases with the impact velocity, with an increase of the sphere diameter, with a lower surface wettability, and with a lower surface tension. Typical outcomes of the impact include (1) complete rebound, (2) splash, and (3) a final deposition stage after a series of spreading and recoiling phases. Finally, a novel, practical model is proposed, which can reasonably predict the maximum deformation of low Reynolds number impact of droplets onto hydrophobic or superhydrophobic spherical solid surfaces.

Abstract: Application of biocatalytic membrane is promising in food, pharmaceutical, and water treatment industries, whereas enzyme immobilization is the key step of biocatalytic membrane preparation Thus, how to minimize the negative effect of immobilization on enzyme performance is required to answer In this work, we proposed a platform for biocatalytic membrane preparation and immobilization mechanism investigation based on polydopamine (PDA) coating, which was demonstrated by immobilizing five commonly used enzymes (laccase, glucose oxidase, lipase, pepsin, and dextranase) on three commercially available membranes via three immobilization mechanisms (electrostatic attraction, covalent bonding, and hydrophobic adsorption), respectively By examining the enzyme loading, activity, and kinetics under different immobilization mechanisms, we found that except for dextranase, enzyme immobilization via electrostatic attraction retained the most activity, whereas covalent bonding and hydrophobic adsorption were detrimental to enzyme conformation Enzyme immobilization via covalent bonding ensured a high enzyme loading, and hydrophobic adsorption was only suitable for lipase and dextranase immobilization Moreover, the properties of functional groups around the enzyme active center should be considered for the selection of suitable immobilization strategy (ie, avoid covering the active center by membrane carrier) This work not only established a versatile platform for biocatalytic membrane preparation but also provided a novel methodology to evaluate the effect of immobilization mechanisms on enzyme performance

Abstract: In this study, composite photocatalysts were produced from NiTiO3 and N2-rich precursors (dicyandiamide, melamine, urea, and thiourea) under N2 flow conditions. The goal of the study was to investigate the interaction between NiTiO3 and the synthesized g-C3N4. The properties of the g-C3N4/NiTiO3 (CNT) composites were different depending on the starting materials. Dicyandiamide and thiourea created strong connections with NiTiO3 and resulted in the generation of Ti–N and Ti–O–S bonds. Urea and melamine, however, had difficulty forming g-C3N4 structures or interconnections with NiTiO3. The Ti–N and Ti–O–S bridges in the composite photocatalysts led to increased photocatalytic activity as well as inhibition of the recombination rate. Additionally, the band diagrams of g-C3N4 prepared from dicyandiamide and thiourea exhibited positions suitable for the Z-scheme charge-transfer model with NiTiO3, implying that the composite photocatalysts were applicable for photocatalytic degradation of organic contaminants u...

Abstract: The structural complexity of soft gels is at the origin of a versatile mechanical response that allows for large deformation, controlled elastic recovery, and toughness in the same material. A limit to exploiting the potential of such materials is the insufficient fundamental understanding of the microstructural origin of the bulk mechanical properties. Here we investigate the role of the network topology in a model gel through 3D numerical simulations. Our study links the topology of the network organization in space to its nonlinear rheological response preceding yielding and damage: our analysis elucidates how the network connectivity alone could be used to modify the gel mechanics at large strains, from strain-softening to hardening and even to a brittle response. These findings provide new insight for smart material design and for understanding the nontrivial mechanical response of a potentially wide range of technologically relevant materials.

Abstract: The controllable and efficient electrochemical preparation of highly crystalline graphene quantum dots (GQDs) in an aqueous system is still challenging. Here, we developed a weak electrolyte-based (typically an ammonia solution) electrochemical method to enhance the oxidation and cutting process and therefore achieve a high yield of GQDs. The yield of GQDs (3–8 nm) is 28%, approximately 28 times higher than the yield of GQDs prepared by other strong electrolytes. The whole preparation process can be accomplished within 2 h because of the effective free radical oxidation process and the suppressed intercalation-induced exfoliation in weakly ionized aqueous electrolytes. The GQDs also showed excellent crystallinity which is obviously better than the crystallinity of GQDs obtained via bottom-up approaches. Moreover, amino-functionalization of GQDs can be realized by manipulating the electrolyte concentration. We further demonstrate that the proposed method can also be expanded to other weak electrolytes (suc...

Abstract: Numerous studies have focused on the remarkable adhesive properties of polydopamine, which can bind to substrates with a wide range of surface energies, even under aqueous conditions. This behavior suggests that polydopamine may be an attractive option as a surface treatment in structural bonding applications, where good bond durability is required. Here, we assessed polydopamine as a surface treatment for bonding aluminum plates with an epoxy resin. A model epoxy adhesive consisting of diglycidyl ether of bisphenol A (DGEBA) and Jeffamine D230 polyetheramine was employed, and lap shear measurements (ASTM D1002 10) were made (i) under dry conditions to examine initial bond strength and (ii) after exposure to hot/wet (63 °C in water for 14 days) conditions to assess bond durability. Surprisingly, our results showed that polydopamine alone as a surface treatment provided no benefit beyond that obtained by exposing the substrates to an alkaline solution of tris buffer used for the deposition of polydopamine. This implies that polydopamine has a potential Achilles' heel, namely, the formation of a weak boundary layer that was identified using X-ray photoelectron spectroscopy (XPS) of the fractured surfaces. In fact, for longer deposition times (2.5 and 18 h), the tris buffer-treated surface outperformed the polydopamine surface treatments, suggesting that tris buffer plays a unique role in improving adhesive performance even in the absence of polydopamine. We further showed that the use of polydopamine-3-aminopropyltriethoxysilane (APTES) hybrid surface treatments provided significant improvements in bond durability at extended deposition times relative to both polydopamine and an untreated control.