Gyula Julius Vancso

In marine industries, severe economic losses are caused by accumulating organisms on surfaces in biofouling processes. Establishing a universal and nontoxic protocol to eliminate biofouling has been a notoriously difficult task due to the complexity of the marine organisms' interactions with surfaces and the chemical, mechanical, and morphological diversity of the surfaces involved. The tremendous variety of environmental parameters in marine environments further complicates this field. For efficient surface engineering to combat fouling, secretion, chemical structure, and properties of biobased adhesives and adhesion mechanisms must be understood. Advanced characterization techniques, like Atomic Force Microscopy (AFM), now allow one to study the three parameters determining surface adhesion and, eventually, fouling, i.e., morphology, chemistry, and surface mechanical modulus. By AFM, characterization can now be performed across length scales from nanometers to hundreds of micrometers. This review provides an up-to-date account of the most promising AFM-based approaches for imaging and characterizing natural adhesives provided by marine organisms. We summarize the current understanding of the molecular basis and the related relevant processes of marine fouling. We focus on applications of AFM "beyond imaging", i.e., to study interactions between adhesives and the surfaces involved. Additionally, we discuss the performance enhancement of polymer antifouling coatings using information derived from AFM. Knowledge and control of marine adhesion can be applied to prevent marine fouling, as well as to design bioadhesives to enhance potential medical applications. We present some milestone results and conclude with an outlook discussing novel possibilities for designing antifouling coatings and medical bioadhesives.

Strong bonding at polymer-metal oxide interfaces is of high importance for lightweight thermoplastic composite structures. However, interfacial adhesion in polymer-metal material systems often poses grand challenges in applications, and hence, tailoring the molecular interactions is necessary. Here, the interfacial adhesion between polycarbonate (PC) and titanium (Ti) is optimized by utilizing metal ion-containing polydopamine (M⁺PDA) produced using two methods, i.e., postdeposition and codeposition with respect to the PDA polymerization. M⁺PDA thin films were formed on the surface of titanium wires, which were then comolded with a PC matrix to form pullout samples in order to evaluate the interfacial energy of adhesion (G _a). For the postdeposition process, Fe³⁺-, Fe²⁺-, Co²⁺-, Ni²⁺-, Cu²⁺-, or Zn²⁺-containing PDA layers were evaluated. Fe³⁺PDA and Fe²⁺PDA coatings resulted in a significant increase of G _a between Ti and PC, while the other metal ions had an insignificant effect. For the codeposition process, Cu²⁺ was utilized, and CuPDA films of various Cu²⁺:DA ratios were evaluated. G _a values for these systems followed an increasing trend by increasing the Cu²⁺:DA ratio until a plateau was reached at a 1:1 value. The M⁺ content had no influence on the values of G _a, regardless of the deposition process utilized. In addition to the specific results to obtain strong adhesion at PC-Ti interfaces, by FTIR, AFM, and solid-state NMR, we also provide insights into hitherto unknown features regarding the surface morphology and chemistry of M⁺-containing PDA films.

Thirst quencher: “Smart” coatings keep plants hydrated. Novel polymer films on leaves harvest water from the air, offering a potential solution to drought in a changing climate.

Polydopamines (PDA) are a popular class of materials and promising candidates as adhesives for new fastening techniques. PDA layers can be formed on a wide range of substrates in various environments. Here, we present a novel method for functionalizing PDA-based copolymer films by using click chemistry. These copolymers adhere strongly to various surfaces and simultaneously have active groups that allow the attachment of functional groups. We discuss the coupling of two types of chitosan and a rhodamine B dye molecule to the alkyne groups of the copolymers by employing click reactions. Azidopropyl methacrylate (AzMA), methyl methacrylate (MMA), and dopamine methacrylamide (DOMA) are copolymerized and codeposited with (3-aminopropyl)triethoxysilane on silicon wafers, polyethylene (PE), and polytetrafluoroethylene (PTFE). AzMA provides the surfaces with azides for use in click reactions, MMA functions to control the polymer as a nonfunctional diluent, whereas DOMA provides adhesion, as well as cross-linking groups. After codeposition, the dyes are grafted to the copolymer to illustrate the ability of the films to link functional groups covalently. Fourier transform infrared spectroscopy confirms the successful click reaction in solution, and atomic force microscopy shows the surface morphologies following grafting. Fluorescence microscopy provides evidence of successful grafting. As an example of a possible application, layers exhibiting antifouling properties are prepared. Chitosan grafted to PE is tested for antifouling performance. These functionalized layers show nonspecific inhibition of protein adsorption. We find that chitosan can lower the adsorption of fluorescein-labeled bovine serum albumin (BSA) protein by more than 90% for the best performing fluorescein-labeled BSA protein and by more than 90% for the best-performing layer. These results demonstrate the viability of our PDA-based copolymers for surface functionalization through click chemistry grafting at challenging adhesion to surfaces.

We present an optical study of the spontaneous emission of lead sulfide (PbS) nanocrystal quantum dots in 3D photonic band gap crystals made from silicon. The nanocrystals emit in the near-infrared range to be compatible with 3D silicon nanophotonics. The nanocrystals are covalently bound to polymer brush layers that are grafted from the Si-air interfaces inside the nanostructure by using surface-initiated atom transfer radical polymerization. The presence and position of the quantum dots were previously characterized by synchrotron X-ray fluorescence tomography. We report both continuous wave emission spectra and time-resolved, time-correlated single photon counting. In time-resolved measurements, we observe that the total emission rate greatly increases when the quantum dots are transferred from suspension to the silicon nanostructures, likely due to quenching (or increased nonradiative decay) that is tentatively attributed to the presence of Cu catalysts during the synthesis. In this regime, continuous wave emission spectra are known to be proportional to the radiative rate and thus to the local density of states. In spectra normalized to those taken on flat silicon outside the crystals, we observe a broad and deep stop band that we attribute to a 3D photonic band gap with a relative bandwidth of up to 26%. The shapes of the relative emission spectra match well with the theoretical density of states spectra calculated with plane-wave expansion. The observed inhibition is 4-30 times, similar to previously reported record inhibitions, yet for coincidental reasons. Our results are relevant to applications in photochemistry, sensing, photovoltaics, and efficient miniature light sources.

Joining thermoplastic polymers (TPMs) and metals to form lightweight hybrid structures is of growing industrial and commercial importance. The performance of such materials relies on the bonding strength and endurance of the formed TPM–metal interfaces. The available joining technologies and the mechanisms that govern interfacial adhesion are reviewed in this contribution, highlighting thermal bonding as a commercially attractive joining method. By focusing on molecular interactions to optimize interfacial adhesion, the use of dopamine as a building block to form polydopamine (PDA) based adhesive interlayers in such interfaces is discussed. This work also highlights the potential of PDA to be applied as a load‐bearing adhesive—a notion considered to date unfeasible.

Aptamers are widely used in biosensing due to their specific sensitivity toward many targets. Thus, gold nanoparticle (AuNP) aptasensors are subject to intense research due to the complementary properties of aptamers as sensing elements and AuNPs as transducers. We present herein a novel method for the functional coupling of thrombin‐specific aptamers to AuNPs via an anionic, redox‐active poly(ferrocenylsilane) (PFS) polyelectroyte. The polymer acts as a co‐reductant and stabilizer for the AuNPs, provides grafting sites for the aptamer, and can be used as a redox sensing element, making the aptamer‐PFS‐AuNP composite (aptamer‐AuNP) a promising model system for future multifunctional sensors. The aptamer‐AuNPs exhibit excellent colloidal stability in high ionic strength environments owing to the combined electrosteric stabilizing effects of the aptamer and the PFS. The synthesis of each assembly element is described, and the colloidal stability and redox responsiveness are studied. As an example to illustrate applications, we present results for thrombin sensitivity and specificity using the specific aptamer.

Silicon (Si) is made printable by dispersing Si nanoparticles in a single organic solvent. Viscoelastic properties of the prepared inks as well as the uniformity of inkjet-printed thin films are investigated in dependence on the Si volume fraction. It has been demonstrated that no ink additives are needed to completely suppress the occurrence of the coffee ring effect. This is obtained by increasing the ink's volume fraction to induce gelation in order to generate elasticity. The printability of our inks is investigated in terms of Weber, Reynolds, and Ohnesorge numbers and found to be maintained even at high particle loads due to shear-thinning viscosity behavior. When printed onto tungsten (W) substrates, Si inks with ϕ(Si) = 0.4% and ϕ(Si) = 2.1% leave a ring stain after drying, whereas coffee rings are absent for inks with ϕ(Si) = 3.0% and above. The reason for this is a significant ink elasticity achieved by the buildup of a gel network for higher particle loads, which leads to thixotropy-like properties. These are low viscosity for printability and elevated elasticity during ink drying, made possible by a breakup of the gel network during drop formation in conjunction with a rapid network reformation after deposition.