modified by several types of additives such as low molecular weight surfactants and proteins, [3][4][5] particles, [6][7][8][9] or polymers. [10][11][12][13][14][15][16] Hereby, the adsorption of surface-active entities can occur by adsorption of unimers to form eventually more or less homogeneous monolayers. However, amphiphiles are often present in colloidal form as micelles. Since other colloidal particles, e.g., nanoparticles and microgels, can adsorb to interfaces in a pickeringlike fashion, intact micelles might also be prone to adsorb to the interface. [10,17,18] However, little is known on the fate of such interfacially attached micelles. In most cases, the kinetics of the rearrangements toward a monolayer are hard to capture.Generally, the interfacial tension is regarded as a primary indicator of adsorption processes, often deemed sufficient to trace changes at liquid interfaces. However, the involvement of certain substances or combinations can lead to complex interfaces with additional rheological properties, completely different to the ones of the pure interface. [1,19,20] Examples could involve, e.g., interfacial polymerization [21] (including classical nylon thread fabrication) or even interfacial crosslinking (bubble tea preparation). In some of these cases, the interfacial film is rather thick. However, also monolayers of amphiphiles can exhibit viscoelastic properties being essential for the properties of the whole system. Hence, Though amphiphiles are ubiquitously used for altering interfaces, interfacial reorganization processes are in many cases obscure. For example, adsorption of micelles to liquid-liquid interfaces is often accompanied by rapid reorganizations toward monolayers. Then, the involved time scales are too short to be followed accurately. A block copolymer system, which comprises poly(ethylene oxide) 110 -b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride} 170 (i.e., PEO 110 -b-qPDPAEMA 170 with quaternized poly(diisopropylaminoethyl methacrylate)) is presented. Its reorganization kinetics at the water/n-decane interface is slowed down by electrostatic interactions with ferricyanide ([Fe(CN) 6 ] 3-). This deceleration allows an observation of the restructuring of the adsorbed micelles not only by tracing the interfacial pressure, but also by analyzing the interfacial rheology and structure with help of atomic force microscopy. The observed micellar flattening and subsequent merging toward a physically interconnected monolayer lead to a viscoelastic interface well detectable by interfacial shear rheology (ISR). Furthermore, the "gelled" interface is redox-active, enabling a return to purely viscous interfaces and hence a manipulation of the rheological properties by redox reactions. Additionally, interfacial Prussian blue formation stiffens the interface. Such manipulation and in-depth knowledge of the rheology of complex interfaces can be beneficial for the development of emulsion formulations in industry or medicine, where colloidal stability or adapted permeabil...

Variable interfacial tension could be desirable for many applications. Beyond classical stimuli like temperature, we introduce an electrochemical approach employing polymers. Hence, aqueous solutions of the nonionic–cationic block copolymer poly­(ethylene oxide)114-b-poly­{[2-(methacryloyloxy)­ethyl]­diisopropylmethylammonium chloride}171 (i.e., PEO114-b-PDPAEMA171 with a quaternized poly­(diisopropylaminoethyl methacrylate) block) were investigated by emerging drop measurements and dynamic light scattering, analyzing the PEO114-b-qPDPAEMA171 impact on the interfacial tension between water and n-decane and its micellar formation in the aqueous bulk phase. Potassium hexacyanoferrates (HCFs) were used as electroactive complexants for the charged block, which convert the bishydrophilic copolymer into amphiphilic species. Interestingly, ferricyanides ([Fe­(CN)6]3–) act as stronger complexants than ferrocyanides ([Fe­(CN)6]4–), leading to an insoluble qPDPAEMA block in the presence of ferricyanides. Hence, bulk micellization was demonstrated by light scattering. Due to their addressability, in situ redox experiments were performed to trace the interfacial tension under electrochemical control, directly utilizing a drop shape analyzer. Here, the open-circuit potential (OCP) was changed by electrolysis to vary the ratio between ferricyanides and ferrocyanides in the aqueous solution. While a chemical oxidation/reduction is feasible, also an electrochemical oxidation leads to a significant change in the interfacial tension properties. In contrast, a corresponding electrochemical reduction showed only a slight response after converting ferricyanides to ferrocyanides. Atomic force microscopy (AFM) images of the liquid/liquid interface transferred to a solid substrate showed particles that are in accordance with the diameter from light scattering experiments of the bulk phase. In conclusion, the present results could be an important step toward economic switching of interfaces suitable, e.g., for emulsion breakage.

No abstract

The controlled growth of surface‐modifying polymer films by electrodeposition often fails because of the lack of redox activity of these compounds. Here, electroactive complexants help to electrodeposit non‐electroactive polymers. Hence, we investigate the counterion‐induced electrodeposition of polyelectrolytes: three quaternized poly(N,N‐dialkylaminoethyl methacrylate)s (qPDAAEMA), in particular their methyl, ethyl, and isopropyl derivatives (i. e. qPDMAEMA, qPDEAEMA, and qPDPAEMA), provide transparent solutions in the presence of hexacyanoferrate(II) (ferrocyanide) at specific concentration windows of the KCl supporting electrolyte. Below a certain KCl concentration, insolubility dominates irrespective of the hexacyanoferrate valency, whilst above an upper threshold, full solubility is observed. Between these limits, oxidation reversibly electrodeposits polymer/hexacyanoferrate(III) (ferricyanide) complexes. Hydrodynamic voltammetry (and data analysis using in‐house software) provides access to the deposition efficiency (DE). qPDEAEMA with ethyl substituents shows highest DEs; larger or smaller substituents fall short because of a balance between “hydrophobicity” and charge separation, shifting the window toward smaller salt concentrations with increasing alkyl size. We always observe a DE maximum close to the minimum salt concentration, whilst electrochemical quartz crystal microbalance (EQCM) measurements indicate a change in film water content close to the maximum. These effects, being also discussed in terms of polymer conformation, can direct the future engineering of electroassisted coatings.