Film Stability during Postassembly Morphological Changes in Polyelectrolyte Multilayers Due to Acid and Base Exposure

The mechanism of the transition from a continuous morphology to a porous morphology within polyelectrolyte multilayers (PEMs) of linear poly(ethylene imine) (LPEI) and poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) and PAA assembled by the layer-by-layer (LbL) technique is examined. These morphological changes were created by both acidic and basic postassembly treatments. Basic postassembly treatment is shown to create different types of porosity than acidic postassembly treatment. The morphological variation from the introduction of porosity to the collapse of these porous structures and the dissolution of films under postassembly treatments was observed by AFM, optical microscopy, quartz crystal microbalance (QCM), and SEM. These morphological transitions which are a result of structural rearrangement of weak polyelectrolytes due to pH changes are closely related to the neutralization of the polycations and the ionization of polyanions. Results obtained from FTIR spectroscopy and QCM confirm that polyelectrolytes are being selectively or partially released from the polyelectrolyte multilayers thin films (PEMs) in response to the pH treatment as a function of exposure time. In conclusion, here new information is presented about the structural reorganization found in a number of weak polyelectrolyte systems. This information will be useful in designing functional materials based on polyelectrolytes

Facile Assembly Enhanced Spontaneous Fluorescent Response of Ag⁺ Ion Containing Polyelectrolyte Multilayer Films

Fluorescent organic–inorganic composite materials exhibiting “turn-on” response are often based on conjugated small molecules. Conjugated polymers, however, often exhibit a “turn-off” response in combination with metal ions. Here we present fluorescent turn-on behavior of a branched poly­(ethylene imine)-poly­(acrylic acid)-Ag⁺ ion complex in a thin film. The material is characterized by UV–vis, spectrofluorometry, XPS, and ICP-MS. The turn-on response is exhibited only with all three components present, implying that the optically active metal coordination complex contains amine and carboxylic acid groups. This behavior is observed in the solid state, meaning this material could be easily integrated into devices. We demonstrate sensing of formaldehyde vapor as well as halide containing solutions based on fluorescence quenching. This fluorescent material is simply made using the layer-by-layer technique and commercially available polymers

Layer-by-Layer Rose Petal Mimic Surface with Oleophilicity and Underwater Oleophobicity

Surfaces designed with specific wetting properties are still a key challenge in materials science. We present here a facile preparation of a surface assembled by the layer-by-layer technique, using a colloidal dispersion of ionomer particles and linear polyethylene imine. The colloidal ethylene-<i>co</i>-methacrylic acid (EMAA) particles are on the order of half a micron in size with surface features from 40 to 100 nm in width. The resultant surface has roughness on two length scales, one on the micron scale due to the packing of particles and one on the nanoscale due to these surface features on the EMAA particles. This hierarchical structure results in a hydrophobic surface with good water pinning properties (∼550 μN). We show that there is a balance between maximizing contact angle and water pinning force. Furthermore, this surface is oleophilic with regard to many organic solvents, also demonstrating underwater oleophobicity, and given the difference in wetting between aqueous and organic phases, this material may be a candidate material for oil/water separations

Polyelectrolyte Multilayers and Complexes to Modify Secondary Interactions in Ethylene-<i>co</i>-methacrylic Acid Ionomers

Ethylene-<i>co</i>-methacrylic acid (EMAA) ionomers are incorporated into polyelectrolyte complexes and thin films fabricated with the layer-by-layer technique using mixed solvent systems of THF and water. EMAA ionomers have been reported to have self-healing properties. The thin films were optically clear and can be made as a coating or freestanding. Their composition was determined with elemental analysis. DSC showed these polymer blend materials to have suppressed polyethylene crystallinity compared to bulk EMAA and an increased amount of energy required to create the order-to-disorder transition of disrupting the associations between the ionic groups of the ionomer

Tuning Wet Adhesion of Weak Polyelectrolyte Multilayers

Weak polyelectrolyte multilayers (PEMs) assembled by the layer-by-layer method are known to become tacky upon contact with water and behave as a viscoelastic fluid, but this wet adhesive property and how it can be modified by external stimuli has not yet been fully explored. We present here a study on the wet adhesive performance of PEMs consisting of branched poly­(ethylene imine) and poly­(acrylic acid) under controlled conditions (e.g., pH, type of salt, and ionic strength) using a 90° peel test. The multilayers demonstrate stick–slip behavior and fail cohesively in nearly all cases. The peel force is the highest at neutral pH, and it decreases in both acidic/basic environments because of inhibited polyelectrolyte mobility. The addition of salts with various metal ions generally reduces the peel force, and this effect tracks with the ionic strength. When transition metal ions are used, their ability to form coordination bonds increases the peel force, with two exceptions (Cu²⁺ and Zn²⁺). With a transition metal ion such as Fe³⁺, the peel force first increases as a function of the concentration and then eventually decreases. The peel force increases proportionally to the peel rate. The films are also characterized via zeta potential (when assembled onto colloidal particles) and shear rheometry. This work provides insight into both the wet adhesive properties of PEMs and the interactions between PEMs and metal ions

Tuning Wet Adhesion of Weak Polyelectrolyte Multilayers

Weak polyelectrolyte multilayers (PEMs) assembled by the layer-by-layer method are known to become tacky upon contact with water and behave as a viscoelastic fluid, but this wet adhesive property and how it can be modified by external stimuli has not yet been fully explored. We present here a study on the wet adhesive performance of PEMs consisting of branched poly­(ethylene imine) and poly­(acrylic acid) under controlled conditions (e.g., pH, type of salt, and ionic strength) using a 90° peel test. The multilayers demonstrate stick–slip behavior and fail cohesively in nearly all cases. The peel force is the highest at neutral pH, and it decreases in both acidic/basic environments because of inhibited polyelectrolyte mobility. The addition of salts with various metal ions generally reduces the peel force, and this effect tracks with the ionic strength. When transition metal ions are used, their ability to form coordination bonds increases the peel force, with two exceptions (Cu²⁺ and Zn²⁺). With a transition metal ion such as Fe³⁺, the peel force first increases as a function of the concentration and then eventually decreases. The peel force increases proportionally to the peel rate. The films are also characterized via zeta potential (when assembled onto colloidal particles) and shear rheometry. This work provides insight into both the wet adhesive properties of PEMs and the interactions between PEMs and metal ions

Tuning Wet Adhesion of Weak Polyelectrolyte Multilayers

Weak polyelectrolyte multilayers (PEMs) assembled by the layer-by-layer method are known to become tacky upon contact with water and behave as a viscoelastic fluid, but this wet adhesive property and how it can be modified by external stimuli has not yet been fully explored. We present here a study on the wet adhesive performance of PEMs consisting of branched poly­(ethylene imine) and poly­(acrylic acid) under controlled conditions (e.g., pH, type of salt, and ionic strength) using a 90° peel test. The multilayers demonstrate stick–slip behavior and fail cohesively in nearly all cases. The peel force is the highest at neutral pH, and it decreases in both acidic/basic environments because of inhibited polyelectrolyte mobility. The addition of salts with various metal ions generally reduces the peel force, and this effect tracks with the ionic strength. When transition metal ions are used, their ability to form coordination bonds increases the peel force, with two exceptions (Cu²⁺ and Zn²⁺). With a transition metal ion such as Fe³⁺, the peel force first increases as a function of the concentration and then eventually decreases. The peel force increases proportionally to the peel rate. The films are also characterized via zeta potential (when assembled onto colloidal particles) and shear rheometry. This work provides insight into both the wet adhesive properties of PEMs and the interactions between PEMs and metal ions

Omniphobic Slippery Coatings Based on Lubricant-Infused Porous Polyelectrolyte Multilayers

Omniphobic and slippery coatings from lubricant-infused, textured surfaces have recently been shown to have superior properties including low contact angle hysteresis and low sliding angles. Here, we present an omniphobic slippery surface prepared by infusing a fluorinated lubricant into a porous polyelectrolyte multilayer. These surfaces repel water and decane with sliding angles as low as 3°. One advantage of polyelectrolyte multilayers is the ease with which they can coat nonplanar surfaces, demonstrated here

Omniphobic Slippery Coatings Based on Lubricant-Infused Porous Polyelectrolyte Multilayers

Omniphobic and slippery coatings from lubricant-infused, textured surfaces have recently been shown to have superior properties including low contact angle hysteresis and low sliding angles. Here, we present an omniphobic slippery surface prepared by infusing a fluorinated lubricant into a porous polyelectrolyte multilayer. These surfaces repel water and decane with sliding angles as low as 3°. One advantage of polyelectrolyte multilayers is the ease with which they can coat nonplanar surfaces, demonstrated here

Omniphobic Slippery Coatings Based on Lubricant-Infused Porous Polyelectrolyte Multilayers

Omniphobic and slippery coatings from lubricant-infused, textured surfaces have recently been shown to have superior properties including low contact angle hysteresis and low sliding angles. Here, we present an omniphobic slippery surface prepared by infusing a fluorinated lubricant into a porous polyelectrolyte multilayer. These surfaces repel water and decane with sliding angles as low as 3°. One advantage of polyelectrolyte multilayers is the ease with which they can coat nonplanar surfaces, demonstrated here