Selective Ion Transport and Complexation in Layer‐by‐Layer Assemblies of p‐Sulfonato‐ calix[n]arenes and Cationic Polyelectrolytes

The first study of ion transport across self‐assembled multilayered films of p‐sulfonato‐calix[n]arenes and poly(vinyl amine) (PVA) is presented. The films are prepared by the alternate electrostatic layer‐by‐layer assembly of the anionic calixarenes and cationic PVA on porous polyacrylonitrile (PAN) supports. We use tetra‐p‐sulfonato‐calix[4]arene (calix4), hexa‐p‐sulfonato‐calix[6]arene (calix6), and octa‐p‐sulfonato‐calix[8]arene (calix8) as the calixarenes. Ultraviolet (UV) studies indicate that dipping solutions of pH 6.8, without a supporting electrolyte, are most suited for film preparation. Calix8 is adsorbed in higher concentrations per layer than calix6 or calix4, probably because desorption is less pronounced. The permeation rates, P_Rs, of monovalent alkali‐metal chlorides (Li, Na, K, Cs), magnesium chloride, divalent transition‐metal chlorides (Ni, Cu, Zn), trivalent lanthanide chlorides (La, Ce, Pr, Sm), and sodium sulfate across the calix4/PVA, calix6/PVA, and calix8/PVA membranes are studied and compared with the corresponding P_R values across a poly(styrene sulfonate) (PSS)/PVA multilayer membrane prepared under the same conditions. The P_R values of the alkali‐metal salts are between 4 and 17 × 10^–6 cm s^–1, those of magnesium chloride and the transition‐metal salts are 0.2–1.3 × 10^–6 cm s^–1, and those of the lanthanide salts are about 0.1 × 10^–6 cm s^–1. Possible origins for the large differences are discussed. Ion transport is first of all controlled by electrostatic effects such as Donnan rejection of di‐ and trivalent ions in the membrane, but metal‐ion complexation with the calixarene derivatives also plays a role. Complexation occurs especially between Li⁺ or Na⁺ and calix4, Mg²⁺, or Cu²⁺ and calix6, Cu²⁺, Zn²⁺, or the lanthanide ions and calix8. Divalent sulfate ions are found to replace the calixarene polyanions in the membrane. UV studies of the permeate solutions indicate that calix4 especially is displaced during sulfate permeation.     

Fabrication of a “Soft” Membrane Electrode Assembly Using Layer‐by‐Layer Technology

A new type of thin‐film electrode that does not utilize conducting polymers or traditional metal or chemical vapor deposition methods has been developed to create ultrathin flexible electrodes for fuel cells. Using the layer‐by‐layer (LbL) technique, carbon–polymer electrodes have been assembled from polyelectrolytes and stable carbon colloidal dispersions. Thin‐film LbL polyelectrolyte–carbon electrodes (LPCEs) have been successfully assembled atop both metallic and non‐metallic, porous and non‐porous substrates. These electrodes exhibit high electronic conductivities of 2–4 S cm^–1, and their porous structure provides ionic conductivities in the range of 10^–4 to 10^–3 S cm^–1. The electrodes show remarkable stability towards oxidizing, acidic, or delaminating basic solutions. In particular, an LPCE consisting of poly(diallyldimethyl ammonium chloride)/poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid)/carbon–platinum assembled on a porous stainless steel support yields an open‐circuit potential similar to that of a pure platinum electrode. With LbL carbon–polymer electrodes, the membrane‐electrode assembly (MEA) in a fuel cell can be made several times thinner, assume multiple geometries, and hence be more compact. The mechanism for LPCE deposition, electrode structure, and miniaturization will be presented and discussed, and demonstrations of the LbL electrodes in a traditional Nafion‐based proton fuel cell and the first demonstration of a thin‐film hydrogen–air “soft” fuel cell fully constructed using multilayer assembly are described.     

Freely Suspended Layer‐by‐Layer Nanomembranes: Testing Micromechanical Properties

Freely suspended nanocomposite layer‐by‐layer (LbL) nanomembranes composed of a central layer of gold nanoparticles sandwiched between polyelectrolyte multilayers are fabricated via spin‐assisted LbL assembly. The diameter of the circular membranes is varied from 150 to 600 μm and the thickness is kept within the range of 25–70 nm. The micro‐ and nanomechanical properties of these membranes are studied using a combination of resonance‐frequency and bulging tests, and point‐load nanodeflection experiments. Our results suggest that these freely suspended nanomembranes, with a Young's modulus of 5–10 GPa are very robust and can sustain multiple significant deformations. They are very sensitive to minor variations in pressure, surpassing ordinary semiconductor and metal membranes by three to four orders of magnitude and therefore have potential applications as pressure and acoustic microsensors.     

Pseudobilayer Vesicle Formation via Layer‐by‐Layer Assembly of Hydrophobically Modified Polymers on Sacrificial Substrates

A bilayer of a hydrophobically modified polyelectrolyte, octadecyl poly(acrylamide) (PAAm), sandwiched between the layers of a hydrophilic polyelectrolyte, poly(ethyleneimine) (PEI), is prepared by the sequential electrostatic–hydrophobic–electrostatic‐interaction‐driven self‐assembly on planar and colloid substrates. This process results in a PEI/[PAAm]₂/PEI‐multilayer‐coated substrate. The removal of a PAA/PEI/[PAAm]₂/PEI‐multilayer‐coated decomposable colloidal template produces hollow capsules. Irregular hydrophobic domains of the [PAAm]₂ bilayer in the PEI/[PAAm]₂/PEI‐multilayer capsule are infiltrated with a lipid to obtain a uniform, distinct hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure.     

Inside Front Cover: Freely Suspended Layer‐by‐Layer Nanomembranes: Testing Micromechanical Properties (Adv. Funct. Mater. 5/2005)

A study of the micromechanical properties of layer‐by‐layer nanomembranes composed of a center layer of gold nanoparticles is reported by Tsukruk and co‐workers on p. 771. The micro‐ and nanomechanical properties of these membranes are measured using a combination of resonance‐frequency tests, bulging tests, and point‐load nanodeflection experiments. These freely suspended nanomembranes (right) with an elastic modulus of 5–10 GPa are very robust and can sustain multiple significant deformations (left, image obtained by B. Rybak and P. Kladitis). They are sensitive to variations in pressure and therefore have potential applications in pressure and acoustic sensors. Freely suspended nanocomposite layer‐by‐layer (LbL) nanomembranes composed of a central layer of gold nanoparticles sandwiched between polyelectrolyte multilayers are fabricated via spin‐assisted LbL assembly. The diameter of the circular membranes is varied from 150 to 600 μm and the thickness is kept within the range of 25–70 nm. The micro‐ and nanomechanical properties of these membranes are studied using a combination of resonance‐frequency and bulging tests, and point‐load nanodeflection experiments. Our results suggest that these freely suspended nanomembranes, with a Young's modulus of 5–10 GPa are very robust and can sustain multiple significant deformations. They are very sensitive to minor variations in pressure, surpassing ordinary semiconductor and metal membranes by three to four orders of magnitude and therefore have potential applications as pressure and acoustic microsensors.     

Tubular Titania Nanostructures via Layer‐by‐Layer Self‐Assembly

Nanostructured titania‐polyelectrolyte composite and pure anatase and rutile titania tubes were successfully prepared by layer‐by‐layer (LbL) deposition of a water‐soluble titania precursor, titanium(IV ) bis(ammonium lactato) dihydroxide (TALH) and the oppositely charged poly(ethylenimine) (PEI) to form multilayer films. The tube structure was produced by depositing inside the cylindrical pores of a polycarbonate (PC) membrane template, followed by calcination at various temperatures. The morphology, structure and crystal phase of the titania tubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and UV‐vis absorbance measurements. The as‐prepared anatase titania tubes exhibit very promising photocatalytic properties, demonstrated by the degradation of the azodye methyl orange (MO) as a model molecule. They are also easily separated from the reaction system by simple filtration or centrifugation, allowing for straightforward recycling. The reported strategy provides a simple and versatile technique to fabricate titania based tubular nanostructures, which could easily be extended to prepare tubular structures of other materials and may find application in catalysis, chemical sensing, and nanodevices.     

Layer‐by‐Layer Fabrication and Characterization of Gold‐Nanoparticle/Myoglobin Nanocomposite Films

Multilayer thin films of ～ 7 nm diameter gold nanoparticles (GNPs) linked with horse heart myoglobin (Mb) are fabricated, for the first time, by layer‐by‐layer (LbL) assembly on glass slides, and silicon and plastic substrates. The GNP/Mb nanocomposite films show sharp surface plasmon resonance (SPR) absorption bands that are used to follow the LbL growth of the film and to determine the kinetics of GNP adsorption on the Mb‐modified surface. The GNP/Mb nanocomposite films are characterized using atomic force microscopy, transmission electron microscopy, polarized UV‐vis spectroscopy, and spectroscopic ellipsometry. The GNPs in the multilayer films are spatially separated from one another, and interparticle interactions remain in the film, making it optically anisotropic. The GNP/Mb nanocomposite films are stable in air at temperatures up to 100 °C, and can withstand successive immersions in strongly acidic and basic solutions. The SPR absorption band of the GNP/Mb nanocomposite film in air exhibits a red‐shift in the wavelength maximum and an increase in the maximum absorbance relative to that in water. This result, which is in contrast to that observed with a GNP monolayer on an aminosilane‐functionalized substrate, suggests the shrinkage in air and swelling in water of Mb molecules embedded in the nanocomposite film.     

Time Controlled Protein Release from Layer‐by‐Layer Assembled Multilayer Functionalized Agarose Hydrogels

Axons of the adult central nervous system exhibit an extremely limited ability to regenerate after spinal cord injury. Experimentally generated patterns of axon growth are typically disorganized and randomly oriented. Support of linear axonal growth into spinal cord lesion sites has been demonstrated using arrays of uniaxial channels, templated with agarose hydrogel, and containing genetically engineered cells that secrete brain‐derived neurotrophic factor (BDNF). However, immobilizing neurotrophic factors secreting cells within a scaffold is relatively cumbersome, and alternative strategies are needed to provide sustained release of BDNF from templated agarose scaffolds. Existing methods of loading the drug or protein into hydrogels cannot provide sustained release from templated agarose hydrogels. Alternatively, here it is shown that pH‐responsive H‐bonded poly(ethylene glycol)(PEG)/poly(acrylic acid)(PAA)/protein hybrid layer‐by‐layer (LbL) thin films, when prepared over agarose, provided sustained release of protein under physiological conditions for more than four weeks. Lysozyme, a protein similar in size and isoelectric point to BDNF, is released from the multilayers on the agarose and is biologically active during the earlier time points, with decreasing activity at later time points. This is the first demonstration of month‐long sustained protein release from an agarose hydrogel, whereby the drug/protein is loaded separately from the agarose hydrogel fabrication process.     

Surface Imprinting in Layer‐by‐Layer Nanostructured Films

In this Full Paper, we develop a novel approach for the generation of stable molecularly imprinted sites in polymeric films by combining the layer‐by‐layer (LbL) technique and photochemical crosslinking of the layered structure. After photo‐crosslinking, the imprinted films show high reproducibility and rapid loading and unloading of imprinted sites by the template molecules. Moreover, the competitive adsorption of template molecules and redox labels into the imprinted film using electrochemical methods indicates that the imprinted film has higher affinity for template molecules. We believe this approach may have some advantages over traditional ways of preparing imprinted sites in polymer matrices and it may open a new avenue for the functionalization of LbL films.     

TiO2‐Based Composite Nanotube Arrays Prepared via Layer‐by‐Layer Assembly

A simple and versatile technique has been developed to prepare TiO₂ and TiO₂‐based composite (TiO₂–CdS and TiO₂–Au) nanotube arrays. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray (EDX) analysis, X‐ray diffraction (XRD), thermogravimetric analysis (TGA), UV‐vis spectroscopy, and photoluminescence (PL) spectroscopy are used to characterize their morphology, structure, composition, and properties. The TiO₂–CdS nanotubes contained many TiO₂ and CdS quantum dots and exhibited a novel PL band in the blue‐wavelength range. The reported strategy will be useful for fabricating nanoparticle–nanoparticle composite nanostructure arrays, which are suitable for applications in catalysis, chemical sensors, nanoelectrodes, and nanodevices.     

Enhanced Electrochromism with Rapid Growth Layer‐by‐Layer Assembly of Polyelectrolyte Complexes

In this work, a facile method to deposit fast growing electrochromic multilayer films with enhanced electrochemical properties using layer‐by‐layer (LbL) self‐assembly of complex polyelectrolyte is demonstrated. Two linear polymers, poly(acrylic acid) (PAA) and polyethylenimine (PEI), are used to formulate stable complexes under specific pH to prepare polyaniline (PANI)/PAA‐PEI multilayer films via LbL deposition. By introducing polymeric complexes as building blocks, [PANI/PAA‐PEI]_n films grow much faster compared with [PANI/PAA]_n films, which are deposited under the same condition. Unlike the compact [PANI/PAA]_n films, [PANI/PAA‐PEI]_n films exhibit porous structure that is beneficial to the electrochemical process and leads to improved electrochromic properties. An enhanced optical modulation of 30% is achieved with [PANI/PAA‐PEI]₃₀ films at 630 nm compared with the lower optical modulation of 11% measured from [PANI/PAA]₃₀ films. The switching time of [PANI/PAA‐PEI]₃₀ films is only half of that of [PANI/PAA]₃₀ films, which indicates a faster redox process. Utilizing polyelectrolyte complexes as building blocks is a promising approach to prepare fast growing LbL films for high performance electrochemical device applications.     

Lubricant‐Infused Nanoparticulate Coatings Assembled by Layer‐by‐Layer Deposition

Omniphobic coatings are designed to repel a wide range of liquids without leaving stains on the surface. A practical coating should exhibit stable repellency, show no interference with color or transparency of the underlying substrate and, ideally, be deposited in a simple process on arbitrarily shaped surfaces. We use layer‐by‐layer (LbL) deposition of negatively charged silica nanoparticles and positively charged polyelectrolytes to create nanoscale surface structures that are further surface‐functionalized with fluorinated silanes and infiltrated with fluorinated oil, forming a smooth, highly repellent coating on surfaces of different materials and shapes. We show that four or more LbL cycles introduce sufficient surface roughness to effectively immobilize the lubricant into the nanoporous coating and provide a stable liquid interface that repels water, low‐surface‐tension liquids and complex fluids. The absence of hierarchical structures and the small size of the silica nanoparticles enables complete transparency of the coating, with light transmittance exceeding that of normal glass. The coating is mechanically robust, maintains its repellency after exposure to continuous flow for several days and prevents adsorption of streptavidin as a model protein. The LbL process is conceptually simple, of low cost, environmentally benign, scalable, automatable and therefore may present an efficient synthetic route to non‐fouling materials.     

Porous Nanofilm Biomaterials Via Templated Layer‐by‐Layer Assembly

Hydrogel‐like biomaterials are often too soft to support robust cell adhesion, yet methods to increase mechanical rigidity (e.g., covalent cross‐linking the gel matrix) can compromise bioactivity by suppressing the accessibility or activity of embedded biomolecules. Nanoparticle templating is reported here as a strategy toward porous, layer‐by‐layer assembled, thin polyelectrolyte films of sufficient mechanical rigidity to promote strong initial cell adhesion, and that are capable of high bioactive species loading. Latex nanoparticles are incorporated during layer‐by‐layer assembly, and following 1‐ethyl‐3‐[3‐dimethylaminopropyl]carbodiimide/N‐hydroxysulfosuccinimide (EDC‐NHS) cross‐linking of the polyelectrolyte film, are removed via exposure to tetrahydrofuran (THF). THF exposure results in only a partial reduction in film thickness (as observed by ellipsometry), suggesting the presence of internal pore space. The attachment, spreading, and metabolic activity of pre‐osteoblastic MC3T3‐E1 cells cultured on templated, cross‐linked films are statistically similar to those on non‐templated films, and much greater than those on non‐cross‐linked films. Laser scanning confocal microscopy and quartz crystal microgravimetry indicate a high capacity for bioactive species loading (ca. 10% of film mass) in nanoparticle templated films. Porous nanofilm biomaterials, formed via layer‐by‐layer assembly with nanoparticle templating, promote robust cell adhesion and exhibit high bioactive species loading, and thus appear to be excellent candidates for cell‐contacting applications.     

Polyelectrolyte‐Clay‐Protein Layer Films on Microfluidic PDMS Bioreactor Surfaces for Primary Murine Bone Marrow Culture

Poly(dimethylsiloxane) (PDMS) microbioreactors with computerized perfusion controls would be useful for engineering the bone marrow microenvironment. However, previous efforts to grow primary bone marrow cells on PDMS substrates have not been successful due to the weak attachment of cells to the PDMS surface even with adsorption of cell adhesive proteins such as collagen or fibronectin. In this work, modification of the surface of PDMS with biofunctional multilayer coatings is shown to promote marrow cell attachment and spreading. An automated microfluidic perfusion system is used to create multiple types of polyelectrolyte nanoscale coatings simultaneously in multiple channels based on layer‐by‐layer deposition of PDDA (poly(diallyldimethyl ammonium chloride)), clay, type IV collagen and fibronectin. Adherent primary bone marrow cells attached and spread best on a surface with composition of (PDDA/clay)₅ (Collagen/Fibronectin)₂ with negatively charged fibronectin exposed on the top, remaining well spread and proliferating for at least two weeks. Compared to traditional more macroscopic layer‐by‐layer methods, this microfluidic nanocomposite process has advantages of greater flow control, automatic processing, multiplexed fabrication, and use of lesser amounts of polymers and protein solutions.     

Flexible and Robust 2D Arrays of Silver Nanowires Encapsulated within Freestanding Layer‐by‐Layer Films

Freestanding layer‐by‐layer (LbL) films encapsulating controlled volume fractions (? = 2.5–22.5 %) of silver nanowires are fabricated. The silver nanowires are sandwiched between poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/PSS) films resulting in nanocomposite structures with a general formula of (PAH/PSS)₁₀PAH Ag(PAH/PSS)₁₀PAH. The Young's modulus, toughness, ultimate stress, and ultimate strain are evaluated for supported and freestanding structures. Since the diameter of the nanowires (73 nm) is larger than the thickness of the LbL films (total of about 50 nm), a peculiar morphology is observed with the silver nanowires protruding from the planar LbL films. Nanowire‐containing LbL films possess the ability to sustain significant elastic deformations with the ultimate strain reaching 1.8 %. The Young's modulus increases with increasing nanowire content, reaching about 6 GPa for the highest volume fraction, due to the filler reinforcement effect commonly observed in composite materials. The ultimate strengths of these composites range from 60–80 MPa and their toughness reaches 1000 kJ m^–3 at intermediate nanowire content, which is comparable to LbL films reinforced with carbon nanotubes. These robust freestanding 2D arrays of silver nanowires with peculiar optical, mechanical, and conducting properties combined with excellent micromechanical stability could serve as active elements in microscopic acoustic, pressure, and photothermal sensors.     

Spray Layer‐by‐Layer Electrospun Composite Proton Exchange Membranes

Polymer electrolyte films are deposited onto highly porous electrospun mats using layer‐by‐layer (LbL) processing to fabricate composite proton conducting membranes. By simply changing the assembly conditions for generation of the LbL film on the nanofiber mat substrate, three different and unique composite film morphologies can be achieved in which the electrospun mats provide mechanical support; the LbL assembly produces highly conductive films that coat the mats in a controlled fashion, separately providing the ionic conductivity and fuel blocking characteristics of the composite membrane. Coating an electrospun mat with the LbL dipping process produces composite membranes with “webbed” morphologies that link the fibers in‐plane and give the composite membrane in‐plane proton conductivities similar to that of the pristine LbL system. In contrast, coating an electrospun mat using the spray‐LbL process without vacuum produces a uniform film that bridges across all of the pores of the mat. These membranes have methanol permeability similar to free‐standing poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6‐dimethyl 1,4‐phenylene oxide) (PDAC/sPPO) thin films. Coating an electrospun mat with the vacuum‐assisted spray‐LbL process produces composite membranes with conformally coated fibers throughout the bulk of the mat with nanometer control of the coating thickness on each fiber. The mechanical properties of the LbL‐coated mats display composite properties, exhibiting the strength of the glassy PDAC/sPPO films when dry and the properties of the underlying electrospun polyamide mat when hydrated. By combining the different spray‐LbL fabrication techniques with electrospun fiber supports and tuning the parameters, mechanically stable membranes with high selectivity can be produced, potentially for use in fuel cell applications.     

Layer‐by‐Layer Controlled Perovskite Nanocomposite Thin Films for Piezoelectric Nanogenerators

Perovskite nanoparticle‐based nanocomposite thin films strictly tailored using unconventional layer‐by‐layer (LbL) assembly in organic media for piezoelectric nanogenerators (NGs) are demonstrated. By employing sub‐20‐nm BaTiO₃ nanoparticles stabilized by oleic acid ligands (i.e., OA‐BTO_NPs) and carboxylic acid (COOH)‐functionalized polymers, such as poly(acrylic acid) (PAA), the resulting OA‐BTO_NP/PAA nanocomposite multilayers are prepared by exploiting the high affinity between the COOH groups of PAA and the BTO_NPs. The ferroelectric and piezoelectric performance of the (PAA/OA‐BTO_NP)_n thin films can be precisely controlled by altering the bilayer number, inserted polymer type, and OA‐BTO_NP size. It is found that the LbL assembly in nonpolar solvent media can effectively increase the quantity of adsorbed OA‐BTO_NPs, resulting in the dramatic enhancement of electric power output from the piezoelectric NGs. Furthermore, very low leakage currents are detected from the (PAA/OA‐BTO_NP)_n thin films for obtaining highly reliable power‐generating performance of piezoelectric NGs.     

Covalent Layer‐by‐Layer Assembly of Conjugated Polymers and CdSe Nanoparticles: Multilayer Structure and Photovoltaic Properties

Hybrid thin films of conjugated polymers and CdSe nanoparticles have been fabricated by using a layer‐by‐layer (LbL) approach driven by covalent coupling reactions. This method permits facile covalent crosslinking of the polymer/nanoparticle interlayers in common organic solvents, which provides a general route for preparing robust and uniform functional thin films. The deposition process is linearly related to the number of bilayers as monitored by UV‐vis absorption spectroscopy and ellipsometry. Characterization of the multilayer structures has been carried out by fluorescence spectroscopy, X‐ray photoelectron spectroscopy (XPS), and grazing‐angle Fourier‐transform infrared spectroscopy (FTIR). Techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM) have also been used. A preliminary application of the hybrid films in the development of organic photovoltaics is presented. Upon illumination with white light at 10 mW cm^–2, the self‐assembled multilayer films exhibit steady photocurrent responses with an overall optical‐to‐electrical power conversion efficiency of 0.71 %.     

Enhanced Photocatalytic Activity using Layer‐by‐Layer Electrospun Constructs for Water Remediation

Endocrine disruptors such as bisphenol A (BPA) are environmental pollutants that interfere with the body's endocrine system because of their structural similarity to natural and synthetic hormones. Due to their strong oxidizing potential to decompose such organic pollutants, colloidal metal oxide photocatalysts have attracted increasing attention for water detoxification. However, achieving both long‐term physical stability and high efficiency simultaneously with such photocatalytic systems poses many challenges. Here a layer‐by‐layer (LbL) deposition approach is reported for immobilizing TiO₂ nanoparticles (NPs) on a porous support while maintaining a high catalytic efficiency for photochemical decomposition of BPA. Anatase TiO₂ NPs ≈7 nm in diameter self‐assemble in consecutive layers with positively charged polyhedral oligomeric silsesquioxanes on a high surface area, porous electrospun polymer fiber mesh. The TiO₂ LbL nanofibers decompose approximately 2.2 mg BPA per mg of TiO₂ in 40 h of illumination (AM 1.5G illumination), maintaining first‐order kinetics with a rate constant (k) of 0.15 h^?1 for over 40 h. Although the colloidal TiO₂ NPs initially show significantly higher photocatalytic activity (k ≈ 0.84 h^?1), the rate constant drops to k ≈ 0.07 h^?1 after 4 h of operation, seemingly due to particle agglomeration. In the BPA solution treated with the multilayered TiO₂ nanofibers for 40 h, the estrogenic activity, based on human breast cancer cell proliferation, is significantly lower than that in the BPA solution treated with colloidal TiO₂ NPs under the same conditions. This study demonstrates that water‐based, electrostatic LbL deposition effectively immobilizes and stabilizes TiO₂ NPs on electrospun polymer nanofibers for efficient extended photochemical water remediation.     

Preparation of Protamine–Titania Microcapsules Through Synergy Between Layer‐by‐Layer Assembly and Biomimetic Mineralization

A novel approach combining layer‐by‐layer (LbL) assembly with biomimetic mineralization is proposed to prepare protamine–titiania hybrid microcapsules. More specifically, these microcapsules are fabricated by alternative deposition of positively charged protamine layers and negatively charged titania layers on the surface of CaCO₃ microparticles, followed by dissolution of the CaCO₃ microparticles using EDTA. During the deposition process, the protamine layer induces the hydrolysis and condensation of a titania precursor, to form the titania layer. Thereafter, the negatively charged titania layer allows a new cycle of deposition step of the protamine layer, which ensures a continuous LbL process. The morphology, structure, and chemical composition of the microcapsules are characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and X‐ray photoelectron spectroscopy. Moreover, these protamine–titania hybrid microcapsules are first employed as the carrier for the immobilization of yeast alcohol dehydrogenase (YADH), and the encapsulated YADH displays enhanced recycling stability. This approach may open a facile, general, and efficient way to prepare organic–inorganic hybrid materials with different compositions and shapes.