Junqi Sun

Layer-by-layer assembly for rapid fabrication of thick polymeric films

In the past two decades, layer-by-layer (LbL) assembly has been proven to be a convenient and versatile method to fabricate functional films. However, using traditional dipping LbL assembly to fabricate micrometer-thick films is time consuming. Compared with ultrathin films, micrometer-thick films prepared by LbL assembly possess enhanced mechanical stability, and allow deposition of a significantly increased amount of materials and the integration of multiple functions. These merits of thick films produced by LbL assembly can result in new functions and allow the functions of ultrathin films fabricated by LbL assembly to be optimized. In this tutorial review, the methods for rapid fabrication of thick polymeric films involving LbL assembly are reviewed. The functions of such films that are relevant to their micrometer thickness are discussed.

A facile layer-by-layer deposition process for the fabrication of highly transparent superhydrophobic coatings

A facile layer-by-layer deposition process is developed to fabricate highly-transparent superhydrophobic coatings, which comprise the underlying antireflective nanoporous silica layer and the top transparent superhydrophobic SiO(2) nanoparticle layer.

Intumescent Flame-Retardant and Self-Healing Superhydrophobic Coatings on Cotton Fabric

Flame-retardant and self-healing superhydrophobic coatings are fabricated on cotton fabric by a convenient solution-dipping method, which involves the sequential deposition of a trilayer of branched poly(ethylenimine) (bPEI), ammonium polyphosphate (APP), and fluorinated-decyl polyhedral oligomeric silsesquioxane (F-POSS). When directly exposed to flame, such a trilayer coating generates a porous char layer because of its intumescent effect, successfully giving the coated fabric a self-extinguishing property. Furthermore, the F-POSS embedded in cotton fabric and APP/bPEI coating produces a superhydrophobic surface with a self-healing function. The coating can repetitively and autonomically restore the superhydrophobicity when the superhydrophobicity is damaged. The resulting cotton fabric, which is flame-resistant, waterproof, and self-cleaning, can be easily cleaned by simple water rinsing. Thus, the integration of self-healing superhydrophobicity with flame retardancy provides a practical way to resolve the problem of washing durability of the flame-retardant coatings. The flame-retardant and superhydrophobic fabric can endure more than 1000 cycles of abrasion under a pressure of 44.8 kPa without losing its flame retardancy and self-healing superhydrophobicity, showing potential applications as multifunctional advanced textiles.

All Spraying Processes for the Fabrication of Robust, Self-Healing, Superhydrophobic Coatings

The spraying method is developed for the fabrication of mechanically robust and self-healing superhydrophobic coatings, which comprise highly porous and rough polyelectrolyte coatings preserved with low-surface-energy healing agents. These coatings can repetitively and autonomically restore superhydrophobicity in humid environments. After depletion of healing agents, superhydrophobic coatings with dual healing agents can regain their self-healing ability by re-spraying fluoroalkylsilane.

Polyelectrolyte Multilayers Impart Healability to Highly Electrically Conductive Films

Healable, electrically conductive films are fabricated by depositing Ag nanowires on water-enabled healable polyelectrolyte multilayers. The easily achieved healability of the polyelectrolyte multilayers is successfully imparted to the Ag nanowire layer. These films conveniently restore electrical conductivity lost as a result of damage by cuts several tens of micrometers wide when water is dropped on the cuts.

Mechanically Stable Antireflection and Antifogging Coatings Fabricated by the Layer-by-Layer Deposition Process and Postcalcination

Complexes of poly(diallyldimethylammonium chloride) (PDDA) and sodium silicate (PDDA-silicate) are alternately deposited with poly(acrylic acid) (PAA) to fabricate PAA/PDDA-silicate multilayer films. The removal of the organic components in the PAA/PDDA-silicate mulilayer films through calcination produces highly porous silica coatings with excellent mechanical stability and good adhesion to substrates. Quartz substrates covered with such porous silica coatings exhibit both antireflection and antifogging properties because of the reduced refractive index and superhydrophilicity of the resultant films. A maximum transmittance of 99.86% in the visible spectral range is achieved for the calcinated PAA/PDDA-silicate films deposited on quartz substrates. The wavelengths of maximum transmittance could be well tailored by simply changing the deposition cycles of multilayer films. The usage of PDDA-silicate complexes allows for the introduction of high porosity to the resultant silica coatings, which favors the fabrication of antireflection and antifogging coatings with enhanced performance. Meanwhile, PDDA-silicate complexes enable rapid fabrication of thick porous silica coatings after calcination because of the large dimensions of the complexes in solution. The easy availability of the materials and simplicity of this method for film fabrication might make the mechanically stable multifunctional antireflection and antifogging coatings potentially useful in a variety of applications.

Layer-by-Layer Deposition of Polyelectrolyte−Polyelectrolyte Complexes for Multilayer Film Fabrication

Positively charged poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complexes (noted as PAH-PAA) with a molar excess of PAH were layer-by-layer (LbL) assembled with polyanion poly(sodium 4-styrenesulfonate) (PSS) to produce multilayer films. The film structure and deposition behavior of the PAH-PAA/PSS films were influenced by the structure of PAH-PAA complexes in solution. For the PAH-PAA complexes with a low ratio of PAA to PAH the PAH-PAA complexes have low-level cross-linking and are flexible. The resultant PAH-PAA/PSS films have a thin film thickness and smooth surface and exhibit a nonlinear deposition behavior where the amount of PAH-PAA complexes and PSS deposited in each deposition cycle are larger than in its previous cycle. The PAH-PAA complexes with a high ratio of PAA to PAH have high-level cross-linking and are rigid. The PAH-PAA/PSS films constructed from the rigid PAH-PAA complexes have a large film thickness and rough surface and exhibit a linear deposition behavior. Deposition of the PAH-PAA/PSS films was well characterized by quartz crystal microbalance, atomic force microscopy, and scanning electron microscopy. The thermally cross-linked PAH-PAA/PSS films can be released from substrate to form stable free-standing films by an ion-triggered exfoliation method. Meanwhile, positively charged PAH-PAA complexes can be LbL assembled with negatively charged PAH-PAA complexes with a molar excess of PAA to produce multilayer films. Use of polyelectrolyte-polyelectrolyte complexes as building blocks for LbL fabrication provides a facile way to tailor the structures of the resultant films by simply changing the structure of the complexes in solution.

Rapid and substrate-independent layer-by-layer fabrication of antireflection- and antifogging-integrated coatings

The antireflection- and antifogging-integrated coatings are widely useful in daily life because they can effectively enhance the transmission of light and meanwhile considerably prevent water condensation. Herein, we present a rapid, straightforward and substrate-independent method for the fabrication of antireflection- and antifogging-integrated coatings by layer-by-layer deposition of mesoporous silica (MSiO2) nanoparticles and poly(diallyldimethylammonium chloride) (PDDA). Quartz substrates covered with (MSiO2/PDDA)*3 coatings exhibit both antireflection and antifogging properties because the highly porous MSiO2 nanoparticles and their loose stacking in MSiO2/PDDA coatings enable the fabrication of superhydrophilic porous coatings with a low refractive index. A maximum transmittance of 99.9% in the visible spectral range is achieved for the (MSiO2/PDDA)*3 coatings deposited on quartz substrates. The antireflection and antifogging coatings can be conveniently deposited on daily used plastic substrates such as polycarbonate and Columbia resin CR-39. The rapid fabrication of the antireflection and antifogging (MSiO2/PDDA)*3 coatings is benefited from the large dimension and the fast adsorption kinetics of MSiO2 nanoparticles.

Assembly of alternating TiO2/v\CdS nanoparticle composite films

A composite film comprising TiO2 and CdS nanoparticles was fabricated based on an alternating deposition method; this was confirmed by UV–VIS spectroscopy, TEM, and photocurrent measurements.

Fabrication of a Stable Polyelectrolyte/Au Nanoparticles Multilayer Film

The fabrication of stable polyelectrolyte/Au nanoparticle multilayer films was achieved by the UV irradiation of layer-by-layer self-assembled multilayers consisting of diazoresins and Au nanoparticles. The method promises to be a simple and efficient strategy to construct covalently attached organic/inorganic multilayer hybrids.