Letter www.acsami.org
Anti-Fogging/Self-Healing Properties of Clay-Containing Transparent Nanocomposite Thin Films Matt W. England, Chihiro Urata, Gary J. Dunderdale, and Atsushi Hozumi* National Institute of Advanced Industrial Science and Technology (AIST), 2266-98, Anagahora, Shimoshidami, Nagoya 463-8560, Japan S Supporting Information *
ABSTRACT: Highly transparent antifogging films were successfully prepared on various substrates, including glass slides, silicon, copper and PMMA, by spin-coating a mixture of polyvinylpyrrolidone and aminopropyl-functionalized, nanoscale clay platelets. The resulting films were superhydrophilic and showed more than 90% transmission of visible light, as well as excellent antifogging and self-healing properties.
KEYWORDS: Antifogging, self-healing, hydrogel, nanocomposite, artificial clay, aminosilane, polyvinylpyrrolidone
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generally highly hydrophilic and possess self-healing properties which are induced by the reformation of broken bonds after mechanical damage. Among the various materials so far reported, we have focused on a noncovalent clay-cross-linked nanocomposite gel. This composite, first reported by Patil et al.,23 is a hydrogel formed from high-molecular-weight (MW) polyvinylpyrrolidone (PVP; MW ∼1300 kDa) and a dispersion of a synthetic aminopropyl-functionalized clay platelets (AMP-clay), with a 2:1 phyllosilicate structure consisting of a two-dimensional magnesium oxide (brucite) core flanked by functionalized silicate sheets.23−28 The resulting composite gels were reported to be highly transparent, stable in both air and water, and retained their shapes even after absorbing up to 3000 wt % water.23 They also showed good stability in high ionic strength solutions and within the pH range of 4−10, as well as self-healing properties after being damaged or cut into pieces,23,29 although the gel was reported not form using lower MW (∼40 kDa) PVP.23 Despite these composite gels showing hydrophilic and self-healing properties, and seeming to meet the high demand for practical functional coatings, their thin film behavior and applicability as an antifogging coating has not yet been studied. Here we explore the use of these unique composites as antifogging coatings and report on their properties, durability, and self-healing abilities. The AMP-clay was prepared using a one-pot ethanolic sol−gel synthesis as described in previous reports (experimental details in the Supporting Information).23−26,28−30 Briefly, magnesium chloride hexahydrate (MgCl2·6H2O) was dissolved in ethanol, after which 3-aminopropyl triethoxysilane (APTES), which was
ormation of water droplets on transparent solid surfaces (fogging) scatters light and reduces optical transmission, which can both be a major issue for the everyday use of eyeglasses, windshields and goggles, and also reduce the efficiency of medical/analytical instruments, solar energy panels and other industrial equipment.1−3 To prevent fogging, extensive research on the control of surface wetting/dewetting behavior, typically using superhydrophobicity and superhydrophilicity, has been reported over the past decade.2,4−7 However, superhydrophobic surfaces with very high static contact angles (CAs, θS) of over 150° are not ideal under high humidity conditions, because droplets can form on contact with water.8,9 On the other hand, superhydrophilic surfaces with very low θS (
