Preparation of superhydrophilic nanosilica/polyacrylate hard coatings on plastic substrate for antifogging and frost‐resistant applications

Abstract

A series of photosensitive hydrophilic agents (T20) comprising Tween-20, isophorone diisocyanate, and 2-hydroxyethyl methacrylate moieties were synthesized and used in the preparation of antifog/frost resistant (AFF) hard coatings on plastic substrates. By means of a hydrophilic/hydrophobic bilayer design, the prepared coatings demonstrated not only AFF property but also water resistibility. The bottom layer is an organic-inorganic composite consisting of SiO 2 nanoparticles embedded in a polymeric network of crosslinked dipentaethritol hexaacrylate. The AFF layer incorporates T20 in the formulations and links covalently with the bottom layer through a UV-curing polymerization process. Various methods, for example, FTIR, SEM, contact angle, and steam/defrosting tests, were employed to characterize the prepared coatings. Optimally, the coatings were found to be transparent, strong (4H, pencil hardness), adhering perfectly (level 5B) to the poly(methyl methacrylate) substrate, and could be soaked in water for 24 h at 25 C without losing hydrophilicity (contact angle~0 ) or antifogging capability.Recently, a new promising approach was reported which introduced the layer-by-layer (LBL) assembly technique to prepare coatings that demonstrated both antifogging and antifrosting effects. [35][36][37][38][39] For example, Lee et al. assembled PVA/PAA multilayers and then post-treated with poly(ethylene glycol) methyl ether (PEG) to produce AFF coatings. 37 The PEG segments were found to serve, in addition to PVA and PAA, as sites to absorb nonfreezing water and prevent formation Additional Supporting Information may be found in the online version of this article.

Preparation of organic–inorganic hybridized dual‐functional antifog/antireflection coatings on plastic substrates

“…The coatings are also frost-resistant, as is demonstrated in Ref. 34. However, there would be a period (~45 s) of loss of transparency if the coatings were exposed in a cold environment for a while and then moved to a warm environment.…”

“…DBTDL (0.1 wt % of the total of 2-HEMA plus IPDI) was used as the catalyst for this urethanation reaction. After 2 h of reaction, Tween 20 was added and the reaction was continued for another 2 h. The molar ratio of 2-HEMA:IPDI:Tween 20 was set to 1:1:0.47, 34 and the solid content of the solution was adjusted to 20 wt % by means of MEK. The organo-nanosilica, MSiO 2 , was prepared by a modified sol-gel method developed previously, [33][34][35]38 compare Scheme 2(a,b).…”

“…After 2 h of reaction, Tween 20 was added and the reaction was continued for another 2 h. The molar ratio of 2-HEMA:IPDI:Tween 20 was set to 1:1:0.47, 34 and the solid content of the solution was adjusted to 20 wt % by means of MEK. The organo-nanosilica, MSiO 2 , was prepared by a modified sol-gel method developed previously, [33][34][35]38 compare Scheme 2(a,b). Briefly, TEOS was mixed with 2-propanol to form a solution, and then HCl (aq) with the molar ratio of H 2 O/ TEOS equal to 4 was added to initiate the hydrolysis and condensation of TEOS.…”

“…Steam tests were carried out to examine the AF capability of the AFAR coatings. [33][34][35] The sample was placed on top of a beaker with the AF surface exposed to saturated steam at~95 C. Condensation of water droplets occurring on the tested surface was photographed. Hardness of the coatings was determined by the pencil test (ASTM D3363), using standard pencils (JIS K5400, Mitsubishi) of different hardness (1~9H) at the load of 750 g. Tape tests (ASTM D3359) were performed to evaluate the adhesiveness of the coatings on the substrate.…”

“…[19][20][21]23,30 Recently, water-resistant AF coatings with a bilayer configuration were developed in our laboratory. [33][34][35] For example, the bottom layer, serving as a binder and a mechanical support, was an inorganic-organic composite of organically modified silica (MSiO 2 ) and polyacrylate. The top layer incorporated 2-hydroxyethyl methacrylate (HEMA)-modified Tween 20 as the hydrophilic agent, and bonded covalently to the bottom layer through UV-curing.…”