Inorganic-Organic Nanocomposite Based Hard-Coatings on Plastics Using In Situ Generated Nano SiO 2 Bonded with Si-O-Si PEO Hybrid Network

Transcription

1 Inorganic-Organic Nanocomposite Based Hard-Coatings on Plastics Using In Situ Generated Nano SiO 2 Bonded with PEO Hybrid Network Samar Kumar Medda and Goutam De* SUPPORTING INFORMATION Absorbance (arb. unit) Si-CH 2 CH 3 Ethanol C-O Methanol C-O (a) GLYMO TEOS n-butanol mixture (b) 20 min hydrolysis at 27±1 C (c) 90 min reflux at 79±1 C (d) after 2h of Al(acac) 3 addition Si-OH Ethanol C-O Epoxy str Epoxy str Wavenumber (cm -1 ) Figure S1. FTIR spectra recorded at different stages of the sol preparation as indicated in the body of the figure. 1

2 An approximate density calculation based on the nominal composition of the cured hard-coatings: An approximate density value of the cured hard-coating has been calculated using its nominal composition i.e wt% silica-37.46% PEO. In this calculation we have considered the true density value of amorphous silica i.e. 2.2 g cm 3 and in case of PEO 1.13 g cm 3. It may be noted here that the density of silica has been considered 2.2 g cm 3 considering the whole component is fully dense; the density value of PEO is an approximate value considering roughly an average M w of ~100, With these approximations the calculated density of the coating is found to be g cm 3 using the mixing rule. However, in true sense the density of the coating should be less than this calculated value because we considered the highest density value of silica (the density of network silica should be less than the silica nanoparticles) in this calculation. So the estimated density value (1.70 g cm 3 ) obtained by the X-ray reflectivity (XRR) method can be considered accurate. 2

3 Standard testing procedures of hard-coatings on plastics 16,30-32 There are several standard tests that are used in the plastic ophthalmic lens industry to quantify the abrasion resistance and adhesion of coatings. Cross cut and adhesive tape test of the coatings following DIN or ASTM D 3359 specifications was performed to evaluate the adhesion of the coatings with the plastic surface. 16,30 This standard procedure is as follows: Using a cutting device such as a razor blade, six parallel cuts 1.5 mm ± 0.5 mm apart and approximately 15 to 20 mm in length are made in the coating on the front or convex surface of the lens. Another six parallel cuts 1.5 mm ± 0.5 mm apart are made in the coating perpendicular to the first set. This forms a cross-hatched pattern of squares over which tape is applied, such as Birla 3M Scotch Magic Tape #810. The tape then is pulled rapidly as close to an angle of 180 as possible, and the percent adhesion is quantified by the amount of coating removed from the squares in the cross-hatched pattern. The 180 reference means that the tape is pulled back over itself in a direction that is nearly parallel to the substrate surface. The abrasion test of the coated plastic surface was performed using a US military specification lens coating hardness tester kit in accordance with MIL-F ,30 The kit contains one brass instrument with a spring that was calibrated for 2.5 lbs of pressure. The eraser (rubber-pumice stone composite) inserts provided with the instrument are manufactured and certified to conform to US federal specification MIL-E-12397B. The test was performed by rubbing across the coated surface (20 cycles or more) with the eraser bearing 2.5 lbs of pressure followed by inspection (visual or using microscope) of scratches if any. Pencil hardness of the coated surface was evaluated following ASTM D 3363 specifications using a pencil hardness tester (BYK Gardner instrument). 30 The pencil hardness value is given according to grade of pencil such as 9B-9H. For testing the sample, first pencil is inserted into the machine then it must touch the test surface, and is tighten the lamping screw. Then pencil is moved over the surface about 6-12 mm under a fixed load of 750 gm and a fixed angle of 45 degrees. The test is repeated using successive grade pencils where one does not scratch and next one does scratch. The pencil grade for which it does not scratch the sample is the value of hardness. 3

4 Coated lenses were also subjected to several other tests e. g. chemical durability (boiling in salt solution 30,31 ), keeping in physiological NaCl solution for 40 h, 32 3-min ultrasonic treatment in N/20 NaOH solution, 3-min ultrasonic treatment in 10% tartaric acid solution 32 and thermal 30,31 tests. This boiling in salt solution test 30,31 evaluates the ability of a hard-coat to adhere to a substrate (sheet, lens or other shape) and the susceptibility of the coating to crazing. A coated lens is subjected to five to ten cycles of thermal shock by submersing the coated lens for two minutes in a boiling salt water solution which comprises 3.5 liters of deionized water, grams of sodium chloride, and 29.2 grams of sodium dihydrogen orthophosphate, followed by submersing the coated lens for one minute in water at 24±2 C Coating performance is quantified by whether or not coating layer detachment or complete delamination from the substrate occurs, and by whether or not crazing of the coating occurs. The thermal test 30,31 evaluates the ability of a hard-coat to adhere to a substrate of any shape (sheet, lens, other shape etc.) and the susceptibility of the coating to crazing at an elevated temperature. A coated substrate is subjected to six hours of thermal aging in an air circulating oven at 80 C and coating performance is quantified by whether or not crazing of the coating occurs. 4

5 Table S1. Test results of the Thermally Cured Nanocomposite Coatings Deposited on CR-39 Grade Plastic Lens-Substrates Having Coating Thickness µm. Name of the Test Specifications Result Adhesion 16,30,31 Abrasion 16,30,32 DIN or ASTM D 3359 MIL-F Eraser: MIL-E-12397B ASTM class 5B (highest standard) No scratches on the surface of the coating after more than 100 abrasion cycles Pencil ASTM D H hardness 31,32 Boiling salt water 31,32 Chemical endurance test Coating can resist up to 10 cycles Thermal Test 31,32 80 C for 6 h in an air oven No cracking/crazing of the coating Isopropanol test Kept 40 h in isopropanol Physiological salt solution test h in 0.9 wt% NaCl solution at room NaOH solution test Tartaric acid solution test 32 temperature 3-min ultrasonic treatment in N/20 NaOH solution at room temperature 3-min ultrasonic treatment 10% tartaric acid solution 5