Supporting Information
Characterisation of the coatings on Si wafers by IR ATR spectra
To determine the characteristics of the different FAS-SiQAC (S1), SiQAC+FAS (S2), FAS and SiQAC coatings and their influence on the functional properties of the modified cotton fabric samples, the chemical composition of the FAS and SiQAC precursors was determined from the IR transmission spectra of FAS and SiQAC deposited on Si substrates (Figs. S1 and S2). Because FAS and SiQAC are both commercially available precursors for which the chemical compositions are not explicitly known, the spectra were analysed in comparison to the spectra of chemically similar precursors with clearly defined structures, i.e., 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES, 95%, ABCR) (Fig. S3a) and octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride (OQAS-TMOS, 60%, ABCR) (Fig. S3b). Surprisingly, good agreement between the FAS and PFOTES spectra (Fig. S1) and the SiQAC and OQAS-TMOS spectra (Fig. S2) confirmed agreement between the chemical compositions of the precursors caused by the similar molecular groups and species present in the coatings.
Because the structural similarity between FAS and PFOTES (Fig. S1) had already been confirmed in our previous research [1], only the key findings are summarised here. The perfluoro chain bands in the spectra of PFOTES were observed at 1240 cm-1 ((νa (CF2) mixed with rocking (CF2)), 1209 cm-1 (νa (CF2) + νa (CF3) and 1144 cm-1 ((νs (CF2) modes [2], but the band assigned to (νs (CF2), deformation νa (CF2)) at 1150 cm-1 was red-shifted to 1144 cm-1. In the case of FAS, the bands of the perfluoro groups were slightly shifted with respect to those of PFOTES and appeared at 1238, 1207 and 1143 cm-1. Some bands appeared with different intensities, which suggest that the length of the perfluoro chains differed for FAS and PFOTES [3].
The IR spectra in Fig. 2 confirm that both precursors, OQAS-TMOS and SiQAC, exhibit characteristic bands at 2917 and 2845 cm-1, as well as bands in the range of 1482 to 1460 cm-1 because of asymmetric and symmetric stretching vibrations of the C–H bonds (νa(CH2), νs(CH2) and ν(CH3)) of the aliphatic alkyl groups, the intensity of which is directly related to the length of the N-alkyl chain [4-6]. A broad band in the spectral region of 3400 to 3000 cm-2, which corresponds to the OH stretching vibration, reveals the presence of moisture but this band could also be related to free silanol OH stretching vibration [1, 4, 7]. The IR spectra of OQAS-TMOS and SiQAC differed with respect to the bands in the spectral region of 1300–600 cm-1, which are significant for different silicon groups in the chemical structure. Si–OMe bands at 1190, 1080 and 817 cm-1 were present in the spectrum of the non-hydrolysed OQAS-TMOS. The intensity of these bands significantly decreased after the hydrolisation reaction in the presence of acidified water and a strong Si–OH band at 910 cm-1 appeared instead [1, 7]. The band at 1021 cm-1 arising from the stretching vibration of Si−O−Si from silicate was hardly detected in the spectrum of the hydrolysed OQAS-TMOS. Although the silanol group band at 922 cm-1 could clearly be seen in the SiQAC spectrum, a broad band that was slightly split into a doublet was observed in the spectral region from 1200 – 1000 cm-1. The bands at 1120 and 1095 cm-1 belong to the νas(Si−O−Si) and νs(Si−O−Si) stretching modes, which were attributed to the various condensation products (T1 T2 T3) of the Si−O−Si network formed after the condensation of completely [4] hydrolysed SiQAC (Fig. 2a, dotted line). Such a split is known to occur when siloxane chains become longer [45], which shows that the chemical structures of the OQAS-TMOS and SiQAC precursors differ to some extent. This is a reasonable result because the first compound is soluble in alcohol and the second is a waterborne product. Identification of the bands characteristic for FAS and SiQAC coatings is also presented in Table S1.
Fig. S1. ATR IR spectra of non-hydrolysed (a) and hydrolysed PFOTES (b) and FAS (c) deposited on Si substrate.
Fig. S2. ATR IR spectra of non-hydrolysed (a) and partially hydrolysed OQAS-TMOS (b) and SiQAC (c) deposited on Si wafer.
Table S1: Identification of the bands characteristic for FAS and SiQAC coatings.
Coating / Wavenumber (cm-1) / Vibrational modea) / ReferenceFAS / 1238 / νas(CF2) mixed with rocking (CF2) / 1-3
1207 / νas (CF2) + νas (CF3) / 1-3
1143 / νs (CF2) / 1-3
1070 / Si−O−Si / 1-3
SiQAC / 2917, 2845, 1482 / νas(CH2), νs(CH2) and ν(CH3) / 4-6
1120, 1095 / νas(Si−O−Si) and νs(Si−O−Si) / 4
922 / Si−OH / 4-6
a) ν – valence; νas – valence asymmetrical; νs – valence symmetrical.
PFOTES
OQAS-TMOS
Fig. S3. Chemical structure of (a) 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) and (b) octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride (OQAS-TMOS).
Liquid contact angles for the coatings deposited on glass substrates
The results of contact angle measurements with water, formamide, diiodomethane on the coated glass substrates are presented in Fig. S4. It can be seen from Fig. 4a that the two-component FAS+SiQAC coating applied during the S1 procedure exhibited higher contact angles for all tested liquids than the corresponding contact angles on the coating applied by the S2 procedure. Whereas the liquid contact angles increased with concentrations from 2.5% to 7.5% of FAS and SiQAC in the sol, irrespective of the application procedure (i.e., from sample A to sample C), the contact angles of water and formamide slightly decreased when the precursor concentration increased to 10% (samples D-S1 and D-S2). It can be inferred that the concentration of the two precursors in the mixture and the application procedure directly influence the repellence of the two-component coatings. These results differ from those obtained for the one-component FAS coating (Fig. 4b), for which excellent repellence was obtained at the lowest precursor concentration of 2.5% for all tested liquids and remained almost unchanged as the precursor concentration increased. As expected, the contact angles of all tested liquids for samples SiQAC A to SiQAC D were much lower than those for samples FAS A to FAS D (Fig. 4b), which indicates a lower repellence of the octadecyldimethylammonium groups of the antimicrobial precursor SiQAC compared with the fluoroalkyl moieties of the water- and oil- repellent precursor FAS. Accordingly, the presence of SiQAC in the SiQAC+FAS (S2) coating caused a decrease of the coating repellence, which was especially pronounced for samples A-S2 and B-S2.
a)
b)
Fig. S4. Contact angles of diiodomethane (DIM), water (W) and formamide (FA) on glass substrates coated with two-component FAS-SiQAC (S1) and SiQAC+FAS (S2) coatings with different sol concentrations applied by the S1 and S2 procedures (a) and coated with one-component FAS and SiQAC coatings (b) with different sol concentrations. Sol concentration: 2.5%, sample A; 5.0%, sample B; 7.5%, sample C; 10.0%, sample D.
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