Marine antifouling efficacy of amphiphilic poly(coacrylate) grafted PDMSe: effect of graft molecular weight
Cary A. Kuliashaa, John A. Finlayb, Sofia C. Francob, Anthony S.Clareb, Shane J. Stafslienc,and Anthony B. Brennana
aDepartment of Materials Science and Engineering, University of Florida, Gainesville, FL, USA;bSchool of Marine Science and Technology, Newcastle University, Newcastle upon Tyne, UK;cOffice of Research and Creative Activity, North Dakota State University, Fargo, ND, USA
Supplemental Information
Bulk Copolymer Characterization
GPC analysis was performed on bulk copolymer samples collected from grafting solutions and purified via dialysis. The Mw of the bulk copolymer was used to estimate the graft molecular weight as a function of changing the concentration of the chain transfer agent, TGA (Figure S1). These results indicate that the TGA mediated chain growth polymerization could produce a wide range of Mw’s; however, the precise control of Mwwas lacking as indicated by high deviations in Mw obtained batch-batch. Better Mw control is possible utilizing living polymerization techniques; however, it is unlikely that the large range of overall Mw’s produced utilizing TGA would be possible with living techniques.
Figure S1.(a) Effect of increasing [TGA] on the MWof bulk copolymer purified from solution and (b) representative GPC chromatograms of copolymers with different MW values produced by varying [TGA]. Data points represent the arithmetic mean with error bars representing one standard deviation, n=4
ATR-FTIR analysis of homopolymers was performed to identify distinguishable peaks that could be used for copolymer analysis (Figure S2). Copolymer composition was estimated by performing peak fitting analysis of the carbonyl region (Figure S3) and fitting the respective heights of each of the three carbonyls normalized by the -CH2 bend to a Beer’s law type relation. This relation was derived by performing IR analysis of blends of PAA conjugated with Na+ (neutral dialyzed) and PAAm at different ratios (Figure S4). Blends were made by solvating the homopolymers in water (pH=7.5), allowing them to mix thoroughly, and drying them to a homogenous film. TheBeer’s law relationships for AA and AAm contentshow good linear relationships (Figure S5). PMA was not incorporated into these blends due to its insolubility in water, and PMA composition was estimated by subtracting the calculated composition of AA and AAm from 100%. These relationships were validated by performing the same peak fitting procedure on poly(AA Na+-c-AAm-c-MA) blended with varying concentrations of either PAA or PAAm.
Figure S2. ATR-FTIR spectra of poly(acrylate) homopolymers.All polymers were synthesized in lab, purified by dialysis, and dried by rotary evaporation. The 1452 cm-1 peak is the -CH2 bend attributed to the polymer backbone. Carbonyl designations are as follows: 1732 cm-1 PMA, 1704 cm-1 PAA, 1664 cm-1 PAAm, and 1556 cm-1 PAA Na+.
Figure S3. ATR-FTIR spectra of a ternary poly(co-acrylate) bulk sampleshowing the fitted peaks utilized for copolymer composition analysis.
Figure S4. ATR-FTIR spectra of a homopolymers, homopolymer blends, and ternary copolymer utilized to calculate the Beer-Lambert law relationship.
Figure S5. Beer’s law type of relation used for copolymer compositional analysis. The carbonyl peak height (either 1556 cm-1 for PAA or 1664 cm-1 for PAAm) was normalized with the -CH2 bend at 1452 cm-1.
PCAgPDMS Characterization
The Owens-Wendt method was used to calculate the surface free energy (SFE), γS(mN/m),of test surfaces using W-MI and MI-GL probe liquid pairs. Equation S1 was used to calculate the surface’s polar and dispersive (γSp and γSd) components using the measured contact angle (θ) of each liquid and polar/dispersive values found in Table S1. The overall SFE, γS, was determined by averaging the values of the probe liquid pairs obtained using Equation S2.
(S1)
(S2)
Table S1. SFE values for probe liquids used for SFE calculations of PDMSe surfaces.
Probe Liquid / γL(mJ/m2) / γLd
(mJ/m2) / γLp
(mJ/m2)
W / 72.8 / 21.8 / 51.0
MI / 50.8 / 48.5 / 2.3
GL / 63.4 / 36.0 / 27.4
TA.XT Plus texture analyzer by Stable Microsystems using a 5 kg load cell was used to perform tensile tests on PDMSe test coatings. Testing was performed on dog-bone samples (soaked in water for >100 h) according to ASTM D412-15A. The elastic modulus (E) was calculated according to the slope of the stress-strain curve within the elastic regime of the tests. Grafting caused no change in the elastic modulus compared to PDMSe.
PCAgPDMS coatings adsorbed water due to the hydrophilic nature of the surface grafts in a fashion not seen for PDMSe coatings, and this swelling resulted in a change in the optical appearance of the coatings. ATR-FTIR was used to confirm that swelling of water, not some other unknown reason, caused the change seen in optical appearance and mass. IR analysis of swollen PCAgPDMS samples was able to detect two intense absorbance bands centered around 3400 cm-1 and 1650 cm-1 consistent with the IR absorbance of H2O (Figure S7). Dehydrating these samples by either vacuum or desiccation eliminated these water peaks.
Figure S6. (a)Stress-strain data averaged between three samples per coating, and (b) the same data restricted to the linear portion within the elastic regime. The Elastic modulus of 1.16 MPa was consistent for both PDMSe and PCAgPDMS coatings.Both coatings slipped from the tensile machine’s grips at higher strains as indicated by the large drops in stress seen in part a.
Figure S7.ATR-FTIR spectra of PCAgPDMS coatings swollen in water (blue) or dessicated (red) and PDMSe control swollen in water (black).Water adsorption by the PCAgPDMS samples was due to the acrylate grafts. Inset figures show the two main areas of water absorbance in the (a) >3000 cm-1 region and (b) the fingerprint region from 1800-1300 cm-1.
PCAgPDMS N. incerta Bioassay Data
Sample leachate toxicity against Navicula incerta was assessed by introducing diatoms into overnight extracts (ASW with nutrients) of treatment coatings and evaluating growth after 48 h via fluorescence of chlorophyll (Figure S8). Growth in coating leachates was reported as a fluorescence ratio compared to a positive growth control (fresh nutrient medium) and a negative growth control (medium + bacteria + 6 μg/ml triclosan).PCAgPDMS samples displayed no evidence of leachate toxicity; however, IS700 and IS900 samples showed mild toxicity despite the 7 day tap water immersion.PCAgPDMS coatings did not impact the 48 h biofilm growth compared to the PDMSe control, but IS700 and IS900 showed diminished growth likely due to their mild toxicity.
Figure S8.(a) Coating leachate toxicity towards N. incerta and (b)N. incerta biofilm growth after 48 h on coatings in 24-well plates. Data is from Bioassay 5, and error bars represent one standard deviation. The dashed line for part (a) is included as a visual reference for the positive growth control. Groups that share the same letter are statistically equivalent, α=0.05.
Figure S9.Initial attachment (2 h settlement) and removal of N. incerta by (a)138 kPa water jet impact pressure on coated 24-well plates (bioassay 6), and (b)26 Pa water shear stress on coated glass slides (bioassay 8). Inset percentage values represent the percentage removal of diatoms due to applied water pressure. Error bars represent 95% confidence intervals. Groups that share the same letter (black or grey) are statistically equivalent, α=0.05.
Table S2. Percentage removal values of N. incerta diatoms performed on 24-well plates between two bioassays at both impact pressures of 69 and 138 kPa.
Bioassay 5 / Bioassay 6Coating / % Removal 69 kPa / % Removal 138 kPa / Coating / % Removal 69 kPa / % Removal 138 kPa
PDMSe / 37.3 ± 2.4 / 59.3 ± 3.9 / PDMSe / 37.3 ± 4.5 / 66.3 ± 6.8
PCAgPDMS Mw=994 kg/mol / 63.4 ± 8.1 / 86.4 ± 2.8 / PCAgPDMS Mw=1,022 kg/mol / 35.9 ± 2.3 / 74.4 ± 3.1
PCAgPDMS Mw=835 kg/mol / 52.2 ± 8.9 / 83.5 ± 1.9 / PCAgPDMS Mw=619 kg/mol / 49.6 ± 3.9 / 82.5 ± 4.6
PCAgPDMS Mw=441 kg/mol / 53.1 ± 7.2 / 75.6 ± 6.0 / PCAgPDMS Mw=397 kg/mol / 28.0 ± 7.5 / 72.0 ± 6.3
PCAgPDMS Mw=221 kg/mol / 51.4 ± 4.4 / 75.3 ± 2.6 / PCAgPDMS Mw=227 kg/mol / 43.7 ± 3.8 / 73.7 ± 1.8
IS700 / 7.2 ± 2.7 / 24.5 ± 13 / IS700 / ----- / -----
IS 900 / 23.2 ± 4.9 / 51.7 ± 2.7 / IS 900 / 9.0 ± 6.6 / 53.6 ± 10
IS 1100SR / 53.0 ± 4.6 / 88.3 ± 1.2 / IS 1100SR / 26.3 ± 9.9 / 77.2 ± 3.0
*Percentageremoval is reported by comparing each count of diatom biomass remaining post-removal to the mean diatom initial biomass pre-removal per coating type. Arithmetic average ± 95% confidence interval, n=4.IS 700 was excluded from bioassay 6 due to issues with coating adherence to well plates.
Table S3. Percentage removal values of N. incerta diatoms performed on coated glass slides for two bioassays.
Bioassay 7 / Bioassay 8Coating / % Removal
26 Pa / Coating / % Removal
26 Pa
PDMSe / 0.0 ± 0.2 / PDMSe / 10.4 ± 3.9
PCAgPDMS Mw=1,319 kg/mol / 39.1 ± 4.2 / PCAgPDMS Mw=1,022 kg/mol / 34.3 ± 6.1
PCAgPDMS Mw=1,190 kg/mol / 54.6 ± 3.4 / PCAgPDMS Mw=619 kg/mol / 35.4 ± 5.4
PCAgPDMS Mw=138 kg/mol / 46.4 ± 4.9 / PCAgPDMS Mw=397 kg/mol / 26.7 ± 5.4
PCAgPDMS Mw=80 kg/mol / 40.9 ± 5.4 / PCAgPDMS Mw=227 kg/mol / 33.0 ± 6.5
*Percentageremoval is reported by comparing each count of remaining diatom density post-removal from 30 counts on each replicate to the mean initial diatom density pre-removal per coating type, and an arc-sine transformation was performed to obtain more representative error bars due to the nature of the percentage values. Arithmetic average ± 95% confidence interval, n=3
Statistical Analysis
Parametric one-way ANOVA makes several assumptions such as homogeneity of variance and normality that were tested for, and the results of these tests as well as the F-statistics for the ANOVA’s run for all bioassay data is shown in Table S4. The Shapiro-Wilk test and corresponding Q-Q plots were used to confirm that the data used was normally distributed. This test was performed on all U. linza attachment density data per coating per bioassay and all N. incerta initial and remaining biomass data per coating per bioassay. The results of each test are not reported due to the shear size of the data set (60 individual tests and plots). Levene’s test was used tests thenull hypothesis that the population variances are equal, to confirm homogeneity of variance (Table S4). If the null hypothesis was rejected by a p values < 0.05, both the Welch and the Brown-Forsycthe tests were used to determine significance instead of the ANOVA F-statistic.
Bioassay # / Data Set / Levene’s / One-Way ANOVA / Welch / Brown-Forscythe1 / Attachment Density / F(4,445)=27.282, p=0.000 / ------/ F(4,216)=228.925, p<0.05 / F(4,205)=523.550, p<0.05
2 / Attachment Density / F(4,445)=99.039, p=0.000 / ------/ F(4,218)=238.706, p<0.05 / F(4,114)=850.025, p<0.05
5 / Initial Attachment / F(7,16)=1.403, p=0.271 / F(7,16)=19.425, p<0.05 / ------/ ------
5 / Remaining Attachment, 69 kPa / F(7,16)=2.128, p=0.100 / F(7,16)=51.303, p<0.05 / ------/ ------
5 / Remaining Attachment, 138 kPa / F(7,16)=2.336, p=0.076 / F(7,16)=48.767, p<0.05 / ------/ ------
6 / Initial Attachment / F(6,14)=1.902, p=0.151 / F(6,14)=24.495, p<0.05 / ------/ ------
6 / Remaining Attachment, 69 kPa / F(6,14)=1.185, p=0.369 / F(6,14)=13.868, p<0.05 / ------/ ------
6 / Remaining Attachment, 138 kPa / F(6,14)=1.386, p=0.287 / F(6,14)=3.439, p<0.05 / ------/ ------
7 / Initial Attachment / F(4,445)=1.050, p=0.381 / F(4,445)=5.581, p<0.05 / ------/ ------
7 / Remaining Attachment / F(4, 445)=4.827, p=0.001 / ------/ F(4,220)=78.444, p<0.05 / F(4,398)=85.566, p<0.05
8 / Initial Attachment / F(4,445)=0.842, p=0.499 / F(4,445)=2.965, p<0.05 / ------/ ------
8 / Remaining Attachment / F(4,445)=3.672, p=0.006 / ------/ F(4,222)=11.409, p<0.05 / F(4,404)=16.319, p<0.05
Table S4. Statistical Summary
1