Amphiphilic Balance: Effect of the Hydrophilic-Hydrophobic Ratio on Fouling-Release Surfaces.

This study demonstrated the importance of identifying the optimal balance of hydrophilic and hydrophobic moieties in amphiphilic coatings to achieve fouling-release (FR) performance that surpasses that of traditional hydrophobic marine coatings. While there have been many reports on fouling-release properties of amphiphilic surfaces, the offered understanding is often limited. Hence, this work is focused on further understanding of the amphiphilic surfaces. Poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) were used to create a series of noncross-linked amphiphilic additives that were then added to a hydrophobic-designed siloxane-polyurethane (SiPU) FR system. After being characterized by ATR-FTIR, XPS, contact angle analysis, and AFM, the FR performance was evaluated by using different marine organisms. The assessments showed that the closer the hydrophilic and hydrophobic moieties in a system reached a relatively equalized level, the more desirable the FR performance of the coating system became. A balanced ratio of hydrophilicity-hydrophobicity in the system at around 10-15 wt % of each component had the best FR performance and was comparable to or better than commercial FR coatings.

A Preliminary Study of Thermosets from Epoxy Resins Made Using Low-Toxicity Furan-Based Diols.

Glycidyl ethers are prepared from a series of furan-based diols and cured with a diamine to form thermosets. The furan diols demonstrate lower toxicity than bisphenol-A in a prior study. The diglycidyl ethers show improved thermal stability compared to the parent diols. Cured thermosets are prepared at elevated temperature using isophorone diamine (IPDA). Glass transition temperatures are in the range of 30-54 °C and depend on the structure of the furan diol. Coatings are prepared on steel substrates and show very high hardness, good adhesion, and a range of flexibility. Properties compare favorably with a control based on a bisphenol-A epoxy resin. The study demonstrates that epoxy resins based on furan diols, which have been shown to have lower toxicity than bisphenol-A, can form thermosets having properties comparable to a standard epoxy resin system; and thus, are viable as replacements for bisphenol-A epoxy resins.

Energy renormalization for temperature transferable coarse-graining of silicone polymer.

The bottom-up prediction of thermodynamic and mechanical behaviors of polymeric materials based on molecular dynamics (MD) simulation is of critical importance in polymer physics. Although the atomistically informed coarse-grained (CG) model can access greater spatiotemporal scales and retain essential chemical specificity, the temperature-transferable CG model is still a big challenge and hinders widespread application of this technique. Herein, we use a silicone polymer, i.e., polydimethylsiloxane (PDMS), having an incredibly low chain rigidity as a model system, combined with an energy-renormalization (ER) approach, to systematically develop a temperature-transferable CG model. Specifically, by introducing temperature-dependent ER factors to renormalize the effective distance and cohesive energy parameters, the developed CG model faithfully preserved the dynamics, mechanical and conformational behaviors compared with the target all-atomistic (AA) model from glassy to melt regimes, which was further validated by experimental data. With the developed CG model featuring tremendously improved computational efficiency, we systematically explored the influences of cohesive interaction strength and temperature on the dynamical heterogeneity and mechanical response of polymers, where we observed consistent trends with other linear polymers with varying chain rigidity and monomeric structures. This study serves as an extension of our proposed ER approach of developing temperature transferable CG models with diverse segmental structures, highlighting the critical role of cohesive interaction strength on CG modeling of polymer dynamics and thermomechanical behaviors.

Silicone elastomers and the Persson-Brener adhesion model.

Many modern anti-icing and anti-fouling coatings rely on soft, low surface energy elastomeric materials such as polydimethylsiloxane for their functionality. While the low surface energy is desirable for reducing adhesion, very little work considers the larger contribution to adhesive failure caused by the viscoelastic nature of elastomers. Here we examine several different siloxane elastomers using a JKR adhesion test, which was operated over a range of different speeds and temperatures. Additionally, we characterize the dynamic mechanical modulus over a large range of frequencies for each material. We note that surface energies of the materials are all similar, but variation in adhesion strength is clear in the data. The variation at low speeds is related to elastomer architecture but the speed dependence itself is independent of architecture. Qualitative correlations are noted between the JKR adhesion measurements and the dynamic moduli. Finally, an attempt is made to directly compare moduli and adhesion through the recent Persson-Brener model. Approximations of the model are shown to be inaccurate. The full model is found to be accurate at low speeds, although it fails to precisely capture higher speed behaviour.

Durable siloxane-polyurethane coatings for mitigating freshwater mussel fouling.

Siloxane-polyurethane hybrid coatings were assessed for biofouling control caused by freshwater mussels. Invasive species such as zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels have rapidly spread through the waterways in the United States causing major concerns in reservoir infrastructure and freshwater lakes. Current coating solutions such as biocidal anti-fouling coatings are not suitable given the released biocides which may accumulate in reservoirs. Biocide free fouling release coatings based on silicone elastomers do not have adequate mechanical durability. The siloxane-polyurethane (SiPU) coatings were evaluated using model organism laboratory assays and real-life performance was evaluated in the freshwater field environment. Two coating compositions displayed excellent performance in field trials for up to 2+ years. The surface analysis experiments of the coatings indicate that the morphology of the coatings is affected by the formulations' solvent choice. These coatings show great promise in mitigating biofouling predominated by freshwater mussels.

Grooming of fouling-release coatings to control marine fouling and determining how grooming affects the surface.

Grooming may be an effective technique to control marine biofouling without damaging the coating or discharging active ingredients into the environment. This study assessed the grooming performance of three experimental biocide-free siloxane polyurethane (SiPU) fouling-release coatings. Coatings were statically immersed in Port Canaveral, Florida, and groomed every two weeks for five months using three different brush types. The ungroomed panels became heavily fouled with biofilm, tubeworms, barnacles, and bryozoans. Two of the brushes were able to control the fouling with a coverage of <5%. The commercial silicone elastomer coating was damaged from grooming procedures, while the SiPU coatings were not. Laboratory biological assays were carried out and mirrored the grooming results. Through surface characterization techniques, it was concluded that the coatings were unaffected by the grooming procedures. This study shows that marine fouling on durable SiPU fouling-release coatings can be controlled via grooming without damage or changing the surface properties.

Towards Upcycling Biomass-Derived Crosslinked Polymers with Light.

Photodegradable, recyclable, and renewable, crosslinked polymers from bioresources show promise towards developing a sustainable strategy to address the issue of plastics degradability and recyclability. Photo processes are not widely exploited for upcycling polymers in spite of the potential to have spatial and temporal control of the degradation in addition to being a green process. In this report we highlight a methodology in which biomass-derived crosslinked polymers can be programmed to degrade at ≈300 nm with ≈60 % recovery of the monomer. The recovered monomer was recycled back to the crosslinked polymer.

Critical Amphiphilic Concentration: Effect of the Extent of Amphiphilicity on Marine Fouling-Release Performance.

Amphiphilic surfaces, containing both hydrophilic and hydrophobic domains, offer desirable performance for many applications such as marine coatings or anti-icing purposes. This work explores the effect of the concentration of amphiphilic moieties on converting a polyurethane (PU) system to a coating having fouling-release properties. A novel amphiphilic compound is synthesized and added at increasing amounts to a PU system, where the amount of the additive is the only variable in the study. The additive-modified surfaces are characterized by a variety of techniques including ATR-FTIR, XPS, contact angle measurements, and AFM. Surface characterizations indicate the presence of amphiphilic domains on the surface due to the introduction of the self-stratifying amphiphilic additive. The fouling-release properties of the surfaces are assessed with three biological assays using Ulva linza, Cellulophaga lytica, and Navicula Incerta as the test organisms. A change in the fouling-release performance is observed and plateaued once a certain amount of amphiphilicity is attained in the coating system, which we call the critical amphiphilic concentration (CAC).

Surface modifying amphiphilic additives and their effect on the fouling-release performance of siloxane-polyurethane coatings.

In this work, surface-modifying amphiphilic additives (SMAAs) were synthesized via hydrosilylation using various polymethylhydrosiloxanes (PMHS) and allyl-terminated polyethylene glycol monomethyl ethers (APEG) of varying molecular weights. The additives synthesized were incorporated into a hydrophobic, self-stratifying siloxane-polyurethane (SiPU) coating system to produce an amphiphilic surface. Contact angle experiments and atomic force microscopy (AFM), in a dry and hydrated state, were performed to assess changes in surface wettability and morphology. The antifouling and fouling-release (AF/FR) performances were evaluated by performing laboratory biological assays using the marine bacterium Cellulophaga lytica, the microalga Navicula incerta, the macroalga Ulva linza, the barnacle Amphibalanus amphitrite, and the marine mussel, Geukensia demissa. Several of the formulations showed improved AF/FR performance vs the base SiPU and performed better than some of the commercial standard marine coatings. Formulations containing SMAAs with a low grafting density of relatively high molecular weight PEG chains showed the best performance overall.

A Preliminary Environmental Assessment of Epoxidized Sucrose Soyate (ESS)-Based Biocomposite.

Biocomposites can be both environmentally and economically beneficial: during their life cycle they generally use and generate less petroleum-based carbon, and when produced from the byproduct of another industry or recycled back to the manufacturing process, they will bring additional economic benefits through contributing to a circular economy. Here we investigate and compare the environmental performance of a biocomposite composed of a soybean oil-based resin (epoxidized sucrose soyate) and flax-based reinforcement using life cycle assessment (LCA) methodology. We evaluate the main environmental impacts that are generated during the production of the bio-based resin used in the biocomposite, as well as the biocomposite itself. We compare the life cycle impacts of the proposed biocomposite to a functionally similar petroleum-based resin and flax fiber reinforced composite, to identify tradeoffs between the environmental performance of the two products. We demonstrate that the bio-based resin (epoxidized sucrose soyate) compared to a conventional (bisphenol A-based) resin shows lower negative environmental impacts in most studied categories. When comparing the biocomposite to the fossil fuel derived composite, it is demonstrated that using epoxidized sucrose soyate versus a bisphenol A (BPA)-based epoxy resin can improve the environmental performance of the composite in most categories except eutrophication and ozone layer depletion. For future designs, considering an alternative cross-linker to facilitate the bond between the bio-based resin and the flax fiber, may help improve the overall environmental performance of the biocomposite. An uncertainty analysis was also performed to evaluate the effect of variation in LCA model inputs on the environmental results for both the biocomposite and composite. The findings show a better overall carbon footprint for the biocomposite compared to the BPA-based composite at almost all times, demonstrating a good potential for marketability especially in the presence of incentives or regulations that address reducing the carbon intensity of products. This analysis allowed us to pinpoint hotspots in the biocomposite's supply chain and recommend future modifications to improve the product's sustainability.

Comparison of laboratory and field testing performance evaluations of siloxane-polyurethane fouling-release marine coatings.

A series of eight novel siloxane-polyurethane fouling-release (FR) coatings were assessed for their FR performance in both the laboratory and in the field. Laboratory analysis included adhesion assessments of bacteria, microalgae, macroalgal spores, adult barnacles and pseudobarnacles using high-throughput screening techniques, while field evaluations were conducted in accordance with standardized testing methods at three different ocean testing sites over the course of six-months exposure. The data collected were subjected to statistical analysis in order to identify potential correlations. In general, there was good agreement between the laboratory screening assays and the field assessments, with both regimes clearly distinguishing the siloxane-polyurethane compositions comprising monofunctional poly(dimethyl siloxane) (PDMS) (m-PDMS) as possessing superior, broad-spectrum FR properties compared to those prepared with difunctional PDMS (d-PDMS). Of the seven laboratory screening techniques, the Cellulophaga lytica biofilm retraction and reattached barnacle (Amphibalanus amphitrite) adhesion assays were shown to be the most predictive of broad-spectrum field performance.

Programmed photodegradation of polymeric/oligomeric materials derived from renewable bioresources.

Renewable polymeric materials derived from biomass with built-in phototriggers were synthesized and evaluated for degradation under irradiation of UV light. Complete decomposition of the polymeric materials was observed with recovery of the monomer that was used to resynthesize the polymers.

Biobased, Macro-, and Nanoscale Fungicide Delivery Approaches for Plant Fungi Control.

In this report, two polymeric matrix systems at macro and nanoscales were prepared for efficacious fungicide delivery. The macroscale delivery systems used millimeter-scale, spherical beads composed of cellulose nanocrystals and poly(lactic acid). The nanoscale delivery system involved micelle-type nanoparticles, composed of methoxylated sucrose soyate polyols. Sclerotinia sclerotiorum (Lib.), a destructive fungus affecting high-value industrial crops, was used as a model pathogen against which the efficacy of these polymeric formulations was demonstrated. Commercial fungicides are applied on plants frequently to overcome the transmission of fungal infection. However, fungicides alone do not persist on the plants for a prolonged period due to environmental factors such as rain and airflow. There is a need to apply fungicides multiple times. As such, standard application practices generate a significant environmental footprint due to fungicide accumulation in soil and runoff in surface water. Thus, approaches are needed that can either increase the efficacy of commercially active fungicides or prolong their residence time on plants for sustained antifungal coverage. Using azoxystrobin (AZ) as a model fungicide and canola as a model crop host, we hypothesized that the AZ-loaded macroscale beads, when placed in contact with plants, will act as a depot to release the fungicide at a controlled rate to protect plants against fungal infection. The nanoparticle-based fungicide delivery approach, on the other hand, can be realized via spray or foliar applications. The release rate of AZ from macro- and nanoscale systems was evaluated and analyzed using different kinetic models to understand the mechanism of AZ delivery. We observed that, for macroscopic beads, porosity, tortuosity, and surface roughness governed the efficiency of AZ delivery, and for nanoparticles, contact angle and surface adhesion energy were directing the efficacy of the encapsulated fungicide. The technology reported here can also be translated to a wide variety of industrial crops for fungal protection. The strength of this study is the possibility of using completely plant-derived, biodegradable/compostable additive materials for controlled agrochemical delivery formulations, which will contribute to reducing the frequency of fungicide applications and the potential accumulation of formulation components in soil and water.

Studying the Effect of Pre-Polymer Composition and Incorporation of Surface-Modifying Amphiphilic Additives on the Fouling-Release Performance of Amphiphilic Siloxane-Polyurethane Coatings.

Combining amphiphilic fouling-release (FR) coatings with the surface-active nature of amphiphilic additives can improve the antifouling/fouling-release (AF/FR) properties needed to offer broad-spectrum resistance to marine biofoulants. This work is focused on further tuning the amphiphilic character of a previously developed amphiphilic siloxane-polyurethane (SiPU) coating by varying the amount of PDMS and PEG in the base system. Furthermore, surface-modifying amphiphilic additives (SMAAs) were incorporated into these amphiphilic FR SiPU coatings in varying amounts. ATR-FTIR, contact angle and surface energy measurements, and AFM were performed to assess changes in surface composition, wettability, and morphology. AF/FR properties were evaluated using laboratory biological assays involving Cellulophaga lytica, Navicula incerta, Ulva linza, Amphibalanus amphitrite, and Geukensia demissa. The surfaces of these coatings varied significantly upon changes in PDMS and PEG content in the coating matrix, as well as with changes in SMAA incorporation. AF/FR properties were also significantly changed, with formulations containing the highest amounts of SMAA showing very high removal properties compared to other experimental formulations, in some cases better than that of commercial standard FR coatings.

High biobased content epoxy-anhydride thermosets from epoxidized sucrose esters of Fatty acids.

Novel highly functional biobased epoxy compounds, epoxidized sucrose esters of fatty acids (ESEFAs), were cross-linked with a liquid cycloaliphatic anhydride to prepare polyester thermosets. The degree of cure or conversion was studied using differential scanning calorimetry (DSC), and the sol content of the thermosets was determined using solvent extraction. The mechanical properties were studied using tensile testing to determine Young's modulus, tensile stress, and elongation at break. Dynamic mechanical analysis (DMA) was used to determine glass-transition temperature, storage modulus, and cross-link density. The nanomechanical properties of the surfaces were studied using nanoindentation to determine reduced modulus and indentation hardness. The properties of coatings on steel substrates were studied to determine coating hardness, adhesion, solvent resistance, and mechanical durability. Compared with the control, epoxidized soybean oil, the anhydride-cured ESEFAs have high modulus and are hard and ductile, high-performance thermoset materials while maintaining a high biobased content (71-77% in theory). The exceptional performance of the ESEFAs is attributed to the unique structure of these macromolecules: well-defined compact structures with high epoxide functionality. These biobased thermosets have potential uses in applications such as composites, adhesives, and coatings.

Impact of structure and functionality of core polyol in highly functional biobased epoxy resins.

Highly functional biobased epoxy resins were prepared using dipentaerythritol (DPE), tripentaerythritol (TPE), and sucrose as core polyols that were substituted with epoxidized soybean oil fatty acids, and the impact of structure and functionality of the core polyol on the properties of the macromolecular resins and their epoxy-anhydride thermosets was explored. The chemical structures, functional groups, molecular weights, and compositions of epoxies were characterized using nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI MS). The epoxies were also studied for their bulk viscosity, intrinsic viscosity, and density. Crosslinked with dodecenyl succinic anhydride (DDSA), epoxy-anhydride thermosets were evaluated using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile tests, and tests of coating properties. Epoxidized soybean oil (ESO) was used as a control. Overall, the sucrose-based thermosets exhibited the highest moduli, having the most rigid and ductile performance while maintaining the highest biobased content. DPE/TPE-based thermosets showed modestly better thermosetting performance than the control ESO thermoset.

A preliminary study on the properties and fouling-release performance of siloxane-polyurethane coatings prepared from poly(dimethylsiloxane) (PDMS) macromers.

Siloxane-polyurethane fouling-release (FR) coatings based on aminopropyl terminated poly(dimethylsiloxane) (PDMS) macromers were prepared and characterized for FR performance via laboratory biological assays. These systems rely on self-stratification, resulting in a coating with a siloxane-rich surface and polyurethane bulk. Previously, these coating systems have used PDMS with multiple functional groups which react into the polyurethane bulk. Here, aminopropyl terminated PDMS macromers were prepared, where a single amine group anchors the PDMS in the coating. Coatings were prepared with four molecular weights (1000, 5000, 10,000, and 15,000 g mol⁻¹) and two levels of PDMS (5% and 10%). High water contact angles and low surface energies were observed for the coatings before and after water immersion, along with low pseudobarnacle removal forces. Laboratory bioassays showed reduced biofilm retention of marine bacteria, good removal of diatoms from coatings with low molecular weight PDMS, high removal of algal sporelings (young plants), and low removal forces of live barnacles.

Automated image-based method for laboratory screening of coating libraries for adhesion of algae and bacterial biofilms.

Assessment and down-selection of non-biocidal coatings that prevent the adhesion of fouling organisms in the marine environment requires a hierarchy of laboratory methods to reduce the number of experimental coatings for field testing. Automated image-based methods are described that facilitate rapid, quantitative biological screening of coatings generated through combinatorial polymer chemistry. Algorithms are described that measure the coverage of bacterial and algal biofilms on coatings prepared in 24-well plates and on array panels, respectively. The data are used to calculate adhesion strength of organisms on experimental coatings. The results complement a number of physical and mechanical methods developed to screen large numbers of samples.

Soysome: A Surfactant-Free, Fully Biobased, Self-Assembled Platform for Nanoscale Drug Delivery Applications.

A new class of biobased nanocarriers, soysomes, has been discovered and investigated. These nanocarriers are derived from a synthetically accessible, scalable macromolecule, methoxylated sucrose soyate polyol (MSSP), derived from chemical building blocks obtained from soybean oil and sucrose. We observed for the first time that MSSP, when dissolved in an organic solvent of different polarity and slowly added to an aqueous phase at a predetermined rate under "nanoprecipitation" conditions, will form a stable, self-assembled structure with a size range from 100 to 200 nm depending on the polarity difference between the precipitating solvent pairs. Without the aid of poly(ethylene glycol) or any surfactants, these soysomes were found to be stable in water for an extended period and can withstand the destabilizing effect of time, temperature, and pH. We also found that the soysomes were able to encapsulate and release a hydrophobic bioactive compound, such as curcumin. Both MSSP and their self-assembled structures were highly biocompatible and did not trigger cellular toxicity to mammalian cell lines. Our experiments showed that such 100% biobased, noncytotoxic material as MSSP and a related class of products have the potential for use toward the sustainable manufacturing of drug nanocarriers for biomedical applications.

Thermosensitive polymers: synthesis, characterization, and delivery of proteins.

Three triblock copolymers based on the poly(lactide) or poly(lactide-co-glycolide) and poly(ethylene glycol) or poly(ethylene oxide) blocks were synthesized and characterized. The weight average molecular weight and number average molecular weight were determined by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy, respectively. Fourier transform infrared spectroscopy was used to determine the completion of synthesis of polymers. Thermoreversible sol-gel transition temperature and concentration were determined by an inverted tube method. Two formulations each of three synthesized polymers containing 5% (w/v) of lysozyme or bromelain but differing in polymer concentrations (20-30%, w/v) were prepared and studied for in vitro release of the incorporated protein. In vitro biocompatibility of the delivery systems was studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay. Biological activities of lysozyme and bromelain were determined by enzyme activity assays. Critical gelling concentrations were found in the range of 20-30% (w/v). In vitro biocompatibility study showed that all the formulations were biocompatible. Increasing the polymer concentration led to a decrease in burst release and extended the in vitro release of proteins. Furthermore, biological activities of lysozyme and bromelain in released samples were found to be significantly (p<0.05) greater in comparison to the control. Thus, the above thermosensitive polymers were able to deliver proteins in biologically active forms at a controlled rate for 2-8 weeks.