Adsorption Isotherm and Mechanism of Ca2+ Binding to Polyelectrolyte.

Polyelectrolytes, such as poly(acrylic acid) (PAA), can effectively mitigate CaCO3 scale formation. Despite their success as antiscalants, the underlying mechanism of binding of Ca2+ to polyelectrolyte chains remains unresolved. Through all-atom molecular dynamics simulations, we constructed an adsorption isotherm of Ca2+ binding to sodium polyacrylate (NaPAA) and investigated the associated binding mechanism. We find that the number of calcium ions adsorbed [Ca2+]ads to the polymer saturates at moderately high concentrations of free calcium ions [Ca2+]aq in the solution. This saturation value is intricately connected with the binding modes accessible to Ca2+ ions when they bind to the polyelectrolyte chain. We identify two dominant binding modes: the first involves binding to at most two carboxylate oxygens on a polyacrylate chain, and the second, termed the high binding mode, involves binding to four or more carboxylate oxygens. As the concentration of free calcium ions [Ca2+]aq increases from low to moderate levels, the polyelectrolyte chain undergoes a conformational transition from an extended coil to a hairpin-like structure, enhancing the accessibility to the high binding mode. At moderate concentrations of [Ca2+]aq, the high binding mode accounts for at least one-third of all binding events. The chain's conformational change and its consequent access to the high binding mode are found to increase the overall Ca2+ ion binding capacity of the polyelectrolyte chain.

Biodegradable Alkali-Swellable Emulsion Polymers: Industrial and Commercial Thickeners.

Sustainability and circularity are key issues facing the global polymer industry. The search for biodegradable and environmentally-friendly polymers that can replace conventional materials is a difficult challenge that has been met with limited success. Alternatives must be cost-effective, scalable, and provide equivalent performance. We report that latexes made by the conventional emulsion polymerization of vinyl acetate and functional vinyl ester monomers are efficient thickeners for consumer products and biodegrade in wastewater. This approach uses readily-available starting materials and polymerization is carried out in water at room temperature, in one pot, and generates negligible waste. Moreover, the knowledge that poly(vinyl ester)s are biodegradable will lead to the design of new green polymer materials.

Simple Genomic Traits Predict Rates of Polysaccharide Biodegradation.

Natural and chemically modified polysaccharides are extensively employed across a wide array of industries, leading to their prevalence in the waste streams of industrialized societies. With projected increasing demand, a pressing challenge is to swiftly assess and predict their biodegradability to inform the development of new sustainable materials. In this study, we developed a scalable method to evaluate polysaccharide breakdown by measuring microbial growth and analyzing microbial genomes. Our approach, applied to polysaccharides with various structures, correlates strongly with well-established regulatory methods based on oxygen demand. We show that modifications to the polysaccharide structure decreased degradability and favored the growth of microbes adapted to break down chemically modified sugars. More broadly, we discovered two main types of microbial communities associated with different polysaccharide structures─one dominated by fast-growing microbes and another by specialized degraders. Surprisingly, we were able to predict biodegradation rates based only on two genomic features that define these communities: the abundance of genes related to rRNA (indicating fast growth) and the abundance of glycoside hydrolases (enzymes that break down polysaccharides), which together predict nearly 70% of the variation in polysaccharide breakdown. This suggests a trade-off, whereby microbes are either adapted for fast growth or for degrading complex polysaccharide chains, but not both. Finally, we observe that viral elements (prophages) encoded in the genomes of degrading microbes are induced in easily degradable polysaccharides, leading to complex dynamics in biomass accumulation during degradation. In summary, our work provides a practical approach for efficiently assessing polymer degradability and offers genomic insights into how microbes break down polysaccharides.

Biodegradability as an Off-Ramp for the Circular Economy: Investigations into Biodegradable Polymers for Home and Personal Care.

Consumer pressure for globe-conscious products is pushing brand-owners big and small to provide transparency on the origin and fate of their ingredients. One such market where sustainable product growth has outpaced market growth is in home and personal care. Products in this space clean or care for our bodies, our homes, our environments, and the materials we encounter every day. Many of these materials are used and then washed down the drain, making the fate of these products a tangible end point for the consumer. Life cycle assessment (LCA) is a well-established methodology for determining potential environmental impacts of products and can be used to quantify the overall carbon footprint of the raw materials, the process to manufacture, and the transportation of the product around the globe. LCAs are calibrated to one metric, often kilograms of carbon dioxide (CO2) equivalents, to capture the overall carbon footprint. One aspect notably absent from many LCAs is the end of life for the product. Interestingly, consumers are driving a push for biodegradable materials that would not persist in the environment, but as materials biodegrade, they release carbon dioxide to the atmosphere. This release of CO2 places the benefits of biodegradation on the ultimate fate of raw materials in contradiction with carbon reduction methods such as carbon capture and carbon recycling that improve the LCA of a given product. In this Account, we describe the impact of biodegradation on the circular economy and discuss the development of natural, modified natural, and synthetic polymers to provide biodegradable alternatives to less degradable materials in the home and personal care markets. Building a chemical toolbox which can meet the functional and economical requirements of products on the market today while improving their sustainability profile is a huge challenge, which will not have a single answer. Among many current internal research initiatives, one vignette will be highlighted to showcase the research on a synthetic polymer with improved biodegradability for the dish care market. This novel polyelectrolyte, a copolymer of itaconic acid, acrylic acid, and vinyl acetate, was designed to break down into digestible daughter products in a wastewater treatment plant while demonstrating stability both on the shelf and in the dishwasher.

Two-dimensional liquid chromatography with active solvent modulation for studying monomer incorporation in copolymer dispersants.

A pseudo-comprehensive two-dimensional liquid chromatography approach with size exclusion chromatography in the first dimension and gradient reversed-phase liquid chromatography in the second dimension was successfully developed for the characterization of vinyl acetate/acrylic acid copolymers and vinyl acetate/itaconic acid/acrylic acid terpolymers. Active solvent modulation was exploited to prevent the polymer breakthrough in the second dimension separation caused by the strong solvent used in the first dimension. The conditions of the active solvent modulation valve were optimized to achieve sufficient on-line dilution and to completely prevent polymer breakthrough without adding excessive time to the modulation cycle. Using this approach, copolymers made with different monomer ratios and processes were studied. Heterogeneous composition distribution due to insufficient monomer incorporation was detected in some of the copolymer samples. We demonstrated that with active solvent modulation, the two-dimensional liquid chromatography approach is no longer limited to water-soluble polymers and can be used for a broader range of polymers and copolymers.

Covalent formation of nanoscale fullerene and dendrimer patterns.

Localized patterns of amine-terminated monolayers obtained via the surface modification of a monolayer with the biased probe of an atomic force microscope were used to covalently attach buckminsterfullerene or dendrimers to the surface, affording lines as narrow as 20 nm.

Generating an etch resistant "resist" layer from common solvents using scanning probe lithography in a fluid cell.

A novel scanning probe lithography scheme is introduced involving the field-induced deposition of etch resistant material generated from common organic solvents such as n-octane, toluene, ethyl alcohol, and dioxane in the tip/sample gap region of a liquid cell. An NH(4)F/H(2)O(2)/H(2)O etchant transfers these structures into 7 nm tall posts in a negative-tone fashion, indicating that an etch resistant, likely carbon-based material is produced by field-induced decomposition of the solvent. This is in sharp contrast to the positive tone images that result from a similar process involving water as the gap electrolyte followed by a similar fluorine-based etching.

AFM-induced amine deprotection: triggering localized bond cleavage by application of tip/substrate voltage bias for the surface self-assembly of nanosized dendritic objects.

An alpha,alpha-dimethyl-3,5-dimethoxybenzyloxycarbonyl (DDZ)-protected amine monolayer can be selectively deprotected by the application of a voltage bias from a conducting AFM tip to afford localized nanoscale patterns that can be visualized by self-assembly of dendritic molecular objects with terminal carboxylic acid groups and different aspect ratios.