RESUMEN

Silicone-in-water emulsions have found widespread use as lubricants, water repellants, softeners, binders, antiblocking agents, antislip agents, and defoamers across a diverse range of markets including textiles, coatings, pharmaceuticals, and home and personal care. Stable incorporation of silicone emulsions into formulated products for these applications can be a challenge. This study seeks to enable formulation by investigating the impact of the degree of ethoxylation of sodium lauryl ether sulfate (SLES) surfactants on their ability to displace surfactant stabilizer at the silicone-water interfaces of polydimethylsiloxane (PDMS)-in-water emulsion droplets. Building this understanding will greatly enable the manufacture of home and personal care products prepared by introducing silicone emulsions into SLES-rich formulations. Nuclear magnetic resonance (NMR) measurements reveal that SLES can displace the triethanolamine dodecylbenzenesulfonate stabilizer at the droplet surfaces. Both capillary electrophoresis (CE) measurements and molecular dynamics simulations of the interfacial tension (IFT) between silicone and water measurements suggest that SLES mixtures with a higher average degree of ethoxylation are more surface active at the silicone─water interface. The molecular dynamics simulations predict a systematic decrease in PDMS-water IFT with increase in degree of ethoxylation (simulations predict a decrease of 1.3 mN/m per mole of ethylene oxide). Optical microscopy reveals that the presence of SLES at the droplet surfaces promotes the formation of loose flocs of droplets that break up upon dilution. Overall, these fundamental insights will aid in formulating silicone emulsions into products to achieve optimal performance.

RESUMEN

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.

Asunto(s)

RESUMEN

The curing of coatings of two types of siloxane containing materials, silica gel and silsesquioxane, at a modest temperature (<280℃) was studied with in situ heating Fourier transform infrared spectroscopy (FT-IR) in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2D-COS) analyses. The result revealed detailed structural evolution of these two different gels. When the silica gel was heated, (Si-O)6 rings appeared from the random Si-O-Si network formed after sol gel reaction, followed by condensation of silanol groups. Upon further heating, the existing (Si-O)4 rings were broken down and converted into (Si-O)6 structures, and finally isolated silanols appeared. The transition from (Si-O)4 rings to (Si-O)6 rings was observed by IR and further confirmed with positron annihilation lifetime spectroscopy (PALS). In comparison, during the curing of hybrid silsesquioxane, the condensation of silanols happens immediately upon heating without the rearrangement of Si-O-Si network. Afterwards, the fraction of (Si-O)6 ring structure increased. (Si-O)4 structures exhibited higher stability in hybrid silsesquioxanes. In addition, the amount of silanols in silsesquioxane continued to reduce without the generation of isolated silanol in the end. The different curing behavior of silsesquioxanes from silica gel originates from the organic groups in silsesquioxanes, which lowers the cross-linking density and reduces the rigidity of siloxane network.

RESUMEN

Anatase titanium dioxide nanoparticles are derivatized with the polymerizable reagent (3-methacryloxypropyl)trimethoxysilane to provide dispersions in organic solvent. The titania core particles are characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The organic component structures and thickness are elucidated using nuclear magnetic resonance (NMR), quasielastic light scattering (QELS), and size-exclusion chromatography (SEC). Thin, high-refractive-index coatings prepared from the organic dispersions are characterized by atomic force microscopy (AFM). The combination of microscopies, spectroscopy, light scattering, and separation techniques provides unique information on the structure, thickness, morphology, and size distributions of the surface-treated nanoparticles that is difficult to obtain by any single technique. The findings indicate titania platelets with a modal diameter of 9.8 nm and a thickness of approximately 1.5 nm. The particles are coated with a 1.5-1.9 nm thick organic ligand layer, and a substantial population of 2 nm siloxane oligomers is detected. The analytical methodology presented may also be useful for characterizing other anisotropic organic-inorganic nanoparticles and their dispersions.