Impact of Degree of Ethoxylation on Sodium Lauryl Ether Sulfate Surfactant Adsorption onto Silicone-in-Water Emulsion Droplets.

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.

Removing acoustic ringing baseline curvature in 13 C NMR spectra for quantitative analyses.

13 C nuclear magnetic resonance (NMR) is traditionally considered an insensitive technique, requiring long acquisition times to measure dilute functionalities on large polymers. With the introduction of cryoprobes and better electronics, sensitivity has improved in a way that allows measurements to take less than 1/20th the time that they previously did. Unfortunately, a high Q-factor with cryoprobes creates baseline curvature related to acoustic ringing that affects quantitative NMR analyses. Manual baseline correction is commonly used to compensate for the baseline roll, but it is a time-intensive process. The outcome of manual baseline correction can vary depending on processing parameters, especially for complicated spectra. Additionally, it can be challenging to distinguish between broad peaks and baseline rolls. A new anti-ring pulse sequence (zgig_pisp) was previously reported to improve on the incumbent single pulse experiment (zgig). The original report presented limited comparison data with 13 C NMR, but a thorough validation is needed before broader implementation can be considered. In this work, we report the round-robin testing and comparison of zgig_pisp and zgig pulse sequences. During the testing phase, we found that zgig_pisp is practically equivalent to zgig to ±2% for the majority of integrals examined. Additionally, a short broadband inversion pulse (BIP) was demonstrated as an alternative to the originally reported adiabatic CHIRP shaped pulse. The zgig_pisp pulse sequence code for Bruker spectrometers is also simplified.

Insights into the behavior of ethylene oxide-1,2-epoxybutane diblock copolymers in water as a function of temperature and the presence of colloidal silica.

HYPOTHESIS: Nonionic surfactants have been widely used for many consumer products and industrial processes, and their applications often involve temperature-cycling across cloud point temperature (Tcloud). To explore the behavior of nonionic surfactants across Tcloud and when mixed with colloidal silica at a very dilute concentration around 0.1 wt%, a series of 1,2-epoxybutane-capped alcohol ethoxylates (BAEs) with various cloud points is used as a model system. EXPERIMENTS: BAEs with cloud points from 15 to 64 °C were successfully prepared by varying the lengths of 1,2-epoxybutane (BO) and ethylene oxide (EO) blocks and their phase behavior across Tcloud was studied using nuclear magnetic resonance spectroscopy (NMR), dynamic light scattering (DLS) and differential scanning calorimetry (DSC). FINDINGS: In the absence of silica, the NMR signals are not greatly affected by the cloud point transition, but both the water and surfactant exhibit a decrease in spin-spin relaxation time once the temperature reaches the Tcloud. In the presence of silica, the NMR spectra indicate significantly reduced mobility of the EO portion relative to the alkyl and BO segments. Furthermore, our results suggest that the BAE surfactants are not fractionally clouding out or precipitating with a portion of the compositional distribution during the cloud point transition.