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In order to enhance the optical clearing effect of topically applied optical clearing agents (OCAs), we evaluated the effect of propylene glycol (PG) as a chemical penetration enhancer (PE) on optical clearing of skin in vitro by observation and measurement of optical-transmittance and diffuse-reflectance spectra. Three OCAs, i.e., glycerol, D-sorbitol and PEG400, and two other penetration enhancers, Azone and Thiazone, were used in this study. The results indicated that the decrease of reduced scattering coefficient caused by OCA/PG was larger than that by pure OCA, and the change by OCA/water was the least after the same treatment time. There were significant differences for the reduced scattering coefficient at 630 nm after 120 min application of agents between OCA and OCA/PG. The efficacy of optical clearing caused by OCA/PG depended on the OCA itself. When PEG400 was mixed with three different PEs, we found the optical clearing were different. The penetration enhancing ability of PG was much better compared to Azone, and suboptimal to Thiazone. Also, this study provides evidence for the use of PG as a PE in order to improve skin optical clearing.

In bioelectrical potential measurement with restricted skin-electrode contact area, such as in dense array EEG measurement where the electrolyte bridging effect¹ is a major concern for signal reliability, an enhanced electrolyte solution is required for the skin-electrode impedance to reach the sufficiently low level within the minimum time interval. In this study, an electrolyte gel with its skin permeation ability enhanced by ethanol or propylene glycol has been investigated. The standard skin-electrode impedance measurement was carried out on the forehead in an area of 6 mm in diameter using standard Ag/AgCl EEG electrodes. The gel solutions with 0%, 7%, 18% and 28% of enhancers by volume are compared. The results show that both ethanol and propylene glycol reduce the permeation barrier of the stratum corneum so that ions in the electrolyte gel can penetrate more readily into the skin, enhancing the skin-electrode conductivity in reaching the steady value at a faster rate. It was further found that for the gel with higher percentage of ethanol, lower minimum skin-electrode impedance value was obtained. However, as the percentage of propylene glycol increased, it fails to attain low steady impedance values in the skin-electrode impedance measurements.

Methylal can be blended in diesel oil to reduce gas pollutants and to improve performance of a diesel engine. Methylal (Dimethoxymethane, DMM) can be synthesized by the reversible reaction of methanol excess and formaldehyde or paraformaldehyde to eliminate the chemical equilibrium. A mixture of methylal and methanol can be separated by extractive distillation system that combines with an extractive distillation (EDC) and entrainer recovery (RDC) column. Disadvantage of the extractive distillation system is the great energy consumption especially in the EDC. The design of EDC needs to be optimized the energy consumption and product purity. In this work, a conventional entrianer (DMF) was substituted by a lower-toxic of entrainer such as propylene-glycol. The response surface methodology (RSM) was used to optimize the condition in EDC design. The parameters and their interactions had significant effect on energy consumption in the reboiler and product purity. The optimal parameters of EDC could be determined by RSM with simulation runs and the predicted results by the RSM gave good agreement with the simulated results. Purity of 99.90 % methylal was withdrawn in the overhead of the EDC that could be achieve.