“…In our design, the drop forms on the pointed capillary tip such that a small (∼40 μm, measured by visual microscopy) and essentially constant distance of wetting occurs, as illustrated in Figure . This wetting produces an additional adhesive force that contributes to the data obtained. , Several instrumental variables determine the drop formation and detachment rate. − The condition for drop detachment is achieved when the forces due to the liquid clasping thetip of the capillary are overcome by the force of gravity, F G , on the mass of the drop, where F S is the force due to the liquid−air surface tension and F W,v is the vertical component of the adhesion wetting force, F W , such that F W extends along the surface of the wetted portion of the capillary tip . Note that it is the vertical component of the adhesion force that quantifies the opposition to drop detachment due to adhesion, even though the effect is occurring at the liquid−solid interface.…”
Section: Theory and Instrument Designmentioning
confidence: 99%
“…Also, note that γ cos θ in eq 3 corresponds to the difference between the solid−air and liquid−solid interfacial tensions. Inserting eqs 2−4 into eq 1 and simplifying, the condition for drop detachment is Note that the quantity γ(1 + cos θ cos α) is a modified form of the work of adhesion for our tip geometry. , When α = 90°, i.e., for a flat capillary tip without vertical wetting occurring, eq 5 reduces to which is the commonly applied form of the drop weight method for determining γ. Additionally, for most applications, the density is essentially constant, that of the bulk solvent, so corrections for density are not needed. − 1 (A) Instrument design. Samples are introduced into the flow with an injection valve, pass through a capillary, and form a repeating drop at the capillary tip.…”
Section: Theory and Instrument Designmentioning
confidence: 99%
“…The drop profile simultaneously contains information on surface tension at the air−liquid interface and adhesion on the side of the capillary tip, so the pressure-based DSTD effectively provides an automated contact angle measurement . Although adhesional wetting at the capillary tip has been indicated as a problem in the measurement of liquid−liquid surface tension, we report that the adhesional effect with a pointed capillary tip can provide valuable multidimensional information. Work described here indicates that the drop profile contributions due to surface tension and adhesion are easily observed and readily separated for chemical analysis on flowing liquids.…”
A multidimensional dynamic surface tension detector (DSTD) for flowing liquid samples is reported. The DSTD is based on measuring the pressure with time of a repeating drop formed by the flow of liquid out the end of a pointed stainless steel capillary. This pressure-based DSTD provides information on dynamic surface tension at the air-liquid interface and adhesion at the solid-liquid interface on the side of the pointed capillary tip for each drop of surfactant solution, resulting in rapid characterization of complex samples. The signal obtained with the pressure-based DSTD is characterized, and a method is developed for extraction of the desired analytical information from the pressure signal. The DSTD was calibrated with 2-propanol over the range of 0-0.30 in relative surface tension lowering, Δγ/γ. The experimentally obtained Δγ/γ was in agreement with a theoretical model and published data for Δγ/γ over this range. A data analysis method was developed to adapt the DSTD to applications such as liquid chromatography and flow injection analysis, where the concentration of surfactant changes as a function of time. The DSTD signal yields a pressure-based Δγ/γ that is due to surface tension alone and a time-based Δγ/γ that is a combination of both surface tension and adhesion, providing essentially a contact angle measurement on a flowing sample. The data analysis method involves plotting the pressure-based and time-based surface tension measurements against each other at the same surfactant concentration for each pair of measurements, yet over a range of concentrations to establish a slope. This is referred to as a dynamic analysis plot and is applied in the characterization of various surfactants such as dodecyl sulfate ion-paired with tetrabutylammonium, industrial surfactant solutions FC-171 and FC-129, and biological surfactants tetradecyl maltoside, benzyldimethyldodecylammonium bromide, and 3-(N-decyl-N,N-dimethylammonio)-1-propanesulfonate. The slopes of the dynamic analysis plots for these surfactants were found to be unique, generally independent of concentration, and useful for understanding the type and degree of operating surface interactions. The FC-171 solution was found to exhibit considerable adhesion at the capillary tip, while dodecyl sulfate was found to have a small adhesion effect. Adhesion for dodecyl sulfate solutions was significantly enhanced by coating the stainless steel capillary tip with a hydrophobic polymer. Thus, there is potential for tuning the extent of the surface tension and adhesion effects for selective chemical analysis. The detection limit for dodecyl sulfate ion-paired with tetrabutylammonium is 0.9 ppm. Application of the DSTD for liquid chromatography is demonstrated, and the multidimensional data are shown to be useful in identifying and characterizing the poly(ethylene glycol)s separated from 2-propanol.
“…In our design, the drop forms on the pointed capillary tip such that a small (∼40 μm, measured by visual microscopy) and essentially constant distance of wetting occurs, as illustrated in Figure . This wetting produces an additional adhesive force that contributes to the data obtained. , Several instrumental variables determine the drop formation and detachment rate. − The condition for drop detachment is achieved when the forces due to the liquid clasping thetip of the capillary are overcome by the force of gravity, F G , on the mass of the drop, where F S is the force due to the liquid−air surface tension and F W,v is the vertical component of the adhesion wetting force, F W , such that F W extends along the surface of the wetted portion of the capillary tip . Note that it is the vertical component of the adhesion force that quantifies the opposition to drop detachment due to adhesion, even though the effect is occurring at the liquid−solid interface.…”
Section: Theory and Instrument Designmentioning
confidence: 99%
“…Also, note that γ cos θ in eq 3 corresponds to the difference between the solid−air and liquid−solid interfacial tensions. Inserting eqs 2−4 into eq 1 and simplifying, the condition for drop detachment is Note that the quantity γ(1 + cos θ cos α) is a modified form of the work of adhesion for our tip geometry. , When α = 90°, i.e., for a flat capillary tip without vertical wetting occurring, eq 5 reduces to which is the commonly applied form of the drop weight method for determining γ. Additionally, for most applications, the density is essentially constant, that of the bulk solvent, so corrections for density are not needed. − 1 (A) Instrument design. Samples are introduced into the flow with an injection valve, pass through a capillary, and form a repeating drop at the capillary tip.…”
Section: Theory and Instrument Designmentioning
confidence: 99%
“…The drop profile simultaneously contains information on surface tension at the air−liquid interface and adhesion on the side of the capillary tip, so the pressure-based DSTD effectively provides an automated contact angle measurement . Although adhesional wetting at the capillary tip has been indicated as a problem in the measurement of liquid−liquid surface tension, we report that the adhesional effect with a pointed capillary tip can provide valuable multidimensional information. Work described here indicates that the drop profile contributions due to surface tension and adhesion are easily observed and readily separated for chemical analysis on flowing liquids.…”
A multidimensional dynamic surface tension detector (DSTD) for flowing liquid samples is reported. The DSTD is based on measuring the pressure with time of a repeating drop formed by the flow of liquid out the end of a pointed stainless steel capillary. This pressure-based DSTD provides information on dynamic surface tension at the air-liquid interface and adhesion at the solid-liquid interface on the side of the pointed capillary tip for each drop of surfactant solution, resulting in rapid characterization of complex samples. The signal obtained with the pressure-based DSTD is characterized, and a method is developed for extraction of the desired analytical information from the pressure signal. The DSTD was calibrated with 2-propanol over the range of 0-0.30 in relative surface tension lowering, Δγ/γ. The experimentally obtained Δγ/γ was in agreement with a theoretical model and published data for Δγ/γ over this range. A data analysis method was developed to adapt the DSTD to applications such as liquid chromatography and flow injection analysis, where the concentration of surfactant changes as a function of time. The DSTD signal yields a pressure-based Δγ/γ that is due to surface tension alone and a time-based Δγ/γ that is a combination of both surface tension and adhesion, providing essentially a contact angle measurement on a flowing sample. The data analysis method involves plotting the pressure-based and time-based surface tension measurements against each other at the same surfactant concentration for each pair of measurements, yet over a range of concentrations to establish a slope. This is referred to as a dynamic analysis plot and is applied in the characterization of various surfactants such as dodecyl sulfate ion-paired with tetrabutylammonium, industrial surfactant solutions FC-171 and FC-129, and biological surfactants tetradecyl maltoside, benzyldimethyldodecylammonium bromide, and 3-(N-decyl-N,N-dimethylammonio)-1-propanesulfonate. The slopes of the dynamic analysis plots for these surfactants were found to be unique, generally independent of concentration, and useful for understanding the type and degree of operating surface interactions. The FC-171 solution was found to exhibit considerable adhesion at the capillary tip, while dodecyl sulfate was found to have a small adhesion effect. Adhesion for dodecyl sulfate solutions was significantly enhanced by coating the stainless steel capillary tip with a hydrophobic polymer. Thus, there is potential for tuning the extent of the surface tension and adhesion effects for selective chemical analysis. The detection limit for dodecyl sulfate ion-paired with tetrabutylammonium is 0.9 ppm. Application of the DSTD for liquid chromatography is demonstrated, and the multidimensional data are shown to be useful in identifying and characterizing the poly(ethylene glycol)s separated from 2-propanol.
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