Journal of Colloid and Interface Science, Mar 1, 2022
l-carnitines in our body systems can be readily converted into acyl-l-carnitines which have a pro... more l-carnitines in our body systems can be readily converted into acyl-l-carnitines which have a prominent place in cellular energy generation by supporting the transport of long-chain fatty acids into mitochondria. As biocompatible surfactants, acyl-l-carnitines have potential to be useful in technical, personal care and healthcare applications. However, the lack of understanding of the effects of their molecular structures on their physical properties has constrained their potential use. This work reports the study of the influence of the acyl chain lengths of acyl-l-carnitines (CnLC) on solubility, surface adsorption and aggregation. Critical micellar concentrations (CMCs) of CnLC were determined by surface tension measurements. Neutron reflection (NR) was used to further examine the structure and composition of the adsorbed CnLC layer. The structural changes of the micellar aggregates under different concentrations of CnLC, pH and ionic strength were determined by dynamic light scattering (DLS) and small angle neutron scattering (SANS). C12LC is fully soluble over a wide temperature and concentration range. There is however a strong decline of solubility with increasing acyl chain length. The adsorption and aggregation behavior of C14LC was therefore studied at 30 °C and C16LC at 45 °C. The solubility boundaries displayed distinct hysteresis with respect to heating and cooling. The CMCs of C12LC, C14LC and C16LC at pH 7 were 1.1 ± 0.1, 0.10 ± 0.02 and 0.010 ± 0.005 mM, respectively, with the limiting values of the area per molecule at the CMC being 45.4 ± 2, 47.5 ± 2 and 48.8 ± 2 Å2 and the thicknesses of the adsorbed CnLC layers at the air/water interface increasing from 21.5 ± 2 to 22.6 ± 2 to 24.2 ± 2 Å, respectively. All three surfactants formed core-shell spherical micelles with comparable dimensional parameters apart from an increase in core radius with acyl chain length. This study outlines the effects of acyl chain length on the physicochemical properties of CnLCs under different environmental conditions, serving as a useful basis for developing their potential applications.
Bubble profile analysis tensiometry is used to study the surface rheological behavior of mixed SD... more Bubble profile analysis tensiometry is used to study the surface rheological behavior of mixed SDS/C(12)EO(5) and SDS/C(14)EO(8) solutions. The experimental dependencies of the viscoelasticity modulus and phase angle are studied in a wide range of surfactant concentrations of the individual sodium dodecyl sulfate (SDS) and C(m)EO(n) solutions and SDS/C(n)EO(m) mixtures at various mixing ratios. By generating harmonic oscillations of the bubble area at low oscillation amplitudes, the relaxation behavior at oscillation frequencies between 0.005 and 0.2 Hz was studied. The applied theoretical approach to describe the dilational rheology of surfactant mixtures requires the specification of the equations of state of the mixed surface layer and the adsorption isotherm of the mixture's components. For the systems studied, the theoretical model considers different adsorption mechanisms for the different surfactants. In particular, the adsorption behavior of oxyethylated surfactants was described by the reorientation model (assumes two adsorption states of surfactant molecules with different molar areas), including an intrinsic compressibility of molecules in the state of minimal area. For the SDS component, the adsorption was assumed to be governed by the Frumkin model, which also accounts for the intrinsic compressibility. Satisfactory agreement between experimental data and theoretical calculations of the viscoelasticity modulus and the phase angle is obtained.
Journal of Colloid and Interface Science, Jun 1, 2021
HYPOTHESIS l-carnitine plays a crucial role in the cellular production of energy by transporting ... more HYPOTHESIS l-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated l-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits. EXPERIMENTS This work evaluated the surface adsorption of lauroyl-l-carnitine (C12LC) and its aggregation behavior. The size and shape of the aggregates of C12LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C12LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations. FINDINGS At pH 7, the limiting area per molecule (ACMC) of the zwitterionic C12LC adsorbed layer at the air/water interface was found to be 46 Å2 from surface tension and neutron reflection, smaller than the values of C12PC, C12E5, DTAB, C12C4betaine and C12C8betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å2, indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C12LC. As the concentration increased, area per molecule reached a plateau of 37-39 Å2, indicating the dissolution of the more surface-active lauric acid into the micelles of C12LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core-shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C12LC potentially attractive as a solubilizing agent.
Journal of colloid and interface science, Jan 15, 2018
The methyl ester sulfonates represent a promising group of anionic surfactants which have the pot... more The methyl ester sulfonates represent a promising group of anionic surfactants which have the potential for improved performance and biocompatibility in a range of applications. Their solution properties, in particular their tolerance to hard water, suggests that surface ordering may occur in the presence of multi-valent counterion. Understanding their adsorption properties in a range of different circumstances is key to the exploitation of their potential. Neutron reflectivity and surface tension have been used to characterise the adsorption at the air-aqueous solution interface of the anionic surfactant sodium tetradecanoic 2-sulfo 1-methyl ester, CMES, in the absence of electrolyte and in the presence of mono, di, and tri-valent counterions, Na, Ca, and Al. In particular the emphasis has been on exploring the tendency to form layered structures at the interface. In the absence of electrolyte and in the presence of NaCl and CaCl and AlCl at low concentrations monolayer adsorption ...
Journal of Colloid and Interface Science, Mar 1, 2022
l-carnitines in our body systems can be readily converted into acyl-l-carnitines which have a pro... more l-carnitines in our body systems can be readily converted into acyl-l-carnitines which have a prominent place in cellular energy generation by supporting the transport of long-chain fatty acids into mitochondria. As biocompatible surfactants, acyl-l-carnitines have potential to be useful in technical, personal care and healthcare applications. However, the lack of understanding of the effects of their molecular structures on their physical properties has constrained their potential use. This work reports the study of the influence of the acyl chain lengths of acyl-l-carnitines (CnLC) on solubility, surface adsorption and aggregation. Critical micellar concentrations (CMCs) of CnLC were determined by surface tension measurements. Neutron reflection (NR) was used to further examine the structure and composition of the adsorbed CnLC layer. The structural changes of the micellar aggregates under different concentrations of CnLC, pH and ionic strength were determined by dynamic light scattering (DLS) and small angle neutron scattering (SANS). C12LC is fully soluble over a wide temperature and concentration range. There is however a strong decline of solubility with increasing acyl chain length. The adsorption and aggregation behavior of C14LC was therefore studied at 30 °C and C16LC at 45 °C. The solubility boundaries displayed distinct hysteresis with respect to heating and cooling. The CMCs of C12LC, C14LC and C16LC at pH 7 were 1.1 ± 0.1, 0.10 ± 0.02 and 0.010 ± 0.005 mM, respectively, with the limiting values of the area per molecule at the CMC being 45.4 ± 2, 47.5 ± 2 and 48.8 ± 2 Å2 and the thicknesses of the adsorbed CnLC layers at the air/water interface increasing from 21.5 ± 2 to 22.6 ± 2 to 24.2 ± 2 Å, respectively. All three surfactants formed core-shell spherical micelles with comparable dimensional parameters apart from an increase in core radius with acyl chain length. This study outlines the effects of acyl chain length on the physicochemical properties of CnLCs under different environmental conditions, serving as a useful basis for developing their potential applications.
Bubble profile analysis tensiometry is used to study the surface rheological behavior of mixed SD... more Bubble profile analysis tensiometry is used to study the surface rheological behavior of mixed SDS/C(12)EO(5) and SDS/C(14)EO(8) solutions. The experimental dependencies of the viscoelasticity modulus and phase angle are studied in a wide range of surfactant concentrations of the individual sodium dodecyl sulfate (SDS) and C(m)EO(n) solutions and SDS/C(n)EO(m) mixtures at various mixing ratios. By generating harmonic oscillations of the bubble area at low oscillation amplitudes, the relaxation behavior at oscillation frequencies between 0.005 and 0.2 Hz was studied. The applied theoretical approach to describe the dilational rheology of surfactant mixtures requires the specification of the equations of state of the mixed surface layer and the adsorption isotherm of the mixture's components. For the systems studied, the theoretical model considers different adsorption mechanisms for the different surfactants. In particular, the adsorption behavior of oxyethylated surfactants was described by the reorientation model (assumes two adsorption states of surfactant molecules with different molar areas), including an intrinsic compressibility of molecules in the state of minimal area. For the SDS component, the adsorption was assumed to be governed by the Frumkin model, which also accounts for the intrinsic compressibility. Satisfactory agreement between experimental data and theoretical calculations of the viscoelasticity modulus and the phase angle is obtained.
Journal of Colloid and Interface Science, Jun 1, 2021
HYPOTHESIS l-carnitine plays a crucial role in the cellular production of energy by transporting ... more HYPOTHESIS l-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated l-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits. EXPERIMENTS This work evaluated the surface adsorption of lauroyl-l-carnitine (C12LC) and its aggregation behavior. The size and shape of the aggregates of C12LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C12LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations. FINDINGS At pH 7, the limiting area per molecule (ACMC) of the zwitterionic C12LC adsorbed layer at the air/water interface was found to be 46 Å2 from surface tension and neutron reflection, smaller than the values of C12PC, C12E5, DTAB, C12C4betaine and C12C8betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å2, indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C12LC. As the concentration increased, area per molecule reached a plateau of 37-39 Å2, indicating the dissolution of the more surface-active lauric acid into the micelles of C12LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core-shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C12LC potentially attractive as a solubilizing agent.
Journal of colloid and interface science, Jan 15, 2018
The methyl ester sulfonates represent a promising group of anionic surfactants which have the pot... more The methyl ester sulfonates represent a promising group of anionic surfactants which have the potential for improved performance and biocompatibility in a range of applications. Their solution properties, in particular their tolerance to hard water, suggests that surface ordering may occur in the presence of multi-valent counterion. Understanding their adsorption properties in a range of different circumstances is key to the exploitation of their potential. Neutron reflectivity and surface tension have been used to characterise the adsorption at the air-aqueous solution interface of the anionic surfactant sodium tetradecanoic 2-sulfo 1-methyl ester, CMES, in the absence of electrolyte and in the presence of mono, di, and tri-valent counterions, Na, Ca, and Al. In particular the emphasis has been on exploring the tendency to form layered structures at the interface. In the absence of electrolyte and in the presence of NaCl and CaCl and AlCl at low concentrations monolayer adsorption ...
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