Thermoporometry measurements of human hair via differential scanning calorimetry.

OBJECTIVE: Hair fibres possess an inherently porous structure, which is affected by physical and chemical agents from the environment, as well as those from cosmetic treatments. The present work aims to investigate the potential of a calorimetric method for evaluating the changes of hair porosity, in terms of pore size and size distribution. METHODS: The temperature of the phase transition from solid to liquid is known to be depressed if the liquid is confined within a pore. This shift in temperature can be measured by a calorimetric method like differential scanning calorimetry, DSC. This method is termed thermoporometry and it is the tool used for investigating hair porosity in this work. RESULTS: Virgin and bleached hair fibres are measured by DSC and, by using the equations developed for water behaviour confined in pores of a solid, the size and size distribution of the hair pores are evaluated, and the influence of the cosmetic treatment on the pores is discussed. CONCLUSION: Thermoporometry measurements of hair produced results in good agreement with those obtained by other methods for measuring hair porosity. The analysis of the data suggests that the fibre pores are mostly of a radius of 4 nm, and that the bleaching process increases the total volume of pores through the addition of smaller pores. A prolonged bleaching process appears to reduce the amount of fine pores produced by the first short process, resulting in fewer, but larger, cavities, most likely through a process of pore-merging.

OBJECTIF: Les fibres capillaires possèdent une structure intrinsèquement poreuse, qui est affectée par les agents physiques et chimiques de l'environnement, ainsi que par ceux des traitements cosmétiques. Le présent travail vise à étudier le potentiel d'une méthode calorimétrique pour évaluer les changements de porosité des fibres, en termes de taille et de distribution des pores. MÉTHODES: On sait que la température de la transition de phase entre le solide et le liquide est abaissée si le liquide est confiné dans un pore. Ce changement de température peut être mesuré par une méthode calorimétrique telle que la calorimétrie différentielle à balayage (DSC). Cette méthode est appelée thermoporométrie et c'est l'outil utilisé pour étudier la porosité des fibres capillaires dans ce travail. RÉSULTATS: Les fibres capillaires vierges et blanchies sont mesurées par DSC et, en utilisant les équations développées pour le comportement de l'eau confinée dans les pores d'un solide, la taille et la distribution des pores des fibres sont évaluées, et l'influence du traitement cosmétique sur les pores est discutée. CONCLUSION: Les mesures de thermoporométrie sur les fibres capillaires ont donné des résultats en bon accord avec ceux obtenus par d'autres méthodes de mesure de la porosité des cheveux. L'analyse des données suggère que les pores de la fibre ont pour la plupart un rayon de 4 nm et que le processus de blanchiment augmente le volume total des pores par l'ajout de pores plus petits. Un processus de blanchiment prolongé semble réduire la quantité de pores fins produits par le premier processus court, ce qui se traduit par des cavités moins nombreuses mais plus grandes, très probablement par un processus de fusion des pores.

Thermodynamics and Viscoelastic Property of Interface Unravel Combined Functions of Cationic Surfactant and Aromatic Alcohol against Gram-Negative Bacteria.

Lipopolysaccharides (LPSs), the major constituents of the outer membranes of Gram-negative bacteria, play a key role in protecting bacteria against antibiotics and antibacterial agents. In this study, we investigated how a mixture of cationic surfactants and aromatic alcohols, the base materials of widely used sanitizers, synergistically act on LPSs purified from Escherichia coli using isothermal titration calorimetry (ITC), surface tension measurements, and quartz crystal microbalance with dissipation (QCM-D). ITC data measured in the absence of Ca2+ ions showed the coexistence of exothermic and endothermic processes. The exotherm can be interpreted as the electrostatic binding of the cationic surfactant to the negatively charged LPS membrane surface, whereas the endotherm indicates the hydrophobic interaction between the hydrocarbon chains of the surfactants and LPSs. In the presence of Ca2+ ions, only an exothermic reaction was observed by ITC, and no entropically driven endotherm could be detected. Surface tension experiments further revealed that the co-adsorption of surfactants and LPS was synergistic, while that of surfactants and alcohol was negatively synergistic. Moreover, the QCM-D data indicated that the LPS membrane remained intact when the alcohol alone was added to the system. Intriguingly, the LPS membrane became highly susceptible to the combination of cationic surfactants and aromatic alcohols in the absence of Ca2+ ions. The obtained data provide thermodynamic and mechanical insights into the synergistic function of surfactants and alcohols in sanitation, which will enable the identification of the optimal combination of small molecules for a high hygiene level for the post-pandemic society.

Unsaturated fatty acid salts remove biofilms on dentures.

Candidiasis-causing Candida sp. forms biofilms with various oral bacteria in the dentures of the elderly, making it harder to kill and remove the microorganism due to the extracellular polymeric substances. We found that biofilms on dentures can effectively be removed by immersion in an unsaturated fatty acid salt solution. Using optical coherence tomography to observe the progression of biofilm removal by the fatty acid salt solution, we were able to determine that the removal was accompanied by the production of gaps at the interface between the biofilm and denture resin. Furthermore, microstructural electron microscopy observations and time-of-flight secondary ion mass spectrometry elucidated the site of action, revealing that localization of the fatty acid salt at the biofilm/denture-resin interface is an important factor.

Specific localisation of ions in bacterial membranes unravels physical mechanism of effective bacteria killing by sanitiser.

Antimicrobial resistance is a major threat to public health. Although many commercial sanitisers contain a combination of cationic surfactants and aromatic alcohols, the physical mechanisms where these two substances bind to or how they disturb bacterial membranes are still largely unknown. In this study, we designed a well-defined model of Gram-negative bacteria surfaces based on the monolayer of lipopolysaccharides with uniform saccharide head groups. Since commonly used X-ray reflectivity is sensitive to changes in the thickness, roughness and electron density but is not sensitive to elements, we employed grazing incidence X-ray fluorescence. In the absence of Ca2+, cationic surfactants can penetrate into the membrane core with no extra support by disturbing the layer of K+ coupled to negatively charged saccharide head group at z = 17 Å from the air/chain interface. On the other hand, Ca2+ confined at z = 19 Å crosslink charged saccharides and prevent the incorporation of cationic surfactants. We found that the addition of nonlethal aromatic alcohols facilitate the incorporation of cationic surfactants by the significant roughening of the chain/saccharide interface. Combination of precise localisation of ions and molecular-level structural analysis quantitatively demonstrated the synegtestic interplay of ingredients to achieve a high antibacterial activity.

Emergence of Strong Nonlinear Viscoelastic Response of Semifluorinated Alkane Monolayers.

Viscoelasticity of monolayers of fluorocarbon/hydrocarbon tetrablock amphiphiles di(FnHm) ((CnF2n+1CH2)(Cm-2H2m-3)CH-CH(CnF2n+1CH2)(Cm-2H2m-3)) was characterized by interfacial dilational rheology under periodic oscillation of the moving barriers at the air/water interface. Because the frequency dispersion of the response function indicated that di(FnHm) form two-dimensional gels at the interface, the viscosity and elasticity of di(FnHm) were first analyzed with the classical Kelvin-Voigt model. However, the global shape of stress response functions clearly indicated the emergence of a nonlinearity even at very low surface pressures (π ≈ 5 mN/m) and small strain amplitudes (u0 = 1%). The Fourier-transformed response function of higher harmonics exhibited a clear increase in the intensity only from odd modes, corresponding to the nonlinear elastic component under reflection because of mirror symmetry. The emergence of strong nonlinear viscoelasticity of di(FnHm) at low surface pressures and strain amplitudes is highly unique compared to the nonlinear viscoelasticity of other surfactant systems reported previously, suggesting a large potential of such fluorocarbon/hydrocarbon molecules to modulate the mechanics of interfaces using the self-assembled domains of small molecules.

Existence of Two-Dimensional Physical Gels even at Zero Surface Pressure at the Air/Water Interface: Rheology of Self-Assembled Domains of Small Molecules.

Films of mesoscopic domains self-assembled from fluorocarbon/hydrocarbon diblock copolymers (FnHm) at the air/water interface were found to display highly elastic behavior. We determined the interfacial viscoelasticity of domain-patterned FnHm Langmuir monolayers by applying periodic shear stresses. Remarkably, we found the formation of two-dimensional gels even at zero surface pressure. These monolayers are predominantly elastic, which is unprecedented for surfactants, exhibiting gelation only at high surface pressures. Systematic variation of the hydrocarbon (n=8; m=14, 16, 18, 20) and fluorocarbon (n=8, 10, 12; m=16) block lengths demonstrated that subtle changes in the block length ratio significantly alter the mechanics of two-dimensional gels across one order of magnitude. These findings open perspectives for the fabrication of two-dimensional gels with tuneable viscoelasticity via self-assembly of mesoscale, low-molecular-weight materials.

A role of the anteiso branch of 18-MEA in 18-MEA/SPDA to form a persistent hydrophobicity to alkaline-color-treated weathered hair.

The effect of the anteiso-branch moiety of 18-MEA (18-methyleicosanic acid) to create a persistent hydrophobicity of alkaline-color-treated weathered hair treated with 18-MEA/SPDA (stearoxypropyldimethylamine) was investigated by comparing a straight-chain fatty acid (n-heneicosanoic acid, n-HEA) and an iso-branch fatty acid (19-methyleicosanic acid, 19-MEA) with the anteiso-branch fatty acid (18-MEA), using dynamic contact angle measurements, quantification of 18-MEA by LC/MS, and temperature controlled atomic force microscopy (AFM). The dynamic contact angle measurements indicated that the anteiso-branch moiety of 18-MEA is critical for the creation of a persistent hydrophobicity to alkaline-color-treated weathered hair. The temperature-controlled AFM investigations revealed that the anteiso-branch moiety of 18-MEA in the 18-MEA/SPDA system produces a persistent hydrophobicity to alkaline-color-treated weathered hair by providing higher fluidity to the upper region of the 18-MEA/SPDA layer.