Evaluation of the surface properties of hair with acoustic emission analysis.

OBJECTIVE: The tactile sensation of hair is an important consumer-perceivable attribute. There are limited instrumental options to measure the haptic properties of hair. In this study, we introduce a novel technique using the acoustic emissions produced when skin comes in contact with dry hair in a stroking motion. METHODS: Using a free-field microphone with a frequency response of 8-12,500 Hz, we recorded acoustic emission data of the interaction of skin with hair. Data were captured with Electroacoustics Toolbox software and analysed with Matlab. Acoustic emission profiles were generated allowing us to monitor the acoustic response at distinct frequencies. RESULTS: Various experiments were conducted to develop this novel technique as a suitable measure to monitor the surface properties of hair. Increasing the normal force and velocity of the interaction led to an increase in acoustic emissions. We also examined the acoustic profile of hair that underwent chemical treatment. For example, bleached hair produced a much higher magnitude acoustic response than the corresponding virgin hair. On the other hand, hair conditioner systems mitigated the acoustic response. Finally, investigations of textured hair revealed that the three-dimensional structure of the hair fibre assembly and its ability to return to its original state when perturbed produce the most dominant acoustic response for this type of hair. CONCLUSION: We introduce a cutting-edge method to reproducibly evaluate the surface properties of hair. Different types of hair geometry produce unique acoustic profiles as do hair types that experience harsh damaging treatments. This is also a very practical and efficient way to evaluate the degree of protection or conditioning of the fibre.

OBJECTIF: La sensation tactile des cheveux est un attribut important perceptible par le consommateur. Il existe des options instrumentales limitées pour mesurer les propriétés haptiques des cheveux. Dans cette étude, nous introduisons une nouvelle technique utilisant les émissions acoustiques produites lorsque la peau entre en contact avec les cheveux secs dans un mouvement de caresses. MÉTHODES: En utilisant un microphone champ libre avec une réponse en fréquence de 8 à 12 500 Hz, nous avons enregistré des données d'émission acoustique de l'interaction de la peau avec les cheveux. Les données ont été capturées avec le logiciel Electroacoustics Toolbox et analysées avec Matlab. Nous avons généré des profils d'émission acoustique. De cette manière nous pourrions surveiller la réponse acoustique à des fréquences distinctes. RÉSULTATS: Nous avons fait diverses expériences pour développer cette nouvelle technique comme mesure appropriée pour surveiller les propriétés de surface des cheveux. L'augmentation de la force normale et de la vitesse de l'interaction entre la peau et les cheveux ont causé une augmentation des émissions acoustiques. Nous avons également examiné le profil acoustique des cheveux ayant subi un traitement chimique. Par exemple, les cheveux décolorés ont produit une réponse acoustique de beaucoup plus grande amplitude que les cheveux vierges correspondants. D'autre part, les systèmes d'après shampooing ont atténué la réponse acoustique. Enfin, des investigations sur des cheveux texturés ont révélé que la structure tridimensionnelle de l'ensemble de fibres capillaires et sa capacité à revenir à son état d'origine lorsqu'il est perturbé produisent la réponse acoustique la plus dominante pour ce type de cheveux. CONCLUSION: Nous introduisons une méthode de pointe pour évaluer de manière reproductible les propriétés de surface des cheveux. Différents types de géométrie de cheveux produisent des profils acoustiques uniques, tout comme les types de cheveux qui subissent des traitements agressifs. C'est également une manière très pratique et efficace d'évaluer le degré de protection ou de conditionnement des cheveux.

Characterization of yield stress and slip behaviour of skin/hair care gels using steady flow and LAOS measurements and their correlation with sensorial attributes.

Gels made with three different polymers widely used as rheology modifiers in cosmetic formulations (cross-linked poly(acrylic acid), cross-linked poly(maleic acid-alt-methyl vinyl ether) copolymer and cross-linked poly(acrylic acid-co-vinyl pyrrolidone) copolymer) were characterized by rheological and sensory evaluation methods to determine the relationship between sensorial perception and corresponding rheological parameters. Both conventional rheological characterization methods and a more recent method, Fourier Transform Rheology with Large Amplitude Oscillatory Flow data (LAOS), were utilized to characterize the material with and without wall slip. Sensorial analyses were implemented in vivo to evaluate the perceived ease of initial and rub-out spreadability, cushion, pick-up and slipperiness attributes of the gels. Results were statistically analysed by both variance (ANOVA) and principle component analysis (PCA). Sensorial panel testing characteristics discriminated the three materials, and PCA analyses revealed that sensory attributes could be well predicted by rheological methods. Rheological experiments, without wall slip, revealed that gel strength in the linear viscoelastic region (LVR) and yield stress of these materials are similar, but exhibit significantly different wall slip and thixotropy behaviour in the low shear rate region under wall slip conditions. Above the critical shear rate, which corresponds to the yield stress, all tested materials did not slip and behaved as conventional, shear thinning polymeric fluids. In particular, the rheological parameters and sensorial perception of the 1% cross-linked vinyl pyrrolidone/acrylic acid copolymer were significantly affected by wall slip and/or thixotropy-related shear banding phenomena.

The effect of various cosmetic pretreatments on protecting hair from thermal damage by hot flat ironing.

Hot flat irons are used to create straight hair styles. As these devices operate at temperatures over 200 °C they can cause significant damage to hair keratin. In this study, hair thermal damage and the effect of various polymeric pretreatments were investigated using FTIR imaging spectroscopy, DSC, dynamic vapor sorption (DVS), AFM, SEM, and thermal image analysis. FTIR imaging spectroscopy of hair cross sections provides spatially resolved molecular information such as protein distribution and structure. This approach was used to monitor thermally induced modification of hair protein, including the conversion of α-helix to ß-sheet and protein degradation. DSC measurements of thermally treated hair also demonstrated degradation of hair keratin. DVS of thermally treated hair shows the reduced water regain and lower water retention, compared to the non-thermally treated hair, which might be attributed to the protein conformation changes due to heat damage. The protection of native protein structure associated with selected polymer pretreatments leads to improved moisture restoration and water retention of hair. This contributes to heat control on repeated hot flat ironing. Thermally stressing hair led to significantly increased hair breakage when subjected to combing. These studies indicate that hair breakage can be reduced significantly when hair is pretreated with selected polymers such as VP/acrylates/lauryl methacrylate copolymer, polyquaternium-55, and a polyelectrolyte complex of PVM/MA copolymer and polyquaternium-28. In addition, polymeric pretreatments provide thermal protection against thermal degradation of keratin in the cortex as well as hair surface damage. The morphological improvement in cuticle integrity and smoothness with the polymer pretreatment plays an important role in their anti-breakage effect. Insights into structure-property relationships necessary to provide thermal protection to hair are presented.