Quantification of Human Hair Moisturization with Cosmetic Products by Dynamic Vapor Sorption.

An attempt has been made to evaluate and quantify the moisturizing efficacy of cosmetic products by dynamic vapor sorption method. The possibility of quantifying this effect by the application of the second law of thermodynamics to sorption hysteresis has been demonstrated. The results show that the ordinary conditioner actives in rinse-off formulations show limited moisturizing capabilities. However, specially formulated products can show, quantifiably, both moisturizing and desiccating effects. From the Brunauer, Emmett and Teller (BET) theory, total pore volume obtained from the literature by nitrogen adsorption, and the sorption data from this work, it has been possible to show that the sorbed water in hair does not distribute uniformly in the hair. This is in agreement with the X-ray diffraction measurements and the more recent work on small angle neutron scattering on D2O-saturated hair.

Heat transfer in human hair.

OBJECTIVE: In the process of daily grooming, human hair often undergoes heat treatments. These treatments create temperature gradients inside individual hair fibres or bundles of hair which can lead to hair damage. METHODS: Mathematical models were built for heat transfer in a single hair as well as thin tresses of hair during blow drying. RESULTS: Mathematical analysis led to temperature profiles suggestive of fast transfer of heat in a single hair mainly through conduction. However, in a hair assembly, the process involved both conduction and convection leading to a slower rate of heat transfer. Penetration of heat to the centre of the hair assembly took minutes rather than seconds. CONCLUSION: This model is useful in understanding hair damage potential in styling hair with high temperature devices such as flat irons and processes which involve deforming hair at relatively high temperatures.

OBJECTIF: Les cheveux sont souvent soumis à de fortes chaleurs lors de la toilette quotidienne. Ces traitements créent des gradients de température à l'intérieur de chaque cheveu ou des mèches qui peuvent conduire à des lésions. MÉTHODES: Des modèles mathématiques ont été créés afin d'observer la diffusion de la chaleur dans un seul cheveu ainsi que dans de fines mèches de cheveux pendant le séchage. RÉSULTATS: L'analyse mathématique a donné des profils de température évocateurs de diffusion rapide de la chaleur dans chaque cheveu en utilisant la conduction. Cependant, dans une mèche de cheveux, le processus implique la conduction et la convection, ce qui réduit la diffusion de la chaleur. La pénétration de la chaleur au centre de la mèche se compte en minutes plutôt qu'en secondes. CONCLUSION: Ce modèle est utile à la compréhension des lésions potentielles des cheveux dans la coiffure à haute température avec des dispositifs tels que les plaques à lisser et dans les processus qui impliquent de déformer les cheveux en les soumettant à une forte chaleur.

Hair breakage by combing and brushing--a comment on: T. A. Evans and K. Park, A statistical analysis of hair breakage. II. Repeated grooming experiments, J. Cosmet. Sci., 41, 439-456 (2010).

Literature dealing with the mechanisms of hair breakage in combing and brushing published so far has been reviewed as a background for the critical evaluation of the method and data analysis of the paper "Statistical Analysis of Hair Breakage. II" by Evans and Park (1). Accumulated knowledge about hair breakage in these grooming processes indicates that hair breakage in combing and brushing results from tangling, looping, knotting, and impact loading. Fatiguing, though responsible for some weakening of the fiber in the grooming process, it is unlikely to be a significant factor in hair breakage in combing and brushing.

The effect of treatments on the shear modulus of human hair measured by the single fiber torsion pendulum.

Previous studies with the single fiber torsion pendulum have alluded to the ability of this device to selectively measure different regions of a fiber, namely, the core and the sheath. This selective ability of the torsion pendulum was explored further as a means of better understanding treatments effects. First, a substantial reduction in shear modulus was caused by simply abrading the hair fiber surface to remove the cuticle layer. In another experiment, bleaching was found to have a softening effect on the cuticle layer since the shear modulus was reduced significantly. Next, the fibers were subsequently treated with either Polyquaternium-10 or cetyl trimethylammonium bromide (CETAB) and measured again. The CETAB treatment resulted in an increase in the shear modulus indicating fortification of the cuticle layer. Polyquaternium-10 treatment increased the shear modulus slightly. These different effects are explained by the molecular sizes of these compounds-CETAB is a small molecule which can penetrate into the cuticle layer while Polyquaternium-10 is too large to do so. Lastly, the effect of moisture was evaluated by varying the humidity inside a chamber surrounding the sample mounted in the torsion pendulum. This showed a substantial inverse relationship between humidity level and shear modulus that was much more pronounced for bleached hair fibers than for untreated.

Effect of oil films on moisture vapor absorption on human hair.

In this paper sorption and desorption of water vapor on hair fibers treated with various oils is investigated, using a dynamic vapor sorption (DVS) apparatus. Results show lower "equilibrium" sorption of moisture for various oil-treated samples compared to the untreated sample. Coconut oil-treated hair had a higher regain than mineral oil-treated hair. Although treating the hair samples with oil reduced moisture pickup, a considerable amount of moisture vapor was still able to penetrate into hair fibers. Calculated hysteresis plots show that the samples treated with different oils have slightly higher moisture retention at low relative humidities compared to that of the untreated sample, which suggests a beneficial effect. The calculated moisture diffusion coefficients for oil-treated samples were much lower compared to the untreated hair fibers, suggesting that surface oil films and penetrated oil molecules form a diffusion barrier. A moisture diffusion model is discussed in terms of the possible role of fiber swelling on restrictive narrowing of the cell membrane complexes (CMCs), which form the diffusion pathways in the fiber. The effect of film thickness on moisture absorption and the reverting of the sorption isotherm to that of the untreated hair after removal of the oil film shows that oil film is the main resistance to moisture diffusion. The lowering of the diffusion coefficient of water vapor by oil films will slow the loss of moisture, an effect similar to "moisturization" of hair.

Penetration of cationic conditioning compounds into hair fibers: a TOF-SIMS approach.

Cationic conditioning compounds protect against hair damage caused by cosmetic chemical treatments and grooming practices. They also enhance the retention of moisture. However, the question as to whether they do this superficially by residing on the hair surface or by penetrating into the fiber remains unanswered. In this work, an attempt has been made to show the penetration of a low-molecular-weight cationic conditioning compound into the hair cortex using the time-of-flight secondary ion mass spectrometry (TOF SIMS) method, applied in earlier research to show the penetration of oils into hair. An example of the practical benefit of such penetration into the cortex in greatly improving the fatigue resistance of hair has been discussed.

Investigation of penetration abilities of various oils into human hair fibers.

In this work we have explored capillary adhesion between hair fibers treated with different types of oils. With coconut, olive, and sunflower oils the capillary adhesion was found to decrease with time, but not with mineral oil. Application of heat reduced the capillary adhesion further for coconut and sunflower oils. Again, this was not observed with mineral oil. Based on an earlier study, where coconut oil was found to penetrate hair while mineral oil was unable to do so, it was hypothesized that the reduction in capillary adhesion resulted from the penetration of oil into the fiber, leaving a thinner oil film on the surface. Such a reduction in capillary adhesion can be explained by changes in Laplace pressure and in the areas of liquid bridges formed between the fibers. The thinning of oil films on the surface of hair has been confirmed independently by goniophotometric measurements on single hair fibers treated with coconut, sunflower, and mineral oils. Thick films of oil (thicker than approximately 0.5 microm) are known to mask the scale structure. As the oil is absorbed into the hair, the film thins with time and application of heat, and the scale structure reappears. This change can be conveniently determined by measuring the scale angle, using the well established goniophotometric protocol. The agreement between the two methods supports the concept that the reduction in capillary adhesion between hair fibers is most likely due to thinning of oil films by absorption of oil into the hair.

Effects of thermal treatments with a curling iron on hair fiber.

The effect of curling hair with a curling iron has been investigated. Possibilities of thermal damage with repeated curling according to, and in violation of, the manufacturer's specifications have been studied. The propensity of hair surface to damage depends on the moisture content of the hair, and these experiments have been conducted in both wet and dry conditions, with and without application of tension, and with short or prolonged times. Scanning electron microscopic (SEM) examination revealed that fibers treated under the dry condition (50% RH) show radial and axial cracking along with scale edge fusion. Similar thermal treatment on wet hair resulted in severe damage of the type described above, as well as bubbling and buckling of the cuticle due to the formation and escaping of steam from the fiber. Fibers subjected to repeated curling in the dry condition show slight increases in tensile mechanical properties, characteristic of a crosslinked fiber. Fibers treated with conditioners show an improvement in characteristic life, especially in the case of low-molecular-weight conditioners, such as CETAB, which can penetrate into the hair fiber (shown by TOF-SIMS analysis).

Torsional method for evaluating hair damage and performance of hair care ingredients.

In this study, we have developed a single hair fiber torsional pendulum method to determine the role of the cuticle and the cortex on torsional properties with respect to fiber cross-sectional area, fiber rigidity, and energy dissipation at 65% RH and in the wet state. Our results demonstrate that in fine diameter fibers with a high cuticle-to-cortex ratio, the cuticula exert a significant effect on the torsional deformation behavior of hair fibers at both normal humidities and in the wet condition. In addition, our data indicate that energy dissipation is confined to fibers with a high cuticle-to-cortex ratio, and the amount of energy dissipated becomes more pronounced with increasing water content. The torsional properties of hair spray-treated fibers suggest that the deposited hair spray film masks the properties of the base fiber and imparts its own dissipative character to the measurement. Since tensile mechanical properties are often used to make claims about the performance of hair care products, we have compared the results obtained from torsional and tensile measurements on over-processed bleached hair fibers conditioned with Polyquaternium-10 and cetyl trimethylammonium bromide (CETAB) to evaluate which method is more advantageous. Our data demonstrate that torsional measurements can distinguish hair care products which reinforce the cuticle from those which affect the cortex, while tensile measurements showed no significant differences.

Studies of light scattering from ethnic hair fibers.

One of the most desirable hair attributes to consumers, irrespective of ethnic background, is hair shine. The light reflected from a fiber has two components, specular and diffuse. The specular fraction of reflected light from the front surface of the fiber is generally recognized as a contributor to high luster. The distinction between specular and diffuse reflection is, however, not always clearly defined. In this study an attempt has been made to differentiate between specular and diffuse reflectance by analyzing mathematically goniophotometric curves of light reflected from unaltered single hair fibers from European, African, and Asian ethnic groups. The effect of macroscopic characteristics of the hair fibers, such as fiber diameter, cross-sectional shape, and curvature on luster is demonstrated. Results indicate that broadening of the specular peak reduces luster values, and is related to these characteristics. Thus, specular peak broadening is one of the important features to take into account when evaluating luster. Therefore, a new method for luster evaluation from goniophotometric curves is proposed. Additionally, we present the general model for light scattering, showing how scattering by surface roughness of different origin and magnitudes, and the scattering and absorption processes by the hair's interior, affect the position of the specular reflectance peak and its broadening.

Effect of hair color on luster.

The effect of color on instrumentally evaluated luster of hair dyed to different colors and depths of shades is studied. For natural hair colors, such as blond, brown, and black, the increase in luster with increasing color is associated with a decrease in diffusely scattered light as a result of light absorption by melanin granules. On dyed hair the interpretation of data from a goniophotometer (GP) is more complicated. Using the colors covering the extremes and middle of the visible spectrum, our results demonstrate how dye composition (single or multicomponent), concentration, and penetration depth into the fiber affect the absorptive and scattering processes within the hair fiber to impact luster. Finally, we make an attempt to study the effect of hair color on subjective evaluation of luster. An equation for perceived luster, taking into account the spectral sensitivity of the human eye is derived. Theoretical considerations show that the luster of hair of different colors is perceived differently by the human eye.

Chemical and photo-oxidative hair damage studied by dye diffusion and electrophoresis.

Microspectrophotometric and electrophoretic methods were used to characterize and quantify the effects of primary damage to hair from chemical and photochemical oxidative processes. The diffusion of molecules proceeding from the fiber surface to the center of untreated and modified (by chemical and photochemical oxidative processes) hair fibers was mapped by fluorescence microscopy and quantified by calculating diffusion coefficients of a fluorescent molecule. In addition, an electrophoretic separation technique, namely, SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), was used not only to substantiate the results obtained in the microfluorometric study, but also to show how the main classes of proteins of unaltered hair are modified by cosmetic chemical treatments, light exposure, and combinations of these two processes. UV microspectrophotometry is an alternate analytical method to evaluate photo-oxidative damage in hair, and supports the results obtained by microfluorometry.

Effects of conditioners on surface hardness of hair fibers: an investigation using atomic force microscopy.

Conditioners are known to have a prophylactic effect on hair damage caused by cosmetic chemical treatments or mechanical grooming procedures. They are known to impart softness and smoothness to hair by moisturizing the fiber. Since the amount of conditioners deposited on the fiber is very small in quantity, it is conceivable that mainly the surface is moisturized. This is especially true of polymeric conditioners, which deposit preferentially on the surface of the fiber, rather than penetrate into the cortex. Therefore, this study strictly investigates whether cationic polymeric conditioners impart softness to the surface cuticle cell as a result of their hydrophilicity, with no regard to its applicability to cosmetic effects. Such softening can be detected by indentation of the surface and can be quantified by measuring the depth of the indent in real time. Atomic force microscopy (AFM), equipped with nano-indentation capability, is ideally suited for this purpose. In this work it was used to determine changes in the microhardness (micromechanical properties) of the hair fiber surface as a result of fiber/conditioner/moisture interactions. In a preliminary study, we observed that the scale faces of hair treated with Polyquaternium 10 (PQ-10) conditioner gave deeper indents, while scale edges yielded shallower ones in comparison to cuticle cells of untreated hair. This suggests that the conditioner softens the scale face and hardens the scale edges. However, because of significant amounts of conditioner residues left on the scale face, this conclusion was rather ambiguous. Therefore, the study was repeated in which multiple indentations were made on the surface cuticle cells of a larger number of the same hair fibers before and after multiple applications of the conditioner. This reduces errors due to fiber-to-fiber variation in pre-existing microhardness differences in surface cuticle cells. Also, the larger number of fibers investigated in the current work allowed for a statistical outcome. This latter study has led to a rather definite conclusion that the scale face is indeed softened by polymeric conditioners such as Polyquaternium-10 (PQ-10). These studies will ultimately help in the development of conditioners with suitable moisturizing and softening effect on hair.

Secondary ion mass spectrometric investigation of penetration of coconut and mineral oils into human hair fibers: relevance to hair damage.

An attempt has been made to show the difference in the penetrability of coconut oil and mineral oil in human hair. We have used secondary ion mass spectrometry (SIMS) in combination with a time-of-flight (TOF) mass spectrometer. Characteristic ions formed by the pure components when bombarded with gallium ions have been identified with their m/z values. The distribution of the ion, characteristic of the particular treatment, has been established in the cross sections of hair treated with coconut and mineral oils. The results show that coconut oil penetrates the hair shaft while mineral oil does not. The difference may be due to the polarity of the coconut oil compared to the nonpolar nature of the mineral oil. The affinity of the penetrant to the protein seems to be the cause for this difference in their behavior. This study also indicates that the swelling of hair is limited by the presence oil. Since the process of swelling and deswelling of hair is one of the causes of hair damage by hygral fatigue, coconut oil, which is a better penetrant than mineral oil, may provide better protection from damage by hygral fatigue.