Automated Measurement of Spatially Resolved Hair-Hair Single Fiber Adhesion.

The adhesion force between individual human hair fibers in a crosshair geometry was measured by observing their natural bending and adhesive jumps out of contact, using optical video microscopy. The hair fibers' natural elastic responses, calibrated by measuring their natural resonant frequencies, were used to measure the forces. Using a custom-designed, automated apparatus to measure thousands of individual hair-hair contacts along millimeter length scales of hair, it was found that a broad, yet characteristic, spatially variant distribution in adhesion force is measured on the 1 to 1000 nN scale for both clean and conditioner-treated hair fibers. Comparison between the measured adhesion forces and adhesion forces modeled from the hairs' surface topography (measured using confocal laser profilometry) shows they have a good order-of-magnitude agreement and have similar breadth and shape. The agreement between the measurements and the model suggests, perhaps unsurprisingly, that hair-hair adhesion is governed, to a first approximation, by the unique surface structure of the hairs' cuticles and, therefore, the large distribution in local mean curvature at the various individual contact points along the hairs' lengths. We posit that haircare products could best control the surface properties (or at least the adhesive properties) between hairs by directly modifying the hair surface microstructure

Colloidal Structure and Physical Properties of Gel Networks Containing Anionic Surfactant and Fatty Alcohol Mixture

We investigated the mechanical properties, thermal behavior, physical state, and colloidal structure of a model gel network formulated with various ratios of sodium dodecyl sulfate polyacrylamide (SDS) and cetyl/stearyl fatty alcohol (FA) mixture in constant amounts of water (89%). The metastable gel, formed by slowly cooling stirred samples from temperatures above the chain melting temperature (Tm) of the long chain FA, has a lamellar structure with a periodic inter bilayer spacing of approximately 30nm. The bilayers remain homogeneous with SDS being immobilized in the FA matrix upon chain freezing. The chain length mismatch leads to an increased structural disorder among the alkyl chains upon SDS incorporation among the FA. As a result, the elastic modulus decreased with increasing SDS content. Conclusions were based on a large number of experiments involving differential scanning calorimetry, rheology, 1H NMR spectroscopy, and small angle x-ray scattering. Results from this work have uncovered the physical nature of these networks and gave insight into the role of anionic surfactants on the assembly, physical state, and mechanical properties of gel networks

Automated Measurement of Spatially Resolved Hair-Hair Single Fiber Adhesion.

The adhesion force between individual human hair fibers in a crosshair geometry was measured by observing their natural bending and adhesive jumps out of contact, using optical video microscopy. The hair fibers' natural elastic responses, calibrated by measuring their natural resonant frequencies, were used to measure the forces. Using a custom-designed, automated apparatus to measure thousands of individual hair-hair contacts along millimeter length scales of hair, it was found that a broad, yet characteristic, spatially variant distribution in adhesion force is measured on the 1 to 1000 nN scale for both clean and conditioner-treated hair fibers. Comparison between the measured adhesion forces and adhesion forces modeled from the hairs' surface topography (measured using confocal laser profilometry) shows they have a good order-of-magnitude agreement and have similar breadth and shape. The agreement between the measurements and the model suggests, perhaps unsurprisingly, that hair-hair adhesion is governed, to a first approximation, by the unique surface structure of the hairs' cuticles and, therefore, the large distribution in local mean curvature at the various individual contact points along the hairs' lengths. We posit that haircare products could best control the surface properties (or at least the adhesive properties) between hairs by directly modifying the hair surface microstructure