The tribological properties between taut hair fibers in wet conditions were investigated to evaluate the tangling/detangling performance of shampoo formulations during washing (particularly rinsing). A new setup for friction measurements between taut hair fibers was established. Using the setup, tribological properties of hair fibers treated with two shampoo formulations, whose tangling performances were different, were investigated. The base formulation for the shampoos was the same; the only difference was the type of amino-modified silicones used as conditioning agents. Shampoo (Sp) A (poor detangling performance) incudes water-insoluble silicone, and Sp B (excellent detangling performance) includes water-soluble silicone. The tribological behaviors between taut hair fibers treated with the diluted solutions of the Sp were very different; the Sp A-treated hair exhibited stick-slip sliding, whereas the Sp B-treated hair exhibited smooth sliding. This difference presumably comes from the different coacervation behaviors in the diluted solutions and resulting structure of conditioning film formed on hair surfaces. The smooth sliding (ideal for detangling) of Sp B-treated hair comes from the two-layer structure of the conditioning film on hair; positively charged amino-modified silicone dissolved in water adsorbed immediately on negatively charged hair surface, followed by the physical adsorption of coacervates on the adsorbed silicone layer. The outer coacervate layer is easily removed during sliding, and smooth sliding comes from the low friction of the silicone layer. The relationship between the type of amino-modified silicones, conditioning film formation on the surface, and tribological properties was discussed, which gives insights into designing Sp formulations with excellent detangling performance.
The confined film
structures and tribological properties of the
dilute aqueous solution of a silicone-based amphiphilic block copolymer,
bis-isobutyl poly(ethylene glycol) (PEG)-14/amodimethicone (BIPA)
copolymer, between mica surfaces were investigated. The BIPA copolymer
existed as positively charged water-soluble aggregates in the solution.
The adsorption behavior of the BIPA copolymer aggregates on a mica
surface from solution was studied using an atomic force microscope
(AFM); the result showed the immediate formation of a uniform adsorbed
BIPA copolymer layer, followed by the gradual deposition of BIPA aggregates
on the top of the adsorbed layer. Friction measurements were carried
out using the surface forces apparatus (SFA) for the confined films
of BIPA copolymer solution between mica surfaces, which revealed two
different sliding film structures depending on the elapsed time after
surface preparation. The sliding film consisting of two adsorbed BIPA
copolymer layers was obtained for a relatively short elapsed time
(not longer than 3 h), which had an extremely low friction coefficient
μ (of the order of 10–5). The sliding film
on the following day (elapsed time of approximately 24 h) had the
structure of a deposited/kinetically trapped BIPA aggregate layer
confined between the opposing adsorbed layers, and the μ values
were within the range from 10–4 to 10–3. Our results suggest that the different elapsed time ranges and
resulting absence or presence of the intervening layer of trapped
aggregates between the absorbed layers determine the tribological
properties of the confined films. Molecular friction mechanisms are
discussed for the two sliding structures, which give insight into
using amphiphilic block copolymer aggregates for a new class of aqueous
lubrication system to design extremely low friction interfaces.
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