Bioinspired Self-Assembled 3D Patterned Polymer Textures as Skin Coatings Models : Tribology and Tactile Behavior

• It is well known that during evolution, specific surface patterns emerged (e.g., on lotus leaves and butterfly wings) endowed with many remarkable surface properties (superhydrophobicity, vibrant structural color, delicate textures, etc.). In order to obtain these natural effects in cosmetics, we look for ways to transfer topographic patterns in coatings and treatments. Textured polymer surfaces were studied to explore their friction properties on the microscale and possible correlations with human tactile friction on the macroscale. We have chosen self-assembling block and random copolymers as model systems to prepare reliable biomimetic films with different micrometer and nanometer scale randomly patterned and randomly rough surfaces. The surface texture of the films was characterized by atomic force microscopy (AFM), and their tribological (friction) properties were studied with a surface forces apparatus (SFA) at a low sliding speed of 3 μm/s and at a speed of 10 cm/s relevant to realistic applications. The results are evaluated in terms of polymer segment mobility, interpenetration, entanglement and relaxation at interfaces, surface texture as described by roughness parameters, and interlocking of asperities. A stiction spike (static friction) was commonly found for the randomly patterned glassy polymer films. Random roughness patterns made from semi-crystalline polymers above their Tg gave high friction at low speed, but their friction coefficients were reduced at high speed due to less time for local entanglement and relaxations. The friction response of one of them was also affected differently by humidity than that of glassy polymer films. Tactile friction measurements with a human finger sliding against the polymer films revealed that the textures also provided differences at the macroscale, although the dynamic changes possibly due to lipid transfer, occlusion of moisture and/or damage of the films makes it difficult to draw robust conclusions. Finally, as an example, it is shown that these textures can be transferred to a soft elastomeric skin mimic substrate. This study introduces the concept of surface patterning by self-assembly to deliver tactile sensorial properties in coatings.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Tribologi (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Tribology (hsv//eng)

Keyword

Atomic force microscopy

Polymer self-assembly

Roughness

Skin model

Surface forces apparatus

Surface texture

Tactile friction

Tribology

copolymer

polymer

Article

biomimetics

force

friction

humidity

molecular weight

priority journal

Publication and Content Type

ref (subject category)

art (subject category)