20 Functional Photoactive Materials Based on Flexible π Molecules
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High-temp. bonding
1.6
1.2
0.2
25 °C 100 °C UV-LED
100 °C
Shear strength (unit: MPa)
UV-LED
320 mJ/cm 2
(a)
(b)
Photomelting
by UV-LED
Fig. 20.7 Performance of the light-melt adhesive. The light-melt adhesive can work at 100°C,
while hot-melt adhesives cannot be used at high temperature. On the other hand, it can be removed
quickly by warming to the temperature range of the liquid crystalline phase and ap-plying ultraviolet
light
(a)
(b)
Glass surface
Glass surface
Adhesive thin film
Cohesion force
Adhesion force
(c)
Tight stacking structure
with high cohesive force
Fig. 20.8 Columnar liquid crystal structure is the key to high shear strength. a The adhesive
strength is determined by adhesion force (the interaction between the adhesive/substrate interface)
and cohesive force (the self-interacting force of the adhesive material). b Since the shear strength
did not change regardless of the hydrophilicity of the glass substrate surface, it was not the adhesion
force but the cohesive force that determined the shear strength of the sample specimen. c The
V-shaped molecular skeleton strongly interacts with each other to form a columnar liquid crystal
structure, thereby generating a high cohesive force