Mechanism of wrinkle formation in curing coatings

Depthwise Viscosity Gradients in UV‐Cured Epoxy Coatings

“…An 80 µm thick coating with 0.2 wt% PI concentration did not show any wrinkling (Figure 5a), but a similarly thick coating with 2 wt% PI showed wrinkling defects (Figure 5b). The formation of wrinkles is consistent with the mechanism proposed by Basu et al12 The diffusion of epoxy monomer into the pre‐cured surface layer or skin causes swelling, which is constrained by the substrate, and leads to compressive stress. To relieve this stress the skin buckles out‐of‐plane, causing the wrinkling defects.…”

“…The skin can develop compressive stress due to the swelling from the diffusion of unreacted monomer beneath. When the compressive stress is high enough to make the skin buckle, wrinkles appear on the coating surface 12, 13…”

Effective formation of hierarchical wavy shapes using weak photopolymerization and gradual thermal curing process

“…With the increasing interest in the various applications of periodic surface patterns, a great deal of research has been devoted to the development of fabrication technologies for wrinkles [17][18][19][20][21][22][23][24][25][26]. Ding et al produced partial wrinkle patterns on the surface of a copper grid using the O 2 -plasma process [17], and Lin et al succeeded in generating wrinkle patterns based on distortion rate disparity caused by surface tension [12].…”

“…Guvendiren et al proposed a process of producing wrinkles through the expansion and contraction of a polymer film by moisture absorption [18]. The thermal mismatch of bi-layered heterostructures causes buckling that generates surface wrinkles [19,20]. Park et al proposed a simple method to form wrinkles by a repetitive volume dividing (RVD) process [21].…”

Effect of oligomer length on the buckling of long and high aspect ratio microwalls UV embossed from oligomer/monomer mixtures

“…Short oligomer increases polymerization rate but results in low conversion. Short oligomer length also results in high cross-linked density and improved modulus but excessive stress and defects such as cracking, delamination, and buckling [1,11,12]. Wen et al reported on the effect of oligomer length on the stress development in neat photocross-linkable oligomers [13].…”