Solvent-Free Deposition of Ultrathin Copolymer Films with Tunable Viscoelasticity for Application to Pressure-Sensitive Adhesives

Abstract

A new fabrication method for an ultrathin (500 nm thick) pressure-sensitive adhesive (PSA) was demonstrated by utilizing a series of in situ cross-linked viscoelastic copolymer films. Viscoelastic films composed of poly(2-hydroxyethyl acrylate- co-2-ethylhexyl acrylate) were synthesized successfully in a one-step manner by an initiated chemical vapor deposition (iCVD) process, where free-radical polymerization is triggered in the vapor phase either by heat or UV, or a combination of both. In particular, the photoinitiated chemical vapor deposition method generated a highly cross-linked polymer film, whereas cross-linking of the copolymer film was suppressed greatly in the conventional thermal iCVD method. A combination of thermal and photoinitiated chemical vapor deposition could regulate the cross-linking density of the copolymer films. We controlled the cross-linking density of the copolymer films to exhibit a viscoelastic property so that they would readily adhere to various kinds of substrates with only 500 nm thick copolymer PSA. The adhesion performance of the PSA was systematically optimized by tuning the copolymer composition as well as the cross-linking density, and consequently a high shear strength of more than 85.2 ± 5 N/cm was achieved despite the 500 nm thickness. In addition, the PSA was completely transparent. We expect that the ultrathin PSAs developed in this work will be utilized widely for the realization of various soft electronic devices, which usually require strong adhesion, tunable viscoelastic properties, and optical transparency.

Nanoscale control by chemically vapour-deposited polymers

“…For laminating substrates, parts, and encapsulation layers for flexible and stretchable devices, durability is enhanced by reducing the overall stacking thickness, including the need for thinner adhesive layers. High-shear strength iCVD pressure sensitive adhesives require only 500 nm of thickness 108 , a 200-fold reduction over conventional pressure sensitive adhesives. Controlling the degree of crosslinking in the iCVD copolymer led to the viscoelastic behavior required for interfacial bonding.…”

Conformal 3D Nanopatterning by Block Copolymer Lithography with Vapor-Phase Deposited Neutral Adlayer

“…The G′ and G″ were retained almost constant up to 200 °C, demonstrating no significant change in the elastic property nor thermal decomposition of pDVB. 37 Moreover, the loss factor (tan δ), defined by the ratio between G′ and G″ (G″/G′), was maintained less than one, while the G′− G″ crossover was not observed throughout the measured temperature range. All these analysis results clearly confirm that the pDVB preserved the intrinsic elastic property in a wide temperature range.…”

Rational Design of Waterborne Polyurethane Pressure Sensitive Adhesives for Different Working Temperatures

“…Different balances between the liquid-like component and solid-like component can lead to different PSA performances [11][12][13][14][15][16][17].…”

“…It is found that high performance PSA must have a proper combinational property of both liquid-like (viscous part) and solid-like (elastic part), and the liquid-like means a low modulus of elasticity and a high dissipation of viscosity, whereas the solid-like means a high modulus of elasticity and a low dissipation [ 8 , 10 ]. Different balances between the liquid-like component and solid-like component can lead to different PSA performances [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”