Highly Stretchable and Transparent Optical Adhesive Films Using Hierarchically Structured Rigid-Flexible Dual-Stiffness Nanoparticles

Abstract

The demand for new forms of flexible electronic devices has led to the evolution of individual components comprising optical adhesive films that provide excellent optical transparency and high bonding strength while offering remarkable elasticity with high strain and recovery properties. Herein, a new type of highly elastic and transparent adhesive film is proposed using tailored rigid-flexible dual-stiffness nanoparticles (DSNs) composed of a rigid inorganic core and an elastic reactive coil shell. The hierarchically structured nanoparticles were prepared from SiO2 nanoparticles via the sequential surface modification with photoreactive flexible chains. The fabricated elastic adhesive film containing DSNs with an average diameter of 20 nm showed a high optical transmittance of 92% and adhesion strength of 19.9 N/25 mm. Increasing the content of the tailored nanoparticles in the adhesive film improved the elastic properties of the film such as elastic modulus (7.0 kPa), stress relaxation ratio (18.4%), and strain recovery rate (73.6%) due to the efficient elastic motion of the embedded DSNs. In addition, as the surface grafting density of elastic coil groups in the nanoparticle increased, a stronger bonding network was formed between the nanoparticles and the acrylic polymer matrix, thereby further improving the stress relaxation ratio (18.0%) and strain recovery rate (77.1%) of the optical film. Thus, the utilization of novel dual-stiffness nanoparticles produces optical adhesive films with high elasticity and optical transparency that are capable of withstanding external forces such as folding and stretching, which is essential for flexible electronic devices.

Fully recyclable multifunctional adhesive with high durability, transparency, flame retardancy, and harsh-environment resistance

“…In addition, multifunctionality, such as transparency and flame retardancy, is a key requirement for reversible adhesives in many specific applications. For example, bonding of devices for optical applications often needs to maintain high transparency ( 25 , 26 ), while adhesives for electronic device applications often require high flame retardancy to reduce potential fire risks ( 27 ). Unfortunately, there are few reports on reversible adhesives with multifunction, probably because of the lack of suitable material design and construction methods.…”

Stretchable Heterogeneous Polymer Networks of High Adhesion and Low Hysteresis

“…11,42 As another example, we demonstrate the uses of HEA for assembling thin laminates. Such a scenario of using soft adhesives to assemble multiple layers of distinct mechanical properties is becoming pervasive, for instance, in the flexible/ stretchable screens of portable devices, 12,20,21 whereby repeated deformation is unavoidable. However, the existing optically clear adhesives, adhered to adherends of much higher modulus, suffer from creep over repeated deformations, resulting in an interfacial fracture or wrinkling, 15 both of which dramatically deteriorate the optical performances of the devices.…”

“…For example, residual strain accumulates under cyclic stretching to cause buckling, slow relaxation gives rise to a substantial level of residual stress, which is often the culprit of surface cracking and stress corrosion, and the strain mismatch between the adhesive and adherend leads to wrinkling . Whereas intense efforts have been devoted recently to developing adhesives with mitigated viscoelasticity, ,− previous works have mostly employed monolithic polymer networks which inevitably compromise between two contradictory properties: i.e., hyperelasticity and adhesiveness. Although subtle microstructures have been constructed on the surface of hyperelastic elastomers, − their microfabrication is complex, time-consuming, and difficult to scale up.…”

Highly Stretchable, Soft, and Clear Viscoelastic Film with Good Recoverability for Flexible Display

“…Acrylic PSAs have been widely used in display, electronics, and automobile industries due to their good optical properties, high weathering resistance, robust adhesion, and facile modification. − Additionally, acrylic polymers can be conveniently prepared by radical polymerization, which is commonly practiced in industry . Acrylic CVF for flexible displays has been previously reported. ,− For example, Park et al . designed rigid-flexible nanoparticles composed of a rigid core and an elastic reactive coil shell, forming linkages with a matrix polymer chain and thereby improving recovery with high adhesion strength.…”

“…7 Acrylic CVF for flexible displays has been previously reported. 15,29−31 For example, Park et al 32 designed rigid-flexible nanoparticles composed of a rigid core and an elastic reactive coil shell, forming linkages with a matrix polymer chain and thereby improving recovery with high adhesion strength. However, most studies reported so far have not yet focused on the practical requirements of low T g and low modulus.…”