Waterborne, Nanocomposite Pressure‐Sensitive Adhesives with High Tack Energy, Optical Transparency, and Electrical Conductivity

Abstract

Pressure-sensitive adhesives (PSAs) adhere instantly and firmly to nearly any surface under the application of light pressure, without covalent bonding or activation.[1] PSAs are increasingly used for demanding applications, such as interconnects in electronic assemblies. [2] The debonding of PSAs occurs by a cavitation process [3,4] followed by cavity expansion to create fibrils [5] that extend in traction. These processes contribute to the energy of adhesion, E a . [6,7] To be an effective PSA, a material must be neither too stiff nor too liquid, and it must dissipate significant energy in deformation. Here, we show that the addition of carbon nanotubes (CNTs) to a PSA makes it stiffer yet more dissipative, which is an ideal, yet unusual, combination. The CNTs impart electrical conductivity to the PSA while increasing E a by 85 % and retaining optical transparency. Because of tightening environmental legislation, [8] there is a trend to manufacture PSAs using waterborne processing, such as colloidal dispersions, [9] to reduce emission of organic solvents. The adhesive properties of waterborne PSAs are inferior to conventional materials, [10,11] creating an urgent need for materials development. A potential remedy is the creation of nanocomposites containing CNTs. Recently, polymer colloid technology, that is, latex, has been exploited to create CNTpolymer composites for structural applications. [12][13][14][15][16][17] CNTs are not naturally water soluble, but several different emulsifiersan anionic surfactant (sodium dodecyl sulfate [12,13,16,17] ), a cationic surfactant, [17] and a water-soluble polymer (gum arabic) [14,15] -have been employed to disperse and stabilize them in water. Surfactants and water-soluble polymers in latex films [18] are known to decrease their water resistance [19] and to degrade adhesive performance.[11] Hence, we avoided dispersions of CNTs prepared with these materials. It has been recognized that the interfaces in polymer/CNT nanocomposites can have an influence on the viscoelasticity. [20][21][22] Soft polymers that are chemically grafted onto CNTs can potentially offer energy dissipation at the interface. To explore this possibility, we prepared nanocomposites using single-walled CNTs (SWNTs) that were functionalized with hydrophilic poly(vinyl alcohol) (PVA) via an esterification reaction [23] to render them dispersible and stable in water and to create a dissipative interface. Transmission electron microscopy [23] has revealed complete coverage of the SWNTs by the polymer and provided evidence for nanotube debundling. The functionalized SWNTs, referred to hereafter as PVA-SWNT, were blended with a poly(butyl acrylate) (P(BuA)) latex dispersion via sonication. A sophisticated means of evaluating adhesive performance is via probe-tack experiments in which a probe is brought into contact with a PSA surface and then removed at a constant velocity. [5,6] Figure 1 shows typical tack curves of P(BuA)/ PVA-SWNT adhesives measured at two debonding speeds of 10 and 100 lm s -1 . The de...

Improved Adhesive Strength and Toughness of Polyvinyl Acetate Glue on Addition of Small Quantities of Graphene

“…While such additives are usually included to alter the adhesive properties, [7][8][9] some researchers have used additives to improve the mechanical properties of the adhesive. 10,11 In addition, it is worth noting that in the last few years a small number of researchers have begun to explore using nano-materials as additives in adhesives [9][10][11][12] One of the most commonly used thermoplastic adhesives is polyvinyl acetate (PVAc). 4,10,13,14 We note that this material is not to be confused with polyvinyl alcohol (PVA), a polymer that has been much studied as a nano-composite matrix.…”

Design and fabrication of colloidal polymer nanocomposites

“…Another example is nanocomposite adhesives from soft polymer colloids and carbon nanotubes. [84] The carbon nanotubes are used to tune the viscoelastic properties (elastic modulus and energy dissipation rate) of the nanocomposites and enhance the pressure-sensitive adhesive properties.…”

Importance of Molecular Friction in a Soft Polymer−Nanotube Nanocomposite

“…The MWNT dispersions were blended while stirring into a colloidal dispersion of poly(butyl acrylate-coacrylic acid) (poly(BuA-co-AA)), prepared by emulsion polymerization, as described previously 16 ( Figure 1a). The polymer is lightly crosslinked so that there is a gel fraction of 30%.…”

“…16,17 To make these nanocomposites, the nanotubes are dispersed in water through the physisorption of a hydrophilic poly(vinyl pyrrolidone) (PVP). In the dry nanocomposite, PVP is then located mainly at the interface between the nanotube and the rubbery matrix.…”