Adhesion properties of physically crosslinked elastic gels of poly(sodium acrylate)–poly(acrylic acid) mixtures evaluated by a point contact method

Abstract

Adhesion properties of physically crosslinked hydrogels consisting of partially hydrated poly(sodium acrylate) (PSA) and poly(acrylic acid) (PAA) were investigated. The adhesion force and separation energy between the gels in swollen states were measured using a simple tack-evaluation technique by a point contact. As a result, the adhesion properties were significantly affected by the PSA/PAA ratio, which resulted from the fact that the physical and chemical properties of gels were changed through the replacement of PSA by PAA at gelation. The measurements of attenuated total reflectance Fourier transform infrared spectroscopy and the dynamic shear viscoelasticity suggested that the number of nonionized carboxyl groups increased and the stiffness increased with increasing the PAA ratio, respectively. In order to understand the adhesion properties further, the apparent contact area was evaluated by a stamp experiment using vermilion ink. The relationships between the adhesion properties and the physical and chemical features of gels are discussed in terms of the surface molecular interaction, the elastic and viscous properties of the bulk, and the apparent and true contact areas of the present system. From these results, the factors that determine the adhesion curve and the uniqueness and advantages of the present evaluation method are clarified.