Adaptive amphiphilic interaction mechanism of hydroxypropyl methylcellulose in water

Hydroxypropyl methylcellulose (HPMC), an FDA-approved water-soluble cellulose derivative, has been used in various wet-adhesion applications in construction products, paints, and drug delivery for 70 years. Despite the various applications, its adhesion mechanism in water has not been elucidated. Here, we measure the adhesion characteristics of HPMC against itself, hydrophilic and hydrophobic surfaces as a function of temperature using a surface forces apparatus (SFA) in water. The results show that HPMC adheres strongly to all tested surfaces, regardless of hydrophobicity. The adhesive strength of HPMC increases with temperature because of entropy-driven hydrophobic interactions and is comparable to or exceeds the wet-adhesion strength of most biological adhesives, including those of mussels and cephalopods. In addition, the elevated temperature induces swelling in HPMC layer, resulting in the exposure of more hydrogen bonding sites, thereby increasing adhesion with the hydrophilic surface. The bulk compression test of the HPMC-silica composite material is consistent with the SFA data and indicates that the water content and temperature are critical variables for the adhesion of HPMC to inorganic surfaces regardless of hydrophobicity. Because adhesive and coating technologies have shifted toward environmentally-friendly systems, these results provide a basis for the fabrication of organic solvent-free HPMC-based composites for future applications.