Polymer Gels Exhibiting High Pressure-Sensitive Adhesion to Polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) is attractive for high-frequency communications but adheres very poorly to other materials due to its very low surface energy. Conventionally, surface treatments of PTFE are used to increase the polarity of the PTFE surface and enable bonding to materials with increased surface free energy. However, surface treatments are difficult to scale, can damage surfaces, and often lack reproducibility. Therefore, developing a material that can make PTFE adhere well to other materials without surface treatment is highly desirable. In this study, we aimed to develop a new material with strong adhesion to PTFE. We synthesized three polymer gels from dodecyl acrylate (DA) and 2-(dimethylamino) ethyl acrylate (DMAE): the homopolymer gels PDEAE and PDA, and the copolymer gel P(DEAE-<i>co</i>-DA). The copolymer gel P(DEAE-<i>co</i>-DA) exhibited high pressure-sensitive adhesion to PTFE, recording the highest adhesive strength (<i>F</i> = 430.0 N/m) and the highest peel energy (<i>G</i> = 713.4 J/m²) compared to the homopolymer gels PDEAE and PDA. Mechanical testing showed PDEAE had the greatest strength and toughness, PDA balanced stiffness and extensibility, and P(DEAE-<i>co</i>-DA) was the most flexible and extensible. The P(DEAE-<i>co</i>-DA) with the smoothest surface (Sz ≈ 0.176 µm) showed the highest <i>F</i> and <i>G</i>, implying that surface roughness did not contribute significantly to the interfacial adhesion between the gels and the PTFE. Based on the surface free energy σs and work of adhesion Wa values, the adhesive strength to PTFE was predicted to be PDEAE > P(DEAE-<i>co</i>-DA) > PDA, but the measured <i>G</i> in peel tests contradicted this, indicating that the gels' viscoelastic deformation and energy dissipation dominate the measured <i>F</i> and <i>G</i>. The frequency-dependent viscoelastic data and relaxation times <i>τ</i> and activation energies Ea suggested optimal adhesion requires a balance of adhesion (mobility for energy dissipation (short <i>τ</i>, low Ea)) and sufficient cohesion (high G'). P(DEAE-<i>co</i>-DA) achieved this balance, explaining its high measured <i>F</i> and <i>G</i>. With precise control of polymer chain mobility, the adhesion of P(DEAE-<i>co</i>-DA) gels can likely be improved further. Future work will employ block copolymerization and monomer-ratio control to tune molecular motion and enhance adhesion to PTFE.