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Impact of Solvent on the Mechanical and Adhesive Properties of Solvent Swollen Polymer Gels

Joseph L. Lenhart and Phillip J. Cole. Sandia National Laboratories, PO Box 5800 MS 0888, Albuquerque, NM 87185

A gel is a physically or chemically cross-linked polymer highly swollen by solvent. Mechanically the solvent creates a “soft solid”, which is easily deformable yet still recovers from deformation due to the elastic nature of the cross-links in the polymer. Polymer gels offer potential in a wide array of applications, because the gel properties can be tuned by varying the polymer type, solvent type, and solvent loading. In addition, small molecule additives and fillers can be incorporated into the gel formulation to further enhance the properties. Potential applications include drug delivery, biomedical implants, artificial muscles, food and cosmetics, separation systems, display devices, electronics, batteries, optical devices, and sensors to name a few. While varying solvent types and loading provides a wealth of potential applications, the high solvent loading invokes unique materials challenges because the solvent-polymer partitioning impacts the gel microstructure and the resulting properties. The solvent in a gel can play a critical role in the performance of devices. For example, polymer gels can undergo a volume phase transition when external conditions such as temperature, pH, solvent, or concentration of chemical or biological analytes, is altered. In some applications, this swelling-shrinking phenomenon can potentially be exploited to make devices. Examples are sensors for biological and chemical contaminants, controlled lubrication layers, etc. In other applications it is undesirable to have a gel exhibit phase separation, particularly when gel adhesion to a substrate is critical for the device performance. The objective of current research is to design a polymer gel that will perform over very broad temperature ranges both above and below room temperature. Key to this objective is a fundamental understanding regarding the role of the polymer-solvent interactions on the gel phase behavior, partitioning, microstructure, and properties. A combination of swelling, rheology and tack adhesion testing is presented illustrating the role of the solvent on the gel mechanical and adhesion properties, and on the gel microstructure.