Controlled Cracking and Shape Recovery in Polymers.

Abstract

Cracks and pores in polymers can be used as functional micro/nano structures, enabling mass-processing fabrication that is simple and cost-effective. Such technologies are especially popular for biological applications. To unlock the full potential of these technologies, we need to understand the behaviors and the mechanics behind them. An accurate prediction and precise control of these traditionally stochastic processes are desired to enhance the precision and repeatability of subsequent experiments and analyses. For this purpose, a crack control strategy based on a coupling of Linear Elastic Fracture Mechanics (LEFM) and flaw statistics was developed, addressing the problem for a wide range of materials. Channels fabricated by cracking can narrow and generate nanoconfinements accompanied by a nanoscale squeezing flow that can facilitate the linearization of DNA and chromatin. To develop optimal nanochannel operation parameters and avoid unfavorable partial collapse, the non-uniform closure of liquid-filled channels was studied. The analyses suggested time scales for different narrowing and closure conditions to occur which can be used as a reference to tailor the operation parameters. The study of an elliptic channel in an infinite elastic body reveals the change in shapes and sizes during crack closure, which helps characterize the channel geometry during the dynamic process and understand the capabilities and limitations of the technique. Pores in viscoelastic polymers can heal spontaneously driven by interfacial tension. A finite element model was developed to investigate the effect of temperature and geometry on the healing process. Material characterization was conducted for a specific polymer of PLGA which is one of the most commonly used biomaterials. In comparisons of simulation with experimental observations, simulation successfully predicted the various healing time based on material properties and environment.