Braun Group People
Soo Hyoun Cho
Former Graduate Student in Materials Science and Engineering
B.S. Pohang University of Science and Technology (South Korea), 1993
M.S. Pohang University of Science and Technology (South Korea), 1995
Research Engineer in POSCO Technical Research Center (South Korea), 1995-2002
My research induces a smart functionality of biological materials to artificial polymers: an autonomic healing ability that can compensate defects and damages. We have developed a new approach to self-healing polymers, which has a number of advantages over the previous self-healing system1. This new approach greatly extends the capability of self-healing polymers by introducing tin catalyzed polycondensation of hydroxyl end-functionalized polydimethylsiloxane (HOPDMS) and polydiethoxysiloxane (PDES) based healing chemistry[2].
Autonomic healing concept, which is characteristic behavior of living creature, has been developed for polymer composites. Self-healing polymer composite can be an excellent candidate for novel material such as space application. For this self-healing function, the polycondensation reaction of HOPDMS) with PDES could be applied for healing material in the presence of organotin catalyst. Furthermore, the polycondensation reaction of polydimehylsiloxane(PDMS) is accomplished at room temperature with high catalyst stability against water and oxygen exposure.
Current system for autonomic healing polymer composite is epoxy vinyl ester which includes phase-separated PDMS liquid droplets and micro-encapsulated organotin catalyst. In the case of crack propagation into the matrix, the released catalyst within microcapsules gives rise to the polymerization of PDMS, thus the polymer composite can reveal healing property.The self-healing efficiency of the polymer composite is investigated via the comparison of fracture toughness between virgin samples and self-healed ones according to the composite conditions such as composition and healing temperature. The polymer composite showed excellent self-healing property at moderate temperature by incorporating the healing material, PDMS droplets and catalyst microcapsules. This system possesses a number of important advantages over the previous self-healing methodology, including a) the healing chemistry remains stable in humid or wet environments, b) the chemistry is stable to an elevated temperature (> 100 °C), enabling healing in higher-temperature thermoset systems, c) the components are widely available and comparatively low in cost, and d) the concept of phase separation of the healing agent greatly simplifies processing, as the healing agent can now be simply mixed into the polymer matrix.2These achievements significantly increase the probability that self-healing could be extended not only to polymer composites but also to coatings and thin films in harsh environments.
My current research focus is on self-healing polymer coatings which entirely prevent corrosion of a metal substrate after deep scratch damage. We developed a self-healing coating solution to be easily applied for substrate materials, and developed a self-healing system which enables the use of almost any polymer matrix. Thus, we expect this research may greatly extend the lifetime of anti-corrosion polymer coatings and reduce the repair cost of coating layers.
Figure 1. Schematic of self-healing process: a) self-healing composite consisting of microencapsulated catalyst (yellow) and phase-separated healing-agent droplets (white) dispersed in a matrix (green); b) crack propagating into the matrix releasing catalyst and healing agent into the crack plane; c) a crack healed by polymerized PDMS (crack width exaggerated). Scanning electron microscopy (SEM) images of d) the fracture surface, showing an empty microcapsule and voids left by the phase-separated healing agent, and e) a representative microcapsule showing its smooth, uniform surface. [2]
1. S. R. White, N. R. Sottos, P. H. Geubelle, J. S. Moore, Autonomic healing of polymer composite, Nature 409, 794-797 (2001).
2. S. H. Cho, H. M. Andersson, S. R. White, N. R. Sottos, P. V. Braun, Polydimethylsiloxane-based self-healing materials, Advanced Materials, 18, 997-1000 (2006).Click here to link to the Self-healing group web page
Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign