טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRotbaum Yonathan
SubjectOn the Mechanical Properties of Inverse Freezing Gels
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Daniel Rittel


Abstract

Methylcellulose (MC) hydrogels display thermoreversible gelation upon heating. These hydrogels are abundantly employed in a variety of applications, rendering study of their mechanical properties relevant and important. Here we studied the mechanical behavior of MC solution and hydrogels, emphasizing their feasibility for shock mitigation. First, we characterized the mechanical response to compression loading, which reveals positive correlation between the flow stress and the MC concentration, temperature and the strain-rate. Moreover, rigorous investigation, demonstrates how the flow stress of the MC gels can be tuned and modified by the using rigid particles as an additive. The study provides new guidelines for the effect particle type, size and concentration on the flow stress of the MC composite. In addition, we have successfully managed to imitate the effect of nanometric boron-carbide particles on the MC gel flow stress by using molecular additives. This discovery, enable one to alter the MC gels flow stress by simpler and chipper means, without the risk of particle sedimentation within the composite. Finally, we showed for the first time, evidence for shock induced sol→gel phase transition which uptake large amount of energy. This discovery sheds light on the attenuation capabilities of MC solution, when submitted to weak and violent shock.