The research objective of this Faculty Early Career Development (CAREER) project is to develop a new system identification and control methodology to enable rapid broadband viscoelastic measurements. By mapping soft material responses at multiple scales, the proposed methodology will be realized in nanoscale measurements using scanning probe microscopy (SPM). Currently there are many barriers to measurements of material properties at the nano-, meso-, and macro-scales. They include (i) quasi-static or sinusoidal-oscillatory excitation methods which are either too simple or too slow to rapidly excite the complex behaviors exhibited by soft materials, (ii) hardware dynamics creeping into the measured material properties, particularly when the measurement is at a high frequency, and (iii) significant nonlinearity (such as hysteresis) and system uncertainties. The proposed research will overcome these barriers through the integration of optimal input design for time-varying vescoelastic model identification with the system-inversion theory for rapid tracking-transition switching and large system uncertainties. New iterative control and optimal control techniques will also be developed to allow the high-speed output tracking needed for exerting the optimal excitation input with minimal trade-off of system bandwidth. The outcome of the proposed research is expected to be the measurement of time-varying viscoelastic parameters of soft materials over a frequency range at least 10 fold larger and within a time frame at least 10 fold shorter.
The work will introduce a new paradigm of multi-scale soft material sciences and engineering, and help unravel rate-dependent phenomena like wound healing by linking the macro-/meso- scale measurements to the nano- scale. The realization of the proposed methodology at the nanoscale will improve SPM as the key enabling tool for nanosciences and nanotechnologies, advance our understanding of rapid nanoscale phenomena like dentin collagen dehydration, and accelerate the synthesis and design of nano-/bio- materials including bio-compatible polymers for drug delivery. The PI?s close collaboration with a leading SPM manufacturer will accelerate the technology transfer. The proposed CAREER education activities will promote nanotechnology education in mechanical engineering, through curriculum improvements (including a new course, a teaching module and a web-based SPM simulator), open lab tours for a total of 450 high-school girls by leveraging two well-established outreach programs at ISU, internships for undergraduate women students and high-school science teachers, and industrial internships for graduate students.
