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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
Alfred J. Crosby
Alan J. Lesser
Jessica D. Schiffman
Polymer and Organic Materials
Hydrogels are constructed with polymer networks swollen with water, which are soft and with much smaller shear moduli than bulk moduli. Due to the similar moduli to biological tissues, synthetic hydrogels have been used for biological applications. While interfacial properties are important for many of the applications of soft materials, quantifying these properties is challenging for ultra-soft materials. Ultra-softness causes difficulties in measuring interfacial properties with conventional force-based methods. For example, soft specimens deform largely under gravity and external forces, and thus the assumptions of the established methods are invalid. Additionally, many of the applications for hydrogels require them to form interfaces with biological tissues that exist within living systems. Therefore, it is difficult to use conventional test methods to quantify the properties of these internal interfaces. Thus, new methods are needed to help overcome these challenges.
In this dissertation, we will discuss elasto-adhesion and fluid-elastic dynamics for providing new approaches to measuring the interfacial energy of ultra-soft materials and for quantifying the fluid-elastic balance under external pressure. The dissertation includes the following chapters. In Chapter 1, we review the basic information related to ultra-soft hydrogels, the history of fracture/interface mechanics, and the application of contact mechanics to interface energy. In Chapter 2, we establish a non-intervention method to measure the interfacial energy of self-contact ultra-soft hydrogels by observing the effect of surface and strain energy competition on the defined interface. The closed width is related to the elasto-adhesion length scale (lEA), and we validate this method by comparing the lEA value with a conventional force-based test. The validated method is applied to quantify the effect of the hydrogel preparation environment on the interfacial properties of hydrogels with a curing condition where force-based tests cannot be used to probe the interfacial property. In Chapter 3, we introduce the needle-induced cavitation method to the interfacial property measurement. By inserting a needle into an interface and applying pneumatic pressures, we observe critical pressures in the pressure history. The critical pressure is not only dependent on the interfacial energy but also related to the normal stress at the interface due to the elastic deformation, which is referred to as residual stress. We determine the critical pressures in the absence of residual stress effect, and the critical energy release rate is derived by converting the critical pressure dependence of the needle size. The derived algorithm provides a value close to the value of Chapter 2 with the same hydrogel samples. In Chapter 4, we introduce a series of liquid geometries deposited in the elastic matrix with the dynamic liquid injection system. A needle is inserted into the solid and punctures a channel. The dynamic liquid injection provides an applied pressure to inject Newtonian fluid into the ultra-soft elastic with a constant moving speed. The injected liquid deforms the channel into cylinders or spheres, and different deposited liquid geometries are observed. By analyzing the coexistence of surface energy and two elastic deformation modes, we explain the formation mechanism of four liquid geometries and the spontaneousness of the final configuration by calculating the pressure and energy difference. In Chapter 5, we summarize the observation in the dissertation and provide outlooks of the related research.
Fu, Hongbo, "QUANTIFYING ELASTO-ADHESION AND FLUID-ELASTIC DYNAMICS FOR ULTRA-SOFT HYDROGEL INTERFACES" (2022). Doctoral Dissertations. 2619.
Available for download on Friday, September 01, 2023