Pore Size Dependence of Hydrodynamic Friction in Hydrogels on Smooth Surfaces Open Access

Abstract

Hydrogels are three-dimensional polymer matrices capable of absorbing large volumes of water. Because of their features such as biocompatibility, temperature resistance and sensitivity, they are extensively being used in industrial and agricultural applications, ranging from diaper linings that absorb the moisture away from the baby’s skin to boosting water retention in soil. Hydrogels’ other unique mechanical properties such a low friction make them promising biomaterials that have potential to be used as prime candidates for biosensors, drug-delivery vectors and improved contact lenses. Their extensive use and quirky qualities drive the need to further our understanding of the mechanical behavior of these hydrogels. Using a custom low-force tribometer, we investigated gel friction of spherical hydrogels on acrylic discs under a variety of environmental conditions. Previous research has indicated that gel frictional coefficients as a function of speed follow a non-monotonic trend. Upon reaching a critical sliding velocity, we observed a dynamic frictional transition with transient behavior. Our results can be interpreted as a competition between the shear rate in the fluid versus the relaxation time it takes the polymer chains to return to equilibrium after being disturbed. Before we establish a set model for this regime, we investigated hydrodynamic frictional behavior for velocities leading up to the critical velocity. Our results showed a pore size dependence on friction of hydrogels on smooth surfaces at this low-velocity regime. Having varied several environmental conditions such as gel structure, load and salinity, we determined a relationship between pore size and gel friction. 

Table of Contents

Table of Contents 

Introduction 

Solid-Liquid Duality…………………………………………….………......1 

Applications of Hydrogels…………………………………….………......2 

Non-Classical Friction………………………………………………......…3 

Frictional Transition Regimes in Hydrogel Systems……….……....4 

Hertzian Contact of Elastic Hydrogel systems…………………...…10 

Materials and Methods 

Types of Hydrogels……………..…………………………………….......12 

Ultra-Low Friction Tribometer…………………………………….......15 

Determining Contact Area …………………………………..…..……..15 

Results and Discussions 

Friction Coefficient vs Load……………………………………..……...17 

Changing Pore Size…………………………………………………….....19 

Determining Contact Area under Varying Load……………….…..21 

Determining Pore Size and Elastic Modulus………………………..22 

Final Remarks 

Conclusion………………………………………………………..……......25 

Future Directions…………………………………………….................25 

References …………………………………………………………….......26 

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	B.A.
Submission	Honors Thesis
Language	English
Research Field	Physics, General Physics, Fluid and Plasma
Keyword	Gel Friction Hydrogel
Committee Chair / Thesis Advisor	Justin Clifford Burton, Emory University
Committee Members	Jed Brody, Emory University Douglas Mulford, Emory University

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