Characterize the molecular dynamics of materials for 4D printing

Rauzan, Brittany Maureen

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https://hdl.handle.net/2142/99497 Copy

Description

Title

Characterize the molecular dynamics of materials for 4D printing

Author(s)

Rauzan, Brittany Maureen

Issue Date

2017-12-04

Director of Research (if dissertation) or Advisor (if thesis)

Nuzzo, Ralph G.

Doctoral Committee Chair(s)

Nuzzo, Ralph G.

Committee Member(s)

• Braun, Paul V.
• Moore, Jeffrey S.
• Zimmerman, Steven C.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

4D printing

Abstract

4D printing is a nascent field that is foundational for fabrication of complex 3D objects with programmable, temporal attributes that undergo exceptional configuration changes of the 3D structure. While gel-based composite inks are at the crux, the lack of a foundational, materials chemistry printing-centric approach results in an impasse to implement 4D printing as a novel, exemplary materials assembly paradigm. In my thesis, two printing-centric approaches are developed: 1) molecular dynamics of microstructure of clay in composite inks and 2) translation of rheological behavior of yield stress fluids to quality of printing. These printing-centric approaches are combined in order to advance the field of 4D printing towards fabrication of spatiotemporal patterning to fabricate 4D structures. Polymer/clay composite inks are the crux of 4D printing, however, there is a lack of fundamental understanding as to how physiochemical dynamics of the polymer/clay composite impact printability of these inks. Using a model system, N-isopropylacrylamide/Laponite, the electrostatic interactions between Laponite platelets is modified to tune critical rheological properties in order to improve printability. Rheological measurements and X-ray scattering experiments are carried out to monitor the nano/micro-structural dynamics and complex physicochemical interactions of Laponite as it impacts complex modulus in the linear region, flow behavior, thixotropy, and yield stress of the composite ink. Modification of the electrostatic interactions between platelets reduces the yield stress of the material, while maintaining a complex microstructure that allows for sufficient recovery times upon removal of stress to form stable filaments. A printing-centric approach is established based on a fundamental understanding of electrostatic inter-particle interactions, harnessing the innate microstructure of Laponite in 4D printing of composites. The established printing-centric approach on molecular dynamics of microstructure in clay composite inks is applied to two systems: 1) temporally-dynamic 4D-printed scaffolds that are capable of programming 3D cellular decision-making and 2) programmable soft aquatic actuators (SAAs) that respond to external magnetic fields. Programming 3D cellular decision-making requires filaments to be printed at biologically-relevant diameters (~<100 µm) for dentition-mimetic 3D scaffolds. The ability to modify electrostatic inter-particle interactions, allows for printing filaments of a biocompatible, no protein treatment polymer/composite material, 2-hydroxyethyl methacrylate/Laponite. The polymer/composite is used with another 4D printing material, poly-2-hydroxyethyl methacrylate, in order to program both short-term cellular attachment and direct long-term osteodifferentiation. Extending the established printing-centric approach for surface modification and controlling particle interactions, the polymer/composite 2-hydroxyethyl methacrylate/Laponite and poly-2-hydroxyethyl methacrylate gels are combined to formulate a high-performance, high-resolution composite, UniH, with filament resolution of 30 µm. The underlying materials chemistry of polymer/clay composites allows for programming temporally biological-dynamic 4D scaffolds independent of protein treatments. Patterning ionotropic material gradients within a structure is foundational for assembly of 4D soft aquatic actuators (SAAs). 4D printing is used to fabricate complex, doubly responsive (spatial and temporal) ionic, multi-material soft actuators. Extending the printing-centric approach for polymer/clay composites, the viscosifying agent, multivalent salts, small molecules, and nanoparticles are used to create chemo-mechanical gradients. The ion gradients are key since by changing the valency of the binding agents, the modulus of the material can be programmed within a structure. Magnetic nanoparticles are incorporated into the gel composites to produce a class of radially symmetric, 4D-printed soft aquatic actuators (SAAs) that respond to external magnetic fields in programmatic ways that are dictated by their underlying 3D ionotropic hydrogel gradients. The ability to program aquatic creatures that are selectively actuated in response to a magnetic field serves as a fundamental example of the capabilities of 4D printing to create the next generation of actuators. From the prior described polymer/clay composite materials, it is difficult to extrude filaments with diameters less than 30 μm, which are necessary for both biomimetic scaffolds and to reduce diffusion limited-kinetics in actuators. Particle-free emulsion yield stress fluids are of particular interest due to the ability to produce a yield-stress fluid that is not stabilized by particles, which may cause aggregation and jamming at the nozzle during printing. Particle free silicone oil-in-water emulsions with polymer additives, different molecular weights of poly (ethylene oxide), are examined to understand how extensibility of the emulsion impacts 4D printing properties. The 4D printed emulsion structures are used to fabricate elastomers, which are mechanically robust – a property not part of the printed emulsion.

Graduation Semester

2017-12

Type of Resource

text

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Copyright and License Information

Copyright 2017 Brittany Maureen Rauzan

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