Paper Number
SC17 

Session
Suspensions & Colloids

Title
Shear-induced microstructural gradients in colloidal gels for composite hydrogel fibers

Presentation Date and Time
October 16, 2018 (Tuesday) 11:05

Track / Room
Track 1 / Galleria I

Authors (Click on name to view author profile)

1. Cardenas-Vasquez, E. Daniel (North Carolina State University, Chemical and Biomolecular Engineering)
2. Hsiao, Lilian C. (North Carolina State University, Department of Chemical and Biomolecular Engineeirng)

Author and Affiliation Lines (in printed abstract book)
E. Daniel Cardenas-Vasquez and Lilian C. Hsiao
Department of Chemical and Biomolecular Engineeirng, North Carolina State University, Raleigh, NC 27606

Speaker / Presenter 
Cardenas-Vasquez, E. Daniel

Text of Abstract
Thermoresponsive nanoemulsions that contain a bridging polymer are known to self-assemble into colloidal gel structures above the critical gel temperature. We incorporate thermoresponsive nanoemulsions into composite hydrogels fibers by using ultraviolet (UV) light to photopolymerize the liquid precursor in a continuous process. The oil-in-water nanoemulsions consist of fluorescently dyed poly(dimethyl siloxane) (PDMS) droplets (droplet size 2a = 40nm, volume fraction f = 0.2) suspended in a continuous phase of poly(ethylene glycol) diacrylate as the crosslinker and sodium dodecyl sulfate as the surfactant. Steady shear experiments of the precursor show a shear thinning behavior at temperatures higher than the gel point, and temperature ramp rheology (rate = 1ºC/min) performed on the precursor shows that the gelation temperature is T_gel = 29ºC. We tune the precursor flow rate (0.2-0.9 mL/min) as well as the precursor temperatures (22ºC = T = 40ºC) to obtain photopolymerized hydrogel fibers with various microstructures. A velocity profile of the precursor flow in the channel, obtained by solving the Navier-Stokes equations for a yield stress fluid, suggests that the spatial variations in microstructure within the fibers may arise due to selective yielding of the colloidal gels during shear. Using this method, we synthesize composite hydrogel fibers with a variety of microstructural gradients in the velocity gradient direction of flow. The characteristic length scales of the colloidal microstructure are quantified using confocal microscopy and cryogenic scanning electron microscopy. The results show that local gradients in shear flow could be used to deliberately introduce microstructural variations in the manufacturing of composite soft materials, with applications such as hydrogel membranes, microfluidic platforms, and functional fibers.