skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Decoupling of Mechanical and Transport Properties in Organogels via Solvent Variation
Organogels have recently been considered as materials for transdermal drug delivery media, wherein their transport and mechanical properties are among the most important considerations. Transport through organogels has only recently been investigated and findings highlight an inextricable link between gels’ transport and mechanical properties based upon the formulated polymer concentration. Here, organogels composed of styrenic triblock copolymer and different aliphatic mineral oils, each with a unique dynamic viscosity, are characterized in terms of their quasi-static uniaxial mechanical behavior and the internal diffusion of two unique solute penetrants. Mechanical testing results indicate that variation of mineral oil viscosity does not affect gel mechanical behavior. This likely stems from negligible changes in the interactions between mineral oils and the block copolymer, which leads to consistent crosslinked network structure and chain entanglement (at a fixed polymer concentration). Conversely, results from diffusion experiments highlight that two penetrants—oleic acid (OA) and aggregated aerosol-OT (AOT)—diffuse through gels at a rate inversely proportional to mineral oil viscosity. The inverse dependence is theoretically supported by the hydrodynamic model of solute diffusion through gels. Collectively, our results show that organogel solvent variation can be used as a design parameter to tailor solute transport through gels while maintaining fixed mechanical properties.  more » « less
Award ID(s):
1904047
PAR ID:
10252141
Author(s) / Creator(s):
; ;
Editor(s):
Di Chenna, Pablo H.
Date Published:
Journal Name:
Gels
Volume:
7
Issue:
2
ISSN:
2310-2861
Page Range / eLocation ID:
61
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Journal of Polymer Science)
    Abstract Establishing the independent tunability of transport and mechanical properties in polymer gels would significantly contribute to their implementation as transdermal drug delivery media, among other things. The work conducted herein uses facile changes in the formulation of physically crosslinked styrenic ABA/AB block copolymer organogels to alter their mechanical properties independently from the mass transport of an internally‐loaded nanocarrier. Such independent tunability is made possible by altering the relative amounts of ABA triblock and AB diblock copolymers while holding total copolymer concentration fixed. Specifically, three series of gels each with a fixed total copolymer concentration (10, 20, or 30 wt%) comprised of varying triblock copolymer concentration are studied. Small angle x‐ray scattering confirms that, at the nanoscale, only gel network connectivity changes within each series, while mechanical and release experiments show that increasing network connectivity leads to significant growth of gel moduli, but little change in nanocarrier release rate. 
    more » « less
  2. ; ; ; (, Journal of Polymer Science)
    Abstract Organogels possess characteristics that make them promising materials for enhancing our understanding of nanostructure‐diffusion relationships in gels and for use in diffusion‐centered applications including drug delivery and nanoreactor media. Unlike hydrogels, however, there are no well‐recognized techniques for measuring the fundamental diffusion parameter of diffusivity,D, in organogels. The present work establishes a technique for measuringDbased upon Fourier‐transform infrared spectroscopy. Physically crosslinked gels composed of poly[styrene‐b‐(ethylene‐butylene)‐b‐styrene] and aliphatic mineral oil are used to showcase the new technique's capability. Diffusivity of unimers—oleic acid—and reverse micelles—sodium dioctyl sulfosuccinate (AOT)—within as‐prepared and preswollen gels is quantified and resultant values are commensurate with studies of unimer and micelle diffusion in hydrogels. The case of AOT diffusion is further validated through small‐angle X‐ray scattering analysis, which is in close agreement (<20% difference). 
    more » « less
  3. ; ; ; ; ; (, Journal of Polymer Science Part B: Polymer Physics)
    ABSTRACT Mechanical properties including the failure behavior of physically assembled gels or physical gels are governed by their network structure. To investigate such behavior, we consider a physical gel system consisting of poly(styrene)‐poly(isoprene)‐poly(styrene)[PS‐PI‐PS] in mineral oil. In these gels, the endblock (PS) molecular weights are not significantly different, whereas, the midblock (PI) molecular weight has been varied such that we can access gels with and without midblock entanglement. Small angle X‐ray scattering data reveals that the gels are composed of collapsed PS aggregates connected by PI chains. The gelation temperature has been found to be a function of the endblock concentration. Tensile tests display stretch‐rate dependent modulus at high strain for the gels with midblock entanglement. Creep failure behavior has also been found to be influenced by the entanglement. Fracture experiments with predefined cracks show that the energy release rate scales linearly with the crack‐tip velocity for all gels considered here. In addition, increase of midblock chain length resulted in higher viscous dissipation leading to a higher energy release rate. The results provide an insight into how midblock entanglement can possibly affect the mechanical properties of physically assembled triblock copolymer gels in a midblock selective solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019,57, 1014–1026 
    more » « less
  4. ; ; ; ; ; ; (, Advanced Functional Materials)
    Gels are used in the oilfield. For example, during oil recovery, organogels are pumped underground into fractures within oil‐bearing rock, so as to block fluid flow. However, after several days, the gels must be degraded (liquefied) to enable oil extraction through the fractures. To degrade gels, ‘degrading agents’ as well as external stimuli have been examined. Here, a concept is demonstrated that avoids external agents and stimuli:self‐degrading organogelsbased on the self‐assembly of molecular gelators. The gels are a) extremely robust (free standing solids) at timet= 0 and (b) degrade spontaneously into a sol after a set timet=tdegrthat can be minutes, hours, or days. These properties are achieved by combining two readily available molecules — the organogelator (1,3:2,4)‐dibenzylidene sorbitol (DBS) and an acid (e.g., hydrochloric acid, HCl) — in an organic solvent. DBS self‐assembles into nanoscale fibrils, which connect into a 3‐D network, thereby gelling the solvent. The acid type and concentration set the value oftdegrat a given temperature. Degradation occurs because the acid slowly hydrolyzes the acetals on DBS, thereby converting DBS into small molecules that cannot form fibrils. DBS gels with a pre‐programmed “degradation clock” can be made with both polar and non‐polar organic solvents. The concept can be a game‐changer for oil recovery as it promises to make it safer, more efficient, and sustainable. 
    more » « less
  5. ; ; ; ; ; ; ; (, The Journal of Chemical Physics)
    We develop a multiscale simulation model for diffusion of solutes through porous triblock copolymer membranes. The approach combines two techniques: self-consistent field theory (SCFT) to predict the structure of the self-assembled, solvated membrane and on-lattice kinetic Monte Carlo (kMC) simulations to model diffusion of solutes. Solvation is simulated in SCFT by constraining the glassy membrane matrix while relaxing the brush-like membrane pore coating against the solvent. The kMC simulations capture the resulting solute spatial distribution and concentration-dependent local diffusivity in the polymer-coated pores; we parameterize the latter using particle-based simulations. We apply our approach to simulate solute diffusion through nonequilibrium morphologies of a model triblock copolymer, and we correlate diffusivity with structural descriptors of the morphologies. We also compare the model’s predictions to alternative approaches based on simple lattice random walks and find our multiscale model to be more robust and systematic to parameterize. Our multiscale modeling approach is general and can be readily extended in the future to other chemistries, morphologies, and models for the local solute diffusivity and interactions with the membrane. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email