Fickian and Non-Fickian Diffusion in Heavy Oil + Light Hydrocarbon Mixtures

Diffusive mass transfer is expected to play a key role in existing and proposed solvent-added processes for heavy oil production. Composition–distance profiles arising during free diffusion scale as a function of the joint variable (distance/time^<i>n</i>_<i>w</i>). Simple fluids are governed by Fickian diffusion, where <i>n</i>_<i>w</i> = 0.5. For nanostructured fluids, the value of <i>n</i>_<i>w</i> can be as low as <i>n</i>_<i>w</i> = 0.25, known as the single-file limit, but more typically, the value for the exponent falls between these two limits and is composition-dependent. In this work, five published data sets, comprising free diffusion composition profiles for Athabasca bitumen fractions and for Cold Lake bitumen + light hydrocarbons obtained using diverse apparatus, are probed from this perspective. Additional experimental results are provided for Athabasca bitumen + toluene mixtures over the temperature range of 273–313 K, and results from positive and negative control experiments for two well-defined mixtures(0.25 mass fraction carbon nanotubes + polybutene) + toluene, and polybutene + tolueneare also provided. The value of <i>n</i>_<i>w</i> for the negative control experiment remains at 0.50 ± 0.05 over the entire composition range, and for the positive control experiment, the value drops to <i>n</i>_<i>w</i> = 0.30 ± 0.02 at low toluene mass fraction. Although the quality of the diffusion profile data in the data sets analyzed is variable, the values of the exponent <i>n</i>_<i>w</i> are shown to be light-hydrocarbon-dependent and increase from <i>n</i>_<i>w</i> ∼ 0.25 at low light-hydrocarbon mass fraction up to <i>n</i>_<i>w</i> ∼ 0.50 at high light-hydrocarbon mass fraction. Secondary convective effects are also noted in free diffusion experiment outcomes at long times. The industrial applications of these findings are currently being evaluated, but it is clear that the time for light hydrocarbons to penetrate a fixed distance into nano- and micro-structured hydrocarbon resources is greater than the value anticipated for unstructured fluids

From Structure to Properties of Composite Films Derived from Cellulose Nanocrystals

Many natural materials exhibit a multilayer structure in which adjacent layers rotate in a helicoidal manner. The remarkable optical and mechanical properties of these materials have motivated research and development of man-made materials with similar morphology. Among them, composite materials by cellulose nanocrystals (CNCs) and polymers have attracted great interest; however, the relationship between the cholesteric structure and the material properties is not well understood. We used the composite CNC–polymer latex films with random, stratified, and cholesteric morphologies, all with the same compositions, to explore the effect of structure on the optical and mechanical properties of the composite films. Films with a cholesteric structure exhibited strong extinction, circular dichroism, and high stiffness; however, they had lower toughness than the films with the cholesteric stratified morphology. Films with disordered morphologies exhibited the highest toughness and the lowest stiffness. These trends were attributed to the confinement effects and the difference in polymer distribution in the films. These results provide guidance for the preparation of biomimetic cholesteric films with targeted optical and mechanical properties

Injectable Shear-Thinning Fluorescent Hydrogel Formed by Cellulose Nanocrystals and Graphene Quantum Dots

In the search for new building blocks of nanofibrillar hydrogels, cellulose nanocrystals (CNCs) have attracted great interest because of their sustainability, biocompatibility, ease of surface functionalization, and mechanical strength. Making these hydrogels fluorescent extends the range of their applications in tissue engineering, bioimaging, and biosensing. We report the preparation and properties of a multifunctional hydrogel formed by CNCs and graphene quantum dots (GQDs). We show that although CNCs and GQDs are both negatively charged, hydrogen bonding and hydrophobic interactions overcome the electrostatic repulsion between these nanoparticles and yield a physically cross-linked hydrogel with tunable mechanical properties. Owing to their shear-thinning behavior, the CNC-GQD hydrogels were used as an injectable material in 3D printing. The hydrogels were fluorescent and had an anisotropic nanofibrillar structure. The combination of these advantageous properties makes this hybrid hydrogel a promising material and fosters the development of new manufacturing methods such as 3D printing

Shear-Induced Alignment of Anisotropic Nanoparticles in a Single-Droplet Oscillatory Microfluidic Platform

Flow-induced alignment of shape-anisotropic colloidal particles is of great importance in fundamental research and in the fabrication of structurally anisotropic materials; however, rheo-optical studies of shear-induced particle orientation are time- and labor-intensive and require complicated experimental setups. We report a single-droplet oscillatory microfluidic strategy integrated with in-line polarized light imaging as a strategy for studies of shear-induced alignment of rod-shape nanoparticles. Using an oscillating droplet of an aqueous isotropic suspension of cellulose nanocrystals (CNCs), we explore the effect of the shear rate and suspension viscosity on the flow-induced CNC alignment and subsequent relaxation to the isotropic state. The proposed microfluidic strategy enables high-throughput studies of shear-induced orientations in structured liquid under precisely controlled experimental conditions. The results of such studies can be used in the development of structure-anisotropic materials

Patterning of Structurally Anisotropic Composite Hydrogel Sheets

Compositional and structural patterns play a crucial role in the function of many biological tissues. In the present work, for nanofibrillar hydrogels formed by chemically cross-linked cellulose nanocrystals (CNC) and gelatin, we report a microextrusion-based 3D printing method to generate structurally anisotropic hydrogel sheets with CNCs aligned in the direction of extrusion. We prepared hydrogels with a uniform composition, as well as hydrogels with two different types of compositional gradients. In the first type of gradient hydrogel, the composition of the sheet varied parallel to the direction of CNC alignment. In the second hydrogel type, the composition of the sheet changed orthogonally to the direction of CNC alignment. The hydrogels exhibited gradients in structure, mechanical properties, and permeability, all governed by the compositional patterns, as well as cytocompatibility. These hydrogels have promising applications for both fundamental research and for tissue engineering and regenerative medicine