Browsing by Author "Garcia Greca, Luiz"
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- Controlling superstructure formation and macro-scale adhesion via confined evaporation of cellulose nanocrystals
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-01) Borrero-López, Antonio M.; Garcia Greca, Luiz; Rojas, Orlando J.; Tardy, Blaise L.The self-assembly of cellulose nanocrystals can tether their interfacial interactions and the associated properties of their constructs. For instance, assemblies of highly aligned cellulose nanocrystals (CNCs) bear improved mechanical strength, barrier properties, and piezoelectric response. In this study, the self-assembly of CNC superstructure was assessed under various confinement geometries, enabling optimization of the long-range order within the microstructures formed. The confinement involved the planar capillary (with a rectangular cross-section)formed between two glass substrates with silicone boundaries. The impact of temperature, width and thickness of the capillary plane on self-assembly of the micro-scaled lamellar structures was evaluated. Thinner capillaries and lower temperatures were found to considerably improve long-range order and increase the frequency of the periodic microstructures formed. The drying process was monitored by rheological analysis, which showed an initial fast drying followed by slow drying due to the hindered diffusion through lamellae. The adhesive properties of the formed superstructures were evaluated. The shear strength was shown to depend on the orientation of the superstructures and therefore of the CNCs. About 4 MPa adhesion strength was obtained when the lamellar superstructures were perpendicularly aligned with respect to the in-plane force applied, while ca. 3 MPa adhesion was obtained for parallel alignment. The experimental framework described herein enabled the evaluation of the impact of the dimensions of a drying meniscus on self-assembly of anisometric colloids while also linking cellulosic assemblies with their interfacial supramolecular interactions. This simple framework brings forward the possibility to correlate the behavior of nanometric objects with micro- and macro-scaled observations, e.g., macro-scaled mechanics of adhesion. - Effect of Anisotropy of Cellulose Nanocrystal Suspensions on Stratification, Domain Structure Formation, and Structural Colors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-05-12) Klockars, Konrad; Tardy, Blaise; Borghei, Maryam; Tripathi, Anurodh; Garcia Greca, Luiz; Rojas Gaona, OrlandoOutstanding optical and mechanical properties can be obtained from hierarchical assemblies of nanoparticles. Herein, the formation of helically ordered, chiral nematic films obtained from aqueous suspensions of cellulose nanocrystals (CNCs) were studied as a function of the initial suspension state. Specifically, nanoparticle organization and the structural colors displayed by the resultant dry films were investigated as a function of the anisotropic volume fraction (AVF), which depended on the initial CNC concentration and equilibration time. The development of structural color and the extent of macroscopic stratification were studied by optical and scanning electron microscopy as well as UV–vis spectroscopy. Overall, suspensions above the critical threshold required for formation of liquid crystals resulted in CNC films assembled with longer ranged order, more homogeneous pitches along the cross sections, and narrower specific absorption bands. This effect was more pronounced for the suspensions that were closer to equilibrium prior to drying. Thus, we show that high AVF and more extensive phase separation in CNC suspensions resulted in large, long-range ordered chiral nematic domains in dried films. Additionally, the average CNC aspect ratio and size distribution in the two separated phases were measured and correlated to the formation of structured domains in the dried assemblies. - Infiltration of Proteins in Cholesteric Cellulose Structures
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-05-10) Bast, Livia K.; Klockars, Konrad W.; Garcia Greca, Luiz; Rojas, Orlando J.; Tardy, Blaise L.; Bruns, NicoCellulose nanocrystals (CNCs) can spontaneously self-assemble into chiral nematic (cn) structures, similar to natural cholesteric organizations. The latter display highly dissipative fracture propagation mechanisms given their "brick" (particles) and "mortar" (soft matrix) architecture. Unfortunately, CNCs in liquid media have strong supramolecular interactions with most macromolecules, leading to aggregated suspensions. Herein, we describe a method to prepare nanocomposite materials from chiral nematic CNCs (cn-CNCs) with strongly interacting secondary components. Films of cn-CNCs were infiltrated at various loadings with strongly interacting silk proteins and bovine serum albumin. For comparison and to determine the molecular weight range of macromolecules that can infiltrate cn-CNC films, they were also infiltrated with a range of poly(ethylene glycol) polymers that do not interact strongly with CNCs. The extent and impact of infiltration were evaluated by studying the optical reflection properties of the resulting hybrid materials (UV-vis spectroscopy), while fracture dissipation mechanisms were observed via electron microscopy. We propose that infiltration of cn-CNCs enables the introduction of virtually any secondary phase for nanocomposite formation that is otherwise not possible using simple mixing or other conventional approaches. - Lignin-first integrated hydrothermal treatment (HTT) and synthesis of low-cost biorefinery particles
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-01-21) Vergara Lourencon, Tainise; Garcia Greca, Luiz; Tarasov, Dmitry; Borrega, Marc; Tamminen, Tarja; Rojas Gaona, Orlando; Balakshin, MikhailHydrothermal treatments (HTT) are used in the biorefineries to effectively valorize carbohydrate fractions and their products. However, lignin is often marginalized as a secondary component. Herein, we propose a new biorefinery approach focused on lignin valorization. We demonstrate that high-value lignins can be extracted using a simple, green, and affordable process consisting of an optimized HTT followed by lignin extraction with aqueous acetone under ambient conditions. Significantly, the chemical structure and molecular mass of the lignin can be tailored by the selection of the process variables while maintaining a high yield, in the range of ∼60-90%. For example, the average molecular mass (Mw) of the isolated lignins is in the range between 2.5 and 5 kDa, while the amount of β-O-4 linkages is 4-28 per 100 Ar. The extracted lignins are further used to generate micro- and nanoparticles by using an aerosol flow system. The introduced lignin profiling affords control of particle properties, including average size and distribution, surface energy, and wettability. Overall, the suggested approach allows customization of lignin products while achieving a 58% reduction in the lignin particles production costs compared to the lowest prime figures reported so far.