RESUMO
Supramolecular assembly of biobased components in water is a promising strategy to construct advanced materials. Herein, electrostatic complexation was used to prepare wet-resilient foams with improved mechanical property. Small-angle X-ray scattering and cryo-transmission electron microscopy experiments showed that suspensions with oppositely charged cellulose nanofibers are a mixture of clusters and networks of entangled fibers. The balance between these structures governs the colloidal stability and the rheological behavior of CNFs in water. Foams prepared from suspensions exhibited maximum compressive modulus at the mass composition of 1:1 (ca 0.12 MPa), suggesting that meaningful attractive interactions happen at this point and act as stiffening structure in the material. Besides the electrostatic attraction, hydrogen bonds and hydrophobic contacts may also occur within the clustering, improving the water stability of cationic foams. These results may provide a basis for the development of robust all- cellulose materials prepared in water, with nontoxic chemicals.
Assuntos
Celulose/química , Nanopartículas/química , Eletricidade Estática , Cátions , Força Compressiva , Microscopia Crioeletrônica , Óxidos N-Cíclicos/química , Ligação de Hidrogênio , Processamento de Imagem Assistida por Computador , Teste de Materiais , Microscopia Eletrônica de Transmissão , Reologia , Espalhamento de Radiação , Propriedades de Superfície , Suspensões , Água/química , Microtomografia por Raio-XRESUMO
The preparation of inclusion complexes based on α-cyclodextrin (α-CD) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) was investigated aiming to reveal complexation particularities and thermodynamic and kinetic aspects as a function of the oligomer architecture. Small-angle X-ray scattering and isothermal titration calorimetry measurements revealed that oligomer molecular weight controls both the kinetics and thermodynamics of inclusion. Unlike linear ethylene glycol polymers, OEGMA groups possess a methacrylate group, which seems to act as a stopper, affecting their mode of complexation. Nuclear magnetic resonance spectra and relaxation measurements support the fact that methacrylate groups lie outside the α-CD ring and that a full sequential complexation of the oligomer ethylene oxide groups is not observed. These results allied to the temperature sensitivity of these oligomers and enable possible routes for chemical modifications and design of new stimuli-responsive materials.
RESUMO
Cellulose nanofibers (CNF) can present a high viscosity and thixotropic behavior when dispersed in water. In this work, CNF isolated from sugarcane bagasse and modified by N-oxyl-2,2,6,6-tetramethylpiperidine (TEMPO) oxidation was added to a solution of carboxymethyl cellulose (CMC). This process produced an unexpected viscosity due to a synergistic effect that was observed macroscopically through rheology analysis. The phenomenon known as depletion flocculation was observed, which was caused by the reduction of the excluded volume. The interactions of the system were studied by ultraviolet-visible spectroscopy (UV-Vis), optical microscopy, and cryogenic transmission electron microscopy (cryo-TEM), which demonstrated the presence of the particle/polymer repulsion and subsequent formation of domains composed of aligned micro and nanocellulose particles clusters and nanofibers distributed throughout the sample, forming a percolated 3D structure responsible for a strong gelling and colloidal stability.
Assuntos
Carboximetilcelulose Sódica/química , Celulose/química , Nanopartículas/química , Estrutura Molecular , Tamanho da Partícula , Espectrofotometria Ultravioleta , Propriedades de SuperfícieRESUMO
Cellulose nanofibers (CNF) were isolated from Curauá fibers (Ananas erectifolius L. B. Smith) through a mechanical grinder preceded by mild chemical treatment. Morphology and surface characteristics of the fibers were followed until it reaches the nanoscale as long and flexible nanofibers. In aqueous suspensions, SAXS techniques revealed that such nanofibers present a twisted ribbon structure while rheological measurements demonstrate its high viscosity and a thixotropic behavior. These characteristics suggests the potential application of CNF in biomedical field, which, in turn, stimulates the toxicological studies of such materials. The obtained materials do not show any sign of cytotoxicity by direct or indirect assays for cell viability and cell morphology using Vero cells. Moreover, during the adhesion test, the cells demonstrated higher affinity to the CNF surface. It can be related to its surface properties and its obtaining conditions, which did not use any hazardous chemicals.