Interactions between dry cellulose were studied using model systems, cellulose beads, and cellulose films, usingcustom-built contact adhesion testing equipment. Depending on the configuration of the substrates in contact,Polydimethylsiloxane (PDMS) film, cellulose films spin-coated either on PDMS or glass, the interaction showsthree distinct processes. Firstly, molecular interlocking is formed between cellulose and cellulose when there is asoft PDMS thin film backing the cellulose film. Secondly, without backing, no initial attraction force between thesurfaces is observed. Thirdly, a significant force increase, ΔF, is observed during the retraction process for cel­lulose on glass, and there is a maximum in ΔF when the retraction rate is increased. This is due to the kinetics of acontacting process occurring in the interaction zone between the surfaces caused by an interdigitation of a finefibrillar structure at the nano-scale, whereas, for the spin-coated cellulose surfaces on the PDMS backing, there isa more direct adhesive failure. The results have generated understanding of the interaction between cellulose-rich materials, which helps design new, advanced cellulose-based materials. The results also show thecomplexity of the interaction between these surfaces and that earlier mechanisms, based on macroscopic materialtesting, are simply not adequate for molecular tailoring.

The drying behavior of regenerated cellulose gel beads swollen with different nonsolvents (e.g., water, ethanol, water/ethanol mixtures) is studied in situ on the macroscopic scale with an optical microscope as well as on nanoscale using small-angle/wide-angle X-ray scattering (SAXS/WAXS) techniques. Depending on the cellulose concentration, the structural evolution of beads during drying follows one of three distinct regimes. First, when the cellulose concentration is lower than 0.5 wt %, the drying process comprises three steps and, regardless of the water/ethanol mixture composition, a sharp structural transition corresponding to the formation of a cellulose II crystalline structure is observed. Second, when the cellulose concentration is higher than 5.0 wt %, a two-step drying process is observed and no structural transition occurs for any of the beads studied. Third, when the cellulose concentration is between 0.5 and 5.0 wt %, the drying process is dependent on the nonsolvent composition. A three-step drying process takes place for beads swollen with water/ethanol mixtures with a water content higher than 20%, while a two-step drying process is observed when the water content is lower than 20%. To describe the drying behavior governed by the cellulose concentration and nonsolvent composition, a simplified phase diagram is proposed.

Polyethylene oxide (PEO) is one of the most widely used polymeric ion conductors which has the potential for a wide range of applications in energy storage. The enhancement of ionic conductivity of PEO-based electrolytes is generally achieved by sacrificing the mechanical properties. Using layer-by-layer (LbL) self-assembly with a nanoscale precision, mechanically strong and self-healable PEO/polyacrylic acid composite thin films with a high Li+ conductivity of 2.3 ± 0.8 × 10−4 S cm−1 at 30 °C, and a strength of 3.7 MPa is prepared. These values make the LbL composite among the best recorded multifunctional solid electrolytes. The electrolyte thin film withstands at least 1000 cycles of striping/plating of Li at 0.05 mA cm−2. It is further shown that the LbL thin films can be used as separators for Li-ion batteries to deliver a capacity of 116 mAh g−1 at 0.1 C in an all-LbL-assembled lithium iron phosphate/lithium titanate battery. Finally, it is demonstrated that the thin films can be used as ion-conducting substrates for flexible electrochemical devices, including micro supercapacitors and electrochemical transistors.

The nano- to microscale structures at the interface between materials can define the macroscopic material properties. These structures are extremely difficult to investigate for complex material systems, such as cellulose-rich materials. The development of new model cellulose materials and measuring techniques has opened new possibilities to resolve this problem. We present a straightforward approach combining micro-focusing grazing-incidence small-angle X-ray scattering and atomic force microscopy (AFM) to investigate the structural rearrangements of cellulose/cellulose interfaces in situ during drying. Based on the results, we propose that molecular interdiffusion and structural rearrangement play a major role in the development of the properties of the cellulose/cellulose interphase; this model is representative of the development of the properties of joint/contact points between macroscopic cellulose fibers.

The mechanical properties as well as the size changes of swollen cellulose beads were measured in situ during solvent evaporation by atomic force microscopy (AFM) indentation measurement combined with optical microscopy. Three factors are proposed to govern the mechanical properties of the cellulose beads in the swollen state and during drying: (i) the cellulose concentration, (ii) the interaction between the cellulose entities, (iii) the heterogeneity of the network structure within the cellulose beads.

The macro- and microstructural evolution of water swollen and ethanol swollen regenerated cellulose gel beads have been determined during drying by optical microscopy combined with analytical balance measurements, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Two characteristic length scales, which are related to the molecular dimension of cellulose monomer and elongated aggregates of these monomers, could be identified for both types of beads by SAXS. For ethanol swollen beads, only small changes to the structures were detected in both the SAXS and WAXS measurements during the entire drying process. However, the drying of cellulose from water follows a more complex process when compared to drying from ethanol. As water swollen beads dried, they went through a structural transition where elongated structures changed to spherical structures and their dimensions increased from 3.6 to 13.5 nm. After complete drying from water, the nanostructures were characterized as a combination of rodlike structures with an approximate size of cellulose monomers (0.5 nm), and spherical aggregates (13.5 nm) without any indication of heterogeneous meso- or microporosity. In addition, WAXS shows that cellulose II hydrate structure appears and transforms to cellulose II during water evaporation, however it is not possible to determine the degree of crystallinity of the beads from the present measurements. This work sheds lights on the structural changes that occur within regenerated cellulose materials during drying and can aid in the design and application of cellulosic materials as fibers, adhesives, and membranes.

Preparation of lightweight and biocompatible hollow capsules holds great promise for various advanced engineering applications. Here, we use a heterogeneously modified structure of cellulose, which on the molecular level increases the flexibility of the capsule shell, to form hollow capsules. These capsules expand in the wet state when they are exposed to an external stimulus, in the present case a decreased external pressure. The capsules were prepared by a dropwise precipitation of a propane-saturated solution of cellulose partially modified to dialcohol cellulose, dissolved in a mixture ofN,N-dimethylacetamide and lithium chloride, into a non-solvent. The mechanical properties of the capsules were determined by measuring the expansion of the capsules upon a controlled decrease in external pressure. In addition, indentation measurements using atomic force microscopy were used to independently quantify the moduli of the capsule walls. The results show that the wet, modified cellulose capsules are much softer and, upon the same pressure change, expand significantly more than those made from unmodified cellulose. The greatest expansion observed for the modified capsules was 1.9 times the original volume, which corresponds to a final density of the expanded capsules of about 14 kg m(-3). These capsules therefore hold great potential to form green and lightweight foam-like materials.