Self-standing films (45-μm thick) of native cellulose nanofibrils (CNF) were synthesized and characterized for their piezoelectric response. The surface and the microstructure of the films were evaluated with image-based analysis and scanning electron microscopy (SEM). The measured dielectric properties of the films at 1 kHz and 9.97 GHz indicated a relative permittivity of 3.47 and 3.38 and loss tangent tan  of 0.011 and 0.071, respectively. The films were used as functional sensing layers in piezoelectric sensors with corresponding sensitivities of 4.7 to 6.4 pC/N in ambient conditions. This piezoelectric response is expected to increase remarkably upon film polarization resulting from the alignment of the cellulose crystalline regions in the film. The CNF sensor characteristics were compared with those of polyvinylidene fluoride (PVDF) as reference piezoelectric polymer. Overall, the results suggest that CNF is a suitable precursor material for disposable piezoelectric sensors, actuator or energy generators with potential applications in the fields of electronics, sensors and biomedical diagnostics.

Amorphous titanium dioxide (a-TiO2) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO2 without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO2 induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO2 is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO2. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O– species within a-TiO2 that are essentially electronic defects in the anionic framework.

Some bacterial strains such as Komagataeibacter xylinus are able to produce cellulose as an extracellular matrix. In comparison to wood-based cellulose, bacterial cellulose (BC) holds interesting properties such as biodegradability, high purity, water-holding capacity, and superior mechanical and structural properties. Aiming toward improvement in BC production titer and tailored alterations to the BC film, we engineered K. xylinus to overexpress partial and complete bacterial cellulose synthase operon that encodes activities for BC production. The changes in cell growth, end metabolite, and BC production titers from the engineered strains were compared with the wild-type K. xylinus. Although there were no significant differences between the growth of wild-type and engineered strains, the engineered K. xylinus strains demonstrated faster BC production, generating 2-4-fold higher production titer (the highest observed titer was obtained with K. xylinus-bcsABCD strain producing 4.3 ± 0.46 g/L BC in 4 days). The mechanical and structural characteristics of cellulose produced from the wild-type and engineered K. xylinus strains were analyzed with a stylus profilometer, in-house built tensile strength measurement system, a scanning electron microscope, and an X-ray diffractometer. Results from the profilometer indicated that the engineered K. xylinus strains produced thicker BC films (wild type, 5.1 μm, and engineered K. xylinus strains, 6.2-10.2 μm). Scanning electron microscope revealed no principal differences in the structure of the different type BC films. The crystallinity index of all films was high (from 88.6 to 97.5%). All BC films showed significant piezoelectric response (5.0-20 pC/N), indicating BC as a promising sensor material.

The overall mechanical performance of ionic elastomers, such as carboxylated nitrile rubber (XNBR), is largely governed by ionic clusters formed during the cross-linking of the elastomers with zinc oxide. These ionic aggregates promote microphase separation and show additional high-temperature relaxation behavior in dynamic mechanical analysis. In this study, the nature of these ionic aggregates is explored for the first time. We find that some zinc-containing compounds, such as zinc–aluminum-layered double hydroxide and zinc chloride, do not exhibit any extra high-temperature dynamic mechanical relaxation processes, although ionic cross-linking reactions with XNBR occur with all of these zinc compounds. Detailed analysis by Fourier-transform infrared spectroscopy and dynamic mechanical analysis revealed that this high-temperature relaxation behavior does not originate from ionic cross-linking but is associated with the formation of an additional zinc-enriched polymer phase that arises due to reactions between carboxylic groups and zinc oxide. Infrared spectroscopic investigation indicates further that a tetrahedrally coordinated complex facilitates the formation of a zinc–carboxylic polymeric network. Clear microphase separation of the ionic polymer in the elastomer could be directly visualized by transmission electron microscopy for the first time.

Nanocellulose and chitosan have recently started to get attention as environmentally friendly piezoelectric materials for sensor and energy harvesting applications. Conversely, current commercially available flexible piezoelectric films made of for example polyvinylidene difluoride (PVDF) are relatively expensive and made from non-renewable materials. We measured the piezoelectric responses (2-8 pC/N) for solvent casted films based on nanocellulose, microcrystalline chitosan and their blends. In addition, the tensile properties of the piezoelectric films were characterized to find out if chitosan could be used to enhance the flexibility of the brittle nanocellulose films. Based on the results, plain chitosan is an interesting piezoelectric material itself. In addition, blending nanocellulose and chitosan could be a potential method for tailoring the properties of solvent casted low cost, green piezoelectric films. media. Depending on the chitin source, the degree of deacetylation should reach approximately 50% before this solubility is achieved. (Rinaudo, 2006) In nature, chitosan is reportedly produced by only some fungi (Grifoll-Romero et al., 2018). Nanocellulose and chitosan have been studied for numerous applications due to their simple water based solution processing, renewable raw material sources, low cost, biocompatibility