This work compares solvent-cast poly­(ethylene oxide) (PEO) nanocomposites reinforced with cellulose nanocrystals (CNCs) and fumed silica. Mechanical properties and crystallization behavior were investigated over a range of polymer molecular weights (10 000–100 000 g/mol) and particle loadings (1–10 wt %). Polymer adsorption to CNCs and fumed silica was found to alter PEO undercooling and inhibit crystal nucleation. Atomic force microscopy revealed PEO adsorbs to CNCs in a shish-kebab morphology that is readily incorporated into the crystalline domains of the polymer. Tensile testing and nanoindentation showed that Young’s modulus increased by more than 60% for CNC reinforced nanocomposites, and that the Halpin–Kardos model could effectively describe the mechanical properties. Fumed silica reinforced nanocomposites were fit to the Guth–Gold micromechanical model using effective particle volume fractions. Although only solvent-cast nanocomposites were investigated, this work provides new insight into the interactions that control dispersion, crystallization, and mechanical reinforcement.

Hydrazide-derivatized poly(N-isopropylacrylamide-co-acrylic acid) microgels gave strong adhesion to wet, TEMPO oxidized, regenerated cellulose membranes without a drying or heating step. Adhesion was attributed to hydrazone covalent bond formation with aldehyde groups present on the cellulose surfaces. This is one of only three chemistries we have found that gives significant never-dried adhesion between wet cellulose surfaces. By contrast, for cellulose joints that have been dried and heated before wet testing, the hydrazide-hydrazone chemistry offers no advantages over standard paper industry wet strength resins. The design rules for the hydrazide-microgel adhesives include: cationic microgels are superior to anionic gels; the lower the microgel cross-link density, the higher the adhesion; longer PEG-based hydrazide tethers offer no advantage over shorter attachments; and, adhesion is independent of microgel diameter. Many of these rules were in agreement with predictions of a simple adhesion model where the microgels were assumed to be ideal springs. We propose that the unexpected, high cohesion between neighboring microgels in multilayer films was a result of bond formation between hydrazide groups and residual NHS-carboxyl esters from the preparation of the hydrazide microgels.

For many applications, it is imperative that changes in polymer surface topography, especially periodic patterns, can be triggered on command by a well-defined remote signal. In this contribution, we report a light-induced cascade of changes in wrinkling wavelengths on thin polymer layers supported by an elastomeric substrate under tensile stress. Through the applied supramolecular design, the effect of varying the ratio of light-active and light-passive components can be easily assessed, and it is shown that both the cascade type as well as the rate of the progress of the dynamic light-induced changes can be tuned by this ratio as well as by the light intensity. Furthermore, for the reported phenomena to occur, nominally only every 20th polymer repeat unit needs to be occupied by a chromophore, which makes the conversion of the sub-nanometer photoisomerization reaction into 10 μm scale changes of periodic surface patterns extremely efficient.

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<p>In the fields of functional materials, interfacial chemistry, and microscale devices, surface structuring provides an opportunity to engineer materials with unique tunable properties such as wettability, anti-fouling, crack propagation, and specific surface area. Often, the resulting properties are related to the feature sizes of the structured surfaces and therefore, it is necessary to accurately quantify these topographies. This work presents a step-by-step description of a method for the quantification of the size of periodic structures using 2D discrete Fourier Transform analysis coupled with data filtering techniques to optimize feature size extraction and reduce user bias and error. The method is validated using artificial images of periodic patterns as well as scanning electron microscopy images of gold films that are structured on different substrates. While image Fourier Transform has been used previously and is a built-in feature in some commercial and open-source image analysis software, this work details image pre-processing and feature extraction steps, and how to best apply them, which has not been described in detail elsewhere. This method can analyze engineered or natural periodic topographies (e.g., wrinkles) to enable the design of patterned materials for applications including photovoltaics, biosensors, tissue engineering, flexible electronics, and thin film metrology.</p>