The swelling behavior of SU-8 is studied. It is well known that negative resist swells under the influence of common processing liquids, developers, solvents, etc. However, when SU-8 is used as a construction material for plating molds, or for permanent structures, for instance in microfluidics or as active mechanical components in the MEM structure, a more quantitative investigation is needed. In this paper, the volume change is measured when the SU-8 epoxy is submersed in common processing liquids. An analytical model is derived to link the diffusion mechanism to the mechanical response of the SU-8 material. Using the obtained model, the diffusion constants are calculated from the mechanical displacement measurements. Also, the derived model can be used for the prediction of the mechanical behavior of SU-8 structures in the future. The swelling behavior is also correlated with the internal stresses that exist in the SU-8 film. This helps to understand crack formation and delamination of SU-8 patterns during processing. The results show that the built-in stress in the SU-8 epoxy is strongly dependent on the ambient or submersion liquid and that this effect in itself is strongly dependent on the softbake procedure of the polymer. The built-in stress in SU-8 was found to be maximum when submersed in propylene glycol methyl ether acetate and in isopropyl alcohol, both liquids that are used during the development, and found to be very low in water.

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Compressive properties of 3 different natural fiber composites are measured, based on flax, bamboo and coir fibre. It was found that bamboo performs the best of these 3 natural fibers in compression. If the compressive properties are compared to the tensile properties it can be seen that flax and bamboo composites reach between 60 and 80% of the tensile values, which is very encouraging. Coir fiber composites even perform better in compression than in tension.

Insight in the emulsifying and emulsion stabilizing potential of carrot pectin subdomains was established in the present study. For this purpose, (i) carrot pectin fractions enriched in linear homogalacturonan (HG) and branched rhamnogalacturonan (RG) regions were produced, (ii) specific structural and physicochemical properties of the isolated pectin fractions were analyzed and (iii) stability studies of emulsions where the different isolated pectin fractions were used as the sole emulsifier were performed. Firstly, structural characterization confirmed the successful isolation of the subdomains from the original acid extracted carrot pectin generating three structurally diverse carrot pectin samples: acid extracted pectin (NA), HG rich pectin fraction (NA-HG) and RG rich pectin fraction (NA-RG). The main structural differences among these pectin samples were degree of methylesterification, linearity and molar mass. Analysis of the interfacial tension after pectin adsorption onto an oil droplet, demonstrated surface activity of all pectin samples, except for NA-RG at pH 2.5. Overall, carrot pectin created more stable emulsions at pH 2.5 compared to pH 6.0. Additionally, emulsions stabilized by the more complex NA are less prone to creaming than emulsions stabilized by NA-HG or NA-RG. Flocculation was identified as the main destabilization phenomenon in the emulsions stabilized by NA-HG and NA-RG at pH 6.0. NA stabilized emulsions remained relatively stable during 14 days of refrigerated storage. Therefore, it can be stated that the presence of both linear and branched regions in the pectin structure result in more stable emulsions as compared to the individual subdomains.

This paper gives an overview of a series of experiments conducted in order to characterize the mechanical behavior of two photodefinable epoxies. In particular, it focuses on the stiffness of the materials. The (complex) modulus is measured using five different methods: conventional nanoindentation, continuous stiffness measurement nanoindentation, nanoindentation on MEM structures, dynamic tensile tests and static tensile tests. The measured moduli range from 0.9 to 7.4 GPa for SU-8 and from 1 to 4.1 GPa for Epoclad, depending on the type of experiment and the loading speeds used in the experiments. Results reveal that conventional nanoindentation is not well optimized for polymer characterization and that there is a need for stiffness measurements using more fundamental approaches like a (dynamic) tensile test.