Laura Taajamaa

Bicomponent fibre mats with adhesive ultra-hydrophobicity tailored with cellulose derivatives

Morphologies featured in bicomponent 2D ultrathin films were reproduced on 3D non-woven microfibre structures. Fibre networks were constructed by electrospinning hydrophobised cellulose derivatives, trimethylsilyl cellulose (TMSC) and cellulose triacetate (CTA), dissolved in a common solvent. Diverse morphologies were obtained depending on the polymer blend ratio: electrospinning of TMSC produced non-continuous micron fibres with shallow dints, TMSC/CTA 5 : 1 flat micron fibres with regular pore arrays, TMSC/CTA 1 : 1 wrinkled micron fibres decorated with shallow dints and occasional larger pores, TMSC/CTA 1 : 5 flat micron fibres with ellipsoidal porous structures and finally, CTA that led to smooth micron and submicron fibres. The fibre mats were ultra-hydrophobic with characteristic water contact angles of ca. 150 degrees. In addition, they were characterised by high contact angle hysteresis, and water droplets adhered to the substrate even after tilting the system upside down. Through conversion of the respective components to cellulose, chemical and adsorption properties of the fibre networks could be tuned without significantly altering the large-scale network morphology.

Protein-assisted 2D assembly of gold nanoparticles on a polysaccharide surface

Site-specific assembly of gold nanoparticles on a polysaccharide surface was accomplished via a straightforward method exploiting interfacial polymer blends, selective protein adsorption and electrostatic interaction. The method could be useful in further applications due to the universal nature of the utilized phenomena.

Phase-specific pore growth in ultrathin bicomponent films from cellulose-based polysaccharides

The preparation of ultrathin (<100 nm) bicomponent films from hydrophobic polysaccharides with phase-specific pore growth was demonstrated and the underlying phenomena behind morphology formation were fundamentally investigated. The films were constructed, in a single-step process, by spin coating mixtures of trimethylsilyl cellulose (TMSC) and cellulose triacetate (CTA) from a common solvent. Atomic force microscopy (AFM) revealed a nano- and micron-scale phase separated structure, typical for interfacial polymer blends. Vertical phase separation had resulted in a continuous layer of TMSC next to the substrate with laterally phase separated CTA and TMSC on top. Furthermore, X-ray photoelectron spectroscopy (XPS) and contact angle measurements indicated the presence of a thin overlayer of TMSC. In addition, increased relative humidity conditions during spin coating resulted in the formation of pores when the CTA weight percent in the blend was in the range from 17 to 83% (i.e., in TMSC/CTA blend ratios 5 : 1, 2 : 1, 1 : 2, and 1 : 5). Closer analysis of the morphology indicated that the pores resided exclusively in the CTA phase. Hypothetically, the formation of the observed peculiar morphologies was ascribed to various phenomena occurring upon spin coating: vertical and lateral polymer phase separation, dewetting under humid atmosphere, and layer inversion during dewetting. It is concluded that the obtained ultrathin polysaccharide films with tailored surface pores, morphology and wettability are expected to be useful in emerging nanotechnologies while having the advantage of an effortless manufacturing process.