Cornelia Bellmann

Water-Repellent Textile via Decorating Fibers with Amphiphilic Janus Particles

We investigated morphology and wetting properties of textiles modified by chemically immobilized amphiphilic micrometer and submicrometer large Janus particles. The Janus particles bind by their reactive side to the textile surface, while their hydrophobic side faces the environment. It was found that the character of immobilization of the Janus particles on textile depends on their size: larger particles bind between fibers, while smaller ones bind to the fiber surface. In both cases, immobilization of Janus particles results in the hydrophobization of the hydrophilic textile surface. Finally, we demonstrated that submicrometer large Janus particles are very efficient for the design of water-repellent textiles.

Biocompatible polymeric materials with switchable adhesion properties

We report on the design, investigation and comparison of the adhesive properties of poly-(N-isopropylacrylamide) and biocompatible polyethylene glycol-based thermoresponsive brushes. Specifically, a poly-(N-isopropylacrylamide), PNIPAM, poly-(oligo(ethylene glycol) methyl ether methacrylate-co-2-(2-methoxyethoxy)ethyl methacrylate), P(OEGMA-MEO2MA), and poly-(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(propylene glycol) methacrylate), P(OEGMA-OPGMA) brushes were synthesised on planar silicon wafers and silica particles via the surface-initiated atom transfer radical polymerisation. Switching of swelling and surface charge were investigated using spectroscopic ellipsometric and zeta-potential measurements, respectively. Adhesion properties were studied in situ in aqueous solutions at different temperatures using three kinds of AFM probes with well defined tips geometries and radii. We found that: (1) adhesion properties of all polymer brushes reversibly switch with temperature—polymer brushes are completely non-adhesive below the Low Critical Solution Temperature (LCST) and become sticky above the LCST; (2) adhesive force scales nonlinearly with the probe radius; (3) adhesion energy, obtained using Derjaguin/Muller/Toporov approaches, decreases with the increase of the tip radius that is attributed to different depth of penetration of the probes in the polymer layer; (4) adhesion decreases in the sequence PNIPAM – P(OEGMA-MEO2MA) – P(OEGMA-OPGMA). Based on dynamic light scattering and cryo-TEM experiments, the latter effect is attributed to the formation of a thin oligoethylene glycol shell around the hydrophobic polymer core in the case of P(OEGMA-OPGMA). We expect that the P(OEGMA-OPGMA) system, which demonstrates less sticky adhesion properties, could be particularly promising for cell adhesion experiments and tissue engineering.

Tailoring uptake and release of ATP by dendritic glycopolymer/PNIPAAm hydrogel hybrids: first approaches towards multicompartment release systems

A multicompartment release system is described which combines the advantages of dendritic architectures and hydrogels to enhance the desired delivery features in complex biological compartments. Here, a hydrogel hosts dendritic glycopolymers as nanocontainers and a delivery system for drug molecules. The dendritic glycopolymer used consists of a hyperbranched poly(ethylene imine) with a maltose shell and acts as a host for the guest molecule adenosine triphosphate disodium salt hydrate (ATP). The ATP uptake and release from the dendritic host have been elucidated in detail with dependence on the dendritic glycostructure and pH. The complex interactions within the three components ATP, dendritic glycopolymer and hydrogel have been evaluated and could be fine-tuned. A selective release at pH 5.4–7.4 only of ATP from the multicompartment release system ATP@dendritic glycopolymer@hydrogel has been achieved when a boronic acid containing hydrogel was used which allowed chemical binding between the maltose units from the dendritic glycopolymer and the boronic acid (BA) units in the hydrogel. However, when using a hydrogel without BA units, simultaneous release of ATP and the dendritic glycopolymer scaffold from the ATP@dendritic glycopolymer@hydrogel multicompartment release system is observed in the pH range 2–7.4. This multicompartment release system can be applied in complex biological environments with changing pH values and has potential in biomedical applications and sensory devices.

Intelligent Materials with Adaptive Adhesion Properties Based on Comb-like Polymer Brushes

We investigated the adaptive adhesion properties of comb-like random copolymer brushes made of poly(ethylene glycol) (PEG)-poly(dimethylsiloxane) (PDMS) grafted on flat and rough substrates. The properties of the brush layers were investigated using ARXPS, contact angle, electrokinetics, null ellipsometry, and adhesion measurements. It was found that hydrophobic PDMS segments segregate at the brush topmost layer in the dry state. However, hydrophilic PEG chains segregate at the brush topmost layer in the wet state. The adhesion properties of fabricated materials were tested using the AFM colloid probe technique and probe tack tester. It was found that the adhesive properties depend strongly on the mechanical properties (stiff/soft) and chemical functionality (hydrophobicity/hydrophilicity) of the applied adhesion tester as well as on the chemical composition, surface roughness, and thickness of the brush. In particular, hydrophobic PDMS and hydrophilic PEG adhere more strongly to hydrophobically modified and hydrophilic native colloid probes, respectively. Thick brushes are more adhesive than thin ones, and brushes grafted to flat substrates are stickier than those grafted to rough substrates when measured with a hard AFM probe. Unlike the results of adhesion measurements performed using hard AFM probes, the PDMS surface probed by soft pressure-sensitive adhesives (PSA) is almost nonadhesive. However, PEG is strongly adhesive, and the adhesion increases with the PEG fraction in the brush when probed by both hydrophilic and hydrophobic soft adhesives. The surfaces roughness also has a considerable effect on adhesion. Contrary to the adhesion measurements performed by hard AFM colloid probes, the adhesion of rough surfaces measured with a soft PAA or SIS tack tester is greater than that on the corresponding flat one.

Solvatochromic and electrokinetic studies of banana fibrils prepared from steam-exploded banana fiber.

Steam explosion technique was used to isolate banana fibrils from banana fiber. The surface polarity of banana fiber, banana fibril, and chemically-treated banana fibril was investigated by ultraviolet/visible spectroscopy using solvatochromic probe dye molecules. The empirical Kamlet-Taft solvatochromic polarity parameters such as hydrogen bond donating ability HBD (alpha), hydrogen bond accepting ability HBA (beta), the dipolarity (pi*), Gutman acceptor number, and Reichardts ET(30) values for the banana fiber, banana fibril, and chemically-treated banana fibril were determined. It was observed that banana fibril has higher HBD value than banana fiber. Chemical treatment of the banana fibril has lowered the HBD value. The results of the empirical polarity parameters determined were found to be consistent with the results of electrokinetic measurements. The functional groups on the surface of banana fiber, banana fibril, and chemically-treated banana fibril was further analyzed using Fourier transform infrared spectroscopy (FTIR). FTIR spectra revealed the dissolution of the various components from the banana fiber after steam explosion which was further confirmed by scanning electron microscopy.

Endowing Carbon Black Pigment Particles with Primary Amino Groups

A readily synthetic route to endow the surface of hydrophobic carbon black (CB) particles with primary amino groups has been developed. The adsorption of the water-borne polyelectrolyte copolymer poly(vinyl amine-co-vinyl amide) (PVAm) on CB was studied as function of pH and polyelectrolyte concentration. The amino-functionalization process of CB with PVAm strongly depends on pH. As shown by electrokinetic measurement as function of pH, the content of accessible primary amino groups on the surface of CB increases with increasing the OH- concentration. The alternative functionalization of the CB surface with an anionic polyelectrolyte is demonstrated for the adsorption of poly(ethylene-alt-maleic anhydride) (PEMSA). About 50 mg of PVAm can be adsorbed on 1.0 g of CB, which is sufficient to completely alter the surface net charge. The aim of the introduced functional amino groups is their ability to act as anchoring groups for subsequent surface reactions improving the CBs process ability, compatibility, and adhesion properties.

Hybrid Nanoalloy: Nanofibers Fabricated by Self‐Assembling Dendrimers Mediate In Situ CdSe Quantum Dots and Their Metallization with Discrete Gold Nanoparticles

Controlling the assembly of individual nanoparticles into welldefi ned nanostructures by self-assembled hybrid materials is a powerful technique to fabricate novel functional nanomaterials. [ 1 ] This type of nanofabrication facilitates the formation of different anisotropic nanostructures. [ 2 ] Among these types of nanostructures, 1D nanostructured hybrid organic–inorganic materials [ 3 ] have attracted signifi cant attention, not only because of their unique physical properties, but also because they can be used as building blocks to achieve a high degree of integral functionality useful for the next generation of miniaturized devices. Herein we report on a simple approach to fabricate metallized high density semiconducting hybrid nanofi bers based on self-assembled dendrimer templated CdSe nanoparticles in situ at room temperature. The dendrimer@CdSe hybrid nanofi bers are prepared by a wet chemical method in aqueous medium and have been used as a scaffold to deposit discrete metallic nanoparticles. Dendrimers are globular macromolecules composed of a core, dendrons, and surface groups. [ 4 ] Dendrimers possess many merits such as well-defi ned molecular structures and monodispersity in molecular weight. [ 5 ] Poly(propyleneimine) (PPI) is a common type of dendrimer consisting of tertiary amine groups in the dendritic scaffold and peripheral primary amine groups (Figure 1-SI, Supporting Information). [ 6 ] The unique dendritic architecture of PPI provides a simple tool to modulate intermolecular interactions by dissimilarity in the protonation state between the dendritic scaffold (core) and peripheral shell. [ 7a ]

Fabrication of carbon/silica hybrid materials using cationic polymerization and the sol‐gel process

Silica particles with different morphology have been functionalized with carbon shells by different synthetic procedures. In the key step, the bare silica particles are functionalized by a specific cationic surface polymerization with furfuryl alcohol (FA). The polyfurfuryl alcohol (PFA)/silica hybrid particles have been also post-functionalized with maleic anhydride (MSA) by a Diels Alder reaction. Simultaneously occuring cationic polymerization of FA and sol-gel process with TEOS has been used for producing interpenetrating carbon-silica hybrid materials. The thermal transformation of the PFA component on silica into the carbon phase has been carried out under argon atmosphere in a temperature range from 700 °C to 900 °C. The influence of the former morphology of the silica on the homogenity of the resulting carbon layer is shown by zetapotential measurements and electron microscopic investigations.

Probing the surface polarity of native celluloses using genuine solvatochromic dyes

The surface polarity of native celluloses has been investigated by the following solvatochromic dyes: dicyano-bis (1,10)-phenanthroline iron (II) Fe(phen)2 (CN)2 (1), bis(4-N,N-dimethylamino)-benzophenone (2), and cou-marine 153 (3). Linear Solvation Energy (LSE) relationships and the UV/Vis data have been used to characterize the surface polarity of different native cellulose batches in terms of the empirical Kamlet–Taft polarity parameters α (hydrogen bond acidity), β (hydrogen bond basicity), and π * (dipolarity/polarizability). α, β, π *and calculated Reichardts E T (30) values are reported for various native and regenerated cellulose samples with different degrees of crystallinity. The degree of crystallinity of the cellulose samples has been determined by X-ray. The microcrystalline environment of cellulose can be exactly parameterized in terms of the α, β and π *values. It shows a fairly strong acidity α and a low dipolarity/polarizability. For the amorphous sections smaller α and larger π * values are observed. The correspondence of the empirical polarity parameters determined has been discussed in relation to results from pyrene fluorescence and zetapotential measurements.

Electrokinetic and solvatochromic studies of functionalized silica particles

Zeta potential plots, Kamlet-Tafts α (hydrogen bond-donating, HBD), β (hydrogen bond-accepting, HBA), and π* (dipolarity/polarizability) parameters as well as Gutmanns DN (donor numbers) are presented for 12 differently functionalized (i.e. alkyl, cyanoalkyl, aminoalkyl, and imidazolidine) silica particles. The pH-dependent zeta potential plots were measured in aqueous solution, whereas the solvatochromic studies were performed in 1,2-dichloroethane and cyclohexane as solvents using a special UV/visible spectroscopic technique. For the determination of the solvatochromic polarity parameters, a set of carefully characterized polarity indicators was employed: Cu(tmen)(acac)+B(C6H5)4 - for β and DN; dicyano-bis(1,10-phenanthroline)iron(II) for α; 4,4′-bis(N,N-dimethylamino)benzophenone for π*; and an aminobenzofuranone derivative {3-(4-amino-3-methylphenyl)-7-phenyl-benzo[1,2b : 4,5b′]difuran-2,6-dione} (ABF) for α, β, and π*. The calculation of the polarity parameters was carried out via linear solvation energy (LSE) correlation equations using the Kamlet-Taft solvent parameters as a reference system. A linear correlation between the electrokinetically determined value of the isoelectric point and the β parameter of the functionalized silicas is demonstrated.