Filtern
Dokumenttyp
Schlagworte
- Adhesion-promoting layers (1)
- Barriereentladung (1)
- Corona (1)
- Dielectric barrier discharge (1)
- Electrospray deposition (1)
- Haftvermittler (1)
- Polymer aerosols (1)
- Polymer surface modification (1)
- Schälfestigkeit (1)
Polyolefins are chemically inert and do not adhere well to metals, polymers or inorganics. To overcome this problem, polyolefin surfaces were modified thermally, plasmachemically, or by flame treatment with different oxygen-containing groups, however, unfortunately, such treatments were accompanied by undesired, adhesion lowering polymer degradation. To solve this dilemma, solutions of synthetic polymers and copolymers were prepared, sprayed into the barrier discharge or electrosprayed without discharge and deposited as thin adhesion-promoting layers. The deposited polymer layers from poly(vinylamine), poly(ethylene glycol)-poly(vinyl alcohol) copolymers and poly(acrylic acid) were endowed with monotype functional groups. Using the aerosol - dielectric barrier discharge only a fraction of functional groups survived the deposition process in contrast to the electrospray in which all functional groups were retained.
Optical polarimetry measurements of the orientational order of a discotic liquid crystal based on a pyrene derivative confined in parallelly aligned nanochannels of monolithic, mesoporous alumina, silica, and silicon as a function of temperature, channel radius (3–22 nm) and surface chemistry reveal a competition of radial and axial columnar orders. The evolution of the orientational order parameter of the confined systems is continuous, in contrast to the discontinuous transition in the bulk. For channel radii larger than 10 nm we suggest several, alternative defect structures, which are compatible both with the optical experiments on the collective molecular orientation presented here and with a translational, radial columnar order reported in previous diffraction studies. For smaller channel radii our observations can semi-quantitatively be described by a Landau–de Gennes model with a nematic shell of radially ordered columns (affected by elastic splay deformations) that coexists with an orientationally disordered, isotropic core. For these structures, the cylindrical phase boundaries are predicted to move from the channel walls to the channel centres upon cooling, and vice-versa upon heating, in accord with the pronounced cooling/heating hystereses observed and the scaling behavior of the transition temperatures with the channel diameter. The absence of experimental hints of a paranematic state is consistent with a biquadratic coupling of the splay deformations to the order parameter.