4 research outputs found
A moisture-absorbing and abrasion resistant transparent coating on polystyrene
A common phenomenon concerning cold surfaces which are subjected to a warmer, more humid atmosphere is condensation in the form of water droplets (fogging) or even ice crystals (icing). Thus, a previously transparent object becomes opaque because light is scattered by the droplets or crystals. This may impair the usability of that object. We developed an anti-fogging/icing coating which overcomes the problem of fogging and icing by being able to absorb the condensing water and preventing it from crystallizing. The coating consists of poly(1-vinyl-2-pyrrolidone) (PVP) crosslinked by UV light using hydrogen peroxide (H2O2). Benzophenone (BP) is used to attach PVP to the surface of the polystyrene (PS) substrate. At temperatures as low as -60°C, the PVP coating can absorb up to 70 wt% of water and still inhibit its crystallization. However, at surface temperatures of around -18°C, opacity is only observable at 150 wt% of absorbed water and higher. An increasing coating thickness as well as a decreasing crosslink density improves the anti-fogging/icing effect because the coating can absorb more water. The abrasion resistance of the coating is impaired by a decreasing crosslink density
Inhomogeneity in Hydrogels Synthesized by Thiol–Ene Polymerization
Hydrogels synthesized via thiol–ene
polymerization were
characterized with respect to their macroscopic properties via elasticity
measurements and to their microscopic properties, in particular inhomogeneity,
by dynamic light scattering. For comparison, identical studies were
made on polyacrylamide (PAAm) hydrogels prepared by free-radical chain-growth
cross-linking copolymerization. Mechanical measurements prove that
for both types of gels the degree of network imperfections is widely
varied by varying concentration, while the macroscopic properties
observed at particular concentrations are very similar. However, the
fraction of static scattering which is a measure of gel inhomogeneity
depends significantly on the type of network studied when the measurement
is performed in the state of preparation. The majority of the thiol–ene
gels appear homogeneous, contrary to the PAAm gels. The situation
is completely different in the equilibrium swollen state, where all
gels exhibit extremely high and almost identical fractions of static
scattering intensity, irrespective of the type of reaction or the
concentration employed in their synthesis. These observations imply
that (i) there is no clear correlation between network imperfections
and homogeneity and (ii) the type of cross-linking reaction controls
the concentration inhomogeneity in the state of preparation but not
(iii) the inhomogeneity of network density. The latter is seen when
the gels are swollen