Laboratory & Research

The problem

UV curing in Laboratory & Research

Put UV light onto the sample and a rotational rheometer becomes a photo-instrument. The rheometer keeps oscillating while the light is on, tracking the storage modulus G′ and the loss modulus G″ through the whole cure — and where the two cross, you have the gel point, read directly rather than inferred. Photo-DSC does the same for the heat of reaction. In both, the light is not illumination; it is the variable being applied.

That puts unusual demands on the source. The dose has to be identical from run to run or the curves are not comparable — so intensity has to hold as the lamp ages, not merely start high. The shutter has to open on the instrument's command, because time zero of the measurement is the moment the light arrives. And the light usually has to travel down a light guide into a closed measuring cell and through a quartz plate, which means the number that matters is the irradiance at the sample, not at the lamp.

ETIA supplies that module. The OmniCure® S2000 is the broad-spectrum choice — a 250–600 nm mercury source with closed-loop feedback holding output constant over lamp life, delivered through a light guide, with the shutter under external control. The OmniCure LX500 is the LED alternative where a narrow band at 365, 385, 395 or 405 nm matches the photoinitiator and the sample must not take the infrared load a lamp brings with it. Published photo-rheology work runs exactly this way: an Anton Paar MCR302 with an OmniCure S2000 at 250–450 nm, plate/plate at a 0.3 mm gap, tracking G′, G″, tan δ and complex viscosity in real time.

We supply the light module, not the rheometer. Instrument builders come to us to specify a source, its optics and its coupling into a new platform; laboratories come to us to keep an installed setup running when the original lamp is ageing or has been discontinued, and to put traceable radiometry on the sample plane so this year's curves still compare with last year's.