From: jeroen@nospam.please   
      
   Joe Gwinn wrote:   
   > On Mon, 26 Oct 2020 20:07:16 +0100, Jeroen Belleman   
   >  wrote:   
   >   
   >> On 2020-10-26 18:33, Joe Gwinn wrote:   
   >>> On Mon, 26 Oct 2020 16:58:44 +0100, Jeroen Belleman   
   >>>  wrote:   
   >>>   
   >>>> On 2020-10-26 15:57, Phil Hobbs wrote:   
   >>>>> On 10/26/20 9:35 AM, Jeroen Belleman wrote:   
   >>>>>> While playing with polarizing filters, I found a plastic ruler that   
   >>>>>> turns out to rotate the polarization angle of the light passing   
   >>>>>> through it by almost exactly 90 degrees. The ruler is of a 1mm   
   >>>>>> thick colourless plastic, rather flexible, clearly not the usual   
   >>>>>> polyethylene or polystyrene. It does not itself polarize light, it   
   >>>>>> just rotates it. The angle of rotation does not seem to depend on   
   >>>>>> wavelength. It's made in China.   
   >>>>>>   
   >>>>>> What plastic could this be?   
   >>>>> There are quite a lot of optically-active plastics.  Optical activity   
   >>>>> is normally strongly dispersive--what wavelengths did you use?   
   >>>>>   
   >>>>> Cheers   
   >>>>>   
   >>>>> Phil Hobbs   
   >>>>>   
   >>>> Just natural, white light. Some plastics show coloured fringes   
   >>>> when inserted between two polarizing sheets, which is sort-of   
   >>>> what I expected. This Chinese ruler is special: It rotates   
   >>>> the polarization. Inserted between two parallel polarizers, it   
   >>>> has four orientations spaced by 90 degrees where it blocks the   
   >>>> light. But it is not itself polarizing: I see no intensity   
   >>>> variations when looking through it with a single polarizer, nor   
   >>>> when superimposing multiple layers of the same plastic.   
   >>>> There are no colours.   
   >>> It's very likely to be polystyrene.   
   >>>   
   >>> Joe Gwinn   
   >>>   
   >>   
   >> Polystyrene typically shows coloured fringes, stresses frozen in   
   >> the material, does it not? The transparent plastic CD box I have   
   >> here, presumably polystyrene, certainly does.   
   >   
   > Clear CD boxes are usually polystyrene. and yes that is how that   
   > behaves.  So, I agree that polystyrene is ruled out.   
   >   
   >   
   >>   The Chinese ruler   
   >> is different. There are no visible stress fringes. It just rotates   
   >> the polarization by basically the same angle for all colours   
   >> everywhere. It doesn't 'feel' like polystyrene either. Too flexible   
   >> and rather tough, not brittle.   
   >   
   > If you dissolve it in acetone, do you get a powder residue?   
   >   
   > In other words, is the rotation due to the plastic, or to a mineral   
   > filler (if any)?   
   >   
   >   
   >> I'd like to find a clean sheet of the stuff, so that I can make   
   >> some more serious measurements. My wife objects to me cutting up   
   >> her rulers.   
   >   
   > Liquid crystal polymers (LCPs) are typically very tough.  But I'm not   
   > sure any are transparent.  Or that one would make cheap rulers from   
   > LCPs.   
   >   
   > Wonder if it's polycarbonate, which is transparent like polystyrene.   
   > But I don't recall that it rotates polarization.   
   >   
   > Where did this mystery ruler come form?   
   >   
   > Joe Gwinn   
      
      
   It's Chinese, I can't read the brand name. It's a 'comma shaped   
   French curve ruler'. There are lots of brands that look alike.   
      
   Jeroen Belleman   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)