A330 relief pilot is informed after the fact and relates that a conflict developed between between the Captain and First Officer resulting in lost comm departing Scottish airspace.

Narrative

I was actually in a crew bunk just beginning my crew rest (first break) during the timeframe of the event. When I returned from first break the Captain and later the other First Officer related similar versions of the following: During this rotation there was some personal conflict between the Captain and the other First Officer. During this specific event the Captain asked the other First Officer to update the MCDU with a newly received EEP and ETP's. The First Officer stated that she was the pilot flying and he should be doing the update. The Captain then took over the PF duties and told the F/O to do the update. The F/O began the update and the Captain then stated he was going to make a top of climb PA and that he was off of the radios. The F/O missed a frequency change issued by Scottish ATC. I believe this occurred because she was off headset and had her speakers turned down/off. The Captain completed his PA and began PF duties and verified the updated EEP and ETP's. At some point appx 5-7 minutes later either the CA or F/O noticed the lack of radio communication. I believe the CA may have been slow to come back 'on' the radios after making the PA and assumed the F/O was monitoring the radios. At this time radio communication was reestablished with ATC and ATC informed the Crew that they had been out of radio contact for 60 km and a violation may have to be filed. Ultimately better interpersonal communication between the CA and FO is needed. A strong factor in this loss of radio communication with ATC was a high level of animosity between the CA and FO. Throughout this rotation the FO was consistently hesitant/slow to perform her duties and when she did so she was often 'inaccurate' and defensive. On this final leg of a multi-day day trip; this less than professional performance by the FO began to wear on the Captain. There was minimum communication between the two by this point and when the FO was not willing to update the FMS as the CA requested the CA became very frustrated.