text: Q:
  
  Why did Loki surrender in Avengers? If he did this willingly, what were his intentions?
  
  In the opening scenes of Avengers, we see that Loki is apparently bullet-proof. Furthermore, we see that Asgardians are overall immune to small explosions and similar attacks.
  So why did Loki surrender after his fight with Captain America, when Stark appeared at Stuttgart, Germany? Was it part of his plan, or was he genuinely wary of Iron Man’s arsenal?
  In a later conversation, Captain asks 
  
  “I wanna know why Loki let us take him.”
  
  And if so, what were his intentions behind letting SHIELD take him?
  
  A:
  
  It was so Loki (and his sceptre) would get access to the Helicarrier.  While there, his sceptre induced a Hulk episode.  Loki's henchmen, led by Hawkeye, severely damaged the Helicarrier.  And the Avengers were scattered.  Hulk/Banner fell from the ship, Thor did as well.  The only person who knew where the Tesseract was (Banner) failed to spread this information, this delayed the Avengers in preventing the establishment of the portal.
  In addition, Loki had accomplished what he sought to accomplish in Germany.  He retrieved the eye scan for Hawkeye, who stole the iridium necessary for the portal machine.
  Loki allowed himself to be captured, so as to weaken the Avengers, and it worked.  Iron Man showed up too late to prevent the portal from being established.  Had Loki and henchmen not attacked, Banner and Stark's search for the Tesseract would have located it early enough for the team to recapture it.  This would have then prevented the Chitauri invasion.
  
  