American Dana Vollmer won the women\'s 100m butterfly Olympic gold medal Sunday in a world record time of 55.98sec. Vollmer added the Olympic gold to the world title she claimed last year as she bettered the previous world record of 56.06sec set by Sweden\'s Sarah Sjostrom on July 27, 2009 at the World Championships in Rome. Lu Ying of China took silver while Australia\'s Alicia Coutts took bronze.