Are you wondering why your campaign's content has a 0% open rate? Is it less interesting? Unengaging content and poor email lists can have a significant impact on open rate. What about creating a new Gmail account? Can this have an effect on the open rate?
It takes a little bit of time and sending from a new email address for the message to be recognized by inboxes. But as you keep sending over the course of the month, this is something that will eventually level off.
Furthermore, if your segmentation is so narrow that the campaign is only sent to a small number of recipients, it is not surprising that there were no opens. That is to be expected.