Sorry I'm reiterating a few points that Dave made, but I'm in agreement that researching how to interact with others doesn't always help. Especially since every person acts differently, there is no tried and true way to talk to other people.
It sounds like when you talk to others, there is no flow to the conversation, after you're done asking a quesiton you move on to the next one. Be okay with silence and lulls. Even my best friends, who I feel comfortable talking with about any subject (and I mean any subject), we have moments of nothing to our conversations. And it's okay. We take a minute to think about what was said, which sometimes brings up other points, leading to a natural flow in the conversation. Or if we have nothing to say, we sit in silence for a moment and a completely different topic gets brought up.
Do you get bored in conversation easily? I mean, I know I can have some pretty stupid conversations with my friends, that mean absolutely nothing, but I enjoy it fully. The other day we talked for two hours making up death-matches and 'who would win' scenarios. Yeah, not deep conversation.
The idea of coming up with a persona isn't a bad one, but what I would do instead is take inspiration from someone who exists. Know somebody who's very social and good at it? Channel them, but don't be them. It can give you an extra boost of confidence without seeming fake.
At a party, or social event, I suggest sitting close to everyone, even if you aren't participating in the conversation. It's surprising how often you can simply listen to everyone and still be involved. This one tends to work for me quite a bit because I'm terribly shy, so I struggle a lot in group settings, but sitting there listening to everyone's stories let's them know that I'm interested in them and I want to be there. Also, when it comes to group events, I like to 'trade off'. What I mean is, at one event, I'll try to be very social and talk with many people, sharing stories; being loud. But then at the next event, I'll hang back and be in the background. Not having the pressure of being social at every party may ease you into a bit better, so you have more focused practice and less, as you put it, failed conversations.
The subject of your PhD shouldn't be a turn off to anyone, but I wouldn't come out of the gate saying to everyone 'Hello, my name is ___ and I have a PhD in physics.' while shaking their hand. As your wife mentioned, it's in the delivery. If you were to say this to me, that you have a PhD, I would find it fascinating, but you would have to carry the conversation some because I'm not well-versed in that subject. Observing others' body language is a good indicator if discussing physics is an okay topic.
Anyway, sorry this is long, but I hope it helps some.