Given the disruptions COVID-19 caused to normal research processes, including international collaboration, this study sought to understand scientists' experiences collaborating internationally during the pandemic on COVID-19-related research. Specifically, it explored US scientists' tie formation and reasons for international research collaboration with Chinese scientists. The study employed a sequential exploratory mixed methods design collecting interview and survey data from US scientists who co-published articles related to COVID-19 with Chinese scientists. The findings revealed the role of network mechanisms, such as transitivity, opportunity of contact, and homophily, in promoting relationship formation and maintenance. Moreover, they showed the greater role that bonding social capital played in helping scientists access valuable knowledge, skills, and resources to enhance their research potential. Lastly, they demonstrated how particularized trust based on prior interactions and experiences encouraged relationship formation and collaboration between US and Chinese scientists. Together, these results provide new insights in informing future policies and guidelines related to supporting international collaboration and, ultimately, shared pandemic challenges.