Selfsimilar blowup of unstable thin-film equations M. PughD. Slepcev 76A2035K2535G2535R35thin-film equationsselfsimilar solutionssingularity formation We study selfsimilar blowup of long-wave unstable thin-film equations with critical powers of nonlinearities: $u_t = -(u^nu_{xxx} + u^{n+2}u_x)_x$. We show that the equation cannot have selfsimilar solutions (with zero contact angles) that blow up in finite time if $n \geq 3/2$. We show that for $0 < n < 3/2$ there are compactly supported, symmetric, selfsimilar solutions (with zero contact angles) that blow up in finite time. Moreover, there exist families of these solutions with any number of local maxima. We also study the asymptotic behaviour of these selfsimilar solutions as $n$ approaches $3/2$ and obtain a sharp lower bound on the height of solutions one time unit before the blowup. We also prove qualitative properties of solutions; for example, the profile of a selfsimilar solution that blows up in finite time can always be bounded from below by a compactly supported steady state. Indiana University Mathematics Journal 2005 text pdf 10.1512/iumj.2005.54.2569 10.1512/iumj.2005.54.2569 en Indiana Univ. Math. J. 54 (2005) 1697 - 1738 state-of-the-art mathematics http://iumj.org/access/