We extend Wertheim’s thermodynamic perturbation theory to derive the association free energy of a multicomponent mixture for which double bonds can form between any two pairs of the molecules’ arbitrary number of bonding sites. This generalization reduces in limiting cases to prior theories that restrict double bonding to at most one pair of sites per molecule. We apply the new theory to an associating mixture of colloidal particles (“colloids”) and flexible chain molecules (“linkers”). The linkers have two functional end groups, each of which may bond to one of several sites on the colloids. Due to their flexibility, a significant fraction of linkers can “loop” with both ends bonding to sites on the same colloid instead of bridging sites on different colloids. We use the theory to show that the fraction of linkers in loops depends sensitively on the linker end-to-end distance relative to the colloid bonding-site distance, which suggests strategies for mitigating the loop formation that may otherwise hinder linker-mediated colloidal assembly.
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An articulation point of a connected graph is a point that, if removed, will disconnect the graph into two or more graphs.42 An irreducible graph is free of articulation points. For example, a pair of points or any closed cycle of points is irreducible, but three points bonded collinearly are not irreducible because the middle point is an articulation point.
A ⊆ B denotes that A is a subset of B, including the improper subset A = B.
A partition of set A is a grouping of the elements of A into one or more non-empty sets using every element exactly once. For example, if A = {a, b, c}, then {{a}, {b}, {c}}, {{a}, {b, c}}, {{a, b}, {c}}, {{a, c}, {b}}, and {{a, b, c}} are all partitions of A. P(A) denotes the set of all possible partitions of A. The last partition, into only a single subset {A}, is called an improper partition.
A∖B = {a ∈ A|a ∉ B} denotes the set difference, i.e., all elements that are in A but not in B.
Forgiving some abuse of notation, the label of a single site A should be replaced by a set {A} when it represents a set of bonded sites.
|A| denotes the number of elements in set A.
A ⊂ B denotes that is a proper subset of B, i.e., there is at least one element of B that is not in A so A ≠ B.