the new ligands can simply add to, increasing the total ligand coverage. Alternatively, added ligands can displace and coordinate to sites occupied by native surface ligands in a ligand exchange reaction, either maintaining the surface coverage or in some cases reducing total ligand coverage. These factors can be described in the framework of coordination chemistry, where ligands are given L-, X-, and Z-type classifications depending on whether the coordinating ligand donates two, one, or zero electrons, respectively, to form a bond with a surface atom. For example, in cadmium sulfide and indium phosphide quantum dots, carboxylates coordinating to the metal ion surfaces are considered X-type ligands and can be displaced by other X-type ligands such as phosphonates. Similarly, cadmium or indium carboxylates coordinating to an underlying sulfur or phosphorus atom are considered Z-type ligands and can be displaced by other Z-type ligands such as zinc chloride. Previous work to better understand the factors influencing these ligand exchange reactions has utilized a combination of experimental measurements and modeling techniques. Isothermal titration calorimetry can be used to measure the heat of a reaction as one reactant is titrated into another. When applied to exchange reactions with nanocrystals, a solution of colloidally stable nanocrystals can be titrated with a small amount of an exchange ligand to determine the heat of reaction as ligands are exchanged at sites on the nanocrystal surface. These reactions can also be studied using quantitative H NMR measurements, which, when used in combination with measurements of the nanocrystal size and solution concentration, can determine the average the number of bound ligands per nanocrystal at a specific point in an exchange reaction. Several models have been developed to analyze the results from these experimental methods; however, many traditional models are not equipped to handle complex surface interactions. Common isothermal titration calorimetry modeling approaches or isotherm methods, such as the Langmuir isotherm, fail to capture the effects of composition dependent inter-ligand interactions on the surfaces of nanocrystals. As a result, analyses of isothermal titration calorimetry or 1 H NMR measurements alone may lead to inaccurate results. When considering ligand exchange reactions on the surfaces of colloidal nanocrystals, several factors can influence how a reaction occurs. The solvent used to suspend the nanocrystals can influence the equilibrium between ligands on the surface and those free in the solvent, altering how readily two ligands will exchange sites on the nanocrystal surface. The difference in coordination energy between exchanging head groups will greatly influence the extent to which the reaction progresses; however, the tail groups of the ligands can also play a significant role. When ligands pack densely on the surface of a nanocrystal, the internal rotations of the aliphatic chains, or their available dynamic volume, are reduced and van der Waals interactions occur between the ligand tail groups. For example, straight-chained aliphatic tail groups can pack in a denser, more crystalline mannercompared to bent-chain tail groups-leading to greater inter-ligand interactions. Additionally, the length of the aliphatic chain can influence the strength of the van der Waals interactions, where longer aliphatic chains have stronger interactions. Recent work has also demonstrated the effect that nanocrystal curvature can have on the thermodynamics of ligand exchange reactions. Through an analysis with a modified "single set of independent binding sites" model, greater nanocrystal curvature was found to correlate with increased exothermicity and greater spontaneity of the exchange reaction. This finding is attributed to greater surface reactivity and due to the larger angle of separation between the aliphatic chains on higher curvature quantum dots. The larger angle of separation between aliphatic chains leads to a less hindered geometry, making the surface more accessible for ligand exchange. Assuming the angle of separation between the aliphatic chains of ligands does modulate with nanocrystal curvature, as has been observed by H NMR measurements on gold nanoparticles, several other factors may influence reaction thermodynamics. In addition to creating hindered geometries, a smaller angle of separation between aliphatic chains would increase inter-ligand van der Waals interactions and decrease the entropy of surface coordinated aliphatic chains, due to the restriction of internal rotations from a decrease in their available dynamic volume. If the restricted internal rotations of surface ligands are restricted enough, this could result in an ordered organic coordinating ligand shell. We hypothesize that the angle of surface ligand separation, and thus curvature, is the main contributing influence modulating the thermodynamics of ligand exchange reactions on different sized nanocrystals.