<p>The impact of molecular level surface chemistry for aerosol water-uptake and droplet growth is not well understood. In this work, spherical, non-porous, monodisperse Polystyrene Latex particles treated with different surface functional groups are exploited to isolate the effects of aerosol surface chemistry for droplet activation. PSL is effectively water-insoluble and changes in the particle surface may be considered a critical factor in the initial water-uptake of water insoluble material. The droplet growth of two surface modified types of PSL (PSL-NH<sub>2</sub> and PSL-COOH) along with plain PSL was measured in a supersaturated environment with a Cloud Condensation Nuclei Counter (CCNC). Three droplet growth models - traditional Köhler (TK), Flory-Huggins Köhler (FHK) and the Frenkel-Halsey-Hill adsorption theory (FHH-AT) were compared to experimental data. The experimentally determined single hygroscopicity parameter, <em>κ</em>, was found in the range from 0.002 to 0.04. The traditional Köhler prediction assumes Raoult’s law solute dissolution and underestimates the water-uptake ability of the PSL particles. FHK can be applied to polymeric aerosol; however, FHK assumes the polymer is soluble and hydrophilic. Thus, the FHK model generates a negative result for hydrophobic PSL and predicts non-activation behavior that disagrees with the experimental observation. The FHH-AT model assumes that a particle is water-insoluble and can be fit with 2 empirical parameters (<em>A<sub>FHH</sub></em><sub> </sub>and <em>B<sub>FHH</sub></em>). The FHH-AT prediction agrees with the experimental data and can differentiate the water uptake behavior of the particles due to surface modification of PSL surface. PSL-NH<sub>2</sub> exhibits slightly higher hygroscopicity than the PSL-COOH, while plain PSL is the least hygroscopic among the three. This result is consistent with the polarity of surface functional groups and their affinity to water molecules. Thus, changes in <em>A<sub>FHH</sub></em><sub> </sub>and <em>B<sub>FHH</sub></em> can be quantified when surface modification is isolated for the study of water-uptake. The fitted AFHH for PSL-NH<sub>2</sub>, PSL-COOH and plain PSL is 0.23, 0.21 and 0.18 when <em>B<sub>FHH</sub></em> is unity. To simplify the use of FHH-AT for use in cloud activation models, we also present and test a new single parameter framework for insoluble compounds, <em>κ<sub>FHH</sub></em>. <em>κ<sub>FHH</sub></em> is within 5 % agreement of the experimental data and can be applied to describe a single-parameter hygroscopicity for water-insoluble aerosol with surface modified properties.</p>