Unexpectedly high amounts of aminium salts have been detected in ambient aerosol particles, prompting investigations into their role in new particle formation and nanoparticle growth. Amine uptake and particle-phase processes, including the effects of phase state and non-ideal mixing, are poorly understood. In this study, we conducted kinetic multi-layer modeling of dimethylamine (DMA) uptake by crystalline and aqueous ammonium sulfate (AS) and mixed ammonium sulfate-sucrose particles based on measurements at different relative humidity (RH) values. The temporal evolution of particle mass increases and the humidity dependence were successfully reproduced by considering the amine/ammonium exchange reaction and formation of hygroscopic dimethylaminium sulfate. Thermodynamic equilibrium predictions suggest that aqueous sucrose and AS mixtures undergo phase separation at RH < 94%. The kinetic model simulations reveal that DMA uptake is limited by diffusion of DMA and AS through a viscous sucrose-rich shell at lower RH, resulting in strong concentration gradients in the particle bulk. The model predicts that the true uptake coefficients would range from 2.0 × 10-5 to 2.6 × 10-3 for initially solid particles at low RH, while they can be as high as 0.70-0.82 in aqueous particles at high RH. Uptake coefficients increase when RH and associated particle water content increase, while they generally decrease when the molar fraction of sucrose increases at a specific value of RH. Using new measurements of ambient amines from the Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) field campaign as a reference, the model is extrapolated to particles with a diameter of 30 nm and amine mixing ratios in the ppt range to emulate atmospheric conditions. At 70% RH or higher with particles in the liquid phase, amine uptake can lead to a mass increase of approximately 20-60%.