Aqueous suspensions of platinum colloidal nanoparticles of varying size and polydispersity have been produced by ablation of a platinum target with a nanosecond Q-switched Nd:YAG laser. Several laser wavelengths (1064, 532 and 266 nm) and stabilizing agents (citrate and polymers PEG, PVA and PVP) were employed. Laser ablation with the infrared and visible wavelengths leads to spherical amorphous nanoparticles with a bimodal distribution of diameters, featuring a global maximum in the range 5-10 nm and a shoulder extending to 25 nm. Such bimodal distributions plausibly arise from thermal and explosive vaporization mechanisms occurring in different time scales, as proposed in earlier studies.Ultraviolet ablation of Pt at 266 nm, reported here for the first time, produces crystalline nanoparticles of small size (1-4 nm diameter), with a weak onset of larger particles (6-8 nm). The ablation at 266 nm also produced an appreciable yield of large rod-like particles of size ∼ 10 x 70 nm 2 , especially in the presence of PEG and PVA. The Pt nanoparticles served to fabricate films capable of assisting the laser desorption ionization (LDI) of a model peptide. The best analytical performance for LDI mass spectrometric detection was obtained with Pt nanoparticles surface functionalized with citrate and PVA.
The transport properties of colloids in anisotropic media constitute a general problem of fundamental interest in experimental sciences, with a broad range of technological applications. This work investigates the transport of soft spherical colloids in binary mixtures with rod-like particles by means of Monte Carlo and Brownian Dynamics simulations. Layered phases are considered, that range from smectic phases to lamellar phases, depending on the molar fraction of the spherical particles. The investigation serves to characterize the distinct features of transport within layers versus those of transport across neighboring layers, both of which are neatly differentiated. The insertion of particles into layers and the diffusion across them occur at a smaller rate than the intralayer diffusion modulated by the formation of transitory cages in its initial stages. Collective events, in which two or more colloids diffuse across layers in a concerted way, are described as a non-negligible process in these fluids.
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