The mechanism of nanotriangle formation in multivesicular vesicles (MMV) is investigated by using time-dependent SAXS measurements in combination with UV–vis spectroscopy, light, and transmission electron microscopy. In the first time period 6.5 nm sized spherical gold nanoparticles are formed inside of the vesicles, which build up soft nanoparticle aggregates. In situ SAXS experiments show a linear increase of the volume and molar mass of nanotriangles in the second time period. The volume growth rate of the triangles is 16.1 nm³/min, and the growth rate in the vertical direction is only 0.02 nm/min. Therefore, flat nanotriangles with a thickness of 7 nm and a diameter of 23 nm are formed. This process can be described by a diffusion-limited Ostwald ripening growth mechanism. TEM micrographs visualize soft coral-like structures with thin nanoplatelets at the periphery of the aggregates, which disaggregate in the third time period into nanotriangles and spherical particles. The 16 times faster growth of nanotriangles in the lateral than that in the vertical direction is related to the adsorption of symmetry breaking components, i.e., AOT and the polyampholyte PalPhBisCarb, on the {111} facets of the gold nanoplatelets in combination with confinement effects of the vesicular template phase.

The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering.

Due to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in the presence of Ag⁺ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption.

This review is devoted to recent applications and fundamental aspects of hydrophobic polyampholytes—unique macromolecules containing acid, base, and hydrophobic groups that simulate the behavior of proteins, amphoteric polypeptides, or poly(nucleotides) in solutions. Attention was primarily focused on hydrophobically modified polyampholytes (HMPA), sometimes called hydrophobic polyampholytes or amphoteric “polysoaps.” The dependence of structural, morphological, hydrodynamic, and conformational properties of HMPA on external stimuli such as pH medium, temperature, ionic strength, water-organic solvents is outlined. This work demonstrates the self-assembly of HMPA into micelles, reverse micelles, vesicles, lamellar aggregates, dendrimers, fractal structures, clusters, and other highly organized matters. The self-organization of HMPA at air-liquid, liquid-liquid, and solid-liquid interphase is a key problem for designing Langmuir-Blodgett (LB), layer-by-layer (LbL) films and surface modifications. The preparation and characterization of metal nanoparticles stabilized by HMPA along with applications of HMPA-protected metal nanoparticles in catalysis are summarized. Recent research and applications include HMPA as an enhanced oil recovery (EOR) agent, pour point depressant (PPD), and wax inhibitor. Biomedical and agricultural applications of HMPA, including cryopreservation of living cells by hydrophobic polyampholytes in the clinical practice of reproductive medicine, are outlined. Thus, the systematic analysis of literature data regarding the characterization and application of HMPA inspires other researchers to take new directions and viewpoints on this exclusive and exciting subject.