ACHIEVEMENTS IN THE METHODS OF CHARACTERIZING COLLOIDS

Colloid chemistry arose in the middle of the 19th century. In 1861, the famous English chemist T. Graham carried out extensive diffusion of various substances in aqueous solutions. He discovered that some substances (gelatin, agar-agar, etc.) diffuse in water many times slower than, for example, solids and acids. In addition, these substances did not crystallize when the solutions were supersaturated, forming a gelatinous sticky mass. In ancient Greek, glue is called “kolla”, and Graham called these “special” substances “colloids”. This is how the name of the science appeared – colloid chemistry. Based on his experiments, Graham put forward a very bold hypothesis about the existence in nature of two diametrically opposite classes of chemical substances – “crystalloids” and “colloids”. This idea attracted great interest from many scientists, and at the beginning of the 19th century, colloid chemistry began to develop very quickly and fruitfully, with the main focus being on chemical aspects. During these years, many substances with colloidal properties were discovered. At the same time, various methods for purifying and preserving colloids (inorganic, molecular and protein substances) were developed, original and highly sensitive methods for studying colloids were created to measure the size of dispersed particles, the surface tension of pure liquids and solutions, the rate of electrophoresis and a number of other parameters of colloidal systems. However, as more and more new colloidal systems were discovered, Graham’s system lost its appeal. It was replaced by the concept of the universality of the colloidal (dispersed) state. The experimental work of P.P. Weimarn (1906-1910), a professor at the St. Petersburg Mining Institute, played a decisive role in its approval. It has been shown in many examples that even typical colloids (e.g. gelatin) can be isolated in crystalline form and, conversely, a colloidal solution (e.g. table salt in benzene) can be prepared from “crystalloid” substances. Based on these results, Weimarn put forward the following proposition: “The state is not determined by any features of the composition of the substance; on the contrary, it has been proven that colloids can be spoken of as solid, liquid, gaseous, soluble and insoluble substances. When determining the conditions of each substance, “can be in a colloidal state.” Colloidal systems are physical and chemical mixtures. These are dispersed systems, usually two-component, with the appearance of physical homogeneous systems, although in the procedure the two components do not move between each other molecularly. The concept of “colloidal” refers to the order of sizes of molecules dispersed in a certain medium, when this molecule has a diameter of approximately 1 to 100 nm. These include, for example, solutions of substances such as peptides, proteins, starches and synthetic polymers. The surface area of ​​the contacting phases can be a macroscopic value.

Advancements in colloid characterization techniques have significantly enhanced our understanding of colloidal systems, leading to innovations across various fields such as materials science, pharmaceuticals, and environmental science. One notable technique is Dynamic Light Scattering (DLS), which has been widely employed to measure the size distribution of nanoparticles in colloids. Recent improvements in DLS have increased its sensitivity and accuracy, enabling the characterization of smaller particles and more complex systems. Enhanced data analysis algorithms have also been developed to better differentiate particle sizes in polydisperse samples.

Another transformative advancement is Cryo-Electron Microscopy (Cryo-EM), which allows researchers to visualize samples at near-atomic resolution without the need for staining or fixation. This capability is particularly beneficial for studying biological colloids, such as proteins and viruses, providing valuable insights into their structure and interactions.

Atomic Force Microscopy (AFM) has also seen significant advancements, offering high-resolution imaging and force measurements at the nanoscale. Innovations in AFM techniques, such as force spectroscopy and imaging in liquid environments, facilitate a more comprehensive understanding of colloidal interactions, surface properties, and particle behavior.

Nanoparticle Tracking Analysis (NTA) is another critical method that provides real-time analysis of particle size and concentration by tracking the Brownian motion of individual nanoparticles. This technique is increasingly important for characterizing complex colloidal systems, especially those used in drug delivery applications.

Rheology techniques assess the flow and deformation of colloidal systems, offering insights into their viscoelastic properties. Recent advancements in rheological studies have enabled researchers to examine non-Newtonian behavior in colloids, which is crucial for applications in food science and cosmetics.

Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) are powerful techniques for studying the structural characteristics of colloids at the nanoscale. Improvements in beamlines and detector technologies have enhanced the resolution and data quality of these techniques, facilitating studies on complex colloidal structures.

Surface Plasmon Resonance (SPR) is used to study interactions at the colloidal surface, such as binding events between nanoparticles and biomolecules. Recent innovations in SPR technology, including portable devices and real-time monitoring capabilities, have broadened its applicability in colloidal research.

Mass spectrometry techniques have also evolved, with innovative methods like imaging mass spectrometry allowing researchers to analyze the composition of colloidal systems. These techniques enable the identification and quantification of different components within complex mixtures.

Advanced microscopy techniques, such as super-resolution fluorescence microscopy and hyperspectral imaging, provide detailed insights into the distribution and dynamics of colloidal particles at the nanoscale. These methods allow researchers to explore interactions and behaviors that were previously inaccessible.

Finally, advancements in computational modeling techniques, including molecular dynamics simulations and Monte Carlo methods, complement experimental approaches. These computational tools predict the behavior of colloidal systems under various conditions, leading to a deeper understanding of stability and interactions.

Together, these advancements in characterization techniques have opened new avenues for research and application in colloid chemistry. As technologies continue to improve and integrate, they promise to provide richer and more nuanced insights into the behavior and properties of colloidal systems, driving innovation across multiple disciplines.

1. Graham, T. (1861). On the diffusion of liquids and gases. Philosophical Transactions of the Royal Society of London, 151, 109-139.
2. Weimarn, P. P. (1910). Experimental studies on colloidal systems. Journal of Physical Chemistry, 14, 1167-1187.
3. Berg, J. M., Tymoczko, J. L., & Stryer, L. (2012). Biochemistry. W.H. Freeman and Company. (This book provides context for the biochemical aspects of colloids.)
4. Sperling, L. H. (2006). Introduction to Physical Polymer Science. Wiley-Interscience. (This source discusses colloids in the context of polymer science.)

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