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Nanoparticle Handling and Formulation
Published in Ko Higashitani, Hisao Makino, Shuji Matsusaka, Powder Technology Handbook, 2019
Wolfgang Peukert, Stefan Romeis
All nanoparticle systems and applications have in common that the interfacial and surface properties of the particles play a central role. The ratio of van der Waals adhesion forces to particle weight scales with particle diameter x−2 and is, for instance at 1 µm, in the order of 106 (in case of smooth particles in the gas phase). Macroscopic properties can only be tailored by microscopic design of the interfaces. Surface chemistry and physics determine on the one hand the particulate interactions with fluid or solid phases. The types of interactions are van der Waals, electrostatic forces and polarization effects, hydrogen bonds and chemical bonds.42 On the other hand, particle interactions control particle and structure formation. For formulation of (nano-)particulate systems, we start conceptually at the particle surface which “transports” the respective particle interactions, thus leading to the desired structure. Vice versa, structure formation can only be understood by considering the relevant interactions which are determined by the particle surface. This concept is illustrated in Figure 5.24.7 for oxide particles in an aqueous solution. Particle interactions can be understood in the view of well-known DLVO-theory as a superposition of van der Waals and electrostatic double layer forces (see Section 5.24.4). This general concept can also be applied to more complicated and less understood types of interactions, e.g. interactions between polymer-modified particles where entropic and structural effects have to be included as well.
Atomic Force Microscopy
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
Double-layer forces are electrostatic forces that arise from the superposition of the surface charge of the sample and the diffuse layer of ions in solution that are screening the surface charge. Because of thermal motion, the ions in solution do not completely screen the surface charge close to the sample, but rather form a “cloud” away from the surface that screens the surface charge only over a certain thickness of the charge “double layer.” As the ion concentration is increased, more ions are available to screen the charge, and the screening distance is reduced.
Physicochemical Factors in Particle Aggregation
Published in Roger S. Wotton, The Biology of Particles in Aquatic Systems, 2020
Bruce D. Johnson, Kate Kranck, Dwight K. Muschenheim
Electrical double-layer forces arise because surfaces in water are usually ionizable. In air, charges can influence particle motion over distances of many times the particle size. However, in water, the surface charge is balanced by a diffuse layer of counter ions in the solution. The potential energy of repulsion of such electrical double layers can extend appreciable distances into the solution, but this range is reduced with increasing ionic strength. Considerations of the net effect of van der Waals attraction and double-layer repulsion comprise DLVO theory,30 named after Derjaguin, Landau, Verwey, and Overbeek, the originators of the theory. Surfaces approaching in water experience net interactions that are a function of particle geometry, the separation dependence of van der Waals, and electrical double-layer forces. Types of interaction potentials that might occur include: Repulsion at all separations (except at very small separation distances where solvation forces become important). This case corresponds to stability for suspended particles, i.e., at least in theory, aggregation does not occur.Attraction at long distances of separation, repulsion at intermediate distances, and attraction at short distances. For this condition, aggregation can occur in the relatively shallow “secondary minimum” at long separation distances or, if the activation energy barrier can be overcome, in the deep primary minimum. Weak associations are the result of flocculation in the secondary minimum and, while flocculation in the primary minimum is certainly favored thermodynamically, slow flocculation is the result.Attraction at all separations. In this case, rapid flocculation occurs, i.e., all particle collisions result in aggregation.
Stability and collapse of amphiphilic copolymer aggregates in contact with hydrophilic mica surfaces
Published in Journal of Dispersion Science and Technology, 2020
Xin Xu, Bhavna Gupta, Jennifer P. Nguyen, Ruting Jin, Manuel Garcia, Satvinder Kaur, Syed K. Hasan, Arthur C. Watterson, Marina Ruths
Amphiphilic copolymers can form aggregates (core-shell micelles) that fulfill many of the requirements of drug delivery systems. They are more stable than aggregates formed by small surfactant molecules because of their high molecular weight (covalent bonding) and low mobility in the hydrophobic core. This leads to a low critical micelle concentration (CMC) so that many drug-carrying aggregates can be formed with only a small amount of polymer. The copolymers can be tailored to have hydrophilic and hydrophobic regions of different sizes, affecting their solubility in water, overall aggregate shape and size, ability to solubilize hydrophobic, small molecules in their interior, and their long-term stability. The core-shell formation occurs through a complex interplay of intermolecular forces such as hydrophobic interactions, electrostatics (double-layer forces), and hydrogen bonding. A judicious choice of polymers can ensure that the aggregates will release their content slowly as they are hydrolyzed by naturally occurring enzymes in the body.[9,10,14]
Interactions between apolar, basic and acidic model oils and a calcite surface
Published in Journal of Dispersion Science and Technology, 2019
Xiaoyan Liu, Karen L. Feilberg, Wei Yan, Erling H. Stenby, Esben Thormann
It is well-known that the exact magnitudes of the surface potential of the probes are influenced by the ionic strength and pH of the solutions, and while the pH values of the silane solutions used in this study are close to the pH of 1 mM NaCl (5.69), the ionic strength is significantly higher. To this end, we expect the numerical values of the surface potentials at high ionic strength to be lower than the values reported in Table 2. An exact determination of the surface potentials at high ionic strength is however difficult due to the effective screening of electrostatic double layer forces. However, in this study, we only need the qualitative information that the apolar model oil and the acidic model oil probes are negatively charged while the basic model oil probe is positively charge.
Numerical modeling of red blood cell interaction mechanics
Published in Mechanics of Advanced Materials and Structures, 2023
The second part of the study (Figure 4) additionally reveals the effect of electrostatic double layer forces on the cell. The results are presented in the second part of Table 2. Although, as shown in the previous case (Figure 3), the cell tends to adhere to the surface, but under the influence of the electrostatic double layer force (Figure 4) at the same velocity indicated in this study, the cell will not come into contact with the inner surface of the vessel during the interaction. The cell will stop near the surface without reaching it. Although the cell had no physical contact with the surface, it was still deformed due to the effect of the electrostatic double layer force. Such a deformation is characteristic of a soft cell-type material, which in this study has an elastic modulus of 5 kPa (Table 1). Such a phenomenon can be called deformation without contact. The process itself (Figure 4) is close to the case where a cell has contact (Figure 3). Compared to other cases considered (Figures 3 and 5), the maximum value of the repulsive force achieved during cell interaction (Figure 4) is the largest. The force displacement curve has a hysteresis character. Under the action of the adhesion force, the cell will remain at a certain distance from the surface, but without contact. The cell did not completely detach from the surface, the process ended when the detachment took place. The further process, as in the first part, is considered the sticking process, but it occurs when the cell is at a certain distance. The sticking process is not considered in this study. A description of the sticking process can be found in Jasevičius and Kruggel-Emden [34], Jasevičius et al. [35].