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Colloids Interfaces, Volume 9, Issue 4 (August 2025) – 5 articles

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17 pages, 2732 KiB

Open AccessFeature PaperArticle

Influence of Cellulose Nanocrystals and Surfactants on Catastrophic Phase Inversion and Stability of Emulsions

by Daniel Kim and Rajinder Pal

Colloids Interfaces 2025, 9(4), 46; https://doi.org/10.3390/colloids9040046 - 11 Jul 2025

Viewed by 83

Abstract

This study presents the first quantitative comparison of catastrophic phase inversion behavior of water-in-oil emulsions stabilized by nanocrystalline cellulose (NCC) and molecular surfactants with different headgroup charge types: anionic (sodium dodecyl sulfate referred to as SDS), cationic (octadecyltrimethylammonium chloride referred to as OTAC), nonionic (C12–14 alcohol ethoxylate referred to as Alfonic), and zwitterionic (cetyl betaine referred to as Amphosol). By using conductivity measurements under controlled mixing and pendant drop tensiometry, this study shows that NCC markedly delays catastrophic phase inversion through interfacial jamming, whereas surfactant-stabilized systems exhibit concentration-dependent inversion driven by interfacial saturation. Specifically, NCC-stabilized emulsions exhibited a nonlinear increase in the critical aqueous phase volume fraction required for inversion, ranging from 0.253 (0 wt% NCC) to 0.545 (1.5 wt% NCC), consistent with enhanced resistance to inversion typically associated with the formation of rigid interfacial layers in Pickering emulsions. In contrast, surfactant-stabilized systems exhibited a concentration-dependent inversion trend with opposing effects. At low concentrations, limited interfacial coverage delayed inversion, while at higher concentrations, increased surfactant availability and interfacial saturation promoted earlier inversion and favored the formation of oil-in-water structures. Pendant drop tensiometry confirmed negligible surface activity for NCC, while all surfactants significantly lowered interfacial tension. Despite its weak surface activity, NCC imparted strong coalescence resistance above 0.2 wt%, attributed to steric stabilization. These findings establish distinct mechanisms for governing phase inversion in particle- versus surfactant-stabilized systems. To our knowledge, this is the first study to quantitively characterize the catastrophic phase inversion behavior of water-in-oil emulsions using NCC. This work supports the use of NCC as an effective stabilizer for emulsions with high internal phase volume. Full article

(This article belongs to the Special Issue Rheology of Complex Fluids and Interfaces: 2nd Edition)

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24 pages, 3309 KiB

Open AccessArticle

Optical Investigation of the Combined Effect of pH and Temperature on the Interactions of BSA Protein with Iron Oxide Nanoparticles

by Elena A. Molkova, Ruslan M. Sarimov, Tatyana A. Matveeva, Alexander V. Simakin, Arthur G. Akopdzhanov, Dmitriy A. Serov, Maksim B. Rebezov, Maxim E. Astashev, Konstantin V. Sergienko, Mikhail A. Sevostyanov, Dmitriy O. Khort, Igor G. Smirnov, Alexey S. Dorokhov, Andrey Yu. Izmailov and Sergey V. Gudkov

Colloids Interfaces 2025, 9(4), 45; https://doi.org/10.3390/colloids9040045 - 7 Jul 2025

Viewed by 246

Abstract

The effect of pH and temperature on the interaction of sodium citrate-coated magnetic iron oxide nanoparticles (IONPs) with the BSA protein was studied using optical methods. The optical properties of aqueous colloids of BSA, IONPs, and BSA with IONPs were studied with pH changes in the range of 2–12 and temperature in the range of 25–85 °C. It was found that at pH 2.0, no significant changes in the optical properties were observed with increasing temperature in aqueous colloids containing a mixture of BSA with IONPs. Temperature affects the optical properties of BSA colloids with IONPs in the pH range from 5.0 to 8.0. Moreover, by increasing the temperature at these pH levels, it is possible to control the particle size in the colloids. In general, both temperature and pH have a significant effect on the properties of the aqueous colloid of BSA with IONPs and allow for the control of interactions between BSA and IONPs, namely, the processes of aggregation, particle reclustering, and protein denaturation. Full article

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30 pages, 4213 KiB

Open AccessFeature PaperReview

The Effect of Adsorption Phenomena on the Transport in Complex Electrolytes

by Ioulia Chikina, Michel Beaughon, Pierre Burckel, Emmanuelle Dubois, Ivan T. Lucas, Sawako Nakamae, Ozlem Sel, Hubert Perrot, Régine Perzynski, Thomas J. Salez, Blanca E. Torres-Bautista and Andrey Varlamov

Colloids Interfaces 2025, 9(4), 44; https://doi.org/10.3390/colloids9040044 - 7 Jul 2025

Viewed by 146

Abstract

Over the last decade, numerous impedance studies of the conductivity of suspensions containing colloidal (dielectric, semiconducting or metallic) particles have often led to the conclusion that the well-known Maxwell theory is insufficient to quantitatively explain the properties of these systems. We review some of the most characteristic results and show how the applicability of the Maxwell’s theory can be restored taking into account the adsorption phenomena occurring during AC impedance measurements in nanoparticle suspensions. The latter can drastically change the capacitance of the metal-electrolyte cell boundaries from the standard value, making it strongly dependent on the nanoparticle concentration. This factor significantly affects conductivity measurements through RC circuit characteristics. We present an analysis of available impedance measurement data of the dependence of conductivity on the nanoparticle concentration in this new paradigm. In order to emphasize the novelty and the acute sensitivity of ac-diagnosis to the presence of adsorption phenomena at the metal-electrolyte interface, direct adsorption determinations at such interfaces by using two modern experimental techniques are also presented. The main result of this work is the restoration of Maxwell’s theory, attributing the observed discrepancies to variations in cell conductance. Full article

(This article belongs to the Special Issue Feature Reviews in Colloids and Interfaces)

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16 pages, 1991 KiB

Open AccessArticle

Effect of Dielectric Constant on Interaction Between Charged Macroions in Asymmetric Electrolyte

by Khawla Qamhieh

Colloids Interfaces 2025, 9(4), 43; https://doi.org/10.3390/colloids9040043 (registering DOI) - 1 Jul 2025

Viewed by 192

Abstract

The mean force between two highly like-charged macroions in the presence of monovalent counterions and added multivalent salt within solvents of varying dielectric constants was studied using Monte Carlo simulations. Without additional salt, the mean force is strongly repulsive at all macroion separations [...] Read more.

ϵ_{r}

≥ 30. However, in solvents with

ϵ_{r}

≤ 30, macroions experience effective attraction, indicating that attractive interactions between highly charged macroions can occur even without multivalent salt in nonpolar solvents with low dielectric constants. The total multivalent counterion charge-to-total macroion charge ratio is defined as β which determines the amount of salt that is added to the system. At β = 0.075, the mean force becomes attractive at short separations in solvents with

ϵ_{r}

= 54 containing 1:3 salt, as well as in all solvents with 1:5 salt, while still exhibiting significant repulsion at longer separations. In contrast, for solvents with 1:3 salt and dielectric constants

ϵ_{r}

= 68 and

ϵ_{r}

= 78.4, the mean force turns attractive at a higher salt concentration, around β = 0.225. The shift in the mean force to an attractive state at short separations signifies charge inversion on the macroion surface when a sufficient amount of salt is present. At a stoichiometric ratio of multivalent counterions, long-range repulsion vanishes, and attraction becomes significant. However, with excess salt, the strength of the attractive mean force diminishes. Additionally, the attractive force at a given salt concentration increases as the dielectric constant decreases and is stronger in systems with 1:5 salt than in those with 1:3 salt. Full article

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9 pages, 1292 KiB

Open AccessFeature PaperArticle

Exploring the Feasibility of a Microchip Laser Ablation Method for the Preparation of Biopolymer-Stabilized Gold Nanoparticles: Case Studies with Gelatin and Collagen

by Nazgul Assan, Tomoyuki Suezawa, Yuta Uetake, Yumi Yakiyama, Michiya Matsusaki and Hidehiro Sakurai

Colloids Interfaces 2025, 9(4), 42; https://doi.org/10.3390/colloids9040042 - 20 Jun 2025

Cited by 1 | Viewed by 454

Abstract

Introducing small-sized metal nanoparticles directly into biopolymers susceptible to thermal and chemical stimulations remains a significant challenge. Recently, we showed a novel approach to fabricating gold nanoparticles through pulsed laser ablation in liquid (PLAL) using a microchip laser (MCL). Despite its lower pulse energy compared to conventional lasers, this technique demonstrates high ablation efficiency, offering the potential to produce composites without compromising the distinctive structure of biopolymers. As a proof of concept, we successfully generated gelatin-stabilized gold nanoparticles with a smaller size (average diameter of approximately 4 nm), while preserving the unchanged circular dichroism (CD) spectra, indicating the retention of gelatin’s unique structure. Extending this technique to the preparation of type I collagen-stabilized gold nanoparticles yielded non-aggregated nanoparticles, although challenges in yield still persist. These results highlight the potential of the microchip laser ablation technique for producing metal nanoparticles within a vulnerable matrix. Full article

(This article belongs to the Special Issue State of the Art of Colloid and Interface Science in Asia)

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