Surfactant chain length and concentration influence on the interfacial tension of two immiscible model liquids: a coarse-grained approach

Synthesis, surface activity, and corrosion inhibition capabilities of new non-ionic gemini surfactants

Several environmentally acceptable non-ionic gemini surfactants are synthesized in this work using natural sources, including polyethenoxy di-dodecanoate (GSC12), polyethenoxy di-hexadecanoate (GSC16), and polyethenoxy di-octadecenoate (GSC18). The produced surfactants are confirmed by spectrum studies using FT-IR, 1HNMR, and 13CNMR. It explored and examined how the length of the hydrocarbon chain affected essential properties like foaming and emulsifying abilities. Surface tension examinations are used to assess the surface activity of the examined gemini surfactants. The lower value of critical micelle concentrations (0.381 × 10-4M) is detected for GSC18. Their spontaneous character is shown by the negative values of the free energy of adsorption (ΔGads) and micellization (ΔGmic) which arranged in the order GSC18 > GSC16 > GSC12. Based on theoretical, weight loss, and electrochemical investigations, these novel surfactants were investigated for their possible use in inhibiting carbon steel from corroding in 1 M HCl. Measuring results show that GSC18 inhibits corrosion in carbon steel by 95.4%. The isotherm of adsorption evaluated for the investigated inhibitors and their behavior obeys Langmuir isotherm.

The effect of changing the molecular structure of the surfactant on the dissolution of lamellar phases

Dissolution processes of surfactants, especially when in the lamellar phase, into water are important for product formulation. Understanding this process at a molecular level will help to enhance product design and control surfactant processes. The main goal of this study is to examine the effect of different lengths of surfactants and the hydrophobic to hydrophilic ratio on the dissolution process of surfactants. To achieve this goal dissipative particle dynamic (DPD) simulations were used. Lamellar equilibrium simulations were carried out for different surfactant chain lengths at 80 vol% with water. The surfactant chains were each run in a simulation box of dimensions 20 × 20 × 20 until equilibrium was reached. The lamellar phase formed for all different surfactant chain lengths and, after the initial equilibrium the surfactant systems were then simulated with a water box for dissolution. The dissolution process was tracked by visual analysis, local concentration analysis, micelle size, and a zonal model to calculate the diffusion parameter. Results show that as the surfactant chain length increased by adding more of the hydrophobic beads, the dissolution process slowed down. Increasing the hydrophilic part of the surfactant speeds up the dissolution process, but the effect of adding more of the hydrophobic part is greater than the effect of adding more of the hydrophilic part on the dissolution process.

Effect of sequence distribution of block copolymers on the interfacial properties of ternary mixtures: a dissipative particle dynamics simulation

In this paper, the dissipative particle dynamics (DPD) simulations method is used to study the effect of sequence distribution of block copolymers on the interfacial properties between immiscible homopolymers. Five block copolymers with the same composition but different sequence lengths are utilized for simulation. The sequence distribution is varied from the alternating copolymer to the symmetric diblock copolymer. Our simulations show that the efficiency of the block copolymer in reducing the interfacial tension is highly dependent on both the degree of penetration of the copolymer chain into the homopolymer phase and the number of copolymers at the interface per area. The linear block copolymers AB with the sequence length of τ = 8 could both sufficiently extend into the homopolymer phases and exhibit a larger number of copolymers at the interface per area. Thereby the copolymer with the sequence length τ = 8 is more effective in reducing the interfacial tension compared to that of diblock copolymers and the alternating copolymers at the same concentration. This work offers useful tips for copolymer compatibilizer selection at the immiscible homopolymer mixture interfaces.

In this paper, the dissipative particle dynamics (DPD) simulations method is used to study the effect of sequence distribution of block copolymers on the interfacial properties between immiscible homopolymers.

Water/oil interfacial tension reduction - an interfacial entropy driven process

The interfacial tension (IFT) of a fluid-fluid interface plays an important role in a wide range of applications and processes. When low IFT is desired, surface active compounds (e.g. surfactants) can be added to the system. Numerous attempts have been made to relate changes in IFT arising from such compounds to the specific nature of the interface. However, the IFT is controlled by an interplay of factors such as temperature and molecular structure of surface-active compounds, which make it difficult to predict IFT as those conditions change. In this study, we present the results from molecular dynamics simulations revealing the specific role surfactants play in IFT. We find that, in addition to reducing direct contact between the two fluids, surfactants serve to increase the disorder at the interface (related to interfacial entropy) and consequently reduce the water/oil IFT, especially when surfactants are present at high surface density. Our results suggest that surfactants that yield more disordered interfacial films (e.g. with flexible and/or unsaturated tails) reduce the water/oil IFT more effectively than surfactants which yield highly ordered interfacial films. Our results shed light on some of the factors that control IFT and could have important practical implications in industrial applications such as the design of cosmetics, food products, and detergents.

DPD Study on the Interfacial Properties of PEO/PEO-PPO-PEO/PPO Ternary Blends: Effects of Pluronic Structure and Concentration

Using the method of dissipative particle dynamics (DPD) simulations, we investigated the interfacial properties of PEO/PEO-PPO-PEO/PPO ternary blends composed of the Pluronics L64(EO₁₃PO₃₀EO₁₃), F68(EO₇₆PO₂₉EO₇₆), F88(EO₁₀₄PO₃₉EO₁₀₄), or F127(EO₁₀₆PO₇₀EO₁₀₆) triblock copolymers. Our simulations show that: (i) The interfacial tensions (γ) of the ternary blends obey the relationship γF68 < γL64 < γF88 < γF127, which indicates that triblock copolymer F68 is most effective in reducing the interfacial tension, compared to L64, F88, and F127; (ii) For the blends of PEO/L64/PPO and the F64 copolymer concentration ranging from c_cp = 0.2 to 0.4, the interface exhibits a saturation state, which results in the aggregation and micelle formation of F64 copolymers added to the blends, and a lowered efficiency of the L64 copolymers as a compatibilizer, thus, the interfacial tension decreases slightly; (iii) For the blends of PEO/F68/PPO, elevating the Pluronic copolymer concentration can promote Pluronic copolymer enrichment at the interfaces without forming the micelles, which reduces the interfacial tension significantly. The interfacial properties of the blends contained the PEO-PPO-PEO triblock copolymer compatibilizers are, thus, controlled by the triblock copolymer structure and the concentration. This work provides important insights into the use of the PEO-PPO-PEO triblock copolymer as compatibilizers in the PEO and PPO homopolymer blend systems.

Effects of Repulsion Parameter and Chain Length of Homopolymers on Interfacial Properties of An/Ax/2BxAx/2/Bm Blends: A DPD Simulation Study

We explored the effects of the repulsion parameter (aAB) and chain length (N_HA or N_HB) of homopolymers on the interfacial properties of A_n/A_x/2B_xA_x/2/B_m ternary polymeric blends using dissipative particle dynamics (DPD) simulations. Our simulations show that: (i) The ternary blends exhibit the significant segregation at the repulsion parameter (aAB = 40). (ii) Both the interfacial tension and the density of triblock copolymer at the center of the interface increase to a plateau with increasing the homopolymer chain length, which indicates that the triblock copolymers with shorter chain length exhibit better performance as the compatibilizers for stabilizing the blends. (iii) For the case of N_HA = 4 (chain length of homopolymers A_n) and N_HB (chain length of homopolymers B_m) ranging from 16 to 64, the blends exhibit larger interfacial widths with a weakened correlation between bead A_n and B_m of homopolymers, which indicates that the triblock copolymer compatibilizers (A_x/2B_xA_x/2) show better performance in reducing the interfacial tension. The effectiveness of triblock copolymer compatibilizers is, thus, controlled by the regulation of repulsion parameters and the homopolymer chain length. This work raises important considerations concerning the use of the triblock copolymer as compatibilizers in the immiscible homopolymer blend systems.

Dissipative Particle Dynamics Study on Interfacial Properties of Symmetric Ternary Polymeric Blends

We investigated the interfacial properties of symmetric ternary A_n/A_mB_m/B_n and A_n/A_m/2B_mA_m/2/B_n polymeric blends by means of dissipative particle dynamics (DPD) simulations. We systematically analyzed the effects of composition, chain length, and concentration of the copolymers on the interfacial tensions, interfacial widths, and the structures of each polymer component in the blends. Our simulations show that: (i) the efficiency of the copolymers in reducing the interfacial tension is highly dependent on their compositions. The triblock copolymers are more effective in reducing the interfacial tension compared to that of the diblock copolymers at the same chain length and concentration; (ii) the interfacial tension of the blends increases with increases in the triblock copolymer chain length, which indicates that the triblock copolymers with a shorter chain length exhibit a better performance as the compatibilizers compared to that of their counterparts with longer chain lengths; and (iii) elevating the triblock copolymer concentration can promote copolymer enrichment at the center of the interface, which enlarges the width of the phase interfaces and reduces the interfacial tension. These findings illustrate the correlations between the efficiency of copolymer compatibilizers and their detailed molecular parameters.

Simulation of GAP/HTPB phase behaviors in plasticizers and its application in composite solid propellant

Dissipative particle dynamics and molecular simulations were carried out to investigate the phase behaviors of glycidyl azide polymer (GAP)/hydroxyl-terminated polybutadiene (HTPB) polymer blend in dioctyl sebacate (DOS), and mixture of DOS and bis(2,2-dinitropropyl)formal/acetal (A3), respectively. The rheology of GAP/HTPB propellant slurry plasticized by A3/DOS was studied. First, single-phase aggregations of GAP and HTPB appear slightly in A3/DOS whereas it is conspicuous in DOS, which results from the small surface tension between the GAP/HTPB plasticized by A3/DOS and the weak thermal diffusion of this blend. Furthermore, with the plasticizing ratio (po/pl) increasing to 1.2, the GAP/HTPB propellant slurry plasticized by A3/DOS exhibits small viscosity and yield stress, and the Newtonian-like behavior of slurry improves its manufacturability. Finally, integral GAP/HTPB-based propellant can be obtained using A3/DOS as plasticizers.