Controllable Self-Assembly of Amphiphilic Dendrimers on a Silica Surface: The Effect of Molecular Topological Structure and Salinity

The adsorption kinetics and equilibrium of amphiphilic dendrimers based on poly­(amidoamine) modified with a dodecyl chain, G<i>_n</i>QPAMC₁₂ (<i>n</i> represents the generation number), with different generation numbers at a silica–water interface have been investigated. The effect of molecular shape with different charge characteristics on the adsorption kinetics, adsorption isotherms, and the conformation of a self-assembled layer has been elucidated. For the adsorption kinetics, two steps were observed including the adsorption of individual molecules at concentrations below the critical micelle concentration (cmc) and the predominant adsorption of aggregates above the cmc. However, the adsorption isotherm, as a function of the generation number, presented an exceptional characteristic, in which a decrease in adsorption mass with different levels occurred in a high generation of amphiphilic dendrimers, depending on the balance of hydrophobic interaction and electrostatic repulsion. Atomic force microscopy imaging showed that flattened films with pores (spacing) of various shapes and roughness of 3–4 nm were formed, of which the pores (spacing) decreased obviously as the generation number increased. The addition of electrolyte (NaBr) has a great effect on the film morphology formed by the G₃QPAMC₁₂ dendrimer adsorbed at the silica–water interface, showing that the film became closer with smaller pores with increased NaBr concentration

Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Modulation of the fibrillogenesis of amyloid peptide Aβ(1−40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) has been studied. Both UV−vis and AFM results show that C12C6C12Br2 monomers can promote the fibrillogenesis of Aβ(1−40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Aβ(1−40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Aβ(1−40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Aβ(1−40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the α-helix to β-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Aβ(1−40) aggregates also vary upon increasing C12C6C12Br2 concentration

Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Modulation of the fibrillogenesis of amyloid peptide Aβ(1−40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) has been studied. Both UV−vis and AFM results show that C12C6C12Br2 monomers can promote the fibrillogenesis of Aβ(1−40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Aβ(1−40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Aβ(1−40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Aβ(1−40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the α-helix to β-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Aβ(1−40) aggregates also vary upon increasing C12C6C12Br2 concentration

Aggregation Properties of a Novel Class of Amphiphilic Cationic Polyelectrolytes Containing Gemini Surfactant Segments

A novel class of amphiphilic cationic polyelectrolytes, poly(A-co-G)s, comprising of gemini type surfactant segment 1,3-bis(N,N-dimethyl-N-dodecylammonium)-2-propylacrylate dibromide (G) and acryloyloxyethyl trimethyl ammonium chloride (A), were synthesized. Their aggregation properties were investigated by employing fluorescence spectroscopy, dynamic light scattering, transmission electron microscopy, and ζ-potential measurements. For comparison, a series of polyelectrolytes containing a traditional single alkyl chain surfactant unit (acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide (D)), poly(A-co-D)s, were also synthesized and investigated. It was found that the critical aggregation concentration (cac) of poly(A-co-G)s is much lower than that of poly(A-co-D)s. The huge interpolymer aggregates (with a hydrodynamic radius of >450 nm) occur in poly(A-co-G)s aqueous solution, and the size of aggregates increases with the increase of the molar content of the gemini-type surfmer segment and the concentration of the copolymer. The size of aggregates in poly(A-co-D)s aqueous solution is much smaller than poly(A-co-G)s, which also increases with the increase of the molar content of the single alkyl chain surfmer segment and the concentration of the copolymer. The results of aggregation number and charge density of aggregate in poly(A-co-G)s and poly(A-co-D)s indicate that the copolymers have a strong tendency toward interpolymer aggregation and the aggregates in poly(A-co-G)s are much more compact than those of poly(A-co-D)s. These results are interpreted in terms of the synergistic effects of double hydrophobic chains on the gemini surfactant unit

Self-Aggregation of Amphiphilic Dendrimer in Aqueous Solution: The Effect of Headgroup and Hydrocarbon Chain Length

The self-aggregation of amphiphilic dendrimers G₁QPAMC_<i>m</i> based on poly­(amidoamine) PAMAM possessing the same hydrophilic group but differing in alkyl chain length in aqueous solution was investigated. Differences in the chemical structures lead to significant specificities in the aggregate building process. A variety of physicochemical parameters presented monotonous regularity with the increase in alkyl chain length in multibranched structure, as traditional amphiphilic molecules. A significant difference, however, existed in the morphology and the microenvironment of the microdomain of the aggregates, with G₁QPAMC_<i>m</i> with an alkyl chain length of 16 intending to form vesicles. To obtain supporting information about the aggregation mechanism, the thermodynamic parameters of micellization, the free Gibbs energy Δ<i>G</i>_mic, and the entropy Δ<i>S</i>_mic were derived subsequently, of which the relationship between the hydrophobic chain length and the thermodynamic properties indicated that the self-assembly process was jointly driven by enthalpy and entropy. Other than traditional surfactants, the contribution of enthalpy has not increased identically to the increase in hydrophobic interactions, which depends on the ratio of the alkyl chain length to the radius in the headgroup. Continuous increases in the hydrophobic chain length from 12 to 16 lead to the intracohesion of the alkyl chain involved in the process of self-assembly, weakening the hydrophobic interactions, and the increase in −Δ<i>H</i>_mic, which offers an explanation of the formation of vesicular structures

Dilational Properties of Novel Amphiphilic Dendrimers at Water–Air and Water–Heptane Interfaces

In this work, a series of novel amphiphilic dendrimers taking polyamidoamine dendrimer as the core with different hydrophobic tails QPAMC_m were synthesized and the dilational properties were studied as monolayers by dilational rheological measurements at the water–air and water–<i>n</i>-heptane interfaces to explore the nature of adsorption behaviors. The results showed that the maximum values of the dilational modulus seemed to have no obvious variation in a wide change of hydrophobic chain length at the surface. However, there was considerable variability in the tendency of the influence of bulk concentration on the dilational modulus at the two different interfaces. It was interestingly found that the diffusion-exchange process slowed down with the increase of alkyl chain length leading to more elastic nature of adsorption film, which was contrary to the tendencies of conventional single chain and gemini surfactants. It is reasonable to consider that, in the case of the molecule having short chain length such as QPAMC₈, the alkyl chains are too short to overlap across the headgroup, enable the intermolecular hydrophobic interaction to be predominant with increasing of surface concentration, which enhances the elasticity and shows the slowest diffusion-exchange process. Whereas, when the chain length increases to 12 or 16, the alkyl chains are long enough to act intramolecularly to form intracohesion conformation, which results in enhancing the diffusion-exchange process. In conclusion, the interfacial behaviors are dictated by the size ratio between the tail and headgroup. A reasonable model with respect to the molecular interaction was proposed on the basis of experimental data. The results of interfacial tension relaxation and dynamic light scattering (DLS) experiments, in accord with the proposed mechanism, also present the unusual tendency comparing to the traditional single or gemini surfactants

Coexistence of Antiadhesion Performance, Intrinsic Stretchability, and Transparency

Antiadhesion performance, stretchability, and transparency are highly desirable properties for materials and devices in numerous applications. However, the existing strategies for imparting materials with antiadhesion performance generally induce rigidity and opacity, and principle is yet to be provided for designing materials that combine these important parameters. Here, we show that four factors including a low surface energy, appropriate cross-linking, availability of a homogeneous and amorphous composite, and a smooth material surface can be used to design an intrinsically stretchable and transparent polymer film with antiadhesion performance against various liquids including water, diiodomethane, hexadecane, cooking oil, and pump oil. The film can be obtained via simply molding a waterborne polymer network at ambient temperature. Furthermore, the film can retain its antiadhesion performance and outstanding transparency even when it is subjected to large mechanical deformations reaching up to 1800%, and its maximal fracture strain exceeds 3000%. These design concepts offer a general platform for achieving multiple material functionalities, and may open new avenues for the surface functionalization of stretchable materials and devices

Coexistence of Antiadhesion Performance, Intrinsic Stretchability, and Transparency

Antiadhesion performance, stretchability, and transparency are highly desirable properties for materials and devices in numerous applications. However, the existing strategies for imparting materials with antiadhesion performance generally induce rigidity and opacity, and principle is yet to be provided for designing materials that combine these important parameters. Here, we show that four factors including a low surface energy, appropriate cross-linking, availability of a homogeneous and amorphous composite, and a smooth material surface can be used to design an intrinsically stretchable and transparent polymer film with antiadhesion performance against various liquids including water, diiodomethane, hexadecane, cooking oil, and pump oil. The film can be obtained via simply molding a waterborne polymer network at ambient temperature. Furthermore, the film can retain its antiadhesion performance and outstanding transparency even when it is subjected to large mechanical deformations reaching up to 1800%, and its maximal fracture strain exceeds 3000%. These design concepts offer a general platform for achieving multiple material functionalities, and may open new avenues for the surface functionalization of stretchable materials and devices

In Situ Investigation on the Effect of Salinity and pH on the Asphaltene Desorption under Flowing Conditions

There is a limited understanding of the microscale interactions between fluid–oil–solid interfaces, which could be a stumbling block to the development of relevant technologies and industries. With this in mind, we applied an in situ method, quartz crystal microbalance with dissipation (QCM-D), on the interactions among the fluid–oil–solid phases and investigated the desorption process of the asphaltene model molecule from silica surfaces during a flow of LSW at the conditions of different ion types, salinities, or pH values. The salinity effect plays a bigger role than that of the pH effect on the asphaltene desorption and, furthermore, the divalent ions (such as SO42–, Mg2+, or Ca2+) show a stronger effect than that of monovalent ions (such as Cl–, Na+, or K+). Our study provides a new strategy for the investigation of the interactions between fluid–oil–solid interfaces

Coexistence of Antiadhesion Performance, Intrinsic Stretchability, and Transparency

Antiadhesion performance, stretchability, and transparency are highly desirable properties for materials and devices in numerous applications. However, the existing strategies for imparting materials with antiadhesion performance generally induce rigidity and opacity, and principle is yet to be provided for designing materials that combine these important parameters. Here, we show that four factors including a low surface energy, appropriate cross-linking, availability of a homogeneous and amorphous composite, and a smooth material surface can be used to design an intrinsically stretchable and transparent polymer film with antiadhesion performance against various liquids including water, diiodomethane, hexadecane, cooking oil, and pump oil. The film can be obtained via simply molding a waterborne polymer network at ambient temperature. Furthermore, the film can retain its antiadhesion performance and outstanding transparency even when it is subjected to large mechanical deformations reaching up to 1800%, and its maximal fracture strain exceeds 3000%. These design concepts offer a general platform for achieving multiple material functionalities, and may open new avenues for the surface functionalization of stretchable materials and devices