Interfacial rheology: An overview of measuring techniques and its role in dispersions and electrospinning

Abstract

Colloidal disperse systems represent the increasing number of modern delivery systems whose primary characteristic, a large interfacial area, causes thermodynamic instability. Therefore, the foremost challenge in dispersion design is the reduction of interface instability and an understanding of the behaviour of interfaces. Interfacial rheology is one of the most powerful tools for observing occurrences at the interphase. As previously mentioned, the stability of such systems is provided by the formation of a stable interfacial layer of surfactants around each dispersible particle. The stability of these systems can be improved by using more than one surfactant, but it must be kept in mind that different surfactants can have varying mechanisms of stabilisation, some of which can be mutually incompatible. Surfactant selection is therefore crucial and must be based on physicochemical properties, stability of the interfacial film, mobility of the molecules in the interfacial film, HLB, film formation kinetics, compatibility and interactions between molecules on the surface, CMC, etc. Interfacial rheological properties have yet to be thoroughly explored. Only recently, methods have been introduced that provide sufficient sensitivity to reliably determine viscoelastic interfacial properties. In general, interfacial rheology describes the relationship between the deformation of an interface and the stresses exerted on it.Due to the variety in deformations of the interfacial layer (shear and expansions or compressions), the field of interfacial rheology is divided into the subcategories of shear and dilatational rheology. While shear rheology is primarily linked to the long-term stability of dispersions, dilatational rheology provides information regarding short-term stability. Interfacial rheological characteristics become relevant in systems with large interfacial areas, such as emulsions and foams, and in processes that lead to a large increase in the interfacial area, such as electrospinning of nanofibers.

Nanofibers and their biomedical use

“…Of the various loading possibilities, physical entrapment is currently the most widespread, since the drug in the nanofibers is protected against unfavorable environmental conditions and it offers good control over the drug release (8). Moreover, incorporation of a drug in nanofibers is relatively easy to perform, since the drug is simply dissolved in the polymer solution prior to electrospinning and the formation of an amorphous drug is favoured due to a very limited time being available for drug recrystallization during the fiber formation (9,11). A typical release profile from such nanofibers exhibits an initial burst effect followed by an almost linear, sustained release (1,5).…”

“…Although various methods, such as self-assembly, phase separation or electrospinning, can be used for their preparation, only the electrospinning technology, which uses high voltage supply to transform a polymer solution into solid nanofibers, is versatile, efficient, widely used and applicative on the industrial scale ( Fig. 3) (10,11).…”

Rheology behaviors of stable electrohydrodynamic direct-write jet

“…Rošic 23 et al reported that the interfacial rheological parameters were determined by polymer concentration, directly affect jet initiation and diameter reducing. Pelipenko 24 et al showed that the interfacial rheological characteristics were relevant in systems with large interfacial areas, which help to decrease the jet diameter and format nanofiber. Since the shorter spinneret to collector distance, EDW charged jet has less relax time to be elongated and refined.…”

Filmes De Langmuir De Ésteres De Polietilenoglicol Derivados De Ácidos Graxos

“…As caraterísticas viscoelásticas do bulk e da interface podem ser avaliadas por meio de vários procedimentos experimentais, dos quais podem se destacar os experimentos de relaxação da tensão, relaxação da deformação e/ou medidas oscilatórias (Pelipenko et al, 2012). Os experimentos oscilatórios permitem avaliar a resposta de fluidos complexos na região viscoelástica linear através da aplicação de um cisalhamento oscilatório de amplitude baixa.…”

“…Neste tipo de medidas, os métodos mais comumente usados são os métodos diretos de rotação em reômetros com geometria cilíndrica concêntrica ou com geometria de cone e placa (PELIPENKO et al, 2012). Neste trabalho, foi utilizado um reômetro HAAKE MARS (Thermo Scientific) com geometria de cone e placa como mostrado na figura 18 para determinar os módulos elástico e viscoso do bulk da solução aquosa de tensioativo.…”