11/28/2023 0 Comments Cnf pickering emulsion modeling![]() ![]() Microgel “bottom-up” preparation methods can be further classified into those formed by homogeneous nucleation, emulsification and complex formation (Pelton and Hoare 2011), each of which will be briefly discussed below. 2008 Dendukuri and Doyle 2009 Pich and Richtering 2010). Some examples of microgel synthesis will be briefly described below, however we refer readers to comprehensive reviews for a more detailed discussion of these aspects (Saunders and Vincent 1999 Ballauff and Lu 2007 Burey et al. Different approaches may be preferred depending on the level of control required during synthesis and the nature of the polymeric material but, generally, a specific distribution of a functional groups, a narrow microgel size distribution and high colloidal stability are desired (Pelton and Hoare 2011 Agrawal and Agrawal 2018). The former routes (i and ii) are often referred to as “bottom-up” and the latter (iii) as “top-down” approaches (Torres et al. It is important to distinguish between the terms “macrogel” and “microgel” at this stage: macrogel refers to a large, cross-linked structure or “a bowl of jelly,” whilst microgels are discrete particles (illustrated in Fig. 1b: (i) from monomer (ii) from polymer (iii) from macrogel (Pelton and Hoare 2011). Three general approaches to microgel synthesis, as defined by Pelton et al., are given in Fig. 2018), medicine (Agrawal and Agrawal 2018), and agriculture (Abd El-Rehim 2005). This is reflected by the huge potential impact of microgels in a wide variety of industries, such as food (Murray 2019a), cosmetics (Boularas et al. Although they may aggregate to different extents in ‘solution,’ the polymer network remains stable.Īltering the synthetic method and conditions of formation allows one to access to a broad range of gel particles with specific morphologies, sizes and microstructures, depending on the desired application. Unlike surfactant micelles and other self-assembling molecular aggregates, they have a static composition. In some cases, thermodynamic parameters such as temperature and pH can be used to control their degree of swelling (DOS) and such microgels are often referred to as “intelligent” or “responsive,” since they may shrink and expand in response to an external stimulus (Fig. Their swelling ‘state’ is to an extent governed by the cross-link density, polymer/solvent compatibility and the presence (or not) of electrical charges (Pelton and Hoare 2011). Microgels are made up of a covalently, or strong physically cross-linked polymer network that must be dispersed in and swollen by the solvent. They are often now referred to as “colloidal dispersions of gel-like particles”, in which each individual microgel exists as a long-lived, kinetically stable particle (Dickinson 2015). Originally, the term microgel was introduced in 1949, with the word “micro” referring to the gel particle size and “gel” meaning the ability of the particles to swell in organic solvents (Baker 1949 Pelton and Hoare 2011). Microgel particles (also referred to as “microgels”) are a class of soft colloidal species which are receiving increasing interest in the area of emulsion stabilisation (Dickinson 2015). A brief overview of cellulose processing is also given, describing the dissolution and reprecipitation routes used to functionalise cellulose without covalent modification and the potential for cellulose particles and CMGs to act as O/W and W/O emulsion stabilisers. This review aims to summarise some of the recent progress made in the microgel field including their ability to act as emulsion stabilisers, with a focus on cellulose microgels (CMGs). Furthermore, the surface activity of cellulose has proven difficult to harness and therefore its ability to act as an emulsion stabiliser has been almost exclusively applied to oil-in-water (O/W) emulsions, with very few reports on its water in oil (W/O) activity. However, its use as a functional material is often somewhat hindered by its insolubility in water and most other organic solvents. Cellulose, being a natural, biodegradable polymer, is an attractive ingredient for gels and microgels. Microgels made with biocompatible polymers such as proteins and polysaccharides in particular offer an environmental advantage and currently form a very active area of research. Classed as soft colloidal particles, their ability to swell to differing degrees in certain solvents and to rearrange once attached to an interface makes them highly suitable for systems requiring long-term stabilization, such as formulations in the food, agricultural, cosmetic and pharmaceutical industries. Microgel particles have recently emerged as an alternative route to emulsion stabilisation. ![]()
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