María-Teresa Celis's research while affiliated with University of the Andes (Venezuela) and other places

Publications (11)

Article
Latex emulsions depend strongly on the polymer composition, and particle size distribution, which in turn is a function of the preparation of the latex, and on the formulation and composition variables. This study reports measurements of particle size and particle size distribution of latex emulsions as function of the reaction time and the type an...
Article
The droplet size distribution (DSD) of emulsions is the result of two competitive effects that take place during emulsification process, i.e., drop breakup and drop coalescence, and it is influenced by the formulation and composition variables, i.e., nature and amount of emulsifier, mixing characteristics, and emulsion preparation, all of which aff...
Article
In emulsification processes, the estimation of the droplet size distribution is important data not only because it is linked with the manufacturing process, but also because it is an important parameter affecting the emulsion stability. The aim of this research is to use the ultraviolet-visible transmission spectrum as a tool for emulsion character...
Article
Polymer and copolymer emulsion lattices based on styrene and butyl-metacrylate monomers are commercially important for many paints, adhesives, and coatings applications. The latex properties depend strongly on the copolymer composition, and particle size distribution, which in turn is function of the preparation of the latex and on the formulation...
Article
Emulsification processes results in the generation of droplets populations produced from the dynamic equilibrium between the breakup and coalescence phenomena determined primarily by the formulation and composition variables, mixing characteristics and emulsion preparation. The information contained in the UV-vis spectrum on the absorption and scat...
Article
The properties of the emulsions can be described by the droplet size distribution, which gives a statistical inventory of the dispersed phase fragmentation. This research reports measurements of droplet size distribution from multiwavelength transmission data and estimated of droplet size from electron microscope/osmium tetroxide technique. The qua...
Article
Commercial ethoxylated nonionic surfactant mixtures containing alcohol cosurfactant exhibit a three-phase behavior whose formulation strongly varies with the water/oil ratio. As a consequence, a change in water/oil ratio can result in a sequence of up to three different emulsion inversion processes, through a combination of formulation and composit...
Article
Droplet populations are generated from the dynamic equilibrium between the breakup and coalescence phenomena occurring during the emulsification process. Adequate estimation of the droplet size and droplet size distribution is important, not only because they are related to the manufacturing process but also because the droplet size distribution pr...
Article
In emulsion polymerization, the formation of particles has an important effect on the rate of reaction and on the final properties of the latex. To investigate particle nucleation mechanisms in emulsion polymerization it is necessary to establish the initial conditions of the emulsified system before the reaction takes place. This research reports...
Article
The initial location of the stirrer in the emulsification vessel can induce the resulting emulsion type. The interpretation in terms of mixing phenomena leads to the use of the local water-to-oil ratio (WOR) concept in the formulation-composition map. The know-how associated with this phenomenology allows us to interpret in a straightforward way th...

Citations

... Among other properties, the latex particle size and its distribution, for example, have an influence on the surface properties of the dried polymer film or, alternatively, can provide information about the kinetics of the reaction as well as the number of radicals per particle [13,14]. To obtain knowledge and control of the particle size, it is essential to use the right analytical methods [15,16]. The most common methods for particle size measurements are offline analysis, for example, dynamic light scattering (DLS) or disc centrifuge (DC). ...
... Although homogenization effectively reduced the sizes of oil droplets and the complex coacervates, the absence of an emulsifier resulted in their quick aggregation and larger particle sizes. e presence of Tween 80 decreased the surface tension between the particles and the aqueous medium, thus facilitating the breakup of the particles and preventing their coalescence [55,56]. Increasing the concentration of Tween 80 also decreased the standard deviation (SD) of the coacervate sizes, indicating a more narrow size distribution. ...
... However, the average diameter varies with temperature. UV-Vis absorption spectroscopy was proposed as a useful technique to analyze the behavior of chromophoric emulsifiers depending on experimental parameters such as concentration and temperature [157]. ...
... The information is obtained from the spectroscopy analysis of a sample measured over a broad range of wavelength (190-820 nm), and /or with the scattered light measured at one or several observation angles, which makes possible particles population analysis with sizes ranging from nanometers to micrometers [24,[27][28][29][30][31] . The systematic spectroscopy study over a wavelength range (190-820 nm) and the analysis of emulsions, in terms of the droplet size distribution in the spectral region (300-820 nm), have been successfully obtained to monitor the emulsification process continuously and in real time [24,31,[32][33][34][35][36][37] . These spectroscopy techniques have been accepted with the osmium tetroxide/electron microscope approach [32] . ...
... UV-Vis spectral measurements of hydrocarbons/SDBS/water emulsions in the range 300-820 nm suggested that the dimensions of the droplets were between 1 μm and 20 μm. These studies show the importance of the absorption and scattering properties obtained from the UV-Vis spectra, which give information about droplets' shape, size distribution and chemical composition [158]. ...
... As such, it does not require prior assumptions regarding to the shape of the particle size distribution [24,30,31]. Systematic spectroscopy study over range of wavelength (190-820 nm) and analysis of emulsions, in terms, of droplet size distribution in the spectral region (300-820 nm) have been successfully obtained and applied to the continuous estimation of the droplet size distribution (DSD), and to the assessment of stability of emulsions [23,26,[32][33][34]. In addition, droplet size distributions of styrene and butyl-methacrylate emulsions have also been obtained from multiwavelength spectroscopy measurements and validated with osmium tetroxide/electron microscope techniques [32]. ...
... Stable solutions were supposed to result films of uniform thickness or uniform surface permeability on drying. Films were considered stable if showed non-significant difference (P < 0.05) between optical density of top and bottom layers after standing of 24 h (Celis & Garcia-Rubio, 2004). Polysaccharides when undergoes gelatinization upon stirring and heating results in increased viscosity and thus contributes to stability (Mehyar, Al-Ismail, Han, & Chee, 2012). ...
... The vertical line location, as far as the WOR value is concerned, depends on the emulsification process, particularly the apparatus and the phase viscosities, as well as the method of mixing the oil and water phases [44,316]. ...
... The modeling of the PSD has received a lot of attention in the scientific community due to the difficulties in experimentally measuring the full PSD of a polymeric dispersion ( Celis et al., 2008;Makan et al., 2016 ). There are two predominant model-ing approaches of emulsion polymerization processes, classified by Vale and McKenna (2005) as level-one and level-two models. ...
... It is evident that despite the advances of the last 30 years, a lot of work remains to be done, even to study apparently simple situations, for instance, on what happens with a change in temperature, a variable that can have opposite formulation effects depending on the surfactants (ionic or nonionic), considerable sedimentation alteration through the viscosity and density of liquid, evaporation, and more. Additionally, most of the consistent studies referred to systems that are at equilibrium, with minor considerations for dynamic properties which have been found to be critical in some cases, including delays and hysteresis in phase inversion 222−225 and apparent equilibration times 226,227 which should be taken into consideration to set up a process design. ...