Search results for "Cloud point"
showing 10 items of 33 documents
Pressure Effects on the Thermodynamics oftrans-Decahydronaphthalene/Polystyrene Polymer Solutions: Application of the Sanchez-Lacombe Lattice Fluid T…
2003
The cloud-point temperatures (T-cl's) of trans-decahydronaphthalene(TD)/polystyrene (PS, (M) over bar (w) = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1-16degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol.-% polymer). The system phase separates upon cooling and T-cl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T-phi plane (where phi signifies volume fractions). The clo…
Shear influence on the phase separation of oligomer blends
1994
Shear influences on the phase separation behaviour of four different blends of ethylene glycol/propylene glycol oligomers, exhibiting upper critical solution temperatures, were investigated. Cloud point curves at rest (turbidity measurements) are reported for all systems, spinodal conditions (light scattering) and tie-lines (analysis of the coexisting phases) are given for some examples. Phase diagrams under shear were obtained from rheological data. They demonstrate that the demixing temperatures of systems where both glycols bear OH end-groups are lowered up to ca. 1°C by shear rates of 1000s−1; the critical composition, generalized to the non-equilibrium conditions of flow, is markedly s…
Surfactant Association: Recent Theoretical and Experimental Developments
1991
A theoretical model describing the association of ionic surfactants into rod-shaped micelles is combined with an approximate formula for the viscosity increase induced by rod-shaped aggregates. It is shown that most of the thermodynamic parameters of the association model can be obtained from viscosity measurements. The approach is applied to micellar solutions of hexadecylpyridinium salts. The pronounced effect of counter-ion concentration on the growth of rod-shaped micelles can be attributed to a slightly higher degree of counter-ion association in the cylindrical part than in the end portions. An attempt is made to explain the finding that the degree of counter-ion association is virtua…
Surfactant-based enrichment of rare earth elements from NdFeB magnet e-waste: Optimisation of cloud formation and rare earths extraction
2023
Appropriate waste and resource management are essential for a sustainable circular economy with reduced environmental impact. With critical resources, e-waste may serve as indirect raw material. For example, with NdFeB permanent magnets, Neodymium (Nd) and the co-present Dysprosium (Dy) are critical rare earth elements (REEs). However, there exists no economically viable technology for recycling them from electronic waste (e-waste). Here, a method is presented based on cloud point extraction (CPE). The work involves basic complexation chemistry in a cloud medium with pure REE salts, as well as, with real NdFeB-magnets (nearly 28% REE content by weight) from an old hard disk drive (5.2 g mag…
Interpolymer complex between hydroxypropyl cellulose and maleic acid-styrene copolymer: phase behavior of semi-dilute solutions.
2005
Summary: The phase behavior of a water/hydroxypropyl cellulose/maleic acid–styrene copolymer (H2O/HPC/MAc-S) system was investigated in the semi-dilute range by turbidimetry, rheology, and optical microscopy. The two polymers under investigation form interpolymer complexes via hydrogen bonding. In the case of a total polymer concentration of cpol = 5 mg · mL−1 a second phase segregates upon heating the homogeneous ternary system. By applying a constant shear rate ( = 50 s−1) the phase separation temperature of the system is 10–15 °C lower than for an unsheared one. For cpol = 10 mg · mL−1 phase separation has already occurred at room temperature when the two binary polymer solutions are mix…
Phase separation of polymer blends in solution: A case study
2016
Abstract The phase behavior and phase separation features of the quaternary system poly- l -lactide (PLLA)/poly-rac-lactide (PLA)/dioxane/water were investigated. Experiments were performed with fixed total polymer concentration of 6 wt%, by varying the PLLA/PLA weight ratio. Blend weight compositions examined were 100/0, 80/20, 50/50, 20/80 and 0/100, at fixed dioxane/water weight ratio (87/13). Cloud point measurements reported that the demixing temperatures of blends are close to PLLA in the same mixed solvent, in line with the calculated spinodals. As regards to foam preparation, above the PLA cloud point, morphology is similar to pure PLLA foams; conversely, below PLA cloud point, the …
Evidence of Mechanisms Occurring in Thermally Induced Phase Separation of Polymeric Systems
2014
Thermally induced phase separation is a fabrication technique for porous polymeric structures. By means of easy-to-tune processing parameters, such as system composition and demixing temperature, a vast latitude of average pore dimensions, pore size distributions, and morphologies can be obtained. The relation between demixing temperature and morphology was demonstrated via cloud point curve measurement and foams fabrication with controlled thermal protocols, for the model system poly-l-lactide–dioxane–water. The morphologies obtained at a temperature lower than cloud point showed a closed-pore architecture, suggesting a “nucleation-and-growth” separation mechanism, which produced larger po…
UCST-type behavior of poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) in aliphatic alcohols: solvent, co-solvent, molecular weight, a…
2011
Poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) is shown to possess insoluble–soluble transitions (UCST-type phase behavior) in a large variety of aliphatic alcohols. Samples of different molecular weights ranging from 5 kg mol−1 to 23 kg mol−1 prepared by the RAFT process and featuring different end groups at each end were analyzed by cloud point measurements. Transitions occurred sharply and were fully reversible. The UCST was found to increase with an increasing molecular weight. Hydrophobic (alkyl chain) end groups were found to lower the critical temperature in isopropanol, while rigid aromatic end groups raised the transition temperature. In ternary mixtures of isoprop…
PNIPAM Copolymers Containing Light-Responsive Chromophores: A Method Toward Molecular Logic Gates
2010
A series of thermo-responsive PNIPAM copolymers containing different amounts of fulgimide moieties has been synthesized via a polymer analogous reaction of poly(pentafluorophenyl acrylate). All copolymers were designed to exhibit a lower critical solution temperature (LCST) in water, which was only weakly dependent on the amount of incorporated chromophoric fulgimide groups. The copolymers showed a photocyclization of the fulgimide side groups upon irradiation with UV-light accompanied with a color change. The closed form of the chromophore had a halftime of 136 min for the visible reisomerization and did not affect the LCST of the polymer. This led to the realization of a logic "NOT A" for…
Temperature- and Light-Responsive Polyacrylamides Prepared by a Double Polymer Analogous Reaction of Activated Ester Polymers
2009
Two different series of polyacrylamides containing different amounts of salicylideneaniline moieties have been synthesized via a double polymer analogous reaction of poly(pentafluorophenyl acrylate) (PPFPA). All copolymers were designed to exhibit a lower critical solution temperature (LCST) in aqueous solution, which was dependent on (i) the amount of incorporated chromophoric salicylideneaniline groups and (ii) the isomerization state of the respective salicylideneaniline group. Higher LCST values were measured for UV-irradiated solutions of the copolymers in comparison to the nonirradiated copolymer solutions. A maximum difference in the LCST of up to 13 °C was found for poly(N-cycloprop…